Table of contents :

• Organogenesis

The originally simple aggregate of cells involved in food absorption has thus evolved into a very large and complex structure that is highly patterned in its longitudinal, dorsoventral (DV), left-right (LR), and radial axes. Over the past decade or so, studies in a number of invertebrate and vertebrate model systems, including Caenorhabditis elegans, Drosophila, sea urchins, ascidians, Xenopus, zebrafish, the chick, and the mouse, have provided insights into the genes and cellular mechanisms regulating endoderm formation^{ref1, ref2}. There is a high degree of conservation in some of the transcriptional regulators of endoderm formation; for example, members of the Gata and Forkhead transcription factor families have been implicated in this process across the phyla, although the intercellular events regulating endoderm formation appear to be more divergent. The Wnt signaling pathway has been implicated in the formation of the endoderm in C. elegans, sea urchins, and ascidians, whereas Nodal signaling has been implicated in the formation of the endoderm in vertebrate embryos. However, this apparent lack of conservation of the signaling pathways regulating endoderm formation probably reflects our incomplete understanding of the process. Indeed, we have not yet gained sufficient knowledge to control the efficient differentiation of mammalian stem cells into endoderm, meaning that the investigation of endoderm formation must proceed using multiple approaches in multiple model systems. As mentioned above, the mesoderm can be thought of, at some level, as a derivative of the endoderm and indeed, the endoderm and mesoderm often originate from the same or adjacent regions of the embryo. Although the mechanisms leading to the segregation of these 2 lineages are fairly well understood in C. elegans and sea urchins, for example, much remains to be learned about this process in vertebrates. Again, this knowledge will be necessary to enhance our ability to coax stem cells into various endodermal or mesodermal lineages. After segregating from the mesoderm during late blastula stages, the endoderm undergoes complex morphogenetic processes, first during gastrulation and then as it converges toward the midline and extends to cover the entire anteroposterior (AP) extent of the embryo. These movements lead to the formation of a hollow tube either from the cavitation of a solid rod, as in zebrafish and Xenopus, or the folding of a sheet, as in birds and mammals. Thus, what started out in the most primitive multicellular organisms as a small aggregate of cells involved in food absorption has evolved into a tube several times the length of the organism, so long in fact that it has to fold extensively to fit into the body cavity. At pregnancy week 3-4 :
• buccopharyngeal or oropharyngeal membrane : a transient embryonic septum at the cranial limit of the foregut, in the depths of the stomodeum
• stomodeum : an invagination of the surface ectoderm of the embryo during the fourth week, at the point where later the mouth is formed.
• foregut : the endodermal canal of the embryo cephalic to the junction of the yolk stalk; it gives rise to the pharynx, trachea, thyroid, bronchi and lung (respiratory diverticulum), esophagus, stomach, liver and its ducts (liver bud), and first part of the duodenum
• midgut / mesenteron : the region of the embryonic digestive tube into which the yolk sac opens; it gives rise to most of the intestines (second part of duodenum, jejunum, ileum, right colon, 2/3 of transverse colon)
• hindgut : the embryonic structure from which the distal 1/3 of the transverse colon, left colon, sigma, rectum, and upper part of anal canal are formed
• cloaca : in mammalian embryology, the terminal end of the hindgut before division into rectum, bladder, and genital primordia
• ectodermal cloaca : that portion of the embryonic cloaca originally external to the cloacal membrane.
• entodermal cloaca : that portion of the embryonic cloaca originally internal to the cloacal membrane.
• congenital or persistent cloaca : the congenital persistence of a common cavity into which the intestinal, urinary, and reproductive ducts open
• cloacal membrane : the thin, temporary barrier between the hindgut and the exterior, formed by the endoderm of the hindgut and the ectoderm of the cloaca of the embryo; its dorsal part forms the anal membrane.
• anal plate : the anal part of the cloacal membrane
• cloacal or urorectal septum : the caudally and outwardly growing wedge of endoderm-covered mesoderm that divides the cloaca into the urogenital sinus and rectum
• anal membrane : the dorsal part of the cloacal membrane after its division by the urorectal septum.
• proctodeum / anal pit : an invagination of the surface ectoderm of the embryo at the point where later the anus is formed
• distal tongue bud / lateral lingual swelling : either of the 2 oval swellings, one on each side of the median tongue bud in the embryo; they grow over the median tongue bud and converge to form the anterior part of the tongue
• median tongue bud / tuberculum impar : a small tubercle in the midline on the floor of the pharynx of the embryo, between the ends of the first and second pharyngeal arches (mandibular and hyoid arches), which is a primordium of the tongue. It forms no recognizable part of the adult tongue
• tooth bud : a knoblike tooth primordium developing into an enamel organ surrounded by a dental sac and encasing the dental papilla
• tooth germ :
• meconium : a dark green, gelly mucilaginous material (60-200 ml) in the intestine of the full-term fetus, being a mixture of the secretions of the liver (bile), pancreas, and intestinal glands, gastrointestinal epithelium, and some amniotic fluid. It is expelled within 12-24 hours since delivery.
• 27% in delivery room
• 69% within 12 hours
• 100% within 24 hours
Complications include meconium ileus and meconium aspiration syndrome (MAS).

The precise location of these accessory organs as well as the demarcation of the various territories along the gut tube has been attributed to a set of complex yet mostly uncharacterized interactions between the gut and the surrounding mesoderm, both of which appear to be patterned along the AP axis. For example, in Drosophila, specific Hox genes are expressed in localized regions of the midgut endoderm and the visceral mesoderm surrounding it.
• One of the best-studied examples is the regulation of labial expression in the endoderm by Ubx, which itself is expressed in the adjacent mesoderm^ref. By regulating Bmp and Wnt signals, Ubx controls the segmental expression of labial, which in turn regulates the differentiation of a specialized set of endodermal cells.
• Hox genes have also been implicated in endoderm patterning in chordates. They are expressed in specific AP domains in both the endodermal and mesodermal germ layers, and loss- and gain-of-function experiments have illustrated a few of their roles in patterning the gut along the AP axis^{ref1, ref2, ref3}. For example, Hoxd-13 is expressed in the hindgut region of mouse and chick embryos^{ref1, ref2, ref3}, and mice that are homozygous mutant for this gene have a hindgut defect^ref. In addition, misexpression of Hoxd-13 in the embryonic chick midgut mesoderm results in the induction of aspects of hindgut morphology in the midgut epithelium^ref. Therefore, mesodermal expression of Hox genes can function in the mesoderm-endoderm interactions to pattern the endodermal epithelium, although the downstream targets of the Hox genes that induce this patterning remain unknown. Similarly, how the pattern of Hox gene expression is determined is unclear, although it lies downstream of the events that pattern the early embryo. There is also strong evidence that retinoic acid signaling is involved in patterning the endoderm along the AP axis^ref, probably acting directly on Hox gene expression^{ref1, ref2}. In addition to Hox genes, at least 2 ParaHox transcription factor genes, Cdx2 and Pdx1, are critical for gut tube development.
• Cdx2 is specifically important for hindgut development in humans, mice, and Drosophila
• Pdx1 is critical for pancreas formation in humans and mice^ref. Cdx2 likely patterns the vertebrate gut by regulating Hox gene expression in the endoderm, as it appears to do so in Drosophila, C. elegans, and the mouse spinal cord^ref.
In summary, the early patterning of the embryo determines the expression pattern of ParaHox, Hox, and other transcription factor genes in the endoderm and adjacent mesoderm. Thereafter, a complex dialogue between these 2 tissues leads to the final pattern of the gut tube along the AP axis. In addition to its elaborate patterning along the AP axis, the gut also undergoes some fascinating morphogenetic processes, including extensive and, at least initially, highly stereotyped looping movements. Again, as is the case with AP patterning, the adjacent mesoderm appears to play a critical role in this process. For example, the initial looping of the zebrafish foregut appears to result from the asymmetric displacement of the neighboring lateral plate mesoderm^ref. Whether the subsequent and extensive looping movements of midgut derivatives seen in higher vertebrates are also driven by the surrounding tissues remains to be investigated. Although the mammalian gut tube forms through a folding process, rearrangement of the endodermal epithelium leads to the complete occlusion of the lumen^ref. Defects in the subsequent recanalization, or reluminization, of the gut tube can lead to partial stenosis or duplication of the digestive tract. As the lumen expands and epithelial cells proliferate, the gut epithelium, possibly because it is constrained in its outer diameter by the surrounding muscle layer, starts undergoing folding morphogenesis. This process leads to the formation of characteristic fingerlike intestinal villi, which greatly increase the absorptive surface of the digestive tract^{ref1, ref2, ref3, ref4, ref5}. Pitlike intestinal crypts also form at the base of the villi, and they contain the stem cells that serve as the source of epithelial cells for the entire intestinal surface. The life-span of differentiated intestinal epithelial cells in humans is estimated to be approximately 4 days, with as many as 1400 cells per villus shed into the lumen on a daily basis. There are four cell types currently recognized in the intestinal epithelium. Enterocytes secrete enzymes that help digest sugars and proteins and absorb nutrients. Goblet cells, most abundant in the posterior gut, secrete mucus, which protects against shear stress and chemical damage (among other functions). The rare enteroendocrine cells secrete hormones such as serotonin, substance P, cholecystokinin, gastrin, and secretin. Paneth cells secrete antimicrobial peptides such as defensins (cryptdins), as well as enzymes such as lysozyme and phospholipase A2 (and they live for about 20 days). The signaling pathways and transcriptional effectors regulating the differentiation of these cells are only starting to be investigated and, not surprisingly, a role for Notch signaling in this process has been reported^{ref1, ref2}. Another interesting question concerns the migration of these different cell types in the radial axis, because Paneth cells remain at the bottom of the crypts while the other cell types migrate upward toward the tip of the villi. Ephrin signaling has been implicated in this fascinating process, which begs for further investigation^ref. Intestinal stem cells have been studied for many years because of their well-defined position, extreme sensitivity to chemo- and radiotherapy, and likely association with the development of cancer^{ref1, ref2, ref3, ref4, ref5}. Each crypt is estimated to contain 1-6 stem cells and, in the mouse intestine, each of these cells appears to divide about once a day. Interestingly, despite the roughly equivalent number of stem cells in the large and small intestine in humans, the incidence of cancer in the former is about 70 times greater than in the latter, for reasons that remain largely unknown. Recent work has started to shed light on the genes that regulate the behavior of the intestinal stem cells in vivo. For example, Wnt signaling has been implicated in many aspects of intestinal stem cell biology, including stem cell maintenance and the proliferation/differentiation switch in intestinal crypts and subsequent positioning of the differentiated cells^{ref1, ref2, ref3}. However, many interesting issues remain unresolved, including how Wnt signaling regulates so many different aspects of stem cell biology, as well as the identity and location of the putative Wnt source close to the crypt bottom^{ref1, ref2}. As the gut tube forms, cells from the lateral plate mesoderm begin to encircle it. These cells proliferate and differentiate into connective tissue as well as the characteristic circular and longitudinal muscle layers. At the same time, cranial neural crest cells migrate ventrally, and once in contact with the developing gut, they migrate posteriorly to colonize its entire AP extent. Defects in this process lead to the common intestinal motility disorder Hirschsprung disease^ref. Again, the tissue interactions leading to the differentiation of both mesodermal and ectodermal cells in the vicinity of the gut endoderm are only starting to be investigated at the molecular level.  The most visible manifestation of DV and LR patterning of the gut is in the stereotyped emergence of gut-associated organs such as the thyroid, lungs, liver, and pancreas. For example, the thyroid and lungs bud from a ventral region of the foregut, and the homeobox gene Nkx2.1 / TITF1, whose expression is restricted ventrally, is required for this process^ref. Concomitant with the looping movement mentioned above, the gut is also thought to rotate slightly, thereby blurring the lines between DV and LR patterning. However, as with the other patterning events (AP and radial), the surrounding mesodermal tissues are thought to play critical roles in patterning the gut along the DV and LR axes and in the resulting emergence of the various organ buds. Hedgehog, Bmp, Fgf, and Wnt signaling have all been implicated in various aspects of gut development^{ref1, ref2, ref3, ref4}. Such studies have revealed that these signaling pathways are used at multiple steps of the process, as the endoderm and mesoderm become involved in an increasingly complex set of interactions. As a consequence, understanding the role of these signaling pathways in gut development will require sophisticated genetic studies in which one modulates them with precise spatiotemporal control. For example, expressing the pan-Hedgehog (Hh) inhibitor Hedgehog-interacting protein (Hhip) in the intestinal epithelium (using the mouse Villin1 promoter) has shed some light on the complex role of Hh signaling in patterning the intestinal crypt-villus axis^ref. Further insights into the signaling pathways regulating gut development are likely to come from such intricate loss- and gain-of-function approaches. In addition to the hardwired program of gut development discussed above, it is clear that environmental influences, such as diet^ref and the microbial community of the gut^ref, play important roles in the differentiation and function of the gut. For example, in mammals, the changing dietary input in the pre- and postnatal periods imposes different demands on the intestine and influences its morphology, enzymatic diversity, and transport. In addition, the diet contains substances such as polyamines and epidermal growth factor that do not play a nutritional role but appear to directly stimulate the growth of the intestinal epithelium^ref. Similarly, C. elegans worms adjust the size of their pharynx, intestine, and intestinal microvilli depending on their nutritional state^ref, and such plasticity is also seen in the willow ptarmigan, in which the winter consumption of fibrous food is associated with relatively long caecae. Investigations into the cellular and molecular underpinnings of such phenomena are just beginning. In addition to the few disorders mentioned earlier in this article, naturally occurring human gut malformations are not rare; in fact, they are a major cause of perinatal morbidity and mortality. Also, because the endoderm extends along most of the AP axis of the embryo, it plays critical roles in many developmental events. For example, the anterior or pharyngeal endoderm contributes substantially to craniofacial structures and lies in close proximity to the developing heart, and thus defects in this tissue are likely to play a major role in the formation of these organs. It is clear, however, that although we can make educated guesses about which signaling pathway is likely to be defective in a select subset of gut malformations^ref, much work remains to be done to establish molecular causality. In this regard, human genetic studies of gut malformations have certainly lagged behind those of the cardiovascular system, for instance. And as has already been illustrated regarding other organ systems such as the cardiovascular system, more subtle mutations in key developmental genes are likely to predispose one to gut disease and/or functional defects. Closer interactions between clinical and basic scientists interested in the gastrointestinal tract will greatly accelerate the pace of discovery in these areas. Compared to readily accessible organs such as the limb, or to organs such as the heart and pancreas that are the focus of resourceful charities, the gut has been left behind. However, it is clear from the few vignettes presented here that the many fascinating developmental, evolutionary, and medical aspects of the gut will continue to attract much attention and generate pertinent information.
• Organs
• beaker, caliciform, chalice or goblet cells : a unicellular mucous gland found in the epithelium of intestines. Droplets of mucigen collect in the upper part of the cell and distend it, while the basal end remains slender, and the cell assumes the shape of a goblet.
• trefoil factors (TFFs) are protease-resistant peptides that promote epithelial cell migration and mucosal restitution during inflammatory conditions and wound healing in the gastrointestinal tract. Members of the trefoil family are characterized by having at least one copy of the trefoil motif, a 40-amino acid domain that contains 3 conserved disulfides. To date, the molecular mechanism of TFFs action and their possible role in tumor progression are unclear
• TFF1 / pS2 (gastric mucosa, conjuctival goblet cells)
• TFF2 / spasmolytic polypeptide (gastric mucosa)
• TFF3 / intestinal trefoil factor (goblet cells of the intestines and colon)
TFF1, TFF2, and TFF3 are paralogous genes located within a 55 kb region on chromosome 21q22.3
• mouth / os : the anterior or proximal opening of the alimentary canal, which is bounded anteriorly by the lips and which contains the tongue and teeth
• sublingual crescent : the crescent-shaped area on the floor of the mouth, formed by the lingual wall of the mandible and the adjacent part of the floor of the mouth.
• stomatognathic system : the structures of the mouth and jaws, considered collectively, as they subserve the functions of mastication, deglutition, respiration, and speech
• masticatory system or apparatus / organs of mastication : the organs and structures involved in mastication, including the teeth and jaws and their supporting structures, temporomandibular joints, mandibular muscles, accessory facial muscles, tongue, lips, cheeks, and oral mucosa together with their innervation
• jaw or mandibular movement : any movement of which the mandible is capable
• free mandibular movement : any unhampered movement of the mandible.
• functional mandibular movements : those movements of the mandible which occur in the performance of some function, as mastication, swallowing, articulation of vocal sounds, and yawning.
• border movement : any extreme compass of mandibular movement limited by bone, ligaments, or soft tissues; usually applied to horizontal mandibular movements.
• masticatory movements : those movements of the mandible occurring in the mastication of food.
• Bennett movement : the lateral shift of the mandibular condyles and articular disks in the direction of the working bite as the lower jaw swings in preparation for mastication
• opening movement : a mandibular movement during jaw separation.
• intermediary or intermediate movements : mandibular movements between the extremes of mandibular excursions.
• posterior opening movement : the opening movement of the mandible about the terminal hinge axis.
• lip : either the upper or lower fleshy margin of the mouth, together called labia oris
• labial groove : an embryonic groove produced by degeneration of the central cells of the labial lamina, which later becomes the vestibule of the oral cavity.
• lip line : a line at the level to which the margin of either lip extends on the teeth
• high lip line : the greatest height to which the maxillary lip is raised
• low lip line : the lowest position of the lower lip during the act of smiling or voluntary retraction.
• tuberculum labii superioris / tubercle of upper lip / procheilon / labial tubercle : the central prominence of the superior border between the skin and the mucous membrane of the upper lip, marking the distal termination of the philtrum
• oral cavity (see also diseases of oral cavity)

Ontogenesis :
• primordial, premaxillary or primary palate : that portion of the palate in embryonic development that forms first, being contributed by the median nasal process
• secondary palate : in embryonic development, the part of the palate that forms later than the primordial palate, by fusion of the lateral nasal process
• ductus incisivus / incisive duct /incisor canaliculus / incisor duct : a passage sometimes found in the incisive canal that interconnects the nasal and oral cavities during embryonic development; it occasionally fails to close
Anatomy :
• Fleischmann's follicle : an occasional follicle in the mucosa of the floor of the mouth, near the anterior border of the genioglossus muscle.
• palate : the tissues forming the roof of the mouth that separates the oral and nasal cavities
• hard palate / palatum durum : the anterior part of the palate, characterized by an osseous framework, covered superiorly by mucous membrane of the nasal cavity and, on its oral surface, by mucoperiosteum
• palatum osseum / bony (hard) palate : the bony part of the anterior 2/3 of the roof of the mouth, formed by the palatine processes of the maxillae and the horizontal plates of the palatine bones
• vibrating line : an imaginary line across the palate that separates its immovable portion, the hard palate, from its movable portion, the soft palate
• soft palate / palatum molle / velum palatinum : the fleshy part of the roof of the mouth, extending from the posterior edge of the hard palate; from its free inferior border is a projection of variable length, the pendulous palate / uvula
Cell types :
• surface cell in squamous epithelia of the oral cavity
• basal stem cell of squamous epithelia of the oral cavity
• salivary glands (see also diseases of salivary glands)

Cell types :
• mucous cell (secreting  polysaccharides)
• serous cell (secreting glycoproteic enzymes)
• von Ebner gland cell / gustatory gland (secretion wash out gustatory papillae) : serous secreting glands in the posterior part of the tongue near the vallate papillae
Anatomy : glandulae oris
• glandulae salivariae majores / major salivary glands : the larger exocrine glands of the oral cavity
• internal salivary gland
• submaxillary gland / submandibular gland / glandula submandibularis => ductus submandibularis / submandibular duct / ductus submaxillaris / submaxillary duct of Wharton / Wharton's duct opens at the sublingual caruncle. Sympathetic or ganglionic saliva is submaxillary saliva produced in response to stimulation of its sympathetic nerve supply : it is more viscid and turbid than that of the unstimulated gland.
• sublingual gland / Rivinus gland / glandula sublingualis =>
• ductus sublingualis major / major sublingual duct / Bartholin's duct opens alongside the submandibular duct on the sublingual caruncle
• ductus sublinguales minores / minor sublingual ducts / canals or ducts of Rivinus / Walther's ducts open along the crest of the sublingual fold
Sublingual saliva is that produced by the sublingual gland, the most viscid of all.
• external salivary gland / parotid gland / glandula parotidea => ductus parotideus / parotid duct / Blasius' duct / Stensen's canal or duct / duct or canal of Steno empties into the oral cavity opposite the second superior molar. Parotid saliva is that produced by the parotid gland; thinner and less viscid than the other varieties
• admaxillary gland / accessory parotid gland / glandula parotidea accessoria
• glandulae salivariae minores / minor salivary glands (MSG) / lesser salivary glands (LSG) : the smaller exocrine glands of the oral cavity
• buccal glands / cheek glands / glandulae buccales / malar gland : the serous and mucous glands on the inner surface of the cheeks
• glandula incisiva : a small intraoral gland in the median line of the upper jaw near the incisors.
• lingual glands / glandulae linguales / glands of tongue : the mucous and serous glands on the surface of the tongue
• Bauhin's glands / Blandin and Nuhn's glands / apical glands of tongue / glandulae linguales anteriores / intramuscular glands of tongue : deeply placed mucoserous glands near the apex of the tongue.
• palatine glands / glandulae palatinae : the mucous glands on the soft palate and the posteromedial part of the hard palate.
• glandulae labiales oris / labial glands of the mouth : the serous and mucous glands on the inner part of the lips.
• retromolar glands / glandulae molares / molar glands : the glands on the external aspect of the buccinator muscle, their ducts piercing it to open on the internal aspect of the cheek
• Suzanne's gland : a mucous gland of the mouth, beneath the alveololingual groove
Saliva : the clear, alkaline, somewhat viscid secretion that serves to moisten and soften the food, keeps the mouth moist, and contains
• a-amylase, a digestive enzyme which converts starch into maltose
• mucin
• serum albumin
• salivary corpuscle : a white blood cell that has migrated through the oral epithelium and is mixed in the saliva
• epithelial debris
• potassium thiocyanate
• toxins
• lactoperoxidase
• SIgA
• lactoferrin
• lysozyme
• acidic Pro-rich proteins (PRPs)
• histatins
• teeth (see also diseases of teeth)

Phylogenesis : dimer theory : the theory that the tooth organ of primates is composed of 2 halves, each of which is a representative of an independent tooth in the lower orders of animals.
Odontogenesis : at week 6 of pregnancy cells from neural crest migrate into maxillary region inducing ectoderm to proliferate into the dental lamina / lamina dentalis / dentogingival lamina (a horizontal band projecting perpendicularly from the vestibular lamina and extending into the substance of the embryonic gum, assuming a horseshoe-like shape to conform with the dental arches)
• lateral dental lamina / lateral enamel strand : a lateral band of cells believed to be functionally and structurally similar to the parent dental lamina, which connects the developing tooth germ to the dental lamina
• primitive dental groove : a groove in the border of the jaws of the embryo
• developmental grooves or lines / segmental lines : fine grooves or lines marking the fusion area between adjacent cusps, named according to the portion of the crown which they connect
• mesiobuccal developmental groove : the mesial of the two buccal grooves ordinarily found on the mandibular first molar
• mesiolingual developmental groove : a groove marking the junction of the fifth cusp with the palatal surface on an upper molar tooth.
• lingual developmental groove : a developmental groove on the lingual surface of a posterior tooth.
• occlusal groove : one of the developmental grooves on the occlusal surface of a posterior tooth
• supplemental grooves : grooves on the surface of a tooth that do not mark (as do the developmental grooves) the junction of the primary lobes of the tooth.
Staging :
• lamina-bud stage (weeks 6-7) : initial formation of the tooth bud and development of dental lamina
• cup stage (weeks 8-9) : formation of the enamel cap and dental papilla in the tooth germ and organization of the dental cells into 3 layers (dentin and pulp)
• bell stage (week 10 - eruption) : morphodifferentiation and histodifferentiation in which the enamel organ changes in shape from a cap to a bell that has 4 distinct layers.
Cell types : preeruptive stage : the period of tooth development, before tooth eruption, characterized by growth of the coronal portion of the tooth, prior to the beginning of the growth of the root.
• ameloblast / adamantoblast / enamel cell => enamel matrix
• amelogenins (degraded by MMP20 / enamelysin)
• X chromosome
• Y chromosome
• enamelanin
• ameloblastin
• tuftelin 1
• dentin sialophosphoprotein (DSPP) (transient expression)
=hydroxyapatite crystals calcification (85% of final enamel volume)=> enamel : hard, calcified, white tissue covering dentin of the crown of tooth. During foetal amelogenesis the pulp of enamel organ and the intermediate layer of adamantoblasts (lost at birth) produce enamel : Tomes' processes are finger-like projection of the ameloblast, occurring during the secretory phase of the cell, which extends from the point of separation of the adjacent cell membrane to the distal free surface. Stellate reticulum is the soft, middle part of the enamel organ of a developing tooth, the cells being separated by an increase in the gelatinous intercellular substance that forces the cells apart without breaking the intercellular connections, giving them a stellate appearance and providing protection later for the enamel-forming cells
• Hannover's intermediate enamel membrane : the inner layer of cells within the enamel organ of the dental germ in the fetus
• enamel knot : a small dense group of epithelial cells in the stellate reticulum of a developing tooth, which disappears before enamel formation begins.
• dentinoenamel membrane : a continuous thin membrane laid down by ameloblasts adjoining the basement membrane separating them from the dentin in an early developing tooth
• Nasmyth's membrane : primary (enamel) cuticle
• odontoblast / dentin cell (undergoes activation to repair fractures) => odontocyte => predentin
• dentin sialophosphoprotein (DSPP)
• dentin matrix acidic phosphoprotein
• matrix, extracellular phosphoglycoprotein with ASARM motif (MEPE)
=calcification=> dentin : that part of the tooth that is beneath enamel and cementum, between the pulp and the enamel, comprised of a series of dentinal tubules (microscopic canals that run from the outside of the dentin to the nerve inside the tooth) stacked on top of each other.
• incremental, accretion, calcification or Retzius' l's lines / Retzius' parallel striae : lines showing the successive layers deposited in a tissue. In the enamel, they are brown striations visible under transmitted light and colorless in reflected light. They may be observed under the microscope in longitudinal sections as oblique lines running inward from the surface and toward the root and in cross sections as rings similar to those in a tree trunk. Dry dentin often shows a series of somewhat parallel lines caused by imperfectly calcified dentin arranged in layers
• incremental lines of Ebner : delicate lines indicating periods of rest between daily increments of dentin, which are visible on ground sections of a tooth
• imbrication lines of Pickerill : lines formed by ends of rod bundles that overlie one another and are arranged in scalariform fashion on the surface of the crown of a tooth; seen on longitudinal sections of a tooth together with the incremental lines, but forming areas not completely contained in the enamel
• lines of Schreger / Hunter-Schreger bands, Schreger's bands or striae, and zones of Schreger : the dark and light lines visible under reflected light in a ground section of a tooth, which terminate at the dentinoenamel junctions, coinciding with the enamel prism curvatures. The dark bands are known as diazones, and the light ones as parazones
• neonatal line : a line seen on longitudinal sections of a tooth, showing a demarcation between the structures present at birth and those deposited postnatally; in cross sections, the lines are seen as rings (neonatal rings), and their variations indicate adaptational changes in tooth formation
• lines of Owen / contour lines / Salter's lines : the sweeping bands seen on longitudinal section that outline the growth of the coronal or radicular dentin, representing a lag of several days between calcification phases, each lasting about 4 days
• cementoblast => cementocyte => cementum : hard connective tissue covering the tooth root, serves as the anchor point for the ligaments that join the tooth to the boney tooth socket. It is the softest part of the tooth structures
• imbrication or incremental lines of cementum : very fine dark lines present in longitudinal sections of a tooth, which follow the contour of the root and border with wider light bands, revealing the cyclic activity of cementogenesis
Anatomy :


• gingival sulcus : space between gum and tooth
• gingival crevicular fluid (GCF) is the clear fluid which continually flushes out the sulcus. In a state of health, there is little gingival crevicular fluid; however as inflammation increases, the amount of GCF increases also.
• gingiva / gum : soft tissues overlying the crowns of unerupted teeth and encircling the necks of those that have erupted, covering the alveolar bone and serving as the supporting structure for sub-adjacent tissues
• free gingiva : the marginal part of the gingival (gums) that can be deflected from the tooth surface. The free gingiva forms a collar around the tooth.
• gingival crevice / gingival margin / gumline : area of gingiva closest to the tooth surface
• free gingival groove : a shallow groove on the facial surface of the gingiva, running parallel to the margin of the gingiva at a distance of 0.5 to 1.5 mm., and usually at the level of, or somewhat apical to, the bottom of the gingival sulcus
• keratinized gingiva : the oral surface of the gingiva extending from the mucogingival junction to the gingival margin. In gingival health, the coronal portion of the sulcular epithelium may also be keratinized
• interdental papilla : refers to the "v" shaped gum tissue between individual teeth
• interdental groove : a linear, vertical depression on the surface of the interdental papillae; it functions as a sluiceway for the egress of food from the interproximal areas.
• frenum : muscle fibers covered by a mucous membrane that attaches the cheek, lips and or tongue to associated dental mucosa
• frenulum linguae / frenulum of tongue / frenum of tongue : the vertical fold of mucous membrane inferior to the tongue, attaching it to the floor of the mouth
• buccal frenum : a fold of mucous membrane connecting the alveolar ridge to the cheek and separating the labial vestibule from the buccal vestibule
• frenulum labii inferioris / frenulum of lower lip : the fold of mucous membrane on the inside of the middle of the lower lip, connecting the lip with the gums
• frenulum labii superioris / frenulum of upper lip : the fold of mucous membrane on the inside of the middle of the upper lip, connecting the lip with the gums
• alveolar bone : the bone which surrounds the root of the tooth, holding it in place. Loss of this bone is typically associated with severe periodontal disease
• alveolus / socket : the hole in the jawbone into which the tooth fits
• periodontal ligament / alveolodental ligament or membrane / desmodontium / peridental or periodontal membrane : the fibrous connective tissue that surrounds the cementum, separating it from and attaching it to the alveolar bone. It extends from the base of the gingival mucosa to the fundus of the bony socket, and its main function is to hold the tooth in its socket.
• syndesmosis dentoalveolaris / dentoalveolar syndesmosis / gomphosis : one of the fibrous joints by which a tooth is held in its socket
• Hertwig's sheath / root sheath : an epithelial extension of the cervical loop of the enamel organ, consisting of the inner and outer enamel epithelium, and directing the number and morphological growth of the roots. It is bordered externally by the dental sac and internally by developing cementum and root dentin, and ultimately becomes the epithelial diaphragm : an epithelial structure that narrows the opening into the pulp chamber, diminishing its caliber. It is in close contact with the bone forming the fundus of the developing alveolus, from which it is separated by the dental sac
• Malassez rest : the remaining cells of the root sheath in the periodontal ligament, which persist and sometimes form an epithelial network and occasionally develop into a dental cyst.
• pulp cavity : the space within a tooth which contains the soft pulp / pulpa dentis, the living part of the tooth, located inside the dentin, containing nerve tissue and the blood vessels which supply nutrients to the tooth.
• root canal : the portion of the pulp cavity inside the root of a tooth; the chamber within the root of the tooth that contains the pulp
• root / radix denti : the anatomic portion of the tooth that is covered by cementum and is located in the alveolus where it is attached by the periodontal apparatus; radicular portion of tooth.
• apex : the tip or end of the root end of the tooth.
• furcation : the anatomic area of a multirooted tooth where the roots diverge.
• cementoenamel junction (CEJ) / cervix dentis / neck is the point at which the crown and root come together
• cervical line : an anatomical landmark determined by the junction of the enamel- and the cementum-covered portions of a tooth (the cementoenamel junction); the dividing line between the crown and root portions of a tooth.
• crown / corona dentis
• anatomical crown : that portion of tooth normally covered by, and including, enamel.
• corona clinica / clinical crown / extra-alveolar crown : that portion of the tooth above the clinical root, i.e., the portion exposed beyond the gingiva, and thus visible in the oral cavity
• buccolingual diameter : the distance from the buccal to the lingual surface of a tooth crown at its widest point or greatest curvature.
• cusp : pointed or rounded eminence on or near the masticating surface of a tooth.
• pit : a recessed area found on the surface of a tooth, usually where the grooves of the tooth meet
Dental arch : the curved composite structure of the natural dentition and the residual ridge, or the remains thereof after the loss of some or all of the natural teeth
• quadrant : one of the 4 equal sections into which the dental arches can be divided; begins at the midline of the arch and extends distally to the last tooth.
• sextant : one of the 6 relatively equal sections into which a dental arch can be divided, for example: tooth numbers 1-5; 6-11; 12-16; 17-21; 22-27; 28-32. Sometimes used for recording periodontal charting


Dental regions :
• vertical axis
• crown
• occlusal region
• intermediate region
• cervical region
• root
• cervical region
• intermediate region
• apical region
• anteroposterior axis
• mesial region
• intermediate region
• distal region
• laterolateral axis
• facial or vestibular region
• labial region
• buccal region
• intermediate region
• lingual region
Dentition : the teeth in the dental arch.
• teething : the effects of baby teeth pushing through gums.
• operculum : the flap of tissue over an unerupted or partially erupted tooth
• eruption : when teeth first peek through gums
• diastema : a space, such as one between 2 adjacent teeth in the same dental arch
• anterior diastema : a space between the incisor teeth, generally one between the maxillary central incisors
• ugly duckling stage : a development stage in the mixed dentition when the upper central and lateral incisors may be flared, with the crowns distally and with diastema present before the maxillary canine teeth erupt.
• anterior, labial or morsal teeth : these are the 6 teeth located in the front of the mouth, and are used as cutting (biting) surfaces rather than chewing surfaces
• incisor (teeth) /dentes incisivi : 8 front teeth
• central incisors
• lateral incisors
Used to cut, gnaw and tear food.
• incisal edges : refers to the biting edges of the anterior teeth.
• mamelon : one of three tubercles sometimes present on the cutting edge of an incisor tooth.
• canines / cuspid (teeth) / dentes canini : 4 pointed conical teeth located between the incisors and the first molars
• eye tooth : colloquial term for a canine tooth of the maxilla
• stomach tooth : a canine tooth of the mandible.
• incisal angle : one of the angles formed by the junction of the incisal and the mesial or distal surfaces of an anterior tooth; called the mesial and distal incisal angle respectfully.
• anterior arch length : the length of a line segment within the median plane perpendicular to and extending from the line connecting the first premolars to the most labial point on the anterior arch, usually to the point between the maxillary central incisors
• buccal, cheek or posterior teeth are those used for grinding food, having large crowns and broad chewing surfaces
• premolars / bicuspid (teeth) / dentes premolares (P) : the permanent teeth between the canines and the molars; there are 2 on either side in each jaw
• upper premolars are bicuspid
• lower have from 1 to 3 cusps
Premolars are succedaneous to the deciduous molar teeth
• molars / dentes molares : the most posterior teeth on either side in each jaw, totaling 8 in the deciduous dentition (2 on each side, upper and lower), and usually 12 in the permanent dentition (3 on each side, upper and lower). They are the grinding teeth, having large crowns with broad chewing surfaces. Symbol M.
• upper molars characteristically have 4 major cusps and 3 roots
• Carabelli cusp or tubercle : an accessory cusp on the lingual aspect of the mesiolingual cusp of an upper molar, which may be unilateral or bilateral and may vary considerably in size; it is common in Caucasians but quite rare in East Asians and certain other groups
• lower first molars characteristically have 5 cusps, and the remaining lower molars 4 cusps. Normally all lower molars have 2 roots
• wisdom teeth / third molars / dens molaris tertius / dens serotinus : the tooth most distal to the medial line on either side in each jaw, so called because it is the last of the permanent dentition to erupt, usually at the age of 17 to 21 years. Some people are born without third molars.
• paramolar / supernumerary molar : a supernumerary tooth, usually small and rudimentary, sometimes found in the maxilla buccally or lingually to a molar or interproximally between 2 of the first 2 molars
• occlusal : the biting surface of the posterior teeth
• diodontous animals
• deciduous or primary dentition : the 20 baby, deciduous, milk or primary teeth. They are shed and replaced by the permanent teeth. They begin to calcify at about month 4 of fetal life, and near the end of the month 6 they all have begun to develop. See also deciduous tooth stem cells. Timing of eruption :
• maxillary deciduous teeth : paracone : the mesiobuccal cusp of a maxillary tooth of mammals, which normally occludes between the paraconid and hypoconid of the corresponding lower molar
• central incisors : 7 1/2 months
• lateral incisors : 8 months
• canines : 16-20 months
• first molars : 12-16 months
• second molars : 20-30 months / 2 1/2 years
• mandibular deciduous teeth :
• first incisors : 6 1/2 months
• second incisors : 7 month
• canines : 16-20 months
• first molars : 12-16 months
• paraconid : the mesiobuccal cusp of a mandibular molar tooth.
• second molars : 20-30 months
Mandibular teeth erupt before maxillary teeth. First molar erupt before canines. The deciduous dentition formula (one side) is as follows : I 1/2 C 1/1 M 2/2 = 10. Symbol D.
• permanent dentition : the 32 permanent teeth. Timing of eruption :
• maxillary permanent teeth
• first incisors : 7-8 years
• second incisors : 8-9 years
• canines : 11-12 years
• first premolars : 10-11 years
• second premolars : 10-12 years
• sixth-year molar : the permanent first molar tooth, so called because it usually erupts at the age of 6 years just posterior to the last molar of the deciduous dentition : 6-7 years
• twelfth-year molar : the permanent second molar tooth, so called because it usually erupts at the age of 12-13 years
• third molars : 17-21 years
• mandibular permanent teeth
• first incisors : 6-7 years
• second incisors : 7-8 years
• canines : 9-10 years
• first premolars : 10-12 years
• second premolars : 11-12 years
• first molars : 6-7 years
• second molars : 11-13 years
• third molars : 17-21 years
They take their position posterior to the deciduous teeth and erupt in succession, whenever the jaws grow sufficiently to accommodate them. Upper incisors cover lower incisors by 0-2 mm (physiological overbite); growth of maxillary bone carries upper teeth more anteriorly than lower teeth (Mediterranean closure : upper central incisor greater than lower one => every cuspid in upper teeth goes behind correspondent cuspid in lower teeth), while mandibular displacement.
• succedaneous teeth / successional teeth : the permanent teeth that have deciduous predecessors in the dental arch. Exfoliation of the deciduous teeth is brought about by resorption of their roots, and the succedaneous permanent teeth take their place
• accessional teeth : the molar teeth of the permanent dentition, so called because they do not supplant any deciduous predecessors in the dental arch
The permanent dentition formula (one side) is as follows: I 2/2 C 1/1 P 2/2 M 3/3 = 16
• occlusion : any contact between biting or chewing surfaces of maxillary (upper) and mandibular (lower) teeth in all mandibular positions and movements
• occlusal harmony : proper occlusion of the teeth occurring in various positions of the mandible.
• functional occlusal harmony : such occlusion of the teeth in all positions of the mandible during mastication as will provide the greatest masticatory efficiency without imposing undue strain or trauma on the supporting tissues.
• glide : a smooth continuous movement
• mandibular glide : the side-to-side, protrusive, and intermediate movement of the mandible occurring when the teeth or other occluding surfaces are in contact.
• occlusal glide : the movement induced by deflective tooth contact that diverts the mandible from a normal path of closure to a centric jaw relation
• curve of occlusion / dental curve / occlusal curvature / curva occlusalis : a curved surface that makes simultaneous contact with major portions of the incisal and occlusal prominences of the existing teeth
• on a sagittal plane : Spee curve (anatomic curvature of the occlusal alignment of teeth, beginning at the tip of the lower canine, following the buccal cusps of the natural premolars and molars, and continuing to the anterior border of the ramus)
• on a frontal plane : Wilson curve (the curvature of the cusps of the teeth as projected on the frontal plane; that of the inferior dental arch is concave and that of the superior dental arch is convex)
• interarch or interridge distance : the vertical distance between the maxillary and mandibular arches (alveolar or residual) under certain conditions of vertical dimension that must be specified.  The vertical distance between the maxillary and mandibular ridges
• interocclusal distance / freeway space / interocclusal clearance, gap, or space : the distance between the occluding surfaces of the maxillary and mandibular teeth when the mandible is in physiologic rest position
• dental guides
• incisor guide : cuspid of lower incisors flow on back surfaces of upper incisors
• canine guide is used during lateral movements
• mastication : the act of chewing
• mandibular movements : Posselt envelope of motion (the area within which all movements are possible : G=>A movement is not spontaneous)
• hinge position : the position of the condyle in the temporomandibular joint from which an opening by hinge movement is possible beyond the amplitude of rest position.
• condylar hinge position : the position of the condyles in the glenoid fossa at which hinge axis movement is possible.
• mandibular hinge position : a position of the mandible that allows the condyles to move on the hinge axis during the opening or closing of the jaws.
• terminal hinge position / centric relation / centric jaw relation / median retruded jaw relation / terminal hinge position /  true centric : the position of the mandible, obtained principally by operator guidance, in which the condyles are in the rearmost uppermost position in the fossae of the temporomandibular joint
• centric position : the rest position of the mandible, as it is influenced by the muscle tone, while the patient remains standing or is sitting with jaw open, from which the teeth will come into centric occlusion when the jaw is closed.
• occlusal position / occlusal relation : a functional position of the jaws in which contact between some or all of the upper and lower teeth occurs when the mandible is closed, which may or may not coincide with centric occlusion
• posterior border position / posterior border jaw relation : the most posterior position of the mandible at any specific vertical relation to the maxillae
• rest position / physiologic rest position / rest jaw relation : the position of the mandible when its muscles are at rest, the body is in the upright standing or sitting position, and the eyes are focused toward the horizon; the lips are slightly touching and the distance between the upper and lower teeth has a free-way space of about 2 to 5 mm
Periodontium / alveolar periosteum / odontoperiosteum / paradentium / peridontium : the tissues that invest or help to invest and support the teeth, including :
• periodontal ligament
• gingivae
• cementum
• alveolar and supporting bone
• tongue / lingua / glossa : the movable, muscular organ on the floor of the mouth, subserving the special sense of taste and aiding in mastication, deglutition, and the articulation of sound
• ductus thyroglossalis / thyroglossal duct / duct of His or Vater / Bochdalek's duct / His canal / thyrolingual duct : a duct in the embryo extending between the thyroid primordium and the posterior part of the tongue, which opens as the foramen caecum; the distal part usually differentiates to form the pyramidal lobe the thyroid and the remainder becomes obliterated, but occasionally persists into adult life, giving rise to cysts, fistulas, or sinuses
• copula linguae : a median ventral elevation on the embryonic tongue formed by union of the second pharyngeal arches; it represents the future root of the tongue.
• frenulum linguae / frenulum of tongue / frenum of tongue : the vertical fold of mucous membrane inferior to the tongue, attaching it to the floor of the mouth

Cell types :
• surface cell in squamous epithelia
• basal stem cell of squamous epithelia
• see also taste
• orthognathic : functional relationship of maxilla and mandible.
• oropharynx / pars oralis pharyngis : the division of the pharynx lying between the soft palate and the upper edge of the epiglottis.
• palatopharyngeal sphincter : a transverse band of muscle fibers in the posterior wall of the pharynx, derived from the superior constrictor or palatopharyngeal muscle, which contracts during swallowing to form Passavant's bar; it also contracts during speech in persons with cleft palate.
Coats : tunica mucosa pharyngis : the mucous coat of the pharynx
• neck
• 
• hypopharynx / pars laryngea pharyngis / laryngopharynx : the portion of the pharynx that lies below the upper edge of the epiglottis and opens into the larynx and esophagus
• retrocricoid area / pharyngo-esophageal junction
• pharyngolaryngeal splint / recessus piriformis / piriform recess or sinus : a pear-shaped fossa in the wall of the laryngeal pharynx lateral to the arytenoid cartilage and medial to the lamina of the thyroid cartilage
• posterior area / posterior pharyngeal wall
• pharyngoesophageal junction : the area where the esophagus and pharynx meet
• pharyngoesophageal sphincter : a region of higher muscular tone at the pharyngoesophageal junction, involved in movements of swallowing.
• esophagus / oesophagus / gullet (see also diseases of esophagus) : the musculomembranous passage extending from the pharynx to the stomach
• upper esophageal sphincter (UES) : the upper 3–5 cm of the esophagus, including the cricopharyngeal muscle, which prevents the aspiration of air from the pharynx into the esophagus
• cervical esophagus / pars cervicalis oesophagi or esophagi / cervical part of esophagus : the part of the esophagus located in the cervical region, posterior to the trachea and the recurrent laryngeal nerves, anterior to the longus colli muscle and vertebral column, and medial to the lobes of the thyroid gland and the common carotid arteries (C5-T1)
• thoracic esophagus / pars thoracica oesophagi or esophagi / thoracic part of esophagus : the part of the esophagus located in the thoracic region, posterior to the trachea and pericardium and anterior to the vertebral column (T1-T12)
• upper third
• middle third
• lower third
• diaphragmatic esophagus
• lower esophageal sphincter (LES) / gastroesophageal sphincter : the terminal few centimeters of the esophagus, which prevents reflux of gastric contents into the esophagus
• abdominal esophagus / pars abdominalis oesophagi or esophagi / abdominal part of esophagus : the part of the esophagus below the diaphragm, joining the stomach (from hiatus to cardias)
Anatomical variations in caliper
• strictures :
• cricoid stricture
• aortic stricture
• bronchial stricture
• diaphragmatic stricture
• phrenic ampulla : the dilatation at the lower end of the esophagus.
Coats :
• tunica adventitia oesophagi : the adventitious coat of the esophagus.
• tunica muscularis oesophagi : the muscular coat of the esophagus.
• tunica mucosa oesophagi : the mucous coat of the esophagus
Cell types :
• surface cell in squamous epithelia of the esophagus
• basal stem cell of squamous epithelia of the esophagus
• glandulae oesophageae / esophageal glands / glandulae esophageae : the mucous glands in the submucosa of the esophagus
• interstitial cells of Cajal (CD117 / c-kit⁺) : pleomorphic cells of the myenteric plexus having an oval nucleus and long, branching cytoplasmic processes that interlace with processes of adjacent cells, interspersed between the circular and longitudinal muscle layers of the gastrointestinal tract and in the smooth muscle of the esophagus; they are thought to act as pacemakers and give rise to gastrointestinal stromal tumours (GIST)
• enteric plexus
Vascularization :
• upper esophageal artery (receiving lower thyroid artery, which also drains into azygos vein) enters upper cava vein
• lower esophageal artery (receiving left gastric artery) enters left gastric vein
• cardioesophageal esophagogastric or gastroesophageal junction : the site of transition from the stratified squamous epithelium of the esophagus to the simple columnar epithelium of the cardia of the stomach
• cardiac sphincter / cardioesophageal sphincter : muscle fibers about the opening of the esophagus into the stomach.
• gastroesophageal refluxes (GER) :
• prevalence : physiological if short-lasting, asymptomatic and involving only the distal esophagus ("happy splitter")
• 50% in 3-month infants
• 67% in 4-months infants
• 5% in 12-months infants
• episodes lasting > 5' : 9.7/day at 0-11 months, 6.8/day at 1-9 yrs, 3.2/day in adults
• reflux index (time in which esophageal pH < 4) : 11.7% in 0-11 months, 5.4% at 1-9 yrs, 2% in adults
• threshold with gastroesophageal reflux disease (GERD) : 73 a days
• abdomen / belly / venter : that portion of the body which lies between the thorax and the pelvis; it contains a cavity (abdominal cavity) separated by the diaphragm from the thoracic cavity above, and by the plane of the pelvic inlet from the pelvic cavity below, and lined with a serous membrane, the peritoneum. This cavity contains the abdominal viscera and is enclosed by a wall (abdominal wall) formed by the abdominal muscles, vertebral column, and the ilia. It is divided into 9 regions by 4 imaginary lines projected onto the anterior wall (see illustration); 2 of the lines pass horizontally around the body (the upper at the level of the cartilages of the 9th ribs, the lower at the tops of the crests of the ilia), and 2 extend vertically on each side of the body from the cartilage of the 8th rib to the center of the inguinal ligament. The regions are:
• 3 upper—right hypochondriac, epigastric, left hypochondriac
• 3 middle—right lateral, umbilical, left lateral
• 3 lower—right inguinal, pubic, left inguinal..

Regions of abdomen bounded according to (A) the standard and (B) a variant system:
• 1, epigastric
• 2, right hypochondriac
• 3, left hypochondriac
• 4, right lateral (or lumbar)
• 5, umbilical
• 6, left lateral (or lumbar)
• 7, right inguinal (or iliac)
• 8, pubic (hypogastric)
• 9, left inguinal (or iliac)
• peritoneum : the serous membrane lining the abdominopelvic walls and investing the viscera. A strong, colorless membrane with a smooth surface, it forms a double-layered sac that is closed in the male and is continuous with the mucous membrane of the uterine tubes in the female
• peritoneum parietale / parietal peritoneum : the peritoneum that lines the abdominal and pelvic walls and the inferior surface of the thoracic diaphragm.
• peritoneum viscerale / visceral peritoneum : a continuation of the parietal peritoneum reflected at various places over the viscera, forming a complete covering for the stomach, spleen, liver, ascending portion of the duodenum, jejunum, ileum, transverse colon, sigmoid flexure, upper end of rectum, uterus, and ovaries; it also partially covers the descending and transverse portions of the duodenum, the cecum, ascending and descending colon, the middle part of the rectum, the posterior wall of the bladder, and the upper portion of the vagina. It holds the viscera in position by its folds, some of which form the mesenteries, connecting portions of the intestine with the posterior abdominal wall; other folds, the omenta, are attached to the stomach; and still others form the ligaments of the liver, spleen, stomach, kidneys, bladder, and uterus. The potential space between the visceral and the parietal peritoneum is the peritoneal cavity, which consists of the pelvic peritoneal cavity below and the general peritoneal cavity above. The general cavity communicates by the epiploic foramen / omental foramen / foramen omentale / foramen of Winslow (situated below and behind the porta hepatis) with the cavity of the greater omentum / lesser peritoneal cavity.
• Morison's pouch : a pouch of peritoneum inferior to the liver and to the right of the right kidney and extending inferiorly to the transverse mesocolon
• excavatio rectouterina / rectouterine excavation / Douglas' cul-de-sac / pouch of Douglas / Douglas' space / rectouterine, rectovaginal, uterovesical, or vesicouterine pouch : a sac or recess formed by a fold of the peritoneum dipping down between the rectum and the uterus
• pararectal pouch : the lateral part of the excavatio recto-uterina
• abdominovesical pouch : the pouch formed by reflection of the peritoneum from the anterior abdominal wall to the distended bladder.
• excavatio rectovesicalis / rectovesical excavation or pouch : the space between the rectum and the bladder in the peritoneal cavity of the male
• excavatio vesicouterina / uterovesical or vesicouterine excavation or pouch : the space between the bladder and the uterus in the peritoneal cavity
• paracystic pouch : the lateral part of the excavatio vesico-uterina
• uteroabdominal pouch : the compartment of the pelvic cavity anterior to the uterus and broad ligaments.
• obturator or paravesical pouch : the lateral part of the uteroabdominal pouch, beside the bladder and in which the obturator canal opens
• peritoneum urogenitale / urogenital peritoneum : the peritoneum lining the urogenital structures in the lower pelvis.
• ligamentum serosum / serous ligament : a fold of peritoneum or other serous membrane that helps to hold an organ or part in position and transmits blood vessels and nerves.
• ligamentum duodenorenale / duodenorenal ligament : a fold of peritoneum that passes from the duodenum to the right kidney.
• ligamentum phrenicocolicum / phrenicocolic ligament : a peritoneal fold that passes from the left colic flexure to the adjacent costal portion of the diaphragm.
• ligamenta hepatis / hepatic ligaments : the ligaments of the liver
• ligamentum coronarium hepatis / coronary ligament of liver : the line of reflection of the peritoneum from the diaphragmatic surface of the liver to the under surface of the diaphragm.
• ligamentum triangulare dextrum hepatis / right triangular ligament of liver : the pointed right extremity of the coronary ligament of the liver where the superior and the inferior layer join in their attachment to the diaphragm.
• ligamentum triangulare sinistrum hepatis / left triangular ligament of liver : a triangular extension of the left extremity of the coronary ligament, which helps to attach the left lobe of the liver to the diaphragm.
• ligamentum hepatocolicum / hepatocolic ligament : an occasional fold of peritoneum, an extension of the lesser omentum to the right, passing from the lower surface of the liver near the gallbladder to the right colic flexure.
• ligamentum hepatoduodenale / hepatoduodenal ligament : a peritoneal fold that passes from the porta hepatis to the superior portion of the duodenum. It is continuous on the left with the gastrohepatic ligament, and on the right it forms one of the borders of the epiploic foramen. It contains the hepatic artery, portal vein, bile duct, nerves, and lymphatics.
• ligamentum hepatorenale / hepatorenal ligament : a fold of peritoneum that passes from the back part of the lower surface of the liver to the front of the right kidney and forms the right margin of the epiploic foramen.
• ligamentum falciforme hepatis / falciform ligament of liver / broad ligament of liver : a sickle-shaped sagittal fold of peritoneum that helps to attach the liver to the diaphragm, separates the right and left lobes of the liver, and extends from the coronary ligament of the liver behind to the umbilicus in front
• ligamentum latum uteri / broad ligament of uterus : a broad fold of peritoneum extending from the side of the uterus to the wall of the pelvis; it is divided into the ...
• mesosalpinx : the part of the broad ligament of the uterus above the mesovarium, composed of layers that enclose the uterine tube.
• mesovarium : the portion of the broad ligament of the uterus between the mesometrium and mesosalpinx, which is drawn out to enclose and hold the ovary in place.
• ligamentum ovarii proprium / ovarian ligament / utero-ovarian ligament : a musculofibrous cord in the broad ligament, joining the ovary to the upper part of the lateral margin of the uterus just below the attachment of the uterine tube
• mesometrium : the portion of the broad ligament below the mesovarium, composed of the layers of peritoneum that separate to enclose the uterus
• ligamentum lienorenale, phrenicolienale, phrenicosplenicum, splenorenale / splenorenal, lienophrenic, phrenicosplenic, or splenophrenic ligament : a peritoneal fold that passes from the diaphragm to the concave surface of the spleen
• ileocecal pouch : a peritoneal pouch at the ileocecal junction
• Waldeyer's fossa : the recessus duodenalis inferior and recessus duodenalis superior considered as one space.
• recessus duodenalis inferior / inferior duodenal recess : a pocket in the peritoneum on the left side of the ascending portion of the duodenum, bounded by the inferior duodenal fold
• recessus duodenalis superior / recessus duodenojejunalis / superior duodenal recess : a peritoneal pocket behind the superior duodenal fold
• Gruber-Landzert fossa : a recess in the peritoneum in the same situation as the superior duodenal recess, but extending downward behind the duodenojejunal angle.
• fossa intermesocolica transversa : a recess of the peritoneum in the same situation as the recessus duodenalis superior, but extending transversely
• infraduodenal fossa : a recess in the peritoneum below the third portion of the duodenum
• parajejunal fossa : a pouch of peritoneum below the lower end of the first part of the jejunum
• recessus hepatorenalis / hepatorenal recess : a peritoneal pouch between the liver and the kidney
• recessus ileocecalis or ileocaecalis inferior / inferior ileocecal recess : a peritoneal pocket situated behind the ileocecal fold, above the vermiform appendix below the ileum, and medial to the cecum;
• recessus ileocecalis or ileocaecalis superior / superior ileocecal recess : a peritoneal pocket situated behind and below the vascular cecal fold, above the ileum and medial to the lower end of the ascending colon
• recessus inferior bursae omentalis / inferior omental recess : the lower portion of the omental bursa, including its extension down into the great omentum. It is bounded in front by the posterior wall of the stomach, and behind by the pancreas, the transverse colon and its mesocolon, the left suprarenal gland, and part of the left kidney.
• recessus infundibuli or infundibularis / infundibular recess : a funnel-shaped depression in the anterior part of the floor of the third ventricle of the brain, within the infundibulum of the hypophysis
• recessus intersigmoideus / intersigmoidal recess : a shallow peritoneal pocket running downward and to the left at the base of the sigmoid mesocolon
• splenic fossa of omental sac / recessus lienalis or splenicus / splenic recess : an extension of the omental bursa to the left behind the gastrosplenic ligament almost to the spleen
• fossa of Jonnesco : the duodenojejunal fossa between the superior and inferior duodenal folds
• Landzert's fossa / recessus paraduodenalis / paraduodenal recess : a pocket occasionally found in the peritoneum behind a fold containing a branch of the left colic artery
• subsigmoid fossa : a fossa between the mesentery of the sigmoid flexure and that of the descending colon
• processus vaginalis peritonei (a.k.a. canal of Nuck / Nuck's diverticulum in the female) : a diverticulum of the anterior parietal peritoneal membrane extending into the inguinal canal, developing at the third month of intrauterine life, accompanying the round ligament down to the homolateral labium majus in the female, or the testis in its descent into the scrotum in the male (tunica vaginalis testis); usually completely obliterated in the female (otherwise forming Nuck's duct cyst); patency varies with age :
• 80-94% in newborns
• 50% at age 1
• 40% at age 2
• 15% in adults (the distal region is normally patent in the male)
• mesenterium / mesentery : the peritoneal fold attaching the small intestine to the posterior abdominal wall
• caval mesentery : a ridge, at the right of the embryonic mesogastrium, in which develops a hepatic segment of the inferior vena cava
• ventral mesentery : the embryonic mesentery attaching the stomach and the proximal duodenal region of the primordial intestine to the ventral body wall.
• Riolan's arch : the arch formed by the mesentery of the transverse colon
• mesoappendix / mesenteriolum processus vermiformis : the peritoneal fold attaching the appendix to the mesentery of the ileum
• mesocolon : the process of the peritoneum by which the colon is attached to the posterior abdominal wall. It is divided into ascending, transverse, descending, and sigmoid or pelvic portions, according to the segment of the colon to which it gives attachment.
• mesocolon ascendens / ascending or right mesocolon : the peritoneum attaching the ascending colon to the posterior abdominal wall, usually obliterated when the ascending colon becomes retroperitoneal.
• mesocolon descendens / descending or left mesocolon : the peritoneum attaching the descending colon to the posterior abdominal wall; it is usually absent because the descending colon is ordinarily retroperitoneal.
• mesocolon sigmoideum / sigmoid, pelvic or iliac mesocolon : the peritoneum attaching the sigmoid colon to the posterior abdominal wall
• mesocolon transversum / transverse mesocolon : the peritoneum attaching the transverse colon to the posterior abdominal wall.
• mesorectum : the fold of peritoneum connecting the upper portion of the rectum with the sacrum
• omentum / epiploon : a fold of peritoneum extending from the stomach to adjacent organs in the abdominal cavity
• omentum majus / greater omentum / great epiploon / colic omentum / gastrocolic omentum : a prominent peritoneal fold suspended from the greater curvature of the stomach and passing inferiorly a variable distance in front of the intestines; it is attached to the anterior surface of the transverse colon.
• mesogastrium : the portion of the primordial mesentery that encloses the stomach, and from which the greater omentum is developed.
• ligamentum gastrocolicum / gastrocolic ligament : a peritoneal fold, part of the greater omentum, that extends from the greater curvature of the stomach to the transverse colon.
• ligamentum gastrophrenicum / gastrophrenic ligament : a fold of peritoneum continuous with the gastrosplenic ligament, extending from the right undersurface of the diaphragm to the cardiac part of the stomach.
• ligamentum gastrolienale or gastrosplenicum / gastrosplenic ligament or omentum / splenogastric omentum / gastrolienal or splenogastric ligament : a peritoneal fold extending from the greater curvature of the stomach to the hilum of the spleen
• omentum minus / lesser omentum or epiploon / gastrohepatic omentum / Willis' pouch : a peritoneal fold joining the lesser curvature of the stomach and the first part of the duodenum to the porta hepatis.
• lesser omentum / ligamentum hepatogastricum / hepatogastric ligament : a peritoneal fold, part of the lesser omentum, that passes from the under surface of the liver to the lesser curvature of the stomach.
• epiploic or omental foramen / foramen omentale or epiploicum : the opening connecting the greater and the lesser peritoneal sacs, situated below and behind the porta hepatis
• pancreaticosplenic omentum : a fold of peritoneum connecting the tail of the pancreas and the visceral surface of the spleen.
• pericolic membrane : occasional bands of peritoneum extending between the abdominal wall and the serosa of the colon
• plica paraduodenalis / paraduodenal fold : an occasionally found peritoneal fold containing a branch of the left colic artery
• Treitz's arch : an arch sometimes found in the paraduodenal fold, composed of the left superior colic artery and the inferior mesenteric vein
Cell types : serous cell
• ligamentum teres hepatis : a fibrous cord, the remains of the left umbilical vein, extending from the porta hepatis, where it is attached to the left branch of the portal vein, out through the fissure of the ligamentum teres and the falciform ligament to the umbilicus.
• fascia of Camper : the superficial layer of the superficial fascia of the abdomen.
• Cloquet's fascia : the condensation of extraperitoneal tissue closing the femoral ring (septum femorale).
• Treitz's fascia : fascia posterior to the head of the pancreas
• subperitoneal or extraperitoneal fascia or tissue / fascia extraperitonealis or subperitonealis : the thin layer of areolar connective tissue separating the parietal peritoneum from the abdominal walls
• Richet's fascia : a fold of extraperitoneal fascia enveloping the obliterated umbilical vein
• exocrine stomach / gaster / ventriculus (see also diseases of stomach and physiology of endocrine stomach) :  the musculomembranous expansion of the alimentary tract between the esophagus and the duodenum. Food mixed with gastric secretion forms a semifluid substance (chyme) suitable for further digestion by the intestine.

Macroscopic anatomy :
• hypertonic
• orthotonic
• hypotonic
• atonic
Areas :
• cardiac stomach : the portion of the stomach close to the esophagus
• curvatura major gastris / curvatura gastrica major / greater curvature of stomach / greater gastric curvature : the left or lateral and inferior border of the stomach, marking the inferior junction of the anterior and posterior surfaces
• curvatura minor gastris / curvatura gastrica minor / lesser curvature of stomach / lesser gastric curvature : the right or medial border of the stomach, marking the superior junction of the anterior and posterior surfaces
• cardia / pars cardiaca gastris / cardiac or cardial part of stomach : the part of the stomach immediately adjacent to and surrounding the cardiac opening of the esophagus, distinguished only by the presence of the cardiac glands, and lacking acid (parietal) and pepsin (chief) cells
• incisura cardialis / cardial or cardiac notch of stomach / incisura cardiaca gastris : a notch at the junction of the esophagus and the greater curvature of the stomach
• fundus gastricus / gastric fundus / fundus of stomach / fundus ventricularis / fundus ventriculi : that part of the stomach to the left and above the level of the entrance of the esophagus
• fornix gastricus / gastric fornix / fornix of stomach / fornix ventricularis / fornix ventriculi : a term used in radiographic anatomy to refer to the arch of the fundus of the stomach
• body of stomach / corpus ventriculare, ventriculi or gastricum / gastric body : that part of the stomach between the fundus and the pyloric part
• antrum pylori or pyloricum / pyloric, Willis or gastric antrum : the dilated portion of the pyloric part of the stomach, between the body of the stomach and the pyloric canal
• ligamenta pylori / ligaments of Helvetius : thickened bands of the longitudinal muscular layer of the stomach situated on the anterior and the posterior surfaces of the antrum pyloricum
• pyloric canal / canalis pyloricus : the short, narrow part of the stomach extending from the gastroduodenal junction to the pyloric antrum
• pylorus : the distal aperture of the stomach surrounded by a strong band of circular muscle, and through which the stomach contents are emptied into the duodenum. It is variously used to mean pyloric part of the stomach, pyloric antrum, pyloric canal, pyloric opening, and pyloric sphincter.
• prepyloric sphincter : a band of muscle fibers in the wall of the stomach proximal to the pyloric sphincter.
• valvula pylori / pyloric valve : a prominent circular fold of mucous membrane at the pyloric orifice of the stomach
• pyloric sphincter / musculus sphincter pyloricus : a thickening of the circular muscle of the stomach around its opening into the duodenum
• incisura angularis gastris or ventriculi / angular incisure or notch of stomach / gastric notch : the lowest point on the lesser curvature of the stomach, marking the junction of the cranial two-thirds and caudal one-third of the stomach
Coats :
• tunica mucosa gastris

Inner look :
• pliques
• longitudinal pliques in small curve
• cerebroid pliques in large curve
• areoles result from tone of muscularis mucosae
• areae gastricae / gastric areas : small patches of gastric mucosa, 1 to 5 mm in diameter, separated by the plicae villosae and containing the foveolae (gastric pits); they present a reticular pattern on endoscopy and double-contrast radiography
Cell types :
• stomach lining mucous cells : EP₃ and M₃ on basolateral membrane
• glands :
• cardiac glands : mucin-secreting glands at the cardiac end of the stomach surrounding the entrance of the esophagus into the stomach; they are similar to pyloric glands
• fundic glands / fundus glands / gastric glands : numerous branched simple tubular glands located in the mucosa of the fundus and body of the stomach; they consist of mucous neck cells, principal cells, parietal cells, and enteroendocrine cells
• intermediate glands : in a narrow region between the fundic and pyloric glands
• pyloric glands / glandulae pyloricae : the mucin-secreting glands of the pyloric part of the stomach; they consist of rare parietal cells and enteroendocrine cells, but have no principal cells
Cell types :
• mucous neck cells : cells found in the necks of gastric glands; they fill the spaces between the parietal cells and are filled with pale transparent granules.
• gastric gland chief or peptic or principal or zymogenic cells secrete
• pepsinogen : 5 types of zymogens of pepsins are known :
• group I pepsinogen / pepsinogen A (PgA)
• pepsinogen 3
• pepsinogen 4
• pepsinogen 5 / pepsinogen F
• group II pepsinogen / pepsinogen C (PgC) / progastricsin is an aspartic protease
• prochymosin / rennin : an aspartatic protease that catalyzes the cleavage of a single bond in casein to form soluble paracasein, which then reacts with calcium to form a curd, insoluble paracasein and is responsible for milk coagulation. It is found in the fourth stomach of the calf and other ruminants in a number of mammalian offspring, but the human genome contains only a pseudogene. A commercial preparation, rennet, is used for making cheese and rennet custards
Pepsin activity is higher at pH = 4. Phylogenetic analyses based on these sequences indicate that progastricsin diverged first followed by prochymosin, and that pepsinogens A and F are most closely related. 2 aspartates in the center of the cleft, Asp³² and Asp²¹⁵, function as catalytic residues, and thus pepsinogens are classified as aspartic proteinases. Conversion of pepsinogens to pepsins proceeds autocatalytically at acidic pH by 2 different pathways, a 1-step pathway to release the intact activation segment directly, and a stepwise pathway through a pseudo-pepsin(s). The active-site cleft is large enough to accommodate at least seven residues of a substrate, thus forming S4 through S'3 subsites. Hydrophobic and aromatic amino acids are preferred at the P1 and P'1 positions. Interactions at additional subsites are important in some cases, for example with cleavage of kappa-casein by chymosin. 2 potent naturally occurring inhibitors are known: pepstatin, a pentapeptide from Streptomyces, and a unique proteinous inhibitor from Ascaris. Pepsinogen genes comprise nine exons and may be multiple, especially for pepsinogen A. The latter and progastricsin predominate in adult animals, while pepsinogen F and prochymosin are the main forms in the fetus/infant. The switching of gene expression from fetal/infant to adult-type pepsinogens during postnatal development is noteworthy, being regulated by several factors, including steroid hormones.
• pepsin unit : a unit for measuring the proportion of pepsin in the gastric juice.
• gastric gland acid or oxyntic or parietal cells / border cells / Heidenhain's cells : large spheroidal or pyramidal cells that secrete
• hydrochloric acid (H⁺Cl^-)
• intrinsic factor production
They are found scattered along the walls of the gastric glands, with their tapered ends pushed between the chief cells. They express EP₃, H₂, CCK₂, and M₃ on basolateral membrane
Gastric juice :
• [H⁺] = 160 mEq/L => pH = 0.8-1.8
• [K⁺] = 5-10 mmol/L
• acid secretion

	males	females
basal	3.0±2.0 mEq/hr = 0.8±0.6 mEq/hr	2.0±1.8 mEq/hr = 0.6±0.5 mmol/s
maximal	23±5 mEq/hr = 6.4±1.4 mEq/hr	16±5 mEq/hr = 4.4±1.4 mmol/s

Gastric fluid at Weizmann Institute
• tunica submucosa gastris / submucous coat
• tunica muscularis gastris : the muscular coat of the stomach, composed of ...
• circular fibers
• longitudinal fibers
• oblique fibers
Gastric emptying is delayed (=> satiety) by :
• CCK1 receptors on the pyloric sphincter :
• fat-rich meal
• protein-rich meal
• gastrin
• secretin
but not sugar-rich meals
• tunica serosa gastris : the serous coat of the stomach
• gastric pacemaker : a saddle-shaped area of the greater curvature of the stomach at the junction of its proximal and middle thirds, where originate electric potentials which regulate the frequency of gastric contractions.
• exocrine liver / hepar (see also diseases of exocrine liver and physiology of endocrine liver) : a large gland of a dark-red color situated in the upper part of the abdomen on the right side. Its domed upper surface fits closely against and is adherent to the inferior surface of the right diaphragmatic dome, and it has a double blood supply from the hepatic artery and the portal vein. It comprises thousands of minute lobules, the functional units of the liver. Its manifold functions include the storage and filtration of blood, the secretion of bile, the excretion of bilirubin and other substances formed elsewhere in the body, and numerous metabolic functions, including the conversion of sugars into glycogen, which it stores.

While the sexual dimorphism of the liver has been recognized for several decades, scientists are only recently beginning to uncover the genes involved : regulator of sex limitation 1 (Rsl1) and Rsl2 are 2 KRAB-ZFP gene family members that repress male-specific liver gene expression in female mice^ref
Hepatogenesis : the specification of the vertebrate liver is thought to occur in a 2-step process, beginning with the establishment of competence within the foregut endoderm for responding to organ-specific signals, followed by the induction of liver-specific genes. On the basis of expression and in vitro studies, it has been proposed that the Foxa transcription factors establish competence by opening compacted chromatin structures within liver-specific target genes. Foxa1 and Foxa2 (forkhead box proteins A1 and A2) are required in concert for hepatic specification in mouse. In embryos deficient for both genes in the foregut endoderm, no liver bud is evident and expression of the hepatoblast marker AFP is lost. Furthermore, Foxa1/Foxa2-deficient endoderm cultured in the presence of exogenous FGF2 fails to initiate expression of the liver markers albumin and transthyretin. Thus, Foxa1 and Foxa2 are required for the establishment of competence within the foregut endoderm and the onset of hepatogenesis^ref.
Coats :
• tunica fibrosa hepatis / fibrous tunic of liver : the fibroelastic layer that surrounds the liver beneath the peritoneum; it is continuous at the hepatic portal with the perivascular fibrous capsule.
• tunica serosa hepatis : serous coat of the liver.
• area nuda hepatis / bare area of liver : the superior surface of the liver, adjacent to the diaphragm, that lacks a peritoneal covering; its boundaries are formed by the hepatic coronary ligament proper and the triangular ligaments
• fossa ductus venosi : fossa of ductus venosus: an impression on the posterior part of the diaphragmatic surface of the liver in the fetus, lodging the ductus venosus
• fossa sagittalis sinistra hepatis : a longitudinal fissure in the left lobe of the liver, composed of the fossa venae umbilicalis in front and the fossa ductus venosi dorsally
• fossa vesicae biliaris / fossa of gallbladder / fossa vesicae felleae : the fossa on the posteroinferior surface of the liver that lodges the gallbladder and helps to separate the right and left lobes
• fossae sagittales hepatis :
• fossae sagittales dextrae hepatis : a longitudinal fissure in the right lobe of the liver.
• fossa sagittalis sinistra hepatis : a longitudinal fissure in the left lobe of the liver, composed of the fossa venae umbilicalis in front and the fossa ductus venosi dorsally.
Cell types :
• hepatocytes / liver, hepatic or parenchymal cells (70%) are arranged in cords between the capillaries and remain after liver transplantation
• synthetize many proteins :
• albumin
• clotting factors
• haptoglobin
• produce bile and secrete it into smal channels (bile canaliculi) between adjacent hepatocytes. The bile collects in bile ducts formed by biliary epithelial cells and drains from the liver into the gallbladder (or, if the gallbladder has been removed, bile drains directly into the duodenum).
• regulate carbohydrate, fat, and protein metabolism
• detoxify the ammonia product of nitrogen metabolism
• break down drugs
• cholangiocytes are modified hepatocytes gGT⁺ secreting bile
• non parenchymal cells (NPC) are eventually exchanged with host cells after liver transplantation
• sinusoidal cells
• endothelial cells :
• sinusoidal endothelial fenestrae (SEF)
• Kupffer cells / stellate cells of the liver (2%; placed between endothelial cells or into lumen of sinusoids. Their nucleus is more vesicular than that of endothelial cells. After a liver transplant, these cells come from the RES of the recipient)
... line the sinusoids, thus separating hepatocytes from blood
• perisinusoidal space of Disse contains :
• plasma allowing exchange of plasma proteins, nutrients, and metabolites
• Ito cells / stellate lipocytes / interstitial cells / fat- or vitamin A-storing cells of liver : they also synthesize collagen and may be involved in hepatic tissue repair and be responsible for the excess collagen produced in liver cirrhosis.
• pit cells
• liver stem cells
Microscopic anatomy :
• hepatic or portal triads : the grouping of the tributaries of the hepatic artery, vein, and bile duct at the angles of the lobules of the liver (portal area / portal space). It is a complex composed of :
• terminal hepatic vein (THV) (branches of the portal vein)
• terminal branches of hepatic artery
• bile duct : bile flows in direction opposite to blood
• nerve
• liver lobules / lobuli hepatitis
• "classic" or traditional liver lobule : the unit drained by a central vein
• portal lobule : the unit supplied and drained by a portal triad
• liver acinus : the unit supplied and drained by terminal branches of portal triad vessels

Macroscopic topographic anatomy : segments are defined according to vascular marks detected during imaging (e.g. falciform ligament, plane of middle hepatic vein, ..). Each segment has a proper segmental root consisting of vascular afferences (portal vein branch and hepatic artery branch) and biliary efferences. At hilus both porta vein and hepatic artery divide into right and left branches. 45% has anatomical variants (e.g. hepatic artery from mesenteric artery, portal trifurcation, ...). Oxygenated blood enters the liver from the heart via the hepatic artery (25%) and from the gut via the hepatic portal vein (75%), mixes in the sinusoids, and drains via the hepatic central vein back to the heart. Hepatic sphincter is a thickened portion of the muscular coat of the hepatic veins near their entrance into the inferior vena cava. In 80% of cases the middle and left suprahepatic veins join and then the right ones joins to the common trunk.
Old anatomical terminology :
• lobus hepatis sinister / left lobe of liver : the smaller of the 2 main lobes of the liver. Anteriorly, it is separated from the right lobe by the falciform ligament. Posteroinferiorly, it is separated from the caudate and quadrate lobes by the attachment of the gastrohepatic ligament and the ligamentum teres
• lobus hepatis dexter / right lobe of liver : the largest of the 4 lobes of the liver. Anteriorly, it is separated from the left lobe by the falciform ligament. Posteroinferiorly, it is separated from the caudate lobe by the inferior vena cava and from the quadrate lobe by the gallbladder. Used in the broad sense, the term includes the caudate and quadrate lobes
• appendicular or linguiform Riedel's lobe : an anomalous tongue-shaped mass of tissue projecting from the right lobe of the liver
Macroscopic functional and surgical anatomy (Coinaud's segments (CS), 1957) : 3 vertical planes that divide the liver into 4 segments and of a transverse scissura that further subdivides the segments into 2 subsegments each. The 2 hemilivers are divided by Cantile's cholecystocleaving line / middle portal scissure (an ideal line joining the middle suprahepatic vein (approximated radiologically as the left border of the inferior vena cava (IVC)) and the gallbladder)
• segment I = caudate lobe
• processus caudatus hepatis / caudate process : the right of the 2 processes seen on the caudate lobe of the liver.
• processus papillaris hepatis / papillary process of liver / Spiegel's lobe : the left of the 2 processes seen on the caudate lobe of the liver.
Surgeons have divided the caudate lobe into 3 parts: papillay process, caudate process, and the paracaval portion corresponding to the dorsally located parenchyma in front of the inferior vena cava. All 3 parts are supplied by primary branches originating from the left and right portal veins, including the hilar bifurcation area : this double vascularization explains why the caudate lobe hypertrophies during cirrhosis. The hilar bifurcation branch often (50%) supplies the paracaval portion and it sometimes (29%) extends its territory to Spiegel's lobe. It was postulated by Couinaud that the paracaval portion or the S9 is not defined by its supplying portal vein branch but by its 'dorsal location' in the liver. Couinaud's caudate lobe or dorsal-liver concept cause, and still now causes, great logical confusion for surgeons^ref.
• right liver : divided by the right suprahepatic vein / right portal scissure (an ideal line joining the right border of the inferior vena cava with the midpoint of the line joining right liver border and gallbladder fundus) into ...
• right paramedian sector: divided by the right branch of the portal vein into ...
• segment VIII / right anterosuperior segment = vascularized by the upper branch of the anterior branch of the right branch of the portal vein
• segment V / right anteroinferior segment  = vascularized by the lower branch of the anterior branch of the right branch of the portal vein
• right posterolateral (posterior in vivo and lateral in vitro) sector
• segment VII / right posterosuperior segment  = vascularized by the upper branch of the posterior branch of the portal vein
• segment VI / right posteroinferior segment = vascularized by the lower branch of the posterior branch of the portal vein
• left liver : divided by the left suprahepatic vein / left portal scissure (an ideal line joining the left border of the inferior vena cava to the midpoint of left hepatic border) into ...
• left posterolateral sector (posterior in vivo and lateral in vitro) = segment II
• left medial sector = separated by the falciform ligament into ...
• segment III / left anterolateral segment
• segment IV = lobus quadratus hepatis / quadrate lobe of liver : a small lobe of the liver bounded on the right by the gallbladder, which separates it from the right lobe, and on the left by the ligamentum teres, which separates it from the left lobe. It is sometimes divided by the portal vein into :
• IVA / left superomedial segment
• IVB / left inferomedial segment


• Goldsmith-Woodburne classification (1957) names Coinaud's sectors as segments, and Coinaud's segments as subsegments.
• Liebermeister's grooves : developmental grooves on the surface of the liver.
• portal vein segments (PVS)
A major obstacle to coherent terminology for liver anatomy and resections has been that American and French anatomists have divided the left side of the liver through different planes. Couinaud divided the left hemiliver into "sectors" by a plane through the left hepatic vein. Healey and Schroy divided it into "segments" through the umbilical fissure. One anatomic justification for Couinaud's system of sectors is that the transverse portion of the left portal vein was said to terminate by dividing into the umbilical portion of the left portal vein and the vein to segment II. However, corrosion cast studies fail to consider the position of the ligamentum venosum, the structure defining the end of the transverse portion of the left portal vein. Therefore, it is uncertain whether the branch to segment II is a terminal branch of the transverse portion o