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Anatomy 4.3 November 8, 2011
The GIT Histology Dr. Ma. Cristina Elma-Zulueta
OUTLINEDigestive SystemI. ORAL CAVITYII. TONGUEIII. TEETHIV. PHARYNXV. ESOPHAGUSVI. STOMACH
A. CARDIAB. FUNDUSC. BODYD. PYLORUS
VII. SMALL INTESTINEVIII. LARGE INTESTINEIX. APPENDIXX. ANUS
*Text in Times New Roman are lifted from the book
Objectives:At the end of the study, the student should be able to understand the histologyof the GIT:
Describe the different lingual papillae. Describe the structure of the tooth. Review histologic structure of tonsils. Name and describe the layers of the walls of the tract. Differentiate histologically the different segments of the tract. Differentiate the glands in the different areas of the stomach. Describe the modifications.
DIGESTIVE SYSTEM
Consists of the tract from the mouth (oral cavity) to the anus, aswell as the digestive glands emptying into this tract, primarily thesalivary glands, liver, and pancreas
Has the same layers throughout the whole tract
4 Principal Layers
1. MUCOSA OR MUCOUS MEMBRANE (LINING) EPITHELIUM LAMINA PROPRIA loose connective tissue rich in blood vessels,lymphatics, lymphocytes and smooth muscle cells; sometimes alsocontaining glandso MUSCULARIS MUCOSAE/INTERNA - separates mucosa from
submucosa
2. SUBMUCOSA contains denser connective tissue with many bloodand lymph vessels and the submucosal plexus of autonomic nerves
3. MUSCULARIS PROPRIA/EXTERNA the autonomic myenteric nerve plexus is contained in the connective tissue between these twomuscle layers
INNER CIRCULAR OUTER LONGITUDINAL
4. SEROSA/ADVENTITIA SEROSA a thin layer of connective tissue, rich in blood vessels,lymphatics, and adipose tissue, with a simple squamous covering(mesothelium )
ADVENTITIA consisting of connective tissue containingvessels and nerves, lacking mesothelium
Main Function of Digestive tract epithelial lining provide selectively permeable barrier between contents of tract and
tissue of the body Facilitate transport and digestion of food Promote absorption of products of this digestion Produces hormones for the activity of the digestive system Produces mucus for lubrication and protection
nice to know: the lamina propria and the submucosa contain abundant lymphoid
nodules as protection from bacterial invasion in the lamina propria, IgA is also secreted as a form of protection
also against viral and bacterial invasion
I. ORAL CAVITY
Lined by stratified squamous epithelium keratinized ornonkeratinized depending on the region
Keratinized: gingiva & hard palate
Non-keratinized: soft palate, lips, cheeks & floor of mouth
HARD PALATE Stratified squamous keratinized Forms deep invaginations called epithelial ridges Has thick collagen fiber bundles that firmly bind with palatal mucosa
Figure 1: Hard Palate Figure 2: Soft Palate
SOFT PALATE Lined by stratified squamous, non-keratinized Interdigitates with lamina propria forming rete apparatus Movable structure attested by presence of skeletal muscle Core has numerous salivary mucous glands
LIP Two sides: covered by skin mucosa and oral mucosa Contains striated muscles and minor salivary glands Vermillion/Vermillion zone:
o Transition zone between normal skin and lip mucosao Where epidermis is very thin, lightly keratinizedo Lacks gland for oil and sweat
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Figure 3: Lip
Lip. oral mucosa (OM), skin (S), hair follicles (F) and associated glands.(V)vermilion zone , is prone to excessive dryness and chapping in cold,dry weather. Internally, the lips contain much striated muscle (M)and many minor salivary glands (G).
II. TONGUE
Stratified squamous non-keratinized epithelium Mass of striated muscle Muscle fibers cross one another in 3 planes Mucous membrane strongly adherent to muscle Dorsal surface: covered anteriorly by papillae
Figure 4: Tongue and Lingual Papillae
CLINICAL CORRELATON
The opposing forces of the Genioglossus muscle on each side of thetongue keep it in the middle. The LEFT genioglossus pushes thetongue to the right while the RIGHT genioglossus pushes thetongue to the left. If tongue is deviated to a side, you can pinpointwhich nerve was damaged.
Terminal Sulcus V-shaped groove th at separates the posterior third of the tongues
dorsal surface from the anterior two thirds.
Anterior two-thirds Body of the tongue With lingual papillae of four types, all containing cores of connective
tissue covered by stratified squamous epithelium
FILIFORM PAPILLAE Very numerous Elongated conical shape or pointed Heavily keratinized Epithelium lacks taste buds Provides rough surface that facilitates food movement duringchewing
FUNGIFORM PAPILLAE Less numerous Lightly keratinized Mushroom in shape With connective tissue cores Have scattered taste buds on their upper surfaces Irregularly interspersed with filiform papillae
FOLIATE PAPILLAE Poorly developed in adults Consist of parallel ridges and furrows on the side of the tongue Taste buds are present
CIRCUMVALLATE PAPILLAE Least numerous Largest Over half the taste buds on the human tongue Form a V-shaped line before the terminal sulcus Von Ebner glands (serous salivary glands) empty into deep groovesthat surround this papilla
Posterior third Root of tongue The mucosa of the root is filled with masses of lymphoid nodules
separated by crypts, all of which comprise the lingual tonsils Stratified squamous non-keratinized epithelium Without lingual papillae
5 qualities in human taste perception: Saltiness (metal ions) Sourness (hydrogen ions from acids) Sweetness (sugars and related organic compounds) Bitterness (alkaloids and certain toxins) Umami or savory (amino acids)*tastants
TASTE BUDS Ovoid structure containing 50-75 cells Half are elongated gustatory/taste cells Other cells: basal stem cells & supportive cells Taste pore: opening where gustatory cells microvilli project Cells are constantly replenished every 7-10days present on fungiform and foliate papillae but are much moreabundant on vallate papillae.
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Figure 5: Taste Buds
III. TEETH
Consists of:o Crown exposed above the gingivao Neck constricted part of the tooth at the gumo Roots below the gingiva that hold the teeth in bony sockets
called alveoli
Figure 6: Teeth
DENTIN Comprise the bulk of the tooth Calcified tissue containing 70% Ca hydroxyapatite Matrix consists of type 1 collagen fibers & glycosaminoglycans Matrix produced by odontoblasts
ENAMEL Hardest component of human body 98% hydroxyapatite 2 unique proteins: amelogenin & enamelin Has no collagen Consists of enamel rods Matrix produced by ameloblasts Produced by cells of ectodermal origin, whereas most of the otherstructures of teeth derive from mesodermal and neural crest cells .
PERIODONTIUM Comprises structures responsible for maintaining the teeth in themaxillary & mandibular bones
Consists of:o Cementum covers the dentin of the root; similar in composition
to bone o Periodontal ligament connective tissue with collagen fiber
bundles connecting the cementum and the alveolar bone of thetooth socket
o Alveolar bone in immediate contact with the periodontalligament, which serves as its periosteum
o Gingiva mucous membrane firmly bound to the periosteum of themaxillary and mandibular bones composed of stratified squamousepithelium and lamina propria with numerous connective tissue
papillae
IV. PHARYNX Transitional space between oral cavity & respiratory & digestivesystems
Forms an area of communication between nasal region & larynx Lined by stratified squamous epithelium near esophagus &respiratory epithelium near nasal cavity
Contains tonsils
V. ESOPHAGUS
MUCOSA: Non-keratinized stratified squamous epithelium Has same major layers as the rest of GIT SUBMUCOSA: contains esophageal glands(mucus-secreting) LAMINA PROPRIA (LP): esophageal cardiac glands (mucus- secreting;
found in the LP near the stomach) MUSCULARIS EXTERNA
o Proximal third: skeletalo Middle third: skeletal & smootho Distal third: smooth
Most distal portion is covered by serosa
The rest is enclosed by adventitia
ESOPHAGOGASTRIC JUNCTION Junction of the esophagus and the cardiac region of the stomach An abrupt change in the mucosa from stratified squamous epitheliumto simple columnar epithelium invaginating as gastric pits
Mucosa contains esophageal cardiac glands that opens into thesuperficial gastric pits
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Figure 7: Esophagogastric Junction
VI. STOMACH Mixed exocrine-endocrine organ that digests food and secreteshormones
Main functions are to continue the digestion of carbohydratesinitiated in the mouth, add an acidic fluid to the ingested food,transform it by muscular activity into chyme
Regions:o Cardiao Funduso Bodyo Pylorus short coiled secretory portion
Rugae longitudinal directed folds in the mucosa and submucosa ofthe empty stomach which usually flattens when it is filled with food
Gastric Pits- invaginations found in the lamina propria Pyloric sphincter- thickening of middle circular layer of muscularisexterna
HISTOLOGIC REGIONAL DIFFERENCES Cardia
o Narrow circular region at the transition between the esophagus andthe stomach
o Mucosa: contains tubular glands, usually branched, with coiledsecretory portions called cardial glands o Short gastric pit
Figure 8: Stomach (Cardia)
Fundus/Bodyo Lamina propria: filled with branched, tubular gastric glands
Figure 9: Stomach (Fundus/Body) Pylorus
o Funnel-shaped region opening into the small intestineo Gastric pits become deeper and the length of the glands will be
shorter or of the same sizeo Middle layer of muscularis is greatly thickened to form the pylor
sphincter
Figure 10: Stomach (Pylorus)
Figure 11: Pyloric Sphincter
HISTOLOGIC REGIONAL SIMILARITIES Lining of epithelium: simple columnar epithelium with mucus-
secreting cells Submucosa has NO GLANDS; found in LAMINA PROPRIA instead No lymphoid aggregates; no villi; with rugae
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Muscularis has 3 muscle layerso Inner Obliqueo Middle Circularo Outer Longitudinal
Most of cells of the gastric glands are mucus- secreting to protectthe wall from HCL
Covered by thin serosa
Figure 12: Stomach
GASTRIC GLAND Has an isthmus, a neck, and a base
Distribution of epithelial cells in the glands is not uniform
Figure 13: Gastric Gland
PARIETAL CELL Present mainly in the upper half of gastric glands w/ fewer in thebase
Large, rounded or pyramidal Central spherical nucleus Intensely eosinophilic cytoplasm because it contains a lot ofmitochondria for production of HCl & intrinsic factor.
Secretory activity is stimulated through cholinergic nerve endingsand by histamine and a polypeptide called gastrin
MUCOUS (NECK) CELLS Irregular in shape, with the nucleus at the base of the cell Columnar cells with mucous in their apex
CHIEF/ZYMOGENIC/PEPTIC CELLS Predominate in the lower region of the tubular glands Cytoplasmic granules contain pepsinogen Produce lipase and hormone leptin Basophilic Columnar
ENTEROENDOCRINE CELLS Epithelial cell type in the mucosa throughout the digestive tract Secretes short polypeptides Enterochromaffin Cells (EC cells) found on the basal lamina ofgastric glands of the fundus and secret serotonin
G Cells in contact with the glandular lumens in the pylorus andlower body of the stomach that produce gastrin
STEM CELLS Found in the neck region of the glands Low columnar cells with basal nuclei and divide asymmetrically
VII. SMALL INTESTINE
Site of terminal food digestion, nutrient absorption, and endocrinesecretion
Lining epithelium: simple columnar with striated border Plicae circulares
o series of permanent circular or semilunar folds o consists of mucosa and submucosao best developed in the jejunum
Villi: epithelium & lamina propria Intestinal crypts/ Crypts of Leiberkuhn: short tubular glands
between villi
Cells lining the intestinal epithelium Enterocytes
o absorptive cellso tall columnar cells with an oval nucleuso striated(brush) border on apical surface
Goblet cellso Less abundant in duodenum, more abundant in ileumo Produce mucins that are hydrated and cross-linked to form mucuso Protect and lubricate the lining of the intestine
Paneths Cello Broad base with narrow apex, at the base of intestinal gland;o exocrine cells with large eosinophilic secretory granules in their
apical cytoplasm that contains lysozymeo functions in innate immunityo regulate the microenvironment of intestinal crypts
Enteroendocrine cellso secrete peptides - have both endocrine and paracrine effectso part of diffuse neuroendocrine system
Microfold (M) cellso Specialized epithelial cells overlying the lymphoid follicles of
Peyers patcheso endocytose antigens and transport them to the underlying
macrophages and lymphoid cells
For Figure 14: Small IntestineAbsorptive surface of the small intestine. (a): The mucosa &submucosa are the inner two of the guts 4 concentric layers. (b): Plicae circulars, the absorptive area. (c, d): They are lined byfinger like projections called villi . Each villus contains lamina propriaconnective tissue with microvasculature & lymphatics called lacteals(e): At the apical cell membrane of each enterocyte are densemicrovilli, which serve to greatly the absorptive surface of the cell.
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Figure 14: Small Intestine
MICROCIRCULATION blood vessels penetrate the muscularis externa forming plexuses in
the submucosa branches extend through the muscularis mucosae and lamina propria
into each villus, forming a capillary network venules from capillary network will drain into the veins of the
submucosal plexus
LYMPHATIC VESSEL Close-ended tube in the villus Lacteals : run to the region of lamina propria above the muscularis
mucosae for lipid absorption
ENTERIC NERVOUS SYSTEM responsible for intestinal contraction /peristalsis
SUBMUCOSAL/ MEISSNERS PLEXUS in the submucosa MYENTERIC/AUERBACHSPLEXUS- between outer longitudinal and
inner circular layers of muscularis externa
DUODENUM Simple columnar epithelium with striated border Duodenal (Brunners) glands
o found in submucosao large clusters of branched tubular mucous glandso secrete alkaline mucus neutralizes chyme, bring intestinal
contents to optimum pH for pancreatic enzyme action
o protect mucous membrane against acidity of gastric juice
JEJUNUM Villi leaf-like prominence of Plicae circulares No glands in submucosa Paneth cells at the bottom of glands, intensely stained
ILEUM Simple columnar epithelium with brush border Peyers patches : aggregates of lymphoid nodules
FOLDS1. PLICAE CIRCULARES/KERCHRINGS VALVE series of permanentfolds consisting of the mucosa & submucosa having semilunar,circular/spiral form
most developed in jejunum increases surface area by 3-fold
Figure 15: Plicae Circulares2. VILLUS
epith. & lamina propria long outgrowths of the mucosa projection into the lumen 10-fold increase in surface area
3. MICROVILLUS 3000/cell
cylindrical protrusion of the cytoplasm consisting of the cellmembrane enclosing a core of actin microfilaments
20-fold increase in surface area
Table 1. Comparison of the three regions of the small intestineDUODENUM JEJUNUM ILEUM
VILLI Tall & slender Leaf-shaped -LAMINAPROPRIA
- -PayersPatches
SUBMUCOSASubmucosal/
BrunnersGlands
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ILEOCECAL VALVE Marks the end of small intestine Shows an abrupt change in villous pattern which is found in small
intestine mucosa, to the glandular pattern found in colonic mucosa There is also thickening of muscularis mucosa which is smooth
muscle tissue found beneath the mucosal layer of digestive tract.
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Figure 18: Ileocecal Valve
VIII. LARGE INTESTINE/ COLON/ BOWEL
Main functionso absorption of watero formation of fecal mass from undigestible materialo production of mucus - lubricates intestinal surface
INTESTINAL GLANDo Simple columnar INFESTED with goblet cells!o Colonocytes or absorptive cells : columnar, with short, irregular
microvillio with a small number of enteroendocrine cells
MUCOSAo no folds except in distal (rectal) portiono penetrated by tubular intestinal glandso no villi o Lamina Propria
Rich in lymphoid tissue related to the large bacterial populationof the large intestine
MUSCULARIS EXTERNAo Inner circular layer continuous throughouto Outer longitudinal layer gathered in three longitudinal bands
called taenia coli o Haustra: series of sacs caused by the bands of taenia coli
RECTUM Histologically same with colon. Only difference is the outer
longitudinal muscle is continuous
Figure 19: Intestinal Gland
IX. APPENDIX Simple columnar epithelium with goblet cells With continuous outer longitudinal layer, no taenia coli With abundant lymphocytes and lymphoid follicles in the lamina propria and submucosa
evagination of the cecum small, narrow, irregular lumen fewer & shorter glands
X. ANUS
Anal columns (Columns of Morgagni): series of longitudinal foldsformed in mucosa
Recto-anal junction: mucosal lining changes from simple columnarepithelium with goblet cells to non-keratinized stratified squamousepithelium (keratinized- outside)
Anal Transition Zone
Rectum/Anal CanalA. Colorectal Zone upper 3 rd of anal canal; simple columnar epith.B. ATZ middle anal canal; stratified columnar epith. Interposed bet.
simple columnar epith.C. Squamous Zone lower 3 rd of anal canal; stratified squamous epith.
Anal Glands extend into submucosa & even into muscularis externa;branched, straight tubular; secrete mucus
Circumanal Glands skin surrounding anal orificeSubmucosa at Anal Column submucosal venous plexus
SUMMARYLayers Cell - Stomach Cell - IntestinesMucosaSubmucosaMuscularis propriaSerosa/Adventitia
StemMucousParietalZymogenEnteroendocrine
GD
AbsorptivePanethMicrofold cellsGoblet
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