GI tract histo Flashcards
GIT
Hollow organs of GIT have identical fundamental structure
–> 4 layers + diff. nr of sublayers
Tounge
- Ant. region has lingual papillae
- Dorsal surf (behind sulcus terminalis) er w.out papillae
- Root has lingual tonsils
Tongue, basic structure
- It is a mass of striated muscle, cov by mucous membrane
- Mucous membr, smooth on lower surf
- Muscle fibers arranged í three interweaving planes (longitudinal, vertical og transversal)
- Submucosa on lower surface
- Dorsal surface has no submucosa
Tongue, basic structure
- It is a mass of striated muscle, cov by mucous membrane
- Mucous membr, smooth on lower surf
- Muscle fibers arranged í three interweaving planes (longitudinal, vertical og transversal)
- Submucosa on lower surface
- Dorsal surface has no submucosa
Lingual papillae
-Dorsal surf on anterior body has papillae (formed by lamina propria/muc.membrane)
- Filiform papillae;
- most numerous (tall, narrowed)
- cov w stratified sq keratinized epith
- engir taste buds - Fungiform papillae
- narrow stalk
- scattered taste buds
- stratified sq nonkeratinized - Circumvallate papillae
- largest ones
- in front of sulcus terminalis
- each papilla surr. by circular furrow, lined w stratified sq epithelium
- with taste buds - Foliate papillae
- rudimentary in humans
- along posterolateral sides
Taste buds
Intraepithelial taste receptors
-at their base; sensory - neuroepith.cells, synapse w fibers of afferent neurons
- supporting cells: elongated, apical surf w microvilli
- basal stem cells; small cells, near basal lamina
General structure of GIT
1) Tunica mucosa:
- Lamina epithelialis
- Lamina propria mucosa
- Lamina muscularis mucosa
2)Tunica submucosa
3) Tunica muscularis externa
- stratum circulares
- stratum longitudinalis
4)Tunica adventitia/serosa
Tunica mucosa: Lamina epithelialis
- absorption, secretion, protection og barrier against pathogens
- stratified sq. non-keratinized epithelium vs simple columnar epith.
Tunica mucosa: Lamina propria
Loose CT beneath the epithelium
- rich blood + lymph. circulation
- immune cells: plasma cells, macrophages and lymphoid cells
- *MALT hér
- isolated lymphocytes
- aggregates of l.cytes in terminal ileum-PREYERS PATCHES(GALT)
Tunica mucosa: Lamina muscularis mucosa
Few layers of smooth muscle cells beneath Lamina propria
-Natural frontier milli mucosa og submucosa
Enteric nervous system
Gut innervated w its own intrinsic nerve supply;
- nerve fibers
- clusters of nerve cells-peripheral ganglion cells
- glial cells
- ->located across all layers of GIT tube, en mest í MUSCULARIS EXTERNA OG SUBMUCOSA
- Muscularis externa:
- larger myenteric auerbach plx (regulates smooth m contraction, peristalsis, GIT motility)
- Submucosa;
- smaller submucosal meissner plx (regulates mostly glandular secretions, local blood flow)
Tunica submucosa
Loose CT
*Blood + lymph. vessels
- might contain glands:
a) muc.glands í esophagus. b)Brunner glands í duodenum
*Meissner submucosal autonomic nervous plx
Tunica muscularis externa
*skeletal muscle; esophagus og external anal sphincter
- smooth muscle;
a) stratum circular(internal) b)stratum longitud.(external)
*Ventriculus(stomach): 3 muscle layers, fibrae oblique innermost layer
Tunica muscularis externa frh
myenteric auerbach plx:
*Cajal interstitial cells (pacemakers), fyrir complex motility, peristalsis, secretions, transcellular transport, regeneration
–> Together w submucosal meissner plx = autonomic enteric nervous system (neurotransmitters)
Tunica adventitia/Serosa
1)Serosa: Thin layer of CT, cov w mesothelium
2) Adventitia; Thick layer of CT, carrying blood vessels, lymphatic innervation, without outer cover
- Fibers anchor the organ into its outer surroundings
Esophagus
- Tunica mucosa:
- Lamina epithelialis, stratified sq. non-keratinized
- Lamina propria, loose CT. near stomach eru esoph.mucinus glands
- Lamina muscularis: one layer, longitudinal muscle cells
- Tunica muscularis externa:
- stratum circulare (inner)
- stratum longitudinale (outer)
- Upper third esophagus=skeletal muscle
- Middle esophagus=both skel/smooth m
- Lower third=only smooth muscle
- Tunica adventita/serosa:
- loose CT. Only intraperitoneal p. of esophagus has serosa w mesothelium.
Stomach
- Digestion proteins, triglicerides
- forms chyme
- prod. HCL, intrinsic factor and gastric lipase
- prod. hormones (td gastrin, ghrelin)
-Wall consists of: Tunica mucosa Tunica submucosa Tunica muscularis externa Tunica serosa
Layers stomach
1) Tunica mucosa:
* Lamina epithelialis: simple columnar epithelium: secretes alkaline mucous
- epithelium of stomach invaginates into lamina propria=Gastric pits
- Lamina propria: loose CT w fibroblasts, plasma cells, mast cells, lymphocytes and blood vessels
- occupied by tubular glands (ext from base of gastric pits and reach lamina muscularis mucosa
*Lamina muscularis mucosa: one layer smooth muscle
2) Tunica muscularis externa:
- Innermost oblique layer: in cardiac region
- Middle circular layer: in pyloric region (forms pyloric spchinter)
- Outer longitudinal: smá evident hjá pylorus
Glands of stomach
1)cardiac glands 2)gastric glands proper 3)pyloric glands
Glands of stomach
1)Chief cells: columnar or pyramidal cells. Basophilic cytoplasm, nuclei near base, apical part w secretory granules w inactive pepsinogen enzyme and gastric lipase.
2) Parietal cells: Largest. Rounded or pyramidal cells. Spherical nucleus centrally, eosinophilic cytoplasm.
* Apical plasma membrane w invagination–>Intracellular canaliculi
* They produce Gastric Intrinsic factor og HCL
3)Mucous neck cells: Irregular/cuboidal/columnar. Nucleus near base. *prod mucous
4) Stem-Regenerative cells: Low columnar cells, oval nuclei.
* High rate of mitosis
5) Enteroendocrine DNES cells:
* Diffuse neuroendocrine system cells/D-cells: Somatostatin
* G-cells: Gastrin
* Enterochromaffin cells/EC-cells: Serotonin, Histamin
Small intestine: absorption surface
1) Plicae Circulares: Transverse folds of mucosa + submucosa
* Most developed in Jejunum
2) Vili: 0.5-1.5 mm. Long finger-like proj. of Lamina Propria into lumen
3) Microvilli: Modified apical plasmalemma of enterocytes covering intestinal villi
4)Crypts of Lieberkuhn:
*Simple tubular intestinal glands: Invagination of Lamina Epithelia into Lamina Propria
-cov by simple columnar epithelium, Goblet cells, Paneth cells(granulated epith. cells that secrete antimicrobial peptides/proteins t.d lysozyme, alpha-defensins and phospholipase A2),
Regenerative cells and enteroendocrine cells
Small intestine
Tunica mucosa:
- Lamina epithelialis: Simple columnar epith
- Absorptive cells(enterocytes), Goblet cells, Stem cells, Paneth cells, Enteroendocrine DNES cells, M-cells(take up intestinal microbial antigens->deliver them to GALT for immune rspns.)
- Lamina Propria: forming core of vilus. Here are also intestinal glands (crypts of lieberkuhn)
- Lamina propria and submucosa in ileum PEYERS PATCHES(L.nodules)
- Tunica Submucosa: dense irregular CT
- In duodenum, duodenal glands (Brunners glands)
Large intestine
Tunica Mucosa:
- LIberkuhn crypts: Long and lined w very abundant goblet cells, færri absorptive cells og færri enteroendocrine cells.
- No villi, no paneth cells
- Lamina Propria: rich in lymphoid cells+nodules.
Tunica muscularis externa:
- Inner circular, Outer longitudinal
- Outer longitudinal is not continuous along surface–>forming taeniae coli (bands)
Appendix
- Is a diverticulum of the cecum
- General structure similar to large intestine
- fewer og shorter crypts of lieberkuhn
- small, narrow og irregular lumen
- lamina propria og submucosa m l.nodules
- no taeniae coli
- infrequent paneth cells
Digestive glands (or glands associated w dig.system)
1) Liver (hepar)
2) Gallbladder (vesica fellea)
3) pancreas
4) major salivary glands
Prenatal development of dig.glands
1)Liver dev: from endoderm. The base(primordium) ---> hepatic diverticulum
2)Pancreas dev: from endoderm of the duodenum.
From dorsal wall–> dorsal bud
From ventral wall–> ventral bud
(Liver + pancreas dev: weeks 3-5)
3)Parotid gland: From ectoderm.
Epith. of primitive oral cav (stomodeum)
4)Submandibular gland: From endoderm
Epith. of floor of oral cav
5)Sublingual gland: From endoderm
Laterally to primordium of submandibular gland
(Major salivary glands dev: weeks 6-7)
Liver (hepar)
- largest organ um 1.5kg -Triangle shape -Intraperitoneal
- In right upper fjórðung f neðan þind
- 2main lobes, Right lobus dexter og Left lobus sinister.
- On the right are caudate and quadrate lobes
- Peritoneum on surface, except hjá fossa for gallbladder
- Gilsson capsule(capsula fibrosa): on liver surf. Dense irregular CT grows into the hepatic parenchyma along the vessels and bile ducts (esp. in the portal spaces)
- Porta hepatis: On visceral surf. Reinforced gilsson capsule.
- Entry site for proper hepatic A, portal V
- Exit for hepatic veins, common hepatic duct and l.vessels
Liver function
Central metabolic organ:
a) exocrine: bile prod.
b) endocrine: hormone (td angiotensinogen)
- Performs um 500 funct.
- C.hydrate, lipid + prot. metabolism:
- C.hydrate: synth+storage glycogen (glycogenesis or glycogenolysis). Gluconeogenesis from AA, glycerol osfr
-Protein: N-AA synth, E-AA degradation, albumin synth
*coagulation factors:
I) fibrinogen II)prothrombin and V, VII, XIII
*Protein C, Protein S, antithrombin
-Lipid: synth of fatty acids, synth/degradation of cholesterol, triglycerides, phospholipids, lipoproteins(VLDL, HDL), ketone bodies.
Liver function
Central metabolic organ:
a) exocrine: bile prod.
b) endocrine: hormone (td angiotensinogen)
- Performs um 500 funct.
- C.hydrate, lipid + prot. metabolism:
- C.hydrate: synth+storage glycogen (glycogenesis or glycogenolysis). Gluconeogenesis from AA, glycerol osfr
-Protein: N-AA synth, E-AA degradation, albumin synth
*coagulation factors:
I) fibrinogen II)prothrombin and V, VII, XIII
*Protein C, Protein S, antithrombin
-Lipid: synth of fatty acids, synth/degradation of cholesterol, triglycerides, phospholipids, lipoproteins(VLDL, HDL), ketone bodies.
Liver function frh
- erythrocyte forming in first trimester
- blood reservoir (10% of total blood volume)
- bile synth
- detoxification: t.d ammonia, foreign subst..
- hormone synth/degradation: angiotensinogen, thrombopoietin, IGF-1(insulin like growth factor), insulin degradation
- Vitamin/mineral store: vít A, D, B12, E, K. minerals Fe(ferritin), Cu, Zn
- lymph formation
- p. of mononuclear phagocytic system
Liver parenchyma organization
- Hepatic lobule (lobule of central vein): building block of liver
- formed by hepatocytes, arranged in cords, converge radially into central vein
- Hepatic sinusoids: milli cords of hepatocytes (arterial+venous blood)
- Cords of hepatocytes SURR. by reticular fibers
Portal space
Along each hepatic lobules corners eru 3-6 portal spaces, filled w CT.
3 structures (portal-Gilssons Triad)
1) interlobular A (br of proper hepatic A)
2) interlobular V (br of portal V)
3) interlobular bile duct (simple cuboidal epith)
Vascular supply of liver: Dual blood supply
1) Portal vein (deoxynated blood); brings 75% of blood from stomach, intestines and spleen rich in nutrients, low in O2.
2) Proper hepatic A (oxygenated blood): supplies 25% of blood. Low nutrients, High O2.
3)Arterial supply: Abd.aorta --> Celiac A --> common hepatic A -->proper hepatic A --> segmented arteries --> interlobular aa --> circumlobular aa --> sinusoids
- Portal vein –> interlobular vein –> sinusoids
- -> central vein –> (after leaving liver) Hepatic vein
- -> IVC –> right atrium
Bile ducts
1) Intrahepatic:
*bile canaliculi –>
Herrings ducts (simple cuboidal-Cholangiocytes) –>
Interlobular bile duct (Cholangiocytes) –>
Right + left hepatic ducts
3) Extrahepatic:
* Common hepatic duct + cystic duct = common bile duct (ductus choledochus)
* Common bile duct + pancreatic duct =hepatopancreatic ampulla (open on major duodenal papilla)
Liver regeneration
- Regenerative capacity is low under normal cond.
- It regenerates after partial surgical resection (hepatectomy), and after toxic or infectious damage
- loss of parenchyma –> mitosis of hepatocytes (Compensatory hyperplasia)
- Oval cells: regenerative cells, located milli cholangiocytes
Liver parenchyma organization
A classic hepatic lobule (lobule of the central vein)
- portal lobule; central veins of three hepatic lobules, in the middle is one portal space (Triad)
- Hepatic acinus; central veins of two hepatic lobules + two portal spaces. (area supplied by one circumlobular artery + one circumlobular vein)
- distribution of hepatocytes in hepatic acinus acc. to O2 gradient and nutrient content;
1) Zone 1 (periportal): high O2 + nutrients. Td prot synth
2) Zone 2 (transient): average O2 + nutrients
3) Zone 3 (periacinar): low O2 + nutrients. T.d lipid synth og storage, detoxification
Liver parenchyma organization
A classic hepatic lobule (lobule of the central vein)
- portal lobule; central veins of three hepatic lobules, in the middle is one portal space (Triad)
- Hepatic acinus; central veins of two hepatic lobules + two portal spaces. (area supplied by one circumlobular artery + one circumlobular vein)
- distribution of hepatocytes in hepatic acinus acc. to O2 gradient and nutrient content;
1) Zone 1 (periportal): high O2 + nutrients. Td prot synth
2) Zone 2 (transient): average O2 + nutrients
3) Zone 3 (periacinar): low O2 + nutrients. T.d lipid synth og storage, detoxification
Hepatocyte
- Polygonal shape
- forming anastomosing cords
- 70-80% af liver volume
- round nucleus, 1-2 nucleoli (sometimes two nuclei)
- eosinophilic c.plasm (MANY m.chondrias)
- basal surf (vascular pole): facing sinusoids. Has microvilli
- Lateral surf (biliary pole): creates bile ducts. Has microvilli
*Lateral surf: tight junct (occludens), adherent junct(adherens og desmosomes) og gap junct
Hepatocyte frh
RER; synth of albumin, coagulation factors, enzymes
SER: enzymes for biotransformation and detoxification of subst. Synth of bile acids, cholesterol and degredation of heme.
Lysosomes: degredation of damaged plasma proteins, storage of Fe and Cu
Inactive lysosomes: yellow-brown pigment lipofuschin
Nonparenchymal liver cells
1) endothelial cells: simple sq. epith in sinusoids walls (have openings–>discontinuous)
- milli endothelium og hepatocyte surf (blood pole): Perisinusoids space/Space of disse
function: metabolism place, nutrient intake and foreign subst. + their release
2)Kupffer cells/liver macrophages: p of mononuclear phagocytic system. Remove damaged erythrocytes, foreign subst, bacteria. -Irregular shape -Fe reservoir
3) Hepatic stellate cells/cells of lto: -
- in Perisinusoid space -Star shaped
- not easily þekkjanlegar in preperations
- cytoplasm contains lipid droplets-VÍT A storage(50-80% of total body content)
Gallbladder
Pear-shaped hollow organ
- on visceral surf of liver, below right lobe(fossa for vesicae felleae)
- collect, concentrate og release bile into duodenum (cystic duct joins common hepatic duct = common bile duct)
-svo common bile duct + pancr. duct = hepatopancreatic ampulla
Microanatomy gallbladder
1) Tunica mucosa;
- forms mucosal folds, lined w simple columnar epithelium w microvilli (resorptive epith)
- Na/K/ATPase pump to concentrate bile.
*In neck (collum) of gallbladder are mucus glands–>protection of mucosa of bile
*The mucosa forms deep invaginations–>
Rokitansky-Aschoff sinuses
- *Lamina propria; Loose CT
- **Lamina muscularis mucosa is missing!
2) Tunica muscularis;
- bundles of smooth muscle cells oriented circular, longitudinal and oblique (contraction empties gallbladder)
- Contractions initiated by hormone cholecystokinin CCK og regulated by autonom n.system.
3)Tunica serosa/adventitia: Loose CT sheath
Gallbladder-gallstones
Bile: yellow-dark green thick liquid.
- 85% water, bile acids, bile pigments, cholesterol, fatty acids, salts osfr.
- liver prod um 0.7-1.2 l of bile per day
*gallstones/cholelithiasis: due to disparity milli concentration of cholesterol, bile acids and phospholipids
Pancreas
exocrine og endocrine funct.
- Across abd. cav
- under diaphragm
- behind stomach
- milli duodenum og spleen
*retroperitoneal
Microanatomy of pancreas
- CT capsule sends septa–>dividing pancreas into lobes and lobules.
- Septa contain larger ducts, blood, lymphatics and autonom. nerves
Exocrine p. of pancreas
a) secretory portion (pancreatic acini/alveoli): each composed of several serous, pyramidal cells
- the cells are polarized; basal p. is bsophillic (RER, nucleus) and apical p. is eosinophillic (GA and zymogenic granules-inactive precursors of enzymes)
b)duct system; intralobular;;; intercalated (simple sq epith) ---> intralobular (simple cuboidal) ---> interlobular (simple columnar) ---> Main pancreatic duct
**Centroacinar cells; cells of the intercalated duct, which ext into the lumen of the acin. (do not contain zymogenic granules)
Pancreatic juice of exocrine p. of pancreas
Pancr. juice made up of the exocr. component.
- Enzymes: Trypsin, alpha-amylase, lipases, nucleases osfr.
- Og alkaline juices (HCO3-)
- CCK (pancreozymin) stimulates prod. enzymes
- Secretin prod. alkaline juices to neutralize acidic chyme
Pancreas, endocrine part
- endocrine portion makes um 1.5% total volume of pancreas.
- ->mostly in the cauda (tail)
- Islet of langerhans (pancreatic islets);
- round, oval clusters of endocrine cells. Surr by collagen fibers and supp. by fenestrated blood capillaries.
**acute pancreatitis:
sudden life threat. disease due to increased activation of pancr. enzymes. Enzymatic self-digestion and damage to the vessel wall (necrosis) and edema can occur
Salivary glands
- Exocrine glands, main ducts open into oral cav
- prod. saliva og initial digestion of c.hydrates+lipids.
*saliva composition; 98% water minerals enzymes; amylase, lipase leukocytes epith. cells lysozyme IgA
Salivary glands
- Exocrine glands, main ducts open into oral cav
- prod. saliva og initial digestion of c.hydrates+lipids.
*saliva composition; 98% water minerals enzymes; amylase, lipase leukocytes epith. cells lysozyme IgA
Salivary glands
- Exocrine glands, main ducts open into oral cav
- prod. saliva og initial digestion of c.hydrates+lipids.
*saliva composition; 98% water minerals enzymes; amylase, lipase leukocytes epith. cells lysozyme IgA
microanatomy salivary glands
a) secretory portion, 3 cell types
-Serous cells: pyramidal, round nucleus. Basal p. basophilic (RER). Apical p. m secr. granules (t.d amylase).
They form acinus or alveolus (round w small lumen)
- Mucus cells: Columnar. Oval nucleus in basal p. Cytoplasm m mucin. They form a tubule (oval shape)
- Myoepithelial cells: on inner surf. of basement membrane. Squamous cells w long processes. Með myofilaments (actin, myosin) –> contraction empties secretory portion
microanatomy salivary glands
b) duct system er intralobular;
Intercalated—>Striated—>interlobular—>main duct(stratified columnar, stratified sq. nonkeratinized)
Parotid gland
- Paired
- Alveolar
- Bara serous gland
- Many intercalated and striated ducts. Alot of fat cells
*Secretion is sparse, aqeous (alpha-amylase, proteins w antimicrobial effects)
Submandibular gland
- paired
- tubuloalveolar
- seromucus (mostly serous)
- more striated ducts in the serous part heldur en í mucus p.
Sublingual gland
- paired
- tubuloalveolar
- seromucus (mostly mucus)
- few striated ducts, serous cells
- not covered by CT capsule
- main duct joins duct of submandibular gland and form common duct
- -> enters oral cav (at sublingual papilla)
