Histology of Gastrointestinal Tract-1 PDF

College of Applied Medical sciences Department of Medical Laboratory technology Histology of gastrointestinal tract-1 Gastrointestinal tract (alimentary tract): o Mouth o Pharynx o Esophagus o Stomach o Small Intestine o Large intestine o Rectum & Anal canal Functions of the GIT o Passage (T...

College of Applied Medical sciences Department of Medical Laboratory technology Histology of gastrointestinal tract-1 Gastrointestinal tract (alimentary tract): o Mouth o Pharynx o Esophagus o Stomach o Small Intestine o Large intestine o Rectum & Anal canal Functions of the GIT o Passage (Transportation) of food (mouth, oropharynx, esophagus) o Digestion (stomach, intestine) o Absorption (small intestine) o Elimination of residues & absorption of water (large intestine, rectum & anal canal)  Basic structure (1) Mucosa : o Lining epithelium : Stratified squamous non-keratinized in esophagus. Simple columnar in stomach & intestines o Lamina propria (corium): loose CT o Muscularis mucosae: 2 layers of SM:  Inner circular (IC)  Outer longitudinal (OL) (2) Submucosa : Loose CT containing blood vessels (BV), nerves & lymphatics (3) Musculosa : 2 layers of SM: o Inner circular (IC) o Outer longitudinal (OL) (4) Serosa (or adventitia): o Loose CT covered by simple squamous epithelium (mesothelium) The Esophagus 1) Mucosa : o Lining epithelium: stratified squamous epithelium non- keratinized tissues o Lamina propria: o Muscularis mucosa: IC & OL (2) Submucosa : o Loose CT containing BV, nerves & lymphatics o Contain mucous secreting glands (esophageal glands) (3) Musculosa : IC and OL (4) Adventitia: Loose CT The stomach  Function of stomach: o It is a food reservoir (food storage) o Food is acidified & converted by mechanical & chemical action into a thick viscous fluid (the chyme) Stomach o The most dilated part of GIT o Stomach divided anatomically into: cardia, fundus, body & pyloric regions o Fundus & body are similar in structure Cardia of stomach: Its mucosa contains mucous-secreting glands. Fundus of Stomach: I- Mucosa : Gastric pits: Little depressions in the stomach lining where gastric glands open o Epithelium : Simple columnar , mucus secreting. o Lamina propria: loose C.T. containing the fundic glands o Muscularis mucosa: II- Submucosa: o loose C.T. containing BVs, nerves & lymphatics III- Musculosa o Inner oblique (IO) o Middle circular (MC) o outer longutidinal (OL)  so the mechanical action will be in all directions IV- Serosa: o loose C.T. covered with mesothelium Characters of fundic glands 1- Surface mucus cells o Cover the surface & line the pits o Columnar cells o Secrete neutral mucus 2- Mucous neck cells o Located just below gastric pit. o Columnar cells o secretes acidic mucus 3- Parietal or oxyntic cells: o Most numerous in middle portion o Large rounded o Acidophilic cytoplasm o Central rounded nuclei Functions: secretion of: 1- HCL 2- Intrinsic factor (essential for B12 absorption) 4- Chief (Peptic) cells: o Located in the lower 1/3rd of gastric glands. o Large basal nucleus o Basal basophilic & apical acidophilic cytoplasm Function: Secrete pepsinogen 5- Entero-endocrine (APUD) cells: - Located in the basal portion of gastric glands Function: Secretes serotonin, histamine and gastrin. - These are endocrine cells which release their products into the blood vessels.  Pylorus of stomach The pylorus is the furthest part of the stomach that connects to the duodenum Similar to fundus with some changes 1- Pyloric gland characters:  Not crowded  Highly convoluted  pits wider & longer 2) Musculosa: o 2 layers only: Thick IC (pyloric sphincter, PS) & OL Small Intestine It is the site of terminal food digestion, absorption & endocrine secretion. Three parts : o Duodenum: is the first and shortest segment – connect he stomach to the jejunum o Surrounding the head of pancreas o Jejunum: constitutes the proximal 2/5 after the duodenum o Ileum: the distal 3/5 Adaptation of small intestine to its absorptive function: o 6 m long o Plicae circularis (Folds of mucosa & submucosa), It increases surface area 3 folds o Villi: (outgrowth of intestinal mucosa = epithelium + CT corium ) increase surface area 10 folds o Microvilli: (finger-like projections of the apical cell membrane) increase surface area 20 folds General structure of small intestine (1) Mucosa: villi & Crypts a- Epithelial lining : - Simple columnar, Goblet, Paneth, Enteroendocrine, stem cells, M & caveolate cells. b- Lamina propria : C.T. and corium (dermis) c- Muscularis mucosa : IC & OL (2) Submucosa: loose CT containing o Mucus glands in the duodenum (Brunnerʼs glands) o Lymphatic nodules (Payer's patches ) in ileum (3) Musculosa: IC & OL (4) Serosa: o Duodenum contains Brunner’s glands which are mucous secreting glands present in the layer of submucosa Ileum Contains Payer’s patches which are lymphoid follicles present on the antimesenteric side of the ileum N.B. Villi are short above Payerʼs patches Cells lining intestinal mucosa (1) Absorptive columnar cells: Tall columnar cells with apical microvilli (brush border). (2) Goblet cells: Mucus secreting unicellular glands (vacuolated in H&E sections) (3) Enteroendocrine cells: o Similar to those of stomach o More than 15 different types in GIT o Secrete many types of hormones (4) Undifferentiated Columnar Stem Cells (5) Paneth cells: o At the base of crypts only o Pyramidal with basal rounded nuclei o Apical acidophilic & basal basophilic cytoplasm Function: o secrete lysozymes that kill bacteria (6) M-Cells (Membrane-like cells) o Dome shaped with basal cavity packed with lymphocytes and macrophages Function: Antigen presenting cell- transport antigens from the lumen to cells of the immune system (7) Caveolate cells Large intestine It is the site of absorption of water & production of mucous for lubrication Parts of the large intestine are: o Ceacum o Ascending colon o Transverse colon o Descending colon o Sigmoid (pelvic colon) o Rectum o Anal canal Structure of large intestine (1) Mucosa: o No villi o Crypts are wider & deeper o Epithelial lining: No paneth cells  Absorptive columnar cells  Many goblet cells  Enteroendocrine cells  Stem cells o Lymphatic nodules in lamina propria (2) Submucosa: o No glands  Structure of large intestine (3) Musculosa: o Inner circular o Outer longtudinal layer consists of only three bundles of SM (tenia coli) (4) Serosa: o Rich in fat cells (appendices epiploicae, masses of adipose tissue covered with peritoneum) Diagram showing the structure of large intestinal wall Note the very numerous goblet cells in large intestine GLANDS ASSOCIATED WITH THE DIGESTIVE TRACT Salivary glands Pancreas Liver Pancreas Pancreas It is a mixed (exocrine & endocrine parts) gland Its endocrine part is the Its exocrine part is Islet of Langerhans, responsible for secretion which is responsible for of pancreatic juice. release of pancreatic hormones. Produce enzymes include trypsin Secretes the hormones insulin and chymotrypsin to digest and glucagon to control blood proteins; amylase for the sugar levels t digestion of carbohydrates; and lipase to break down fats A. Exocrine Portion (ducts & acini) 1-Acini Spherical structures with narrow lumen. Cells are pyramidal Basal, rounded Nuclei Basal basophilic (rich in rER) Apical acidophilic (zymogen granules) Acini Centroacinose cells: - Squamous cells found lining the lumen of the acini. - They represent the beginning of intercalated duct that invaginate inside the acinus.  2. Duct system Intercalated ducts: lined with simple squamous epith. No intra-lobular ducts. Inter-lobular ducts: simple cuboid epith. Inter-lobar ducts: simple columnar epith. Main pancreatic duct: Columnar cells, some goblet cells & few entero-endocrine cells. 2. Duct system B. Endocrine Portion (Islets of Langerhans) Their number is about 1 million in each pancreas, more numerous at the tail region. Supported & surrounded with delicate reticular fibers, but not capsulated. Formed of cell masses of secreting cells, separated with fenestrated blood capillaries. Multiple pale areas scattered between the darkly stained pancreatic acini Cells of the Islets of Langerhans 1.Beta cells (B): ( 90%of islet cells) Function: release insulin hormone 2.Alpha cells (A): ( 15% ) Function: secrete glucagon hormone 3.Delta cells (D):(10%) Function: secrete somatostatin 4.G-cells: secrete gastrin 5.PP cells: secrete pancreatic polypeptide  3. Liver The largest & the most important metabolic organ (1.5 kg) situated in the upper quadrant of the abdomen. All nutrient materials that are absorbed from the small intestine reach the liver via the portal vein. Most of its blood supply (75%)comes from the portal vein (O2 poor & nutrient rich), and about 25%by hepatic artery (O2rich). Mixed gland, as it has: Exocrine secretion (bile) Endocrine secretion (glucose, plasma proteins).  Classic Hepatic lobule It is the hexagonal mass of liver cells (hepatocytes) drained by one central vein & demarcated by thin C.T. trabecula , thickened only at the corners forming the portal tracts (portal canals).  The hepatocytes (H) are arranged in branching cords or plates (LP) radiating from the central vein (CV) to the periphery. Cords are separated with blood sinusoids (S). Each cord is formed of 2 rows of cells enclosing bile canaliculus. The endothelial lining of the blood sinusoids are separated from the hepatocytes by the space of Disse. Classic Hepatic lobule Hepatocytes Hepatic Blood sinusoids Hepatic sinusoids are present between cords of liver cells. Are lined by 2 types of cells: (1) fenestrated endothelial cells (2) Von Kupffer cells (macrophages) which clean the blood & Destroy senile RBCs Portal tract The C.T. trabecula, surrounding liver lobules are thickened at corners, forming portal tracts (portal canals). Contents of portal tract: 1-Branch of the portal vein: widest, with thin wall. 2-Branch of hepatic artery: rounded, with narrow lumen. 3-Branch of bile duct: lined with cubical epithelium. 4-Lymph vessel.