Digestive System Anatomy PDF

# Gastrointestinal tract - Gastrointestinal tract(alimentary tract) - Mouth - Pharynx - Esophagus - Stomach - Small Intestine - Large intestine - Rectum & Anal canal # Functions of the GIT - Passage (Transportation) of food - mouth, oropharynx, esophagus - Digesti...

# Gastrointestinal tract - Gastrointestinal tract(alimentary tract) - Mouth - Pharynx - Esophagus - Stomach - Small Intestine - Large intestine - Rectum & Anal canal # Functions of the GIT - Passage (Transportation) of food - mouth, oropharynx, esophagus - Digestion - stomach, intestine - Absorption - small intestine - Elimination of residues & absorption of water - large intestine, rectum & anal canal # Structure of the GIT wall - **Mucosa** - Lining epithelium: - Stratified squamous non-keratinized in esophagus. - Simple columnar in stomach & intestines - Lamina propria (corium): loose CT - Muscularis mucosae: 2 layers of SM: - Inner circular (IC) - Outer longitudinal (OL) - **Submucosa**: Loose CT containing blood vessels (BV), nerves & lymphatics - **Musculosa**: 2 layers of SM: - Inner circular (IC) - Outer longitudinal (OL) - **Serosa (or adventitia):** - Loose CT covered by simple squamous epithelium (mesothelium) # **Stomach** - Function of stomach: - It is a food reservoir (food storage) - Food is acidified & converted by mechanical and chemical action into a thick viscous fluid (the chyme) - The most dilated part of GIT - Stomach divided anatomically into: cardia, fundus, body & pyloric regions - Fundus & body are similar in structure ## Cardia of stomach - Its mucosa contains mucous-secreting glands ## Stomach wall - **Mucosa:** - Gastric pits: Little depressions in the stomach lining where gastric glands open - Epithelium: Simple columnar, mucus secreting. - Lamina propria: loose C.T. containing the fundic glands - Muscularis mucosa: 2 layers of SM: - Inner circular (IC) - Outer longitudinal (OL) - **Submucosa:** - loose C.T. containing BVs, nerves & lymphatics - **Musculosa:** - Inner oblique (IO) - Middle circular (MC) - Outer longitudinal (OL) - so the mechanical action will be in all directions - **Serosa:** - loose C.T. covered with mesothelium ## Characters of fundic glands - **Surface mucus cells:** - Cover the surface & line the pits - Columnar cells - Secrete neutral mucus - **Mucous neck cells:** - Located just below gastric pit. - Columnar cells - secretes acidic mucus - **Parietal or oxyntic cells:** - Most numerous in middle portion - Large rounded - Acidophilic cytoplasm - Central rounded nuclei - **Functions:** secretion of: - HCL - Intrinsic factor (essential for B12 absorption) - **Chief (Peptic) cells:** - Located in the lower 1/3rd of gastric glands. - Large basal nucleus - Basal basophilic & apical acidophilic cytoplasm - **Function:** Secrete pepsinogen - **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 - **Pyloric gland characters:** - Not crowded - Highly convoluted - pits wider & longer - **Musculosa:** - 2 layers only: Thick IC (pyloric sphincter, PS) & OL # **Small intestine** - It is the site of terminal food digestion, absorption & endocrine secretion. - Three parts: - **Duodenum:** is the first and shortest segment - connect the stomach to the jejunum - Surrounding the head of pancreas - **Jejunum:** constitutes the proximal 2/5 after the duodenum - **Ileum:** the distal 3/5 ## Adaptation of small intestine to its absorptive function: - 6 m long - **Plicae circularis** (Folds of mucosa & submucosa) it increases surface area 3 folds - **Villi:** (outgrowth of intestinal mucosa = epithelium + CT corium) increase surface area 10 folds - **Microvilli:** (finger-like projections of the apical cell membrane) increase surface area 20 folds ## Small Intestine wall - **Mucosa:** villi & Crypts - **Epithelial lining:** - Simple columnar, Goblet, Paneth, Enteroendocrine, stem cells, M & caveolate cells. - **Lamina propria:** C.T. and corium (dermis) - **Muscularis mucosa:** IC & OL - **Submucosa:** loose CT containing - Mucus glands (Brunner's glands) in the duodenum - Lymphatic nodules (Payer's patches) in ileum - **Musculosa:** IC & OL - **Serosa:** - Loose CT covered by simple squamous epithelium (mesothelium) ## 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 Payer's patches. ## Cells lining intestinal mucosa - **Absorptive columnar cells:** - Tall columnar cells with apical microvilli (brush border). - **Goblet cells:** - Mucus secreting unicellular glands (vacuolated in H&E sections) - **Enteroendocrine cells:** - Similar to those of stomach - More than 15 different types in GIT - Secrete many types of hormones - **Undifferentiated Columnar Stem Cells** - **Paneth cells:** - At the base of crypts only - Pyramidal with basal rounded nuclei - Apical acidophilic & basal basophilic cytoplasm - **Function:** - secrete lysozymes that kill bacteria - **M-Cells (Membrane-like cells)** - 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 - **Caveolate cells** # Large intestine - It is the site of absorption of water & production of mucous for lubrication - Parts of the large intestine are: - Ceacum - Ascending colon - Transverse colon - Descending colon - Sigmoid (pelvic colon) - Rectum - Anal canal ## Large Intestine Wall - **Mucosa:** - No villi - Crypts are wider & deeper - **Epithelial lining:** - No paneth cells - Absorptive columnar cells - Many goblet cells - Enteroendocrine cells - Stem cells - Lymphatic nodules in lamina propria - **Submucosa:** - No glands - **Musculosa:** - Inner circular - Outer longitudinal layer consists of only three bundles of SM (tenia coli) - **Serosa:** - Rich in fat cells (appendices epiploicae, masses of adipose tissue covered with peritoneum) # Glands associated with the digestive tract - Salivary glands - Pancreas - Liver # **Pancreas** - It is a mixed (exocrine & endocrine parts) gland - **Its exocrine part is responsible for secretion of pancreatic juice:** - Produce enzymes include trypsin and chymotrypsin to digest proteins; amylase for the digestion of carbohydrates; and lipase to break down fats. - **Endocrine part:** - Secretes the hormones insulin and glucagon to control blood sugar levels ## 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) - **Centroacinose cells:** - Squamous cells found lining the lumen of the acini. - They represent the beginning of intercalated duct that invaginate inside the acinus. - **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. ## 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 - **Beta cells (B)**: (90% of islet cells) - **Function:** release insulin hormone - **Alpha cells (A):** (15%) - **Function:** secrete glucagon hormone - **Delta cells (D):** (10%) - **Function:** secrete somatostatin - **G-cells:** secrete gastrin - **PP cells:** secrete pancreatic polypeptide # **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. ## Hepatic Blood sinusoids - Hepatic sinusoids are present between cords of liver cells. - Are lined by 2 types of cells: - fenestrated endothelial cells - 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: - Branch of the portal vein: widest, with thin wall. - Branch of hepatic artery: rounded, with narrow lumen. - Branch of bile duct: lined with cubical epithelium. - Lymph vessel.