GIT Lecture PDF

Digestive System Digestive system  Digestive System Digestive Tract Accessory Glands Long muscular tube 1. Salivary glands Begins at the mouth 2. Pancreas Terminates at the anus 3. Liver 4. Gall bladder ...

Digestive System Digestive system  Digestive System Digestive Tract Accessory Glands Long muscular tube 1. Salivary glands Begins at the mouth 2. Pancreas Terminates at the anus 3. Liver 4. Gall bladder  Digestive Tract  Oral cavity  Oropharynx  Oesophagus  Stomach  Small Intestine  Large intestine  Rectum & Anal canal Structure of the wall of the digestive tract: 4 layers: 1. Mucosa Epithelium Lamina propria Muscularis mucosa 2. Submucosa: CT 3. Musculosa: (Inner circular) (Outer longitudinal ) 4. Serosa: Loose CT Mesothelium  1. Mucosa A. Epithelial lining: Protective = Stratified squamous (oesophagus&anus) Secretory = Simple columnar epithelium (Stomach) Absorptive = Simple columnar epithelium (intestine) B. Lamina propria: Loose connective tissue C. Muscularis mucosa: Two thin layers of smooth muscle cells: Inner circular & outer longitudinal 2.Submucosa: Loose C.T contains mucous glands in duodenum and oesophagus. 3. Musculosa: 2 layers Inner circular & Outer longitudinal. Forms wall proper of the tract. Responsible for the peristaltic movement to propels the content of the gut to the anus. 4. Serosa \Adventitia: loose C.T ± Mesothelium  Oesophagus Long, straight, narrow, muscular tube extend from the pharynx to the stomach.  Oesophagus 1. Mucosa: Epithelium: Stratified squamous A non keratinized B. Lamina propria: Loose CT B C. Muscularis mucosa: (Inn circ & Out long) C 2. Submucosa: Loose CT with esophageal glands 3. Musculosa: A (Inn circ & Out long) 4- Adventitia: Connective tissue B Stomach  Stomach Histologically, the stomach is divided into 3 parts: 1. Cardiac region: Surrounds the oesophageal orifice 2. Fundus and body: The main part 3. Pylorus: The termination A. Mucosa: Contains numerous folds (Rugae) and pits inbetween 1. Epithelium: Simple columnar cells Secrete neutral mucous to protect surface of the stomach from the acidity of its secretion 2. Lamina propria: LCT with glands 3. Muscularis mucosa: B. Submucosa: LCT C. Musculosa: 3 layers: Inner oblique Middle circular Outer longitudinal D. Serosa: LCT covered by mesothelium Fundic glands: Simple branched glands contain: 1- Mucous neck cells: Basophilic cells In neck of the glands Secrete acidic mucous 2. Parital or oxyntic cells: Acidophilic cells do not reach lumen Secrete HCL 3. Peptic (chief) cells: Basophilic, Basal, Basal rER, Pepsin 4. Enteroendocrine (Argentaffin cells): Basal, stained with silver Contain infra-nuclear granules. Secrete hormones Gastrin: stimulates secretion of gastric juice. Endorphin: relief pain. Serotonin: local constriction of blood vessels. 5. Stem cells. Pyloric region: Structurally similar to the fundus but it differs in: Pyloric glands contain only: A. Mucous cells B. Enteroendocrine cells C. Stem cells Musculosa: 2 layers (Inner circular & outer Longitudinal. The inner circular layer prominent Forming the pyloric sphincter. Fundic glands Pyloric glands oesphagus  Small intestine Function of Small intestine: 1.Complete digestion of food 2.Absorption 3. Secretion of gastrointestinal hormones It is composed of: 1. Duodenum 2. Jejunum 3. Ileum General structure of the small intestine: A. Mucosa: 1- Epithelium: Simple columnar absorptive Covering the villi and crypts 2. Lamina propria: Loose CT 3. Muscularis mucosa: Inner circular Outer longitudinal B. Submucosa: LCT In the duodenum contains Brunners glands ??? In the ileum contains peyer's patches ???? C. Musculosa: Inner circular and outer longitudinal layers D. Serosa: LCT ± mesothelium Intestinal villi Finger like projections of the mucosa Formed of a core of CT Covered with intestinal epithelium Contains vessels, capillary and lymphatic Strands of smooth muscles derived from muscularis mucosa extend into the villus. Function: Contraction of these muscle fibers aids circulation of lymph through lymphatic vessel. Intestinal epithelium: A. Epithelial cells covering the villi: 1. Simple columnar absorptive cells ( Enterocytes) Apical brush border (microvilli by EM) 2. Goblet cells: Mucus secreting cells scattered among enterocytes. Expanded apical part full of mucous granules. Narrow basal part contain oval nucleus. 3. Enteroendocrine cells: Similar to those present in the stomach. Secrete serotonin, somatostatin and secretin. B. Epithelial cells lining the crypts : 1. Enterocytes 2. Goblet cells 3. Enteroendocrine cells 4.Stem cells 5. Paneth cells: Columnar basophilic cells secreting lysozymes, which have antibacterial activity  Duodenum Jejunum Ileum Broad, shorter Long,slender leaflike Tonguelike Villi Fingerlike Absentover peyer'spatches Gobletcells Few Numerous Numerous Submucosa Brunner's Neitherglands Peyer'spatches glands norpeyer's Brunner's gland: Mucous glands open into the base or sides of the crypt. They secrete alkaline mucous which protect the duodenal mucosa from the acid chyme. Peyer' s patches: Lymphoid aggregations.  The large intestine Cecum Ascending colon Transverse colon Descending colon Sigmoid (pelvic colon) Function: Reabsorption of water and soluble salts  Structure of large intestine 1- Mucosa: Differs from that in small intestine in: *No villi *Thicker because crypts are deeper *No Paneth cells * Many Many goblet cells Lamina propria: Thick and occupied by the crypts Contains solitary lymph nodules Crypts are lined with: 1. Columnar cells 2. Goblet cells 3. Few enteroendocrine cells 4. Stem cells Muscularis mucosa inner circular and outer longitudinal 2-Submucosa: LCT rich in lymphatic nodules 3-Musculosa: Continuous inner circular Outer longitudinal muscle fibers arranged into 3 bundles called taeniae coli. 4-Serosa: Forms fatty projections called appendices epiploicae.  Mucosa Submucosa Musculosa Serosaor adventetia Esophagus St.Sq. non- Oesphageal 2layers:IC&OL Adventitia Kerat. Epith. glands Fundus Fundic glands 3layers:IO,MC, Serosa OL Pylorus Pyloric glands 2layers:IC&OL Serosa (ThickIC= pyloricsphincter) Duodenum Leaf shaped villi, Brunner's 2layers:IC&OL Serosa Few goblet cells glands Jejunum Tongue shaped 2layers:IC&OL Serosa villi, Moderate goblet cells Ileum Finger like villi Payer'spatches 2layers:IC&OL Serosa with, many Goblet cells Largeintestine Crypts only full Serosa 2layers:IC&OL Of goblet cells (appendices OL(3TaeneaColi) epiploicae) Duodenum Ileum Large Intestine  Glands associated with the digestive tract 1. Salivary glands 2. Pancreas 3. Liver 4. Gall Bladder  Salivary glands Exocrine glands present in the oral cavity produce saliva Function of saliva Lubrication Digestion Immunology  Types of salivary glands Major salivary glands Minor salivary glands 1. Parotid. Labial glands (lip). 2. Submandibular Buccal glands (cheek). 3. Sublingual glands. Lingual glands ( tongue) Palatine (soft palate).  Pancreas Mixed exocrine and endocrine glands Histological Structure of pancreas Pancreas Stroma Capsule Trabeculae Reticular CT Parenchyma Exocrine Endocrine Acini Islets Duct System  Pancreatic Parenchyma Exocrine Endocrine Islets of Langerhans Acinus Ducts Rounded clusters of pale cells fenestrated blood capillaries. basal Nuclei Scattered in between acini. Basal basophilia Four types of cells : 1. Beta cells: 70% Apical acidophilia Secrete insulin ↓ glucose level. Basal striations 2.Alpha cells: 25% centroacinose cells Secrete glucagon ↑glucose level. 3. Delta cells: 3% Secrete somatostatin. 4. Pancreatic polyeptide cells: 1-2 % Unknown function. Pancreas  Liver The most important and largest gland The largest metabolic organ (1.5 kg) It is a mixed gland: Exocrine secretion: bile which pass to the intestine Endocrine secretion: substances pass directly to the blood Liver is the interface between the blood and the digestive system All nutrient absorbed from the small intestine reach the liver Blood supply: 1. 75% comes from the portal vein (02 poor & nutrient rich), 2. 25% by hepatic artery (02 rich).  Histology of the liver 1. Cells (hepatocytes) 2. Hepatic artery carrying O2 3. Portal vein carrying blood from GIT 4. Bile ducts to secrete bile Classic Hepatic Lobule Classic Hepatic Lobule Shape: Hexagonal mass of liver tissue Center: Drained with a central vein at its center. Boundaries: Demarcated by thin CT Corners: Thickened at the corners, forming the portal tracts A. Portal tract contains: 1. A branch of the portal vein: widest, with thin wall. 2. A branch of hepatic artery: rounded, with narrow lumen. 3. A branch of the bile duct: lined with cubical epithelium. 4. Lymph vessel. B. Hepatocytes Interconnected in cords or plates. Each cord is formed of 2 cell 2 thickness (rows)‫‏‬ Cell rows enclose bile canaliculi in between Cell cords radiate from center of lobule to periphery Cords of liver cells are separated with blood sinusoids. LM of hepatocytes Large polygonal with one or two nuclei Cytoplasm: Acidophilic (due to mitochondria & sER) Vacuolated (due to dissolved glycogen). EM of hepatocyte: A.The cell membrane: 1. Facing the blood sinusoids: long microvilli 2. Facing the bile canaliculus: short microvilli. 4. Facing neighboring hepatocytes: junctional complexes. B. The Cytoplasm: Hepatocytes are very active cells So they are very rich in organelles & inclusions: 1. Mitochondria: very numerous (1000-2000/cell) 2. rER & ribosomes: abundant to synthesize proteins 3. sER: (metabolism + drug & poison detoxification). 4. Golgi Apparatus: well developed, concerned with secretion (plasma proteins), turnover of the cell membrane & formation of Iysosomes. 5. Lysosomes: also numerous to destroy worn out cellular components, and to digest & eliminate waste products. 6. Microbodies (peroxisomes): very numerous, concerned with metabolism of H202, lipid degradation into glucose & alcohol metabolism. Hepatic Blood Sinusoids: Wide irregular blood spaces Radially arranged in hepatic lobules They are lined by 2 types of cells: (1) fenestrated endothelial cells that are surrounded by (2) a special type of macrophages (von Kupffer) cells. Von Kupffer Cells: macrophage of liver Large branched phagocytic cells, With microvilli & pseudopodia, Lining the liver sinusoids. Rich in Iysosomes & phagocytic particles. Their main functions: Clearing the blood Formation of bile pigments. Phagocytosis of microorganisms coming from the intestine. The Space of Disse (Perisinusoidal Space): The space between hepatocytes & wall of blood sinusoids. It contains: 1. Long microvilli projecting from the surface of hepatocytes 2. Reticular fibers that support the wall of the sinusoids. 3. Blood plasma containing all the nutrients 4. Lipocytes (Ito cells); branching lipid storing cell that store the fat soluble vitamin A in the form of retinyl ester in lipid droplets. Thank You