The Digestive System What is the advantage of a one-way gut?! If you swallow something, is it really inside you?
Functions and Processes of the Digestive System: Move nutrients, water, electrolytes from external to internal environment Protective function Defense mechanisms Mucus, enzymes, acid, lymphoid tissue
The Challenges:! Prevent autodigestion Match input with output
Digestive Homeostasis Requires: 1. Digestion: chemical, mechanical breakdown of food polymers monomers 2. Absorption From GI lumen to ECF Not regulated; "what you eat is what you get."
Digestive Homeostasis Requires: 3. Motility Ingestion, mastication, peristalsis, segmentation Regulated
Digestive Homeostasis Requires: 4. Secretion Exocrine and endocrine (hormones, enzymes, mucus, paracrines) Regulated Many enzymes are secreted as inactive proenzymes known as zymogens
Layers of the GI Tract: 4 tunics 1. Mucosa Absorbs and secretes Mostly columnar epithelium Modifications increase lumen surface area: Rugae in stomach Villi and microvilli in intestine
Layers of the GI Tract - 4 tunics 2. Submucosa Connective tissue Large blood and lymphatic vessels 3. Muscularis Inner circular muscle layer Outer longitudinal muscle layer 4. Serosa Binds and protects Lines abdominal cavity
Basolateral side (apical side) Cellular Orientation
Oral Cavity and Salivary Glands Mastication Salivary amylase Mucus
The Esophagus Pharynx to stomach Lower esophageal sphincter Should there be an S in the LES? Open, cut esophagus from a pig
Stomach Stores food, begins protein digestion, churns bolus and forms chyme Covered w/ rugae and microscopic gastric pits to increase surface area
Contains (exocrine) gastric glands which secrete: mucus HCl intrinsic factor pepsinogen gastrin Proteases Stomach
Stomach What is the function of such low ph? Wait a second... what is the stomach made of? pepsin
How does the gastric mucosa prevent self-digestion? Alkaline mucus Tight junctions Rapid rate of cell division Prostaglandins
Small Intestine Secretions of bicarbonate from the intestine itself and the pancreas neutralize the ph Secretions of other ions, water, mucus
Small Intestine Secretions of digestive enzymes: Disaccharidases Proteases Peptidase Phosphatase Absorption of carbohydrates, amino acids, lipids, electrolytes, bile, vitamins, water takes place here Why so many villi and microvilli?
Large Intestine Ascending, transverse, descending, sigmoid colon, rectum, anal canal Absorbs water and electrolytes
Large Intestine Stores, then passes waste out of the body How much? How often?
Large Intestine Defecation reflex Internal anal sphincter = smooth muscle External anal sphincter = skeletal muscle
Accessories: Liver Nutrient absorbed hepatic portal vein liver hepatic vein systemic circulation
Liver Functions: Bile production and secretion BILE = bile salts, bilirubin, cholesterol, ions and bile acids: bile acids are steroid detergents with polar side chains, allowing interactions w/ polar and non-polar molecules
Liver Functions: Detoxification of blood 1. Excretion of toxic materials into bile 2. Phagocytosis by Kupffer cells 3. Chemical alteration by hepatocytes
Liver Functions: Carbohydrate Metabolism Liver can decrease blood [glucose]: converting it to glycogen converting it to lipids Liver can increase blood [glucose]: production from glycogen production from amino acids
Liver Functions: Lipid Metabolism Synthesis of triglycerides and cholesterol Excretion of cholesterol in bile Break down free fatty acids into ketone bodies (ketogenesis)
Liver Functions: Protein Synthesis Plasma proteins: albumin, fibronectin, opsonin, globulins Hemostasis factors: all factors in hemostasis except for factor VIII Coagulation inhibitors, plasminogen, complement proteins Carrier proteins: albumin, ceruloplasmin, transcortin, haptoglobin, hemopexin, IGF binding protein, retinol binding protein, sex hormone-binding globulin, thyroxinebinding globulin, transthyretin, transferrin, vitamin D binding protein And more...
Accessories: Gallbladder Collects and stores bile from the liver and delivers it to the duodenum via the common bile duct. Gallstones are cholesterol crystals that collect the precipitation of inorganic salts.
Accessories: Pancreas Endocrine fxn: Islets of Langerhans secrete insulin and glucagon into the blood Exocrine fxn: acini cells secrete pancreatic juice into the pancreatic duct
Pancreas Pancreatic enzymes (like many stomach enzymes) are secreted as zymogens Trypsin Chymotrypsin
Pancreatic Juice Water, bicarbonate amylase (digests starch) trypsin (digests proteins) lipase (digests triglycerides) cholesterolesterase (cleaves cholesterol from it's bond w/ other molecules ribonucelase (cleaves RNA chains) dexoyribonuclease (cleaves DNA chains)
So What? Digestive System Disorders Eating disorders Ulcers Vomiting Constipation, Diarrhea Lactose intolerance Cancers of the digestive system