The Digestive System - Penguin Prof Pages and Processes of the Digestive System: • Move nutrients,...
Transcript of The Digestive System - Penguin Prof Pages and Processes of the Digestive System: • Move nutrients,...
What is the advantage of a one-way gut? !If you swallow something, is it really inside you?
The Digestive System
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
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
The Esophagus
• Pharynx to stomach
• Lower esophageal sphincter
• “Should there be an ‘S’ in the LES?”
Open, cut esophagus from a pig
• Stores food, begins protein digestion, churns bolus and forms chyme
• Covered w/ rugae and microscopic gastric pits to increase surface area
Stomach
• 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
• Defecation reflex
• Internal anal sphincter = smooth muscle
• External anal sphincter = skeletal muscle
Nutrient absorbed → hepatic portal vein → liver → hepatic vein → systemic circulation
Accessories: Liver
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, thyroxine-binding 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)