Exam 1 Digestive System, BIOL 20400

Exam 1- BIOL 20400 ================== What are the major organs of the digestive tract? - - Oral Cavity - Pharynx - Esophagus - Stomach - Small Intestine - Large Intestine What are the accessory organs of the digestive tract? - Teeth - Tongue - Salivary Glands - Liv...

Exam 1- BIOL 20400 ================== What are the major organs of the digestive tract? - - Oral Cavity - Pharynx - Esophagus - Stomach - Small Intestine - Large Intestine What are the accessory organs of the digestive tract? - Teeth - Tongue - Salivary Glands - Liver - Gallbladder - Pancreas What is the "Alimentary Canal"? - The path that food takes from the mouth to the anus. What makes up the Gastrointestinal (GI) Tract? - Stomach+ Intestines (short and long) What are the four layers of the digestive tract? (Central to outer) - Mucosa - Submucosa - Houses submucosal plexus - Muscularis Propria- Two parts: circular smooth muscle and longitudinal smooth muscle - Circular smooth muscle houses the myenteric plexus - Adventitia/Serosa Where is the adventitia layer present? - Oral cavity, pharynx, esophagus, and rectum. What is the Serosa layer? - The visceral peritoneum. What are the two enteric nerve plexuses and what do they do? - Submucosal/Meissner's plexus: - Regulations GI SECRETIONS - Located in the submucosa - Myenteric/ Auerbach's plexus: - Controls MOTIL ITY and MOVEMENT of the GI tract (aka peristalsis) - Located between circular and longitudinal muscular layers of the GI tract What is the difference between long and short reflexes in digestion? - Long reflexes involve stuff OUTSIDE the ENS (includes CNS and ANS) - Short reflexes only involve the ENS and respond to stimuli IN the digestive tract. What is peristalsis? Where does it occur? - Waves of contraction by smooth muscles in the digestive tract, used for propulsion of materials. - Occurs in the esophagus, stomach, and intestines. What is segmentation? Where does it occur? - Back and forth contraction and relaxation, used to mix undigested materials with intestinal secretions. (no net movement) - Makes sure chemical digestion and absorption are completed - Occurs in the intestines. What are the major physiological steps of the digestive system? - Ingestion- intake of food - Mechanical and Chemical digestion-breakdown of food (mechanical: chewing, churning, and segmentation) - Propulsion-movement of food particles (swallowing, peristalsis) - Absorption- uptake of nutrients into the epithelial cells and then to blood or lymph - Defecation- elimination of feces What are the four types of teeth and what do they do? - Incisors- blade shaped for clipping and cutting - Front of mouth - 1 root - Canines- pointy teeth for puncturing and shredding - 1 root - Premolars- before molars, have cusps - 1-2 roots - Molars- grinders - 2-3 roots, fused in the third molar How many teeth do adults have? - 16 in the mandible, 16 in the maxilla What are the three main parts of a tooth? - Crown, neck, and root What is enamel? - The outer covering on the crown of the tooth - Hard, mineralized non-living substance - Made up of hydroxyapatite crystals, which have calcium and phosphate What is the cementum? - Boney material that covers the root to anchor the tooth What makes up saliva? - 97-99.5% water - IgA - Lysozyme: kills bacteria - Mucus: binds and lubricates the bolus - Amylase: starts starch digestion - Lipase: begins fat digestion (remember LIPase= lipid=fat digestion) What are the 4 regions of the stomach? - Cardia, Fundus, body, and pyloric part What does the pylorus/pyloric sphincter connect? - The stomach and duodenum (top part of small intestine) What are the three mechanisms that protect the stomach from the acidic environment of the stomach? - Mucous bicarbonate barrier: bicarbonate neutralizes acid - Epithelial tight junctions: stop gastric juice from seeping between them - Replacement: epithelial cells are replaced every 3-6 days What are the main cells in the gastric and pyloric glands and what do they secrete? - Mucous neck cell: secretes mucous and bicarbonate to make the barrier - Parietal cell: secretes gastric acid (HCl) and instrinsic factor - Gastric acid activates enzymes, changes dietary iron to usable form, and destroys pathogens - Chief cell: secretes pepsinogen and gastric lipase - Pepsinogen: activated by gastric acid (HCl) to turn it into pepsin - Lipase: digests fat - G cell: secretes gastrin to increase acid secretion - Enterochromaffin cells: secrete histamine What is gastric juice composed of? - Mostly water, acid, and pepsin How do parietal cells secrete HCl? - Hydrogen and chloride ions are produced separately within the cytosol so the cell isn't hurt from the acid. - How? Carbonic acid breaks down into bicarbonate ion and H+ - Because Cl has a negative charge, it moves easily into the gastric lumen. - H has a positive charge, so it has to move into the lumen by trading with a K ion. (H+/K+ -ATPase pump) - Once H+ and Cl- are in the gastric lumen, they combine to form HCl. What factors stimulate HCl production? - Neural: **acetylcholine** is secreted by parasympathetic nerve fibers of long and short reflex pathways to tell the parietal cell to produce hydrochloric acid. - Hormonal: **Gastrin** (made by g cells in the duodenum and pyloric antrum) signals HCl production - Paracrine: enterochromaffin-like cells (ECFs) secrete **histamine**, which instructs nearby parietal cells to make HCl What are the three phases of gastric acid secretion? - 1: **Cephalic** - 20 % of gastric acid secretion - Taste and smell receptors & thought/sight of food - CNS tells parietal, chief, mucous, and g cells to secrete HCl, pepsinogen, mucus, and gastrin - 2: **Gastric** - 50-60 % of gastric acid secretion - Starts when food gets to the stomach- increases secretions and contractions - pH increases due to food, stimulating HCl secretions - food stretches stomach walls, activating short & long reflexes - If pH gets too acidic (drops below 2), HCl secretion is decreased - 3: **Intestinal** - 5-10 % of gastric acid secretion - The duodenum begins by stimulating secretion but then works to inhibit it. (The small intestine tells the stomach to slow secretion and motility) - When pH is too low, S cells in the duodenum secrete **secretin** - This inhibits gastric secretion and motility. - The arrival of lipids and proteins stimulates CCK secretion from I cells in the duodenum and jejunum. LECTURE 3 What are the three main parts of the small intestine, and what do they do? - Duodenum - Mainly neutralizes acidic chyme - "mixing bowl" - Receives chyme, pancreatic juice, and bile from the 3stomach - The glands secrete juice and bicarbonate-rich mucus - When the pH increases because of - Jejunum - Digestion and absorption - Ileum - Absorption of vitamin B12 and reabsorption of bile salts Where does the small intestine start and end? - Starts: at the end of the stomach with the pyloric sphincter - Ends: ileocecal valve, between ileum and cecum What are the different types of **cells in the small intestine** and what are their functions? - Enteroendocrine cells: secrete hormones like secretin and CCK - Stem cells: intestinal cell renewal - Enterocytes: nutrient digestion and absorption - Goblet cells: produce mucus for lubrication - Paneth cells: secrete antimicrobial peptides What are the two major functions of the small intestine? - Absorb vitamins generated by bacterial action - K, B5, Biotin - Absorb water (compact into feces) LECTURE 4 Amylase is secreted by acinar pancreatic cells (stimulated CCK) Brush border enzymes: - Breaks down anything w more than 3 sugars: DEXTRINASE and GLUCOAMYLASE - Breaks down anything already minimized to 2 sugars: DISACCHARIDASES - Breaks down glucose, fructose and galactose with SUCRASE, MALTASE, and LACTASE Summarize glucose oxidation: - 1\. Glycolysis- glucose breaks down into 2 pyruvates - NADH is made - 2\. Pyruvate processing- pyruvate is changed to acetyl CoA for the krebs cycle - Anaerobic-changed to lactic acid (anaerobic fermentation) - NADH is made - 3\. Krebs cycle-CoA oxidized to CO2 - Oxygen +glucose-\> water and CO2 - NADH and FADH2 are made - 4.electron transport & oxidative phosphorylation- establishes proton gradient needed to make ATP LECTURE 5 What makes up bile? - 95%, 5% solute - Solute= mostly bile acids/salts, part phospholipid (lecithin), cholesterol, proteins, bilirubin - 95% of bile acids are reabsorbed into the liver, 5% left in feces - What is emulsification? - Breaking large pieces - How and where do bile salts facilitate fat digestion? - 1\. Emulsification: bile salts in the duodenum break down the bigggg fat globules into smaller droplets - 2\. Digestion: pancreatic lipases digest triglycerides into fatty acids and 2 monoglycerides - 3\. Micelle formation: the bile salts combine to form micelles, incorporating lipid digestion products - Micelles have a polar outer shell and hydrophobic core because the fatty acids and cholesterol dissolve in the core of the micelle. - How do lipids transport across the intestinal epithelium? - Micelles simply diffuse into the intestinal cell - When inside, the fatty acids and monoglycerides in the micelle convert back into triglycerides and are coated in proteins to form chylomicrons. - Because chylomicrons are too small to enter the capillaries in the intestinal villi, they enter the lacteals, which carries the chylomicrons through the lymphatic system to general circulation - What is a lipoprotein? - Small droplets with cholesterol and triglycerides in the core with proteins and phospholipids in the coating. - What are the different types of lipoproteins? - The more lipid and less protein, the less dense. The more protein, the more dense. - Chylomicron: mostly **triglyceride** - VLDL (very low density lipoprotein): mostly a mix of **triglycerides,** cholesterol, and phospholipid... tiny bit of protein - LDL (low density lipoprotein): more mixed. Mostly **cholesterol** - HDL (high density lipoprotein): like half **protein**, half the rest - How are lipids transported through the body? - Chylomicrons carry TGs from the small intestinal villi to the body's cells - Into lacteal-lymph-bloodstream - Switches to chylomicron remnant to go to the liver - Bloodstream-liver - Gets disassembled in the liver - In the liver, VLDL provides more TG's to body cells and adipose tissue for storage - VLDL changes to IDL, then to LDL - This is gradual as triglycerides are removed - LDL is rich in cholesterol and delivers the cholesterol to the body's cells - As cholesterol is taken away, LDL becomes HDL, which takes excess cholesterol back to the liver to either use or get rid of - It gets rid of cholesterol through the bile it makes - What is lipolysis? - The process of breaking down fats (lipids) to fatty acids and glycerol - It's catabolic: when we need more energy, we have to break down lipids into what we can use (fatty acids and glycerol). - What is lipgenesis? - Creating lipids from other molecules - Its anabolic: when we have too much carbs and amino acids, they are converted into triglycerides and stored for later - This is how eating too many carbs give you excess fat. - Diets high in carbs generate too much acetyl CoA for the citric acid cycle. We don't need that much, so it's converted to fatty acids - Which chemicals act as short term regulators of appetite? - Ghrelin: HUNGER - When your stomach is empty, ghrelin is secreted - Eating food suppresses ghrelin release - Amylin, CKK, and Peptide YY: SATIETY - Amylin: made with insulin by beta cells in the pancreas - CKK: appetite suppressing - Peptide YY: secreted by enteroendocrine cells in the ileum and colon. - Which chemicals act as long term regulators of appetite? - Leptin: indicates current state of energy stores in the body - When body fat mass increases, leptin levels increase - (gaining weight, so leptin tells you to stop eating so much) - Leptin insensitivity can cause obesity - Insulin - Regulates blood glucose - Acts on hypothalamic circuits to suppress appetite - (sugar gets too high, more insulin is being used, which signals to stop eating) - Which acruate neurons do what with eating behaviors? - Neuropeptide Y (**NPY**) and Agouti related peptide (**AgRP**): orexigenic, which means they stimulate appetite - Associated with like ghrelin, CCK, Peptide YY, insulin, and amylin - Propiomelanocortin (**POMC**) is produced and changed to alpha melanocyte stimulating hormone (**a- MSH**): anorexigenic, which means they suppress appetite - Associated with leptin - What is the role of the arcuate nucleus (in the hypothalamus) in the regulation of eating behavior based on each chemical? - 1\. Receives signals from the chemicals controlling eating behavior: - Acts on Orexigenic NPY secreting neurons: - Ghrelin: stimulates NPY secretion - PYY: inhibits NPY secretion - CCK: inhibits NPY secretion - Insulin: inhibits NPY secretion - Acts on Anorexigenic melanocortin-secreting neurons: - Leptin: stimulates melanocortin secretion