Study Guide—Ch. 18: Digestive Physiology
1. What are the major functions of the gastrointestinal system? What is the distinction between the “digestive system” and the “digestive tract?” a. Process of ingesting food and delivery of nutrients to the body b. Storage and elimination of unneeded food
c. Digestive system- GI tract+ accessory organs needed for digestion d. Digestive tract- GI tract: mouth, esophagus, stomach, small intestine, large intestine, rectum, anus
2. What are the overall actions and roles of the individual organs which comprise the digestive system, and how those are integrated into fulfilling the goal of delivering nutrition to the body?
a. Mouth: mastication, chewing with the use of saliva which contains mucus to begin digestion of starches
b. Esophagus: the process of swallowing and relaxing in areas as the food enters those areas to allow for transport to the stomach
c. Stomach: stores food and breaks down into smaller pieces, churns food and mixes with gastric secretions: i.e. chime. Begins protein diegestion and kills bacteria on food We also discuss several other topics like What theory maintains that eating is under the control of receptors in the bloodstream that monitor levels of glucose-the body’s primary metabolic fuel?
d. Small intestine: in charge of most digestion(carbs, proteins, fats), absorption of nutrients; processes bile, salts, vitamins, electrolytes e. Large intestine: absorption of water, elctrolytes, vitamin K and B; production of vitamin K and B, storage/process of feces We also discuss several other topics like Bill is in 7th grade and seems to have a lot of good friends and a lot of enemies. in which social status would he most likely be categorized?
f. Rectum/anus: excretion of feces and waste
3. Understand the functional anatomy of the gut wall—know what goes on in the mucosa, submucosa, muscle layers, and understand the overall role played by the enteric nervous system: two separate but interconnected nerve plexes within the gut wall.
a. Mucosa- single later of epithelial cells: endocrine cells, goblet cells; secretion, absorption Don't forget about the age old question of What is the first electronic computer?
b. Submucosa- connective tissue layer containing larger blood vessels, lyph ducts, and submucosal plexus (meissner’s plexus) of nerves from ENS
c. Muscularis propia-inner layer of circular muscle: affect lumen diameter. Outer layer of longitudinal muscle- affects length myenteric plexus (lies between muscle layer, controls gut motility via contraction/relaxation of layers
d. Serosa- outer covering: connective tissue membrane continuous with peritoneal membrane
4. Be familiar with the two major modes of regulatory signals controlling gut function—GI hormones and neural control via both central and enteric nervous systems. What are the general effects of sympathetic vs parasympathetic signals? What are the two major plexuses of the enteric nervous system—where are they located in the gut wall, which one controls mainly secretory functions of the mucosa, and which one controls muscular movements, i.e. motility? KNOW the roles of the following 3 major gut We also discuss several other topics like It is when the number of jobs in the labor market is lower than the number
of people seeking jobs in that labor market, what is it?
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hormones: gastrin, secretin, and cholecystokinin. Where are they produced/released? What stimulates their secretion? What are their major actions (physiological effects)?
a. Parasympathetic(central) stimulates digestions, absorptions, contraction/relaxation-submucosal
b. Sympathetic(central) inhibits peristalsis and secretion, stimulate contraction of sphincters to prevent movement
c. Hormones causes different actions of hormone to cause digestion or inhibit digestion
d. Enteric nervous system- able to generate reflexes independently from the CNS; if cut neural connections to cns, gut can still engage in regulated function; located in wall of digestive tract If you want to learn more check out What is the yerkes-dodson law?
5. Understand how the intestinal epithelium renews itself, and be familiar with the different types of epithelial cells and their respective roles. a. Rapid epithelial mitosis: slowly dividing(renewal) rapid(replacement) b. Proliferation pushes cells up(migrate up)
c. Enterocytes, enteroendocrine cells, and goblet cells
i. Once they reach the top, cells she ad are replaced
d. Paneth cells move downward-live for 20 days and the phagocytosis occurs
6. Understand the different phases of a meal, i.e. cephalic, gastric, intestinal. Familiarize yourself with the neural and hormonal signaling involved in each— what stimulates those signals, how they are mediated (e.g. long reflex involving the brain, vs. local reflex mediated by the enteric nervous system, vs hormone), what effects are triggered by those signals, and how they fit into the overall control of digestion/absorption.
b. Gastric- stomach digestion and breakdown of proteins and starch, absorption of alcohol and aspirin
i. Pepsin, gastrin, and HCL helps to digest proteins
c. Intestinal-main place of absorption and digestion of all foods, and intake of vitamins, salt, water, etc.
i. Pancreatic, intestinal enzymes
7. What is the route taken by a piece of food through the GI tract? a. Mouth->esophagus->stomach->small intestine-> large intestine- >rectum,anus
8. What is the function of the esophagus?
a. Transport food from the mouth to stomach
b. Soften food
9. What are the functions of the stomach? How does the role of the fundus differ from those of the body (corpus), antrum and pylorus?
a. Cardiac-food deliverd to cardial region for esophagus
b. Fundus-storage; expands to accommodate load (receptive relaxation) limited motility
c. Body-high motility; breaks large molicules into smaller particles; mixed foods with secreted acid enzyme and fluid= chime
d. Pylorus-limits amount emptied, restricts size of emptied particles in chyme
10.What is the mixture of incoming food and gastric sections called? a. chyme
11.Why is the grinding and mixing actions of the stomach important for later enzymatic digestion?
a. It kills bacteria in the food, and allows for nutrients to be absorbed 12.What are the major secretions added to food in the stomach? a. Pepsin, gastrin, HCl, mucus
13.What digestive activity goes on in the stomach?
14.Why is acid secretion important, how is it stimulated, from what cells is it secreted, and why doesn’t it digest the organ?
a. Acid is secreted from parietal cells, it helps to break, soften the food in the stomach, the organ has layers of cells and layer of protective mucus
b. Started by the release of other hormones
15.What is also secreted in the stomach by acid-secreting cells and how is it important for the absorption of a key vitamin?
a. HCl- parietal cells
b. Serves as the optimal pH starter- 1-2 pH and for pepsin activity 16.What are the three major types of movements (motility) involved in both the absorptive and postabsorptive states? Which occur between meals (i.e. in the postabsorptive state), and which occur during the digestive process? a. Migrating myoelectric motor complex- sweeps gut clear and occurs in postabsorptive state
b. Peristalsis- net forward movement by muscular contraction and relaxation behind/ahead of bolus; digestive stage
c. Segmentation- mixing by simultaneously contracting both behind and ahead of bolus; digestive stage
17.Where does most digestion/absorption take place?
a. Small intestine
18.Where are digestive secretions from the pancreas and gallbladder delivered? What turns on these secretions during a meal (see role of gut hormones, secretin & CCK, as specified in Q#4, above)?
a. Small intestine (duodenum)- hormones from the parasympathetic system turn on these secretions such as secretin, CCK, GIP
19.Understand the anatomy of the intestinal epithelium. How is the absorptive surface organized, how is it renewed, and what specific cell types comprise the epithelial layer? What is the crypt? What is the villus? What is the brush border?
b. Mucosa folded into villi; epithelial membrane folded into microvilli c. Stems cells layer 4-5 cells from bottom of crypt( bottom or pit beneath the villi)
d. 2 types of stem cells: slow dividing( stem renewal cells), rapidly dividing( epithelial replacement cells)
i. Continuous proliferation pushes cells up the vilus
e. As cells migrate differ into: enterocytes, enteroendocrine cells, goblet cells (transition time is 3-5 days)
f. Paneth cells are at the niche of the bottom of crypt
g. Villi- consist of capillary/Epithelial cells grown out of the intestinal lining h. Brush border-microvilli foldings on epithelial cells and act as enzymes and help break substances apart
20.What are the main functions of the large intestine?
a. Absorbs water, electrolytes, vitamins k and b
b. Production of vitamin k and b via microbial organisms
c. Storage/process feces
21.Understand the sources and fate of fluid entering the GI tract? a. Either absorbed or carried to renal system
22.Understand the essentials of digestion and absorption of carbohydrates, protein, fat, and vitamins.
a. Carbohydrates, fats, proteins: digestion breaks polymers into monomer building blocks via hydrolysis reactions
b. Absorption takes theses monomers into the blood stream to be used by cells
c. Vitamins are enzymatically split into their component molecules by hydrolysis
23.What are the digestion products of protein, starch and fat? What are the major enzymes involved, and where do they come from
a. Protein: start as polypeptide chain-> amino acids, dipeptides, and tripeptides
b. Carbohydrates: maltose, sucrose, lactose to simple sugar glucose c. Fat: emulsified and lipase(pancreas) break down fat into glycerol; phospholipase digests phospholipids into fatty acids
24.In what form are digestive enzymes secreted from the pancreas, and how are they activated in the lumen of the intestine?
a. Enzymes are secreted as inactive zymogens until they reach the small intestine and activated by trypsin
25.Why is chyme entering the intestine from the stomach inhibitory to pancreatic digestive enzyme function, and how is this inhibition overcome so that digestion can occur? How is that achieved?
a. Liquid to dense chyme enters at different rates to prevent digestive enzymes to break apart the wrong material
b. Also controlled by hormones
26.How is glucose absorbed? How are amino acids absorbed? Why is the digestion/absorption/transport of fat unique; what is the role of emulsifying agents (phospholipids, bile salts) in assisting with handling of these hydrophobic molecules?
a. Glucose is absorbed by facilitated diffusion through glut carriers into interstitial fluid and then cap. Blood of the villus
27.What are the events during the cephalic, gastric and intestinal phases of a meal? How are these events controlled?
a. Cephalic: prepares stomach for arrival of food: reflex signals from medulla via vegal fibers to stimulate submucosal plexus; vegus stimulates acid secretion w/3 mechanisms- direct signal via arch, indirect via histamine, indirect via gastrin
b. Gastric: enhances secretion, mix, acidify, and increase surface area of chyme, break down proteins; 3 mechanisms- neural reflexes triggered by stretching and rise in pH, gastrin release triggered by vagal signals, local release of histamine(stimulates acid secretion)
c. Intestinal: acts to control gastric emptying rate, limit acid secretion, and optimize conditions for enzymatic digestion; 2 reflexes-neural short reflex triggered by distention of duodenum, hormonal stimulation of secretin, CCK, GIP, and presence of hydrogen
28.Understand the importance of control of gastric emptying rate in the overall process of digestion/absorption. What factors limit this rate?
a. Regulated by intestinal signals to prevent complete emptying b. Liquids empty first, solids, slowest, also nutrient-specific control-sense physiochemicals
29.What are chylomicrons? Why are they important for transport of fat form the gut into the body, and what route do they take to get in? How does this differ from the route taken by carbohydrates and protein?
30.What is the overall role of physical barriers, lumen-secreted anti-microbial agents, and the mucosal immune system in protecting from invasion by pathogens?
a. Mucosal barrier prevents bacterial from entering cells and being absorbed into blood stream
b. Defensins fight against the antigens that try to enter barrier 31.Know the following terms: digestion, absorption, motility, peristalsis, segmentation, migrating myoelectric complex, duodenum, jejunum, ileum, mucosa, submucosa, muscularis propria, enteric nervous system (ENS), submucosal plexus, myenteric plexus, gallbladder, acinar cells, exocrine secretion, chyme, pepsinogen/pepsin, intrinsic factor, enterochromaffin-like cells, histamine, parietal cells, chief cells, G cells, gastrin, villus, crypt, microvilli, enterocyte, goblet cell, paneth cell, enteroendocrine cell, brush border, lamina propria, peristalsis, migrating myoelectric complex, segmentation, zymogen, amylase, trypsin, trypsinogen, CCK, secretin, emulsification, bile acid (salt), enterohepatic circulation, lipase, enteropeptidase, disaccharidase, triglyceride, fatty acid, chylomicron, defensin, secondary active transport, intrinsic factor, cephalic pahse, gastric phase, intestinal phase, gastrocolic reflex, Peyer’s parches, follicular associated epithelium (FAE), M cells, cytokines