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Bio143 - phy
Ch. 20
| Question | Answer |
|---|---|
| List the functions of the digestive system | Motility, Digestion, Secretion, and Absorption |
| Describe motility, 1 of the 4 functions of the digestion system | Motility- movement of material in the GI tract |
| Describe digestion, 1 of the 4 functions of the digestion system | mechanical and chemical breakdown of foods into smaller units that can be taken across the intestinal epithelium into the body |
| Describe secretion, 1 of the 4 functions of the digestion system | of water, mucus, enzymes and ions from the ECF to the lumen of the GI tract |
| Describe absorption, 1 of the 4 functions of the digestion system | Active or passive transport of substances from the lumen of the GI tract to circulation to ECF. |
| Functions of the mouth | -Mechanical breakdown of food with mastification -Start of chemical breakdown of food with saliva -The action of the tongue creates a bolus |
| Function of the pharynx | Transports food to the esophagus |
| Function of the esophagus | Transports food to the stomach |
| Components of saliva | Bicarbonate- helps neutralize acid in mouth and esophagus Mucus- softens food and protects the lining of the mouth from abrasion Salivary amylase- enzyme breaks down starch and glycogen Lysozyme- enzyme kills bacteria and helps prevent tooth decay |
| Describe the swallowing reflex event #1 | 1)Tongue pushes bolus into the pharynx stimulating mechanoreceptors on the epiglottis causing it to cover the glottis |
| Swallowing reflex event #2: After mechonreceptors trigger the epiglottis to cover the glottis... | After mechonreceptors trigger the epiglottis to cover the glottis... Upper esophageal sphincter relaxes, bolus enters esophagus, sphincter closes |
| Swallowing reflex event #3: After Upper esophageal sphincter relaxes, bolus enters esophagus, sphincter closes... | stretch receptors are stimulated triggering peristalsis throughout the esophagus toward the stomach |
| Swallowing relflex event #4: After stretch receptors are stimulated triggering peristalsis throughout the esophagus... | Lower esophageal sphincter relaxes and bolus enters the stomach, the sphincter closes. |
| Describe the functions of the stomach | Mechanical breakdown of food with motility of stomach Chemical breakdown of proteins by acid and pepsin Temporary storage of food, regulating its passage into the sm. intestine protection- destroys bacteria and pathogens that are swallowed w/ food. |
| What are the 4 secretory cells of the gastric glands? | Neck cells, Chief cells, Parietal cells and G-Cells |
| Location, products produced and function of the product for Neck cells | Location- upper region of the pits. Secretes- mucus Function- Helps to protect the stomach lining with bicarbonate from the acid. |
| Location, products produced and function of the product for Chief cells | Located- Gastric glands deep in the gastric pits. Secretes- Pepsinogen Function- (endocrine) Precursor for pepsin and gastric lipase which breaks down lipids |
| Location, products produced and function of the product for parietal cells | Location- Gastric glands, deep in gastric pits Secretes- HCl and instrinsic factor Function- (endocrine) HCl- increase acidity. Instrinsic factor- necessary for absorption of vitamin B12. |
| Location, products produced and function of the product for G-Cells | Located- Gastric pits Secretes- Gastrin hormone Functions- (exocrine) Increases motility and acid when bound to receptors. |
| Describe acid secretion by parietal cells event #1 | 1) Inside parietal cells- CO2, H2O and enzyme CA produces H2CO3 (carbonic acid) which is then converted to HCO3- and H+ |
| Describe acid secretion by parietal cells event #2: After H2CO3 is converted to HCO3- and H+... | H+ is actively transported out of the parietal cell into the lumen of the gastric pit by pumps which exchange the H+ out for K+ into the parietal cell. HCO3- exit the cell towards the blood in exchange for Cl- going into the cell. |
| Describe net result of acid secretion by parietal cells in event #2 | H+ and Cl- ions are transported into the lumen while HCO3- is transported into the ISF towards the blood. And K+ is transported into the cell. |
| Functions of the small intestine | Chemical digestion of all nutrient classes by pancreatic enzymes and brushborder enzymes Absorption of digestive end-products, H2O, ions and vitamins Secretion of hormones into bloodstream and HCO3- rich fluid |
| Substances in the small intestine that aid in digestion | HCO3-: Secreted by glands and pancreas which neutralizes acid in chyme from stomach Enzymes: produced by pancreas and brushborder for protein, lipid and CHO digestion Bile: Released to small intestine from gallbladder or liver to aid in lipid digestion |
| Function of the pancreas | Secretion of pancreatic juice containing digestive enzymes and HCO3- Secretion of hormones insulin and glucagon |
| Function of the liver | Secretion of bile containing bile salts and HCO3- Processes absorbed nutrients |
| Describe enterohepatic circulation | The pathway in which bile salts are absorbed in the ileum, return to the liver via the hepatic portal circulation and are eventually resecreted in the bile |
| Describe CHO digestion | Polysaccharides are broken down to disaccharides by amylases in the mouth in the saliva and pancreatic juice in the small intestine. Breakdown is completed to monomers in the small intestine, by a variety of brushborder enzymes. |
| Describe CHO absorption | Glucose are transported across the membrane of mucosal epithelial cells by sodium-linked secondary active transport (Na+ and glucose both entering cell) Glucose exit the cells by facilitated diffusion w/ protein into the ISF and diffuses into the blood. |
| Describe protein digestion | Pepsinogen secreted by chief cells activates pepsin which begins protein breakdown in lumen of stomach. Goes to small intestine where it is inactivated by high pH. Brushborder and pancreas secrete enzymes to digestion into amino acids, di & tripeptides. |
| Describe protein absorption | Amino, di and tripeptides are transported into the epithelial cell by carrier-linked secondary active transport (Na+ and others). Di and tripep's are broken down in cell to amino acids & are transported to ISF by facilitated diffusion & diffuse into blood |
| Describe lipid digestion | Saliva in mouth contains lingual lipase which starts dig. Stomach adds gastric lipase. Sm intestine adds pancreatic lipase forming lg floating fat droplets. Bile is secreted which emulsifies lipids making them less hydrophobic, lipases breakdown easier. |
| Describe lipid absorption | Fatty acids and monoglycerides into epithelial cells via simple diffusion. Molecules enter the smooth ER reassembled into triglyc, packaged by golgi ap to vesicles which exit via exocytosis into the ISF then enters lacteal/lymphatic sys then bloodstream. |
| Explain gastrointestinal regulation | Reflex mechanism invloving 3 phases and includes receptors (mechano, chemo and osmoreceptors) picks up stimulus. Stimulus is interpreted by control center (ENS or CNS). Processing center sends out response to effector cells |
| Explain short reflex pathway | Stimuli signals travel from receptors to ENS and then directly to the effectors |
| Explain long reflex pathway | Stimuli signals travel from receptors to the CNS to the ENS then to the effectors. |
| Explain cephalic phase of GI control | Chemo & mechanoreceptors sense stimulus(emotional state,sight,smell)& sends to CNS to PNS to ENS. ENS stimulates gastrin secretions which causes parietal & chief cells to secrete acid, pepsinogen & motility or skips gastrin secretion stim cells directly. |
| Explain gastric phase of GI control | Proteins enter stomach stimulate osmorec. intiating sh & long reflexes -> ENS to release gastrin. Or distension of stomach stimulates mechanrec. initiate reflexes stimulate ENS to release gastrin. Gastrin stimulates gastric secretion & increases motility |
| Explain intestinal phase of GI control | Sensors in intestine causes reflexes to produce secretion of HCO3-, digestive enzymes and bile and start peristalsis in sm. intestine. Inhibitory reflexes slow gastric emptying while contents are neutralized, digested and absorbed. |
| Explain gastrin | Secreted into stomach with presence of proteins, distension of stomach or PNS input to stomach. Stimulating gastric secretion & motility, ileal motility, relaxes ileocecal sphincter & stimulates mass movement of colon. Active in cephalic & gastric phase. |
| Explain secretin | released in sm. intestine when acid present. Inhibits gastric secretion and motility, stimulates pancreatic HCO3- secretion, potentiates actions of CCK on pancreatic enzyme secretion, stimulates bile secretion by liver. Present in intestinal phase |
| Describe intestinal phase w/ protein (acid) | Amino acid enters SI, chemoreceptors initiate short and long reflexes stimulating release of secretin by SI. Secretin goes into circulation and binds to receptors of pancreatic cells that release HCO3-. |
| Describe intestinal phase w/ glucose (CHO) | Glucose enters SI, osmoreceptors initiate short and long reflexes stimulating release of GIP by SI. GIP goes into circulation and binds to receptors of islet of langerhaans of the pancreas stimulating release of insulin |
| Describe intestinal phase w/ lipid (fat) | Fat enters SI, osmoreceptors initiate short and long reflexes stimulating release of CCK by SI. CCK goes into circulation and binds on receptors of gallbladder cells stimulating contraction and release of bile. |
Created by:
nrem3
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