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19 Cards in this Set
- Front
- Back
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What is the digestive function of the oral cavity?
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- Teeth for mechanical chewing
- Salivary glands for lubrication and salivary amylase and lipase |
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What is the digestive function of the stomach?
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- Mechanical churning
- Release of pepsin, chymosin and lipases - Release of acid to kill bacteria and for the right enzymatic environment |
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What is the digestive function of the small intestine?
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- Smooth muscle for churning and propulsion (peristalsis)
- Pancreas releases pro-digesive enzymes into duodenum - Gall bladder releases bile for fat emulsification - Brush border enzymes help digestion (lactase, maltase, dipeptidase) |
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What is the digestive function of the large intestine?
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- Churning (taeniae coli bands of smooth muscle)
- Bacterial fermentation |
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What flows out of the ampula of vater?
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- Pancreatic fluid containing digestive proenzymes
- Alkaline bicarbonate solution to neutralise stomach acid - Bile containing salts, cholesterol, mucous and water |
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What are the two main exocrine cells in the pancreas?
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- Acinar cells (produce the digestive enzymes that are stored in zymogen granules and an isotonic fluid to carry enzymes)
- Duct cells (produce hydrogen carbonate to make a hypotonic fluid to carry enzymes) |
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How is autodigestion in the pancreas prevented?
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The proenzymes are inactive and stored in zymogen granules.
Their interior is very acidic (trypsin activity is greatest at pH8). Granules contain serine protease inhibitors to guard against autodigestion. |
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How do you get active digestive enzymes in the duodenum?
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Enteropeptidase in the brush border converts tyrpsinogen to trypsin which in turn activates other enzymes in the duodenum.
Pancreatic lipase is secreted in its active form but is ineffective unless bound to colipase. |
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Describe the main events in the secretion of hydrogen carbonate rich fluid from pancreatic duct cells.
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1. H2O + CO2 -- HCO3- + H+ by carbonic anhydrase and HCO3 leaves cell.
2. As HCO3- leaves cell through anion exchanger, Cl- enters. 3. Luminal Cl- provided by cystic fibrosis trans membrane conductance regulator (CFTR) 4. H+ accumulation is prevented by H+/Na+ exchange |
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What causes stomach ulcers?
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- Excess acid secretion
- Problems with neutralisation mechanism |
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What are the pH's of the oral cavity, stomach and small intestine?
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- Oral cavity is around pH7 (amylase)
- Stomach is around pH2 (pepsin) - Small intestine is around pH8 (trypsin) |
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How is activity of the GI tract regulated?
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Endocrine - slow onset, coordinated responses, energetically cheap
Neural - Fast onset, specific responses, energetically expensive In the absence of stimulation there is a slow basal rate |
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What are the 3 phases of GI secretion?
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The stimuli that upregulate GI secretion during the course of a meal can be subdivided into phases;
1. Cephalic (external environment and mouth) 2. Gastric (stomach) 3. Intestinal (intestines) |
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What stimulates the cephalic phase?
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Sight, smell and thought of food. Mediated by activation of parasymapthetic vagas nerve. Ach stimulates secretion from pancreatic duct and acinar cells.
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What stimulates the gastric phase?
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When food is present, stretch sensetive neurones in stomach are activated maintaining parasympathetic outflow by the vagovagal reflex.
G-cells secrete gastrin (which stimulates HCl secretion) in response to amino acids in the stomach. |
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What stimulates the intestinal phase?
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Acidic chyme entering the duodenum can stimulate S-cells to release secret in which acts as a buffer to optimise conditions.
Secretin stimulates hydrogen carbonate secretion from Brunner's glands andd slows H+ secretion from parietal cells. |
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What is CCK?
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CCK - chaolecytokinin is a GI peptide hormone responsible for the digestion of fat and protein. It is released from mucosal I-cells in the duodenum and stimulates the release of digestive enzymes from the pancreas.
CCK stimulates the relaxation of the sphyncter of Oddi and the contraction of the gall bladder. CCK also acts as a hunger supresser by acting on hypothalamus |
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How is the release of chyme from the stomach regulated? Why is it important?
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Gastrin (from G-cells in stomach) and CCK (from I-cells in duodenum) causes contraction of the pyloric sphyncter.
Important because - Enzymatic reactions take time - If food travels too fast it wont be digested properly - Takes time for nutrients to be absorbed across intestinal wall |
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Give the two main transporters for each carbohydrates, fatty acids and amino acids that are present in the intestinal wall.
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Carbohydrates - GLUT2 and GLUT5
(facilitated diffusion) Amino acids - SGLT1 and PepT1 (sodium or hydrogen dependent active transport) Fatty acids - FAT and CD36 (protonation or adding a proton allows facilitated diffusion) |
