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Unformatted text preview: ers, the size of a tennis court! “brush border enzymes”
microvilli are also known as the "brush border"
many SI enzymes are tethered to the microvilli. why? VIII. SMALL INTESTINE (Part I) (cont.)
3. SI role in digestive functions:
a. Secretions in the SI
responds to fats and proteins
stimulates gall bladder, pancreas
inhibits stomach motility Secretin
responds to H+ in the duodenum
stimulates pancreatic release of HCO3
(bicarbonate) Gastric inhibitory peptide (GIP)
stimulates release of insulin (feed-forward)
also inhibits parietal cells (feed-back) PLUS... secretions from the Liver, Gall Bladder and Pancreas...
IX. ACCESSORY ORGANS
Serves the Important digestive function of producing and secreting bile.
the role of bile in digestion:
since fat is non-polar doesn't break down in water, would group into large droplets, relatively low surface area
bile emulsifies large fat globules into "micelles"
increase surface area for lipases to digest fat.
bile DOES NOT DIGEST FAT B. Gall Bladder
1. structure - small, sac-like, under the liver
a. stores and concentrate bile
takes bile in, removes water. b. ejects bile in response to CCK IX. ACCESSORY ORGANS (cont.)
1. structure - glandular organ near stomach and duodenum
2. digestive function
Secretions: “pancreatic juice” composed of:
bicarbonate ions (HCO 3G )
resulting from secretin pancreatic amylase
carb digester, need pancreatic amylase because salivary amylase denatures once it reaches stomach, left without something to digest carbs trypsin
enzyme that digests proteins, need trypsin because pH changes in small intestine, pepsin denatures in small intestine. pancreatic lipase
lingual lipase denatures in small intestine, so pancreatic lipase needed to continue fat digestion. X. SMALL INTESTINE (Part II)
3. role in digestive functions (cont.):
b. Digestion in SI
Carbohydrates Proteins Lipids -> monosaccharides -> amino acids monoglyceride and fatty acids X. SMALL INTESTINE (Part II) (cont.)
3. role in digestive functions (cont.):
c. Motility in SI
weak and slow
Why? slows things down. food as been mixed with lots of stomach and other juices, stretch receptors won't be used as much because food isn't stretching Segmentation
circular muscle squeezing down and mixing and churning contraction so that the absorption of
molecules is maximized
main contractile activity in the SI d. Absorption in SI
Monosaccharides & Amino Acids
absorbed by co-transport with Na+ Lipids
free floating, no active transport
chylomicrons transport fats through body (lipoproteins) without this cells don't know how to respond to fat chylomicrons absorbed into lymphatic system thru lacteals Clinical Application: Lactose Intolerance
Cause: lactase isn't available to break down lactose into monosacchharides
lactase is a good example of brush border enzyme. Explain the symptoms of lactose intolerance.
bloating and gas.
if you don't have lactase, bacteria can still digest it, so digests it in large intestine for bloating and gas.
lactose creates a concentration gradient in large intestine. water rushes to large intestine instead of away, so diarrhea XI. LARGE INTESTINE 5 feet long
1. several sections: cecum, ascending, transverse, descending, and sigmoid colons
2. structure of walls
have no villi, surface area is signiﬁcantly smaller than SI 3. LI role in digestive functions
a. Secretion in LI
mucus and sometimes water b. Digestion in LI
a little by remaining enzymes
most by bacteria c. Absorption in LI
no nutrient absorption for us
any absorption is done by bacteria for their purposes
water reabsorbed as well as vitamins and minerals and electrolytes
folic acid and vitamin K absorbed here (products of bacteria) d. Motility in LI
Peristalsis - wave-like contractions move down length of large intestine
Mass Movements, Churning and Defecation...
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This note was uploaded on 09/30/2013 for the course P 215 taught by Professor Mynark during the Fall '12 term at Indiana.
- Fall '12