GI Lecture 3 - Intestinal Absorption of Nutrients

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  • Created by: LBCW0502
  • Created on: 06-10-19 14:08
Describe the arterial supply and venous drainage in the intestinal epithelium
Artery and vein enter layers (muscle, submucosa, muscularis mucosa and mucosa with villi). Fenestrations (high permeability, prevents filtration of proteins). Epithelium is fenestrated, blood drained into vein (into circulation)
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Which particular feature do excretory organs have?
Fenestrations - to allow rapid flux of water, nutrients and electrolytes
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Describe various features of the small intestine (1)
Villus structures, epithelium. Brush border (luminal membrane of epithelium). Basolateral surface. Entry of nutrients, exit of nutrients via transport proteins. Venous drainage form villi
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Describe various features of the small intestine (2)
Rich blood supply enables prominent absorption. Cells absorbing nutrients, age and regenerate. Crypt lumen. Upper 2/3 of absorption. Most of the water secreted by glands is reabsorbed
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What is the function of the lymphatics?
To drain excess fluid back into the fatty system via the thoracic duct
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What are the effects of cholera?
Poor water reabsorption, watery stool, loss of electrolytes, diarrhoea
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Describe the digestion of carbohydrates and absorption across intestinal villi (1)
Partial breakdown/digestion of carbohydrates in salivary glands. Amylase aids digestion (and maltase). Glucose absorbed across membrane into blood via Na co-transporter. Na high in intestinal lumen and low in the blood
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Describe the digestion of carbohydrates and absorption across intestinal villi (2)
Na-K ATPase pump removes Na from cell (form electrochemical gradient - drives absorption of glucose and Na via Na transporter)
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What does primary active transport require?
Uses ATP for the process to occur
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Describe the absorption of monosaccharides (1)
Glucose and Na transported via SGLT1 (unidirectional process, conformational change in transport protein depends on activity of Na-K ATPase))
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Describe the absorption of monosaccharides (2)
GLUT-1 is a facilitated transport protein, glucose enters the interstitial space (bidirectional transport process). Application - patient who has has surgery cannot eat (parenteral nutrition)
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What is the effect of a cardiac glycoside?
Blocks Na-K ATPase pump, leads to low glucose absorption, low Na electrochemical gradient
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Describe the digestion of proteins and absorption of amino acids and oligopeptides (1)
Proteins enter the stomach, pepsins and HCl break down proteins, digestive enzymes break down proteins into amino acids/di-peptides. Absorption involves Na and H co-transporters
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Describe the digestion of proteins and absorption of amino acids and oligopeptides (2)
Absorption of amino acids via Na transporter. Na is high in intestinal lumen, low in the blood. Pumping of Na and amino acid via Na amino acid co-transport
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Describe the digestion of proteins and absorption of amino acids and oligopeptides (3)
Absorption of small peptides via H transporter. H gradient takes small peptides across cell. Within cell, intracellular peptidases hydrolyse amino acids into blood via facilitated transporter (down concentration gradient).
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Describe the digestion and absorption of fats (1)
Fat enters the stomach, lipase used to break down fats. Secretion of bile salts from liver (allows fats to be miscible in intestinal luminal phase (micelle). Fat diffuses across lipid bilayer. Bile salts are reabsorbed
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Describe the digestion and absorption of fats (2)
Micelle reabsorbed in the SI via pathways. Hepatocytes take up micelles. Liver synthesises extra 5% of bile salts (in case bile salts are lost)
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What are the issues with loss of bile salts?
Liver failure, jaundice, steatorrhea (insufficient reabsorption of bile salts)
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Describe intestinal lipid absorption (1)
Glycerol (short/medium chain fatty acids) can pass through enterocyte and enter blood capillaries due to small size (fenestrations). Pancreatic lipases/biliary bile salts, lecithin/cholesterol adsorb to surface of emulsion droplets from stomach
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Describe intestinal lipid absorption (2)
Lipolytic products ionised, cholesterol acts of further emulsifiers. Bile salt micelles transform multilamellar vesicles into unilamellar vesicles and then into mixed micelles which are composed of bile salts, mixed lipids
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Describe intestinal lipid absorption (3)
Unstirred water layer at mucosal surface of intestine is not a major absorptive barrier. Short/medium fatty acids soluble in water diffuse to enterocyte. Mixed lipids micelles give effective concentration of lipid products for diffusion
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Describe intestinal lipid absorption (4)
Fatty acid/bile salts in micelles reach surface of enterocyte, when reaching low pH, fatty acids leave micelle and enter enterocyte by non-ionic diffusion of by collision and incorporation into lipid bilayer
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Describe intestinal lipid absorption (5)
After entry, bile salts return to lumen, absorbed throughout SI passively and via active transport in distal ileum
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Describe the intestinal absorption of dietary lipids (1)
Fats cross lipid bilayer, enter SER and RER, then Golgi, formation of a chylomicron (exocytosis), absorption into lymphatic vessels (large chain fats), short chain fats enter the blood capillary. Moving fats from blood into target tissues.
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Describe the intestinal absorption of dietary lipids (2)
Need adequate acid secretion, lipase from salivary glands/stomach, need inflow of micelles to move fat to villi, micelle opens, fat particles diffuse across lipid bilayer, long chain fatty acids synthesised into chylomicrons, enters lymphatic vessels
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Describe vitamin absorption (1)
Secondary active transport. Na transporter needed. Some vitamins enter to form chylomicrons. Vitamin A (for chylomicrons taken up by the liver. Vitamin E passes via lymph into bloodstream
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Describe vitamin absorption (2)
Vitamin K produced by intestinal bacteria and absorption of similar A, D and E vitamins
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Other cards in this set

Card 2

Front

Which particular feature do excretory organs have?

Back

Fenestrations - to allow rapid flux of water, nutrients and electrolytes

Card 3

Front

Describe various features of the small intestine (1)

Back

Preview of the front of card 3

Card 4

Front

Describe various features of the small intestine (2)

Back

Preview of the front of card 4

Card 5

Front

What is the function of the lymphatics?

Back

Preview of the front of card 5
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