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Intestines 1 (Digestion and absorption (2 phases digestion (Luminal -…
Intestines 1
Digestion and absorption
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2 phases digestion
Luminal - Enzymes secreted by salivary glands/pancreas
Membranous - Enzymes attached to epithelial surface of intestinal cells
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Segmental contractions
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Mix contents with digestive juices, move contents towards mucosal surface
Intense upon emptying of stomach, short periods of weak segmental (allow weak peristaltic to occur, but soon die out) slow aboral movement
Chyme reaches distal SI, feedback mechanism inhibits proximal SI contractions (neuronal/hormonal mechanisms). Major mechanism for co-ordinating SI intestinal transit to allow maximal digestion/absorption to occur. SI transit approx 3-4 hours regardless of size
Peristaltic contraction
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When one contraction reaches ileum new one starts in duodenum. Migrating myo-electric complex, takes 1-2 hours to propogate down entire SI, empty SI of contents and prevent retrograde flow
Adaptation to diet
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Omnivores - Diet contains high levels of hCHO, SGLT1 remain high, expressed high throughout SI
Ruminants - SGLT1 in neonates high as rumen develops less hCHO pass into SI so SGLT1 expression declines
Horses - SGLT1 highest proximally declining distally in wild horse on grass, domestic horses SI can adapt levels of SGLT1 (especially proximally) dependent on dietary needs
Carb digestion
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Luminal digestive phase, pancreatic amylase (Amylose --> maltose)
Membranous digestive phase
- Maltose -> Glucose+glucose
- Sucrose -> Glucose+fructose
- Lactose -> Glucose+glucose
Carb absorption
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Transferred to liver via hepatic portal vein, stay in circulation or -->glycogen
Motility
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SI emptying - Circular muscle at ileo-colic junction, functions as physiological valve (especially pronounced in horses. Motility increases after feeding, "gastro-ileal reflex"
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