Digestion & Absorption

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  • Created by: Becca
  • Created on: 23-12-13 23:43
What is the function of digestion?
To convert complex foodstuffs into manageable units for absorption
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Where does digestion happen in the GI system? Which enzymes are involved?
Some digestion in the mouth (amylase digests CHOs in neutral pH) & stomach (pepsin digests proteins in acidic pH). Majority of digestion in small intestines due to an ideal arrangement via microvilli increasing surface area
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How is the pancreas involved in digestion & absorption?
Major source of digestive enzymes (from acinar cells) enzymes modified by duct cells, form aqueous alkaline secretion & HCO3- to neutralise acidic chyme, dependent on Cl- exchange
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How are the liver & gall bladder involved in digestion & absorption?
Liver produced secretions, stored in gall bladder. During meals hormones stimulate smooth muscle of gall bladder, expels contents into common bile duct -> duodenum, mixes w/ pancreatic secretions -> liver secretions + pancreatic enzymes mix w/ chyme
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Why is the neutralization of chyme necessary?
Digestion enzyme activity (optimal at neutral//slightly acidic pH), micelle formation (for fat absorption) & protecting duodenal mucosa from autodigestion
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How are carbohydrates digested & absorbed?
Complex CHO digested in mouth/SI (saliavary/pancreatic amylase), enzymes in brush border epithelium convert di-->mono, uptake to epithelial cells, driven by Na+ co-transporter, creates conc gradient, active proteins pull Na+ & sugar gut lumen->blood
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What are lactose, maltose & sucrose broken down into? (di->monosaccharides)
Lactose -> galactose + glucose. Maltose -> glucose + glucose. Sucrose -> fructose + glucose
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How are proteins digested?
Pepsin (needs acidic pH, doesnt work in alkaline pancreatic secretions), proteolytic enzymes (endo/exopeptidases cleave interior/external peptide bonds) activated by trypsin in brush border epithelium, intracellular peptidases break di/tripeptides
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Why do the proteolytic enzymes need to be activated? How are proteins absorbed?
Enzymes secreted into duodenum as inactive precursors to prevent autodigestion. Absorption by passive or facilitated diffusion
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How are fats digested?
Insoluble in H20, pancreatic lipase soluble, emulsifies fat using bile salt -> lipid soluble head + -ve charged H20 soluble tail -> disperses fat by embedding head in droplet, -ve tails repel -> micelle (more soluble)
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What constitutes a micelle?
Bile salts + monoglycerides + free fatty acids
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What happens once a micelle is absorbed? How is it transported?
Monoglyceride + free fatty acid are resynthesised intro triglycerides where they combine with protein, phospholipids & cholesterold -> chylomicrons. Chylomicrons are too big for capillaries so transported to systemic circulation via lymphatic system
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What controls pancreatic secretions?
Vagus nerve: ACh increases secretin & cholycystokinin (CCK). Secretin released in response to acid in duodenum, stimulates HCO3- production. CCK stimulates enzyme rich secretion presence fat & protein. Sympathetic NS/somatostatin decrease secretions
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What is lactose insufficiency & what does it cause?
Intolerance to lactose, produces osmotic diarrhoea & flatulence
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What is gluten enteropathy & what does it cause?
Coeliac disease, gluten causes mucosal damage, decreases villi surface area for absorption, increases delivery nutrients to large intestines -> diarrhoea, flatulence
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What is acute & chronic pancreatitis? What does it cause?
Acute: autodigestion of pancrease by secreted enzymes (pancreatic duct blocked by stones). Chronic: alcohol abuse. Symptoms: steatorrhoea from fat malabsorption (lack of pancreatic lipase), diabetes
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Card 2

Front

Where does digestion happen in the GI system? Which enzymes are involved?

Back

Some digestion in the mouth (amylase digests CHOs in neutral pH) & stomach (pepsin digests proteins in acidic pH). Majority of digestion in small intestines due to an ideal arrangement via microvilli increasing surface area

Card 3

Front

How is the pancreas involved in digestion & absorption?

Back

Preview of the front of card 3

Card 4

Front

How are the liver & gall bladder involved in digestion & absorption?

Back

Preview of the front of card 4

Card 5

Front

Why is the neutralization of chyme necessary?

Back

Preview of the front of card 5
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