Gastrointestinal: Digestion and absoprtion Flashcards
What are the 2 composites of food?
Macro and micro constituents
What are the macro-constituents? (3)
- Carbohydrate
- Protein
- Lipids
What are the micro-constituents? (3)
- Vitamins
- Minerals
- Water
How much carb should we get a day and what is it consumed as?
250-800g a day
Disaccharides or polysaccharides
What are examples of carbs? (6)
Sucrose Lactose Maltose Starch Glycogen Cellulose
What is the carbohydrate problem and what enzymes are used to solve it? (2)
Can only be absorbed as monosaccharides
- Salivary amylase
- pancreatic amylase
What are the 5 other digestion enzymes and where are they located?
Dectrinase Glucoamylase Sucrase Lactase Maltase Located in the brush border of small intestine
How are monosaccharides such as glucose (2) and fructose absorbed?
Glucose: Secondary active transport across apical membrane
Glucose: Facilitated diffusion across basolateral membrane
Fructose: facilitated diffusion across both membranes
How much protein a day should we get and where do we get it from? (3)
125g/day, only need 40-50g though
- consumed in diet
- secreted into lumen of intestinal tract
- sloughed off with cells lining intestinal tract
What are examples of protein digestion products? (3)
- amino acids
- dipeptides
- tripeptides
What are the 3 types of proteases?
Endopeptidases
Zymogens
Exopeptidases
What does a exopeptidase do? (2)
Cleave off A.A. from one end of polypeptide
Product = A.A.
What does an endopeptidase do? (2)
Split polypeptide at interior peptide bonds
Product = small peptide fragment
What do zymogens do? (4)
- inactive storage form of proteases
- Stored im zymogen granules
- Secreted by exocytosis
- Activated by proteolytic activation
How is protein digested in the stomach? (2)
Pepsin is secreted: pepsinogen
Activated by acid
How is pepsin activated and what does it do? (3)
Chief cell secrete pepsinogen
HCl cleaves pepsinogen to pepsin
Parietal cells secrete HCl
List the proteases in the pancreas (3) and the brush border (2):
Pancreas: trypsin, chymotrypsin, carboxypeptidase
Brush border: aminopeptidase, enterokinase
How are amino acids absorbed?
- Cross apical membrane - active transport
- Broken down inside cell to A.A.
- Amino acids cross basolateral membrane - facilitated diffusion
How much lipid should we intake a day?
25-160g/day - 90% triglyceride
Why are lipids hard to digest and absorb? (3)
- Not water soluble
- Do not mix with stomach/intestinal contents
- Form fat droplets
What is the enzyme of lipid digestion called?
Lipase
Where is lipase secreted from and how does it work?
Secreted from the pancreas
Bind to the edge of the fat droplets
What are bile salts and where are they secreted from?
Bile salts break lipids into smaller droplets
Synthesised in the liver from cholesterol
What do triglycerides turn into?
Monoglyceride + 2 fatty acids
How are monoglycerides and fatty acids absorbed? (3)
Simple diffusion across epithelium - due to equilibrium
Enter smooth ER - reform triglycerides
Lipids enter Golgi - packaged into chylomicrons
What happens to chylomicrons? (2)
Secreted by exocytosis into interstitial fluid
Enter lymphatic system via lacteal
What is the route of enterohepatic circulation? (8)
- Liver
- Gallbladder
- Common bile duct
- Duodenum
- Bile salts
- Ileum
- Capillaries
- Hepatic portal vein
How do we absorb vitamins? (3)
Absorbed with lipids (A, D, E, K)
Dissolve in droplets, micelles, chylomicrons
Some require special transport systems (B12)
How do we absorb minerals? (3)
Solvent drag with water reabsorption (Na+)
Passively follows sodium absorption (Cl-)
Passively absorbed (K+)
How do we absorb calcium? (4)
- Actively absorbed in duodenum and jejunum
- Binds to brush border protein
- Transported to epithelial cell
- Transported across basolateral membrane by Ca2+ pump
How do we absorb iron? (5)
- Transferrin secreted by enterocytes in small intestine
- Transferrin binds iron
- Taken into cell by endocytosis
- Some stored as ferritin in enterocytes
- Some transported into blood
How do we absorb and secrete bicarbonate? (2)
Jejunum - bicarbonate ions passively absorbed
Ileum and colon - bicarbonate secreted in exchange for chloride ions
How do we absorb water? (4)
- 7L of secretions
- 2L intake
- Passive absorption
- Follows solutes by osmosis
What are the 3 absorbing abnormalities?
- Failiure of substances to reach absorbing epithelium
- Absorbing substances unavailable
- Loss of absorptive surface
