GI: Monogastric digestion of nutrients Flashcards
How are macronutrients digested?
Broken down by enzyme-catalysed hydrolysis. Single units absorbed by small intestine.
Polysaccharide (startch + glycogen) hydrolysis
By salivary and pancreatic amylate
Dissaccharide (sucrose + lactose) hydrolysis
By disaccharidases (found on brush border membranes of enterocytes microvilli)
Where are monossaccharides absorbed? How is each one absorbed?
At brush border (apical membrane).
- Glucose + Galactose using Na+ co-transport
- Fructose passive transport
Protein hydrolysis
By peptidases/ proteases
Endopeptidases (protein hydrolysis)
- Cleave internal peptide bonds and form short polypeptide fragments
- Fragments non specific co-transport with proton
Exopeptidases (protein hydrolysis)
- Cleave end of polypeptide chain and form free a.a
- Absorption through specific Na+ dependent a.a transporters
List main peptidases in digestion
Stomach: peptin
Pancreas/ duodenal lumen: Trypsin, Chymotrpsin, Elastase
Duodenal brush border: Endopeptidase, dipeptidases and aminopeptidase
Triacylglycerols hydrolysis steps (2)
- Broken down by pancreatic lipases (produces some free fatty acids)
Emulsified by bile salts and mechanical mixing
Mixed micelle
Smallest broken down form of lipids. Able to be absorbed.
Triacylglycerol absorption steps (3)
- Contact apical membrane, bile salts removed, fatty acids enter
- Bound by fatty acid binding protein
- Triacylglycerol reassembled and leave to lacteal
Lipoproteins
Transport lipids through blood
Apoproteins function (3)
Structural, ligand for cell receptors, activators of enzymes
Exogenous lipid transport
From s.intestine to liver
- Uses chylomicrons
Endogenous lipid transport
Liver to peripheral tissues
- VLDLs -> IDLs ->LDL (low density lipoprotein)
HDL functions (2)
Transporting apolipoproteins (maturation and recycling) and cholestrol (peripheral tissues)
Reverse cholesterol transport
Liver -> nascent HDL -> cholesterol from peripheral tissues -> mature HDL… and repeat
Fat soluble vitamins
D,E,K,A
Vitamin A (forms-3)
- Retinoic acid: steroid hormone
- Retinal: Eye function, pigment
- B-carotene: Antioxidant
Vit A deficiencies
- Dry skin/ lesions
- Corneal disorders
- Higher susceptibility to infection
Vit D function + deficiencies
Calcium homeostasis
- Malformed bones (Rickets and Osteomalacia)
- Joint problems
Vit E function + deficiencies
Antioxidant (used with selenium)
- Increased risk of anaemia, cancer and free radical diseases.
Vit K function + deficiencies
Clotting factors
- Bleeding disorders
Free radicals
Contain extra electron. React w/proteins, nucleic acids and lipids
