Digestion Flashcards
(15 cards)
Digestion definition?
When large bio molecules r hydrolysed into smaller molecule’s that can be absorbed across cell membranes
Stage 1 of digestion?
Ingestion - Food is taken into the body through the mouth
Stage 2 of digestion?
Digestion - Breakdown of large (insoluble) molecules (in the food) into small, simple (soluble) molecules (by mechanical and chemical means)
Stage 3 of digestion?
Absorption - The small (soluble) molecules can be absorbed through the lining of the small intestine (the ileum) into the blood
Stage 4 of digestion?
Egestion - Any food that can’t be digested is eliminated from the body (e.g. cellulose in plant cell walls)
Physical v Chemical breakdown of large (insoluble molecules)?
Physical/mechanical breakdown: large food is broken down into smaller pieces by chewing with teeth in the mouth (mastication) and churning of the stomach muscles
Chemical digestion - Digestive enzymes hydrolyse large insoluble molecules into smaller soluble ones which can then be absorbed and used in the body
Digestion & enzymes of carbohydrates?
Amylase: produces by pancreas & salivary glands
- hydrolyses polysaccharides into the disaccharide maltose - by hydrolysing glycosidic bonds (in duodenum)
Membrane-bound disaccharidases: e.g. sucrase & lactase hydrolyse sucrose & lactose into monosaccharides (ileum) (these disaccharides including maltose are digestible)
Digestion & enzymes of proteins?
- endopeptidases - hydrolyse peptide bonds between amino acids in middle of polymer chain (to produce shorter polypeptides)
- exopeptidases - hydrolyse peptide bonds between amino acids at ends of chain (to produce dipeptides/single amino acids)
- membrane-bound dipeptidases - hydrolyse any remaining dipeptides into single amino acids
Where does protein digestion occur?
- starts in stomach, continues in duodenum & fully digested in ileum
Digestion & enzymes of lipids?
- by lipase & action of bile salts
Lipase: produced in pancreas (secretes enzyme into duodenum & ileum) - hydrolyses ester bond in triglycerides -> monoglycerides & fatty acids
Bile salts: produced in liver, stored in gall bladder secreted by bile duct into duodenum & ileum
- emulsify lipids to form tiny droplets (micelles) - increasing SA for lipase to act on
Physical v Chemical digestion of lipids?
Physical: emulsification & micelle formation
- lipids coated in bile salts to create an emulsion (tiny droplets)
- many small droplets provides larger SA to enable faster hydrolysis action by lipase
Chemical (lipase): lipase hydrolyses lipids into glycerol & fatty acids (some monoglycerides)
What are micelles?
- water soluble vesicles formed of fatty acids, glycerol, monoglycerides & bile salts
- deliver fatty acids, glycerol & monoglycerides to csm of ileum epithelial cells for absorption
Adaptations of ileum to increase efficiency of absorption?
- ileum wall covered in villi (folding of ileum surface) - hv thin walls (lined w 1 cell thick epithelial cells) - short diffusion pathway
- epithelial cells hv microvilli
- inside villi - capillary network - can carry away absorbed molecules to maintain conc. gradient
Monosaccharide & amino acid absorption?
- to absorb from ileum lumen to gut: must be higher conc. in lumen compared to epithelial cell (facilitated diffusion) but…
- usually more in epithelial cells so - co transported w Na+
Lipid absorption?
- when micelles encounter ileum epithelial cells - break apart & release the lipid-soluble contents - can simply diffuse across csm to enter epithelial cells
- once in cell - modified back into triglycerides in smooth endoplasmic reticulum
- triglycerides sent to Golgi app via vesicles
- Golgi app processes triglycerides into structures aka chylomicrons (also contain proteins) - these leave app via vesicles
- vesicles move to & fuse w csm - chylomicrons leave cell (exocytosis)
- these r taken up by nearby lymph capillaries aka lymph vessels - contain liquid: lymph - drains into blood later (containing chylomicrons)
