L30 - GI absorption : nutrients Flashcards
name the inactive precursor of pepsin
pepsinogen
where is pepsinogen released from
chief cells of stomach
how is pepsinogen converted to pepsin
pepsinogen + HCL from stomach acid forms pepsin
this is also +ve feedback
describe characteristics of chyme
- acidic
- contains slightly digested fats proteins and sugars
- contains intrinsic factor (enables b12 absorption in SI)
after leaving stomach, what is needed to allow further digestion
pancreatic enzymes
neutral pH
bile salts for fat digestion
what enzyme involved in protein digestion is found on the brush border of enterocytes (duodenum) and what is its function
Enterokinase
- converts the inactive trypsinogen into active trypsin
- trypsin then activates inactive pancreatic enzymes
what type of enzymes are involved in protein digestion, give examples
endopeptidases
trypsin
elastase
chymotrypsin
two examples of exopeptidases and their function
- carboxypeptidase - removes AA’s from carboxyl ends of the recently cleaved short peptides
- aminopeptidase - removes AA’s from amino end of the recently cleaved short peptides
explain the process of digestion of proteins in the duodenum
- enterokinase found on the brush border of enterocytes in the duodenum convert active trypsinogen to the inactive trypsin
- trypsin can then activate other pancreatic proteolytic enzymes (that follow)
- pancreatic trypsin, elastase, chymotrypsin cleave peptide bonds producing short peptides
- carboxypeptidase removes AA’s from the carboxyl end of the newly cleaved peptide
- aminopeptidase removes AA’s from the amino end of the newly cleaved peptide
leaves AA’s / di / tri peptides
examples of endopeptidases
trypsin
elastase
chymotrypsin
how are AA’s absorbed from duodenum
via Na+ linked cotransporters then diffuses through cell into capillary
how are di/tri peptides absorbed into blood from duodenum
- absorbed into cell via H+ linked transporters
- hydorlised further into AA’s
- diffuse into capillary
a small amount can diffuse as di/tri
where does carbohydrate digestion start?
mouth (amylase in saliva)
explain action of pancreatic amylase
cleaves straight chain polysaccharides (cant cleave branches) into short oligosaccharides
what oligosaccharides are produced after pancreatic amylase cleavage
maltose (disaccharide
maltriose (trisaccharide)
how are other disaccharides digested (eg lactose/sucrose)
brush border enzymes e.g si membrane bound disaccharidases cleave into monosaccharides
describe digestion of carbohydrates in the SI
- pancreatic amylase cleaves straight chain polysaccharides (only) into di and tri saccharides (maltose and maltriose)
- brush border disaccharidases further digest these and other disaccharides (eg lactose and sucrose) into monosaccharides