macronutrients Flashcards
what are the functions of carbohydrates?
- energy substrate
- builds macromolecule
- glycogenesis
- spares protein & fat
- substrates for fermentation in colon
- fibre for faecal bulk, excretion dead cells and increase transit time
what is a polyunsaturated fat?
more than one double bond
what is a monounsaturated fat?
single double bond
what are the functions of dietary fat?
- TAG is the primary energy substrate stored in adipose tissues to sustain animals during fasting
- influx of TAG into adipose tissue largely mediated by the action of adipose tissue lipoprotein lipase
- this unregulated in the presence of insulin, fatty acids during fasting
- enhances flavours, increases palatability, gives food mouthfeel
- carriers essential fat soluble vitamins: A, D, E and K
- serves as a component of cell membranes and precursor steroid hormones and vitamins
what is the intake requirement of protein?
- need 0.8/kg/day
- older adults 1.2g/kg/day
- acute illness demand can exceed this: negative nitrogen balance due to inflammation induced catabolism
how many amino acids are there?
20
give a general overview of digestion and absorption
- adaptations to GI tract facilitate difference functions
- stomach: acidic environment; mucous and bicarbonate ions
- small intestine: peristalsis becomes segmentation to squeeze food against intestinal wall and maximise digestion and absorption
- sequence of sphincters: cardiac, pyloric, ileocaecal valve, internal and external sphincters
what function does the buccal cavity have in digestion?
- mastication
- swallowing
- taste: sweet, sour, bitter, salty and umami
how does the stomach digest fat?
- gastric lipase is secreted by gastric cells in the fund mucosa
- acid enzyme that does not require bile acid or colipase for optimal functioning
how is protein digested by the stomach?
- chief cells produce pepsinogen converted to pepsin in the presence of HCl
- acidic environment denatures protein and reduces bacterial load
what bile acids are produced by the liver?
- cholic
- chenodeoxycholic
how does the pancreas help with fat digestion?
- small intestine: pancreatic lipase secreted from the pancreas alongside the cofactor pro-colipase
- pro colipase is activated in the intestinal lumen by trypsin to form colipase
- colipase stabilises pancreatic lipase increasing its efficiency
- pancreatic lipase hydrolyses TG to form monocyglycerol, fatty acids and glycerol
how does the pancreatic proteases help with protein digestion?
- they are synthesised and packaged within secretory vesicles as inactive pro enzymes: trypsinogen and chymotrypsinogen
- the pro enzymes are activated by an enteropeptidase: enterokinase secreted by the mucosal membrane of duodenum
- the secretory vesicles also contain a trypsin inhibitor to serve as a safeguard against trypsinogen converting to trypsin within the pancreas or pancreatic ducts
what are the 2 primary pancreatic proteases?
- trypsin
- chymotrypsin
how does the small intestine help with disaccharide digestion?
- disaccharides further digestion occurs by actin of brush border enzymes: glycogen-amylase, alpha-dextrinase, sucrase and maltase
- these form monosaccharides: glucose, fructose and galactose
how are monosaccharides absorbed in the small intestine?
- absorption of CHO is limited to to glucose, galactose and fructose
- occurs in the small intestine
- capacity ot absorb fructose is limited
how are fatty acids absorbed in the small intestine?
- water soluble mixed micelles pass through the ‘unstirred water’ overlying the microvillus
- monocylglycerol and fatty acids across apical membrane of microvillus through passive diffusion and lipid protein transporter mechanisms
what are the 3 main enzymes that help with protein absorption and where are they found?
- pepsin (stomach)
- trypsin (pancreatic proteases)
- peptidases (brush border enzymes)
what happens to non starch polysaccharides?
microbial fermentation leads to the production of:
- gas: CO2, H2 and CH4
- short chain fatty acidsL acetate, propionate, butyrate
- enhances microbial growth
