macronutrients

Question 1

what are the functions of carbohydrates?

Answer 1

• energy substrate
• builds macromolecule
• glycogenesis
• spares protein & fat
• substrates for fermentation in colon
• fibre for faecal bulk, excretion dead cells and increase transit time

Question 2

what is a polyunsaturated fat?

Answer 2

more than one double bond

Question 3

what is a monounsaturated fat?

Answer 3

single double bond

Question 4

what are the functions of dietary fat?

Answer 4

• 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

Question 5

what is the intake requirement of protein?

Answer 5

• 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

Question 6

how many amino acids are there?

Answer 6

20

Question 7

give a general overview of digestion and absorption

Answer 7

• 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

Question 8

what function does the buccal cavity have in digestion?

Answer 8

• mastication
• swallowing
• taste: sweet, sour, bitter, salty and umami

Question 9

how does the stomach digest fat?

Answer 9

• gastric lipase is secreted by gastric cells in the fund mucosa
• acid enzyme that does not require bile acid or colipase for optimal functioning

Question 10

how is protein digested by the stomach?

Answer 10

• chief cells produce pepsinogen converted to pepsin in the presence of HCl
• acidic environment denatures protein and reduces bacterial load

Question 11

what bile acids are produced by the liver?

Answer 11

• cholic

- chenodeoxycholic

Question 12

how does the pancreas help with fat digestion?

Answer 12

• 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

Question 13

how does the pancreatic proteases help with protein digestion?

Answer 13

• 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

Question 14

what are the 2 primary pancreatic proteases?

Answer 14

• trypsin

- chymotrypsin

Question 15

how does the small intestine help with disaccharide digestion?

Answer 15

• disaccharides further digestion occurs by actin of brush border enzymes: glycogen-amylase, alpha-dextrinase, sucrase and maltase
• these form monosaccharides: glucose, fructose and galactose

Question 16

how are monosaccharides absorbed in the small intestine?

Answer 16

• absorption of CHO is limited to to glucose, galactose and fructose
• occurs in the small intestine
• capacity ot absorb fructose is limited

Question 17

how are fatty acids absorbed in the small intestine?

Answer 17

• 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

Question 18

what are the 3 main enzymes that help with protein absorption and where are they found?

Answer 18

• pepsin (stomach)
• trypsin (pancreatic proteases)
• peptidases (brush border enzymes)

Question 19

what happens to non starch polysaccharides?

Answer 19

microbial fermentation leads to the production of:

• gas: CO2, H2 and CH4
• short chain fatty acidsL acetate, propionate, butyrate
• enhances microbial growth