macronutrients Flashcards
what are the functions of carbohydrates? 4
- energy substrate
- builds macromolecules
- glycogenesis
- spares protein and fat
where can linoleic acids be found? 3
- vegetable oils
- sunflower oils
- meat, poultry and eggs in the form of arachidonic acid
where can linolenic acids be found? 2
- green leafy vegetables
- in oily fish as eicosapentaenoic acid and docosahexaenoic acid
what are the functions of dietary fat? 3
- 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 (LPL)
- This is upregulated in the presence of insulin, fatty acids during fasting
what are essential amino acids?
names? 9
- not synthesised in the body, there is a dietary requirement
- histidine
- isoleucine
- leucine
- methionine
- phenylalanine
- threonine
- tryptophan
- valine
- lysine
describe mechanical digestion in the mouth? 2
- chewing and swallowing
- chemical digestion of carbohydrates and fats
describe the mechanical digestion in the stomach? 3
- peristaltic mixing and propulsion
- chemical digestion of carbohydrates and fats
- absorption of lipid-soluble substances such as alcohol and aspirin
describe the mechanical digestion in the small intestine? 3
- mine and propulsion, primarily by segmentation
- chemical digestion of carbohydrates, fats and polypeptides, nucleic acids
- absorption of peptides, amino acids, glucose, fructose, fats. water, minerals and vitamins
describe the mechanical digestion of the large intestine? 3
- segmental mixing and propulsion
- no chemical digestion (except by bacteria)
- absorption of ions, water, minerals, vitamins and organic molecules
describe 2 adaptations to the GI tract to facilitate different functions?
- Stomach= acidic environment= mucous and bicarbonate ions
- Small intestine= peristalsis becomes segmentation to squeeze food against the intestinal wall and maximise digestion and absorption
describe the sequence of sphincters in the GI tract? 4
- Cardiac
- Pyloric
- Ileocecal valve
- Internal and external sphincters
describe carbohydrate digestion in the buccal cavity?
salivary amylase, limited activity. initiates the breakdown of starches by catalysing the hydrolysis of polysaccharides into disaccharides
describe dat digestion in the buccal cavity?
lingual lipase secreted by the serous glands
describe fat digestion in the stomach? 3
- Stomach- gastric lipase secreted by gastric cells in the fundic mucosa.
- An acid enzyme that does not require bile acid from the liver or colipase from the pancreas for optimal functioning
- Theses enzymes are important in neonates (50% of lipid hydrolysis) and adults (30%)
describe protein digestion in the stomach? 2
- Chief cells produce pepsinogen converted to pepsin int eh presence of HCl
- Acid environment denatures proteins and reduces the bacterial load
describe bile acids from the liver for fat digestion? 2
- Cholic and chenodeoxycholic acid
- Molecules are amphipathic- act as a detergent and have both hydrophobic and hydrophilic properties. This means they can solubilize lipids to form mixed micelles
describe the pancreas and fat digestion? 4
- 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 monoglycerol, fatty acids and glycerol
describe the primary pancreatic proteases? 4
- The two primary pancreatic proteases are trypsin and chymotrypsin
- These 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 the 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
describe absorption of nutrients in the small intestine? 2
- Blood supply= 9 litres of fluid enter the GI tract with 8 litres absorbed through the small intestine
- Large surface area to maximise secretion and absorption
describe small intestine disaccharide digestion?
- Disaccharides further digestion occurs by action of brush border enzymes- gluco-amylase, alpha-dextrinase, sucrase and maltase to form monosaccharides glucose, fructose and galactose
describe carbohydrate absorption in the small intestine? 3
- Absorption of CHO is limited to monosaccharides- glucose, galactose and fructose
- Small intestine
- Capacity to absorb fructose is limited
describe fat absorption? 3
- Small intestine
- Water soluble mixed micelles pass through the unstirred water overlying the microvillus
- Monoclyglycerol and fatty acids cross the apical membrane of the microvillus through passive diffusion and lipid protein transporter mechanisms
describe protein absorption? 6
- Small intestine
- Pepsin (stomach)
- Trypsin (pancreatic proteases)
- Peptidases (brush border enzymes)
- Human peptide transporter 1 (PEPT1)
- Sodium hydrogen exchanger 3 (NHE3)
describe non-starch polysaccharides and other carbohydrates? 7
- NSP (fibre) resistant starch and most oligosaccharide are not digested and absorbed in the small intestine
- Soluble fibres (pectin/gum) are fermented by bacteria in the colon
- Insoluble fibres make up the cellulose roughage in the diet
- Microbial fermentation leads to the production of:
- gas (CO2, H2, CH4),
- short chain fatty acids (acetate (enters the peripheral circulation), propionate (taken up by liver) and butyrate (used by the colonic cells)
- this also enhances microbial growth
