Macronutrients Flashcards
Macro nutrients
Fats
Carbohydrates
Protein
Micro nutrients
Vitamins
Minerals
Trace elements
Dietary fat
TAG is 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
Upregulated in presence of insulin
Adipose tissue releases fatty acids during fasting
Fat digestion: mouth and stomach
Mouth- lingual lipase secreted by serous glands
Stomach- gastric lipase secreted by gastric cells in the fundic mucosa
Fat digestion: small intestine
Bile acids from liver- cholic and chenodeoxycholic acid
Amphipathic- act as detergent has both hydrophobic and hydrophilic properties
Pancreatic lipase secreted from pancreas alongside cofactor pro-colipase
Pro-colipase activated in intestinal lumen by trypsin to form clipase
Colipase stabilises pancreatic lipase
Pancreatic lipase hydrolyses TG to form monocyglcerol, fatty acids and glycerol
Carbohdyrate
Polysaccharide, disaccharide, monosaccharide
Stored as glycogen or fat in presence of insulin
Carbohydrate digestion
Starches digested by a-amylase in saliva and in pancreatic secretions to form maltose, maltotriose and a-dextrins
Fruther digestion occurs by brush border enzymes- glucose amylase, a-dextrinase, sucrase and maltase to form monosaccharides glucose and fructose
Carbohydrate absorption
Limited to the monosaccharides- glucose, galactose and fructose
Occurs in the small intestine
Capacity to absorb fructose is limited
Non starch polysaccharides and other carbohydrates
NSP (fibre) resistant starch and most oligosaccharides are not digested and absorbed in the small intestine
Soluble fibres fermented by bacteria in colon
Insoluble fibres make up cellulose ‘roughage’ in the diet
Non starch polysaccharides
Microbial fermentation leads to production of:
- gas (CO2-H2-CH4)
- short chain fatty acids (acetate, propionate, butyrate)
- also enhances microbial growth
Protein
No store of protein
Adults excrete about 80g nitrogenous waste each day
Daily requirement 0.8/kg/day
Protein requirements
Maintenance- nutritional requirements to stay alive
Growth- positive tissue accretion
Reproduction- tissue specific growth related to reproduction, reproductive function
Protein digestion
Dietary protein , few exceptions, are not absorbed
Through gastric and pancreatic proteins, protein digested within lumen of intestine into medium and small peptides
Protein digestion by pepsin in stomach
Pepsinogen released by chief cells in stomach
HCL released by parietal cells
HCL and pepsinogen released in response to gastrin and vagus nerve
Forms pepsin (active pH 2/3, inactive pH >5)
Protein digestion by pancreatic proteases
Trypsin and chymotrypsin
Synthesised and packaged within secretory vesicles as inactive pro enzymes (tripsonogen and chymotrypsinogen)
Pro enzymes activated by enterokinase
Enterokinase
Enteropeptidase
Secreted by mucosal membrane of duodenum
Sequence of enzyme activation
- Trypsinogen
- Trypsin
- Trypsinogen, chymotrypsinogen, proelastase, procarboxypeptidase
- Trypsin, chymotrypsin, elastase, carboxypeptidase
Absorption of amino acids
Dependent of electrochemical gradient of Na+ across epithelium
Transporters bind amino acids after binding sodium
Fully loaded transporter undergoes conformational change dumps Na+ and amino acid into cytoplasm
Transporter then re-orients back to its original form
Baso lateral membrane of enterocyte contains additional transporters which export amino acids from the cell into the blood
Absorption of peptides
Virtually no absorption of peptides longer than three amino acids but there is abundant absorption of di and tri peptides, probably by a single transport molecule with hydrogen
Vast bulk of di and tri peptides are digested into amino acids by cytoplasmic peptidase
Absorption of intact proteins
Occurs rarely
Very few can get through the gauntlet of soluble and membrane bound proteases intact
‘Normal’ enterocytes do not have the transporters needed to carry proteins across the plasma membrane and they can’t permeate tight junctions
Absorption of intact proteins at birth
Neonates can absorb intact proteins in the small intestine
Most are immunoglobulins which can be absorbed from the very first milk and this imparts early neonatal passive immunity
Close is when the small intestine loses the capacity to absorb intact proteins
