Gas Exchange (DIGESTION + ABSORPTION) Flashcards
Give the 2 types of digestion
Mechanical digestion - During chewing the tongue moves the food around the mouth. The tongue mixes and moistens the food with saliva to form a ball of food referred to as bolus.
Chemical digestion
Define digestion
Large insoluble molecules are hydrolysed into smaller soluble molecules that can be absorbed by the bloodstream
What are carbohydrates hydrolysed into and what enzymes are required
starch –> maltose —> glucose
starch to maltose = salivary amylase (produced in the salivary glands), pancreatic amylase (produced in the pancreas)
maltose to glucose = maltase, a membrane bound disaccharidases
Give examples of membrane bound disaccharidases
Maltase, lactase, sucrase
What are proteins hydrolysed into and what enzymes are required
Proteins –> amino acids
–> requires 3 types of proteases:
Endopeptidases: hydrolyses peptide bonds in the middle of the polypeptide to produce shorter polypeptides, greater surface area, many ends, for exopeptidases to work on
Exopeptidases: hydrolyses peptide bonds at the ends of the polypeptide to produce dipeptides or single amino acids
Membrane bound dipeptidases: hydrolyse any remaining dipeptides into single amino acids
What are lipids hydrolysed into and what enzymes are required
Lipids –> 2 fatty acids and 1 monoglyceride
Requires lipase enzyme and action of bile salts
Describe the role of bile salts in the digestion of lipids
Bile salts are made in the liver and stored in the gall bladder
Bile emulsifies lipids, creating smaller lipid droplets which increases the surface area for lipase to act on so faster hydrolysis
Once lipase hydrolysis lipids to fatty acids and monoglycerides, micelles are formed (micelles are mixtures of bile salts, fatty acids and monoglycerides)
Micelles come into close contact with epithelial cells of the ileum and allow fatty acids and monoglycerides to diffuse through the phospholipid bilayer as the fatty acids and monoglycerides are lipid soluble
Describe the absorption of lipids
Once fatty acids and monoglycerides diffuse into epithelial cells, they are resynthesized to triglycerides with lipid protein in the golgi apparatus/ smooth ER to form chylomicrons
Chylomicrons are removed by exocytosis into the lymphatic vessel in the lacteal system. This eventually drains into the capillary network
How are amino acids and glucose absorbed into the bloodstream
By cotransport
What do the epithelial cells have a lot of?
Golgi apparatus / smooth ER
–> synthesizes lipids
Describe features of the ileum in the small intestine that makes it suitable for absorption
The lining of the ileum is folded - called villi (finger-like projections) increasing the surface area for absorption
The villi have thin walls - one epithelial cell layer thick - therefore a short diffusion pathway for the molecules being absorbed
The epithelial cells also have microvilli, increasing the surface area even more
The villi have a good blood supply to carry away absorbed monomers (maintaining concentration gradients)
Villi are constantly moving so food is in close contact with enzymes so more hydrolysis
Villi has smooth muscle
Ileu has both capillary network and lacteal system
Is smooth muscle voluntary or involuntary
Smooth muscle is involuntary
