Digestion and absorption

Question 1

what is digestion?

Answer 1

relatively large, insoluble molecules are hydrolysed into smaller, soluble molecules that can be absorbed across the cell membranes into the blood stream and delivered into cells in the body.

Question 2

what do enzymes do in digestion

Answer 2

catalyse the hydrolysis.

Question 3

what do the small soluble molecules do?

Answer 3

provide the cells with energy (via resparation)
or build other molecules for cell growth, repair and function.

Question 4

what do protiens form?

Answer 4

hydrolysed into amino acids

Question 5

what do carbohydrates form?

Answer 5

hydrolysed into simple sugars

Question 6

what do lipids form?

Answer 6

hydrolysed into fatty acids.

Question 7

role of glands?
where are the sites of digestion?
role of small and large intestine?

Answer 7

produce digestive juices - salivary and pancreas has glands
stomach and small intestine - sites of digestion
Small intestine - site of absorbtion
Large intestine - site of water absorbtion

Question 8

digestion of starch, say enzymes and where it occurs

Answer 8

lumen of gut
starch + amylase -> maltose
maltose + maltase - >

Inside epithelial cells of small intestine
glucose

Question 9

digestion of proteins say enzymes and where it occurs

Answer 9

lumen of gut
protien + endopeptidase -> polypeptides

polypeptides + exopeptidase ->

inside cell surface membranes of epithelial cell
dipeptides
dipeptides + dipeptidase -> amino acids

Question 10

digestion of lipids say enzymes and where it occurs

Answer 10

lumen of the small intestine
lipids +bile salts -> emulsified lipids
emulsified lipids + lipase -> fatty acids + glycerol

large fat globule -> emulsification
small fat droplets -> digestion
->fatty acids +glycerol

Question 11

what does endopeptidase do and what is secreted with endopeptidase?

Answer 11

hydrolyses peptide bonds within polypeptide chains to produce dipeptides.
Hyddrochloric acid.

Question 12

exopeptidase what does it do?

Answer 12

hydrolyses peptide bonds at the ends of polypeptide chains to produce dipeptides.

Question 13

what does emulsification do?

Answer 13

increase surface area of fatty droplets for action of digestive enzymes.

Question 14

absorption of amino acids

Answer 14

specific amino acid co-transport protiens (carrier protiens)
are found within the cell surface membrane of epithelial cells.

This only occurs when sodium ions are present

for every sodium ion ion that is transported into the cell, an amino acid is transported in.

This occurs via facilitated diffusion - movement of molecules down a concentration gradient

the concentration gradient of sodium ions from the lumen of the ileum into the epithelial cell is maintained by the active transport of sodium ions through the sodium-potassium pump at the other end of the cell.

Question 15

absorption of monosaccharides

Answer 15

glucose carrier protien in the cell surface membrane of the small intestine.

sodium ions and glucose molecules are co-transported through facilitated diffusion.

the concentration gradient of sodium ions is maintained by the active transport of sodium ions in the sodium-potassium pump.

Question 16

role of micelles in the absorption of lipids

Answer 16

products of lipid digestion:
fatty acids, monoglycerides and glycerol

absorbing these products:
monoglyverides and fatty acids associate with phospholipids and bile salts to form micelles (very small fat droplets)

monoglyverides and fatty acids are not very soluble
micelles break down and add to a pool of fatty acids and monoglycerides that are disolved in the small intestine surrounding epithelial cells.

enter epithelium by diffusion

non-polar

Question 17

short fatty acid chains, how do they enter the blood?

Answer 17

directly into the blood via diffusion.

Question 18

longer fatty acids what do they do?

Answer 18

recombine with monoglyverides and glyveriol to form triglycerides in endoplasmic reticulum

these are packaged into lipoprotiens called chylomicrons.