lecture 26 - digestion

Question 1

what is the composition of carbohydrates

Answer 1

long chain of glucose joined by 1-4 glycosidic bonds

Question 2

what are the disaccharides made of

Answer 2

• sucrose = glucose and fructose
• lactose = glucose and galactose
• maltose = glucose and glucose

Question 3

sources of protein in the body

Answer 3

50% from diet
50% from endogenous proteins - secreted into intestine

Question 4

what are the fat soluble vitamins

Answer 4

A, D, E, and K

Question 5

how do the length of fatty acid chain lengths vary

Answer 5

• short chain fatty acids = <6 carbons
• medium chain fatty acids = 6-12 carbons
• long chain fatty acids = 12- 14 carbons

Question 6

properties of digestive enzymes

Answer 6

• extracellular
• organic catalysts
• very specific

Question 7

what are the optimal pH of enzymes throughout the digestive tract

Answer 7

• salivary enzymes = alkaline
• gastric enzymes = acidic
• small intestine = alkaline

Question 8

what is stage one of chemical digestion

Answer 8

enzymes secreted into the lumen

• salivary glands = salivary amylase
• stomach - pepsin
• small intestine = pancreatic enzymes

Question 9

what is stage two of chemical digestion

Answer 9

• in small intestine
  involves enzymes produced by enterocytes and attached to brushborder of enterocytes

Question 10

describe the process of protein luminal digestion

Answer 10

• pepsin in the stomach
• trypsin and chymotrypsin in the small intestine
• carboxypeptidase (COOH terminus) in small intestine

converts proteins to polypeptides

Question 11

describe the process of protein contact digestion

Answer 11

• involves peptidases, many types attached at the brush border
• convert polypeptides into amino acids

Question 12

describe the process of fat chemical digestion

Answer 12

• no contact digestion = occurs in lumen of small intestine

Question 13

what are the stages of fat digestion

Answer 13

• emulsification = motility
• stabilisation = bile salts
• digestion (hydrolysis) = enzymes
• formation of micelles = bile salts

Question 14

what is the first stage of fat digestion and what happens and where does it occur

Answer 14

• emulsification

motility breaks up lipid droplets into small droplets = increases surface area for digestion

stomach = retropulsion
small intestine = segmentation

Question 15

what is the second stage of fat digestion and what happens and where does it occur

Answer 15

• stabilisation

bile salts from the liver have hydrophobic and hydrophilic sides = stabilise the emulsion in the small intestine

• occurs in the small intestine

Question 16

what is the third stage of fat digestion and what happens and where does it occur

Answer 16

• hydrolysis

the cofactor colipase anchors lipase to the surface of the droplet

lipase converts triglycerides to : monoglyceride + free fatty acids

• occurs in the small intestine at surface of emulsion droplets

Question 17

what is the fourth stage of fat digestion and what happens and what are they

Answer 17

• formation of micelles

micelles are small droplets of 20-30 molecules

• products of fat digestion are usually insoluble so kept soluble through the formation of micelles