digestive system

Question 1

describe lipid digestion

Answer 1

• fats and oils emulsified by bile salts
• increases surface area for lipase to hydrolyse
• lipase hydrolyses ester bond in triglycerides to form fatty acids and monoglycerides
• micelles formed

Question 2

describe how triglycerides are absorbed

Answer 2

• micelles contain bile salts and fatty acids/monoglycerides
• higher concentration of monoglycerides/fatty acids than in ileum
• fatty acids and monoglycerides diffuse through cell
• resynthesised as triglycerides at SER
• associate with cholesterol and liboproteins to form chylomicrons and golgi
• packaged into vesicle and secreted by exocytosis
• enter lacteals and pass through lymphatic vessels and into blood stream

Question 3

describe carbohydrate digestion

Answer 3

• mouth:
• chewing breaks down food into smaller pieces, increasing SA
• salivary glands secrete salivary amylase to hydrolyse starch into maltose
  stomach:
• HCl released
• denatures amylase
  small intestine:
• pancreatic amylase hydrolyses glycosidic bonds in starch to form maltose
• alkaline salts in bile neutralises acidic contents from stomach
• peristaltis pushes food along
• membrane bound disaccharidase enzymes hydrolyse disaccharides into monosaccharides

Question 4

what is the role of micelles?

Answer 4

• contain bile salts, fatty acids and monoglycerides
• make fatty acids and monoglycerides more soluble in water
• carry fatty acids to lining of ileum

Question 5

describe how monosaccharides and amino acids are absorbed

Answer 5

1: - Na+-K+ pump - sodium ions out of cell into blood - potassium ions out of blood into cell - active transport
2: - sodium ions from lumen into cell (with glucose/amino acid) - Na+-glucose cotransporter protein - facilitated diffusion
3: - glucose out of cell into blood - protein channel - facilitated diffusion

Question 6

describe protein digestion

Answer 6

• hydrolysing peptide bonds - endopeptidases produce shorter polypeptides, act in middle
• exopeptidases produces dipeptides or amino acids, act on end
• dipeptidases produce amino acids

Question 7

role of golgi in lipid absorption

Answer 7

• modifies triglycerides
• combines triglycerides with proteins
• forms vesicles