Digestion

Question 1

What are physical and chemical digestion and where do they take place?

Answer 1

Physical: chewing is mechanical digestion and churning of food in stomach

Chemical: enzyme action, mouth, stomach, ileum

Question 1

Can you describe how starch is digested by amylases and membrane-bound disaccharidases?

Answer 1

Salivary/pancreatic amylase breaks down starch into maltose
hydrolysing glycosidic bonds
maltose is broken down into glucose by maltase.
glucose is absorbed by co transport with sodium ions.

Question 2

Can you describe digestion of lipids by lipase, including the action of bile salts in mammals?

Answer 2

Stomach: lipids churned into droplets.
Bile from liver stored in gallbladder released to small intestine emulsified droplets to increase surface area.
Increased lipase action
Lipase hydrolyse lipids into fatty acids and monoglycerides.

Question 3

Can you describe digestion of proteins by endopeptidases, exopeptidases and membrane-bound dipeptidases in mammals?

Answer 3

Stomach: endopeptidases hydrolyse peptide bonds within polypeptide chain.
produced more ends increasing surface area for
small intestine: pancreatic juices neutralise acid and exopeptidases hydrolyse peptide bonds at end of the chains, producing dipeptides.

Dipeptidases hydrolyse peptide bonds into AA to be absorbed by co transport with sodium ions.

Question 4

Can you describe how lactose and sucrose are digested?

Answer 4

Disaccharides are too large, only monosaccharides can be absorbed.

Lactases and Sucrases hydrolyse them into glucose, galactose and fructose to be absorbed.

Question 5

Can you describe the structure of the ileum and explain how it is adapted for the function of absorption?

Answer 5

Large surface due to many villi and microvilli, increasing diffusion rate.

Thin walls to decrease diffusion distance

Muscle to churn contents maintain gradients

Constant blood supply maintains gradient.

Question 6

Can you explain how co-transport allows the absorption of amino acids and monosaccharides?

Answer 6

3 sodium out to blood 2 potassium in epithelial cell by AT
conc grad between ileum and epithelial cell established.
Sodium ions and AA/glucose by facilitated diffusion through co transport protein.
AA diffuse against, glucose down gradients.
Moves into the blood

Question 7

Can you explain how triglycerides are absorbed?

Answer 7

Glycerol and fatty acids form micelles
simple diffusion in
SER fatty acids and glycerol recombine to triglycerides.
Golgi modify and add cholesterol form lipoprotein, chylomicron.
Exocytosis into lymph vessel to blood at subclavian.