Chemical Digestion of Food

Question 1

Give examples of the enzymes involved in digesting each of the major classes of nutrients

Answer 1

Carbohydrates: Amylase, specific enzymes Proteins: Proteases e.g. pepsin, trypsin Lipids: Lipases

Question 2

Give examples of defects in the digestive system which cause nutritional defects: CARBOHYDRATES

Answer 2

Cystic fibrosis: Diabetes commonly developed. Thought to be due to persistent pancreatic damage

Shwachman-Diamond Syndrome: No amylase in gut lumen → No digestion

Glucose-galactose malabsorption syndrome: Mutant transporter. Cannot absorb galactose

Question 3

Give examples of defects in the digestive system which cause nutritional defects: PROTEINS

Answer 3

Cystic fibrosis

Shwachman-Diamond Syndrome: No proteases to gut lumen no digestion - no pancreatic proteases to the lumen.

• A pancreatic insufficiency condition

Enterokinase deficiency: Very rare. No production of trypsin (major protease)

Question 4

Give examples of defects in the digestive system which cause nutritional defects: LIPIDS

Answer 4

Congenital bile acid defect

No bile → no emulsification of fats → No lipids for digestion

Shwachman-Diamond Syndrome:

No lipase to gut lumen → no digestion

No pancreatic lipases → No breakdown of lipids

Question 5

Describe normal digestion and absorption of each of the major classes of nutrients: CARBOHYDRATES

Answer 5

Salivary amylase, continued by pancreatic amylase in the small intestine, brush border enzymes (detrinase and glucoamylase) continue digestion to 2 simple sugars –> Maltase, sucrase and lactases breakdown the 3 simple sugars into monosaccharides –> Uptake is seen by the specific channels

Question 6

Describe normal digestion and absorption of each of the major classes of nutrients: PROTEINS

Answer 6

Polypeptides are denatured by pepsin. They are then degraded to oligopeptides by proteases, trypsin, chymotrypsin, elastase etc. Further digestion is seen at the brush border. Sodium coupled transporters allow uptake of amino acids

Question 7

Describe normal digestion and absorption of each of the major classes of nutrients: LIPIDS

Answer 7

TAGS –> FFA –> shorter chain FAs

Question 8

Describe the normal role of the liver and gall bladder in processing nutrients

Answer 8

Production and storage of bile acid respectively. Allows for the emulsification and absorption of fats as lipids.

Question 9

Describe the normal role of the pancreas in processing nutrients

Answer 9

Secretion of enzymes for digestion and bicarbonate ions.

Question 10

Explain why cystic fibrosis causes malabsorption of each of the major classes of nutrients

Answer 10

Due to the thick, viscous mucus associated with CF that blocks the ducts of the pancreas. This prevents the secretion of digestive enzymes and subsequently the nutrients cannot be digested and absorbed.

Question 11

Explain why Celiac/inflammatory disease causes malabsorption of each of the major classes of nutrients

Answer 11

These conditions cause the destruction of the small intestine enterocytes/brush border. This decreases the surface area of the small intestine and therefore decreases absorption. There are also fewer transporters available for absorption.

Question 12

Explain why Celiac/inflammatory disease causes Anaemia

Answer 12

Could be resultant of the formation of ulcers in inflammatory disease, leading to blood loss (bleeding) and subsequently to anaemia

• Iron is transported via the ferroportin transporter. The channel is regulated by hepcidin - normally secreted from hepatocytes. However, inflammation causes increased production of hepcidin and therefore decreased absorption of iron