Carbohydrate digestion

Question 1

Which enzyme is secreted by the salivary glands which begins the digestion of starch to oligosaccharides and shorter polysaccharides?

Answer 1

Salivary amylase, but it is denatured (inactivated) in the stomach.

Question 2

Name some of the products of carbohydrate digestion following the action of salivary amylase and pancreatic amylase.

Answer 2

Disaccharides like sucrose, galactose, maltose.

Question 3

Name some of the products of hydrolysis by the enzymes on the enteric cell’s brush border (e.g maltase, lactase, sucrase).

Answer 3

Monosaccharides like glucose, galactose and fructose.

Question 4

How do the monosaccharides move into the enterocyte?

Answer 4

A glucose transporter that transports glucose and sodium ions into the enterocyte in symport.

Question 5

How does glucose enter the blood?

Answer 5

Glucose diffuses into the blood by facilitated diffusion through a channel (e.g GLUT2), and sodium ions are pumped out of the enterocyte by sodium-potassium ATPase.

Question 6

Where is the sodium-glucose linked transporter?

Answer 6

On the apical surface of the enterocyte.

Question 7

Where is the GLUT-2 transporter?

Answer 7

On the basal surface of the enterocyte.

Question 8

What type of carbohydrate is digested in the colon instead of the small intestine?

Answer 8

Resistant starch,

Question 9

How is resistant starch digested?

Answer 9

Fermentation in the colon by gut microbiota.

Question 10

What are the products of resistant starch digestion?

Answer 10

Short chain fatty acids: butyrate, propionate, acetate.

Question 11

What are the benefits of the products of resistant starch digestion?

Answer 11

Butyrate protects against colorectal cancer, propionate inhibits food intake.
They also adsorb bile acids, so bile acid resorption is inhibited and more cholesterol excreted.

Question 12

Where is glucose-dependent insulinotropic peptide (GIP) secreted, and what is it’s function?

Answer 12

Secreted by K cells in the mucosa of the duodenum and jejunum, it is thought to trigger insulin secretion.

Question 13

Where is gastrin secreted, and what is its function?

Answer 13

Secreted from G cells in the pyloric antrum and duodenum, in response to stomach distension. It is an endocrine hormone. It triggers histamine secretion from enterochromaffin-like cells, and also HCl from the parietal cells, and gut motility.

Question 14

Where is intrinsic factor secreted, and what is its function?

Answer 14

Secreted by parietal cells, it facilitates vitamin B12 absorption in the ileum.

Question 15

What effects occur when insulin is released from the beta cells in the pancreatic islets?

Answer 15

Hepatocytes take up glycogen for storage (glycogenesis).

Cells take up more glucose, and more amino acids for increased protein synthesis, and there is increased lipogenesis.

Question 16

What effects occur when glucagon is released from the alpha cells in the pancreatic islets?

Answer 16

There is increased glycogenolysis in the hepatocytes.

Question 17

Name 5 things contained in saliva.

Answer 17

Water
Ions
Salivary amylase
Lysozyme
Lipase

Question 18

What are the three stages of deglutition?

Answer 18

1) voluntary stage - tongue muscles contract and move upward and backwards to force bolus through the Fauces to the oropharynx
2) (involuntary) pharyngeal stage - bolus of food stimulates receptors in oropharynx to send signals to deglutition centre in brainstem, which triggers soft palate and uvula to move up and close off nasopharynx, larynx to move up so epiglottis shuts laryngopharynx
3) (involuntary) oesophageal stage - bolus of food has entered oesophagus, peristalsis pushes bolus towards stomach, lower oesophageal sphincter relaxes

Question 19

What happens in peristalsis in the oesophagus?

Answer 19

Circular muscle contracts superior to bolus to squeeze food towards stomach. Longitudinal muscle contracts inferior to bolus so wall bulges outwards to receive bolus.