Flashcards in Carbohydrate digestion Deck (19)
Which enzyme is secreted by the salivary glands which begins the digestion of starch to oligosaccharides and shorter polysaccharides?
Salivary amylase, but it is denatured (inactivated) in the stomach.
Name some of the products of carbohydrate digestion following the action of salivary amylase and pancreatic amylase.
Disaccharides like sucrose, galactose, maltose.
Name some of the products of hydrolysis by the enzymes on the enteric cell's brush border (e.g maltase, lactase, sucrase).
Monosaccharides like glucose, galactose and fructose.
How do the monosaccharides move into the enterocyte?
A glucose transporter that transports glucose and sodium ions into the enterocyte in symport.
How does glucose enter the blood?
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.
Where is the sodium-glucose linked transporter?
On the apical surface of the enterocyte.
Where is the GLUT-2 transporter?
On the basal surface of the enterocyte.
What type of carbohydrate is digested in the colon instead of the small intestine?
How is resistant starch digested?
Fermentation in the colon by gut microbiota.
What are the products of resistant starch digestion?
Short chain fatty acids: butyrate, propionate, acetate.
What are the benefits of the products of resistant starch digestion?
Butyrate protects against colorectal cancer, propionate inhibits food intake.
They also adsorb bile acids, so bile acid resorption is inhibited and more cholesterol excreted.
Where is glucose-dependent insulinotropic peptide (GIP) secreted, and what is it's function?
Secreted by K cells in the mucosa of the duodenum and jejunum, it is thought to trigger insulin secretion.
Where is gastrin secreted, and what is its function?
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.
Where is intrinsic factor secreted, and what is its function?
Secreted by parietal cells, it facilitates vitamin B12 absorption in the ileum.
What effects occur when insulin is released from the beta cells in the pancreatic islets?
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.
What effects occur when glucagon is released from the alpha cells in the pancreatic islets?
There is increased glycogenolysis in the hepatocytes.
Name 5 things contained in saliva.
What are the three stages of deglutition?
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