GI hormones and sugar, fat and protein digestion

Question 1

List the four GI hormones

Answer 1

Gastrin

Cholecystokinin (CCK)

Secretin

Glucose- dependent insulinotropic peptide (GDIP)

Question 2

For the hormone gastrin, list:

• Stimuli
• Released by
• Role

Answer 2

Stimuli:
• Protein
• Distention of stomach
• Parasympathetic stimulation

Released by:
Stomach

Role:
• Stimulates gastric secretion
• Stimulate motility
• Stimulates mass movement in colon

Question 3

For the hormone cholecystokinin (CCK) list:

• Stimuli
• Released by
• Role

Answer 3

Stimuli:
• Fat or protein products in duodenum

Released by:
Duodenum and jejunum

Role:
• Inhibits gastric secretion and motility
• Stimulates pancreatic enzyme secretion
• Stimulates HCO3 secretion
• Stimulates bile secretion from liver

Question 4

For the hormone secretin, list:

• Stimuli
• Released by
• Role

Answer 4

Stimuli:
Acid in duodenum (deceased pH)

Released by:
Duodenum and jejunum

Role:
• Inhibits gastric secretion and motility
• Stimulates HCO3 secretion (to increase pH)
• Stimulates bile secretion from liver

Question 5

For the hormone glucose- dependent insulinotropic peptide (GIP) list:

• Stimuli
• Released by
• Role

Answer 5

Stimuli:
• Glucose, fats
• Acid in duodenum
• Distention of duodenum

Released by:
Duodenum and jejunum

Role:
• Inhibits gastric secretion and motility
• Stimulates insulin secretion by pancreas

Question 6

Briefly outline the process of sugar digestion and absorption

Use lactose intolerance as an example

Answer 6

• Mouth: An enzyme called salivary amylase breaks down the sugar into smaller particles
• Intestine: Various enzymes are specific to certain sugars and break them down into monosaccharides so it can be absorbed into the blood stream
• Lactase breaks down lactose into the monosaccharides glucose and galactose
• Maltase breaks down maltose
• Sucrase breaks down sucrose
• Isomaltase breakdowns isomaltose, respectively

Example: lactose intolerance
• Low levels of intestinal lactase = intolerance of milk
• Lactose remains in the GIT = osmotic pressure = diarrhoea-(as body tries to dilute it)

Question 7

Briefly outline the process of protein digestion & absorption.
Define:
Endopeptidases
Exopeptidases

Answer 7

• Stomach: pepsin (enzyme) acts on proteins by breaking the peptide bonds (these hold amino acids together). The protein is shortened to a polypeptide (amino acids linked together)
• Small intestine: pancreatic enzymes such as trypsin, chymotrypsin and carboxypeptidase breakdown the polypeptides into peptides (two amino acids linked together). Eventually these peptides are broken down into amino acids
• Because amino acids are so small, they are able to be absorbed into the bloodstream. However, they must first go to the liver before entering the general blood stream
• The liver takes whatever amino acids it needs and then the body gets the rest
• Endopeptidases: Hydrolyze bonds in polypeptide chains
• Exopeptidases: remove terminal amino acids

Question 8

Briefly outline the process of fat digestion & absorption and issues associated with the inability to digest fat

Answer 8

Small intestine
• Bile salts coat the fat droplets and emulsify them -> break them down into smaller components
• Lipase enzymes are able to work on small (emulsified) fat droplets, and break them down further
• These fats are packaged into micelles.
• Fats move out of micelles via diffusion and into the epithelial cells. At the same time, cholesterol is absorbed through membrane receptors
• The fats combine with cholesterol and proteins in the epithelial cells to form chylomicrons
• The chylomicrons are released into the lymphatic system

Issues:
• Patients without a pancreas will have excess fat in faeces (steatorrhea)
• Too much gastric acidity prevents the formation of stools. Again, steatorrhea
• Lacking fat soluble vitamins (A, D, E, K) ain’t good sis