GI hormones

Question 1

Gastrin

Answer 1

Source: G cells (antrum of stomach)
Action: 
increase H+, 
growth of gastric mucosa, 
motility

Regulation:
Increased by distention, alkalinzation, AA, peptides, vagal stimulation
Decreased by pH <1.5

High in ZES, chronic PPI
Phenylalanine and tryptophan are potent stimulators.

Question 2

Cholecystokinin

Answer 2

Source: I cells (duodenum and jejunum)
Action: 
increased pancreatic secretion, 
gallbladder contraction, 
gastric emptying, 
sphincter of oddi relaxation.

Regulation:
increase by FA and AA

CCK acts on neural muscarinic pathways to cause pancreatic secretion.

Question 3

Secretin

Answer 3

Source: S cells (duodenum)
Action: 
increased pancreatic bicarb secretion, 
decrease gastric acid secretion, 
increase bile secretion

Regulation: increased by acid, fatty ACID in lumen of duodenum.

Increased bicarb neutralizes gastric acid in duodenum, allowing pancreatic enzymes to function.

Question 4

Somatostatin

Answer 4

Source: D cells (pancreatic islets, GI mucosa)

Action:
decrease gastric acid/pepsinogen,
decrease pancreatic/small intestinal fluid secretion, decrease gallbladder contraction,
decrease insulin/glucagon

Regulation:
Increased by acid
Decreased by vagal stimulation

Inhibitory hormone, antigrowth hormone (inhibit digestion/abs of substances needed for growth)

Question 5

Glucose-dependent insulinotropic peptide (GIP)

Answer 5

Source: K cells (duodenum, jejunum)

Action:
Exocrine: decrease gastric H+ secretion
Endocrine: increase insulin release

Regulation:
Increased by FA, AA, oral glucose.

This is why oral glucose is more rapidly used than IV.

Question 6

Vasoactive intestinal polypeptide (VIP)

Answer 6

Source: parasympathetic ganglia in sphincters, gallbladders, small intestine.

Action:
Increase intestinal water and electrolyte secretion
Increase relaxation of intestinal smooth muscle/sphincter.

Regulation:
Increased by distention and vagal stimulation
Decreased by adrenergic output

Question 7

VIPoma

Answer 7

Non alpha, beta islet cell tumor that secretes VIP

Copious Watery Diarrhea, Hypokalemia, and Achlorhydria (WDHA syndrome)

Question 8

Nitric oxide

Answer 8

Action: increase smooth muscle, including lower esophageal sphincter.

Notes: loss of NO secretion is implicated in increased lower esophageal tone of achalasia

Question 9

Motilin

Answer 9

Source: small intestine
Action: produces migrating motor complex (MMCs)
Regulation: increased in fasting state

Notes: motilin receptor agonist (erythromycin) used to stimulate intestinal peristalsis.

Question 10

Intrinsic factor

Answer 10

Source: parietal cells (stomach)
Action: vitamin B12, binding protein required for uptake in terminal ileum

Autoimmune destruction of parietal cells;
chronic gastritis and pernicious anemia

Question 11

Gastric acid

Answer 11

Source: parietal cells (stomach)
Action: decrease stomach pH

Regulation:
Increased by histmaine, ACh, gastrin
Decreased by somatostatin, GIP, prostagladin, secretin.

Question 12

Pepsin

Answer 12

Source: chief cells (stomach)
Action: protein degradation

Regulation: increased by vagal stimulation, local acid

Note: inactive pepsinogen -> pepsin by H+

Question 13

Bicarb

Answer 13

Source: mucosal cells (stomach, duodenum, salivary gland, pancreas) and Brunner’s gland (duodenum)

Action: neutralizes acid

Regulation:
Increased by pancreatic and biliary secretion with secretin

Notes: bicarb trapped in mucus that covers gastric epithelium.

Question 14

Saliva

Answer 14

Secretion from parotid, submandibular, sublingual glands

Stimulates by sympathetic and parasympathetic

Amylase digests starch,
bicarb neutralizes bacterial acids,
mucin lubricates food

Normally hypotonic because of absorption but more isotonic with higher flow rates (less time for absorption)