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Gastrointestinal Physiology > GI Regulatory Substances > Flashcards

GI Regulatory Substances Flashcards

0
Q

What are the two major actions of gastrin?

A
  1. H+ secretion

2. Growth of the gastric mucosa

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1
Q

What are the four functions of gastrointestinal peptides?

A
  1. Contraction and relaxation of the smooth muscle wall and sphincters
  2. Enzyme secretion
  3. Fluid and electrolyte secretion
  4. Trophic (growth)
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2
Q

What two stimuli inhibit gastrin release?

A
  1. Low pH (no need for gastrin)

2. Somatostatin

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3
Q

What cells secret gastrin? Where are these cells located?

A

G cells; Antrum of the stomach

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4
Q

Memory: The three physiological stimuli for gastrin release are all related to…?

A

The ingestion of food

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5
Q

What are the three physiological stimuli for gastrin release?

A
  1. Products of protein digestion (i.e. Amino acids and small peptides)
  2. Stomach distention (the presence of food)
  3. Vagal stimulation (gastrin releasing peptide, GRP)
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6
Q

What portion of the gastrin molecule is the minimum fragment necessary for activity?

A

C-terminal tetrapeptide

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7
Q

Compare the activity of the c-terminal tetrapeptide to the activity of the entire gastrin molecule.

A

C-terminal tetrapeptide has 1/6 the activity of the entire gastrin fragment

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8
Q

List the two different types of gastrin molecules and when you can expect them to be released.

A
  1. G17, “little gastrin” released in response to a meal.

2. G34, “big gastrin” released during the interdigestive period.

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9
Q

Which gastrointestinal paracrine substance is NOT a peptide?

A

Histamine

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10
Q

What are the three categories into which gastrointestinal peptides can be classified?

A
  1. Hormones
  2. Paracrine
  3. Neurocrine
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11
Q

Which classification of gastrointestinal peptide hormones are secreted into the portal and then systemic circulation?

A

Hormones

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12
Q

Which category of gastrointestinal peptides are synthesized in a neuron and diffuse into a synaptic cleft?

A

Neurocrines

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13
Q

Which category of gastrointestinal peptides act locally, diffuse through the interstitial fluid and are secreted locally?

A

Paracrines

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14
Q

What is required in order for Neurocrines to be released?

A

An action potential

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15
Q

What are the four accepted gastrointestinal hormones?

A
  1. Gastrin
  2. Cholecystokinin (CCK)
  3. Glucose-Dependent Insulinotropic Peptide
  4. Secretin
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16
Q

Why does CCK have some gastrin activity?

A

Because the C-terminal five amino acids are identical to that of gastrin and include the tetrapeptide that is minimally necessary for gastrin activity.

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17
Q

Name the two CCK receptors? What other hormones are these receptors responsive to?

A
  1. CCKA: selective for CCK

2. CCKB: equally selective for CCK and gastrin

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18
Q

What is the minimal fragment necessary for the biological activity of CCK?

A

The C-terminal heptapeptide

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19
Q

What are the CCK secreting cells? Where are these cells located?

A

I cells, located in the duodenal and jejunal mucosa of the small intestine

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20
Q

Monoglycerides, fatty acids (but not tricglycerides), small peptides and amino acids are stimuli for the secretion of what GI hormone?

A

CCK

21
Q

What is the major function of CCK?

A

Fat digestion and absorption

22
Q

List the five major actions of CCK.

A
  1. Contraction of gall bladder
  2. Secretion of pancreatic enzymes
  3. Secretion of bicarbonate from pancreas (this is a major function of secretin that is potentiated by CCK)
  4. Growth of the exocrine pancreas
  5. inhibition of gastric emptying (it takes a very long time to allow fat digestion and absorption)
23
Q

CCK slows the rate of chyme delivery between what two GI structures?

A

The stomach and the small intestine

24
Q

Memory: Secretin is the secrete to…

A

Stopping gas (This mnemonic helps you to remember that the actions of secretin will oppose those of gastrin.)

25
Q

What is the active fragment of secretin?

A

All 27 amino acids of secretin are required for biological activity. (Note the entire molecule must also be folded into an alpha helix to be active.)

26
Q

Which cells secrete secretin?

A

S cells

27
Q

Where are the S cells located?

A

Duodenum

28
Q

What is the stimuli for secretin?

A

The presence of H+ and fatty acids in the lumen of the small intestine

29
Q

What are the two functions of secretin (major and minor)?

A

Major:To increase pancreatic and biliary HCO3- secretion
Minor: To inhibit gastrin’s effect on the parietal cells

30
Q

Why is the neutralization of H+ essential for fat digestion?

A

Pancreatic lipases are optimal at a pH of 6-8 and inactive at a pH of 3.

31
Q

Glucose-Dependent Insulinotropic Peptide (GIP) can also be classified as an…

A

Incretin (the major action is to stimulate insulin secretion)

32
Q

Due to amino acid homology, GIP given at pharmacological doses will produce the actions of which fellow GI hormone?

A

Secretin

33
Q

What cells secrete GIP? Where are these cells located?

A

K cells, located in the duodenum and jejunum.

34
Q

Which gastrointestinal hormone responds to all three types of nutrients (glucose, amino acids, and fatty acids)?

A

GIP

35
Q

Memory: GIP responds to all three!

A

This mnemonic helps you to remember that GIP is the ONLY GI hormone that be released in response to the presence of all three nutrients.

36
Q

What are the three physiological actions of GIP?

A

Major: stimulation of insulin secretion
Minor 1: inhibits gastric H+ secretion (inhibits the action of gastrin)
Minor 2: inhibition of gastric emptying

37
Q

Why is oral glucose utilized more rapidly than intravenous glucose?

A

Oral glucose will stimulate the release of GIP, which results in insulin secretion in addition to the insulin secreted by the direct action of absorbed glucose on the beta cells.

38
Q

Name the four candidate hormones secreted by the GI tract and their major physiological actions.

A
  1. Motilin: increases GI motility by initiating interdigestive mayor lectures complexes
  2. Pancreatic polypeptide: inhibits pancreatic secretion of HCO3- and enzymes, but role is ultimately unknown
  3. Enteroglucagon: increases glycogenolysis and gluconeogenesis by the liver
  4. Glucagon-like peptide-1 (GLP-1): stimulates insulin secretion
39
Q

Which two GI regulatory substances are classified as incretins?

A

GIP and Glucagon-like peptide-1 (GLP-1)

40
Q

What region of the GI tract is responsible for the secretion of motilin and when is the motilin secreted?

A

Cells in the upper duodenum; during fasting states

41
Q

What secondary GI organ is responsible for the secretion of pancreatic polypeptide?

A

Pancreas

42
Q

Memory: The function of pancreatic polypeptide is to PPP.

A

Prevent Pancreas from secreting Peptides.

43
Q

What is the stimulus for the release of pancreatic peptides?

A

The ingestion of carbohydrates, proteins or lipids

44
Q

What cells secrete enteroglucagon? What is the stimulus for these cells?

A

Intestinal cells: decrease in blood glucose

45
Q

GLP-1 is the cleavage product of what hormone?

A

Proglucagon

46
Q

What cells secrete GLP-1 and where are these cells located?

A

L-cells; small intestine

47
Q

GLP-1 has 5 physiological actions (major and minor) that make it’s analogues plausible treatment for individuals with diabetes mellitus. What are the 5 actions?

A
  1. Stimulates insulin secretion (major)
  2. Inhibits glucagon secretion
  3. Increases the sensitivity of pancreatic Beta cells to secretagogues
  4. Decreases gastric emptying
  5. Inhibits appetite
48
Q

Name the two GI paracrines.

A
  1. Somatostatin

2. Histamine

49
Q

What type of GI cells secrete somatostatin? What is the stimulus?

A

D cells in the GI mucosa; in response to a decrease in the luminal pH.

50
Q

What non GI organs secrete somatostatin?

A

The hypothalamus and the endocrine pancreas (delta cells)

51
Q

What are the two functions of somatostatin?

A
  1. Inhibits the secretion of all other GI hormones

2. Inhibits gastric H+ secretion

Gastrointestinal Physiology (6 decks)

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