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CVM 711- Physiology > Lecture 46: GI Regulatory Substances > Flashcards

Lecture 46: GI Regulatory Substances Flashcards

1
Q

List some functions of the GIT.

A

Contraction/relaxation of smooth muscle and sphincters
Secretion of enzymes, fluid, and electrolytes
Trophic (growth) effects on tissues
Secretion of other GI peptides

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2
Q

What substances regulate the functions of the GIT?

A

GI peptides, including hormones, neurocrines, and paracrines

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3
Q

What are the four GI hormones?

A

Gastrin
Cholecystokinin (CCK)
Secretin
Glucose-dependent insulinotropic peptide, AKA gastric inhibitory peptide (GIP)

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4
Q

Read the following criteria and determine if it is describing a hormone, paracrine, or neurocrine.

-GI peptides released from endocrine cells of GIT, not glands
-Enter portal circulation, liver, systemic circulation, target cells
-Target could be in GIT or somewhere else

A

Hormones

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5
Q

Read the following criteria and determine if it is describing a hormone, paracrine, or neurocrine.

-Secreted by endocrine cells of the GIT
-Act locally within the same tissue that secretes them

A

GI Paracrine

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6
Q

What is the major GI paracrine hormone?

A

Somatostatin- major inhibitory actions in the GIT

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7
Q

Read the following criteria and determine if it is describing a hormone, paracrine, or neurocrine.

synthesized in neurons of GIT and released after an action potential

A

GI neurocrines

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8
Q

What are some of the major GI neurocrines?

A

Acetylcholine
NE
vasoactive intestinal polypeptide (VIP)
gastrin-releasing pepide (GRP)
Enkephalins
Neuropeptide Y
substance P

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9
Q

What causes gastrin to be released?

A

Secreted in response to physiologic stimulus, carried in blood to a distant site
**Functions independent of neural activity

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10
Q

Gastrin is secreted by what type of cells?

A

Secreted by G cells in the stomach

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11
Q

What are the functions of gastrin?

A

Promote hydrogen ion secretion by gastric parietal cells
Stimulate growth of gastric mucosa (trophic effect)
Increase gastric motility

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12
Q

There are two forms of gastrin. What are they?

A

Big gastrin: secreted between meals and secreted at low basal levels
Little gastrin: secreted in response to a meal aka distension of stomach and presence of things like amino acids and peptides

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13
Q

What inhibits gastrin secretion?

A

Low gastric pH AND somatostatin

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14
Q

What is Zollinger-Ellison syndrome?

A

Gastrinoma (gastrin secreting tumor) in non-B cell pancreas in humans, dogs, and cats

this tumor causes an increase in H+ ion secretion and hypertrophy of gastric mucosa, this can lead to duodenal ulcers

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15
Q

Cholecystokinin (CCK) is secreted by what type of cells?

A

Secreted by I cells of duodenal and jejunal mucosa

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16
Q

CCK is secreted in response to?

A

Presence of fatty acids, amino acids, and peptides

17
Q

What are the five actions of CCK?

A

1) Contraction of gallbladder: eject bile into the small intestine, emulsify lipids
2) Secretion of pancreatic enzymes: lipases to release FA, amylase for starch, need proteases for proteins
3) Secretion of bicarbonate from pancreas: buffering, increases pH of digesta entering the small intestine
4) Growth of exocrine pancreas and gallbladder
5) Inhibition of gastric emptying: increases gastric emptying time, allow adequate time for digestion and absorption

18
Q

Secretion is secreted by what type of cells?

A

S cells of the duodenum

19
Q

Secretin is secreted in response to what?

A

H ions and fatty acids present in the small intestine

20
Q

What actions does secretin have in the small intestine?

A

stimulates the secretion of pancreatic and biliary HCO3-
Inhibits gastrin release from G cells in stomach (same as somatostatin)

21
Q

Gastric-inhibitory peptide (GIP) is secreted by what type of cells?

A

K cells of duodenum and jejunum

22
Q

GIP is secreted in response to what?

A

response to glucose, amino acids, and fatty acids

***Oral glucose load stimulates GIP, intravenous glucose does not

23
Q

What effect does GIP have on the duodenum and jejunum?

A

Stimulates insulin secretion (causes tissues to take up blood glucose)
Inhibits gastric H ion secretion and gastric emptying

24
Q

What are the 4 candidate hormones of the GIT?

A

1) Motilin
2) Pancreatic polypeptide
3) Enteroglucagon
4) Glucagon-like peptide-1 (GLP-1)

Not considered true GI hormones because they fail to meet one or more criteria

25
Q

Motilin is secreted where? What does it do?

A

Secreted by upper duodenum during fasting, it increases GI motility, initiates inter-digestive myoelectric complexes @ 90 minute intervals, which triggers peristaltic waves

26
Q

Pancreatic polypeptide is secreted in response to what? What is its effect?

A

Secreted by pancreas in response to ingestion of carbs, proteins, and lipids

Self-regulates pancreatic secretion- inhibits pancreatic secretion of HCO3- and enzymes

27
Q

Enteroglucagon is secreted in response to what? What is its effect?

A

Secreted by intestinal cells in response to decreased blood glucose

Stimulates the lover to increase glycogenolysis and gluconeogenesis

28
Q

Glucagon-like peptide-1 (GLP-1) is secreted by what kind of cells? What is its role?

A

Secreted by L cells of the SI in response to nutrient ingestion

Secreted in response to nutrient ingestion, it inhibits glucagon secretion, decrease gastric emptying, inhibit appetite

29
Q

Where are GI paracrines released from?

A

Released from endocrine cells, they act locally and don’t enter systemic circulation

30
Q

What are the two GI paracrines?

A

Somatostatin
Histamine

31
Q

Somatostatin is released from where? What is its effect?

A

Secreted by D cells of GI mucosa in response to decreased luminal pH (if luminal pH is decreases, we know food is present)

Inhibits secretion of other GI hormones and gastric H ion secretion

32
Q

Histamine is released from where in the GIT? What is its effect?

A

Major secretion from H ion-secreting area of the stomach

Stimulates H ion secretion by gastric parietal cells- released locally and acts locally

33
Q

Where is the satiety center located in the body?

A

Located in ventromedial nucleus (VPN) of the hypothalamus

Anorexigenic neurons release pro-opiomelanocortin (POMC)- decreases appetite

34
Q

The feeding center is located where?

A

Located in the lateral hypothalamic area (LHA)

Orexigenic neurons release neuropeptide Y (which increases appetite)

35
Q

What substances influence anorexigenic neurons (decreases appetite)?

A

Leptin- secreted by fat cells
Insulin
GLP-1- synthesized and secreted by intestinal cells
Peptide YY- secreted by intestinal L cells following a meal

36
Q

What substances influence orexigenic neurons (increases appetite)?

A

Ghrelin- secreted by gastric cells

CVM 711- Physiology (19 decks)

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