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Gastrointestinal - Physiology > Rao 1 - GI Function > Flashcards

Rao 1 - GI Function Flashcards

1
Q

What are the 4 main functions of the GI tract?

A
  1. Motility - GI tract propels food and mixes it so that it can be excreted and nutrients can be extracted.
  2. Secretion - of substances that break down food and aids in motility
  3. Digestion - food is broken down into smaller particles so that nutrients can be absorbed.
  4. Absorption - allows body to extract nutrients from meals
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2
Q

How is the GI tract similar to the lung and kidney?

A

All of these organs are exposed to the outside environment
**Note the GI tract is exposed to the environment on both sides

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3
Q

What is the role of M cells in the mucosal immune system?

A

They uptake antigens so that they can be presented to the lymphoid tissue in Peyer’s patches in a controlled manner

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4
Q

Bacteria is normally present in selected areas of the the GI tract, what are these places?

A

Bacteria is normally present in the Rectum and Colon. A small amount may be present in the illeum, but in general any bacteria in the small intestine is pathologic.

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5
Q

What are the layers of the Gastrointestinal mucosa?
• what is the function of the muscularis mucosa

A
  • *Epithelium**
  • *Lamina Propria** - loose CT
  • *Muscularis Mucosa** - Propel nutrients from lumen to submucosa
  • *Submucosa -** irregular CT connects the mucosa to muscle layer
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6
Q

What cell gives rise to cells in the crypt and villus cells?
• where is it located?

A

Stem cells are located at the base of the Crypts to proliferate and give rise to cells that migrate upward to become villus cells and crypt cells. These cells diffentiate after migrating to there respective location.

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7
Q

What 3 important features of intestinal tissue are present in the lamina propria?

A
  1. Capillary Network
  2. Lacteals
  3. Enteric Nerves
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8
Q

What 3 categories of bacteria exist in the GI tract?

A
  1. Commensals
  2. Pathogens
  3. Probiotics
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9
Q

What are 6 functions of the bacteria in the GI tract?

A
  • *1. Development of the Mucosal Immune System
    2. Epithelial Proliferation and Differentiation
    3. Metabolic Function
    4. Bile Acid Metabolism
    5. Salvage Nutrients
    6. Probiotics**
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10
Q

How does the blood flow of the GI tract change after a meal?

A

8x increase after a meal

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11
Q

What role does countercurrent blood flow play in the GI tract?

A

Blood shunts between arterioles and venules so 80% of oxygen DOES NOT reach the epithelial cells. Normally this is not a problem, but does leave the tissue susceptible to ischemic damage that can blunt the villi.

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12
Q

What 4 mucosal vasodilator are present in the GI tract?

A
  1. CCK
  2. VIP
  3. Gastrin
  4. Secretin
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13
Q

What are the divisions of innervation of the GI tract?

A

Extrinsic Autonomic NS => consists of sympathetic and parasympathetic NS

Intrinsic Autonomic NS

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14
Q

Parasympathetic component of the Extrinsic Nervous System
• Preganglionic Cell Body location?
• Preganglionic Length?
• Where does preganglionic Synapse?
• Postganglionic Legth?
• Neurotransmitters ued?

A

Preganglionic Cell Body:
*Vagus n. so cell bodies are located in the brainstem
and Pelvic n. so cell bodies in the sacral spinal cord

Parasympathethic PREganglionics are long and synapse with the INTRINSIC nervous system (ENS) with short post ganglionic fibers

  • Parasympathetic Preganglionics = Ach (and NE for sympathetic)
  • Enteric Postganglionics = Substance P (VIP and NO are inhibitory)
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15
Q

Sympathetic component of the Extrinsic Nervous System
• Preganglionic Cell Body location?
• Preganglionic Length?
• Where does preganglionic Synapse?
• Postganglionic Legth?
• Neurotransmitters ued?

A

Short Sympathetic PREganglionic come from the sympathetic chain in the spinal cord and synapse outside of the GI tract in the Prevertebral ganglia (Celiac, Superior mesenteric, and Inferior mesenteric). LONG post ganglionic

Preganglionic Sympathetic NS will use Ach as neurotransmitter. (POSTganglionics will use NE)

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16
Q

T or F: there is communication between the myenteric and submucosal plexi

A

True, they they also communicate with BOTH sympathetic and parasympathetic NS

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17
Q

What neurons are responsible for intergrating information in the ENS turning it into the second brain?

A

Interplexar neurons (allow for the communication necessary to call it a 2nd brain)

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18
Q

What neurotransmitters are excitatory in the ENS?
• which are inhibitory?

A

Excitatory:
• Ach and Substance P

Inhibitory:
• VIP and NO

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19
Q

What are the 5 major hormones of the GI tract?
• how/where are they released?

A

5 major Hormones:
• Gastrin
• CCK
• GIP
• Secretin
• Motilin

These are released into the portal circulation and then into the liver

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20
Q

What are the 5 candidate hormones of the GI tract?

A

• Pancreatic Polypeptide
• Neurotensin
• Substance P
• Glucagon
• Somatostatin

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21
Q

What are the criteria for determining if something is a GI hormone?

A
  1. Stimulation and Activity in different parts of the GI tract
  2. Effective in the absence of nerves
  3. Isolated from site of Stimulation
  4. Substance identified and structure confirmed
22
Q

What are the two major groups of hormones?
• why are they groupe?

A

Hormones are grouped on the basis of structural homology.
Group I
• Gastrin, CCK

Group II
• Secretin, VIP, GIP, Glucagon

23
Q

Gastrin
• Stimuli
• Inhibition
• Actions

A

Stimulus
• Proteins/Amino acids (Tryptophan and phenylalanine)
• Stomach Distention
• Vagal Stimulation (via GRP)
**Note: G34 is released at a constant rate into blood

Inhibition
• Low pH of stomach (High H+)
• Increased somatostatin

Actions
• Stimulates H+ Secretion from parietal cells via Histamine Release from Enterochromaffin (ECF) cells
• Promotes growth of Gastric Mucosa and Enterochromaffin cells

24
Q

Gastrin-17
• what is found at the N-terminus? Significance?
• C-terminus?
• What feature increases activity?

A

N-terminus
• Pyroglutamate - protects from exopeptidases and is required for full activity

C-terminus
• Aminated Phenylalanine

Sulfanation at the 6th C-terminal Tyrosine creates Gastrin II that has increased affinity for the Gastrin receptors

25
Q

Gastrin-17 vs Gastrin-34
• Location of Release?
• Potency
• Stimuli

A

Gastrin-17 is released from G-cells in the antrum of the stomach, while Gastrin-34 is released from the Duodenum.

Gastrin 17 and 34 are equipotent

Gastrin-17 is released in response to proteins, stomach distension, and vagal stimulation while Gastrin-34 is released at a steady rate into the serum during the interdigestive period.

***Remember gastin is a hormone so in either case it will enter the circulation to have activity***

26
Q

Gastrin-17 vs Gastrin-34 half-life

A
  • *Gastrin-17** has a half life around 38 minutes
  • *Gastrin-34** has a half life around 7 minutes
27
Q

What is gly-extended gastrin?
• effect?

A

Glycine-extended gastrin is G-17 that has glycine at the C-terminus before it is cleaved off leaving the aminated Phe

This gastrin DOES NOT act on gastrin/CCK2 receptors, but has its own receptor that leads to trophic effect when stimulated

28
Q

What do Gastrin and CCK have in common structurally?

A

5 C-terminal Amino Acids

**CCK is also sulfonated, but it is at the 7th C-terminal tyrosine rather than the 6th

29
Q

What is the difference in the frequency with which CCK and gastrin are sulfonate?

A

Gastrin is about 1/2 sulfonated

CCK is almost always sulfonated

30
Q

Cholecystokinin (CCK)
• Family
• Site/Cell of secretion

A

Family:
• Gastrin-CCK family

Secreted by I-cells in the duodenum and Jejunum

31
Q

CCK
• Stimulus
• Inhibition
• Primary and secondary functions

A

Stimulus
• Fats (Monoglycerides and Free FAs, NOT TGs)
• Proteins (Small peptides and Amino acids)

Primary Functions:
• HCO3- and Enzyme secretion from pancreas

Secondary Functions:
• Contraction of Gallbladder, Growth of Pancreas and Gallbladder, Inhibition of Gastric Emptying, Decreased Food Intake

32
Q

How does the location of sulfonation affect the activity of the C-terminal regions of gastrin and CCK?
• difference in activity with CCK1 and 2 receptors?

A

Gastrin is sulfonated at the 6th C-terminal residue and has greater affinity for CCK2 receptors that stimulate acid secretion mostly with only weak effects on gallbladder contraction

CCK is sulfonated at the 7th C-terminal residue giving it greater activity for CCK1 receptors that have a greater effect on gallbladder contraction and less of an effect on acid secretion

33
Q

What compounds are in the secretin family of hormones?
• Do they share receptors?

A

Secretin Family:
• Secretin
• VIP
• GIP
• Glucagon

***These all have DIFFERENT RECEPTORS and DIFFERENT ACTIVITY***

34
Q

On what side of the cell would you expect to see granules gathered in an endocrine cell?
• How do these cells know when to release contents?

A

Granules will be at the basal side of the cell because they will get secreted into the blood

Microvilli on the apical surface have chemoreceptors and Physical and Neural Stimulation also cause these cells to release conents

***NOTE: GI endocrine cells are not clustered together so you couldn’t remove them in one chunck surgically

35
Q

Secretin
• Family
• Site/Cell of Secretion
• Stimuli (primary and secondary)

A

Family:
• Glucagon-Secretin family of hormones

Site/Cell of Secretion:
• S-cells in the duodenum

Stimuli:
• Acid in the duodenum (primary) and Fat in the duodenum (secondary)

36
Q

What is the action of Secretin?
• Primary and Secondary?

A

Pancreatic secetion (secondary) and Bililary Secretion of HCO3- (secondary), and pancreatic growth (secondary)

37
Q

GIP
• Family
• Site/Cell of secretion
• Stimuli

A

Family
• Glucagon-Secretin

Site/Cell of Secretion
• K cells in the Duodenum and Jejunum

Stimuli
• ALL COMPONENTS OF A MEAL (protein, carbs, fats)

38
Q

GIP
• Action

A

Increases Insulin Secretion from ß-cells in the islets and decreases H+ secretion

39
Q

Motilin
• Hormone or no?
• Site of Release?
• Stimuli (primary and secondary)

A

Motilin IS a Hormone

Site of Release:
• Duodenum and Jejunum

Stimuli:
• FASTING (according to Costanzo)
• Primary: Nerve Stimulation (cyclic)
• Secondary: Acid and Fat

40
Q

Under Physiological conditions what hormones are secreted from the antrum of the stomach?

A

Gastrin only

41
Q

Under Physiologic Conditions, which hormones are secreted from the Duodenum?

A

ALL of them

• Gastrin, CCK, Secretin, GIP, Motilin

42
Q

Under physiologic conditions, which hormones are secreted from the Jejunum?
• Which could be secreted from there in pathologic conditions?

A

Physiologically:
• CCK, GIP, Motilin

Pathologically:
• Gastrin or Secretin

43
Q

Under Physiologic conditions, what is the only hormone secreted from the Ileum?
• Which could be secreted under pathologic conditions?

A

Physiologically:
• CCK

Pathologically:
• Secretin

44
Q

What are the 3 most important neurocrine peptides of the GI tract?

A
  1. VIP
  2. Bombesin/GRP
  3. Enkerphalins
45
Q

VIP
• Hormone, Neurocrine, or Paracrine?
• Site of Release?
• Actions

A

VIP - NEUROCRINE

Site of release:
• Found EXCLUSIVELY in nerves and is released in the Mucosa and smooth muscle of the GI tract

Actions:
• Relaxation of Spincters and Circular muscle
• Stimulates intestinal and Pancreatic Secretion

46
Q

Bombesin/GRP
• Hormone, Neurocrine, or Paracrine?
• Site of Release?
• Actions

A

Bombesin/GRP - NEUROCRINE

Site of Release:
• Released by Vagal Stimulation and Luminal proteins in the gastric mucosa

Actions:
• Stimulates Gastrin Release

47
Q

Enkephalins (opiates)
• Hormone, Neurocrine, or Paracrine?
• Site of Release?
• Actions

A

Enkephalins (opiates) - Neurocrine

Site of Release:
• Mucosa and Smooth muscles of the GI tract

Actions:
• Stimulates smooth muscle contraction (Lower Esophageal, Pyloric, and Ileocecal Sphincters)
• Inhibits intestinal secretion

48
Q

What are the paracrine hormones of the GI tract?

A

Somatostatin
Histamines

49
Q

Somatostatin
• Hormone, Neurocrine, or Paracrine?
• Site of Release?
• Stimulus/ Inhibition
• Actions

A

Somatostatin - PARACRINE

Site of Release:
• Secreted by D cells in the GI tract (delta cells in the pancreas, and also released from hypothalmus)

Stimulus:
• Low pH

Inhibition:
• Vagal Stimulation

Actions:
• Decrease H+ secretion (decreases Histamine and Gastrin release)
• Decrease GI peptide Hormone release

50
Q

Histamine
• Hormone, Neurocrine, or Paracrine?
• Site of Release?
• Stimulus/ Inhibition
• Actions

A

Histamine - Paracrine

Site of Release:
• Secreted from Oxyntic gland mucosa Enterochromaffin-like Cells

Stimulus:
• Gastrin and Ach

Inhibition:
• Somatostatin, CIMETIDINE, TAGAMENT

Actions:
• Stimulates Acid Secretion from Parietal Cells

51
Q

Zollinger-Ellison Syndrome
• Key Characteristics
• Underlying Pathophysiology

A

Key Characteristics:
• Diarrhea ( inhibition or electrolyte absorption due to acid in the small intestine)
• Steartorrhea (inactivation of Lipase due to low pH in the small intestine)
• Peptic Ulcers (duodenal) - overstimulation of parietal cells by Gastrin

52
Q

Pancreatic Cholera
• Key Characteristics
• Underlying Pathophysiology

A

WDHA syndrome => Watery Diarrhea, Achlorhydria, Hypokalemia

Key Characteristics
• Diarrhea - VIP is a potent stimulator of intestinal secretion
• Achlorhydria - Loss of bicarbonate may lead to Metabolic Acidosis
• Hypokalemia - K+ is lost in diarrhea due loss in the colon

Gastrointestinal - Physiology (8 decks)

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