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GI Physiology > 40 Gastric physiology > Flashcards

40 Gastric physiology Flashcards

1
Q 
Gastric secretions: 2L/day , including:
A. HCl
B. Mucus
C. Pepsin
D. Intrinsic factor
A

All of the above

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2
Q

3 functions of HCl

A
  1. Dissolve food particles
  2. Convert inactive pepsinogen to active pepsin
  3. Bacteriostatic to kill germs
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3
Q

2 functions of mucus

A
  1. Protective coating and lubricant for gastric mucosa

2. Maintain pH of gastric mucosa near neutrality i.e Gastric mucosal barrier

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4
Q

2 functions of pepsin

A
  1. Digest protein

2. Cleave pepsinogen to pepsin as positive feedback mechanism

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5
Q

2 functions of intrinsic factor (essential component of gastric juice!)

A
  1. Bind to absorb vitamin B12 in distal ileum

If not will cause malabsorption of fat (no fat soluble vit A,D,E,K) (K is for blood clotting)

  1. Resection of distal ileum requires injection or oral B12 with IF supplement
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6
Q

2 endogenous substances of the Gastric mucosal barrier?

A

HCl, pepsin

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7
Q

Name 3 protections of the gastric lining

A
  1. Restitution: rapid replacement of damaged cells by mucous neck cells (stem cells)
  2. Mucous coating
  3. Bicarbonate buffering (provide pH gradient)
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8
Q

How is the pH gradient built in order to prevent ulcers?

A

H+ can diffuse directly to the lumen while HCO3- are mixed with the high viscosity mucus layer, causing a HCO3- buffering.

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9
Q

5 structures you need to know about the stomach.

A
  1. Lower esophageal sphincter (LES)
  2. Fundus
  3. Body
  4. Antrum
  5. Pyloric sphincter
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10
Q

Functional anatomy: Which 2 kinds of gland mucosa are present in the stomach? Which is the majority ?

A

Oxyntic gland mucosa (proximal 80%)

Pyloric gland mucosa (distal 20%)

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11
Q

In the oxyntic gland mucosa (acid secreting area), what cells secreted what kind of substances?

A
  1. Parietal cells = oxyntic cells (HCl, intrinsic factor)
  2. ECL (histamine)
  3. D-cells (somatostatin that inhibits gastrin release from antral G cells)
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12
Q

In the pyloric gland mucosa (gastrin-secreting area), what cells secreted what kind of substances?

A
  1. Endocrine G-cells (gastrin)

2. Endocrine D cells (somatostatin to inhibit gastrin release in paracrine manner)

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13
Q

What do surface epithelial cells secrete?

A

Mucus and HCO3-

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14
Q

What do mucous neck cells secrete/ contain?

A

soluble mucous

stem cells

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15
Q

What do parietal cells secrete?

A

HCl

IF

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16
Q

Main function of peptic chief cells?

A

Secreting pepsinogen (precursor of pepsin)

17
Q

What are the 2 substances secreted by endocrine cells in a paracrine fashion?

A
  1. Histamine (by ECF cells)
  2. Somatostatin (by D cells)

Histamine diffuses to the parietal cells to regulate HCl and IF secretion

18
Q

Parietal cells
A. Require ATP for the process of secreting HCl with numerous mitochondria within the cells

B. Utilise H+/K+ ATPase to actively pump H+ at the expense of ATP (primary active transporter)

C. Undergo morphological change: invagination of apical membrane with numerous microvilli upon stimulation for increasing apical H+/K+ ATPase expression to drive active transport of H+

19
Q

In case of vomiting, which 2 ions are lost and what problems will arise?

A

chronic vomitting > hypokalemia: loss of K+ & metabolic alkalosis: loss of H+

20
Q

What ion pumps are present in the luminal cell

A

H+/K+ ATPase pump 1 H+ out and 1 K+ in the cell (luminal K+ is thus recycled)

21
Q

In blood, carbonic anhydrase is present to facilitate CO2 + OH- to become HCO3- in blood.
________ exchanger allow CL- goes to the lumen and create alkaline tide in gastric venous blood during acid secretion

A

Cl-/HCO3- exchanger

22
Q

Relationship of ECL cells and parietal cells: ECF cells synthesize ______ to mediate acid secretion of parietal cells in a ______ fashion.

A

Histamine; paracrine

23
Q

Relationship of endocrine D cells and parietal cells: D cells synthesize ______ to inhibit acid secretion of parietal cells in a ______ fashion.

A

Somatostatin; paracrine

24
Q

Relationship of antral G cells and parietal cells: G cells release ________ to ______ acid secretion.

A

Gastrin; stimulate

25
Q

Relationship of Prostaglandins from mucosal cells and parietal cells:Prostaglandins from mucosal cells ______ acid secretion of parietal cells in a ______ fashion.

A

inhibit; paracrine

26
Q

Relationship of Acetylcholine from nerve cells and parietal cells: Acetylcholine from nerve cells _______ acid secretion of parietal cells in a ______ fashion.

A

stimulates; neurocrine

27
Q

3 basic stimulants for acid secretion and their sites of action are:

A

Histamine, Gastrin and
Ach.

Histamine: H2 receptors on ECL cell
Gastrin: CCK-B on antral G cells
Ach: M3 muscarinic receptor on ECL cell

28
Q

Drugs to inhibit Ach is:

29
Q

Drugs to inhibit histamine is:

A

Cimetidine (H2 blocker)

30
Q

Drug to inhibit gastrin is:

A

Proglumide

31
Q

Neurocrine ENS cell: M3 receptor; Paracrine ECL cell: H2 receptor; Endocrine G cell: CCK-B

While H2 receptors stimulate Gs protein + Adenylate cyclase > cAMP > protein kinase > increase in H+ ;
CCK-B and M3 receptor increases Ca2+ and therefore increase PK, then H+.
The final pathway is :

A

stimulate H+/K+ ATPase

32
Q

Why is it more potent to stop the final pathway to stop acid secretion? What kind of drugs are used?

A

Irreversible binding of H+/K+ ATPase inhibitor/Proton pump inhibitor (PPI) (omeprazole).

33
Q

What are the 3 phases of gastric secretion?

A
  1. Cephalic phase
  2. Gastric phase
  3. Intestinal phase
    1. Cephalic phase
      ○ Neural regulation only (no acid secretion when vagus nerve is cut)
      ○ 30% of acid response
      a. Ach-mediated pathway on parietal cell (predominantly)
      b. GRP-mediated pathway on G-cell
    2. Gastric phase
      ○ Neural and hormonal regulation
      ○ 60% of acid response

a. Neural: long (?) and short reflexes (Ach acts on M3 receptor of parietal cells to secrete acid)
b. Hormonal: at antrum, AA and peptides sensed by chemoreceptor on G cell cause gastrin release

  1. Intestinal phase
    ○ Hormonal regulation (mainly inhibitory)
    10% of acid response
34
Q

What cells are responsible for inhibiting acid secretion? (gastrin release too)

A
  1. Secretin by S cell, responding to acid
  2. Somatostatin by D cell, responding to acid
  3. GIP by K and L cells, responding to glucose

GI Physiology (11 decks)

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