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Phsyiology 210 B > Gastrointestinal Tract 3 - Stomach > Flashcards

Gastrointestinal Tract 3 - Stomach Flashcards

1
Q

How does the stomach do chemical breakdown

A
  • Secretes pepsinogen, Converted to pepsin (protein digesting enzyme)

Secretes HCl for

  • Dissolving food
  • Partially digesting macromolecules in food
  • Sterilization of food
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2
Q

Stomach controls

A
  • rate food enters SI

- intrinsic factor secretion for B12

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3
Q

Is there absorption that occurs across the stomach

A

Very little

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4
Q

Stomach Components

A

Fundus and body:

  • Thin layer of smooth muscle
  • secrete: mucous, pepsinogen, HCl

Anthrum:

  • thicker smooth muscle layer
  • secretes: mucous pepsinogen, gastrin
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5
Q

Major secretions of the stomach

A
  • mucous: prevent self digestion
  • HCl: hydrolysis of proteins
  • pepsinogen: digests proteins
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6
Q

Minor secretions of the stomach

A
  • Intrinsic factor-for B12 absorption
  • Gastrin: (endocrine) stimulates HCl production and stomach motility
  • Histamine: (paracrine) stimulate HCl
  • somatostin: (paracrine) inhibits HCl
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7
Q

Generalized gastric glands

A
  • mucous cells
  • parietal cells
  • chief cells
  • enteroendrocrine cells
  • enterochromaffin-like cells (ECL) cells
  • D cells
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8
Q

Chief cells

A
  • Gastric glands in all regions
  • Secrete pepsinogen
  • Inactive precursor to pepsin (zymogen)
  • Pepsinogen cleaved by acid to pepsin, which accelerates protein digestion.
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9
Q

Enteroendocrine cell

A
  • Gastric glands in antrum
  • AKA G cells
  • Secretes gastrin (hormone)
  • Stimulates HCl production by parietal cell - Stimulates GI motility
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10
Q

D cells

A
  • Gastric glands in all regions (more in antrum)

- Secrete somatostatin: Negative regulator of HCl secretion

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11
Q

Enterochromaffin-like (ECL) cells

A
  • Gastric glands in all regions (more in antrum)
  • Secrete histamine
  • stimulates HCl release
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12
Q

Parietal cell

A
  • Found in gastric glands contained in the fundus/body regions
  • AKA, oxyntic cell
  • Secretes HCl and intrinsic factor
  • Canaliculi increase the surface area of the cells and maximize secretion into the stomach lumen
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13
Q

Parietal cell during secretion

A

1) Acid secretion requires energy-lots of mitochondria

2) Actively secreting cell has better defined “canaliculus”

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14
Q

Acidification of the Stomach Lumen

A
  • Stomach secretes ~ 2L of 0.1 M H+Cl- /day
  • Lumen pH 1 versus cytosol pH 7
  • Multiple transporters/channels involved to acidify stomach while maintaining neural pH in cell
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15
Q

Acidification in the stomach lime through the parietal cells

A
  1. H + /K+ ATPase
    - Luminal membrane.
    - Pumps H+ into lumen in exchange for K+ into cell.
    • ACTIVE transport (ions moved up concentration gradient)
    • electro neutral
  2. Carbonic anhydrase (CA)
    - Catalyzes the formation of H2CO3 from H2O and CO2
    - H2CO3 dissociates into H+ (for secretion into lumen) and HCO3-
  3. Cl-/HCO3- exchanger (secondary active transport)
    - Excess HO- is effluxed from the cell as HCO3- in exchange for Cl-.
    - Critical step (inconjunction with CA) for maintenance of neutral cellular pH
  4. K+ channels
    - K+ recycled back into stomach lumen, via diffusion through channel, = loss of + charge.
  5. Cl- channels
    - Cl-leaks back into stomach lumen via diffusion through channel = compensates for loss of + charge through K+ channels
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16
Q

4 chemical messengers regulate the insertion of the H+/K+ ATPase into the plasma membrane of the parietal cell

A
  • Gastrin (gastric hormone)
  • Acetylcholine (neurotransmitter)
  • Histamine (paracrine): increases gastrin and ACh
  • Somatostatin (paracrine): Inhibits release of HCl, gastrin and histamine
17
Q

Pepsinogen secretion and activation

A

Pepsinogen secreted by chief cells (inactive precursor)

  • Stimulated by ENS
  • Parallels release of HCl

Cleaved and activated to pepsin by acidic pH in stomach lumen

18
Q

What is the advantage of inactive precursor secretion ??

A

Pepsin is active only at low pH- irreversibly inactivated when it enters small intestine

19
Q

Phases of gastric secretion

A

1) Cephalic phase:
- Anticipatory, excitatory, mainly via vagus

2) Gastric phase:
- Major phase, excitatory, mainly via gastrin

3) intestinal phase:
- Mainly inhibitory, due to presence of acid, fat, digestion products and hypertonic solutions in duodenum

20
Q

Acetylcholine, gastrin, and histamine all directly

A

INCREASE acid secretion by parietal cell

21
Q

Somatostatin inhibits

A

acid secretion by parietal cell

22
Q

Acetylcholine also INCREASES acid secretion by the parietal cell by:

A
  • Stimulating the release of gastrin from G-cells (increasing stimulant)
  • Stimulating the release of histamine from enterochromaffin like cells (ECL) (increasing stimulant)
  • Inhibiting somatostatin release from D-cells (inhibiting inhibitor)
23
Q

Gastrin also INCREASES acid secretion by the

A

parietal cell by stimulating histamine

release (increasing stimulant)

24
Q

Once acid secretion is at a high rate

A
  • Parasympathetic input will be reduced (cephalic phase)
  • Negative feedback occurs for gastrin production (acid inhibits release)
  • Somatostatin release increases
25
Q

Why doe somatostanin increase once acid segregation is at a high rate?

A
  • Reduced parasympathetic inhibition of D-cell
  • Direct stimulation of somatostatin release by acid

Somatostatin then:

  • Inhibits acid secretion from parietal cell
  • Inhibits histamine release from ECL cell
  • Inhibits gastrin release from G cell
26
Q

Gastric motility

A
  • Consumption of meal —> smooth muscle relaxation —> stomach can increase to 1.5 L without —> pressure
  • Relaxation mediated by PS nerves to ENS
  • Food stimulates peristaltic waves
  • Closure of pyloric sphincter
27
Q

When Food in the stomach stimulates peristaltic waves:

A
  • Weak contractions in body of the stomach
  • Powerful contraction in antrum
  • Mixes luminal contents and causes the closure of the pyloric sphincter
28
Q

For gastric motility, Closure of pyloric sphincter results in:

A
  • Small amount of stomach contents released to duodenum
  • Most antral contents forced backward towards the body of stomach
  • Mixing of contents with enzymes and acid
29
Q

Does the stomach have pacemaker cells, and if so where?

A

YES, in smooth muscle layer.

30
Q

Does the Basic electrical rhythm cause significant contractions?

A

NO

31
Q

What determines the strength of contraction in the stomach ?

A

Excitatory hormones and NT which further depolarize the slow waves.

32
Q

Strength of contraction (and therefore degree of mixing) decided by

A

stimulatory input (to the antral smooth muscle cells).

33
Q

Vomiting

A
  • Nausea, salivation, breath held in mid-inspiration
  • Glottis closes off trachea
  • Lower esophageal sphincter and esophagus
  • Diaphragm and abdominal muscles contract
  • Reverse peristalsis moves upper intestinal contents into stomach
  • Stomach contents move up through esophagus and out through mouth (soft palate is raised)
34
Q

Vomiting-beneficial and negative consequences

BENEFITS

A

BENEFITS:

  • Removal of harmful substances prior to absorption
  • Bacteria, toxins
  • Nausea and feeling bad should prevent individual from consuming noxious substance again

NEGATIVE:

  • Dehydration
  • Loss of salts (electrolyte imbalance)
  • Metabolic alkalosis due to loss of H+
  • Acid erosion of tooth enamel
35
Q

Ulcers are

A

damaged/eroded area of the GIT mucosa, usually in acidic regions (e.g., esophagus, stomach or most commonly the duodenum)

36
Q

Ulcers are caused by

A
  • Imbalance between “aggressive” factors (acid, pepsin) and “protective”
    factors (mucus, HCO3-).
  • Helicobacter pylori infection major cause (chronic inflammation and
    erosion)
  • NSAIDs (e.g., aspirin, ibuprofen) which decrease prostaglandin production
  • smoking
  • excessive alcohol
  • “stress” (unlikely)
  • gastrinomas (rare)
37
Q

Treatment for ulcers:

A
  • Antibiotics
  • H+/K+ ATPase inhibitor
  • Histamine (H2) antagonist
  • Prostaglandin type drugs
38
Q

Gastric bypass surgery

A

Removal / tieing off of the stomach, food goes straight to the small intestine, meaning u don’t NEED a stomach.

Phsyiology 210 B (24 decks)

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