STOMACH Flashcards by Lauren Nguyen

Major functions of the stomach

Temporal storage for food
Absorption of water-soluble and lipid-soluble substances
- E.g. alcohol, some drugs
Preparation of the “chyme” (semi-fluid material produced by gastric digestion of food) for digestion in the small intestine

How well did you know this?

Not at all

Perfectly

Digestion in the stomach

Physical - muscles contract and relax
Chemical - pepsin breaks down proteins
- Requires acidic medium

How well did you know this?

Not at all

Perfectly

Name the major cells of the gastric (oxyntic) gland and what they secrete

Surface mucous cells - mucus (more alkaline & viscous), HCO₃^-, water
Mucus neck cells - soluble mucus, HCO₃^-, water
Parietal (oxyntic) cells: HCl & intrinsic factor
Chief (zymogen) cells - pepsinogen
D cell - somatostatin
Enterochromaffin-like (ECL) cells: histamine
G cell - gastrin

How well did you know this?

Not at all

Perfectly

What cells are found in teh basal region of gastric glands?

Chief (zymogen) cells

How well did you know this?

Not at all

Perfectly

What cells are found in the antrum?

D cells

How well did you know this?

Not at all

Perfectly

What cells are found in the pyloric region?

G cells

How well did you know this?

Not at all

Perfectly

Functions of HCl & intrinsic factor from parietal cells

HCl -
- Denatures proteins
- Breaks up cell membranes
- Activates pepsinogen
- Antibacterial
- Solubilizes calcium salts
IF - absorption of vitamin B12 in ileum for production of mature RBCs

How well did you know this?

Not at all

Perfectly

Pepsin

Endopeptidase auto-catalytically activated from chief cells’ inactive pepsinogen

refers to all enzymes activated at a pH below 3 by HCl

How well did you know this?

Not at all

Perfectly

Somatostatin from D cells

inhibits acid secretion & gastrin release

How well did you know this?

Not at all

Perfectly

Histamine from ECL ells

Stimulates acid secretion

Increases local blood flow

How well did you know this?

Not at all

Perfectly

Gastrin from G cells

Secreted into the blood (not stomach lumen) to stimulate gastric juice secretion & gastrin/intestinal motility

How well did you know this?

Not at all

Perfectly

Function of gastric acid

Digestion of proteins via acid & proteolytic enzyme production
Absorption, esp vitamin B12
Protects mucosa from bacteria & autodigestion from its own acid & proteolytic enzymes

How well did you know this?

Not at all

Perfectly

Gastric lipase

Homologous to lingual lipase

How well did you know this?

Not at all

Perfectly

Loss of intrinsic factor causes

achlorhydria & pernicious anemia

How well did you know this?

Not at all

Perfectly

Gastric juice:

mucous
pepsin
gastric lipase
intrinsic factorHCl
Other electrolytes: ___, __, and ___

HCO₃- from mucous cells

K+ for H,K-ATPase

Na+ from mucous cells

How well did you know this?

Not at all

Perfectly

How do [HCl], [K+], and [Na+] change as the rate gastric juice secretion increases?

Study These Flashcards

HCl increases sharply (food acts a buffer)

K increases a bit

Na+ falls

As the stomach empties, what happens to the rate of H+ secretion?

Study These Flashcards

It increases

What makes the parietal cell distinct?

Study These Flashcards

Intracellular canliculi

Abundance of mitochodnria

Extensive smooth ER (tubulovesicular membranes)

Resting state of parietal cell vs Stimulated for acid secretion

Study These Flashcards

Resting state: tubulovesicles w H/K-ATPase are underneath the plasma membrane on the apical side.

Stimulation: tubulovesicle membranes fuse into the canalicular membrane to increase the apical membrane’s surface area

–> increases the # of H/KATPase, K+ and Cl- channels into the plasma membrane
–> increases O₂ consumption to support acid secretion

Name the transporters in the parietal cell on the apical vs the basoalteral membrane

Study These Flashcards

Apical:
- H,K-ATPase
- K+ channel
- Cl- channel
Basolateral:
- Na,K-ATPase
- K+ channel
- Cl-/HCO₃^- exchanger

Secreted H+ from the parietal cell are derived mostly from ___

During active HCl secretion, the blood coming from the stomach contains a lot of ___.

Study These Flashcards

H+ secretion is derived mostly from the dissociation of water & the carbonic anhydrase rxn

The blood coming from the stomach contains a lot of HCO₃^- (alkaline tide)b

Name the parietal cell receptors for gastrin, Ach, and histamine (secretagogues) and hwo they mediate their effects

Study These Flashcards

Gastrin: gastrin-cholecystokinin (CCK-B)

Ach: muscarinic receptor, M3

HIstamine: H2 receptor

CCK-B & M3 increase intracellular Ca2+ –> HCl secretion

H2 increases intracellular cAMP –> HCl secretion

Potentiation effect

Study These Flashcards

The effect of any 2 stimulants is greater than the effect of either stimulant alone.

The effect of gastrin, Ach, and histamine will result in an increase in cAMP & Ca2+ –> greatly enhances H/K-ATPase –> more acid secretion

Describe parietal cell activation

Study These Flashcards

Stomach distension stimulates mechanoreceptors
Activates parietal directly thru
1. Short local reflexes
2. Long vago-vagal reflexes (traveling on vagus n)

**Direct** vs **Indirect** action of secretagogues

* Direct*:* Ach, gastrin, and histamine bind **directly** to their respective receptors on the parietal cell --\>stimulate & potentiate gastric acid secretion * Ach from vagus n (CN10) * Gastrin from D cells * Histamine from ECL cells * Indirect: ACH & gastrin stimulate histamine release from ECL cells & mast cells (histaminocytes) in the lamina propria

Cimetidine & Ranitidine

H2 recepto rblockers The block H2 receptors on parietal cells, thus also blocking Ach & gastrin indirect stimulation

Phases of gastric acid secreiton

1. **Basal** (inter-digestive period) 2. **Cephalic** 3. **Gastric** 4. **Intestinal**

**Cephalic phase (shortest)**

Initiated by thought, sight, smell, and taste of food; also influenced by emotion * **Neuro influence**: parasympathetic vagus n releases Ach to stimulate acid secretion by * stimulating parietal cells, G cells, and ECL cells * stimulating chief cells for pepsinogen * **Endocrine mechanism**: Vagal stimulation also causes gastrin release, which acts like Ach

**Gastric** phase (longest)

Triggered by presence of food in stomach due to distension & chemical nature * **Neuro**: stomach distension stimualtes mechanoreceptors --\> parasympathetic secretion of Ach * **Endocrine**: Amino acids & peptides activate G cells --\> Gastrin --\> acid secretion & histamine reslease * Gastrin falls when * stomach pH falls between 2-3 * somatostatin is released from D cells

**Intestinal phase**

Triggered by chyme in the duodenum --\> eneterogastric relfelx * Acid in duodenum --\> **s****ecretin:** inhibits G cells & the parietal response to gastrin * Fatty acids in duodenum --\> **gastric inhibitory peptide (GIP)** and **cholecystokinin (CCK)** inhibits acid secretion and suppress gastrin release

Gastritis & peptic ulcers are ____ caused by \_\_\_

Both are **inflammation of gastric mucosa** cauased by bacterial infection of the mucosa (e.g. h pylori) that stimulates gastric secretion

H Pylori

* Survives acid bc it produces **urease** (hydrolyzes urea to produce ammonia, which neutralizes gastric acid) * Adheres to epithelial cells and stimulates **adhesins, ammonia, proteases,** and **immune response** * Induces G-cells to secrete **gastrin** --\> HCl from parietal cells * However, its augmentation occurs at a moderate rate

What factors predispose to ulcers?

* **Smoking** - increased nervous stimulation of stomach secretory glands * **Alcohol** - breaks down mucosal barrier * **Aspirin & NSAIDs** - breaks down mucosal barrier

How to differentiate between **H pylori infection** and **Zollinger-Ellison Syndrome (ZES)**

**In ZES, there's an abnormally high gastric acid secretion rate associated w duodenal ulcers and tumors** - whereas, gastric ulcers do not produce excessive gastric secretion.

Zollinger-Ellison syndrome

Gastrinomas secrete very high amts of gastrin unregulated --\> extremely high rates of gastric acid secretion * Usually comes w **gastric and duodenal ulcers** * Gastrinomas are typically located in the **pancreas** * **Tx**: * Proton pump inhibitor * H2R blocker * Surgical removal of gastrinoma

STOMACH Flashcards

(36 cards)