10: Esophagus & Stomach Secretions

Characteristics of esophageal secretions

Basically all mucous

Types of glands in the esophagus

• Compound/branched mucous glands in the top and bottom of the esophagus

• Simple mucous glands in the middle

Function of cardiac gastric glands (a type of deep tubular gland)

Secretes mucus

Function of fundic/oxyntic/gastric glands (a type of deep tubular gland)

Secretes HCl, pepsinogen, intrinsic factor, and mucus

Cells in oxyntic glands that secrete mucus

Mucous neck cells

Cells in oxyntic glands that secrete pepsinogen

Peptic/chief cells

Cells in oxyntic glands that secrete intrinsic factor and HCl

Parietal/oxyntic cells

Function of pyloric gastric glands (a type of deep tubular gland)

Secretes mucus and gastrin (and some pepsinogen) in the bottom 20% of the stomach

Surface mucous cell (foveolar cell) function

Secretes a THICK layer of viscous mucus over the entire stomach

Surface mucous cells (foveolar cells) vs goblet cells

Thicker mucus with bicarb added

What stimulates secretion from surface mucous cells (foveolar cells)

Contact with food or any irritation

Epithelium of the non-glandular region of the horse stomach

Stratified squamous epithelium

EGUS pathology

Ulcers in the nonglandular regions

EGUS risk factors

• High grain diet

• Intermittent/bolus feeding

• Being a race horse (running)

Phases of gastric secretion

• Cephalic phase

• Gastric phase

• Intestinal phase

Cephalic phase of gastric secretion

Stimulated by senses and though, nothing is in the stomach

What mediates the cephalic phase of gastric secretion

Neural signals from amygdala and hypothalamus that travel along the vagus nerve

Gastric phase of gastric secretion

Stimulated by food in the stomach

What mediates the gastric phase of gastric secretion

Vagal reflexes, ENS, and gastrin

Intestinal phase of gastric secretion

Stimulated by food in the upper small intestine

What mediates the intestinal phase of gastric secretion

Potentially duodenal mucosa, not entirely known yet

Which phase of gastric secretion results in most of the secretion volume

Gastric phase

Which phase of gastric secretion results in the least secretion volume

Intestinal phase

How does the PS-ANS increase gastric secretions

Ach upregulates activity of peptic cells (pepsinogen), parietal cells (HCl), and mucous cells (mucus)

How does gastrin increase gastric secretions

Gastrin acts on ECL cells that are deep to the parietal cells. The ECL cells produce histamine → parietal cells → HCl secretion

Characteristics of mucus from pyloric glands

Lots of thin mucus that lubricates food

What cells in pyloric glands secrete gastrin

G cells

Why is pepsin secreted as the proenzyme pepsinogen

Prevents autodigestion of cells if it is only active in the gastric lumen

Where does pepsin get deactivated again

In the duodenum

Function of intrinsic factor

From parietal cells, necessary for the absorption of cobalamin

Why is chronic gastritis bad (in relation to glands and cells)

Damages parietal cells → no intrinsic factor → no cobalamin absorption → pernicious anemia

Summary of the process of HCl production

H⁺ and Cl^- are pumped into the canaliculi of parietal cells for secretion, and bicarb is secreted into the blood

Structures that prevent the stomach acid from making its way back into cells or the blood stream

Tight junctions on canaliculi and adjacent cells

How do NSAIDs and steroids cause ulcers

NSAID/Steroids block COX-1 → lowered prostaglandin, which normally helps decrease acid production and increase protective secretions

Types of meds for treating ulcers

• H⁺/K⁺ ATPase inhibitor (omeprazole)

• Histamine-2-receptor antagonist → inhibitory signal to parietal cells (opposite of gastrin)

• Sucralfate → reacts with acid to form a barrier, absorbs pepsin