T3. MOTILITY, GASTRIC SECRETIONS AND DIGESTION IN THE STOMACH

Question 1

What is the structure and location of the stomach?

Answer 1

The stomach is a muscular sac located in the upper left abdominal cavity, inferior to the diaphragm, where food is delivered from the cardiac region to the pyloric sphincter.

Question 2

Where is food delivered in the stomach and where does it end?

Answer 2

Food is delivered to the cardiac region and ends at the pyloric sphincter.

Question 3

What are rugae?

Answer 3

Rugae are folds lining the interior of the stomach that flatten when full and form longitudinal wrinkles when empty.

Question 4

What is the most distensible part of the GI tract?

Answer 4

The stomach is the most distensible part of the GI tract.

Question 5

How is blood from the stomach circulated?

Answer 5

Blood from the stomach enters the hepatic portal circulation, is filtered through the liver, and then returns to the heart.

Question 6

What type of innervation does the stomach receive?

Answer 6

The stomach receives parasympathetic fibers from the vagus nerve and sympathetic fibers from the celiac ganglia.

Question 7

What is the primary function of the stomach?

Answer 7

The primary function of the stomach is food storage.

Question 8

What mixture is formed by the stomach mixing food and secretions?

Answer 8

Chyme: a pasty mixture of semi-digested food.

Question 9

What are the secondary functions of the stomach?

Answer 9

Mix food with gastric secretions, begin protein and fat digestion, and kill bacteria with acid.

Question 10

What are the four tunics of the stomach’s microscopic anatomy?

Answer 10

Mucosa, submucosa, muscularis externa (3 layers), and serosa.

Question 11

What type of epithelium covers the stomach mucosa?

Answer 11

Simple columnar epithelium filled with mucin.

Question 12

What are gastric pits?

Answer 12

Depressions in the mucosa where tubular gastric glands open.

Question 13

What are the three layers of the stomach’s muscularis externa?

Answer 13

Outer longitudinal, middle circular, and inner oblique.

Question 14

What are mucus neck cells and what do they secrete?

Answer 14

Cells that secrete mucus and bicarbonate to protect the stomach lining from acid.

Question 15

What do parietal (oxyntic) cells secrete?

Answer 15

Hydrochloric acid (HCl) and intrinsic factor (for vitamin B12 absorption).

Question 16

What do chief cells secrete?

Answer 16

Gastric lipase and pepsinogen.

Question 17

What do enteroendocrine cells secrete?

Answer 17

Hormones and paracrine messengers: ECL cells (histamine), G cells (gastrin), D cells (somatostatin).

Question 18

How is HCl secretion stimulated?

Answer 18

Indirectly by gastrin and ACh which stimulate histamine release; histamine stimulates parietal cells to secrete HCl.

Question 19

What are the functions of HCl in the stomach?

Answer 19

Denatures proteins, activates pepsin and lingual lipase, digests connective tissue and plant walls, converts Fe3+ to Fe2+, kills pathogens.

Question 20

How is HCl produced by parietal cells?

Answer 20

Carbonic anhydrase forms H+ and HCO3–; H+ pumped out by H+-K+ ATPase; Cl– exchanged for HCO3– and joins H+ in lumen to form HCl.

Question 21

What enzyme system pumps H+ into the gastric gland lumen?

Answer 21

H+-K+ ATPase pump (antiporter using ATP).

Question 22

What is a zymogen and example in the stomach?

Answer 22

Inactive enzyme precursor; example: pepsinogen secreted by chief cells.

Question 23

How is pepsin formed and what does it do?

Answer 23

HCl removes amino acids from pepsinogen to form pepsin; pepsin digests proteins into short peptide chains.

Question 24

What is the autocatalytic effect of pepsin?

Answer 24

Pepsin activates more pepsinogen into pepsin.

Question 25

How does the stomach protect itself from acid and enzymes?

Answer 25

Mucous coat (alkaline mucus), tight junctions, and epithelial cell replacement every 3–6 days.

Question 26

What happens to proteins in the stomach?

Answer 26

Partially digested by pepsin.

Question 27

What happens to carbohydrates in the stomach?

Answer 27

Salivary amylase begins digestion but is inactivated by stomach acid.

Question 28

What happens to dietary fats in the stomach?

Answer 28

10–15% digested by gastric and lingual lipase.

Question 29

Where does most digestion and absorption occur?

Answer 29

In the small intestine after chyme leaves the stomach.

Question 30

What is the receptive-relaxation response of the stomach?

Answer 30

Swallowing center signals stomach to relax to accommodate incoming food.

Question 31

What initiates gastric motility?

Answer 31

Food stretches the stomach, activating a receptor and response leading to rhythmic peristaltic contractions by pacemaker cells.

Question 32

How is gastric function regulated?

Answer 32

By nervous and endocrine systems which stimulate or suppress gastric secretion and motility based on food presence.

Question 33

What are the three phases of gastric activity?

Answer 33

Cephalic phase, gastric phase, and intestinal phase.

Question 34

What occurs during the cephalic phase?

Answer 34

Brain responds to sensory input, signals vagus nerve to stimulate gastric secretion via enteric nervous system.

Question 35

What stimulates the gastric phase?

Answer 35

Swallowed food and semi-digested proteins stretching the stomach or raising pH; stimulates ACh, histamine, and gastrin release.

Question 36

What occurs during the intestinal phase?

Answer 36

Duodenum initially enhances gastric secretion, then inhibits it through the enterogastric reflex and hormone release.

Question 37

What triggers the enterogastric reflex?

Answer 37

Acid and semi-digested fats in duodenum send inhibitory signals via the enteric and sympathetic nervous systems.

Question 38

What hormones inhibit gastric secretion during the intestinal phase?

Answer 38

Secretin and cholecystokinin (CCK), released by duodenal enteroendocrine cells.

Question 39

What other hormones are involved in the intestinal phase?

Answer 39

Glucose-dependent insulinotropic peptide (GIP), which stimulates insulin secretion in preparation for nutrient absorption.

Question 40

How does the pyloric sphincter help regulate digestion?

Answer 40

It contracts tightly to limit chyme entry into the duodenum, allowing time for digestion before more chyme arrives.

Question 41

Do the gastric phases occur separately?

Answer 41

No, they overlap and can occur simultaneously.