Summary Medicine; regulation of gastric acid secretion Review

KEY POINTS
1. HCl + mucus + enzyme + hormone production by gastric mucosa can be
controlled by the CNS
2. Gastric control/Gastric secretion occurs in 3 overlapping phases
a. Named according to the location of the control center
b. CEPHALIC PHASE, GASTRIC PHASE, INTESTINAL PHASE


1 CEPHALIC PHASE
• Begins when you see, smell, taste or think of food (sight, smell, taste,
thought): stimulators
• Cephalic phase is controlled/begun by the CNS ^
• This phase prepares stomach to receive food by INDUCING ACID SECRETION
• The neural output is from the parasympathetic division of the ANS
o Via the vagal nerve (cranial nerve X), part of the ANS
o Vagus nerve stimulates parietal cells directly via neurotransmitter
acetylcholine
• The vagus nerve innervates the submucosal plexus of the stomach and
consequently
o Stimulates mucous cells, chief cells, parietal cells and G cells of
stomach
• Vagal stimulation of G cells releases gastrin hormone into
blood stream (endocrine mechanism) to stomach which
further stimulates parietal cells (to produce HCl)
• Gastrin hormone also stimulates release of histamine from
ECL cells
§ Histamine diffuses from ECL cells through tissue fluid to
stimulate parietal cells (paracrine mechanism)
§ Histamine stimulates parietal cells to produce more
HCl
o In response to stimulation, production of gastric juices SPEED UP up
to 500ml/hr
• Anxiety, stress, fear are inhibitors, they trigger the sympathetic nervous
system and decrease gastric secretion, gastric contractions/motility
• This phase lasts only minutes

gastrin diffuses into the venous system and is delivered via the heart and arterial system to
stimulate the parietal cells of the stomach (an endocrine mechanism)

Release of histamine due to:
1. Vagal nerve stimulation (acetylcholine release)
2. Gastrin action (stimulates release of histamine from ECL cells)

Histamine diffuses from ECL cells → tissue fluid → parietal cells
(paracrine mechanism)

, DIAGRAM OF 1 CEPHALIC PHASE