2002B15 Give a brief account of the mechanisms which regulate gastric secretion.

· Gastric secretions

· Phases: cephalic, gastric, intestinal

· Table of source, product and release stimulus

Into the lumen

· Water

· HCl and IF

· Pepsinogen and gastric lipase

· HCO₃ and mucus

Into blood

· Gastrin

· Histamine

· Somatostatin

Cephalic:

	Pathway	Stimulus	Effect
-Enteric NS
-PSNS	CNX -> ↑local release of ACh	Sight, smell, anticipation of food	↑secretions
-SNS	T5-L1 via coeliac plexus	Anxiety, pain, exercise
-Hormones			See later

Gastric:

	Pathway	Stimulus	Effect
-Enteric NS	Meissner’s submucosal plexus	Luminal macronutrient	↑local ACh release
-PSNS	As above	Rest, food	↑local ACh release
-SNS	As above	Anxiety, pain, exercise, labour	↓local ACh release
-Hormones (see next)			See later

Intestinal:

	Pathway	Stimulus	Effect
-Enteric NS:	Enterogastric reflex	Duodenal macronutrients, H+, ↑osmo, distension	↓gastric secretions
-PSNS	As above (+ superior mesenteric plexus)
-SNS	As above (+ superior mesenteric plexus)
-Hormones	See next		See later

Cell	Product	Release stimulus	Effect
Chief cell	Pepsinogen -> pepsin Gastric lipase	↓ gastric pH ↓ intestinal pH ACh (CNX) Gastrin	Proteolysis (pepsin) Lipolysis
Parietal cell	HCl IF	Gastric peptides Duo peptides ACh (CNX) Gastrin Histamine	1.Proteolysis 2.Activate pepsin 3.Kill microbes 4.Reduce iron to Fe2+ 5.Stimulate pancreatic and biliary secretions Complex B₁₂ (IF)
G cell	Gastrin	ACh -> GRP Gastric distension Gastric peptides Caffeine, alcohol	↑parietal cell activity
D cell	Somatostatin	Gastric acid Duodenal acid GIP, CGRP	↓ chief cell activity ↓ parietal cell activity
E cell	Histamine	ACh Gastrin	↑parietal cell activity
Mucous neck cell	Mucous HCO₃^-	Constitutive (PGE₂) Irritation	Physical barrier Chemical buffer