Gastric Motility & Secretions

Mel & Dave(plus Poppy helped)

Any errors found in this presentation are Mel’s fault, anything good thank Dave

GASTRIC ANATOMY

GASTRIC MOTILITYReceptive RelaxationStomach is empty and

contracted initially

Mucosa and sub-mucosa start highly folded into rugae

Food swallowed – muscle in wall of orad region relaxes

Mediated by the vagus nerve

Enteric neurons release NO and serotonin

Gastric contents remain in a relatively undisturbed state

MixingGastric contractions begin in

body and move towards antrum

Contractions derive from two basic patterns of electrical

activity

Co-ordinated contractions of smooth muscle

Powerful contraction occurs as wave reaches antrum

Pyloric sphincter closes

Retropulsion occurs

EmptyingCo-ordinated contractile activity

of stomach, pylorus and proximal small intestine

Regulated by cholecystokinin (CCK), gastrin, gastric inhibiting polypeptide (GIP) and secretin

GASTRIC MOTILITYIt is important to regulate gastric motility because the duodenum cannot is not as adapted as the stomach is to food storage.

Gastric emptying is regulated in response to contents which are:

• High in fat

• Highly acidic

• Very hypertonic

Receptors in the mucosa of the duodenum and the jejunum sense these properties and release the enteric hormones which inhibit antral contractions and/or elicit contractions of the pyloric sphincter

The hormones that cause contraction of the pyloric sphincter are cholecystokinin (CCK), gastrin, gastric inhibiting polypeptide (GIP) and secretin (this is why they regulate emptying, see previous slide!)

GASTRIC SECRETIONSStomach secretes up to 3L of gastric juice per day

The main components of gastric juice are:

1) Hydrochloric acid

2) Mucus

3) Enzymes – Pepsinogen and Gastric Lipase

4) Intrinsic Factor

These are secreted from different cells within the gastric glands of the gastric mucosa

GASTRIC SECRETIONSGastric hormones are also secreted by the gastric glands – these are responsible for controlling the secretion of gastric juice.

The gastric hormones include:• Gastrin• Histamine• Somatostatin

CONTROL OF GASTRIC ACID SECRETION I tried to simplify

the diagram given in your lectures – if this doesn’t help just stick to yours!

Also I’ve not included the specific receptors as I don’t think that’s important

GI Tract Secretion Overview

Location Name Product Function

GI Tract δ Cells Somatostatin Inhibit Gastrin and Acid Secretion

GI Tract Goblet Mucus Lining GI Tract

Stomach Chief Pepsinogen Digestion of Protein

Stomach Parietal Intrinsic factor & HCL Vitamin B12 Transport and Digestion

Stomach G Cells GastrinStimulated Acid Secretion, Stimulates Gastric

Motility, Inhibits Gastric Emptying, Stimulation of Intestinal Motility

Duodenum Enterochromaffintin like cell (ECL) Histamine Stimulates Acid Secretion, Increases Local Blood

Flow

Duodenum Brunner's Glands Mucus Rich Alkaline Secretion Providing Protection and an Alkaline Environment

Duodenum and Jejunum S Cells Secretin Regulation of Secretions and HCO3-

Ileum Peyers Patches Lymphoid Tissue Immune Cells

Small Intestine Enteroendocrine Cells Cholecystokinin CCK Stimulation of Fat and Protein Breakdown

Small Intestine M Cells Motilin Increases Migrating Motor Complex

Small Intestine Paneth Cells Lysosome Cell Breakdown

Histology Overview

Type of epithelium?

Simple columnarStratified squamousSubmucosal glands? Villi?

Oesophagus Anus

Yes No

Small bowelSubmucosal glands?

Duodenum

Taenia coli?

Yes

Yes No

Lymphoid follicles?

NoNo

Peyer’s patches?

NoYes

Ileum Jejunum Appendix

Colon

Stomach

Yes

Yes No