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 MOTILITY Receptive Relaxation Stomach 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 Mixing Gastric 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 Emptying Co-ordinated contractile activity of stomach, pylorus and proximal small intestine Regulated by cholecystokinin (CCK), gastrin, gastric inhibiting polypeptide (GIP) and secretin

GASTRIC MOTILITY It 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 SECRETIONS Stomach 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 SECRETIONS Gastric 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 LocationNameProductFunction GI Tractδ CellsSomatostatinInhibit Gastrin and Acid Secretion GI TractGobletMucusLining GI Tract StomachChiefPepsinogenDigestion of Protein StomachParietalIntrinsic factor & HCLVitamin B12 Transport and Digestion StomachG CellsGastrin Stimulated 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 DuodenumBrunner's GlandsMucus Rich Alkaline Secretion Providing Protection and an Alkaline Environment Duodenum and Jejunum S CellsSecretinRegulation of Secretions and HCO3- IleumPeyers PatchesLymphoid TissueImmune Cells Small IntestineEnteroendocrine CellsCholecystokinin CCKStimulation of Fat and Protein Breakdown Small IntestineM CellsMotilinIncreases Migrating Motor Complex Small IntestinePaneth CellsLysosomeCell Breakdown

Histology Overview Type of epithelium? Simple columnarStratified squamous Submucosal glands?Villi? OesophagusAnus YesNo Small bowel Submucosal glands? Duodenum Taenia coli? Yes No Lymphoid follicles? No Peyer’s patches? No Yes Ileum JejunumAppendix Colon Stomach Yes No