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