Physiology - Gastric Motility and Pancreatic Function Flashcards
How do peristaltic waves move through the stomach during gastric motility?
Body -> Antrum
How does the contraction of the body compare to that of the antrum and what does this mean for each areas function?
Body has thing muscle -> weak contraction -> no mixing
Antrum has thick muscle -> powerful contraction
- Mixing
- Contraction of pyloric sphincter:
- –Only a small quantity of chyme enters the duodenum
- –Further mixing as antral contents forced back towards body
Food all pushed into antrum food that doesn’t exit folds back like a washing machine
Compare slow wave potentials to pacemaker potentials in the heart
Slow wave potentials, or simply slow waves, have a much slower rate to myocardial waves.
They do not reach threshold each cycle but require an extra “push” (from the enteric nervous system) to cause a contraction.
What do slow waves create?
Slow wave rhythm = basic electrical rhythm (BER)
This comes from pacemaker cells in the longitudinal muscle layer which is structured like a functional syncytium.
When food is present the BER reaches threshold and a peristaltic wave rhythm is set up
How is gastric motility controlled?
Gastrin increases contraction
Distension of stomach wall -> long/short reflexes -> increased contraction
Fat/amino acid/acid/hypertonicity in duodenum inhibits motility
How is acid neutralised in the duodenum?
Bicarbonate secretion from Brunner’s Gland duct cells (submucosal gland)
Forms carbonic acid which dissociates to Co2 and water
What controls duodenal bicarbonate secretion?
Acid in duodenum triggers:
- Long (vagal) and short (ENS) reflexes -> bicarbonate secretion
- Release of SECRETIN from S cells -> Bicarbonate secretion from pancreas and liver
Acid neutralisation inhibits secretin release (negative feedback control)
Why does acid chyme need to be neutralised?
Damage limitation from acid in duodenum
Pancreatic enzymes cannot work in low pH
Higher pH inhibits pepsin (damage limitation)
Briefly describe the endocrine portion of the pancreas
Endocrine portion made up of islets of Langerhans:
- Islet cells produce insulin and glucagon (control blood glucose)
- Also produce somatostatin (controls secretion of insulin and glucagon)
Briefly describe the exocrine portion of the pancreas
Exocrine portion made up of acing cells arranged in lobules
Lobules connected by intercalated ducts
Intercalated ducts flow into -> interlobular ducts -> interlobular ducts -> main pancreatic duct -> common bile duct -> hepatopancreatic ampulla -> out sphincter of oddi
There is also the accessory pancreatic duct.
Alpha cells and beta cells secrete what?
Alpha cells = glucagon
Beta cells = Insulin
What is the function of the exocrine pancreas and the associated cells?
Responsible for digestive function of the pancreas
Duct cells = bicarbonate
Acing cells = digestive enzymes
Explain how pancreatic enzymes are activated
Acinar cells contain digestive enzymes stored as inactive zymogen granules
Prevents autodigestion of pancreas
Enterokinase (bound to the brush border of duodenal enterocytes (so that it can’t activate enzymes in the pancreas or biliary tree)) converts trypsinogen to trypsin.
Trypsin converts all other zymogens to active forms
What do Proteases, Nucleases and Elastases do?
Proteases = cleave peptide bonds Nucleases = Hydrolyse DNA/RNA Elastases = Collagen digestion
What do Phospholipases, Lipases and a-Amylase do?
Phospholipidases = Phospholipids -> fatty acids Lipases = Triglycerides to fatty acids + glycerol a-Amylases = Starch to maltose + glucose
