Gastric Motility and Pancreatic Function Flashcards
How is the body of the stomach involved in peristalsis?
Contains thin muscle which produces weak contraction and therefore is not responsible for mixing
How is the antrum of the stomach involved in peristalsis?
Contains thick muscle, as the oblique layer is more prominent, this produces a powerful contraction for mixing and contraction of the pyloric sphincter
What is the benefit of contraction of the pyloric sphincter during digestion?
Only small volume of chyme allowed into duodenum (prevents dumping syndrome)
Further mixing as antral contents are forced back towards the body of the stomach
What is the basic principle of gastric peristaltic waves?
Stomach muscle contractions a syncytium, with the pacemaker located in the top of the stomach located at the top in the longitudinal layer
Electrical depolarisations are transmitted through cells via gap junctions
What produces gastric peristaltic waves?
Slow wave pattern sets the basic electrical rhythm - it is subthreshold and requires further depolarisation to induce the action potential (to allow contraction to occur)
How does the myenteric plexus effect gastric peristaltic waves?
Has afferent nerves which deliver information from chemical and stretch receptors to the plexus
Stimulation causes plexus interneurones to send information via efferent nerves to smooth muscle cells, stimulating the to fire an action potential –> contraction
What neural and hormonal input can influence gastric motility?
Gastrin
Stomach distension
Fat/acid/amino acid/hypertonicity in duodenum (inhibition of motility)
How does gastrin affect gastric motility?
Increases contraction for mixing of the food
How does distention of the stomach wall affect gastric motility?
Long (to CNS) and short (only in stomach wall) reflexes –> increased contraction
Increased distention = increased contraction
How does fat/amino acid/hypertonicity in the duodenum affect gastric motility?
Inhibits motility
Increased tonicity inhibits motility as it indicates an increase in contents in the duodenum, meaning the stomach is empty and less need for motility
Why does gastric acid need to be neutralised in the duodenum?
If gastric acid enters the duodenum, the epithelium will be burned causing chemical erosion which could form an ulcer that could penetrate the mucosa and submucosa
What is used to neutralise gastric acid?
Bicarbonate (HCO3) from Brunner’s Gland duct cells in the submucosa
What triggers the release of bicarbonate?
Long (vagal) and short (enteric NS) reflexes
Secretin
How does secretin trigger he release of bicarbonate?
Released on S cells and acts on pancreatic and liver cells
Acid neutralisation inhibits secretin release (negative feedback control)
What is the endocrine function of the pancreas?
Release of hormones insulin and glucagon into the bloodstream by diffusion, and therefore is surrounded by lots of vasculature
What is the exocrine function of the pancreas?
Please of digestive enzyme and sodium bicarbonate into the gut lumen for digestion and neutralisation
Where is the head of the pancreas located to with relation to the duodenum?
Within the curvature of the duodenum
What part of the pancreas is responsible for the endocrine function?
Islet of Langerhans: produce cells, glucagon and somatostatin
What part of the pancreas is responsible for the exocrine function?
Acinar cells in the lobules
What is the organisation of ducts in the pancreas from lobules to the duodenum?
Intercalated duct (connects lobules)
- > intralobular duct
- > interlobular duct
- > Main pancreatic duct
- > Ampulla of vater
- > Duodenum
What is the function of the accessory pancreatic duct?
Normally closed, but is there is a block in the common bile duct or after into the duodenum, the accessory duct is used to release pancreatic enzymes into the duodenum (only pancreas)
How are zymogens converted into active enzymes?
The zymogen and trypsinogen are released from the pancreases
Enterokinase (bound to brush border of duodenal enterocytes) converts trysinogen -> trypsin
Trypsin converts all other zymogens to active proteolytic enzymes
What are 6 different categories of pancreatic enzymes?
Preoteases Nucleases Elastases Phospholipases Lipases A-amylase
What is the role of proteases?
Cleave peptide bonds
What is the role of nucleases?
Hydrolyse DNA/RNA
What is the role of elastase?
Collagen digestion (connective tissue)
What is the role of phospholipase?
Phospholipids to fatty acids
What is the role of lipase?
Triglycerides to fatty acids and glycerol
What is the role of A-amylase?
Starch to maltose + glucose
What triggers the release of zymogens from the pancreas?
Cholecystokinin (CCK) -In response to fat/amino acids in the duodenum
Neural control - triggered by nutrients in the duodenum
