Gastric Motility and Pancreatic Function Flashcards
How doe peristaltic waves travel?
From the body to the antrum of the stomach
Why does no mixing occur in the body of the stomach?
It has a thin muscle and so contraction is weak
What does the thick muscle of the antrum of the stomach result in?
Powerful contraction which results in mixing and contraction of the pyloric sphincter
What does contraction of the pyloric sphincter result in?
- Only small quantity of gastric content (chyme) entering duodenum
- Further mixing as antral contents forced back towards body
What generates peristaltic rhythm?
Pacemaker cells in the longitudinal muscle layer
What are slow waves a result of?
Spontaneous depolarisation and repolarisation
What is the slow wave rhythm equal to?
Basic electrical rhythm
What are slow waves conducted through?
Gap junctions along longitudinal muscle layer
How is contraction produced?
-Slow wave depolarisation is sub threshold and therefore requires further depolarisation to induce action potentials
What determines the strength of contraction?
Number of action potentials/waves
How does gastrin affect contraction?
Increases contraction
How does distension of the stomach wall affect contraction?
- Produces long/short reflexes
- Increased contraction
How does fat/acid/amino acid/hypertonicity in the duodenum affect motility?
Inhibits motility
How is acid neutralised in the duodenum?
Bicarbonate is secreted from Brunner’s Gland duct cells (submucosal glands)
What does acid in the duodenum trigger?
- Long (vagal) and short (ENS) reflexes leading to bicarbonate secretion
- Release of secretin from S cells leading to bicarbonate secretion
Describe the negative feedback control of secretin.
.-Secretin leads to bicarbonate secretion from the pancreas and liver
-Acid neutralisation inhibits secretin release
What are the 3 parts of the pancreas?
- Head (within the curvature of the duodenum)
- Body
- Tail (extends to spleen)
What does the endocrine portion of the pancreas contain?
Pancreatic islets (islets of Langerhans)
What do islet cells produce?
- Insulin
- Glucagon
- Somatostatin
What does somatostatin control?
Secretion of insulin and glucagon
What does the exocrine portion of the pancreas contain?
Acinar cells in lobules
How are the lobules of the pancreas connected?
Intercalated discs
What ducts are found within the pancreas?
- Intralobular ducts
- Interlobular ducts
- Main pancreatic duct
Where does the main pancreatic duct join the common bile duct?
Hepatopancreatic ampulla (Sphincter of Oddi)
Where does the hepatopancreatic ampulla enter?
Duodenum
Where do all accessory pancreatic ducts empty?
Duodenum
What is the exocrine pancreas responsible for?
Digestive function of pancreas
What is the anatomical structure of the exocrine pancreas?
- Acini
- Ducts
- Pancreatic duct
What is the function of the exocrine pancreas?
- Secretion of bicarbonate by duct cells
- Secretion of digestive enzymes by acinar cells
How do acinar cells store digestive enzymes?
As inactive zymogen granules
What does storage as zymogen granules prevent?
Autodigestion of pancreas
What does enterokinase do?
Converts trypsinogen to trypsin
Where is enterokinase found?
Bound to brush border of duodenal enterocytes
What does trypsin do?
Converts all other zymogens to active forms
What are the 6 categories of pancreatic enzymes?
- Proteases
- Nucleases
- Elastases
- Phospholipases
- Lipases
- a-Amylase
What do proteases do?
Cleave peptide bonds
What do nucleases do?
Hydrolyse DNA/RNA
What do elastases do?
Collagen digestion
What do phospholipases do?
Triglycerides to fatty acids and glycerol
What does a-Amylase do?
Starch to maltose and glucose
How is pancreatic function under neural control?
Vagal and local reflexes triggered by arrival of organic nutrients in duodenum
How is pancreatic function controlled other than neural control?
-Bicarbonate secretion stimulated by secretin
-Secretin released in repsponce to acid in the duodenum
-Zymogen secretion stimulated by cholecystokinin
CCK released in response to fat/amino acids in duodenum
