The pancreas Flashcards
What are the steps of pancreatic embryology?
- Abdominal accessory organs arise as foregut outgrowths: liver bud, gallbladder, ventral pancreatic bud and duct, dorsal pancreatic bud and duct
2.Proximal duodenum rotates clockwise- takes 11 weeks - Ventral and dorsal pancreatic buds and ducts fuse
Bile and pancreatic ducts join to drain together at major papilla
How is the duodenum arranged?
Divided into D1, D2, D3, D4
What is the right colic flexure also known as?
hepatic flexure (bend in colon)
What is the left colic flexure also known as?
splenic flexure (bend in colon)
What is a method of imaging the pancreas
MRCP- Magnetic Resonance cholangiopancreatography
Angiography- for bleeding- put a needle into the femoral artery to the aorta
What is pancreatic division?
Main pancreatic duct and ventral duct do not fuse together
Patients with this will get recurrent pancreatitis
What is endocrine secretion?
Secretion into blood stream to have effect on distant target organ (autocrine/paracrine)- ductless glands (2% of secretion)
What is exocrine secretion?
Secretion into a duct to have direct local effect (98% of secretion)
What are the main endocrine secretions of the pancreas?
Insulin, glucagon and somatostatin
What is the role of insulin?
Anabolic hormone
Promotes glucose transport into cells and storage as glycogen
decreases blood glucose levels
promotes protein synthesis and lipogenesis
What is the role of glucagon?
Increased gluconeogenesis and glycogenolysis
What’s the role of somatostatin?
“endocrine cyanide”
What cells carry out endocrine secretion?
Islets of langerhans
Secrete hormones into blood- insulin, glucagon, somatostatin, pancreatic polypeptide
Regulate glucose, metabolism and grown effects
What is the role of exocrine secretion of the pancreas?
Secretes pancreatic juice into duodenum via main pancreatic duct /sphincter of oddi/ampulla
Has digestive function
What cells are found in the pancreas
Acini:
- ducts
- grape like clusters of secretory units
- acinar cells secrete proenzymes into ducts
Islets:
- derived from branching duct system
- lose contact with ducts- become islets
- differentiate into alpha and beta cells secreting into blood
How are islets composed?
Alpha cells: form about 15-20% of islet tissue and secrete glucagon
Beta cells: form about 60-70% of islet tissue and secrete insulin
delta cells: form about 5-10% of islet tissue and secrete somatostatin
Acini: islets are highly vascular ensuring that all endocrine cells have close access to site for secretion
What is the role of exocrine secretion of the pancreas?
Secretes pancreatic juice into duodenum via main pancreatic duct /sphincter of oddi/ampulla
Has digestive function
What cells are found in the pancreas
Acini:
- ducts
- grape like clusters of secretory units
- acinar cells secrete proenzymes into ducts
Islets:
- derived from branching duct system
- lose contact with ducts- become islets
- differentiate into alpha and beta cells secreting into blood
How are islets composed?
Alpha cells: form about 15-20% of islet tissue and secrete glucagon
Beta cells: form about 60-70% of islet tissue and secrete insulin
delta cells: form about 5-10% of islet tissue and secrete somatostatin
How are exocrine acini composed?
Exocrine pancreatic units
Have secretory acinar cells: large with apical secretion granules
Duct cells: small and pale
What is pancreatic juice made up out of?
Acinar cells secrete low volume, viscous, enzyme-rich pancreatic juice
Duct and centroacinar cells secrete high volume, watery, HCO3- rich pancreatic juice
How is bicarbonate secreted?
Secreted by duct and centroacinar cells
Pancreatic juice is high in bicarbonate- 120mM with a pH of 7.5- 8.0
It neutralizes chyme from stomach which prevents damage to duodenal mucosa and raises pH to optimum range for digestive enzymes
It washes low volume enzyme secretion out of pancreas into duodenum
How does duodenal pH effect HCO3- secretion rate?
Duodenal pH is <5 there is a linear increase in pancreatic HCO3- secretion
If duodenal secretion is <3 there isn’t as much of an increase in HCO3- secretion
The reason this happens is because bile salts contain HCO3- and also help neutralise chyme
Brunners glands also secrete alkaline fluid
What is the mechanism of pancreatic HCO3- secretion
1.Separation of H+ and HCO3- by carbonic anhydrase
Na+ moves down conc. gradient via paracellular tight junctions and H2O follows
- Cl-/HCO3- exchange at lumen. Na+/H+ exchange at basolateral membrane into bloodstream (by Na/H exchanger type 1- NHE1)- this is driven by an electrochemical gradient (High extracellular Na and Cl-)
- Na+ gradient into cell from blood maintained by Na+/K+ exchange pump. Uses ATP- primary active transport
- K+ returns to blood via K+ channel. Cl- returns to lumen via Cl- channel (cystic fibrosis transmembrane conductance regulator CFTR)
