The Pancreas Flashcards
Describe the structure of the pancreas from tail to uncinate
tail (islet tissue) body neck head uncinate
How does pancreatic juice reach the duodenum
Main and accessory pancreatic ducts
Where is the pancreas
Lies mainly on posterior abdominal wall
Extends from C-shaped duodenum to hilum of spleen
What are the main relations of the pancreas
Coeliac and mesenteric arteries
posterior -IVC, Abdominal aorta, Left kidney
What are the main pancreatic secretions
Insulin - anabolic hormone to promote glucose transport into cells + storage as glycogen
Glucagon - gluconeogenesis and glycogenolysis
Somatostatin - Suppressive
What are the two functional parts of the pancreas
Endocrine (2%) - islets of langerhans (insulin, glucagon, somatostatin, polypeptide), regulation of blood glucose metabolism and growth
exocrine (98&) - secretes juice into the duodenum via the duct, digestive function
Describe exocrine pancreatic cells
Ducts
Acini (grape-like clusters of secretory units)
Acinar cells (secretes pro-enzymes into the ducts)
Describe the endocrine pancreatic cells
Derived from the branching duct system
Lose contact with the ducts to become islets
Differentiate into alpha and beta cells
Tail > head
Describe the composition of islets
Alpha cells - 20%, for glucagon secretion
Beta cells - 60-70%, insulin secretion
Delta cells - 5-10%, somatostatin secretion
Highly vascular so endocrine cells have close access for secretion
What are the two components of pancreatic juice
Low volume, viscous, enzyme-rich - acinar
high volume, watery
HCO3 rich - centroacinar (no granules for enzymes)
Describe how cystic fibrosis affects the pancreas
cystic fibrosis transmembrane conductance regulator means chloride cannot be returned to the lumen
Both endo + exocrine
digestive function comprised + less insulin secretion
Insulin and enzyme supplements
Describe bicarbonate secretion
By duct and centroacinar cells
Pancreatic juice has 5x more bicarbonate in the plasma
As pH decreases the bicarbonate secretion rate increases
Secretion stops at pH 5 as bicarbonate is also found in the bile and brunners glands that secrete alkaline fluid
What is the purpose of bicarbonate
Neutralises acid chyme from the stomach
prevents damage to duodenal mucosa
Raises pH to optimum range for panreatic enzymes to work
Washes low volume enzyme secretion out of pancreas into duodenum
Exlplain the process of bicarbonate secretion
Catalysed by carbonic anyhdrase
Sodium moves between tight junctions which allows water to follow (osmolarity increases)
1. CO2 + H2O -> H+ + HCO3-
2. Bicarbonate moved out in exchange for chloride ions
3. Sodium potassium pump increases the sodium concentration outside the cell
4. Protons pumped out in exchange for sodium
5. Potassium returns out the cell via a potassium channel
6. Chloride returns to the lumen via the chloride channel
Describe acinar cell enzyme secretion
Lipsases, proteases and amylase are synthesised and stored in zymogen granules
zymogens = pro-enzymes
How is auto-digestion on the acini and ducts prevented
Proteases are released as inactive pro-enzymes
Trypsin inhibitor prevents trypsin activation
Enzymes are only activated in the duodenum
What is acute pancreatitis
Blockage of pancreatic duct may overload protection and result in auto-digestion
What can lack of pancreatic enzymes lead to
Malnutrition
What are the side effects of orlistat and what does it do
Inhibits pancreatic lipase
Steatorrhea - increased faecal fat
What is the parasympathetic pathway for innervation of the gut
Vagus nerve
Cholinergic
Describe the phases in control of secretion
cephalic - enzyme-rich component, low volume mobilises the enzymes
gastric - enzyme-rich component, low volume mobilises the enzymes
Intestinal - hormonally mediated, both components of pancreatic juice is stimulated
Describe how enzyme secretion from the acinar cells is controlled
Enzyme secretion is controlled by the vagla reflex and by cholecystokinin (calcium/PLK) - also stimulates bile secretion
- peptides and fat sensed by cells
- CCK released in the blood
- Acinus cell stimulation by
- CCK or the vagus nerve (ACh)
- Stimulation of release of pro-enzymes at the trypsin hub
Describe the control of bicarbonate secretion
Bicarbonate secretion is controlled by release of secretin (cAMP)
- Acidic chyme is sensed by the sensory cells
- secretin secreted into the blood
- pancreatic duct
- cascade
- bicarbonate release
- pH increases and secretin is switch ed off
Describe stimulus interaction of pancreatic juice
CCK alone has no effect on bicarbonate secretion
CCK increases bicarbonate secretion that has been stimulate by secretin
Vagus nerve similar effect
Secretin has no effect on enzyme secretion
