The pancreas Flashcards
How does the pancreas develop?
Foregut and midgut derivative
- dorsal and ventral buds at the junction of f and m
- ventral is part of hepatobiliary bud
Then, duodenum rotates, forming C shape, taking ventral bud with it, allowing it to fuse with dorsal bud.
What are the different areas of the pancreas>
Head neck body tail and uncinate
- tail . - islet most common in tail
Where is the pancreas?
Under . stomach, medial to ileum and side to the spleen
LIES ON POSTERIOR . ABDOMINAL WALL
Supplied by mesenteric artery and coeliac artery
Endo v exo crine
Endo - secretion into blood - effect on distant target organ 2PERCENT
INSULINGLUCAGONSOMATOSTATIN
Exo . - secretion into duct for direct effect 98PERCENT - digestion
How can pancreatic cells be differentiated?
Exocrine
- ducts
- acini - secrete pro-enzymes
Endocrine
- derived from branch
- lose contact and form islets
- further differentiation into alpha or beta cells
Describe islet composition
alpha - 15pc
beta - 60pc
delta - 10pc
What are the parts of pancreatic juice?
bicarbonate
enzyme
released by diff cells
- acinar cells - enzyme release
- duct and centroacinar cells - diff part, not enzymes as no secretory granules
What is the functional unit of the exocrine pancreas and how does it look?
Acinar
- blind ended tubule
How is bicarbonate secreted? - include mechanism
From duct and centroacinar cells
Catalysed by carbonic anhydrase
leading to the formation of HCO3- from carbonic acid.
Na+ moves through tight junction, bringing water with it and forming the liquid part
HCO3- is exchanged for a Cl-
Protons are pumped out into blood - opp end by secondary active transport
Na gradient maintained by Na/K pump
What is the function of the bicarb secretion
Helps neutralise acidic chyme and stops burning of mucosa
raises pH for enzymes to work
Watery base allows . washing of enzymes down to duodenum - prevents buildup
Why might bicarbonate secretion stop at pH 5
Because there are other mechanisms that help neutralsie acid
- Bile has bicarb for chyme
Brunners gland secrete alkaline fluid
How does CF arise?
Mutation of gene but, Cl- channel broke so the secretions are much thicker
How does the splitting of H2CO3 differ in stomach and pancreas?
The H+ in stomach goes to gastric juice, whereas in pancreas it goes to the blood.
The HCO3- goes to blood in stomach but pancreatic juice in pancreas
Thus, the gastric venous blood is alkaline, whereas pancreatic is acidic.
How are enzymes secreted? Are they active? What happens?
Acinar cells
Enzymes that break all fats, carbs and proteins,
Stored in zymogen granules
- pro-enzymes
Hence, they are only activated in the duodenum
- trypsin inhibitor
What might occur if the pancreas were to become blocked?
Overload protection and result in auto-digestion due to accumulation of trypsin that becomes active.
This is acute pancreatitis
Why might pancratic function differ?
Adaptations to diet
- fat high, low protein diet etc
Without pancreatic enzymes, what might occur? Give an example . of drugs that utlise this
Malnutrition, due to the inability to digest foods and obtain nutrients.
Orlistat - lipase inhibitor
- Stops fat digestion and hence intestinal fat absorption
But, leads to steatorrhea
What can cause steatorrhea?
CF
Chronic pancreatitis
Orlistat
Which nervous system controls the pancreatic secretion?
Autonomic system
- Parasympathetic
- Cholinergic
- VAGUS NERVE
How is pancreatic secretion controlled?
Cephalic phase
- reflex to smell
- enzyme mobilisation
Gastric
- pancreatic stimulation by food in stomach
Intestinal
- HORMONAL, when gastric chyme enters duodenum
- Stimulates both components of the juice
What controls secretion of bicarbonate and enzymes?
Bicarb - Secretin - (cAMP_
- purely hormonal
- Presence of acid - senses protons
- Hence, gastric acid becomes less acidic and then decreases action of secretin
Enzyme - Cholecyostokinin - (PLC)
- hormonal and vagal reflex
- peptide and fat levels
- has sensors
- cuases CCK release which goes to acinar cells
- Acinus releases proenzymes
What is the importance of secretin?
First hormone found
What is the other role of CCK
Bile secretion stimulation -
smooth muscle contracts due to it
How is CCK switched off?
Once fats and peptides digested, nothing to stimulate in the lumen
May be other mechanisms
Which hormones cause bicarbonate release?
CCK and secretin both needed!
- CCK has no effect on bicarb secretion
- Secretin has a little effect
- Secretin has no effect on enzyme secretion
Describe the cascade that occurs following the entrance of food into the stomach
Food mixed in sdtomach
Chyme squirted into duodenum
H+ in duodenum causes secretin release, which causes pancreatic juice release - bicarb
Peptides and fat cause rise in CCK - leading to enzyme release
