Pancreas Flashcards
What does the pancreas originate from?
Foregut outgrowths
During the development of the pancreas, which direction does the proximal duodenum rotate?
Clockwise
What happens to the dorsal and ventral pancreatic ducts after 11 weeks?
they fuse
What is the name of the structure which the bile and pancreatic ducts drain together into?
Major papilla
Describe the embryology of the pancreas?
- Abdominal accessory
organs arise as the foregut outgrowths - Proximal duodenum rotates clockwise
- Ventral and dorsal ducts fuse, and form the major papilla
Which major vein runs behind the pancreas?
Inferior vena cava and the portal vein
What are the four sections of the pancreas called?
Head, neck, body and tail
Where does the head of the pancreas fit into?
The circular shape of the duodenum
Which pair of artery and vein runs directly behind the pancreas?
Superior mesenteric artery and vein
Which artery runs along the superior border of the pancreas?
Splenic artery
What does MRCP do?
Magnetic resonance cholangiopancreatography - provides detailed pictures of the hepatobiliary system and pancreas
How do you define Endocrine vs Exocrine secretion?
Endocrine = into blood stream to have an effect on a distant target
Exocrine = into the duct to have a direct local effect
Which endocrine hormones does the pancreas secrete?
- Insullin
- Glucagon
- Somatostatin
What type of hormone is insulin?
An anabolic hormone
What does insulin do?
promotes glucose transport into cells & storage as glycogen
Other than glucose uptake into cells, what does insulin promote?
promotes protein synthesis & lipogenesis
Which are the main endocrine cells of the pancreas?
Islet of Langerhans
What percentage of the gland is responsible for endocrine secretions?
2%
What is the main pancreatic exocrine secretion?
Pancreatic juice
Where does pancreatic juice get secreted into?
Main Pancreatic Duct / Ampulla / Sphincter of Oddi
What are acini?
Acini are grape-like clusters of secretory units
What do acinar cells secrete?
Acinar cells secrete pro-enzymes into ducts
What are Islets derived from and when do they become islets?
Derived from the branching duct system - once they have completely lost contact with ducts = islets
Where are more islets found in the pancreas?
More found in the tail than in the head
What type of secretion do acinar cells partake in?
Exocrine - indo ducts
Where are centro acinar cells found?
Between acinus and duct
What do the intercellular canaliculi drain into?
Drain into pancreatic duct
Which cell type of Islet form 15-20% of the islet tissue?
Alpha cells
What do alpha cells secrete?
Glucagon
Which islet cell type forms about 60-70% of islet tissue type?
beta cells
What do beta cells secrete?
Insulin
What do gamma cells secrete?
Somatostatin
What percentage of islet tissue do delta cells take up?
5-10%
Which are the more vascularised cell type in the pancreas and why?
Islets - ensures that they have close access to a site for secretion
What are the exocrine pancreatic units (acini) composed of?
Secretory acinar cells
Duct cells
What do the duct cells of the acini look like?
Small and pale
What do the secretory acinar cells of the acini look like?
Large with apical secretion granules
What are the two components of the pancreatic juice?
- Bicarbonate
2. Pancreatic enzymes
Which component of the acini secrete the enzyme rich fluid which is viscous and has a low volume?
Acinar cells
Which component of the acini secrete the bicarbonate rich fluid which is watery and has a high volume?
Duct and centroacinar cells
What is hhe concentration of bicarbonate in plasma compared to pancreatic juice?
25 mM compared to 120 in pancreatic juice
What are the two primary roles of bicarbonate which the pancreas secretes?
- Neutralise acidic chyme from stomach
2. Washes low volume enzyme secretion out pancreas
What are the two benefits of neutralising acidic chyme from the stomach?
prevents damage to duodenal mucosa
Raises pH to optimum range for pancreatic enzymes to work
What happens to bicarbonate secretion when the duodenal pH is less than 5?
Linear increase in bicarbonate secretion
What happens to bicarbonate secretion when duodenal pH is less than 3?
Not much more increase in bicarbonate secretion
Why does the rate of HCO3- secretion remain constant when pH is still acid (pH less than 3?
No need for pancreatic bicarbonate -
- Bile also contains HCO3- and helps neutralise acid chyme
- Brunners glands secrete alkaline fluid
What enzyme catalyses the reaction between carbon dioxide and water to produce H+ ions and bicarbonate?
Carbonic anhydrase
In the production of bicarbonate, which substances move through paracellular tight junctions into the lumen of the duct?
Na+ and therefore water follows
Where does the HCO3- generated from the action of carbonic anhydrase go? And what is it exchanged for?
Into the lumen of the pancreatic duct - exchanged for a Cl- ion
Across which membrane in the pancreas does chloride shift occur?
Across the apical membrane - bicarbonate is secreted into the duct
What maintains the Na+ gradient from high to low across the pancreatic duct cell?
The presence of Na+/K+ ATPase Pumps - pumps 3 x Na+ into blood for every 2 K+ into the cell therefre resulting in a high concentration of Na+ outside the cell in the blood
How does Na+ reenter the pancreatic duct cell after it has been pumped up by Na/K+ ATPase?
It flows through an antiporter - Na+/H+ antiporter with Na+ going into the pancreatic duct cell and H+ (which as produced as a byproduct of water and CO2 reaction) leaves the cell
How does K+ return back into the blood after Na+/K+ ATPase pumps it into the cell?
Using a K+ Channel
How does Cl- Return into the blood after being pumped into the cell through the Cl-/ HCO3- exchanged?
CFTR Channel
What is the pH of pancreatic venous blood?
Acidic due to presence of H+ ions into it
What might be the problem for an organ making a cocktail of digestive enzymes?
A disease like acute pancreatitis may result in the enzymes digesting the actual organ itself
What enzymes are found int the enzyme rich acinar cell secretions?
Enzymes for digestion of:
fat (lipases)
protein (proteases)
carbohydrates (amylase)
Where are acinar cell enzymes stored and synthesized?
→ synthesised & stored in zymogen granules
Where are pancreatic enzymes activated?
In the duodenum
Why are the proteases released as inactive pro-enzymes?
protects acini & ducts from auto-digestion
What in the duodenum activates pancreatic enzymes?
Proteases
What activates proteases like trypsinogen?
enterokinase - causes trypsinogen to be converted into trypsin which can activate the other pancreatic enzymes
What might the blockage of the main pancreatic duct lead to?
Might overload protection leading to autodigestion
Where is enterokinase secreted from?
Duodenal mucosa
What is the purpose of enterokinase?
Converts trypsinogen into trypsin
Is lipase secreted as a precursor or a zymogen?
Precursor - secreted in the active form byt requires another enzyme to be active
What does lipase require in order to be activated and effective?
Presence of colipase to be activated
Presence of bile salts in order to be effective
In what way are pancreatic enzyme secretions able to adapt?
They can adapt to diet
What might lack of pancreatic enzymes lead to?
Malnutrition even if dietary input is sufficient
Why are pancreatic enzymes considered more important than salivary, gastric enzymes?
Pancreatic enzymes (+ bile) essential for normal digestion of a meal:
Anti-obesity drug Orlistat inhibits pancreatic lipases – what side effects might you expect?
Steatorrhoea - increase faecal fat
What three situations might you expect to find increased faecal fat, and why?
Decreased intestinal fat absorption:
- Cystic fibrosis
- Chronic pancreatitis
- Orlisat
What are the three phases of pancreatic juice secretion?
Cephalic Phase
Gastric Phase
Intestinal Phase
Which phase of pancreatic juice secretion is considered a reflex?
Cephalic
Describe what happens during the cephalic phase of pancreatic juice secretion?
Only enzyme rich, low volume component from acini is released in response to the sight / smell / taste of food
Describe what happens during the gastric phase of pancreatic juice secretion?
Similar mechanism to cephalic - Stimulation of pancreatic juice secretion from the food arriving in the stomach
Describe what happens during the intestinal phase of pancreatic juice secretion?
gastric chyme enters duodenum
Both components of the pancreatic juice are secreted into duodenum
Which phase of pancreatic juice secretion is hormonally mediated?
Intestinal only
What controls Pancreatic juice enzyme secretion controlled in acini?
- Vagus Nerve
2. Cholecystokinin
Which cells secrete CCK?
I cells
What inhibits pancreatic juice enzyme secretion?
Gastrin
What is Pancreatic juice bicarbonate secretion controlled in duct & centroacinar controlled by?
Secretin
What neurotransmitter is used to stimulate pancreatic enzyme secretion?
ACh via the vagus nerve
What stimulates the release of CCK from duodenal I cells?
Amino acids and fatty acids in the duodenum
What inhibits the release of CCK from I cells?
Trypsin
What is the osmolarity of acinar fluid?
isotonic
What does acinar fluid resemble in terms of concentrations of ions?
Plasma concentrations of Na+, K+, Cl− & HCO3− are all similar
Why is secretin-stimulated secretion richer in HCO3- than acinar secretion?
because of Cl−/HCO3−exchange
what stimulates secretion of H2O & HCO3- from cells lining extralobular ducts?
Secretin
Describe the Secretin / Bicarbonate negative feedback loop?
- Luminal pH drops in duodenum
- This is detected by the S cells in the duodenum and jejunum
- Increases the release of secretin
- This increases bicarbonate secretion which raises the pH
What affect does CCK alone have on bicarbonate secretion?
None
How can bicarbonate secretion be increased?
Having CCK and Secretin stimulus
Does the vagus nerve have any impact on bicarbonate secretion alone?
No
Does secretin have any affect on enzyme secretion?
Secretin has NO EFFECT on enzyme secretion
Describe the summary of a meal?
- Food mixed, digested in stomach, pH 2
- Chyme into duodenum
- This chyme is acidic and therefore pH drops
- This causes more Secretin from S cells to be released - increased pancreatic juice secretion + bile & Brunner’s gland secretions
- Peptides & fat in duodenum cause sharp ↑ in CCK & vagal nerve stimulation
- CCK potentiates the effects of secretin
At what point does CCK and Vagal Nerve Stimulation peak after a meal?
By 30 minutes, continues until stomach empties
Why is CCK needed to potentiate the effect of secretin on aqueous component?
most of duodenum not at ↓pH
