Pancreas; Anatomy and Secretions Flashcards
Pancreas exocrine functions
Acinar cells produce enzymes;
- amylase (for carbs)
- lipase (for lipids)
- trypsin (for proteins)
Releases these into duodenum at Ampulla of Vater through pancreatic duct
The duct is also lined with cells that secrete NaHCO3
Pancreas endocrine functions
Islets of langerhans produce insulin (in B cells) and glucagon (in a cells)
Releases these directly into blood stream
Fat digestion
Lipase
Triglyceride molecule too large to be absorbed, so pancreatic lipase hydrolyses into monoglyceride and free fatty acids.
Hydrolysis requires presence of bile acids
Protein digestion
Pancreas releases trypsinogen, chymotrypsinogen and procarboxypolypeptidase pro-enzymes
This is activated by duodenal enterokinase to trypsin
Trypsin roles
Activates all of the other pro-enzymes
Splits proteins into peptides of various sizes (most abundant)
Carbohydrate digestion
Pancreas and salivary glands secrete amylase
Digest starch and gluycogen
Produces maltose and maltriose
What happens to the maltose/maltiose after this
Small intestine brush border enzymes complete their digestion to glucose
Anatomy of the ducts
At end, the acinar cells secrete the enzymes into acinus.
This travels down intercalated duct
These drain into larger interlobar, then extralobar ducts.
These then meet to form the main pancreatic duct, which joins the common bile duct
Main pancreatic duct
Travels from tail to head (left to right)
Together w bile duct, opens into seconds part of duodenum at ampulla of vater
This opens into duodenum at major duodenal papilla
Sphincters in the route
- Pancreatic duct sphincter at termination of pancreatic duct
- Hepatopancreatic sphincter (oddi) at ampulla of vater
Control flow of pancreatic juice into duo
Where and what level does the pancreas lie
Right side (head) lies across vertebral bodies of L1-L3. Ontop of IVC
Posterior to stomach and transverse mesocolon
Body lies ontop of aorta
Left (tail) is in contact with hilum of spleen
What is the uncinate process
Small portion of head that curves around to the left
hooks around the superior mesenteric vessels
Blood supply to the pancreas
Head - Anterior and posterior superior and inferior pancreatricoduodenal arteries
Remainder supplied by up to 10 branches of splenic artery
Venous drainage of pancreas
To Portal
Splenic (most)
Superior mesenteric veins
Innervation of the pancreas
From splanchnic nerves
Vagi through coeliac and superior mesenteric plexuses
Protection of the pancreas from trypsin
If a little trypsin gets into pancreas then it would autodigest.
Therefore pancreas contains trypsin inhibitor called the kazal inhibitor.
Also acid pH maintenance prevents proenzymes being at their optimum pH
How much fluid does the pancreas secrete a day
about 1.5 L
Bulk is NaHCO3 juice from small ducts, rest is digestive enzymes
Function of the NaHCO3 released
Neutralise gastric acid in the duodenum to about pH 6 or 7
How do the lining cells of duct form NaHCO3?
- CO2 from blood combines with H20 to form HNO3-
- HCO3- actively transported out into lumen via Cl-/HCO3- exchanger
- Na+ moves via paracellular pathway
- Cl- moves out into lumen by CFTR channel to keep gradient
Conc difference between pancreatic juice HCO3- and blood
Bicarbonate in pancreatic juice is derived from blood, therefore its conc is proportional to that in the blood
How do the H+ ions prduced get removed from the cell?
Via Na+/H+ exchanger into the blood.
The Na+ is then pumped back out into the blood by Na+/K+ pump
Movement of water?
Movenemt of HCO3- and Na+ from blood into lumen causes an osmotic gradient, which drives water to move from blood into lumen.
Results in an almost isosmotic solution
Role of bile
Breaks down fats into smaller pieces which are easier for lipase to digest
Stimulation of pancreatic secretion
- Parasymp vagal stimulation (symp inhibits) increase enzyme and aqueous components secretion
- Secretin and CCK released from duodenal mucosa stimulate secretion of aqueous component
- Cephalic phase of pancreatic secretion
Minor in humans
Gastrin released from mucosa of antrum in reponse to vagal stimulation (Ach)
This causes a release of small amount of pancreatic juice w high protein content
- Gastric phase of pancreatic secretion
Gastrin released in response to gastric distention (vago-vagal reflex) and presence of aa in antrum
Continues to stimulate release of pancreatic juice
Vago-vagal reflexes act on receptors on acinar cells to release pancreatic juice w large enzyme amounts
- Intestinal phase of pancreatic secretion
SECRETIN
Longest and most important phase
Secretin released from duodenal mucosal cells in response to acid in lumen.
Secretin acts on pancreatic ducts to release large volume of HCO3- fluid.
Also stimulates bile production in liver
- Intestinal phase of pancreatic secretion
CCK
Also secreted from duodenal mucosa, in response to peptides, aa and fatty acids in lumen
Actions;
- on pancreatic acinar cells to stimulate enzyme synth and release
- on gallbladder to stimulate contraction and relaxation of the hepatopancreatic sphincter. allows release of bile into duo
Somatostatin effect on pancreatic secretion
Inhibits adenylate cyclase and decreases cAMP.
Therefore inhibits secretion of acinar and duct cells
