6- Pancreas

Question 1

5 components of the pancreas

Answer 1

Tail, body, neck, head, uncinate process

Question 2

The 2 functional parts of the pancreas

Answer 2

Endocrine - 2% of gland
Islets of Langerhans
Secretes hormones into blood - Insulin & Glucagon (also Somatostatin and Pancreatic Polypeptide)

Exocrine - 98% of gland.
Secretes (Pancreatic Juice) into duodenum via pancreatic duct/common bile duct.

Question 3

How do exo and endocrine cells differ

Answer 3

Exocrine:
Ducts
Acini are grape-like clusters of secretory units
Acinar cells secrete pro-enzymes into ducts
Endocrine:
Derived from the branching duct system
Lose contact with ducts – become islets
Differentiate into α- and β-cells secreting into blood

Question 4

2 components of pancreatic juice+ where produced

Answer 4

TWO components of pancreatic juice:-
low vol, viscous,enzyme-rich Acinar cells
high vol, watery, HCO3-rich. Duct & Centroacinar cells

Question 5

How is pancreatic bicarbonate secreted

Answer 5

Separation of H+ and HCO3- in cell, catalysed by carbonic anhydrase
Cl/HCO3 exchange at lumen
Na/H exchange at basolateral membrane into bloodstream

Na gradient into cell from blood maintained by active Na/K exchange pump
K and Cl return via channels passively

Question 6

What are zymogens

Answer 6

Pro enzymes

Question 7

How is self digestion prevented in the pancreas

Answer 7

Proteases are released as inactive pro-enzymes ~ protects acini and ducts from auto-digestion
Pancreas also contains a trypsin inhibitor to prevent trypsin activation
Enzymes become activated ONLY in duodenum
Blockage of pancreatic duct may overload protection and result in auto-digestion (= acute pancreatitis)

Question 8

How are enzymes activated in the duodenum

Answer 8

Enterokinase converts trypsinogen into trypsin
Trypsin then converts all the other proteolytic and some lipolytic enzymes (note lipase secreted in active form but requires colipase, which is secreted as precursor)

Question 9

3 phases of secretion

Answer 9

Initial cephalic phase
Reflex response to sight/smell/taste of food

Gastric phase
Stimulation of pancreatic secretion originating from food arriving in the stomach

Intestinal phase (= 70-80% of pancreatic secretion)
Hormonally mediated when gastric chyme enters duodenum.  
BOTH components of pancreatic juice stimulated (enzymes + HCO3 - juice flows into duodenum)

Question 10

How are the 2 components of pancreatic juice controlled

Answer 10

The two components of pancreatic juice are separately controlled
Bicarbonate secretion is controlled by release of a hormone - Secretin (cAMP)
Enzyme secretion is controlled by vagal reflex and by a hormone - Cholecystokinin (CCK) (Ca2+/PLC)

Question 11

How do cck and secretin interact to affect secretion

Answer 11

CCK alone - no effect on bicarbonate secretion
CCK can markedly increase bicarbonate secretion that has been stimulated by secretin
Vagus nerve has similar effect to CCK
Secretin NO EFFECT on enzyme secretion

Question 12

Summarise what happens after eating

Answer 12

Food mixed, digested in stomach, pH 2
Chyme squirted into duodenum
H+ ions in duodenum stimulate release of secretin, stimulating release of pancreatic juice (plus bile and Brunner’s gland secretions) to raise pH to neutral/alkaline.
Peptides + fat in duodenum cause sharp rise in CCK, vagal nerve, stimulating pancreatic enzyme release, peaks by 30 mins, continues until stomach empty.
CCK potentiates effects of secretin on aqueous component (necessary because most of duodenum not at low pH).