The Pancreas

Question 1

Describe the structure of the pancreas from tail to uncinate

Answer 1

tail (islet tissue)
body
neck 
head
uncinate

Question 2

How does pancreatic juice reach the duodenum

Answer 2

Main and accessory pancreatic ducts

Question 3

Where is the pancreas

Answer 3

Lies mainly on posterior abdominal wall

Extends from C-shaped duodenum to hilum of spleen

Question 4

What are the main relations of the pancreas

Answer 4

Coeliac and mesenteric arteries

posterior -IVC, Abdominal aorta, Left kidney

Question 5

What are the main pancreatic secretions

Answer 5

Insulin - anabolic hormone to promote glucose transport into cells + storage as glycogen
Glucagon - gluconeogenesis and glycogenolysis
Somatostatin - Suppressive

Question 6

What are the two functional parts of the pancreas

Answer 6

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

Question 7

Describe exocrine pancreatic cells

Answer 7

Ducts
Acini (grape-like clusters of secretory units)
Acinar cells (secretes pro-enzymes into the ducts)

Question 8

Describe the endocrine pancreatic cells

Answer 8

Derived from the branching duct system
Lose contact with the ducts to become islets
Differentiate into alpha and beta cells
Tail > head

Question 9

Describe the composition of islets

Answer 9

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

Question 10

What are the two components of pancreatic juice

Answer 10

Low volume, viscous, enzyme-rich - acinar
high volume, watery
HCO3 rich - centroacinar (no granules for enzymes)

Question 11

Describe how cystic fibrosis affects the pancreas

Answer 11

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

Question 12

Describe bicarbonate secretion

Answer 12

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

Question 13

What is the purpose of bicarbonate

Answer 13

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

Question 14

Exlplain the process of bicarbonate secretion

Answer 14

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

Question 15

Describe acinar cell enzyme secretion

Answer 15

Lipsases, proteases and amylase are synthesised and stored in zymogen granules
zymogens = pro-enzymes

Question 16

How is auto-digestion on the acini and ducts prevented

Answer 16

Proteases are released as inactive pro-enzymes
Trypsin inhibitor prevents trypsin activation
Enzymes are only activated in the duodenum

Question 17

What is acute pancreatitis

Answer 17

Blockage of pancreatic duct may overload protection and result in auto-digestion

Question 18

What can lack of pancreatic enzymes lead to

Answer 18

Malnutrition

Question 19

What are the side effects of orlistat and what does it do

Answer 19

Inhibits pancreatic lipase

Steatorrhea - increased faecal fat

Question 20

What is the parasympathetic pathway for innervation of the gut

Answer 20

Vagus nerve

Cholinergic

Question 21

Describe the phases in control of secretion

Answer 21

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

Question 22

Describe how enzyme secretion from the acinar cells is controlled

Answer 22

Enzyme secretion is controlled by the vagla reflex and by cholecystokinin (calcium/PLK) - also stimulates bile secretion

1. peptides and fat sensed by cells
2. CCK released in the blood
3. Acinus cell stimulation by
4. CCK or the vagus nerve (ACh)
5. Stimulation of release of pro-enzymes at the trypsin hub

Question 23

Describe the control of bicarbonate secretion

Answer 23

Bicarbonate secretion is controlled by release of secretin (cAMP)

1. Acidic chyme is sensed by the sensory cells
2. secretin secreted into the blood
3. pancreatic duct
4. cascade
5. bicarbonate release
6. pH increases and secretin is switch ed off

Question 24

Describe stimulus interaction of pancreatic juice

Answer 24

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

Question 25

How long does it take for pancreatic enzyme release to peak after a meal

Answer 25

30 minutes

Question 26

Describe the activation and action of trypsin

Answer 26

Duodenal mucosa secretes enterokinase (Enteropeptidase)
that converts trypsinogen to trypsin
trypsin converts proteolytic and some lipolytic enzymes

Question 27

Which enzyme is not activated by trypsin

Answer 27

lipases
Secreted in its active form and requires colipase, secreted as a precursor
Also requires bile salts