THE EXOCRINE AND ENDOCRINE PANCREAS

Question 1

How much of the pancreas is endocrine?

Answer 1

only 10%, the rest is exocrine

Question 2

what is the structure of the endocrine pancreas?

Answer 2

it consists of islets of Langerhans

Question 3

what hormones does the endocrine pancreas secrete?

Answer 3

insulin
glucagon
somatostatin
pancreatic polypeptide
ghrelin

Question 4

what is the role of the endocrine pancreas?

Answer 4

to control hunger sensation and glucose homeostasis

Question 5

what is the role of the exocrine pancreas?

Answer 5

to buffer solution and produce enzymes for food digestion

Question 6

what does the exocrine pancreas produce?

Answer 6

bicarbonate
amylase
protease
lipase

Question 7

describe the structure of the exocrine pancreas

Answer 7

The functional unit of the exocrine pancreas is composed of an acinus and its draining ductule. A ductule from the acinus drains into interlobular ducts, which in turn drain into the main pancreatic ductal system.

Question 8

describe how bicarbonate is produced and secreted from a duct cell

Answer 8

water and CO2 enter the duct cell and carbonic anhydrase converts it to carbonic acid which can dissociate into HCO3- and H+. H+ are exchanged for Na+ by an anti porter and the Na+ are then removed by the Na+/K+ pump. HCO3- are exchanged for Cl- (secretin increases this rate of exchange) and enter the intercalated ducts. Cl- return to the lumen through a channel and Na+ and H2O enter the intercalated ducts.

Question 9

which pumps are present on the apical membrane of ductal cells?

Answer 9

Cl-/HCO3- exchanger

Question 10

which pumps are present on the basolateral membrane of ductal cells?

Answer 10

Na+/K+ ATPase

Na+/H+ exchanger

Question 11

describe the pathophysiology of cystic fibrosis?

Answer 11

a frameshift mutation in the cystic fibrosis transmembrane conductance regulator gene causes fibrosis in the lungs/pancreas/liver/intestine. this leads to abnormal transport of Cl- and Na+ across the epithelium which causes thick secretions which block digestive enzyme movement so they get stuck in the fibrotic organs and begin to auto digest them

Question 12

what’s the function of the cystic fibrosis transmembrane conductance regulator gene?

Answer 12

regulates the movement of chloride and sodium ions across epithelial cell membranes.

Question 13

what are some considerations when taking digestive enzymes pharmacologically?

Answer 13

must be taken before food
they need an enteric coating because they need to bypass the acidic environment of the stomach to enter the small intestine

Question 14

describe which cell types are within the islets in the endocrine pancreas?

Answer 14

alpha cells which secrete glucagon (20%)
beta cells which secrete insulin (70%)
delta cells which produce somatostatin (5%)
epsilon cells which secrete ghrelin (1%)
gamma cells which secrete pancreatic-polypeptide (1%)

Question 15

What’s the function of a pancreatic polypeptide?

Answer 15

it regulates pancreatic secretion by endocrine and exocrine tissue
it can also reduce hepatic glucose production to give a feeling of satiety

Question 16

which hormones secreted by the endocrine pancreas regulate appetite?

Answer 16

ghrelin and potentially pancreatic polypeptide

Question 17

which hormones secreted by the endocrine pancreas regulate glucose homeostasis?

Answer 17

insulin
glucose
somatostatin

Question 18

describe the synthesis of insulin?

Answer 18

preproinsulin is synthesized by the ribosome and then it enters the RER and the signal peptide is cleaved to form pro-insulin which folds and disulphide bonds form. proinsulin moves into the Golgi where the connecting sequence (C peptide) between the alpha and beta chains is cleaved and the alpha and beta chain are connected by disulphide bonds= insulin. insulin is packaged into granules awaiting vagal nerve stimulation.

Question 19

which nerve regulates insulin secretion?

Answer 19

the vagus nerve

Question 20

what are the 2 forms of insulin?

Answer 20

hexameric (inactive/storage) and monomeric (active)

Question 21

describe the structure of the hexameric form of insulin?

Answer 21

it consists of 6 insulin molecules held together by a central zinc molecule

Question 22

describe the structure of the monomeric form of insulin?

Answer 22

an alpha and beta chain linked by disulphide bridges

Question 23

where do you find GLUT 2?

Answer 23

on muscle cells and adipocytes

Question 24

where do you find GLUT 4?

Answer 24

on the liver and pancreas

Question 25

describe how insulin is secreted from the beta cells of the pancreas?

Answer 25

GLUT2 allows glucose to enter the beta cell. glucose is metabolised to formATP which closes ATP-sensitive K+ channels to enable depolarisation. this causes voltage-gated Ca2+ channels to open and allow an influx of Ca2+ to enter. this signals to the beta cell to make monomeric insulin and move insulin granules so they can be released into the bloodstream.

Question 26

describe what happens when insulin binds to its receptor?

Answer 26

the insulin docks onto the 2 alpha chains and this causes the tyrosine kinase domains to become phosphorylated which causes phosphorylation of insulin receptor substrates (IRS). this activation enables GLUT4 to moe to the cell surface membrane so it can allow glucose into the cell and lower blood sugar levels.

Question 27

what should blood glucose levels be between?

Answer 27

4 and 7 mmol/L

Question 28

What’s glucagon effect?

Answer 28

if blood sugar levels fall too low, the pancreas produces and secretes glucagon from alpha cells of the pancreas which act on the liver to cause glycogenolysis

Question 29

how is most of the glucose in the body produced?

Answer 29

from liver glycogenolysis and hepatic gluconeogenesis

a small amount from renal gluconeogenesis

Question 30

how much glucose does the brain use a day

Answer 30

120g- its an obligatory consumer

Question 31

describe the synthesis of glucagon in alpha cells of pancreatic islets?

Answer 31

proprotein convertase 2 cleaves proglucagon into glucagon

Question 32

what is proglucagon cleaned into in the intestinal tract?

Answer 32

glucagon-like peptide 1 and 2 and IP2

Question 33

what does glucagon-like peptide 1 do?

Answer 33

its an incretin so it regulates the amount of insulin secreted

Question 34

what does glucagon-like peptide 2 do?

Answer 34

promotes intestinal growth

Question 35

what are the effects of glucagon?

Answer 35

increased glycogenolysis in liver and skeletal muscles
increased lipolysis
increased gluconeogenesis in the liver

Question 36

what are the effects of insulin?

Answer 36

increased uptake of glucose
increased rate of glucose -> ATP
increased glycogenesis
increased amino acid absorption and protein synthesis
increase TAG synthesis