endocrinepancreas-150424221003-conversion-gate02.pdf

About endocrine pancreatic system.

1. ENDOCRINE
PANCREAS
DR AMBIKA JAWALKAR

2. PANCREAS
•A TRIANGULAR GLAND, WHICH HAS BOTH
EXOCRINE AND ENDOCRINE CELLS, LOCATED
BEHIND THE STOMACH
•ACINARCELLS PRODUCE AN ENZYME -RICH
JUICE USED FOR DIGESTION (EXOCRINE
PRODUCT)
•PANCREATIC ISLETS (ISLETS OF LANGERHANS)
PRODUCE HORMONESINVOLVED IN
REGULATING FUEL STORAGE AND USE.

4. ISLETS OF LANGERHANS
•PAUL LANGERHANS –German medical
student, 1
st
discovered in dogs in 1869
•1-2% of the pancreatic mass
•1-2 million islets in humans
•Beta (β) cells produce INSULIN
•Alpha (α) cells produce GLUCAGON
•Delta (δ) cells produce SOMATOSTATIN
•F cells produce PANCREATIC POLYPEPTIDE

5. INSULIN

6. Frederick G. Bantingand John
Macleod were awarded the Nobel
Prize in Physiology or Medicine in
1923 "for the discovery of insulin."
SOURCE-http://www.nobelprize.org/educational/medicine/insulin/discovery-
insulin.html

8. INSULIN STRUCTURE
•Large polypeptide 51 AA (MW 6000)
•Two chains linked by disulfide bonds.
•A chain (21AA)
•B chain (30 AA)
•The hydrophobic character of the amino acids
at the C-terminal of B-chain is important for
biological activity of Insulin

9. INSULIN STRUCTURE

10. Insulin Synthesis
•Insulin gene is located on the short arm of the
chromosome 11
•Synthesized as Preprohormonecontaining 110
amino acids

11. DNA(chromosome 11) in βcells
mRNA
Preproinsulin–110 aa (signal peptide, A
chain,
B chain, and peptide C)
Proinsulin–86 aa
Insulin–51 aa

12. •Insulin gene encodes a large
precursor of insulin (preproinsulin)
•During translation, the signal
peptide is cleaved (proinsulin)
•During packaging in granules by
golgi, proinsulinis cleaved into
insulin and C peptide

14. C -PEPTIDE
Connects A & B chains
Facilitates folding of A & B chains
Retained in granules
No biological activity, but secreted in equimolar
ratio with Insulin
Hence its concentration in plasma directly
reflects β–cells activity

15. Regulation of insulin secretion
Mainly regulated by feed back control signal
provided by nutrients level in plasma
“ Hormone of Abundancy”

17. PLASMA GLUCOSE

18. MECHANISM OF GLUCOSE
INDUCED INSULIN
SECRETION

20. METABOLISM OF INSULIN
•Insulin circulates freely in plasma
•Its half life is 5-8 min.
•Metabolic clearance is 800ml/min
•Basal insulin release to the circulation is about
0.5-1 unit/hr
•Total release into peripheral circulation in a day is
30 units
•Metabolized mainly in Liver & Kidney

21. MECHANISM OF ACTION
INSULIN RECEPTOR
•A glycoprotein tetramer having 2 α
and 2 βsubunits
•Gene located on chromosome 19
•Insulin binds with αsubunit resulting in
conformational change of receptor
•The HR complex is then internalized by
endocytosis

22. MECHANISM OF ACTION
Binding of Insulin to αsubunit
Conformational change in Receptor (βsubunit)
Activation of tyrosine kinase activity of β
subunit
Autophosphorylationof βsubunit on tyrosine
residues
Phosphorylation of intracellular proteins that
brings about alteration in cell functions

23. MECHANISM OF ACTION
The active tyrosine kinase phosphorylates tyrosineson
Insulin Receptor Substrates (IRS1 & IRS2)
IRSs are docking proteins to which a variety of
downstream proteins bind
Phosphorylation of IRS causes translocation of GLUTs
(Glucose Transport Proteins) to the cell membrane
GLUTS facilitate glucose entry into the cell
Different protein channels are also inserted into the
plasma membrane leading to increased entry of amino
acids, K+, Mg+ & P+

24. GLUCOSE TRANSPORTERS

25. MECHANISM OF ACTION

26. PHYSIOLOGICAL
ACTIONS OF
INSULIN

27. 27
Ganong Review of Medical Physiology 1985 12th ed #258

28. INSULIN ACTION ON
CARBOHYDRATE METABOLISM
LIVER
•Stimulates glucose oxidation
•Promotes glucose storage as glycogen
•Inhibits glycogenolysis
•Inhibits gluconeogenesis
MUSCLE
•Stimulates glucose uptake (GLUT4)
•Promotes glucose storage as glycogen

29. INSULIN ACTION ON
CARBOHYDRATE METABOLISM
ADIPOSE TISSUE
•Stimulates glucose transport into
adipocytes
•Promotes the conversion of glucose into
triglycerides and fatty acids
“ANTI-DIABETOGENIC”

30. INSULIN ACTION ON PROTEIN
METABOLISM
•Facilitates amino acids entry into muscle
cells
•Facilitates protein synthesis in ribosomes
by induction of gene transcription
•Inhibits proteolysis by decreasing
lysosomal activity
“ANABOLIC HORMONE”

31. INSULIN ACTION ON FAT
METABOLISM
LIVER
•Anti ketogenic & Lipogenic
•Stimulates HMG-CoA reductase
ADIPOSE TISSUE
•Promotes storage of fat
•Inhibits lipolysis by inhibiting Hormone
sensitive lipase
•Promotes lipogenesisby stimulating
lipoprotein lipase
“ANTI-KETOGENIC”

32. INSULIN ACTION ON PLASMA K +
CONCENTRATION
•Facilitates rapid entry of K+ into cell by
simulating Na-K ATPase activity
•Thus decreases plasma concentration of
K+
•APPLIED:Insulin is given along with
glucose in the treatment of Hyperkalemia
that occurs in Acute Renal Failure
“PHYSIOLGICAL REGULATOR OF PLASMA
K+ CONCENTRATION”

33. INSULIN ACTION (SUMMARY):
•GLUCOSE UPTAKE IN MOST
CELLS
•GLUCOSE USE & STORAGE
•PROTEIN SYNTHESIS
•FAT SYNTHESIS
Dominates in Fed State Metabolism
Anti-
Diabetogenic
Anabolic
Anti-ketogenic
Lipogenic

34. GLUCAGON

35. •A 29-amino-acid polypeptide hormone that is a
potent hyperglycemic agent
•Produced by αcells in the pancreas
•Its major target is the liver, where it promotes:
•Glycogenolysis–the breakdown of glycogen to
glucose
•Gluconeogenesis–synthesis of glucose from
lactic acid and non carbohydrates
•Release of glucose to the blood from liver cells

36. DNA in αcells
mRNA
Preproglucagon
Proglucagon
Glucagon

38. PHYSIOLOGICAL ACTIONS OF
GLUCAGON
•Stimulates glycogenolysis, gluconeogenesis
& inhibits glycogenesis
•Promotes lipolysis & ketogenesis
•Increases calorigenesis
“Prodiabetogenicand Ketogenic”

39. INSULIN-GLUCAGON
RATIO
•Insulin is hormone of energy storage
•Glucagon is hormone of energy release
•A balance should be maintained for normal
metabolic functions
•After a normal balance diet is 3
•After overnight fasting decreases to 1, may
decrease to as low as 0.4 after prolonged fasting
•Physiological significance –during neonatal
period a low I/G ratio is critical for survival of the
neonate

40. INSULIN & GLUCAGON REGULATE
METABOLISM

41. NORMAL PLASMA GLUCOSE LEVELS
•Fasting : 70 –100mg%
•Postprandial : 100 –140mg%
•RBS : 80 –120mg%

42. PLASMA GLUCOSE
( BLOOD GLUCOSE)
-INSULIN -
GLUCAGON
( BLOOD GLUCOSE) -
EPINEPHRINE
-GROWTH
HORMONE

43. GLUCOSE
HOMEOSTASIS

44. GLUCOSE
HOMEOSTASIS

45. SOMATOSTATIN
•Secreted from D
cells of pancreas
•Also secreted in
hypothalamus & GIT
•A peptide hormone
with 2 forms, one
with 14 AAs & the
other with 28 AAs
Functions:
•Inhibitssecretion of
insulin & glucagon
•Inhibits GI motility*& GI
secretions
•Regulates feedback
control of gastric
emptying

46. PANCREATIC
POLYPEPTIDE
•Secreted from F cells of pancreas
•Polypeptide with 36 amino acids
•Structurally similar to Neuropeptide Y
secreted from hypothalamus
•Secreted in response to food intake
•Inhibitsexocrine pancreatic secretion
•Slows the absorption of food from the GI
tract

47. APPLIED PHYSIOLOGY
INSULIN DEFICIENCY –DIABETES MELLITUS
INSULIN EXCESS –INSULINOMA
GLUCAGON EXCESS –GLUCAGONOMA
SOMATOSTATIN EXCESS –
SOMATOSTATINOMA
CARCINOMA OF PANCREAS

48. DIABETES
MELLITUS
•A serious disorder of carbohydrate
metabolism
•Most common endocrine disorder
•Results from hyposecretionor hypoactivity
of insulin
•The three cardinal signs of DM are:
•Polyuria –huge urine output
•Polydipsia –excessive thirst
•

49. Classification of DM
Type 1 or IDDM -Insulin Dependent Diabetes
Mellitus
Type 2 or NIDDM -Non-Insulin Dependent
Diabetes Mellitus
Other Types of Diabetes Mellitus –MODY, pancreatic
diseases, drug induced (corticosteroids, thiazide
diuretics, phenytoin)
GDM-Gestational Diabetes Mellitus

52. 52
Polyphagia –decreased activity of
satiety center removes its inhibitory
effect on feeding center in brain
Polyuria–is due to osmotic diuresis
Polydipsia–dehydration due to
polyuria stimulates thirst

53. 53
Glycosuria -because when insulin is
not present, glucose is not taken up
out of the blood at the target cells.
So blood glucose is very highly
increased →increased glucose is
filtered and excreted in the urine
(exceeds transport maximum)

54. 54
Ketosis -
Fats and proteins are metabolized
excessively, and byproducts known as
ketone bodies are produced. These are
released into the bloodstream and
cause:
Decreased pH (so increased acidity)
Compensations for metabolic
acidosis
Acetone given off in breath

55. 55
Weight loss -patient eats, but nutrients
are not taken up by the cells and/or
are not metabolized properly
“Disease of Starvation midst of
Plenty”

57. DIAGNOSIS
•Demonstrating persistent hyperglycemia&
glycosuria
•Glucose Tolerance Test (GTT) –oral is
preferred
•Estimation of Fasting Blood Glucose (FBS)
•FBS more than 126mg% in more than two
occasions confirms DM

58. TREATMENT
•Insulin therapy
•Oral hypoglycemicagents
•Life style modifications

59. COMPLICATIO
NS
•Microvascular –diabetic retinopathy,
diabetic nephropathy
•Macrovascular –Myocardial Infarction &
Stroke
•Diabetic neuropathy
•Chronic ulcer & gangrene formation due to
decreased resistance to infection