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MEH > 13. Endocrine Pancreas > Flashcards

13. Endocrine Pancreas Flashcards

1
Q

What are the important polypeptide hormones secreted by the pancreas?

A 
Insulin
Glucagon
Somatostatin
Pancreatic polypeptide
Ghrelin
Gastric
Vasoactive intestinal peptide
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2
Q

What are the major cell types in islets and what do they secrete?

A 
Beta cells - insulin
Alpha cells - glucagon
Delta cells - somatostatin
PP cells - PP
E cells - ghrelin
G cells - gastric
VIP
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3
Q

What are the target tissues of insulin?

A

Liver, adipose tissue, skeletal muscle

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4
Q

What are the target tissues of glucagon?

A

Liver, adipose tissue

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5
Q

What is normal plasma glucose?

A

3.3-6 mmol/L

After a meal 7-8mmol/L

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6
Q

What is the renal threshold of plasma glucose and what does that mean?

A

10mmol/L

Point at which kidneys can no longer reabsorb all the glucose so it is excreted in the urine

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7
Q

Can the renal threshold change?

A

In pregnancy, the renal threshold is decreased

In elderly, renal threshold is increased

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8
Q

What are the properties of insulin and glucagon?

A

Water soluble hormones
Carried dissolved in plasma - no special transport proteins
Short half life
Interact with cell surface receptors on target cells
Receptor with hormone bound can be internalised - inactivation

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9
Q

Describe insulin

A

Hormone of energy storage
Anti-gluconeogenic
Is anabolic - anti-lipolytic and anti-ketogenic

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10
Q

Describe the structure of insulin

A

Big peptide with an alpha helix structure
Consists of 2 unbranched peptide chains which are connected by 2 disulphide bridged to ensure stability
51 amino acids

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11
Q

Describe insulin synthesis from beta cells

A
  1. Pre-proinsulin translation, signal cleavage, proinsulin folding in RER
  2. Proinsulin transported to Golgi
  3. Proinsulin is cleaved to produce insulin and C-peptide
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12
Q

What is margination?

A

Movement of vesicles to cell surface

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13
Q

How do KATp channels regulate insulin secretion?

A

Glucose closes KATP channels in pancreatic beta cells
Metabolic inhibition reopens KATP channels
If metabolism low, KATP channels open, no insulin secreted
If metabolism high (lots of ATP), KATP channels shut, insulin secretion

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14
Q

What are the metabolic effects of insulin?

A

Increases glucose uptake into target cells and glycogen synthesis
In liver it increases glycogen synthesis by stimulating glycogen formation and by inhibiting breakdown
In muscles it inhibits breakdown of AA
In adipose tissue increases storage of triglycerides
Inhibits breakdown of FA

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15
Q

Describe the insulin receptor

A

Insulin binds to insulin receptor in cell surfaces
Receptor is dimer
2 identical subunits spanning the cell membrane
2 subunits are made of one alpha chain and one beta chain, connected by a single disulphide bond
Alpha chain on exterior of cell membrane
Beta chain spans cell membrane in single segment

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16
Q

What is glucagon?

A 
Hormone that opposes insulin
Acts to raise blood glucose levels
Glycogenolytic
Gluconeogenic 
Lipolytic
Ketogenic
Mobilise energy release
17
Q

Describe the synthesis of glucagon

A

large precursor molecule pre-proglucagon, undergoes post-translational processing to produce biologically active molecule
Synthesised in RER and transported to Golgi
Packaged into granules
Granules move to cell surface

18
Q

Describe the structure of glucagon

A

29 amino acids in 1 polypeptide chain

No disulphide bridges so flexible

19
Q

What are the metabolic effects of glucagon?

A

In liver, increases rate of glycogen breakdown (glycogenolysis)
Stimulates pathway for synthesis of glucose from AA (gluconeogenesis)
Net effect is rise in blood glucose levels
Stimulates lipolysis to increase plasma fatty acid

20
Q

What is type 1 diabetes caused by?

A

Absolute insulin deficiency
Autoimmune destruction of pancreatic beta cells
Absolute - pancreatic beta cells destroyed
Relative - secretory response of beta cell is abnormally slow or small

21
Q

What is type 2 diabetes caused by?

A

Normal secretion but relative peripheral insulin resistance
Defective insulin receptor mechanism, change in receptor number and/or affinity
Defective post-receptor events (insulin resistance)
Or excessive or inappropriate glucagon secretion

MEH (22 decks)

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