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gwen - diabetes > Normal Physiology > Flashcards

Normal Physiology Flashcards

1
Q

What stimulates insulin release?

A

Secretion is mediated by glucose entry into beta cells via GLUT-2 transporters

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2
Q

What are the endocrine cells of the pancreas?

A

Islets of langerhans

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3
Q

What are the main cells of the islets of langerhans?

A
  • Alpha - secrete Glucagon
  • Beta - Secrete insulin
  • Delta - Secrete somatostatin
  • F cells - secrete pancreatic polypeptide
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4
Q

What do alpha cells of the islets of langerhans secrete?

A

Glucagon

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5
Q

What do beta cells of the islets of langerhands secrete?

A

Insulin

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6
Q

What do delta cells of the islets on langerhans secrete?

A

Somatostatin

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7
Q

What are the products of the cleavage process of proinsulin (the precursor to insulin)?

A

Insulin and C-peptide

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8
Q

What is the physiology behind insulin release?

A

Increased glucose entry via GLUT-2 transporters. This increases ATP production in Beta cells, and causes ATP dependent K+ transporters to close, leading to a build up of K+ within the cell.

This depolarises the cells and opens voltage dependent Ca2+, which causes a large Ca2+ influx. The Ca2+ signals exocytosis and release of insulin

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9
Q

What is the direct action of insulin on glucose metabolism?

A

Insulin stimulates the mobilization of GLUT-4, which reside in the cytoplasm of unstimulated cells, in insulin receptive cells. GLUT4 migrates to the membrane and is then able to transport glucose into the cell. When insulin stimulation stops, the GLUT-4 transporters return to the cytoplasmic pool.

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10
Q

Which glucose transporter is insulin dependent?

A

GLUT-4

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11
Q

Which glucose transporters are not insulin dependent?

A

GLUT-1, GLUT-2 and GLUT-3

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12
Q

What are examples of tissues which have insulin dependent glucose receptors in them?

A
  • Muscle
  • Fat
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13
Q

Where are GLUT-3 transporters found?

A

Brain neurones and placenta

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14
Q

What effect does insulin have on the liver in a fed state?

A

Insulin activates hexokinase, which lowers glucose concentration in the hepatocyte, creating a concentration gradient into the cell. This is then converted to glycogen

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15
Q

What are the main stimuli for the release of insulin?

A
  1. Increased [BG]
  2. Increased [amino acids]
  3. Glucagon - insulin required to take up glucose created via gluconeogenesis stimulated by glucagon
  4. Incretin hormones - gastrin, secretin, CCK, GLP-1, GIP.
  5. Vagal nerve activity
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16
Q

Where are incretin hormones released from?

A

Released by ileum and jejunem in response to nutrients

17
Q

Why is response to IV glucose response less than response to oral glucose?

A

Due to incretin hormones, effects of insulin and vagal activity - ­ insulin by both direct effect on b cells and vagal stimulation of b cells, plus incretin effects

With IV glucose, only insulin is released.

18
Q

What stimuli decrease the release of insulin?

A
  1. Low [BG]
  2. Somatostatin
  3. Sympathetic a2 effects
  4. Stress - exercise and hypoxia
19
Q

What are the main effects of insulin?

A
  1. Glucose entry into cells
  2. Glycogenolysis in liver and muscle
  3. Amino acid uptake
  4. Increases Protein Synthesis/Inhibits proteolysis
  5. Increases Fat synthesis
  6. Inhibits gluconeogenesis in the liver
  7. K+ entry into cells
20
Q

What is glucagon?

A

Linear peptide hormone produced by a-cells of the pancreatic islet cells. Preproglucagon is cleaved to form glucagon and major proglucagon fragment (MPGF).

21
Q

What are the actions of glucagon?

A

Increased glycogenolysis/gluconeogenesis

22
Q

What stimulates the release of glucagon?

A
  • Low [BG]
  • High [amino acids]
  • Sympathetic innervation and epinephrine, b2 effect
  • Parasympathetic nerves
  • Cortisol
  • Stress - exercise, infection
  • Some GI hormones - CCK and gastrin
23
Q

What stimuli inhibit the release of glucagon?

A
  • Glucose
  • Free fatty acids (FFA) and ketones
  • Insulin
  • Somatostatin
24
Q

What are the actions of epinephrine on glucose metabolism?

A
  • Muscle glycogenolysis
  • Liver glycogenolysis
  • Gluconeogenesis
  • Lipolysis
25
Q

What are the actions of Cortisol?

A
  • Increased gluconeogenesis
  • Inhibition of glucose uptake
  • Lipolysis
  • Protein catabolism
26
Q

What are the main actions of GH in relation to glucose metabolism?

A
  • Gluconeogenesis
  • Inhibition of glucose uptake
  • Lipolysis
27
Q

What is the action of somatostatin?

A

Strongly suppresses the release of both insulin and glucagon in a paracrine fashion.

28
Q

What does an increase in plasma amino acids result in?

A

Increased release of insulin, glucagon and somatostatin

29
Q

What is the response to increased plasma glucose levels?

A

Insulin and somatostatin secretion

30
Q

What happens to glucose metabolism during exercise?

A
  • Increased glucose into skeletal muscle
  • Increased insulin sensitivity of muscle
31
Q

What hormones predominate the fasted state?

A

Glucagon

gwen - diabetes (11 decks)

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