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Physiology > Endocrine Pancreas > Flashcards

Endocrine Pancreas Flashcards

1
Q

What two substances work together to regulate blood glucose after a meal and during fasting?

A

insulin and glucagon

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2
Q

What part of the endocrine pancreas is responsible for synthesizing hormones?

A

pancreatic islets of langerhans

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3
Q

What cells of the endocrine pancreas produce insulin?

A

beta cells

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4
Q

Where are beta cells located?

A

most are in center of islet

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5
Q

What cells of the endocrine pancreas produce glucagon?

A

alpha cells

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6
Q

Where are alpha cells located?

A

most are around outer rim of islet

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7
Q

What cells of the endocrine pancreas produce somatostatin?

A

delta cells

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8
Q

Where are delta cells located?

A

interspersed around beta and alpha cells

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9
Q

What connects alpha cells to each other, beta cells to each other, and alpha cells to beta cells?

A

gap junctions

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10
Q

What allows for communication among islet cells?

A
  • gap junctions
  • blood supply
  • innervation by adrenergic, cholinergic, and peptidergic neurons
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11
Q

What was the first hormone isolated from animal sources, first to have structure determined and mechanism of action described?

A

insulin

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12
Q

Which hormone has an amino acid sequence that varies by species with certain segments highly conserved within vertebrates?

A

insulin

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13
Q

Insulin is synthesized as preprohormone with what 4 peptides?

A
  • signal peptide
  • A and B chains
  • C chain (connecting peptide)
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14
Q

What is the structure of insulin?

A

peptide hormone with 2 chains (A chain and B chain) and 3 disulfide bridges

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15
Q

What do the three disulfide bridges of insulin link?

A
  • 2 brdiges link A and B chains together
  • third bridge is within the A chain
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16
Q

Describe the steps to synthesize insulin.

A
  • synthesized as preprohormone with four peptides
  • proinsulin sent to ER, insulin folds and disulfide bridges form
  • golgi packages into granules, proteases cut C-peptide
  • secretion via exocytosis
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17
Q

The most important stimulator of insulin secretion is what?

A

blood glucose

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18
Q

Describe regulation of insulin secretion.

A
  1. transport of glucose into beta cell via GLUT 2 transporter (facilitated diffusion)
  2. glucose immediately phosphorylated by glucokinase – ATP is a product
  3. ATP closes ATP sensitive K channels – depolarizes membrane
  4. depolarization opens voltage gated Ca channels – Ca flows into cell, inrceasing intracellular Ca
  5. increase in Ca causes exocytosis of insulin granules into venous blood
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19
Q

Does oral or IV glucose cause greatest response due to an “incretin” effect?

A

oral

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20
Q

What substances other than blood glucose stimulate insulin secretion?

A
  • amino acids
  • ketoacids
  • FFA
  • K+, Ca
  • GIP, vagal stimulation (Ach), drugs (sulfonylurea drugs)
  • glucagon
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21
Q

What substances other than blood glucose inhibit insulin secretion?

A
  • fasting
  • exercise
  • somatostatin
  • leptin
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22
Q

Describe the mechanism of action of insulin in peripheral cells.

A
  1. insulin binds alpha subunits, causes conformational change, activates tyrosine kinase in beta subunits
  2. tyrosine kinase phosphorylates other proteins/enzymes involved in physiologic actions of insulin
  3. insulin receptor complex internalized by target cell to be degraded, stored, or recycled
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23
Q

Tyrosine kinase (insulin receptor) has four subunits. Where are they?

A

2 alpha subunits extracellular
2 beta subunits span the mmebrane, have tyrosine kinase on intracellular side

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24
Q

What are the actions of insulin?

A
  • when nutrients are available, insulin makes sure those nutrients are stored
  • insulin directly stimulates glucose uptake into muscle and fat, but not liver
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25
Q

How does insulin store nutrients?

A
  • glucose stored as glycogen in muscle and liver
  • FFA stored as adipose tissue
  • Protein stored in muscle
26
Q

What glucose transporters are insulin independent?

A
  • GLUT 1 found in brain, RBC
  • GLUT 2 found in liver, beta cells of pancreas
  • GLUT 3 found in brain
27
Q

What glucose transporters are insulin dependent?

A
  • GLUT 4 found in fat, muscle, heart
28
Q

Transport of glucose in intestine and kidneys is NOT regulated by insulin, but is ____ dependent and carried out by what transporter?

A
  • Na dependent
  • GLUT 5 transporter in intestine
29
Q

What are the effects of insulin on carbohydrate metabolism?

A
  • decreases blood glucose
  • increases glucose transport into muscle and adipose
  • promotes glycogen formation in liver and muscle
  • inhibits gluconeogenesis and glycogenolysis
30
Q

What are the effects of insulin on lipid metabolism?

A
  • inhibits mobilization and oxidation of FA
  • inhibits ketogenesis in liver
  • promotes FFA storage as triglycerides
  • inhibits FFA uptake in muscle
  • inhibits lipolysis
31
Q

What are the effects of insulin on protein metabolism?

A
  • overall anabolic
  • decreases blood AA
  • increases AA and protein uptake by tissues
  • increases protein synthesis
  • inhibits protein degradation
32
Q

What are other general effects of insulin not related to a specific metabolism?

A
  • promotes K+ uptake into cells by increasing activity of Na/K ATPase
  • promotes phosphate, Mg++ uptake into cells
  • insulin decreases appetite via the satiety center of hyothalamus
  • excess insulin causes hypoglycemia which stimulates cortisol release to increase appetite
33
Q

What acts as a protective mechanism during acute illness to preserve brain’s glucose supply?

A

insulin resistance

34
Q

Insulin resistance can occur via alterations in what?

A

insulin receptors
(either by decreasing number of receptors or decreasing affinity of receptors for insulin)

35
Q

What is insulin resistance?

A
  • when cells fail to respond normally to insulin
  • insulin overproduced: blood insulin and glucose remain high
36
Q

What can cause insulin resistance other than alterations to insulin receptors?

A
  • hormones (cortisol, GH, thyroid hormones, epilepsy, estrogen/progesterone)
  • obesity
  • liver or kidney failure
  • sepsis
  • insulin antibodies
37
Q

What pathophysiology is associated with insulin?

A
  • diabetes mellitus (type 1 and 2)
  • insulinoma
38
Q

Type 1 diabetes mellitus is due to what?

A

insulin deficiency

39
Q

Type 2 diabetes mellitus is due to what?

A

insulin resistance

40
Q

Insulinoma results in what?

A

excessive insulin production by beta cell tumor

41
Q

What can result from lack of insulin or lack of insulin action?

A
  • hyperglycemia
  • hyperlipidemia
  • peripheral tissue protein catabolism
42
Q

True or false: glucagon sequence is identical in all species.

A

true

43
Q

What stimulates glucagon release?

A
  • hypoglycemia
  • protein/AA
  • fasting
  • stress (especially infection)
  • intense exercise
  • cholecystokinin
44
Q

What inhibits glucagon secretion?

A
  • glucose
  • insulin
  • somatostatin
45
Q

Glucagon works through stimulation of what to mediate effects?

A

G-protein/cAMP

46
Q

What are the effects of glucagon?

A
  • increases glycogenolysis, gluconeogenesis, lipolysis, ketoacid formation
  • little to no effect on glucose utilization by peripheral tissues
47
Q

The action of glucagon are opposite the actions of what hormone?

A

insulin

48
Q

What pathophysiology is associated with glucagon?

A
  • glucagonoma
  • hyperglucagonemia/diabetes mellitus associated with infection
49
Q

In hyperglucagonemia, what happens to the ratio of glucagon:insulin?

A

it increases

50
Q

What is the glucagonoma?

A

tumor of alpha cells in pancreas

51
Q

What results from a glucagonoma?

A

results in diabetes mellitus and necrolytic migratory erythema

52
Q

Somatostatin is stimulated by all nutrients, but inhibited by what?

A

insulin

53
Q

What inhibits somatostatin?

A
  • insulin and glucagon
  • GI hormones
  • GI motility, enzymes, gastric acid secretion
54
Q

Somatostatin is secreted by what?

A
  • delta cells of pancreas
  • hypothalamus
  • GI cells
55
Q

How does adipose tissue act as an endocrine organ?

A

secretes hormones influencing feeding behavior, insulin sensitivity, glucose transport

56
Q

What is the action of leptin secreted by adipose tissue?

A
  • inhibits appetite by inhibiting neuropeptide Y
  • increases BMR
57
Q

What is the action of neuropeptide Y?

A

increase appetite

58
Q

What is the action of adiponectin secreted by adipose tissue?

A
  • improves insulin sensitivity
59
Q

High adiponectin results in low risk of?

A

type II diabetes

60
Q

Low adiponectin results in?

A

obesity and diabetes (cats)

61
Q

What substances are secreted by adipose tissue?

A
  • leptin
  • tumor necrosis factor - alpha
  • adiponectin

Physiology (18 decks)

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