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Physiology > Mechanism of Hormone Action and Second Messengers > Flashcards

Mechanism of Hormone Action and Second Messengers Flashcards

1
Q

What is threshold response?

A

minimal concentration of hormone needed to elicit measurable response

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2
Q

The final outcome of interaction of hormone on cells depends on several factors. List them.

A
  • hormone concentration
  • receptor number
  • affinity of hormone for receptor
  • duration of exposure to hormone
  • intraceullar factors such as enzymes and cofactors
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3
Q

Hormone action responsiveness is expressed as?

A

a dose-response relationship

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4
Q

What does maximum response mean?

A

a further increase in hormone will elicit no more response

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5
Q

The magnitude of a response is correlated with what?

A

hormone concentration

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6
Q

What is expressed as the concentration of the hormone that produces half-max response?

A

sensitivity

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7
Q

Alterations in dose-response curve results from changes in what?

A

max responsiveness, sensitivity, or both

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8
Q

A decrease in responsiveness can be caused by what?

A

decrease in number of target cells or total receptors/cell, or concentration of enzymes activated by hormone

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9
Q

In what two ways can sensitivity be changed?

A
  • changing number of receptors
    OR
  • affinity of receptors
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10
Q

Define sensitivity.

A

The concentration of hormone producing 50% of maximal response

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11
Q

Down regulation of receptors does what to sensitivity?

A

decreases it

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12
Q

Up regulation of receptors does what to sensitivity?

A

increases it

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13
Q

What is down regulation of receptors?

A

either number or affinity of receptors decreases even when hormone concentrations is high

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14
Q

What is up regulation of receptors?

A

either number other than affinity of receptors increases

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15
Q

What is the general mechanism of hormone action?

A
  • hormone is recognized and binds to a membrane receptor –> hormone receptor complex
  • hormone receptor complex EITHER coupled to a signal generating mechanism OR must act as one itself
  • generated signal (second messenger) affects intracellular process by altering activity OR concentration of functional or structural proteins
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16
Q

Hormone receptor systems are where?

A

either on cell membrane or within the cell

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17
Q

What receptor system is classified according to membrane receptor structure OR second messenger system used, and usually incurs a rapid response?

A

Classic cell membrane receptor systems

18
Q

What receptor system does not use a second messenger system, but rather an enzyme system such as kinases, and usually incurs a rapid response?

A

catalytic cell membrane receptor systems

19
Q

What receptor system uses cytoplasmic or nuclear receptors, and usually incurs a slow reponse?

A

intracellular receptor systems

20
Q

What hormones use the adenylyl cyclase system?

A
  • Corticotropin releasing hormone/adrenocorticotropic hormone
  • follicle-stimulating hormone, luteinizing hormone
  • thyroid-stimulating hormone
  • antidiuretic hormone
  • calcitonin
  • parathyroid hormone
  • glucagon
21
Q

Can hormones use multiple hormone receptor systems?

A

Yes, some do

22
Q

What hormones use the phospholipase C system?

A
  • gonadotropin-releasing hormone
  • thyrotropin-releasing hormone
  • growth hormone-releasing hormone
  • angiotensin II
  • antidiuretic hormone
  • oxytocin
23
Q

Describe the steps of the adenylyl cyclase system.

A
  • hormone binds receptor coupled by a G protein
  • GTP binds G protein and activates adenylyl cyclase
  • cAMP produced and activates protein kinase A
  • intracellular proteins phosphorylated by protein kinase A, causing physiologic actions
  • phosphodiesterase degrades cAMP, shutting down system
24
Q

Describe the steps of the phospholipase C system.

A
  • hormone binds receptor coupled by G protein
  • GTP binds G protein and activates phospholipase C
  • phospholipase C liberates diacylglycerol (DAG) and IP3 from PIP2
  • IP3 causes Ca2+ release from ER or SR stores
  • Ca2+ and DAG activate protein kinase C, which phosphorylates proteins
25
Q

What hormones utilize the intracellular receptor systems?

A
  • glucocorticoids
  • sex hormones (estrogen, testosterone, progesterone)
  • aldosterone
  • vitamin D
  • thyroid hormones
26
Q

What receptor system uses either cytosolic or nuclear receptors?

A

intracellular receptor systems

27
Q

Describe the steps of the intracellular receptor system.

A
  • steroid hormone diffuses across membrane and binds receptor in cytosol or nucleus
  • receptor undergoes conformational change, complex dimerizes and binds to steroid responsive elements
  • complex is now a transcription factor – mRNA transcribed, translation occurs, new proteins, physiologic action
28
Q

Cell membrane receptor systems are linked to what?

A

one of two second messenger systems

29
Q

Almost all cell membrane receptor systems use what as coupling molecules?

A

G proteins

30
Q

G proteins are active when what is bound?

A

GTP

31
Q

G protins are inactive when what is bound?

A

GDP

32
Q

True or false: G proteins can be inhibitory or stimulatory.

A

True

33
Q

In catalytic receptor systems, catalytic receptors on cell surface are associated with what?

A

enzymes on intracellular side

34
Q

Describe the guanylyl cyclase enzyme system of catalytic receptor systems.

A

GTP –> cGMP –> cGMP-dependent kinase –> phosphorylates proteins

35
Q

Atrial natriuretic peptide and nitric oxide use what enzyme system?

A

Guanylyl enzyme system

36
Q

Describe the serine/threonine kinase enzyme system of catalytic receptor systems.

A

use either protein kinase A or C, as well as Ca2+-calmodulin-dependent protein kinase and mitogen-activated protein kinases to phosphorylate serine and threonine

37
Q

For receptor tyrosine kinases in catalytic receptor systems, tyrosine kinase activity lies where?

A

within the receptor itself

38
Q

Since the tyrosine kinase activity lies within the receptor itself, when the hormone binds what occurs?

A

intracellular portion of receptor phosphorylates itself

39
Q

Tyrosine kinase-associated receptors associate with other proteins that have what?

A

tyrosine kinase activity

40
Q

Can the intraceullar portion of tyrosine kinase-associated receptors phosphorylate itself?

A

No, only true receptor tyrosine kinases

Physiology (18 decks)

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