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Pharmacology for Anaesthetists > Receptor Physiology > Flashcards

Receptor Physiology Flashcards

1
Q

Classify receptors

A
  1. Ionotropic (channel-linked)
  2. Metabotropic (G-protein coupled)
  3. Enzyme (kinase)-linked
  4. Gene transcription linked nuclear receptors
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2
Q

Classify common Ionotropic (channel-linked) receptors. Give common examples

A

LIGAND GATED ION CHANNELS

  1. nicotnic Ach receptor
  2. GABA (type A receptor)
  3. NMDA receptor
  4. 5-HT3 receptor

VOLTAGE GATED ION CHANNELS

  • Ca channels
  • Na Channels
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3
Q

How to ionotropic ion channels work

A

Facilitate movement of ions down their concentration gradient
Passive
Rapid

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4
Q

What is the name of the enzyme and precursors that synthesize acetylcholine

What is the name of the enzyme that catabolises acetylcholine

A

Synthesis
- Choline acetyltransferase (precursors: Acetyl CoA + Choline)

Catabolism
- Acetylcholinesterase to choline and acetate

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5
Q

Describe the structure of the nicotinic Ach receptor

A

Pentameric ligand gated ion channel with 5 subunits including (clockwise from 12 o’clock)

  1. Alpha
  2. gamma (fetal) / Epsilon (adult)
  3. Delta
  4. Alpha
  5. Beta

Active binding sites of Ach are on the two alpha subunits

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6
Q

Describe the functions of the nicotinic receptors at the skeletal muscle NMJ in terms of the following:

  1. Postsynaptic nicotinic receptors
  2. Pre-synaptic nicotinic receptors
  3. Perijunctional nicotinic receptors
A
  1. Postsynaptic nicotinic receptors
    - Initiate muscle contraction
  2. Pre-synaptic nicotinic receptors
    - Mobilization of additional Ach for pre-synaptic release
  3. Perijunctional nicotinic receptors
    - On perijunctional cells but not normally involved in NM transmission. But these receptors are upregulated with prolonged immobilization or following thermal burns
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7
Q

How are central Ach receptors affected by anaesthetic drugs

A

Barbiturates, Propofol and Volatile anaesthetic agents inhibit excitatory nicotinic Ach receptors in the CNS

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8
Q

What is the endogenous ligand for GABA type A receptor and how do anaesthetic agents influence this receptor

A

Engogenous ligand is gamma aminobutyric acid

Activity of GABA type A is enhanced by

  1. Barbiturates
  2. Propofol
  3. R-etomidate
  4. Volatile anaesthetic agents
  5. Benzodiazepines
  6. Glucocorticosteroids
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9
Q

Where is the benzo and volatile/propofol/etomidate/barbiturates binding sites on the GABA type A receptor

A 
Pentameric ligand gated ion chanel (Cl- ionopore)
5 subunits (from 12 o'clock)
  1. Beta
  2. alpha
  3. Beta
  4. alpha
  5. Gamma

Benzo site - between alpha and gamma

All other GA bind to Beta subunit producing positive allosteric modulation

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10
Q

What is the NMDA receptor named after. What is the endogenous and exogenous ligands.

Which anaesthetic agents influence this receptors

A

N-methyl-D-aspartate exogenous ligand for this receptor

endogenous ligands

  1. Glutamate (excitatory)
  2. Glycine (inhibitory)

Ketamine and Magnesium block NMDA receptors

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11
Q

How does the 5HT3 receptor differ from the other 6 5HT receptors and which drugs act on this receptors

A

5HT3 receptor is an ion gated channel

All the other 5HT receptors are G-protein coupled receptors

Ondansetron and Granisetron act on this receptor.

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12
Q

Differentiate between the activated and inactivated seven serpentine transmembrane heterotrimeric G-protein coupled receptor

A

Activated

  • -> Alpha subunit of G-protein is bound to GTP
  • -> Beta and gamma subunits are detached

Inactive:

  • -> Alpha subunit is bound to GDP
  • -> Beta and gamma subunits are attached
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13
Q

Describe the mechanism of action of Gs, Gi and Gq proteins

A

Affects vary according to ligand and tissue site

Gs –> stimulate Adenylate Cyclase –> Increase IC cAMP –> + Protein Kinase A –> Variable effects but often increase IC Ca2+

Gi –> Inhibit Adenylate Cyclase –> Reduced cAMP
(Also activates phospholipase A2)

Gq –> stimulate Phospholipase C –> Increase IP 3 ( increase Ca2+ release ER) AND Increase DAG (Activates protein kinase C)

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14
Q

List Examples of the different Gs, Gi and Gq receptors

A

Gs

  1. B1, B2, B3
  2. D1
  3. H1, H2
  4. Glucagon
  5. ACTH, LH, FSH, VIP, GHRH, TRH
  6. Prostacyclin (PGI2)

Gi

  1. a 2
  2. M2 and M4
  3. 5-HT 1
  4. Opioid receptors
  5. GABA type B receptors

Gq

  1. a1
  2. M1, M3, M5
  3. 5-HT2
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15
Q

What breaks down cAMP

A

Selective PDE inhibitors
- PDEi 1,2,3,4,5,7,and 10

Methylxanthines

  • Caffeine
  • Aminophylline
  • Theophylline
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16
Q

Why are muscarinic receptors so named

A

Muscarine is an alkaloid extracted from various mushrooms and mimics certain actions of Ach.

17
Q

Where are M2 cholinergic receptors found and how do they work

A

Heart
- predominantly on the atria (some ventricular)

Gi protein mediated. Inhibition AC –> reduced cAMP –> negative inotropy (atria), chronotropy and dromotropy.

18
Q

List and describe examples of enzyme (kinase) - linked receptors

A
  1. ANP
    - -> Membrane bound receptor with intrinsic guanylyl cyclase activity –> increase cGMP IC –> phosphorylation of IC enzymes to mediate effects
  2. NO
    - -> Cytosolic guanylyl cyclase stimulated –> cGMP (rather than membrane bound)
  3. Insulin
    - -> Tyrosine kinase membrane receptor
    - -> Ligand binds –> phosphorylation of the tyrosine residues –> activation tyrosine kinase –> phosphorylation of other protein targets –> many effects of insulin (insertion GLUT and gene transcription changes)
19
Q

Describe the receptor binding mechanism for steroid and thyroid hormones

A

Traverse cell membrane –> bind to cytosolic cell receptors. Hormone-receptor complex is now permitted into the cell nucleus to act as a Ligand-regulated transcription factor.

The cytosolic proteins are normally held in an inactive form by other cytosolic inhibitory proteins.

20
Q

Describe the two types of adrenosteroid receptors and where they are found

A

GR
MR

GR widespread

MR nephron and colon epithelial tissue.

21
Q

Describe the mechanism of action of pioglitazone

A

Antidiabetic drug

Agonist at a nuclear receptor (Peroxisome Proliferator - activated receptor) –> controls protein transcription associated with increased sensitivity to insulin in adipose tissue

22
Q

Describe the insulin receptor and how it works

A
  • Enzyme linked receptor
  • 2 alpha + 2 beta subunits (Heterotetramer)
  • Alpha unit = ECF = binding site
  • Beta unit = ICF + spans membrane + contains tyrosine kinase

Insulin binds alpha units –> brings beta units closer together –> mutual phosphorylation of tyrosine kinase + activation of tyrosine kinase which leads to:

  1. Activation transcription factors –> cell growth / division
  2. Protein synthesis / lipogenesis / glycogen formation
  3. Translocation GLUT 4 to cell membrane to increase glucose uptake (from cytosolic vesicle)

Pharmacology for Anaesthetists (37 decks)

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