Introduction. Flashcards
What is an agonist?
A substance that binds to a receptor and activates it.
What is an antagonist?
A substance that binds to a receptor and either blocks it from functioning or it reduces the effects of that receptor.
Adrenergic agonists will stimulate what kind of receptors?
Adrenergic receptors.
What physiological responses are produced when an adrenergic agonist binds to an adrenergic receptor?
Physiological responses that are similar to those of catecholamines.
What are the 2 classes of actions that adrenergic agonists can have?
Direct effects.
Indirect effects.
What are the effects of direct adrenergic agonists?
They bind to and stimulate adrenergic receptors.
What are the effects of indirect adrenergic agonists?
They lead to the release of catecholamines from adrenergic neurons.
What is the major neurotransmitter of adrenergic neurotransmission?
Norepinephrine.
Where is norepinephrine synthesised and stored?
At the terminal end of the pre-synaptic neuron.
What is the first step of norepinephrine synthesis in the pre-synaptic neuron?
Tyrosine is taken from the extracellular environment and converted to DOPA within the cell.
What is the rate limiting step in tyrosine formation?
The conversion of tyrosine to DOPA.
What enzyme converts tyrosine to DOPA?
Tyrosine hydroxylase.
What is the 2nd step of norepinephrine formation after DOPA has been formed?
DOPA is converted by DOPA decarboxylase to dopamine.
What is the 3rd step of norepinephrine formation after dopamine has been formed?
Dopamine is converted to norepinephrine by dopamine beta-hydroxylase.
What steps of norepinephrine formation are carried out in the cytoplasm?
All of the steps that lead to the formation of dopamine.
What steps of norepinephrine formation are carried out in the synaptic vesicle?
The conversion of dopamine to norepinephrine takes place in the synaptic vesicle.
When will the vesicles containing norepinephrine be released?
Following an action potential.
What happens after norepinephrine has been released into the synaptic cleft?
It travels to the post synaptic neuron and binds to adrenergic receptors on the cell membrane.
What happens once norepinephrine has bound to to adrenergic receptors on the post-synaptic cell membrane?
It causes an action potential to be generated in the post-synaptic neuron and this leads to cellular effects.
What happens to norepinephrine in the synaptic cleft after it has induced cellular responses in the post-synaptic neuron?
It is either taken back into the pre-synaptic neuron or it is metabolised by certain enzymes.
What name is given to the process where norepinephrine is taken back into the pre-synaptic neuron?
Re-uptake 1
What is the function of the pre-junctional receptor on the pre-synaptic cell of adrenergic neurons?
It detects norepinephrine in the synaptic cleft and provides negative feedback to stop the release of norepinephrine.
What are the 2 classes of adrenergic receptors?
Alpha receptors.
Beta receptors.
What are the 2 types of alpha receptors?
Alpha-1 receptors.
Alpha-2 receptors.
What are the 2 types of beta receptors?
Beta-1 receptors.
Beta-2 receptors.
Beta-3 receptors.
What kind of adrenergic receptors are of no medical significance?
Beta-3 receptors.
Where are alpha-1 receptors located?
On the post synaptic membrane of the effector organ.
Where are alpha-2 receptors located?
On pre-synaptic nerve endings.
On post synaptic neurons of the beta cells of the pancreas and on blood vessels.
What happens when alpha-1 receptors are activated in blood vessels?
Vasoconstriction.
Alpha-1 receptors are mostly affected by what 3 hormones and in what level of potency?
Epinephrine.
Norepinephrine.
Isoproterenol.
What kind of receptors are alpha-1 receptors?
GCPR’s.
What protein are the GCPR’s of alpha-1 receptors connected to?
A GQ protein.
What happens to the GQ receptor when alpha-1 receptors are activated?
It is activated and the activates phospholipase C which cleaves PIP-3 to form IP-3 and DAG to act as 2nd messengers.
What is the function of IP-3 and DAG in alpha-1 receptors?
AG activates a protein kinase.
IP-3 releases calcium which activates smooth muscle.
Alpha-2 receptors are linked to what protein?
A GI protein.
What is the function of the GI protein that is bound to alpha-2 receptors?
It prevents calcium ions being released into the pre-synaptic neuron so no neurotransmitter can be released.
It inhibits adenylyl cyclase and this leads to smooth muscle contraction.
What protein are beta-1 and beta-2 receptors linked to?
The stimulatory G protein which is GS.
What is the function of the GS protein that is bound to beta-1 and beta-2 receptors?
It activates adenylyl cyclase which converts ATP to cyclic AMP.
What are the effects on the body once the GS protein that is bound to beta-1 and beta-2 receptors has been activated?
It stimulates heart muscle contraction.
It stimulates smooth muscle relaxation.
It stimulates glycogenolysis.
Where are beta-1 receptors located?
In the heart.
In the juxta-glomerular apparatus of the kidney.
In fat cells.
Will beta-1 receptors have a higher affinity for epinephrine or norepinephrine?
It has equal affinity for both.
Increases in heart rate will always be due to what kind of receptors?
Beta-1 receptors.
Where are beta-2 receptors located?
In the blood vessels of skeletal muscle.
In the liver.
In the smooth muscles of the bronchus.
In the GI tract.
In the uterus.
Will beta-2 receptors have a higher affinity for epinephrine or norepinephrine?
Epinephrine.
Epinephrine binding to the beta-1 receptors of the heart will have what 3 effects on the heart?
Increased heart rate.
Increased contractility of the heart.
Increased cardiac output.
Norepinephrine binding to the beta-1 receptors of the heart will have what 2 effects on the heart?
Initial increase in heart rate before it is reduced by vagal stimulation.
Increased contractility of the heart.
Epinephrine binding to the beta-1 receptors of the heart will have what 2 effects on blood pressure?
Increase in systolic pressure.
Decrease in diastolic pressure.
Norepinephrine binding to the beta-1 receptors of the heart will have what 2 effects on blood pressure?
Increase in systolic pressure.
Increase in diastolic pressure.
What receptors are found in the blood vessels of the skin, the mucosa and the kidneys?
Alpha-1 receptors.
Alpha-2 receptors.
Epinephrine binding to the alpha-1 receptors and alpha-2 receptors of the blood vessels will have what effects on blood vessel size?
Vasoconstriction.
Norepinephrine binding to the alpha-1 receptors and alpha-2 receptors of the blood vessels will have what effects on blood vessel size?
Vasoconstriction.
What receptors are found in the blood vessels of the splanchnic organs and heart?
Alpha receptors.
Beta-2 receptors.
Epinephrine binding to the alpha receptors and beta-2 receptors of the blood vessels will have what effects on blood vessel size?
Vasodilation.
Are the compensatory changes to the heart rate following the release of epinephrine?
No, the heart will continue to beat at a high rate.
What adrenergic receptors are found in the bronchial muscle?
Beta-2 receptors.
What effect will epinephrine have on the beta-2 receptors of the bronchial muscle?
Relaxation of the muscle.
What adrenergic receptors are found in the smooth muscle of the GIT?
Alpha-1 receptors.
Alpha-2 receptors.
Beta-2 receptors.
What effect will epinephrine have on the receptors that control the smooth muscle of the GIT?
Relaxation of the muscles.
What effect will norepinephrine have on the receptors that control the smooth muscle of the GIT?
Relaxation of the muscles.
What receptors are found on the detrusor muscle of the bladder?
Beta-2 receptors.
What receptors are found on the sphincter muscle of the bladder?
Alpha-1 receptor.
What effect will epinephrine have when it binds to the detrusor muscle of the bladder?
Relaxation.
What effect will epinephrine have when it binds to the sphincter of the bladder?
Contraction.
What effect will norepinephrine have when it binds to the sphincter of the bladder?
Contraction.
What adrenergic receptors are found on the uterus?
Alpha-1 receptors.
Alpha-2 receptors.
Beta-2 receptors.
What effect will epinephrine have when it binds to the adrenergic receptors of the uterus?
Relaxation/contraction of the uterus.
What adrenergic receptors are found on the vas deferens of the male?
Alpha-1 receptors.
What effect will epinephrine have when it binds to the adrenergic receptors of the vas deferens of the male?
Ejaculation.
What effect will norepinephrine have when it binds to the adrenergic receptors of the vas deferens of the male?
Ejaculation.
What adrenergic receptors are found on the pilomotor muscles of the skin?
Alpha-1 receptors.
What effects will norepinephrine have on the adrenergic receptors of the pilomotor muscles of the skin?
Contraction.
What effects will epinephrine have on the adrenergic receptors of the pilomotor muscles of the skin?
Contraction.
What adrenergic receptors are found on the radial muscle of the iris?
Alpha-1 receptors.
What effects will norepinephrine have on the adrenergic receptors of the radial muscle of the iris?
Contraction/pupil dilation.
What effects will epinephrine have on the adrenergic receptors of the radial muscle of the iris?
Contraction/pupil dilation.
What adrenergic receptors are found on the ciliary muscles of the eye?
Beta-2 receptors.
What effects will epinephrine have on the adrenergic receptors of the ciliary muscles of the eye?
Relaxation.
What effects will norepinephrine/epinephrine have when it binds to beta-2 and alpha-1 receptors of the liver?
Glycogenolysis.
What effects will norepinephrine/epinephrine have when it binds to alpha-2 and beta-2 receptors on the beta cells of the pancreas?
Alpha-2 receptors lead to decreased secretion.
Beta-2 receptors lead to increased secretion.
What are the major functions of alpha-1 receptors?
Vasoconstriction of blood vessels.
Increasing the muscle tone in sphincter muscles.
What is the major function of alpha-2 receptors?
Vasoconstriction of blood vessels.
What is the major function of beta-1 receptors?
An increase in cardiac output.
Vasodilation within skeletal muscle.
What is the major function of beta-2 receptors?
Relaxation of smooth muscle in certain areas of the body.
Glycogenolysis.
Are catecholamines well absorbed via the oral route?
No.
Are catecholamines well absorbed via the subcutanous route?
Yes, but they are absorbed very slowly.
What enzymes will metabolise catecholamines?
Mono-amine oxidase.
Catechol-O-methyltransferase.
How are catecholamines excreted?
In urine.
