CVS 8: Sympathetic nervous and Renin-Angiotensin systems Flashcards
Which region do parasympathetic and sympathetic nerves come from?
Parasympathetic: Craniosacral
Sympathetic: Thoracolumbar
What are baroreceptors and what effect do they have?
- pressure receptors
- increased baroreceptor firing leads to a decrease in sympathetic activity
- reduces hr and blood pressure
Where are baroreceptors found?
Aortic arch
Carotid arteries
Which neurotransmitter do parasympathetic nerves release?
Acetylcholine
Where is ACh released and where might other neurotransmitter substances be released?
SYMPATHETIC:
- Paravertebral sympathetic chain ganglion= ACh
- Effector end= noradrenaline
PARASYMPATHETIC:
- Paravertebral sympathetic chain ganglion= ACh
- Effector end= ACh
What are noradrenaline and adrenaline?
Catecholamines
Where is noradrenaline synthesised?
Terminal varicosities (small nodules at the end of the sympathetic nerve)
How is NA synthesised?
Tyrosine (enters cell) => L- DOPA => Dopamine (enters vesicle) => NA
What are the exceptions to Sympathetic neurones releasing noradrenaline?
The adrenal medulla releases mostly adrenaline instead of Na.
Sweat glands release ACh
How is NA released?
- granular vesicle fuses with varicosity membrane
- exocytic channel opens
- vesicle contents are expressed by exocytosis (requires ATP)
- reuptake of neurotransmitter
- biosynthesis to replenish neurotransmitter
What are the two ways that NA can be removed from the cleft?
- go back to the neurone hat released it
- taken up by extra neuronal cells
Name two enzymes responsible for the breakdown of the transmitter?
COMT (catechol-o-methyl transferase)
MAO (Monoamine oxidase)
What are the two groups of effects of adrenoreceptors? Which receptor do they use?
- Excitatory effect on smooth muscle- alpha adrenoreceptor mediated
- Relaxant effect on smooth muscle + stimulatory effects on heart - Beta adrenoreceptor mediated
Where are the three types of Beta receptors found?
- Beta 1
- cardiomyocytes
- smooth muscle of the GI tract
- Beta 2
- Vasculature
- Bronchi
- Uterine smooth muscle
- Beta 3
- Fat cells (brown fat)
- Possibly smooth muscle of GI tract
THERMOGENESIS
Where are the three types of Alpha receptors found?
- Alpha 1 receptors- found post-synaptically (mostly on effector cells)
- involved in mediating constriction of resistance vessels in response to sympathomimetic amines
- Alpha 2 receptors- found on presynaptic nerve membrane
- Activation by release transmitter causes -ve feedback INHIBITION of further transmitter release
- some post synaptic on VSMCs=> vasoconstriction
Explain how alpha 1 adrenoreceptors work
Gq-protein linked receptor
- when receptor is activated, Phospholipase C converts PIP2 to IP3
- IP3 causes IC stores of Ca2+ to be released
- Increase in IC Ca2+ causes muscle contraction
Explain how Beta adrenoreceptors work
Gs- protein linked receptor
- activates adenylate cyclase
- increases IC levels of cAMP
What are the two different effects Beta adrenoreceptors have dependent on the the of cell the receptor is found on?
SMOOTH MUSCLE and PLATELETS= cAMP is an inhibitor so it prevents activation, makes smooth muscle relax and prevents platelet activation
CARDIOMYOCYTES= cAMP activates the cells
Explain how A2 receptors work***??????
Gi- protein linked receptor
- inhibit adnenylate cyclase
- reduce IC cAMP
- oppose the effects of Ca2+ because it isn’t released from IC stores
What happens during anaphylaxis? And what can be administered to counteract this?
- Anaphylaxis= extreme allergic reaction, vasodilators released and bronchoconstriction
- Adrenaline administered
Which receptors does adrenaline bind to?
a1, a2, B1, B2
What is dopamine and which receptors does it bind to?
- precursor for catecholamines
- has some effect on a1 and B1 receptors
- has its own receptors in vasculature and the kidneys
Name a synthetic catecholamine which is used to treat asthma. Which receptors does it bind to?
Isoprenaline- B1 and B2
Name another synthetic catecholamine and state the receptor that it binds to
Phenylephrine
a1
