The Sympathetic ANS as a Model Flashcards
What is the ANS?
Regulate the function of internal organs
What is the function of the ANS?
Primarily maintains internal environment at homeostasis and cannot function independently of the CNS
What is the sympathetic nervous system of the ANS?
The second major subdivision of the ANS. This systems acts in concert with the PNS to regulate heart, secretory glands, and smooth muscles. “fight or flight”. Have vertebral chain so there is an all or nothing on/off switch
What is the parasympathetic nervous systems of the ANS?
Functions mainly to conserve energy and restore body resources. Reducing heart rate, increasing GI activity.
What is the sympathetic neurotransmitter?
Noradrenaline and adrenaline
What are the sympathetic receptors?
On smooth muscles called adrenergic receptors or adrenoceptors (a- b- receptors)
What is the parasympathetic neurotransmitter?
Acetylcholine
What are the parasympathetic receptors?
On smooth muscles called cholinoceptors (muscarinic receptors on smooth muscle)
Where is noradrenaline released?
Released at sympathetic nerve endings onto smooth muscle (known as neuroeffector junctions)
What are the effects of noradrenaline?
Its effects are supplemented by the action of adrenaline released into the bloodstream from the adrenal medulla (enhancing the all or nothing response)
Both adrenaline and noradrenaline have a very short plasma half-life and have to be administered parenterally, limiting their versatility
What are the four main subtypes of noradrenaline?
A1-, A2, B1-, B2
Where are A1- receptors found?
Small surface vessels e.g. GI tract, skin, Liver
Where are A2- receptors found?
Sympathetic nerve endings
Where are B1- receptors found?
Heart, Juxtaglomerular cells
Where are B2-receptors found?
Large deep blood vessels, bronchial tree, uterus, skeletal muscle, ciliary muscle (eye), liver
Where does noradrenaline have greaters activity?
A-adrenoceptors
Where does adrenaline have greater activity?
Equal activity to a- and b- adrenoceptors
What does it mean to have selective agents?
Agents that target distinct receptor subtypes (with far less side-effects)
E.g. b2-selective agonists
What is the main effect or noradrenaline, where is it found?
Mainly a-stimulation, used to raise blood pressure e.g. after shock, in surgery, causes vasoconstriction
What is the main use of adrenaline, where is it found?
Both a- and b- stimulation. uses as for noradrenaline, also to increase duration of effect of local anaesthetics by constricting surface blood vessels, increases heart rate, bronchodilation
What does cardioprotection mean?
Beta-antagonists e.g. beta-blockers - reduces the effects of noradrenaline and adrenaline
What is a a1-agonist, what is it used for?
Principal effect is vasoconstriction. Used to receive nasal constriction by constricting blood vessels, to raise blood pressure
What are some examples of a1-agonists?
Pseudoephedrine (decongestant), noradrenaline, phenylephrine (eye drops)
What is an example of a selective a2-agonist?
e.g. clonidine
Where are a2 receptors found?
Many sites including brain and spinal cord.
Stimulating a2 receptors cause
Inhibition of noradrenaline release, vasodilation
How does selectivie B2 agonists work?
On bronchial smooth muscle cause bronchodilation, miosis, vasodilation, relaxation of uterus, tremor, glycogenolysis
What are the main uses of B2 agonists?
bronchodilation, delay premature labour, treat hyperkalaemia
What are examples of B2 agonists?
Salbutamol, terbutaline, eformeterol, salametrol
What are some side effects of B2 agonists?
tachycardia, headache, fine tremor, hypokalaemia
What are selective B1 agonists?
Predominately on myocardium. Provide inotropic support in infarction, cardiac surgery
What are some examples of B1 agonists?
Dobutamine, dopamine
What are A1 antagonists?
Used in hypertension - cause peripheral arterial vasodilation by blocking effects of released noradrenaline. Also used in patients with poor circulation or BPH
What are some examples of A1 antagonists?
Doxazosin, terazosin, prazosin, tamulosin
What are some side effects of A1 antagonists?
dizziness, postural hypotension, reflex tachycardia
What are B1 antagonists? (b-blockers)
reduction of sympathetic ‘tone’ especially heart rate - sometimes called cardio protective, protecting the CV system against excessive sympathetic activity
What are some examples of B1 antagonists?
Metoprolol
What is ISA
intrinsic sympathomimetic activity (i.e. partial agonist like effects) which may cause less bradycardia & cold extremities e.g. celiprolol, pindolol
What is the main use of B1 antagonists?
angina, arrhythmias, hypertension, post-MI recovery, heart failure
What B1 antagonists are lipid soluble?
They can cross the blood brain barrier e.g. metoprolol, propranolol, bisoprolol
What B1 antagonists are water soluble?
Cannot cross BB barrier. Avoid or reduce dose in renal impairment e.g. atenolol, celiprolol, nadolol
What are side effects of B-antagonists?
Bronchospasm (avoid in respiratory disease), bradycardia, fatigue, cold extremities, loss or libido, erectile dysfunction, vivid dreams, sleep disturbance, can mask hyppoglycaemia
