What happens to the heart under a sympathetic response?
Heart rate and contractility increase - to increase cardiac output, so more blood goes to muscles. NA and A act on B1 adrenoreceptors, found at:
- SAN: increases freq of pacemaker potentials -> inc HR (tachycardia)
- Conduction system: inc rate of impulses through atria to ventricles
- Muscle cells: inc force of contraction of atria/ventricles -> inc SV
CO = SV x HR
Helps CO rise from a resting 5 l/m to over 20 l/m during exercise
What happens in the lungs under a sympathetic response?
Lungs don't receive sympathetic innervation - bronchioles contain B2-adrenoreceptors which are activated by circulating adrenaline to produce bronchodilation.
So increased air into lungs for greater O2 uptake/CO2 removal
Describe the central control of the sympathetic nervous system
Hypothalamus receives danger/fight or flight signal, it then stimulates the rostral ventral lateral medulla (RVLM), whcih sends impulses down the spinal cord to preganglionic nerves and intermeriolateral medulla of spinal cord -> stimulating sympathetic nerves
What is the effect of sympathetic activity on blood vessels?
NA and A act on a1-adrenoreceptors
- Constriction of arterioles (vasoconstriction) -> increase in TPR
- Constriction of veins -> inc blood to the heart, so increase in Cardiac Output
Increase in CO x TPR will mean an increase in BLOOD PRESSURE
There are also B2-adrenoreceptors on coronary and skeletal muscle arteries -> these dilate increasing blood flow to heart and sk muscle.
What is the effect of the sympathetic stimulation on the kidney?
Sympathetic nerves act on B1 adrenoreceptors found on granular cells in the kidney -> this stimulates release of renin
Renin -> Ang I --ACE--> Ang II -> Increased BP + CO (how?):
- Vasoconstriction of arterioles -> inc TPR
- Release of aldosterone -> Na+/H2O retention -> inc BP + CO
Therefore B1 blockers are successful at decreasing BP.
What is the action of sympathetic innervation in the liver and skeletal muscle in terms of metabolism?
Stimulation of a/b-adrenoreceptors
- Breaks down glycogen into glucose (glycogenolysis)
- Promotes glucose synthesis (gluconeogenesis)
Increasing breakdown of sugars -> forming glucose -> more resp -> more ATP
What is the effect of sympathetic innervation on the pancreas in terms of metabolism?
Stimulation of a-adrenoreceptors
- Decrease release of insulin from Beta-cells* - also stops insulin-induced reductions in glycogenolysis, gluconeogenesis, lipolysis - so you get more of these!
*Less insulin being taken up means less glucose is taken up, so you want glucose to go to areas where energy is needed.
- Glucagon released from alpha-cells
What is the effect of sympathetic innervation on adipose tissue in terms of metabolism?
Stimulation of B-adrenoreceptors
- Increase lipolysis : triglycerides into free fatty acids + glycerol
- Free fatty acids undergo B-oxidation into Acetyl CoA, enter Krebs
- Glycerol - recycled into glycolysis pathway
- Both increase ATP yield
What happens to the GI tract/bladder upon sympathetic stimulation?
Stimulation of a1/2 and B2 adrenoreceptors induces INHIBITION of GI motility
Activation of a1-adrenoreceptors evokes contraction of bladder sphincter, B2-adrenoreceptors induces relaxation of smooth muscle allowing filling.
Bowel/bladder function non-essential during 'fear-fight-flight'
What happens to the eye under sympathetic innervation?
Stim of a1 on dilator pupillae causes dilation of pupil -> more light in retina -> more acute sight
The sweat glands are unique in terms of their sympathetic innervation, how is this and what is the action?
Release of ACh acting at MUS receptors (not NA like normal post-ganglionic) -> induces SWEATING - temperature control during FFF