Control of blood pressure and volume
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What is the role of the CNS in reflex responses?
Modulate reflex responses Initiate responses
Describe the baroreceptor reflex
Homeostatically regulates ABP
Where are baroreceptors found?
Carotid arteries Aortic arch
Where do afferents from baroreceptors go?
To the medulla
What sort of receptors are baroreceptors?
Stretch receptors
What are responses of baroreceptor activity?
Increased sympathetic activity Decreased parasympathetic activity
What is the effect of increased sympathetic activity?
Increased noradrenaline on a adrenoreceptors Venous vessels constrict increasing end diastolic volume Arterioles constrict reducing capillary hydrostatic pressure and increasing total peripheral resistance
What is the effect of decreased parasympathetic activity?
Increased noradrenaline on B1 adrenoreceptors Increase in heart rate Increased contractility increase end systolic volume Increased stroke volume and increased cardiac output
What neurotransmitters are vasoconstrictors?
ADH Angiotensin II
Where in the body does reflex vasoconstriction occur?
Skin GIT Skeletal muscle Kidney Cerebral circulation Coronary circulation
How does blood flow remain constant at different mABP?
Due to changes in arteriolar resistance
When might ABP increase?
Coughing Sneezing Exercising Pain
When might ABP fall?
Standing up Cutaneous circulation dilates heat Haemorrhage Dehydration
Where are volume receptors found?
In the right atrium
Where do afferents of the volume receptor reflex go?
Medulla via vagus nerve
What are the effects of the volume receptor reflex when blood volume falls?
Increased sympathetic activity to the kidney to trigger renal vasoconstriction, decreased renal tubular flow Increased renin release leads to increase in angiotensin II levels Increased ADH release from pituitary gland
How fast is the volume reflex response?
Slow 20 mins
What might cause a fall in blood volume?
Standing position (venous pooling) Haemorrhage Dehydration
What might increase blood volume?
Supine position Large fluid intake Over transfusion