central nervous control of the circulation in health and disease Flashcards
what are the three ares of the central nervous system that controls circulation
- cerebrum and diencephalon
- brainstem (parasympathetic outflow)
- spinal cord (sympathetic outflow)
what is the classification of hypertension
> 140/90
what affects resting bp
- time of the day
- activities
what is the white coat syndrome
- bp is increased by stress/ anger and anxiety
- many people intimidated by health care professionals and only have raised bps in the presence of medical practitioners
- to avoid this you can keep patients relaxed, ambulatory blood pressure monitoring (self monitor)
what is the autonomic innervation of the heart
- sympathetic (sympathetic fibres/nerves innervate the heart from thoracic vertebra T1-T5)
- parasympathetic (vagus nerve- cranial nerve 10)
how does the sympathetic nervous system innervate the heart
- sympathetic fibres release noradrenaline
- bind to alpha 1/2 adrenergic receptors on smooth muscle of blood vessels
- causes Smooth muscle contraction
- leads to vasoconstriction and thus an increased in blood pressure
- sympathetic innervation of adrenal medulla releasing Ach which binds to nicotinic cholinergic receptors
- causes release of adrenaline which can bind to the beta 2 receptors causing vasodilation
what type of feedback is used to control bp
- negative
how can bp be controlled by
- heart rate
- stroke volume
- systemic vascular resistance
how does the baroreceptor reflex work
- increase in blood pressure
- baroreceptor in the carotid and aortic bodies are activated
- causes more sensory innervation to be sent to the brainstem
- increased parasympathetic innervation sent to heart via vagus nerve to decrease heart
- decreased sympathetic innervation so decreased vasoconstriction, venoconstriction and cardiac vigor
how is the baroreceptor reflex activated
- increased blood pressure
- results in more action potentials being fired to brainstem
- decreased blood pressure causes less action potentials (lower frequency) being sent to heart
- at high bps blood vessels are more streched out so more activation of these receptors
from what nerve is sensory innervation sent from baroreceptors
- baroreceptors in carotid bodies send via carotid sinus nerve 9- glossopharyngeal nerve
- aortic bodies send via vagus nerve
what is the relationship ( in terms of graph) between pressure in carotid and afferent impulses/receptor firing
- increasing pressure increases afferent impulses until a certain point where graph levels off and increasing pressure has no effect on receptor firing
- produces sigmoid shape
- in conditions such as hypertension, pregnancy, exercise this graph can shift to the right where the receptors are less sensitive
what is the valsalva maneouver
- used to test the baroreceptor reflex
what is the mechanism behind the valsalva manoeuvre
- exhale against a close glottis
- intrathoracic volume decreases and pressure increases
- compresses blood vessels causing a reduced venous return and therefore decreased cardiac output and decreased pressure
- causes reflex tachycardia
- upon exhalation intrathoracic pressure decreases, blood vessels not squeezed and venous return restores
- increases in cardiac output and increase in bp
- reflex bradycardia
how does the baroreceptor reflex prevent us from fainting when we stand up
- when we stand up, decreased venous return
- decreased stroke volume and cardiac output
- decrease blood pressure
- decreased baroreceptor acitivty
- less signals sent to brainstem so sympathetic activity increases and heart rate increases, vasoconstriction happens restoring blood pressure
what receptors control blood volume and loss of blood
- baroreceptors
- chemoreceptors if there’s altered blood gases
what is the arterial chemoreceptor reflex
- peripheral chemoreceptors in body detects low oxygen levels
- sends signal to brainstem specifically respiratory centre and can increase ventilation
- also stimulates the CVS to increase CO and BP
- if ventilation cannot happen e.g. your holding ur breath it causes bradycardia instead of tachycardia
what happens to CO, HR, BP, SV and TPR during exercise
- HR and CO increases (B1 receptors)
- systemic vascular resistance decreases (B2 receptors)
- systolic blood pressure usually increases and diastolic decreases
- stroke volume tends to increase
note baroreceptor reflex operate at higher range during exercise and are less sensitive
what is the brain bridge reflex
- atrial receptors
- stretch receptors located in atria stimulated by increasing filling pressure causes tachycardia reflex
what does the ventricular mechanoreceptors result in
- increased ventricular filling causes activation of ventricular receptors
- srtimulation causes vasodilation and bradycardia
