9. Neuronal Control of Blood Pressure Flashcards
What are the 2 systems that regulate BP?
Neuronal, fast homeostatic process, -ve feedback
Hormonal (renin-angiotensin-aldosterone system), slow
Where are the blood pressure sensors mainly found?
Carotid sinus in the internal carotid above the bifurcation of carotid arteries.
Some in aortic sinus above aortic valve.
(Sinus walls more stretchy and distend slightly during systole)
Label A and B. What is does A do?
A: catrotid body B: carotid sinus
A: where the carotid chemoreceptors are found
Which nerves are the carotid sinus associated with?
Where are the cell bodies of the carotid sinus afferents?
Stretch in sinus baroreceptors proportional to BP. Causes continuous train of APs in sensory nerve endings, fibres travel to brain in vagus and glossopharyngeal nerves.
CNIX: primarily sensory (afferents from tonge, larynx, pharynx, carotid sinus), CNX: parasympathetic, contains motor output and sensory afferent nerve fibres from lungs, gut, pharynx, larynx and carotid sinus (where cell bodies are in nodose and jugular ganglia).
Describe the baroreceptor reflex if BP is too low.
Low BP -> baroreceptors not stretched enough -> decrease AP number and rate -> CNIX and CNX afferents -> NTS (dorsal surface of lower medulla) -> projects to:
1) nucleus ambiguus: cardioinhibitory centre is inhibited -> decreases parasympathetic vagal output to SAN
2) vasomotor centre in rostral venterolateral medulla -> increases its sympathetic output -> lateral reticulospinal tract to preganglionic neurons of sympathetic NS in interediate part of thoracolumbar ventral horn -> postganglionic neurons to vasoconstrict arteriolar SM via NA on alpha-1 adrenoreceptors -> raised total peripheral resistance -> increases BP
Describe the baroreceptor reflex if BP is too high.
Increased BP -> baroreceptors stretch -> increased AP number and rate -> CNIX and X afferents -> NTS -> NTS projects to:
1) nucleus ambiguus cardioinhibitory centre to increase parasympathetic vagal output to SAN = slows heart and reduced C.O = reduced BP
2) Vasomotor centre sympathetic output inhibited
What are the 2 formulas for MAP?
1) MAP = diastolic + 1/3(pulse pressure)
2) MAP = C.O. x TPR
* NB: PP = systolic - diastolic*
What is hypertension? And hypotension?
In most people with primary hypertension, TPR is raised (mainly due to chronic narrowing/constriction of arterioles) while C.O. remains normal). What are the 3 theories as to why the chronic narrowing occurs?
BP consistantly above 140/90. Or below 90/60.
1) increased tonic vasoconstriction via sympathetic NS
2) endothelium of arterioles damaged -> increased constriction
3) Malfunction of hormonal control system
People with hypertension generally still have controlled BP, just that the set point is high - why is it raised?
stretch receptors in carotid sinus less sensitive than normal = less afferent firing so vasomotor centre senses low BP and increases sympathetic output.
Loss of sensitivity could be due to loss of elastin fibres (aging) or atheroma in carotid sinus. Stiffer walls need more pressure to distend, thus normal BP gives reduced baroreceptor input = increased sympathetic and decreased parasympathetic = increased BP
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How does stress effect BP?
When may chronic stress permanently affect BP?
What is the most important lifestyle change to reduce BP?
Increases sympathetic NS output and BP, but normally only temporarily.
Chronic stress may permanently increase BP especially in TYPE A personalities (ambitious, highly organised, high status conscious, impatient for results, workaholics, multitask). TYPE B: live at lower stress levels, reflective, thoughtful.
Increase exercise levels! Can reduce BP to normal levels often on its own.
