0704- Regulation of BP by reflexes- CG

Question 1

Sensors, integrators and effectors of regulating reflexes

Answer 1

In series: Sensor-afferent-integrator (set point of integrator can be changed)- efferent-effector (which then change sensor)

Question 2

Be cognisant of the anatomy of the reflex pathways

Answer 2

2main reflexes Arterial baroreflex- sympathetic outflow to vessels Sensor- baroreceptors in aortic arch (CN x) and carotid sinus (IX), built on vessel wall Cardiopulmonary reflexes- venous return cardiac stretch veno-atrial mechanoreceptors to control venous return

Question 3

How are MAP, hr, sv and tpr regulated

Answer 3

By the autonomic nervous system MAP = TPR x CO = TPR x SV xHR Efferent pathways Sympathetic outflow- increases SV and HR and TPR (vasoconstrict=- sets resistance vessel and venous tone) Parasympathetic(vaga)- decreases SV and HR Afferent pathways cardiopulmonary receptors, baroreceptors. 2 reflexes- baroreflex and cardiopulmonary reflex

Question 4

Function and effect of the arterial baroreflex

Answer 4

* Negative feedback to brainstem, SNS, heart- valsalva manuveur, uswd to stabilise BP within narrow range ‘beat to beat’ control * Depressor reflex to decrease hr, sv, tpr due to a increase in bp * Modulated via inputs from respiratory and etc enters. * Activated in orthostasis, dehydration, blood loss, shock

Question 5

Neural pathways in AB reflex

Answer 5

Oppositional regulation- balance between SNS and PNS Sympathetic via chain (t1-l3), PNS via s2-4 Sensor- baroreceptors in aortic arch (CN x) and carotid sinus (IX), built on vessel wall (Mechanoreceptors via a fibre- high sensitivity in the range 50-100mmhg- saturation). C fibres can transmit 200mmhg pain bp. Baroreceptors sense pulsatile, varying pressures (adapt to steady pressure

Question 6

AB reflex and exercise

Answer 6

Set point can be reset by exercise reset integration set point- work at higher bp without depressor response. Ab active but HR can be increased (muscle spindle input from legs)

Question 7

Medullary interactions in ab pathway

Answer 7

4 nuclei in medulla- relay and integrate SNS and PNS Nucleus tracts solitarius (NTS) = hub and entry point (afferent inputs by IX/X chemobaro receptor) PNS/vagal pathway- direct to nucleus ambiguens SNS inhibition- GABA interneurons in caudal vasopressor area inhibit rostral vasopressor sympathetic neurons (preganglionics fibres) Also inhibitory via serotonin via raphe nuclei

Question 8

Cardiopulmonary reflex function

Answer 8

Detects blood volume (ie heart gets full = high venous return = activation)via cardiac stretch veno-atrial mechanoreceptors to control venous return. If high volume, increase HR (SNS only) and promotes diuresis/natriuresis. Forms part of long term vol regulation On activation: reduce venous return by renal vasodilation, reducing ADH, increase atrial release of ANP (atrial natriuretic peptide)

Question 9

Describe neural pathway of cardiopulmonary reflex

Answer 9

Mostly a-fibres Mostly Small unmyelinated (80%) Cardiac Mechanoreceptors detect wall tension in ventricle, ventricular chemoreceptors (mediate pain) and coronary artery baroreceptors (perfusion pressure) 20% myelinated veno-atrial mechanoreceptors

Question 10

Appreciate how these reflexes can be modulated by respiration and shock

Answer 10

During inspiration, inspirations centre inhibits vagal output and disinhibits sa node, increases heart rate. Expiration- vagal outflow returns, may result in vasovagal syncope Shock- if BP <80, peripheral chemoreceptors modulate BP- vasoconstriction results in high TPR, and tachycardia- increase BP,