Control of BP Flashcards
Fundamental components of a reflex control system
1) Internal variable to be maintained
2) Receptors sensitive to change in the variable
3) Afferent pathways from the receptors
4) An integrating center for the afferent inputs
5) Efferent pathways from the integrating center
6) Target effectors that alter their activities
mean arterial pressure
= cardiac output x total peripheral resistance
where are the main baroreceptors located
the aortic baroreceptors - are located in the aortic wall
• Afferent fibers follow vagus (Xth cranial) nerve
carotid baroreceptors - located in the carotid artery
Afferent fibers follow (IXth cranial) glossopharyngeal nerve
Baroreceptor activity
– “Stretch receptors” – Firing rate ↑when BP ↑ – Firing rate ↓when BP ↓ – Sensitive around a “set-point” • Can change, e.g. hypertension
Baroreceptor control of blood pressure
Primary purpose of baroreceptor reflex control is to reduce the minute-to- minute variations or arterial pulse
Cardiopulmonary baroreceptors
(“low-pressure receptors”) sense central blood volume
– Atria, ventricles, veins and pulmonary vessels
If rate of cardiopulmonary baroreceptors firing ↓
(signaling ↓ blood volume) then
– sympathetic nerve activity to the heart and blood vessels ↑
Bainbridge Reflex
Sympathetic-mediated reflex in response to increased blood in atria
– ↑HR and ↑ contracClity
– prevents damming of blood in veins etc
Medullary cardiovascular control (MCVC) “vasomotor” centre - Integrated control of BP
sensory area
lateral portion
medial portion
sensory portion
• Input from baroreceptors
lateral portion
efferent sympathetic nerves
medial portion
• Efferent parasympathetic (vagal) nerves
parasympathetic control of the heart
At rest parasympathetic = predominate tone
sympathetic control of the heart
• Sympathetic can significantly effect stroke volume and rate
sympathetic effects on blood vessels
– Continuous low-level tone affects total peripheral resistance
• “sympatheticvasoconstrictortone”exerts“vasomotortone”onvessels • keptpartiallyconstricted
sympathetic control of the veins
• ↓capacitance
therefore ↑venousreturn
therefore ↑strokevol therefore↑cardiacoutput
CNS ischemic response
Emergency pressure control system
When blood flow to the medullary CVCC is ↓↓↓
– ↑ peripheral vasoconstricCon • almost completely occludes some peripheral vessels – ↑ sympatheCc sCmulaCon of heart – ↑↑ systemic arterial pressure • As high as 250 mmHg for 10 min
Intrinsic ability to maintain blood flow safely if BP ↑
– Myogenic theory (acute auto-regulation)
• Stretch-induced vascular depolarisation of smooth muscle due to ↑ arterial pressure
– Metabolic theory (acute auto-regulation)
• ↑ arterial pressure increases O2 and “washes out” local factors
main points
- Neuronal reflex mechanisms exist to maintain BP in the immediate/short term
- These are integrated in the MCVC centre
- Fine control of local blood flow still occurs
- Long term regulation is via blood volume
