Control of BP

Question 1

Fundamental components of a reflex control system

Answer 1

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

Question 2

mean arterial pressure

Answer 2

= cardiac output x total peripheral resistance

Question 3

where are the main baroreceptors located

Answer 3

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

Question 4

Baroreceptor activity

Answer 4

– “Stretch receptors”
– Firing rate ↑when BP ↑ 
– Firing rate ↓when BP ↓
– Sensitive around a “set-point” 
• Can change, e.g. hypertension

Question 5

Baroreceptor control of blood pressure

Answer 5

Primary purpose of baroreceptor reflex control is to reduce the minute-to- minute variations or arterial pulse

Question 6

Cardiopulmonary baroreceptors

Answer 6

(“low-pressure receptors”) sense central blood volume

– Atria, ventricles, veins and pulmonary vessels

Question 7

If rate of cardiopulmonary baroreceptors firing ↓

(signaling ↓ blood volume) then

Answer 7

– sympathetic nerve activity to the heart and blood vessels ↑

Question 8

Bainbridge Reflex

Answer 8

Sympathetic-mediated reflex in response to increased blood in atria
– ↑HR and ↑ contracClity
– prevents damming of blood in veins etc

Question 9

Medullary cardiovascular control (MCVC) “vasomotor” centre - Integrated control of BP

Answer 9

sensory area
lateral portion
medial portion

Question 10

sensory portion

Answer 10

• Input from baroreceptors

Question 11

lateral portion

Answer 11

efferent sympathetic nerves

Question 12

medial portion

Answer 12

• Efferent parasympathetic (vagal) nerves

Question 13

parasympathetic control of the heart

Answer 13

At rest parasympathetic = predominate tone

Question 14

sympathetic control of the heart

Answer 14

• Sympathetic can significantly effect stroke volume and rate

Question 15

sympathetic effects on blood vessels

Answer 15

– Continuous low-level tone affects total peripheral resistance
• “sympatheticvasoconstrictortone”exerts“vasomotortone”onvessels • keptpartiallyconstricted

Question 16

sympathetic control of the veins

Answer 16

• ↓capacitance
therefore ↑venousreturn
therefore ↑strokevol therefore↑cardiacoutput

Question 17

CNS ischemic response

Answer 17

Emergency pressure control system

Question 18

When blood flow to the medullary CVCC is ↓↓↓

Answer 18

– ↑ peripheral vasoconstricCon
• almost completely occludes some
peripheral vessels
– ↑ sympatheCc sCmulaCon of heart
– ↑↑ systemic arterial pressure 
• As high as 250 mmHg for 10 min

Question 19

Intrinsic ability to maintain blood flow safely if BP ↑

Answer 19

– 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

Question 20

main points

Answer 20

• 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