Control of blood pressure

Question 1

What is the importance of the integration and control of the heart and blood vessels.

Answer 1

Seems obvious because it is:

Required to maintain tissue perfusion across whole of the body
– To keep a relatively constant arterial blood pressure
• Too low, blood flow to organs would fail
• Too high, damage to vessels and organs
– To control distribution of the total cardiac output
• 5L/min not sufficient to perfuse entire body
• Needs to respond to tissue demands
• Satisfied by local control mechanisms

Question 2

Describe the nature of nervous control of arterial pressure

Answer 2

V rapid:
Can increase arterial pressure to 2x normal within 5-10s
Can decrease arterial pressure to 50% normal within 10-40s

Question 3

What are the fundamental components of a reflex control system of blood pressure

Answer 3

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 4

What are baroreceptors?

Answer 4

Just as it sounds, a receptor that is sensitive to pressure

Aortic baroreceptors come from the vagus

Question 5

What are floppy babies?

Answer 5

Fucking spooky, run to the consultant

Question 6

What are the main baroreceptor locations?

Answer 6

– Walls of aorta
• Afferent fibers follow vagus (Xth cranial) nerve
– Carotid artery
• Afferent fibers follow (IXth cranial) glossopharyngeal nerve

Question 7

Describe baroreceptor activity in feedback control of mean arterial pressure

Answer 7

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

Question 8

Describe rate of baroreceptor firing

Answer 8

As arterial blood pressure increases, so does the number of impulses from carotid sinus nerves per second, in a rough sigmoid fashion that levels out at top

Question 9

What does green baby vomit mean?

Answer 9

Bile in vomit - not normal
Duodenal atresia(?)
Malrotation w obstruction from midgut volvulus - acute emergency(?)

Question 10

What is the primary purpose of the baroreceptor reflex control?

Answer 10

To reduce the minute-to- minute variations or arterial pulse

Question 11

what is a capillary hemangioma

Answer 11

Abundance of capillaries on site of a baby

Question 12

Describe the action of the cardiopulmonary baroreceptors

Answer 12

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 ↑
– parasympathetic nerve activity to the heart ↓

This all seems like bollocks really, Nash et all say different but this was on the slide so who kens

Question 13

What is the Bainbridge reflex?

Answer 13

Atrial reflex control of BP

Increase in HR due to increase in central venous pressure

Question 14

Describe atrial reflex control of BP

Answer 14

(Bainbridge Reflex)
Sympathetic-mediated reflex in response to increased blood in atria
– ↑HR and ↑ contractility
– prevents damming of blood in veins etc
If aortic/carotid baroreceptors sense high pressure, Bainbridge reflex can over-ride
– How is integration of these signals controlled?

Question 15

Describe the integrated control of BP via MCVC

Answer 15

Medullary cardiovascular control (MCVC) “vasomotor” centre
– Sensory area
• Input from baroreceptors

– Lateral portion
• Efferent sympathetic nerves

– Medial portion
• Efferent parasympathetic (vagal) nerves

Question 16

Discuss target effectors (nervous) in reflex control of blood pressure

Answer 16

Sympathetic and parasympathetic effect the heart – Both control heart rate and normally function
simultaneously
• At rest parasympathetic = predominate tone
• Sympathetic can significantly effect stroke volume and rate

Sympathetic effects on blood vessels
– Continuous low-level tone affects total peripheral resistance
• “sympathetic vasoconstrictor tone” exerts “vasomotor tone” on vessels
• therefore kept partially constricted

– Remember veins also innervated by sympathetic
• ↓capacitance therefore ↑venous return therefore ↑stroke vol therefore ↑cardiac output

Question 17

What is the CNS ischemic response?

Answer 17

Emergency pressure control system – “last ditch stand”
When blood flow to the medullary CVCC is ↓↓↓
– ↑ peripheral vasoconstriction
• almost completely occludes some
peripheral vessels
– ↑ sympathetic stimulation of heart
– ↑↑ systemic arterial pressure 
• As high as 250 mmHg for 10 min

Question 18

Discuss fine control of blood flow

Answer 18

Local control superimposed on organ dist. of CO
– Organs auto-regulate blood flow
• Reactive and active hyperemia
• Independent of innervation / hormonal control

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

Remember not all capillaries in an organ perfused simultaneously

Question 19

Describe all the factors that can affect total peripheral resistance

Answer 19

Hormonal, neural and local controls will affect arteriolar radius which will impact total peripheral resistance

Hematocrit will impact blood viscosity which will impact total peripheral resistance

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

Question 21

Learning outcomes

Answer 21

To identify the components of the feed-back system involved in the reflex control of mean arterial blood pressure (including the receptors, integrating centre, target effectors and associated afferent and efferent pathways), where they are located and how they contribute to regulation of MABP.
To predict how the cardiovascular system will reflexively respond to physiological changes to maintain mean arterial blood pressure.
To explain how tissue demands for blood flow are balanced against the requirement to maintain a mean arterial blood pressure.