Control of blood pressure Flashcards
What is the importance of the integration and control of the heart and blood vessels.
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
Describe the nature of nervous control of arterial pressure
V rapid:
Can increase arterial pressure to 2x normal within 5-10s
Can decrease arterial pressure to 50% normal within 10-40s
What are the fundamental components of a reflex control system of blood pressure
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
What are baroreceptors?
Just as it sounds, a receptor that is sensitive to pressure
Aortic baroreceptors come from the vagus
What are floppy babies?
Fucking spooky, run to the consultant
What are the main baroreceptor locations?
– Walls of aorta
• Afferent fibers follow vagus (Xth cranial) nerve
– Carotid artery
• Afferent fibers follow (IXth cranial) glossopharyngeal nerve
Describe baroreceptor activity in feedback control of mean arterial pressure
– “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 normalDescribe rate of baroreceptor firing
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
What does green baby vomit mean?
Bile in vomit - not normal Duodenal atresia(?) Malrotation w obstruction from midgut volvulus - acute emergency(?)
What is the primary purpose of the baroreceptor reflex control?
To reduce the minute-to- minute variations or arterial pulse
what is a capillary hemangioma
Abundance of capillaries on site of a baby
Describe the action of the cardiopulmonary baroreceptors
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
What is the Bainbridge reflex?
Atrial reflex control of BP
Increase in HR due to increase in central venous pressure
Describe atrial reflex control of BP
(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?
Describe the integrated control of BP via MCVC
Medullary cardiovascular control (MCVC) “vasomotor” centre
– Sensory area
• Input from baroreceptors
– Lateral portion
• Efferent sympathetic nerves
– Medial portion
• Efferent parasympathetic (vagal) nerves
Discuss target effectors (nervous) in reflex control of blood pressure
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
What is the CNS ischemic response?
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
Discuss fine control of blood flow
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
Describe all the factors that can affect total peripheral resistance
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
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
Learning outcomes
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.
