Control of BP (M1 13/11) Flashcards
LO: What is the role of reflexes of the heart in the control of blood pressure?
LO: What is the role of blood vessels in the control of arterial blood pressure?
LO: What is the role of baroreceptors in regulating blood pressure?
LO’s dodo brain
Why does BP need to be monitored and controlled?
Arterial blood pressure needs to be maintained to ensure constant supply of blood to brain and heart
There are two major control mechanisms involved
–Short term (fast response)
–Long term (slow, involves kidney and regulation of the blood volume).
What is the difference between BP, hydraulic pressure, arterial blood pressure and hydrostatic pressure?
- BP: pressure exerted on the wall of the blood vessel
- Hydraulic pressure: flowing blood BP
- Hydrostatic pressure: static, non-moving blood BP
- Arterial BP: BP in arteries
Why do we get pulsing flow?
- Get smooth flow through capillaries, but large arteries have pulsing flow, because the arteries stretch and store blood. This is why in venepuncture, the vein should be bouncy but not pulsing, as that is an artery. In radial pulse, we take the pulse from the radial artery.
What is mean arterial BP?
Average pressure in a patient’s arteries during one cardiac cycle. The mean arterial pressure (MAP) drives blood through the vasculature from the arteries to arterioles, capillaries, venules, veins, and back to the heart. The mean arterial pressure is a time-weighted average of pressure values in large systemic arteries during the cardiac cycle. If the ventricles spent an equal length of time in systole and diastole, the mean arterial pressure could simply be estimated as the mathematical average of systolic and diastolic pressure values. In reality, however, the ventricles spend approximately one-third (1/3) of their time in systole, and two-thirds (2/3) in diastole.Therefore, a simple average of the systolic and diastolic pressure values is not an adequate estimate of the mean arterial pressure. Instead, a simple approximation equation is typically used to estimate the mean arterial pressure, where mean arterial pressure = diastolic pressure + (1/3 × pulse pressure.)
SBP: the maximum arterial pressure during contraction of the left ventricle of the heart.
DBP: minimum arterial pressure during relaxation
MAP can also be though of as a balance between blood flow into the arteries & blood flow out of the arteries, to the tissues. So MAP is also CO X TPR
How does short-term control of arterial blood pressure happen?
- Baroreceptors are high pressure sensory receptors. The AP’S travel via afferent nerves (the vagus nerve on the aortic arch or the glossopharyngeal on the coratid sinus) to the cardio-vascular control centre in the the medulla oblongata of the brainstem
- Respond to changes in stretch of the artery due to changes in BP.
- If increses in stretch due to increase in BP, more AP’s fire, so the CVCC in the medulla causes:
- An increase in parasympathetic output. More Ach is released by the vagus nerve to act on the muscarinic receptors on the SA of the heart. This action decreases pacemaker rate by increasing potassium and decreasing calcium and sodium movement. As the pacemaker slows, so does your heart rate, decreasing BP.
- A decrease in sympathetic output, so less noradrenaline is released from noradrenergic neurons. Noradrenaline normally causes vasoconstriction, so there is now vasodilation. This means there is less total peripheral resistance, so decreasing BP. Also, less noradrenaline binds to beta one receptors on the ventricles and SA node so so force of contraction and heart rate is decreaded. CO is decreased so BP decreases.
What is the CARDIO-VASCULAR CONTROL CENTRE?
- Located in the medulla oblongata of the brainstem
- In a region known as the nucleus tractus solitarius
- Actually consists of 3 regions of neurones
- 2 cardiac centres (excitatory & inhibitory) and 1 vasomotor centre
- Receive input from baroreceptors through afferent nerves to CCC.
- In the peripheral nervous system, an afferent nerve fiber is the axon of a sensory neuron. It is a long process extending far from the nerve cell body that carries an action potential from the sensory neuron toward the central nervous system.
- The inputs to the CCC are the AP from the sensory/afferent nerves from the baroreceptors. Also chemo and proprio receptors and higher brain centres (e.g. hypothalamus)
- Outputs of the CCC:
Autonomic Nervous System
Cardioexcitatory & Vasomotor output is – Sympathetic
Cardioinhibitory output is - Parasympathetic
Why is Carotid Sinus massage useful for Angina?
Stimulates baroreceptors, if careful release of ACH to heart, lowers heart rate, less BP, less angina.
How does VASOVAGAL SYNCOPE (overactivity of the vagus nerve causing fainting, as a result of stress) occur?
Intense stress causes:
- Massive increase in sympathetic cholinergic supply to skeletal muscle leading to decrease in TPR. Ach binds to muscarinic receptors on the smooth muscle and/or endothelium. It has been shown in many arterial vessels that M3 receptors located on the vascular endothelium are coupled to the formation of nitric oxide which is a vasodilator.
- Intense increase in output from CI centre so decrease in HR
Overall, combined effect cause a rapid decrease in BP and reduced flow to brain, so lose consciousness
Why does the Vulcan Grip cause someone to faint?
Stimulates baroreceptors, massive release of ACH to heart, lowers/stops heart rate, no blood to brain.
Other pressure receptors?
Cardiopulmonary Receptors
Low Pressure Receptors
Transmit info about arterial pressure & cardiac filling
Work with Baroreceptors to stabilise blood pressure
Bainbridge Effect – Reflex Tachycardia:
Selective increase in sympathetic flow to SAN but NOT to blood vessels
Increase in VR, causes stretching of atria, and activates ‘A’ fibres. These send info to CVS centre etc.
