Regulation Of Mean Arterial Blood Pressure Flashcards
What factors increase CO ?
INCREASED HR
- increased by decrease in parasympathetic stimulation and an increase in sympathetic stimulation
- increased by release of NA and A from adrenal medulla
INCREASED SV
-increased by sympathetic stimulation and release of NA and A
- increased by venous return - increased by increased blood volume, invent obstruction, skeletal pump and respiratory pump
How do you calculate MAP?
CO * TPR
What factors increase TPR ?
INCREASED BLOOD VISCOSITY - increased by increase in erythrocytes INCREASED TOTAL BLOOD VESSEL LENGTH - increase in body size , obesity DECREASED BLOOD VESSEL RADIUS -vasoconstriction
What is the primary role of cardiovascular regulation ?
It is to maintain a stable MAP
Where is sthe cardiovascular centre ?
In the medulla
- autonomic nerves originate in it
What nerves carries sympathetic activity from the cardiovascular centre and what effect do they have ?
Cardiac accelerator nerve - increase HR and contractility to increase CO
Vasomotor nerve- causes vasoconstriction to increase TPR
What nerve carries parasympathetic activity from the cardiovascular centre and what does it do ?
Vagus nerve- decreases HR to reduce CO
What are the arterial baroreceptors ?
Non-encapsulated nerve endings in adventitial layer of arteries in carotid sinus and aortic arch
Mechanoreceptors which are sensitive to stretch so when BP increases the vessel stretches more and this causes excitation of baroreceptors
Which cranial nerves do the baroreceptors project in to the CV centre ?
9th and 10th
They detect increased stretch which causes a decrease in sympathetic stimulation and an increase in parasympathetic stimulation on the heart
What is the term given to changing from supine to standing position ?
Why does present a challenge to the cardiovascular system ?
Orthostasis
Because of gravity it produces a challenge for getting sufficient cerebral perfusion to prevent fainting
How is cerebral perfusion preserved after orthostasis?
Because there is a decrease in PP and sinus pressure caused by gravity it reduces the baroreceptor stimulation
This causes a decreased in vagus nerve and an increase in vasomotor nerve and cardio accelerator nerve
This causes an increase in HR by 15-20bpm and an increase in contractility
Also increases TPR by vasoconstriction
This altogether increases MAP to about 10-15 mmHg above supine level
What is responsible for controlling MAP in the long term ?
Cardiopulmonary pressure receptors and hormonal influences
What is the primary role of cardiopulmonary stretch receptors ?
Regulate blood volume
- however the blood volume is a determination of CO which with TPR determines arterial pressure
What happens when there is decreased arterial pressure causing decreased stimulation of cardiopulmonary stretch receptors ?
Reflex release of ADH from hypothalamus to cause increase reabsorption of fluid at the kidneys to increase blood volume
- ADH also has vasoconstrictor effects especially on splanchnic circulation which increases TPR
Neural reflex that constricts afferent renal arterioles to reduce glomerular filtration rate to reduce fluid loss and increase blood volume
What are chemoreceptors and where are they located ?
Monitor chemical composition of blood
Carotid bodies and aortic bodies
What chemical imbalances affect chemoreceptors ?
Hypoxia
Hypercapnia
Acidosis
How does chemoreceptors work ?
They can work directly by cause an increase in sympathetic stimulation leading to vasoconstriction
Indirect effect on HR by increasing rate and depth of breathing which increases HR and small vasodilation
Overall effect is an increase in CO and TPR which increases MAP this increase blood
What controls the long term regulation of blood volume ?
Kidney
Explain the renin-angiotensin-aldosterone system ?
System is stimulated by fall in blood pressure so it increases blood volume to increase blood pressure
Renin released from juxtaglomerular cells
Renin converts angiotensinogen to angiotensin 1
Angiotensin converting enzyme converts angiotensin 1 into angiotensin 2
Angiotensin 2 causes vasoconstriction and acts on adrenal gland to release aldosterone which acts on kidney to increase sodium absorption which increases water reabsorption which increases blood volume
Altogether this increases MAP
What are th effects of adrenaline on the cardiovascular system ?
Acts on beta receptors of the heart causing stimulation and increasing HR pans SV so it increases CO
What are the effect on noradrenaline on MAP ?
Acts on alpha receptors in blood vessels causing vasoconstriction which increases TPR and therefore helps to contribute to an increase in MAP
What effect does ANP have on MAP ?
This hormone is released when there is high cardiac filling pressures
It therefore causes vasodilation and promotes sodium excretion so reduces MAP
What effect does NO have on MAP ?
Because it is a gas it only causes vasodilation locally so therefore it had little effect on MAP
