Control Of Blood Flow + Pressure Flashcards
What is the equation to measure blood flow
What is poiseuille’s law
It is an equation used to measure resistance of the vessel
What effect does doubling the radius of a vessel have on the flow
Times 16
What does Reynolds number show
The relationship between pressure, flow and turbulence can be calculated using Reynold’s number
What can cause turbulent blood flow
Increasing velocity e.g by increasing cardiac output
Decreasing viscosity of blood e.g anaemia
What can turbulent flow increase risk of
Thrombosis
What is the pulse pressure
Difference between systolic and diastolic pressure
How to calculate mean aterial blood pressure
MABP = Diastolic Pressure + (1/3 x Pulse Pressure)
What equation is used to measure blood pressure
What are the 2 main baroreceptors and where are they located
Carotid sinus baroreceptors - specialised sensory endings on the glossopharyngeal nerve
Aortic arch baroreceptors - present of vagus nerve
What is the difference between these two graphs
The minute to minute blood pressure changes due to lack of baroreceptors but the overall pressure is normal
How is blood pressure controlled
Sensory information is sent to the medulla ( nucleus tractus solitarius) which sends information various parts of the brain which sends projections to the spinal chord and is mostly involved with regulated vasoconstriction and neurones of sympathetic nervous system that affects the kidneys and heart
What happens when blood pressure decreases
The renal sympathetic nerve increases and an increase in heart rate ( increase HR means increase CO)
A decrease in blood pressure can also exert a powerful vasoconstrictor effect mediated by the sympathetic nervous system, which targets smooth muscle of mainly arteries and arterioles, thus increasing total peripheral resistance
The sympathetic nervous system can also target the adrenal medulla, resulting in an increased release of adrenaline and noradrenaline, which act in the circulation to further augment the vasoconstriction of vessels and increase heart rate
What is renin and where is it secreted from
It is a hormone that increases BP, macula densa cells sense a decrease in Na+, so more renin is released from the juxtaglomerular cells to increase BP
It is also released if low blood volume, low blood pressure, excitation of sympathetic nerves
What does renin do
It cleaves angiotensinogen to angiotensin I
What does angiotensin II do to increase BP
Promotes release of aldosterone
Potent Vasoconstrictor by binding to AT1 receptors
Stimulator of thirst by stimulate release of vasopressin (ADH) from pituitary which increases stroke volume by acting on renal cells to increase aquaporins
What can treat hypertension
The elevation of renal sympathetic tone in hypertension results in an increased secretion of renin, and an overall elevation of the renin-angiotensin-aldosterone system
Many first line anti-hypertensive drugs target this system. For example renin inhibitors, ACE inhibitors, angiotensin II receptor antagonists and mineralocorticoid receptor antagonists
However remember that aldosterone works by reabsorbing sodium in exchange for potassium, so use of these drugs (particularly combinations) can result in hyperkalaemia
