Lecture 12 & 13: Blood pressure Flashcards
What does BP= and what do they stand for
Blood Pressure in the arteries = Cardiac Output x Total Peripheral resistance. As CO is generally tried to be maintained, usually blood pressure can be changed by changing resistance of arterioles
What is the purpose of blood pressure
To drive exchange of substances that occurs at the capillaries only.
As you go through the cardiovascular system what happens to the blood pressure, where is the greatest resistance
The blood pressure drops from mean arterial pressure (~95) to below 10 in the venous section with close to 0 at the vena cavae. The pressure has the greatest drop at the arterioles as they are the 1’ resistance vessels due to vasoconstriction- smooth muscle tone.
Where is all the pulsatility of the blood pressure between diastolic and systolic occur in the Csystem and where is it lost
Occurs in the Aorta and arteries but its dampened in the arterioles because its not good for the capillaries
Pressure changes in the Csystem but what happens to flow
Flow is constant.
How does change in BP drive exchange in the capillaries
In the arterial end of capillaries, the blood hydrostatic pressure and interstitial fluid osmotic pressure which push fluid out, is bigger than the Blood collodial osmotic pressure and interstitial fluid hydrostatic pressure which is pushing fluid in, therefore there is a net filtration pressure that favours filtration, however at the venous end of the capillaries there is a drop in the blood hydrostatic pressure which allows the net filtration pressure to be negative - favouring reabsorption.
What are the pressures in the capillaries and which ones push fluid out or in
Blood hydrostatic pressure and interstitial fluid osmotic pressure push fluid out of capillaries and blood colloid osmotic pressure and interstitial fluid hydrostatic pressure pushes it in.
What causes blood colloid osmotic pressure to pull fluid from interstitial spaces
the large proteins in blood which can’t leave
How do baroreceptors sense changes in arterial blood pressure- what is high pressure
They are stretch sensitive afferent nerves that extend from the carotid sinus and aortic arch to the cardiovascular centre in the medulla oblongata. Every heart beat stretches the artery, therefore activating the nerve endings in the vessel walls. The rate at which impulses are sent tells about the pressure- faster = high
How do baroreceptor reflexes help control blood pressure
They are part of a negative feedback loop and can sense rapid changes in the blood pressure, sending this to CNS. Output by the CNS (brainstem regulating Autonomic control) includes Sympathetic and Parasymp pathways for short responses to lift/drop blood pressure as well as hormonal control for more long lasting.
How does the Sympathetic nervous system help increase blood flow
It can help to cause vasoconstriction in arterioles which reduces the flow to certain organ groups and therefore the other
If an arteriole is constricted in the middle what is the blood pressure and the flow on both sides
Before the constriction, blood pressure increases. After constriction the net filtration pressure in the capillaries decreases and the flow of blood decreases.
Compare the speed at which hormones regulate blood pressure to nervous systems pathways
Hormones are a slow acting response with a longer half life whereas
What hormone increases heart rate and contractility. what effect would this have on blood pressure. Where did this hormone come from
Norepinephrine and Epinephrine. This would increase blood pressure because it increases rate and force of contractions. This came from adrenal medulla that were stimulated by sympathetic pathway
What hormone causes vasoconstriction. what effect would this have on blood pressure. Where did this hormone come from
Angiotension II produced by enzyme Renin in the lungs. It increases blood pressure by increasing TPR by vasoconstriction and it also stimulates secretion of aldersterone which increases absorption of sodium ions
