Flashcards in *Physiology 4 (lecture 4) Deck (31)
What is blood pressure?
The outward (hydrostatic) pressure exerted by blood on blood vessel walls
What is the systemic systolic arterial blood pressure?
the pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart contracts
What should the systemic systolic blood pressure not exceed under resting conditions?
What is the systemic diastolic blood pressure?
The pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart relaxes
What should the systemic diastolic blood pressure not exceed?
What is the word used to describe the way in which blood should normally flow through blood vessels, meaning it is not heard through a blood vessel?
When is blood flow heard through a stethoscope in terms of taking blood pressure?
Not heard when no pressure is applied (laminar flow) or when pressure greater than the systolic blood pressure is applied (flow is blocked)
If the external pressure is between systolic and diastolic pressure, the flow will be turbulent (artery collapses and reopens with each heart beat = snapping sound)
These kortkoff sounds can be heard through a stethoscope
What is the RA pressure?
Close to 0
What drives the blood around the systemic circulation?
A pressure gradient between the aorta and right atrium
What is the central venous pressure?
pressure in the right atrium
What does the pressure gradient that drives the blood around the systemic circulation =?
Pressure gradient = MAP - CVP
What is the mean arterial pressure?
The average arterial blood pressure during a single cardiac cycle, which involves contraction and relaxation of the heart
[(2 X diastolic pressure) + systolic pressure] / 3 or DBP + 1/3rd difference between SBP and DBP
MAP = CO X TPR
MAP = (HR X SV) X TPR
How can MAP be estimated?
By adding DBP + 1/3rd of pulse pressure
What is pulse pressure?
The difference between systolic and diastolic blood pressure readings
What is the norma range of mean arterial blood pressure?
70 - 105 mmHg
MAP of at least what is required to perfuse the coronary arteries, brain and kidneys?
What is total peripheral resistance?
The sum of resistance of all peripheral vasculature in the systemic circulation
What is cardiac output?
The volume of blood pumped by each ventricle of the heart per heart beat
Effect of parasympathetic stimulation on MAP?
Decreases heart rate which therefore decreases cardiac output
Effect of sympathetic stimulation on the MAP?
Causes it to increase - heart rate and stroke volume due to increase in contractile strength of the heart) increases causing cardiac output to increase - vasoconstriction occurs in both arterioles and veins
Where are the 2 groups of baroreceptors located?
What do baroreceptors sense?
Where is the blood pressure control centre?
What are the blood pressure effectors?
Heart (HR, SV)
Blood vessels (TPR)
*negative feedback acts to minimise any disturbance to controlled variables)
What nerve do the carotid baroreceptors send signals to the medulla via?
What nerve do the aortic baroreceptors send signals to the medulla via?
What is a short term regulator of blood pressure?
Baroreceptor reflex (only respond to short term changes meaning if there is a sustained change in BP, the baroreceptors will reset)
What happens to the various afferent and efferent nerve firing when blood pressure drops e.g. standing?
Blood pressure decreases
This causes a decreased firing of carotid sinus afferent nerve fibres
This leads to decreased firing of vagal efferent nerves and an increased firing of sympathetic efferent nerves (both cardiac) - also get increased sympathetic vasoconstrictor acitivty= vagal tone of the heart decreases, increase HR and stroke volume and increased TPR
Increased constrictor tone to the veins increases the venous return to the heart and stroke volume
What happens to venous return when a person stands up?
It decreases due to gravity