5: Control of arterial blood pressure (1) Flashcards
What is blood pressure?
The outward pressure exerted on the walls of blood vessels by blood
What is systemic systolic arterial blood pressure?
The pressure exerted on the walls of the aorta and systemic arteries when the heart contracts
The systemic systolic arterial blood pressure should be no more than ___ mmHg under resting conditions.
140 mmHg
What is systemic diastolic arterial blood pressure?
The pressure exerted on the walls of the aorta and systemic arteries when the heart relaxes
The systemic diastolic arterial blood pressure should be no more than __ under resting conditions.
90 mmHg
Blood flows in normal arteries in a ___ fashion.
laminar
Is normal arterial blood flow audible when using a stethoscope?
No - it’s silent
What would you hear if you auscultated a normal, patent artery?
Nothing
If an external pressure (e.g a pressure cuff) exceeding the systolic blood pressure is applied to an artery, blood flow is ___. What sound would you hear on auscultation?
blocked
Nothing.
If external pressure is between the systolic and diastolic blood pressure of an artery, blood flow becomes ___ whenever blood pressure exceeds cuff pressure.
turbulent
Is turbulent blood flow audible through a stethoscope?
Yes!
What is the name of the series of sounds you hear when recording a patient’s blood pressure?
Korotkoff sounds
When is the first Korotkoff sound heard?
Peak systolic blood pressure
What is the 5th, last Korotkoff sound and when is it heard (in terms of blood pressure)?
Total lack of sound after a muffled/muted sound
Heard at diastolic blood pressure
What drives blood around the systemic circulation?
What is this more commonly known as?
Pressure gradient between the aorta and the right atrium
MEAN ARTERIAL BLOOD PRESSURE (MAP)
What is mean arterial blood pressure?
The average blood pressure during a single cardiac cycle
Keeping in mind that the diastolic phase of the cardiac cycle is around twice as long as the systolic phase, give an equation for mean arterial blood pressure.
MAP = [(2x diastolic pressure} + systolic pressure] / 3
Exam format: MAP = Diastolic pressure + 1/3 (Systolic pressure - diastolic pressure)
If systolic blood pressure is 120mmHg and diastolic blood pressure is 75mmHg, calculate mean arterial blood pressure.
90 mmHg
What are the normal values for systolic and diastolic blood pressure?
Systolic: <140 mmHg
Diastolic: <90 mmHg
What is the normal range for mean arterial blood pressure?
70 - 105 mmHg
A mean arterial blood pressure of at least __ mmHg is required to perfuse the coronary arteries, brain and kidneys.
60 mmHg
Why must mean arterial blood pressure be regulated?
- High enough to perfuse the vital organs (>60 mmHg for coronary arteries, brain and kidneys)
- Low enough not to damage the blood vessels or put extra strain on the heart
Give an equation for mean arterial blood pressure.
MAP = Cardiac Output (CO) x Total Peripheral Resistance (TPR)
What is cardiac output?
The volume of blood pumped by each ventricle per minute
Give an equation for mean arterial blood pressure, breaking it down into its constituent parts.
MAP = CO x TPR
so MAP = SV x HR x TPR
What is total peripheral resistance?
The sum of resistance of all peripheral vasculature in the systemic circulation
Which vessels are responsible for major resistance?
Arterioles
Which receptors are responsible for short-term responses to MAP?
Baroreceptors
What is the control centre which integrates information re: changes in MAP?
Medulla
The short-term regulation of MAP is an example of…
negative feedback.
Where are the baroreceptors found?
1) Aortic arch
2) Carotid sinus
Which cranial nerves carry signals from the aortic and carotid baroreceptors respectively?
Aortic signals carried by CN X - vagus nerve
Carotid signals carried by CN IX - glossopharyngeal nerve
A person’s ___ changes can influence the MAP.
postural
When a person suddenly stands up, venous return to the heart decreases due to…
gravity.
When MAP decreases, what happens to the firing rate of the baroreceptors?
Firing rate decreases
How does the nervous system respond to a sudden MAP change (e.g when standing up suddenly) to restore MAP to normal?
Vagal tone to the heart decreases
Sympathetic tone increases
This increases the heart rate and stroke volume.
Sympathetic constrictor tone increase - vasoconstriction, TPR increases
Venous return and therefore stroke volume increases
The rapid increases in the constituent parts of MAP help return it to normal.
Which disease results from the failure of baroreceptor responses to gravitational shifts in the blood, e.g when moving from horizontal to vertical positions?
Postural _hypo_tension
Baroreceptors only respond to (acute / chronic) changes in blood pressure.
acute
Control of what helps to control MAP in the long term?
Blood volume
