36 - Blood Control and Hypertension Flashcards
Short-term blood pressure regulation
Primarily neural.
The baroreflex
Part of brain that mediates baroreflex
Brainstem autonomic centres, in the medulla.
Nucleus and tractus solitarius
Baroreceptor locations
1)
2)
3)
1) Carotid sinus
2) Aortic arch
3) Pre-glomerular arteriole (near justaglomerular apparatus)
Carotid sinus
Thin-walled, highly-innervated, dilated bulb at base of internal carotid.
Baroreceptor
Neural signals from baroreceptors
More stretch leads to more neural firing.
Therefore brain responds to less firing with sympathetic activation.
Significance of thin wall of carotid sinus
Thinner wall is more compliant than a thicker one.
Therefore more sensitive (more easily-deformable) to changes in blood pressure.
How quickly can baroreceptors respond to changes in bp?
Within one cardiac cycle
How does your body normally assess adequacy of blood flow to organs?
Using blood pressure monitoring
Effect of sympathetic stimulation on cardiovascular function 1) 2) 3) 4) 5)
1) Increase heart rate
2) Decrease AV conduction time
3) Increase cardiac contractility (Ca2+ released in cardiac cells upon sympathetic stim)
4) Increase total peripheral resistance (keep blood in arteries)
5) Increase venous tone (keep blood in arteries)
Effect of parasympathetic stimulation on cardiovascular system
1)
2)
3)
1) Increase AV conduction time
2) Decrease heart rate.
3) Doesn’t really cause vasodilation (except in blood vessels of sweat glands)
Overall effect of baroreflex
Stabilises blood pressure, smooths out variations
Effect of de-innervating carotid baroreceptors
Have great swings in bloodpressure with things like speaking, standing up, eating, defecating.
How quickly can the threshold for baroreflex be changed?
Resets to new pressure levels within one to two days
When to carotid baroreceptors stop firing to medulla?
Below about 60mmHg
How is blood pressure below 60mmHg detected?
By chemoreceptors
Where are chemoreceptors located?
Carotid and aortic bodies outside arteries
What do chemoreceptors detect?
Low O2, high CO2, pH differences.
Linked to poor organ O2 perfusion.
Mean male MAP
94
Mean female MAP
89
Shape of blood pressure distribution graph in population
Unimodal (one peak), tail towards upper end of distribution)
Progression of systolic blood pressure with age
Increases with age
Progression of diastolic blood pressure with age
Increases until ~60 years of age.
After 60, stops increasing, or decreases because of hardening of arterial walls (decreased compliance)
Time of greatest blood pressure increase
Just after birth
When do male and female mean MAPs diverge?
At puberty.
How do body size and bp correlate?
Positively
Diurnal variation of bp
1)
2)
3)
1) About 20mmHg lower at night
2) Less variation at night
3) Less sympathetic stimulation at night
Seasonal variation of bp
1)
2)
1) About 3mmHg lower in summer than winter
2) Because of increased heat (vasodilation), sweat (water loss), increased body weight in winter.
Why has the cutoff for hypertension been falling for the past few years?
Because the cutoff is calculated by the earliest time that treatment benefits outweigh negatives.
Now drugs are safer, more efficacious, so makes sense to treat earlier.
Current cutoff for hypertension
140mmHg systolic
