36 - Blood Control and Hypertension

Question 1

Short-term blood pressure regulation

Answer 1

Primarily neural.

The baroreflex

Question 2

Part of brain that mediates baroreflex

Answer 2

Brainstem autonomic centres, in the medulla.

Nucleus and tractus solitarius

Question 3

Baroreceptor locations
1)
2)
3)

Answer 3

1) Carotid sinus
2) Aortic arch
3) Pre-glomerular arteriole (near justaglomerular apparatus)

Question 4

Carotid sinus

Answer 4

Thin-walled, highly-innervated, dilated bulb at base of internal carotid.
Baroreceptor

Question 5

Neural signals from baroreceptors

Answer 5

More stretch leads to more neural firing.

Therefore brain responds to less firing with sympathetic activation.

Question 6

Significance of thin wall of carotid sinus

Answer 6

Thinner wall is more compliant than a thicker one.

Therefore more sensitive (more easily-deformable) to changes in blood pressure.

Question 7

How quickly can baroreceptors respond to changes in bp?

Answer 7

Within one cardiac cycle

Question 8

How does your body normally assess adequacy of blood flow to organs?

Answer 8

Using blood pressure monitoring

Question 9

Effect of sympathetic stimulation on cardiovascular function 
1)
2)
3)
4)
5)

Answer 9

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)

Question 10

Effect of parasympathetic stimulation on cardiovascular system
1)
2)
3)

Answer 10

1) Increase AV conduction time
2) Decrease heart rate.
3) Doesn’t really cause vasodilation (except in blood vessels of sweat glands)

Question 11

Overall effect of baroreflex

Answer 11

Stabilises blood pressure, smooths out variations

Question 12

Effect of de-innervating carotid baroreceptors

Answer 12

Have great swings in bloodpressure with things like speaking, standing up, eating, defecating.

Question 13

How quickly can the threshold for baroreflex be changed?

Answer 13

Resets to new pressure levels within one to two days

Question 14

When to carotid baroreceptors stop firing to medulla?

Answer 14

Below about 60mmHg

Question 15

How is blood pressure below 60mmHg detected?

Answer 15

By chemoreceptors

Question 16

Where are chemoreceptors located?

Answer 16

Carotid and aortic bodies outside arteries

Question 17

What do chemoreceptors detect?

Answer 17

Low O2, high CO2, pH differences.

Linked to poor organ O2 perfusion.

Question 18

Mean male MAP

Answer 18

94

Question 19

Mean female MAP

Answer 19

89

Question 20

Shape of blood pressure distribution graph in population

Answer 20

Unimodal (one peak), tail towards upper end of distribution)

Question 21

Progression of systolic blood pressure with age

Answer 21

Increases with age

Question 22

Progression of diastolic blood pressure with age

Answer 22

Increases until ~60 years of age.

After 60, stops increasing, or decreases because of hardening of arterial walls (decreased compliance)

Question 23

Time of greatest blood pressure increase

Answer 23

Just after birth

Question 24

When do male and female mean MAPs diverge?

Answer 24

At puberty.

Question 25

How do body size and bp correlate?

Answer 25

Positively

Question 26

Diurnal variation of bp 1) 2) 3)

Answer 26

1) About 20mmHg lower at night 2) Less variation at night 3) Less sympathetic stimulation at night

Question 27

Seasonal variation of bp 1) 2)

Answer 27

1) About 3mmHg lower in summer than winter | 2) Because of increased heat (vasodilation), sweat (water loss), increased body weight in winter.

Question 28

Why has the cutoff for hypertension been falling for the past few years?

Answer 28

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.

Question 29

Current cutoff for hypertension

Answer 29

140mmHg systolic