Cardiovascular system: Blood pressure

Question 1

What is the blood pressure equation?

Answer 1

Cardiac output (CO) * Total peripheral resistance (TPR)

Question 2

What is blood pressure the driving force of?

Answer 2

Nutrient exchange in the capillaries

Question 3

How do capillaries respond to changes in blood pressure?

Answer 3

Not very well, sensitive to changes in blood pressure due to their weak structure of a single cell thick of endothelial cells

Question 4

How does the body try to minimise damage from blood pressure to capillaries?

Answer 4

The body has a set point for blood pressure

Question 5

What does the set point for blood pressure mean?

Answer 5

Throughout the day the body tries to maintain the mean blood pressure (~100mmHg)

Question 6

How does mean blood pressure change throughout the day?

Answer 6

It is pretty constant

Question 7

What condition develops when there is sustained higher mean blood pressure? How does this affect the circulatory system?

Answer 7

This leads to hypertension (FYI defined as 140/90 mmHg –> 14% of NZ has this) causing hypertrophy of the heart

Question 8

How does blood pressure change per heart beat?

Answer 8

There are lots of small changes in blood pressure, the diagram attached shows how there are micro adjustments in blood pressure all the time

Question 9

What is the blood distribution in the body?

Answer 9

Heart = 7%

Systemic capillaries = 7%

Pulmonary vessels = 9%

Systemic arteries and arterioles = 13%

Systemic veins and venues = 64%

Question 10

How is it that the blood volume is so low in then capillaries even though this is where nutrient exchange occurs?

Answer 10

There is a high flow rate through them

Question 11

How does the movement of the blood vary throughout the systemic circuit?

Answer 11

Blood pressure is the highest and also drops rapidly through the arteries (Aorta, arteries and arterioles), pressure is lower in the capillaries and much lower in the veins (venues, veins, vena cavae)

As the blood moves through the circuit there is also less pulsating

Question 12

Why does the blood pressure decrease as the blood moves through the systemic circuit?

Answer 12

As the blood moves through the circuit, vessels absorb some of the energy due to their resistance therefore reduce the pressure of the blood

Question 13

How much of the blood is returned to the heart after each beat?

Answer 13

The same amount is returned as there is delivered

Question 14

How much of the blood that is delivered to the capillary beds is pumped out of the capillary bed normally?

Answer 14

The same amount

Question 15

What happens when not all the blood from the capillary beds is removed?

Answer 15

Causes oedema (i.e. swelling) as there is excess fluid in the interstitial space

Question 16

What are the most important type of blood vessels for controlling blood pressure? Why?

Answer 16

Arteries as they can vasoconstrict/dilate

Question 17

What is the condition of the arteries always?

Answer 17

They always have vascular tone (i.e. always slightly constricted)

Question 18

How is the vascular tone influenced?

Answer 18

By hormones (i.e. noradrenaline), Nerves (in particular sympathetic nerves) and intrinsic factors

Question 19

How is blood in the capillary beds reabsorbed?

Answer 19

The blood pressure is lower at the venous end of the capillaries which allows for net re-absorbtion due to osmotic pressure difference and also some of the fluid is re-absorbed via the lymph system

Question 20

What is the net filtration pressure (NFP) of the capillary at the arterial end? Why?

Answer 20

10mmHg, There is a large blood hydrostatic pressure and the constant blood colloid osmotic pressure is less than this so interstitial fluid is able to drain out of the capillaries

Question 21

What is colloid pressure?

Answer 21

The pressure exerted by the proteins and other substances in the interstitial fluid

Question 22

What is the net filtration pressure (NFP) of the capillary at the venous end? Why?

Answer 22

-9mmHg, There is a smaller blood hydrostatic pressure and the constant blood colloid osmotic pressure is more than this so interstitial fluid is able to drain into the capillaries

Question 23

How are arteries and arterioles controlled?

Answer 23

They are all connected to the brain via the sympathetic nerves

Question 24

How and why does the brain influence blood pressure?

Answer 24

Using sympathetic nerves able to control the degree of constriction

It is able to re-distribute blood to where it is needed (i.e. kidneys usually use ~20% of CO but when exercising, vasoconstricts renal tract to 2-3% CO so more blood for muscles)

Question 25

How are arteries and arterioles measured? What does this create?

Answer 25

They all have receptors such as baroreceptors and proprioceptors which monitor the blood and return the information to the brain –> negative feed back loop

Question 26

What is the arrangement of the blood vessels around the body? Why this?

Answer 26

It is in parallel so that each organ receives the same pressure (i.e. in series the blood pressure of the organ at the end would be so low that it would be insufficient for for exchange)

Question 27

How are baroreceptors able to measure blood pressure?

Answer 27

They sense the stretch of blood vessels

Question 28

How do baroreceptors signal to the brain the pressure changes?

Answer 28

When there is more stretch the nerve fires more

Question 29

How does the negative feedback loop of the baroreceptors work in a situation of decreasing blood pressure?

Answer 29

1 - Baroreceptors will fire less indicating decreasing blood pressure

2 - These signals are communicated back to the brain via afferent nerves

3 - The signal is received by the cardiovascular centre in the medulla

4 - This causes increased sympathetic and decreased parasympathetic stimulation

5 - this increases the secretion of epinephrine and norepinephrine (mainly this one) from adrenal gland increasing stroke volume, heart rate and causes vasoconstriction of the arteries resulting in increased blood pressure –> increases CO and TPR, BP = CO * TPR

6 - once baroreceptors have sensed normal blood pressure again, return back to homeostasis

Question 30

When there is increased blood volume, what does this cause?

Answer 30

Increased blood pressure

Question 31

How does the body regulate high blood pressure?

Answer 31

Cardio effects: Stimulate vasodilation (decreased sympathetic and decrease parasympathetic activity) and decrease CO

Renal effects: Increase fluid secretion

Question 32

What are the relative speeds and effectiveness of action of the cardio and renal effects on high blood pressure?

Answer 32

The cardio effect is fast (i.e. baroreceptors work within a single heart beat) but is only a temporary measure, renal effect is slower to work but it is able to make more significant longer term changes in blood pressure