Vascular control of Circulation

Question 1

What is the difference between the elasticity of arteries and veins?

Answer 1

Arteries are elastic and bounce back

Veins are expandable

Question 2

How do arterioles manage the pulsatile nature of heartbeat and systole?

Answer 2

They resist the pressure prior to entry into capillary beds creating a continuous flow. Entry into capillaries doesn’t need a huge amount of pressure due to drop in volume at capillaries creating adequate pressure difference.

Question 3

How are capillaries different to the other blood vessels?

Answer 3

They are fenestrated, thin and have no smooth muscle. Continuous capillaries are surrounded by epithelial cells

Question 4

What happens to flux if distance of diffusion is increased?

Answer 4

Increasing distance of diffusion will reduce flux

Question 5

Do capillaries change diameter in response to exercise?

Answer 5

Nope

Question 6

Do veins and venules have smooth muscle?

Answer 6

Yes but only a little bit due to low pressure. Venules very small amount

Question 7

Do arterioles have smooth muscle?

Answer 7

Yes and they have a lot of it

Question 8

What gives arteries their elasticity?

Answer 8

Internal elastic layer of tissue and surrounding adventitia (containing collagen and elastin)

Question 9

What do veins have more of elastin or collagen?

Answer 9

Elastin to allow them to expand in response to greater volume

Question 10

What is the difference between elastic arteries and muscular arteries?

Answer 10

The concentration of elastin and smooth muscle

Question 11

Where does most resistance to blood flow take place?

Answer 11

Arterioles

Question 12

What happens to velocity of blood flow?

Answer 12

It is inversely related to CSA and so at the capillaries it is very slow due to massive amount of CSA.

Question 13

What are the 3 different types of capillaries?

Answer 13

Continuous with tight tight junctions and desmosomes between cells forcing nutrients to need to cross the endothelial plamsa membranes to get through making them more regulated and slower diffusion.

Fenestrated capillaries which have holes in them (eg glomerulus) diameter is small enough to only let small proteins and ions through. Nothing is regulated and is purely dependent on pressure and diffusability.

Sinusoids are extremely leaky and have holes that only keep RBCs in the blood and everything else leaves through them.

This is a spectrum rather than default 3 categories.

Question 14

How is total capillary blood flow determined?

Answer 14

CO - Pressure and Resistance

Question 15

How are things moved across the capillary walls?

Answer 15

Diffusion, filtration, and reabsorption

Question 16

What does the blood brain barrier contain?

Answer 16

Continuous capillaries with lots of tight tight junctions.

Question 17

What is Starling’s law?

Answer 17

Filtration pressure is a balance of 2 pressure.

Pressure that promotes filtration

Pressure that promotes reabsorption

Question 18

What is the balance of filtration promoting pressure?

Answer 18

Between Capillary Hydrostatic Pressure (35 -> 16mmHg)

And

Interstitial fluid osmotic pressure (1 mmHg)

Question 19

What is the balance of reabsorption promoting pressure?

Answer 19

Plasma colloid osmotic pressure (approx 36 mmHg)

Interstitial fluid hydrostatic pressure (close to 0 mmHg)

Question 20

NFP = ?

Answer 20

NFP = (CHP + IFOP) - (PCOP + IFHP)

Question 21

What happens to Hydrostatic pressure as you move along the capillary?

Answer 21

It drops significantly and proteins in blood draw blood back in towards the end of the capillaries

Question 22

What is the purpose of the lymphatic system?

Answer 22

Excess fluid moves into the lymphatic fluid.

Question 23

Where is lymphatic fluid returned into circulation?

Answer 23

Thoracic duct empties at the subclavian artery

Question 24

What happens to the body in response to standing?

Answer 24

Reduces blood plasma volume for greater than 10%

Question 25

What happens if fluid is not being absorbed?

Answer 25

Oedema

Question 26

Where is most blood stored?

Answer 26

In venous system

Question 27

What is capacitance?

Answer 27

How well is pressure dealt with. Stiff vessels have low capacitance and elastic vessels have high compliance

Question 28

What is higher compleance veins or arteries?

Answer 28

Veins (more elastin less smooth muscle and less collagen)

Question 29

What is the effect of venoconstriction?

Answer 29

Increase in CO but no direct effect on BP

Question 30

Does arteriole constriction affect capacitance?

Answer 30

No because they have a small amount a volume

Question 31

Why are valves necessary in veins?

Answer 31

They don’t get driven by high pressure

Question 32

How is pulmonary blood flow different to systemic blood flow?

Answer 32

It is almost identical but there is lower pressure and so also lower resistance (resistance is 1/10th of Systemic Vascular Resistance)

Pulmonary vessels have less smooth muscle and low intravascular pressure

Pulmonary pressure is more well distributed.

Question 33

Reasons for difference in pressure between pulmonary and systemic circulations:

Answer 33

Gravity and distance (distance above or below heart affects arterial and venous pressure)

Control of regional perfusion in systemic circulation (large pressure head allows alterations in local vascular resistance to redirect blood flow to areas of increased demand)

Consequence of pressure differences (Left ventricle work load is greater than right ventricle, difference in wall thickness indicates difference in work load)

Question 34

What is the difference in perfusion demands between pulmonary and systemic circulation?

Answer 34

No need to open up capillary beds with pressure in pulmonary circulation whereas in systemic circulation the capillary beds are closed off.