Lecture 17 - Blood flow in veins

Question 1

Describe veins

Answer 1

Keep blood flowing towards the heart (prevent to flow backward by using valves located inside the veins)

The structure is very similar to arteries

Transport blood at lower pressure therefore not as strong as arteries (have thin walls and may be collapsed in normal function)

Receive blood from the capillaries after the exchange of O2 and CO2

Contain about 80% of the total volume of blood in the systemic vascular system

The most important feature of systemic veins is their compliance

Question 2

Transmural pressure equation?

Answer 2

delta p = p_i - p_e
where:

p_i = internal pressure

p_e = external pressure

Question 3

delta p > 0 at exit and and entry

Answer 3

normal flow, vein is open

Question 4

delta p < 0 at exit and entry

Answer 4

vein is collapsed, flow is greatly reduced.

Question 5

delta p >0 at entry but delta p <0 at exit

Answer 5

The entry section is open but the exit section may be collapsed. This does not last and the tube comes back to normal and flow starts again. This generates self-excited oscillations. The flow starts, the pressure drops along the tube and the exit section is choked again (so called “flutter”, a repeating dynamic phenomenon).

Question 6

Stable structure? (elastic instability)

Answer 6

The small disturbance causes a small deformation and once
removed the structure returns to the basic configuration

Question 7

Unstable structure? (elastic instability)

Answer 7

The small disturbance causes a large deformation and
once removed the structure does not return to the basic
configuration