Cardiovascular system haemodynamic and cardiac muscle

Question 1

State ‘Darcy’s Law’

Answer 1

Flow = Pressure Difference / Resistance

Question 2

‘Resistance is inversely proportional to the radius of the vessel’ - Explain why

Answer 2

doubling a vessels radius reduces resistance whereas halving the vessels radius would increase resistance

Question 3

State ‘Poiseuille’s Law’

Answer 3

Resistance = 1/r4

Question 4

How do you combine Darcy’s and Poiseuille’s Laws?

Answer 4

Flow = Pressure difference x r4

Question 5

How is flows relation to pressure and vessel radius directly proportional?

Answer 5

The higher the driving pressure and the larger the radius of a vessel, the higher the flow (and vice versa)

Question 6

What is the equation for ‘velocity’?

Answer 6

Velocity = Flow rate/ Cross-sectional area (CSA)

The narrower the vessel the faster the faster the flow

Question 7

What is the relationship between velocity and total cross-sectional area ?

Answer 7

Flow velocity of blood in the CV system depends on the cumulative radius of all vessels at a similar distance from the heart

Question 8

Why is the combination of large CSA and very low blood flow velocity important in tissues?

Answer 8

This is important for diffusion of gases and exchange of nutrients/waste

E.g., Capillaries

Question 9

What is the difference in excitation-contraction reaction in cardiac vs skeletal muscle?

Answer 9

In skeletal muscle, no extracellular calcium enters whereas the contraction of cardiac muscle cells is dependant of extracellular Ca2+

Question 10

Can tetanic contractions occur in cardiac muscle cells?

Answer 10

No