Lecture 27. Circulation

Question 1

What system is the cardiovascular system?

Answer 1

Dual circulation

Question 2

What do elastic arteries do?

Answer 2

Smooth pulsatile flow

Question 3

What do muscular arteries?

Answer 3

Control resistance to flow

Question 4

What are veins?

Answer 4

Capacitance vessels holding a reservoir of blood

Question 5

What are capillaries?

Answer 5

Exchange vessels

Question 6

What is the common blood vessel structure (from outwards to inwards)?

Answer 6

Tunica adventitia (externa - principally collagen)
Tunica media (elastic tissue and smooth muscle)
Tunica intima (interna - endothelium)
Lumen

Question 7

What do elastic arteries store?

Answer 7

Energy

Question 8

What is the tunica intima?

Answer 8

Single layer

Question 9

When is the energy stored in the wall of elastic arteries released?

Answer 9

In diastole, maintaining the blood flow at this time and smoothing it

Question 10

What. is the Windkessel effect?

Answer 10

As blood is pumped into the aorta and major arteries, they stretch
Thus in systole, more blood flows in than out
The walls of the aorta and elastic arteries recoil in diastole, maintaining blood flow

Question 11

When does aortic pressure rise to a maximum and when does it fall to a minimum?

Answer 11

Rises to a maximum during systole - the systolic pressure
Falls to a minimum during diastole - the diastolic pressure

Question 12

What does blood flow depend on?

Answer 12

Blood vessel radius

Question 13

What determines resistance?

Answer 13

Length of blood vessels
Viscosity of blood
Radius of blood vessels

Question 14

What are the sites of controlled resistance to flow?

Answer 14

Small arteries and arterioles

Question 15

What is Ohms Law?

Answer 15

Q = (P₁ – P₂)/R
Where Q = flow and P₁ – P₂ = pressure difference between the two ends and R is the resistance of the vessel

Question 16

What is blood flow normally?

Answer 16

Laminar - The flow is considered essentially as layers of fluid that move over each other. Flow is fastest at the centre and slowest – essentially stationary – at the outside

Question 17

What is the equation for laminar flow?

Answer 17

R = (8ηl)/πr⁴
Where R = resistance, η = viscosity, l = length, r = radius and π = π

Question 18

What would a reduction in radius by 1/2 change in resistance?

Answer 18

Resistance increases 16 fold

Question 19

When does flow become turbulent?

Answer 19

If velocity is high enough, the layers (laminae) of laminar flow break up and flow becomes disordered

Question 20

What do sphincters control?

Answer 20

Access to the microcirculation

Question 21

What are capillaries designed to optimise?

Answer 21

Diffusion - their structure minimises resistance to diffusion into and from the interstitium

Question 22

What is the permeability of lipid soluble molecules?

Answer 22

Lipid soluble molecules, which include O₂ and CO₂, diffuse easily through capillary cell membranes

Question 23

What is the permeability of hydrophilic molecules?

Answer 23

Travel through pores, via a paracellular route

Question 24

What is the permeability of molecules >60kd?

Answer 24

Not transferred and many plasma proteins are retained in the circulation – important in the equilibrium between plasma and the e.c.f.

Question 25

What are the two compartments of extracellular fluid called?

Answer 25

Plasma and intracellular fluid

Question 26

What determines equilibrium between the plasma and the interstitial fluid?

Answer 26

Hydrostatic pressure and oncotic pressure

Question 27

What determines the filtration pressure?

Answer 27

Filtraction pressure - hydrostatic pressure - oncotic pressure

Question 28

What takes up excess fluid and returns it to the circulation?

Answer 28

Lymphocytes

Question 29

What enhances venous return?

Answer 29

Muscle pump