Circulation of Blood: Lecture 11

Question 1

What is haemodynamics?

Answer 1

The flow of blood from two points (A to B)

Question 2

What are the two factors that affect rate of flow?

Answer 2

○ Pressure different between A and B: if pressure is greater at A than B, rate of flow increases from A to B
○ Resistance to flow: If resistance increases, rate of flow decreases

Question 3

What is Darcy’s law?

Answer 3

Flow of fluid through a porous medium
F = ΔP/R

Question 4

What factors affects rate at which blood moves through the vessels?

Answer 4

○ Pressure
○ Viscosity
○ Vessel length
○ Vessel radius

Question 5

What creates vascular resistance and the factors that affect it?

Answer 5

○ When blood comes into contact with the vessel walls generating friction
○ Vessel length
○ Blood viscosity
○ Vessel radius

Question 6

How does vessel length affect vascular resistance?

Answer 6

○ As vessel length increases, internal surface area increases
○ Resistance increases so rate of flow decreases

Question 7

How does blood viscosity affect vascular resistance?

Answer 7

As viscosity increases (due to high RBC or protein content), resistance increases so rate of flow decreases

Question 8

How does vessel radius affect vascular resistance?

Answer 8

○ Flow is proportional to r^4
○ If Radius is 2x bigger, resistance is 16x less so rate of flow is 16x greater
○ Small changes in arteriole diameter dramatically affect tissue blood flow

Question 9

Order the vessels from fastest rate of flow to slowest rate of flow

Answer 9

Elastic artery -> muscular artery -> vena cavae -> veins -> arterioles -> capillaries

Question 10

Why do elastic arteries have a higher rate of flow than the vena cavae

Answer 10

○ Diameter of vena cave is bigger than elastic artery
○ Elastic artery is at a higher pressure than vena cavae
○ Vena cavae has the lowest pressure

Question 11

What side of the heart generates more presssure and why?

Answer 11

○ Left side: delivers blood through the systemic circuit
○ Systemic circuit has greater surface area so more resistance

Question 12

What is the pressure like on the right side in diastole and systole compared to the left side?

Answer 12

○ In systole (contraction): left side is much higher in pressure than the right side
○ In diastole (relaxation): both sides are at similar low pressures

Question 13

How is blood flow maintained during diastole?

Answer 13

○ In ventricular systole: elastic arteries expand
○ In ventricular diastole: elastic arteries rebound which keeps pressure high to allow blood to move

Question 14

What is systolic pressure and diastolic pressure?

Answer 14

○ Systolic pressure: maximum pressure (90-120mmHg)
○ Diastolic pressure: minimum pressure (60-80mmHg)

Question 15

Where is arterial pressure measured?

Answer 15

Brachial artery

Question 16

What is the dicrotic notch?

Answer 16

Closure of aortic valve`

Question 17

What is the equation for pulse pressure?

Answer 17

Systolic pressure - diastolic pressure

Question 18

What is the equation for mean arterial pressure?

Answer 18

Diastolic blood pressure - 1/3(pulse pressure)

Question 19

What are the steps of the cardiac conduction system?

Answer 19

○ SA node: located in the right atrium, pacemaker cells spontaneously depolarise
○ Internodal pathways: cell-to-cell conduction across atria
○ AV node: delay which allow atrial contraction
○ AV bundle
○ Bundle branches: down the septum of the heart and allow rapid conduction for coordinated ventricular contraction
○ Purkinje fibres: triggers ventricular contraction

Question 20

What does the P wave represent?

Answer 20

Atrial cells depolarising leading to contraction of atria

Question 21

What does the QRS complex represent?

Answer 21

○ Ventricular cells depolarising leading to contraction of ventricles
○ Atrial cells repolarise so they relax

Question 22

What does the T wave represent?

Answer 22

Ventricle cells repolarising so that the ventricles become relaxed

Question 23

What are the pressure-volume changes in the aorta, left atrium and left ventricle in late diastole (start)?

Answer 23

Atria & ventricles are relaxed
Pressure:
○ Aortic pressure > LA pressure > LV pressure
○ AV valve opened but aortic valve is closed
Volume:
○ Atria & ventricles passively filling
○ LV volume increasing

Question 24

What are the pressure-volume changes in the aorta, left atrium and left ventricle in atrial systole?

Answer 24

Atria contracts
Pressure:
○ Atrial pressure rises
Volume:
○ LV volume rises as blood squeezed from atrium

Question 25

What are the pressure-volume changes in the aorta, left atrium and left ventricle in ventricular systole?

Answer 25

Ventricles contract (isovolumetric contraction)
Pressure:
○ LV pressure rises sharply but does not exceed aortic pressure
○ LV pressure > LA pressure: AV valve closes (1st heart sound)
Volume:
○ Isovolumetric contraction: LV volume unchanged as all valves closed

Question 26

What are the pressure-volume changes in the aorta, left atrium and left ventricle in ventricular systole (ejection)?

Answer 26

Ventricles contract
Pressure:
○ LV pressure > Aortic pressure: aortic valve opens
Volume:
○ LV volume falls as blood ejected into aorta

Question 27

What are the pressure-volume changes in the aorta, left atrium and left ventricle in ventricular diastole?

Answer 27

Ventricles relax
Pressure:
○ LV pressure < aortic pressure: aortic valve closes (2nd heart sound)
○ Dichrotic notch due to aortic valve closure
○ LV pressure falls but remains above atria
Volume:
○ Isovolumetric relaxation: LV volume unchanged as all valves closed

Question 28

What are the pressure-volume changes in the aorta, left atrium and left ventricle in late diastole (end)?

Answer 28

Atria & ventricles relaxed
Pressure:
○ LV pressure < LA pressure: Av valves opens
Volume:
○ LV fills, volume rises