P: Circulatory system

Question 1

What are elastic arteries (conduits)

Answer 1

• Aorta & other large arteries
• Numerous layers of elastin fibers which expand when pressure of blood rises during ventricular systole + recoil when ventricles relax

Question 2

What are muscular arteries (resistance vessels)

Answer 2

• Arterioles
• Much less elastic + have thicker layer of smooth muscle which regulates diameter of lumen.

Question 3

Ohm’s law

Answer 3

Rate of blood flow = (change in pressure)/Resistance

Question 4

Major regulators of blood flow are:

Answer 4

• Mean arterial pressure
• Vascular blood vessel diameter
• Blood viscosity

Question 5

Viscosity of normal blood

Answer 5

3

Question 6

If haematocrit = 60 (polycythaemia) viscosity can reach:

Answer 6

> 7
Resistance increases and flow through blood vessels can be compromised.

Question 7

Effects of decreased resistance of blood

Answer 7

Decreased resistance –> increased rate of peripheral blood flow, venous return + cardiac output.
Hypoxia also causes blood vessel dilation + further increases cardiac output.
Sustained increase in pumping workload of heart.

Question 8

What is compliance

Answer 8

volume of blood that can be stored in a blood vessel for each mmHg pressure rise.

Question 9

Compliance/ capacitance equation

Answer 9

change in volume/ change in pressure.
Related to ability of blood vessel to stretch/ distend to accommodate larger volume of blood (distensibility).

distensibility x volume.

Question 10

Distensibility & compliance is determined by:

Answer 10

• Quantity of elastin fibers in vessel wall –> wall can stretch to accommodate additional blood volume.
• Wall thickness.

Question 11

Average blood pressures (systolic/diastolic)

Answer 11

120/80 or 140/90

Question 12

Mean arterial pressure equation

Answer 12

Mean arterial pressure: diastolic pressure + 1/3 (systolic-diastolic pressure)

Question 13

Hypertension

Answer 13

chronically elevated blood pressure –> 20% of adults.

Question 14

Types of hypertension

Answer 14

• Essential hypertension: unclear multifactorial causes such as diet + genetics, 95% of cases
• Secondary hypertension: resulting from another condition (e.g. renal disease), chronically elevated salt and water reabsorption in nephron will increase blood volume and chronically raise bp.

Question 15

Long-term hypertension effects

Answer 15

• Long-term damage to heart and kidneys, is a risk factor for heart attack + stroke
• Ventricles must contract more forcefully to maintain adequate stroke volume, resulting in long term damage to heart muscle (increased afterload)
• High pressure damages endothelial lining of arteries, promotes formation of atherosclerotic plaques, increased risk of heart attack or stroke.

Question 16

Pulse pressure equation

Answer 16

systolic pressure - diastolic pressure.

Question 17

What is pulse pressure

Answer 17

• Left ventricular contraction creates a pulse of systolic pressure as blood is ejected into arteries
• This is transmitted through elastic walls of large arteries
• Velocity of transmission of pressure pulse is -15 times velocity of blood flow