BMS2031 Lecture 2: Week 1. Cardiovascular System and Excitation of the Heart
31 May 2018
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Week 1. Cardiovascular System and Excitation of the
Heart
INTRODUCTION TO THE CARDIOVASCULAR SYSTEM
• Human physiology is the function of the human body
• Cardiovascular system = the tubes (blood vessels) + heart (pump to produce blood flow)
• Circulatory system = blood vessels + heart + fluid (blood)
• Why do we have a circulatory system:
o To transport nutrients and oxygen
o Removal of waste, toxins and carbon dioxide
• Heart valves
Aortic and pulmonary valves
o Semilunar valves
o Allow flow from ventricles into arteries
(aorta or pulmonary artery)
o Prevents back flow
Atrioventricular valves
o Mitral (bicuspid) valve between left and atrium and ventricle
o Tricuspid valve between right and atrium and ventricle
o Allows flow from atria into ventricles
o Prevents back flow
• Pulmonary circuit starts with right ventricle
• Systemic circuit starts with left ventricle
• Blood flow:
o Difference in pressure causes flow
o Flow is proportional to the pressure difference
o Flow is directly proportional if it is laminar
Laminar flow
Turbulent flow
o Smooth
o No swirling
o Silent
o Flow in blood is normally laminar
o Swirling edges
o Noisy (can be heard)
o May occur where flow is restricted or
impeded
o Useful for diagnostic aspects of CVS
function:
Stenotic valve: narrow valve
-> turbulent flow causes murmur
Leaky valve
-> turbulent backflow causes
murmur
• Peripheral resistance (PR):
o The longer the vessel the higher the friction and the higher the PR
o Flow through a vessel increases in proportion to the fourth power of the radius of the
radius
o The narrower the vessel the higher the resistance
• Viscosity:
o Haematocrit is the percentage volume of blood occupied by red blood cells
o Higher haematocrit = higher viscosity (stickiness) = reduced blood flow
o Athletes can artificially elevate haematocrit via synthetic EPO or blood doping
-> this will decrease blood flow but increase oxygen and thus increase performance
o Haematocrit is usually maintained relatively constant
-> can be abnormally low in anaemia
-> can be abnormally high in severe dehydration or synthetic erythropoietin (EPO/Blood
doping)
• 3 factors that determine resistance to flow
1. Length of the tube (can’t be changed) -> resistance is proportional to length
2. Radius of the tube ** -> resistance is proportional to 1/r4
3. Viscosity of the fluid (usually kept constant in healthy individual) -> increase hct =
increase resistance
• Basic flow equation: F = delta P/R
• Decreased diameter = increased resistance = decreased flow
• Pulmonary circulatory (~15mmHg) has lower pressure than Systemic circulatory (~95mmHg)
although the flow is the same for both
-> this is due to the systemic circulation having longer vessels which means they have higher
resistance hence needs a much higher force
