Lecture 12: Cardiovascular System 2

Question 1

Heart valves: name them, and why do we have them?

Answer 1

Tricuspid (right atrioventricular valve)
Bicuspid (left atrioventricular valve) 
Pulmonary semilunar valve
Aortic semilunar valve
Slide 6 for image 

All valves open passively due to pressure gradient
All valves close passively due to pressure gradients
Valve closure produces heart sound

Question 2

When are the two lub dubs heard? What are the events occurring?

Answer 2

S1: first sound
Is a soft, low, “lubb”
-due to AV valve closure
-occurs at the starts if vehicular contraction

S2: second sound is louder, higher “dupp”

• due to SEmilunar valve closure
• occurs at the start if ventricular relaxation

Question 3

The cardiac cycle = ?

Answer 3

Events associated with blood flow through the heart during a single complete heart beat.
-action potentials in myocardial cells produce myocardial cell contraction
-contraction of heart chambers generates cyclical pressure differences between the atria, ventricles and vasculature
-blood flows passively from areas of high pressure to areas of low pressure.
Electrical activity (AP) –> contraction –> pressure differences –> volume changes (blood flow)

Question 4

1st: electrical activity.

How is the electrical activity spread through the heart?

Answer 4

Depolarisation spreads through atrial myocardial cells, depolarisation spreads through ventricular myocardial cells, Repolarisation spreads through ventricular myocardial cells

Question 5

2nd: mechanical activity. What is the relationship between electrical and mechanical events in the heart?

Answer 5

Electrical activity causes (and precedes) mechanical activity
Depolarisation –> contraction
Repolarisation–> relaxation

Contraction of a cardiac chambers is called systole
Relaxation of a cardiac chamber is called diastole
Review slide 17 for image on their contraction with an ECG

Question 6

3rd: pressure differences. Describe how pressure changes lead to flow of blood

Answer 6

Atrial pressure peaks during atrial systole
Ventricular pressure decreases during ventricular diastole
Atrial and ventricular pressures increase slowly when both chambers are in diastole, due to venous return.

Question 7

4th: volume changes (blood flow)

Answer 7

1. Ventricular volume increases during Late diastole as blood flow In from the atria, driven by central venous pressure (blood returning from the veins)
2. Ventricular volume increases during atrial systole
3. Vehicular volume stays constant at the beginning of ventricular systole, before semilunar valves open
4. Ventricular volume decreases during late ventricular systole one the semilunar valves open
5. Ventricular volume stays constant at the beginning of ventricular diastole, until, the AV valves open

Question 8

What is the
End diastolic volume
End systolic volume
Stroke volume

Answer 8

End diastolic volume= volume of blood in ventricle at end of diastole
End systolic volume= volume of blood in ventricle at end of systole
Stroke volume= volume of blood ejected from heart each cycle.
SV= EDV-ESV

Question 9

Cardiac cycle review

Answer 9

1a: ventricular filling
-ventricles relax
-AV valve open
-blood moves passively from atria to ventricle, driven by pressure from veins
1b. Atria contraction
-ventricles relax
-atria contract
-blood moves actively from atria to ventricle
-ventricular pressure
2. Isovolumetric contraction
-ventricle depolarises and contracts
-contraction increases ventricular pressure
-ventricular pressure > atrial pressure
-AV valves closes (1st heart sound)
-no change in ventricular volume because SL valves
CBF