S2: the heart as a pump, control of cardiac output & anatomy of the heart

Question 1

Describe the basic structure of the heart, naming the chambers, valves, and main vessels and the main differences between the right and left heart

Answer 1

4 chambers: right and left atria, right and left ventricles
4 valves: tricuspid (between right ventricle and atrium), pulmonary (between right ventricle and pulmonary trunk), mitral (between left ventricle and atrium) and aortic (between left ventricle and aorta)
Pulmonary vein enters left atrium
Superior and inferior vena cava drain into right atrium

Question 2

Define the terms systole and diastole

Answer 2

Systole = contraction and ejection of blood from ventricles
Diastole = relaxation and filling of ventricles

Question 3

Name the 7 phases of the cardiac cycle in order

Answer 3

Atrial contraction
Isovolumetric contraction
Rapid ejection
Reduced ejection
Isovolumetric relaxation
Rapid filling
Reduced filling

Question 4

Describe when in the cardiac cycle each valve in the heart opens and closes

Answer 4

Phase 2: mitral valve closes
Phase 3: aortic valve opens
Phase 5: aortic valve closes
Phase 6: mitral valve opens

Question 5

Explain the origin of the 1st and 2nd heart sounds

Answer 5

S1 heart sound caused by the closure of mitral and tricuspid valves
S2 heart sound caused by the closure of aortic and pulmonary valves

Question 6

Describe aortic valve stenosis

Answer 6

Causes: degenerative (senile calcification/fibrosis), congenital (bicuspid form of valve instead), chronic rheumatic fever
Can cause microangiopathic haemolytic anaemia (stress on RBCs going through a narrow path)
LV hypertrophy, syncope & angina
Murmur: crescendo-decrescendo

Question 7

Define cardiac output

Answer 7

CO = is the amount of blood the heart pumps in 1 minute

Question 8

Define preload, afterload and contractility

Answer 8

Preload: amount the ventricles are stretched in diastole (related to EDV/CVP)
Afterload: the load the heart must eject blood against (roughly equivalent to aortic pressure)
Contractility: force of contraction for a given fibre length

Question 9

Explain the Frank-Starling Law of the heart

Answer 9

The more the heart fills, the harder it contracts

Stretching the ventricles by increasing the filling of the heart increased the force of contractions

Question 10

Describe rapid filling

Answer 10

Fall in atrial pressure = Y-descent
Ventricular pressure < atrial pressure, mitral valve opens
S3 HEART SOUND normal in children but sign of pathology in adults

Question 11

Describe reduced filling

Answer 11

Rate of filling slows down
Further filling is driven by venous return
End of phase 7 90% full

Question 12

Describe aortic valve regurgitation

Answer 12

Causes: aortic root dilation, valvular damage
Bounding pulse, LV hypertrophy
Murmur: early decrescendo diastolic

Question 13

Describe mitral valve regurgitation

Answer 13

Causes: damage to papillary muscle (MI), LV dilation, myxomatous degeneration
Increases preload
Murmur: holosystolic

Question 14

Describe mitral valve stenosis

Answer 14

Causes: rheumatic fever
Increased LA pressure
RV hypertrophy, thrombus formation, dyspagia (oesophagus compression)
Murmur: snap as valve opens, diastolic rumble

Question 15

Name the intrinsic and extrinsic control mechanisms of the heart

Answer 15

Intrinsic = Starling's law (ensures both sides of the heart pump maintain the same output) 
Extrinsic = autonomic nervous system & circulating adrenaline

Question 16

Describe atrial contraction

Answer 16

Atrial pressure rises due to atrial systole = A wave
Accounts for the final 10% of ventricular filling
Ventricular volumes are maximal = EDV

Question 17

Describe isovolumetric contraction

Answer 17

Ventricular pressure > atrial pressure
Rapid rise in ventricular pressure
Closing of mitral valve = C wave 
No change in ventricular volume
FIRST HEART SOUND = S1

Question 18

Describe rapid ejection

Answer 18

Ventricular pressure > aortic pressure
Aortic valve opens
Atrial pressure initially decreases as the atrial base is pulled downwards as ventricle contracts = X descent
Rapid decrease in ventricular volume

Question 19

Describe reduced ejection

Answer 19

Rate of ejection falls
Atrial pressure gradually rises = V wave
Ventricular repolarisation

Question 20

Describe isovolumetric relaxation

Answer 20

Ventricular pressure < aortic pressure
Brief backflow of blood = aortic valve closes
Dicrotic notch
No change in ventricular volume (rapid decline in ventricular pressure)
ESV
SECOND HEART SOUND = S2