The Heart as a Pump (1.5)

Question 1

Flow in/out of the ventricle is controlled by what VALVES?

Answer 1

ATRIOVENTRICULAR VALVES : mitral (L) and tricuspid (R)

OUTFLOW VALVES : aortic (L) and pulmonary (R)

Question 2

What are the two types of cardiac muscle cells?

Answer 2

MYOCARDIAL CONTRACTILE CELLS (99% of cells) - responsible for the CONTRACTIONS

MYOCARDIAL CONDUCTING CELLS (1% of cells)

Question 3

What are features of the myocardial conducting cells?

Answer 3

Myocardial conducting cells form the CONDUCTION system of the heart

• Much smaller than contractile
• Few myofilaments for contraction
• Function similar to neurones

Question 4

What are the HISTOLOGY features of cardiac muscle fibres?

Answer 4

• striations (due to actin/myosin filaments)
• central positioned nuclei
• intercalated discs (for electrical and mechanical coupling with adjacent cells - see *)
• branching (see arrows)

Question 5

What is a PACEMAKER?

Where are they located?

Answer 5

action potential generated in small group of cells will spread over the whole heart and produce a coordinated contraction - one AP at regular intervals

They are located in the SA NODE in the RIGHT ATRIA

Question 6

Explain the Cardiac AP?

Answer 6

• Pacemaker in the SA node in the right atria
• Excitation spreads over atria (ATRIAL SYSTOLE)
• Reaches the AV node
• 120 ms delay
• Impulse enter the ventricles at BUNDLE OF HIS
• This spreads through ventricle from inner (ENDOCARDIAL) to outer (EPICARDIAL) surface
• Follows the left and right bundle branches along intraventricular septum
• Divide into system of PURKINJE FIBRES that conduct through ventricle
• Ventricles contracts from the apex up, forces blood towards outflow valves (pulmonary/aortic)

Question 7

Explain the flow INTO the LEFT VENTRICLE?

Answer 7

The flow into the LEFT VENTRICLE is controlled by the MITRAL VALVE

OPENS: when atrial pressure exceeds intraventricular pressure

CLOSES: when intraventricular pressure exceeds atrial pressure

Question 8

Explain the flow OUT of the LEFT VENTRICLE?

Answer 8

The outflow valve out of the LEFT VENTRICLE is the AORTIC VALVE

OPENS: when intraventricular pressure exceeds aortic pressure

CLOSES: when aortic pressure exceeds intraventricular pressure

Question 9

Explain closure of the valves in relation to heart sounds

Answer 9

FIRST heart sound : S1 LUB associated with CLOSURE of AV valves (onset of ventricular systole)

SECOND heart sound : S2 DUP associated with CLOSURE of OUTFLOW (end of ventricular systole)

Question 10

When can extra heart sounds be heard?

Answer 10

3rd (S3) early in DIASTOLE

4th (S4) heard in ATRIAL SYSTOLE

Question 11

What is a MURMUR?

What is a common example - and when is it heard?

Answer 11

TURBULENT BLOOD FLOW

It is caused by: STENOSIS (narrowed valve) or INCOMPETENCE (valve not closing properly)

Aortic Stenosis - murmur heard in RAPID EJECTION PHASE

Question 12

CARDIAC OUTPUT = _________ X __________

What are the common values for each?

Answer 12

CO = SV x HR

SV = 80mL, HR = 60bpm, CO = 5l/min-1