EXAM 2 - CV System 1

Question 1

Describe blood flow

Answer 1

Blood enters right Atria from SVC & IVC –> Tricuspid valve –> Right Ventricle –> Pulmonary SLV –> Pulmonary trunk –> L & R pulmonary arteries –> Lungs –> L & R Pulmonary veins –> Left Atria –> Bicuspid/Mitral valve –> Left ventricle –> Aortic SLV –> Aorta

Question 2

Action Potential Steps: CARDIAC contractile cells

Answer 2

1. DEPOLARISATION: (same as AP in neuron)
   - Na+ voltage-gated channel opens, Na+ rushes into cell
   - -90mV to +30mV
2. THE PLATEAU
   - Depolarization caused by Na+ also opens slow Ca2+ channels
   - at +30mv = Na+ channels close, but slow Ca2+ channels remain open, prolonging depolarization
   - seen as a ‘plateau’
3. REPOLARISATION:
   - At 200ms, slow Ca2+ channels closed, and K+ channels open
   - Rapid efflux of K+ repolarises cell to RMP

Question 3

Electrical Conduction Pathway (5 Stepts)

Answer 3

1. SA NODE:
   - Generates impulse (pacemaker of the heart)
2. AV NODE:
   - Pauses impulse for 0.1 Seconds to allow blood to completely empty from Atria
3. AV BUNDLE:
   - Connects Atria to Ventricles
4. BUNDLE BRANCHES:
   - Conduct impulses through the interventricular septum
5. PURKINJE FIBRES (SUBENDOCARDIAL CONDUCTING NETWORK):
   - Depolarize the contractile cells of both ventricles

Question 4

ECG:

Answer 4

P WAVE:
- Depolarization of Atria, initiated by SA node)
- (I.e. leads to atrial contraction)

GAP BETWEEN P & QRS COMPLEX:
- Atrial depolarization complete
- AV node delays impulse by 0.1 second to allow blood to completely empty from Atria

QRS COMPLEX:
- Ventricular depolarization beginning at Apex
- Atrial repolarization occurs

GAP BETWEEN QRS COMPLE & T WAVE:
- Ventricular depolarization complete

T WAVE:
- Ventricular repolarization beginning at Apex

GAP AFTER T WAVE:
- Ventricular repolarization complete

*REMEMBER: Electrical stuff happens BEFORE diastole/systole happens

Question 5

Heart Sounds

Answer 5

‘Lub-Dub’

FIRST ‘LUB’ SOUND: AV Valves closing
- Ventricular systole (contraction)
- THINK: If ventricles are contracting, AV valves NEED to be closed, otherwise blood will go back into Atria. SLV’s are open, as the blood needs to be pushed somewhere

SECOND ‘DUB’ SOUND: SL Valves closing
- Ventricular Diastole (relaxing)
- THINK: If ventricles are relaxing, they are filling with blood. For this to happen, AV valves must be open, and SLV are closed to seal blood off from going anywhere until contraction occurs.

**REMEMBER: SOUNDS = CLOSING OF VALVES

Question 6

Heart Valve Movements

Answer 6

Ventricular filling (relaxing/diastole): AV Valves open, SL Valves closed

Isovolumetric contraction: Both Valves closed

Ventricular ejection (contraction/systole): AV Valves closed, SL Valves open

Isovolumetric relaxation: Both Valves closed

**REMEMBER: Isovolumetric –> Both valves closed

Question 7

Calculating Stroke Volume

Answer 7

End Diastolic Volume (EDV) - End Systolic Volume (ESV) = Stroke volume

‘End Diastolic Volume’ –> At the end of filling/relaxing, how much volume of blood is in the heart

‘End Systolic Volume’ –> At the end of ejecting/contracting, how much volume is in the heart