Lesson 4 - The Heart Beat

Question 1

What are the causes of the “LUB DUB” sound of the heart?

Answer 1

LUB (first heart sound louder): AV valves (tricuspid and bicuspid valves) snap shut to avoid back flow.

DUB (second heart sound weaker): Semilunar valves (aortic valve and pulmonary valve) snap shut to avoid 
back flow.

Question 2

What is the order of contractions (what needs to contract first)?

Answer 2

The atria contract first, sending contractions from top to bottom. Ventricles send blood out of the heart to the rest of the body and lungs. They need to send their contractions from bottom to top. In order to prevent working against each other, the ventricles began their contraction once the atria are finishing up their contraction. The ventricles then contract, sending contractions from bottom to top. They both relax together.

Question 3

How are the 0.80 seconds (60 - 80 bpm) of the cardiac cycle distributed?

Answer 3

The heart is relaxed and the AV valves are open for approximately 0.4 seconds (DIASTOLE). The atria contract for approximately 0.1 seconds (SYSTOLE). The ventricles contract and semilunar valves are open (SYSTOLE).

Question 4

Where are the pacemaker cells located?

Answer 4

The sino-atrial (SA) node and atrioventricular (AV) node are where pacemaker cells are located. The sino-atrial node (SA node) is the natural pacemaker (one signal every 0.8 sec) and the atrio-venticular node (AV node) is secondary pacemaker,in some situations.

Question 5

What does the P Wave on an ECG represent?

Answer 5

During the P Wave, the SA node signalling occurs, atria cells depolarize, there is a wave of depolarization moves the along surface of atria, and there is an interval before the next wave (AV node delays its signal).

Question 6

What does the QRS complex on an ECG represent?

Answer 6

• AV node signaling (Q)

- ventricular cells: depolarization (R-S)

Question 7

What does the T wave on an ECG represent?

Answer 7

• re-polarization of ventricles (refilling with blood)

- Diastole phase of heart (relaxation)

Question 8

What is a defibrillator?

Answer 8

Defibrillation is a process in which an electronic device gives an electric shock to the heart. This helps reestablish normal contraction rhythms in a heart having dangerous arrhythmia or in cardiac arrest. In recent years small portable defibrillators have become available. This process shuts down all contraction. The signal must start from scratch, which is why the heart needs to “restart”..