1. Heart Beat and Blood Pressure

2. Heart Beat Animation

3. What makes a heart beat?
Heart muscle contraction is due to the presence of nodal tissue in two regions of the heart
SA node and AV node

4. SA Node The heart beat is set by the sinoatrial node (SA node)
The SA node is a bundle of specialized nerves
The SA node is located in the right atrium
The SA node stimulates the contraction of both left and right atrium
The SA node acts as a pacemaker setting a rhythm of about 70 beats/min.

5. AV Node AV node is located farther down in the right atrium
It receives the signals from the SA node and acts as a conductor spreading the nerve signals down special tracts toward the ventricles causing them both to contract

6. Coordination of the Beating
• If there was no coordination, the heart cells would all beat randomly (fibrillation)
• Coordinated beating occurs because of the SA node (the pacemaker cells) send nerve impulses to the other cells stimulating them to beat at the right time

7. Coordination of the Beating(2)
Contraction of ventricles
Take blood in from the atria
Pump blood out to the body
Contraction of atria
Take blood in from body
Pump blood into the ventricles
Coordinated beating of one then the other

10. The Cardiac Cycle
The heart beats or contracts 70 times per minute. The human heart will undergo over 3 billion contraction cycles during a normal lifetime.
The cardiac cycle consists of two parts:
1. systole (contraction of the heart muscle)
The contraction of the ventricles that opens the valves and forces blood into the arteries
2. diastole (relaxation of the heart muscle)
When the ventricle fills with blood.
Atria contract while ventricles relax.
Normal cardiac cycles (at rest) take 0.8 seconds.

11. Blood Pressure
Blood pressure is a measure of the force exerted by the blood on the wall of the arteries
An example is 120/80 (systolic pressure/diastolic pressure)
Systolic pressure is the result of the contraction of the ventricles (normal )
Diastolic pressure is during the ventricle relaxation (normal 70-90)

13. Electrocardiogram (ECG)
An electrocardiogram (ECG) measures changes in electrical potential across the heart, and can detect the contraction pulses that pass over the surface of the heart.
There are three slow, negative changes, known as P, R, and T.
Positive deflections are the Q and S waves. The P wave represents the contraction impulse of the atria, the T wave the ventricular contraction.
ECGs are useful in diagnosing heart abnormalities.

16. “Clear!!!”