The Lungs

 

The Lungs are the organ at which gas exchange occurs. 

 

Air takes the following path:

• Air → mouth/nose → trachea → bronchi → alveoli  

 

Alveoli are tiny air sacs surrounded by capillaries

 

Adaptations for Gas Exchange:  

1. Huge surface area (millions of alveoli)  

2. One-cell-thick walls → short diffusion path  

3. Rich blood supply → maintains concentration gradient  

4. Ventilation → fresh air in, stale out which allows constant gas exchange

 

The Heart

 

The human heart has what we call double circulation, meaning blood enters and leaves the heart twice per cycle. Whereas some animals, e.g. certain fish, has single circulation instead.

 

The Heart — Double Circulation  

• Right side → pumps deoxygenated blood to lungs  

• Left side → pumps oxygenated blood to body  

 

The Double Circulatory system means that the lungs and body have separate sides. This makes it efficient as the deoxygenated blood from the body doesn’t contaminate the freshly oxygenated blood from the lungs.

 

Key Blood Vessels:  

• Aorta → oxygenated blood to body  

• Vena cava → deoxygenated blood to heart  

• Pulmonary artery → to lungs  

• Pulmonary vein → from lungs  

• Coronary arteries → supply heart muscle

Diagram.

 

Pacemaker = group of cells in right atrium → controls heartbeat  

Artificial pacemaker = electronic device for irregular hearts when biological pacemaker does not work.