why do we need a ventilation system in our body

Oxygen is required for cell respiration and CO2 is the waste product. Therefore, organisms must take in oxygen from their surroundings and release CO2. Unicellular organisms are able to get sufficient oxygen through diffusion across the membrane. Large animals also depend on diffusion to get their oxygen but they require a specialized ventilation system, which functions to: 1) maintain a concentration gradient, which is necessary for diffusion and 2) increase surface area, which speeds up gas exchange.

In humans, air enters the body through the nose or mouth. From there it passes the trachea, into the bronchi which branch into many smaller bronchioles.

Finally the air ends up tiny membranous sacs called alveoli. O2 diffuses from the air in the alveoli to the blood, and CO2 diffuses from the blood to the air in the alveoli. Human Ventilation System
The human respiratory system contains the organs that allow us to get the oxygen we need and to remove the waste carbon dioxide we don't need.

It contains these parts: various structures in the chest that allow air to move in and out of the lungs. Movements of the ribs, rib muscles and diaphragm allow air into and out of the lungs.

Take care - this is called breathing or ventilation, not respiration. When we breathe in, we inhale. When we breathe out, we exhale. Air passes between the lungs and the outside of the body through the windpipe, called the trachea.

The trachea divides into two bronchi, with one bronchus for each lung. Each bronchus divides further in the lungs into smaller tubes called bronchioles. At the end of each bronchiole, there is a group of tiny air sacs. These air sacs have bulges called alveoli to increase their surface area.