Lung and alveoli function

Ventilation: inspiration

1.) the intercostal and diaphragm muscles contract 2.) this causes the ribcage to move upwards and outwards and the diaphragm to flatten, increasing the volume of the thorax 3.) as the volume of the thorax increases the lung pressure decreases 4.) this causes air to flow into the lungs 5.) inspiration is ana active process-it requires energy

Ventilation: expiration

1.) the intercostal and diaphragm muscles relax 2.) the ribcage moves downwards and inwards and the diaphragm becomes curved again 3.) the thorax volume decreases causing the air pressure to increase 4.) air is forced out of the lungs 5.) expiration is a passive process

Features of alveoli affecting the rate of diffusion:

1.) they have a thin exchange surface- alveolar epithelium is only one cell thick= short diffusion pathway= speeds up diffusion 2.) a large surface area- large number of alveoli= large SA for gas exchange 3.) steep concentration gradient of o2 and co2 between the alveoli and capillaries which increases the rate of diffusion

Alveoli structure

alveoli are surrounded by network of capillaries. each alveolus is made from a single layer of thin flat cells called alveolar epithelium. the walls of the capillaries are made from capillary endothelium. the walls of the alveoli contain elastin which is elastic and helps the alveoli to return to their normal shape after inhaling and exhaling the air.

Lung structure:

as you breathe in, air enters the trachea. the trachea splits into two bronchi-one leading to each lung each bronchus then branches off into smaller tubes called bronchioles the bronchioles end in small air sacs called alveoli which is where gases are exchanged

Gas exchange in the alveoli:

o2 diffuses out of the alveoli, across the alveolar epithelium and capillary endothelium into haemoglobin in the blood. co2 diffuses into the alveoli from the blood and is breathed out.