Human breathing system

Describe the process of inspiration

- external intercoastal muscles contract and ribs + outer pleural membrane pulled upwards and outwards

- diaphragm contracts and it flattens

-reduces pressure in pleural cavity so inner pleural membrane pulled outwards

- lungs expand and increase volume in the alveoli

- so alveolar pressure decreases (so air pressure is greater than pressure in lungs) so air is forced into the lungs

Describe the process of expiration

- intercoastal muscles relax and ribs move downards and inwards

- diaphragm relaxes so domes upwards and membranes move down and in

- volume decreases so pressure increases and air is forced out

Why are alveoli efficient at gas exchange?

- large surface area

- most so gases dissolve and diffuse easily

- short diffusion pathway

- capillary network surrounds alveoli and helps it maintain conc gradient

what is the surfactant?

- found in the inner lining of the alveoli

- stops alveoli collapsing and reduces surface tension

- keeps alveoli moist and reduces amount of effort needed to breathe