The lungs

The lungs are part of the respiratory system and the circulatory system. They are made up of:
-trachea: this is also known as the wind pipe; it is the passage for air between the nasal and mouth passage to the bronchi.
-bronchi: two branches that are connected to the bronchioles, it sepeartes the lungs for the trachea.
-bronchioles: braches for the passage of gases inside the lungs which conect to the alveoli
-alveoli: tiny air sacs that are the site for diffusion inside the lungs.there are millions of these structures in each lung.

The wall of the trachea is highly adapted for effiecient gas exchange; for example:

Rings of cartilidge: these are the structures that help maintain the structure of the trachea, they surround the trachea and prevent colaspe when the internal air pressure is low.it is also flexible.
Goblet cells: secrete sticky mucus which is primarily used in the capture of dust, spores and bacteria thus reducing the chances of infection.
Cilliated cells (cilia): these have tiny hair like projections that waft upwards in a synchronised pattern which moves the sticky mucus through the trachea to trap some substances that are not supposed to be in the body.

Smooth muscle: it contracts on the outside of the trachea to restrict the air flow and make the lumen of the trachea smaller which limits to volume of air going into the alveoli.
Elastic fibres: these stretch when you inhale allowing air in and then recoil to help force gases out.

The structure of the alveoli are adapted for effiecient gas exchange; these are some of the features:
Squamous epithelium: flattened calls which line the wall of the alveoli and allow the gases in the blood and ungs to easily and quickly diffuse through to where's it needed.
Elastic fibres: these are used in the alveoli to help with the expansion of the thorax and the recoil to force air outwards.

What happens during inhalation?
-the Diaphragm contract
- external intercostal muscles contract to raise ribs
-chest cavity volume increases
-chest cavity pressure drops
-air moves into the lungs

What happens during exhalation?
-the diapragm relaxes
-external intercostal muscles relax and ribs fall
-chest cavity volume decreases
-presure in the lungs increases
-air moves out of the lungs.

on average you breathe in and out about 12 times a minute; but there are several things that make you breathe ina nd out momre heavily; such as:
-An asthma attack
-excitment or fear
-medical drugs like adrenaline regulate breathing to a normal rate
-exercising which raises the demand for oxygen to the cells
-a low blood PH can result in hyperventilation (breathing in too fast.)

on the other hand, there are some things that slow the rate of breathing, one of which is:
-narcotics can depress the rate of breathing and the person could stop breathing altogether

There are specific terms for parts of the lung capacity; these are:
-vital capacity: the maximum amount of air that can be breathed in or out
-tidal volume: the volume of air breathed in or out in a normal breathe.
-oxygen uptake: the rate of whhich people use up oxygen.
-residual volume: the volume of air that remains in the lungs even after exhalation.
-Insiratory reserve volume: how much more air that can breathed in after the normal tidal volume.
-expiratory reserve volume: how much more air that can be exhaled after  the normal tidal volume. 

We measure lung capacity using a spirometer, you should knoiw how they work:
- it consists of a chamber of oxygen that floats on a tank of water, a person would breathe into a disposable mouthpiece.
-when the person inhales; the air level decreases inside the spirometer which can be measured; and when the person exhales; they breathe air into the chamber which raises the tank level which i salso measured.
-the movement of the chamber is measured by a datalogger which records the results and produce a trace of the breathing.

There are a few features of the spirometer that make it appropraite for usage. For example:
-there is an area with soda lime to absorb carbon dioxide because if a person is constantly breathing into and out of the same air, there will be a lot of carbon dioxide in the chamber; so it needs to be absorbed.
-there is a dispoable mouth piece that the person breathes into because of risk of infection or transmission of pathogens or other contaminents.

It is possible that you could be asked to compare a spirometer read out, there are some differences you should be able to distinguish.

-A person with asthma would have a lower vital capacity
-A person who smokes would also have a decreased vital capacity.
-It could also be reduced by bad posture or old age or if a person has pneumonia.

it can be higher in people who have a better physical fitness level or someone who is younger.