The respiratory system is the collective name for the organs and tissues which work together to allow a person to breathe. The main parts of the system are the airways, the lungs, the blood vessels in close contact to the lungs and the muscles.
The airways is the collective name of the components that make up the passage that the air takes from the environment to the lungs. The airways consist of the nose, mouth, trachea, larnynx, trachea, bronchi and bronchioles. The nose and mouth are where the air first enters the body. Here the air gets heated and moistened to avoid irritation further down the respiratory system. Small hairs in the nose prevent any particles from entering the airways. After this the air travels down past the voice box and down the trachea towards the lungs where the trachea splits into two tubes called the bronchi. The bronchi then split further into smaller tubes called the bronchioles, which end at fluid filled sacs called alveoli, deep within the lungs. This is the site of gas exchange with the capillaries.
The trachea is also known as the windpipe and is it the long hard tube that runs from the throat down to the lungs. It has approximately 15-20 C shaped cartilage rings running down the length of it, these rings make the trachea more sturdy and able to withstand the change in pressure that occurs with breathing in and out and prevent collapse.
The trachea splits into two tubes called the bronchi. There is a left and a rich bronchi, each going to their respective left or right lung. The bronchi extend into the lobes of the lung. The bronchi contain cartilage rings and are also lined with smooth muscle which secrete mucus into the airways. The epithelital cells which also line the bronchi are cilated and the cilia waft the mucus, along with any particles trapped in the mucus, up towards the mouth where it can be swallowed.
The bronchioles are almost identical to the bronchi except the have a smaller lumen and there are many more of them. They are also lined with smooth muscle and ciliated epithelital cells, however they do not contain any cartilage rings. Each bronchi branches into many bronchioles and these bronchioles branch into more bronchioles. Each branching is known as a generation. At the end of the bronchioles there are fluid filled sacs called alveoli which is where gas exchange takes place.
There are approximately 300 million alveoli in the lungs. They form the junction between the airways and the blood vessels and are the site of gas exchange. They have a very thin membrane to maximise the amount of oxygen and carbon dioxide that can pass through by diffusion, and likewise so do the blood vessels which are in very close proximity. The alveoli also have a large surface area to further maximise the degree of gas exchange that can take place.The large surface area is increased by the many elastic fibres that alevoli contain, these fibres expand and recoil depending on the volume of air that is breathed in.