Once inside the lung the bronchi split several ways, forming tertiary bronchi known as bronchioles. These are very narrow tubes. There is no cartilage within them and they lead to alveolar sacs. Alveoli is another part of the lower respiratory tract, they are individual hollow centres contained within the alveolar sacs. They have very thin walls which allow the exchange of gases oxygen and carbon dioxide. They are surrounded by a network of capillaries, into which the gases pass. The last part of the lower respiratory tract is the diaphragm. This is a broad band of muscle which sits underneath the lungs attaching to the lower ribs, sternum and lumbar spine and forms the base of the thoracic. See diagram below labelled Figure 1 showing a detailed account of the Human Respiratory System, which shows in detail the actual structure as previously explained of the human respiratory tract including the upper and lower tract.
Human Respiratory System .
As previously said the respiratory system is made up of so many different tissues and organs and therefore there are a number of different diseases, conditions and infections which can have an affect and disrupt its normal functioning. Pneumonia is just one infection, which occurs deep in the lungs. It can occur in just one or both lungs and is caused by bacteria, viruses, fungi or parasites. The body filters germs out of the air that we breathe; this keeps the lungs from becoming infected. However these germs can sometimes find a way to enter and cause infections, and the reason for this happening is most likely down to a person's immune system being weak and cannot prevent entry, the germ is extremely strong or the body just fails to filter the germs out of the air we breathe. When the germs that cause pneumonia reach the lungs the organisms settle in air sacs known as alveoli and continue to multiply. As the body sends white blood cells to attack the infections, the alveoli become inflamed and fill up with fluid and pus.