Relate the structure of the respiratory system to the process of ventilation

Figure 1

The respiratory system is made up of the
· Nose
· Pharynx
· Larynx
· Trachea
· Bronchi
· Bronchioles
· Alveoli
· Lungs
· Diaphragm
Figure 1

The nose
The nose is made up of bone, cartilage and fatty tissue; it has two holes known as the nostrils. It is separated into two air passages. Goblet cells in the lining of the nose secrete mucus to help trap and remove unwanted antigens. The nose contains tiny hairs known cilia these form the nose lining and keep the mucus moving towards the exit of the nose. Air enters and leaves the respiratory system through the nose.
(BBC, 2009)

Trachea
This is a long tube, around 12 centimetres in length and 2.5 centimetres wide, which is made up of rings of cartilage to keep it open to allow air to flow down it.

Bronchi
Two cartilage-ringed tubes containing smooth muscle tissue, these tubes branch off from the trachea, the right primary bronchus is wider than the left, which makes it more venerable to foreign antigens. These allow air to travel into the lungs, and enter smaller tubes. The bronchi are able to expand during inspiration, to allow the lungs to expand, and contract during expiration as air is exhaled. (Probert, 2010)

Bronchioles
Small thin tree- like network of tubes that contain less cartilage than the bronchi. The bronchioles become smaller than 0.5 mm in diameter, irregularly shaped discs of cartilage support the first few sections, while the latest levels of the tree have no support whatsoever, these sub-divide into the alveolar ducts. By this time air reaches this part all the foreign antigens have been removed and the air travels into the alveoli.

Alveoli
Tiny air sacs that look like a bunch of grapes, they are one cell thick, this helps to speed up gaseous exchange, this action is vital to live. The lung has many millions of alveoli, this gives the lungs a larger surface area for gas exchange. The alveoli are covered in inter linking capillaries through which blood flows. The alveoli diffuse oxygen into the blood stream which bines with the haemoglobin and gets carried round the body, carbon dioxide is then diffused back from the used blood cells into the alveoli and gets breathed out as this is poisonous to the body.
(Think Quest, 2006)

Diaphragm and intercostals muscles
The alveoli are ventilated by the action of the diaphragm and the intercostals muscles.
The diaphragm is a sheet of tendon surrounded by muscles, when relaxed it is positioned into a dome shape by the organs. When the diaphragm muscles contract it becomes flatter. Intercostal muscles are located between the ribs externally and internally. These intercostal muscles allow the ribcage to pivot upwards and outwards, and downwards and inwards. Breathing involves the diaphragm, intercostals muscles and ribcage creating pressure changes. When we breathe in, the external intercostals muscles contract and the rib cage moves upwards and outwards, creating an increase in lung volume and a decrease in pressure. At the same time the diaphragm muscles contract and causes it to move downwards. When we breathe out, internal intercostals muscles contract and the ribcage moves downwards and inwards, causing a decrease in lung volume and an increase in pressure, whilst the diaphragm muscles relax, and the it returns to the dome shape.
(Wright, 2007)