Structure of the respiratory system

Air normally enters via the nostrils. it goes to the nasal passages which serve as a filter and it warms up the air before it reaches the lungs. The hairs in the nostrils prevent any foreign objects from entering. The mucus and cilia collect dust, bacteria and other particles in the air. The nose has three jobs, it warms, filters and moistens the air before it reaches the lungs. Air then travels from the nasal passage to the pharynx (throat) it leaves the pharynx and passes to the larynx. The voice box (larynx) has vocal chords which are two pairs of membranes that are stretched on the inside of the larynx. When air is breathed out the vocal chords vibrate. We can control the vibrations of vocal chords which enables us to speak. After the larynx the air goes to the trachea. This is a tube which is 12cm long and 2.5cm wide. It is opened by rings of cartilage within its walls. It is also covered with mucus membrane like the nasal passages. Cilia moves the mucus to the pharynx after that they leave the air passages and are swallowed. About the center of the chest the trachea divides into two cartilage-ringed tubes called bronchi. These are also lined with ciliated cells. The bronchi enters the lungs and they spread into tree like branches into smaller tubes called bronchial tubes, The bronchial tubes divide then divide again, their walls become thinner and have less cartilage eventually they become a small group of tubes called bronchioles. At the end of each bronchiole is a tiny chamber which looks like a bunch of grapes. Each one of these contain cup shaped cavities called alveoli. They are thin, moist and surrounded by capillaries. Gas exchange of oxygen and CO2 takes place in the alveoli. Oxygen from the inhaled air diffuses through the walls of the alveoli and capillaries into the red blood cells. The oxygen is then carried by the blood to the body tissues. CO2 is produced by the body's metabolism which returns to the lung via blood, it then diffuses across the capillary and alveolar walls into the air and is removed from your body by breathing out.

The lung on the left side of your body is slightly smaller than the one on the right which leaves room for your heart. Your lungs are also protected by a rib cage which is made up of 12 sets of ribs. Beneath your lungs is your diaphragm which is a domed shaped muscle that works with your lungs to allow you to breath in and out air. When you breathe in your diaphragm tightens and moves downwards, this increases the space in your chest cavity for your lungs to expand. The intercostal muscles between your ribs also help enlarge your chest cavity. They contract to pull your rib cage both upwards and outwards when you breath in.