mammalian gaseous exchange system

• The lungs are a pair of structures with a large surface area located in the chest cavity with the ability to inflate.
• The lungs are surrounded by the rib cage which serves to protect

  them. A lubricating substance is secreted to prevent the friction between rib cage and lungs during inflation and deflation
• External and internal intercostal muscles between the ribs which contract to raise and lower the ribcage respectively. A structure called the diaphragm separates the lungs from abdomen area.
• The air enters through the nose, along the trachea, bronchi and bronchioles which are structures well adapted to their role in enabling passage of air into the lungs. The gaseous exchange takes plance in the walls of alveoli, which are tiny sacs filled with air.
• The trachea, bronchi and bronchioles enable the flow of air into and out of the lungs. The

  airways are held open with the help of rings of cartilage, incomplete in the trachea to allow

  passage of food down the oesophagus behind the trachea
• Trachea and bronchi are similar in structure, with the exception of size; bronchi are narrower
• The bronchi and trachea are composed of several layers which together make up a thick wall. The

  wall is mostly composed of cartilage, in the form of incomplete C rings
• The inside surface of the cartilage that make up the trachea and bronchi is a layer of glandular and connective tissue, elastic fibres, smooth muscle and blood vessels. This is referred to as the ‘loose tissue’. The inner lining is an epithelial layer composed of ciliated epithelium and goblet cells.
• What is the purpose of cartilage?

  Cartilage is involved in supporting the trachea and bronchi, plays an important role in preventing the lungs from collapsing in the event of pressure drop during exhalation
• what is the purpose of the ciliated epithelium?

  The ciliated epithelium is present in resent in bronchi, bronchioles and trachea, involved in moving mucus along to prevent lung infection by moving it towards the throat
• What is the purpose of goblet cells?

  Goblet cells are cells that are present in the trachea, bronchi and bronchioles involved in mucus secretion to trap bacteria and dust to reduce the risk of infection with the help of lysozyme which digests bacteria
• What is the purpose of smooth muscles?

  Smooth has the ability to contract which enables them to play a role in constricting the airway, thus controlling its diameter as a result and thus controlling the flow of

  air to and from alveoli
• What is the purpose of elastic fibres?

  elastic fibres stretch when we inhale and recoil when we exhale thus controlling the flow of air