Respiratory system

• Components of the respiratory system

  • Mouth/nose
  • Pharynx
  • Larynx
  • Trachea
  • Bronchi
  • Bronchioles
  • Alveoli
  • Lungs
• The respiratory system is contained largely within the thorax or chest cavity
• Lungs

  Two spongy organs that almost fill the thorax
• Trachea

  Mouth and nose lead to this structure which is also known as the windpipe. It is a wide tube kept open by the C-shaped rings of cartilage
• Bronchi

  Down from the trachea this is split into two and lead into each lung, and are also supported by rings of cartilage
• Bronchioles


  The bronchi divide into many branches of bronchioles
• Alveoli

  These are at the terminal ends of the bronchioles and are small air-filled sacs that have a wall consisting of a single layer of thin epithelial cells. These are the sites of gas exchange
• Walls of bronchioles and alveoli

  • Contain a lot of elastic tissue, which allow for expansion of the lungs during breathing
• Lungs

  • Surrounded by pleural membranes, a double layer that contains the lungs and also allows for expansion during breathing
• Chest cavity

  • Enclosed by the ribs which are connected to each other by two layers of intercostal muscles
• Diaphragm


  A sheet of muscle that forms the floor of the chest cavity from the abdominal cavity and plays an important part in ventilation of the lungs (breathing)
• Functions of the respiratory system

  • Gaseous exchange: to breathe in oxygen and breathe out carbon (IV) oxide
  • Olfactory assistance: assists with smell
  • Protection: from dusts and microbes entering the body through mucus production, cilia and coughing
• Inspiration/ Breathing in

  1. Contraction of diaphragm, causing it to move down

  2. External intercostal muscles contract which causes the rib cage to move up and outwards

  3. Volume of the chest cavity increases and pressure in the lungs is reduced below atmospheric pressure

  4. Air moves down a pressure gradient to the lungs which results to their expansion

  5. Expansion of the walls of the bronchioles and alveoli
• Expiration or Breathing out

  1. Diaphragm relaxes and moves up

  2. External intercostal muscles relax causing the rib cage to move down and inwards

  3. Chest cavity volume decreases, pressure increases and air is forced out down a concentration gradient

  4. Elastic tissue recoils, increasing pressure in the lungs, helping to force air out
• Forced Expiration

  Internal intercostal muscles contract, causing the rib cage to be pulled in and down more forcefully, expelling air more rapidly from the lungs
• Gaseous exchange

  • Occurs within the alveoli
  • Pulmonary artery carries deoxygenated blood from the heart and the pulmonary vein returns oxygenated blood to the heart
  • Network of capillaries surround the alveoli
  • Wall of the alveoli and capillaries are made up of a single layer of cells, providing a short diffusion pathway for oxygen and carbon dioxide
• Role of alveoli in gas exchange

  • Large surface area to volume ratio
  • Short diffusion distance
  • Good blood supply
• Breathing/ ventilation of the lungs maintain a high concentration of oxygen and low concentration of carbon (IV) oxide in the air within the alveoli