The respiratory system, breathing and respiration

• The function of the respiratory system is to provide the cells of the body with oxygen and to remove carbon dioxide from them in order to facilitate the process of cell respiration
• The human respiratory system contains a series of tubes: the nasal cavity, trachea, bronchi, and bronchioles.
• The trachea stays open during pressure changes (inhaling and exhaling) as it has c-shaped (incomplete), rings of cartilage in its walls to stop it collapsing
• The nasal cavities are lined with ciliated epithelial cells that make mucus and trap micro-organisms. This allows air to be filtered and also for air to be warmed before continuing to the lungs
• In humans, the respiratory system is inside the thorax, a space surrounded by ribs of bone with intercostal muscles between them and a muscular sheet, the diaphragm beneath
• The pleural membranes line the inside of the chest wall(the ribs) and also the outside of the lungs. They reduce friction during breathing as the lungs fill with air and deflate.
• The space between the pleural membranes(pleural cavity) contains a small amount of pleural fluid. This further helps reduce friction during breathing
• At the ends if the bronchiole tubes we find the alveoli. This is where gas exchange takes place between the atmosphere and the blood. In humans, oxygen diffuses into the blood from the alveoli and carbon dioxide goes the other way, diffusing from the blood into the alveoli, where it is breathed out
• Alveoli have a large surface area due to the many alveoli in each lung and each alveolus has a large surface area, together giving a gas exchange surface where the alveoli walls are in contact with blood capillaries in humans of many square metres.
• Alveoli have thin walls with short diffusion distances as there are only two layers of cells separating the oxygen in the alveolus from the red blood cells, meaning there is only a short diffusion distance for the gases involved.
• Alveoli have moist walls which help the gases to pass through the respiratory surfaces because the gases dissolve in the moisture.
• Alveoli have a good blood supply by being surrounded by capillaries to ensure that oxygen diffusing through is carried around the body and carbon dioxide is continually taken to the lungs.
• Alveoli have a large diffusion gradient that encourages oxygen to diffuse into the blood and carbon dioxide to diffuse from the alveoli into the capillaries.
• The ribcage is made of individual ribs that protect the organs within the thorax e.g. lungs, heart, etc.
• The intercostal muscles are found between the ribs, these contract and relax to move the ribcage up and down during breathing
• The larynx is the voice box. It contains vocal cords
• The trachea is the U-shaped tube that connects your larynx to your lungs. It allows passage of air in and out of the lungs.
• The bronchus is a large tube connecting the trachea to the bronchioles
• The bronchiole is a small tube carrying air to and from the alveoli in the lungs
• The alveoli are tiny air sacs where gaseous exchange takes place
• The diaphragm is a large sheet of muscle stretching one side of the chest to the other, it moves up and down during breathing
• The pleural membranes and pleural fluid reduce friction during breathing
• This is the lung model. The balloons represent lungs; the pipe represents the trachea the elastic membrane represents the diaphragm, although it is poor representation of it since it starts out flat in the model, but the diaphragm is dome-shaped when relaxed. The jar represents the ribcage, and it is also poor representation of it since the jar does not move during respiration, and the ribcage does. When the membrane is stretched, the volume of the chest cavity increases, and the pressure of the chest cavity decreases.

  
• When breathing in:

  • The ribcage moves up and out
  • The intercostal muscles contract
  • the diaphragm flattens when muscle contracts
  • The volume in the thorax increases
  • the pressure in the thorax decreases
  • The air moves into the lungs
• When breathing out:

  • The ribcage moves down and in
  • The intercostal muscles relax
  • the diaphragm unflattens when muscle relaxes
  • The volume in the thorax decreases
  • the pressure in the thorax increases
  • The air moves out of the lungs
• The movement of the ribs and lungs during breathing is called ventilation