book- chapter 4

• All cells in the body need oxygen for cellular respiration
• Cells also need a way to remove the carbon dioxide they produce
• In the lungs, oxygen is taken from the air into the blood, which then transports it to cells in all tissues of the body
• In the tissues, blood picks up carbon dioxide and takes it to the lungs for removal into the air
• The circulatory and respiratory systems work together to ensure a constant supply of oxygen to cells and the removal of carbon dioxide
• Organs of the respiratory system include the nose, trachea, bronchi, and lungs
• The nose and nasal cavity warm and humidify air, while hairs and mucus trap debris to prevent it from reaching the lungs
• The pharynx is the region from the nasal cavity to the top of the trachea and oesophagus
• The larynx contains the vocal cords and is known as the voice box
• The trachea, or windpipe, carries air to and from the lungs and is lined with mucous membranes and cilia
• Bronchi branch from the trachea and further divide into bronchioles, which control airflow in the lungs
• Lungs are divided into lobes and contain alveoli, where gas exchange occurs
• Alveoli have a huge internal surface area for gas exchange and are well supplied with blood vessels
• The membrane of the alveolus is thin, allowing for easy diffusion of gases
• The lungs are positioned deep inside the body to prevent excessive evaporation of fluid covering the respiratory surfaces
• The process of gas exchange involves oxygen diffusing into the blood and carbon dioxide diffusing out of the blood in the alveoli
• Expired air contains less oxygen and more carbon dioxide than inspired air
• For diffusion of gases into and out of the blood, there must be a concentration gradient between the air in the alveoli and the blood in the capillaries
• The concentration gradient for oxygen and carbon dioxide is maintained by:

  • The constant flow of blood through the capillaries, where new blood low in oxygen and high in carbon dioxide replaces blood that has picked up oxygen and lost carbon dioxide
  • The movement of air into and out of the alveoli as we breathe in and out, where 'new' air low in carbon dioxide and high in oxygen replaces air that has picked up carbon dioxide and lost oxygen
• There is a net diffusion of oxygen into the blood and carbon dioxide out of the blood due to the concentration gradients between the air and blood
• Emphysema is a disease caused by long-term exposure to irritating particles in the air, leading to damage to the alveoli

  • The alveoli lose their elasticity, are often replaced with fibrous tissue, and may break down, reducing the internal surface area of the lung
  • The loss of elasticity of the lung tissue causes difficulty in ventilating the lungs and inadequate surface area for gas exchange
• Lung cancer involves the development of a mass of cells that divides uncontrollably, often beginning in the walls of the air passages, usually the bronchi

  • Lung cancer is linked to exposure to asbestos fibres, pollutants, and especially tobacco smoking
  • Inhaled smoke particles constantly irritate the mucous membrane lining the air passages, leading to excessive mucus production and the development of a tumour
• Pneumonia is an infection of the lungs that causes inflammation, secretion of fluid and mucus into the alveoli, and reduces the surface area available for gas exchange

  • Lung infections like pneumonia and tuberculosis are spread by droplets from infected individuals through coughing, sneezing, or spitting
• Asthma causes difficulty breathing due to narrowing of the airways caused by smooth muscle contraction, inflammation, and mucus build-up

  • Asthma triggers include respiratory infections, cigarette smoke, allergens, exercise, cold weather, stress, and certain substances in food
  • During an asthma attack, the muscles surrounding the bronchioles go into spasm, causing difficulty in breathing and reduced gas exchange