breathing

• Gaseous exchange

  The exchange of oxygen and carbon dioxide which takes place between air and the blood
• Lungs

  • Situated in the chest area, known as the thorax
  • Have a spongy texture so that they can increase in volume when air enters and decrease in volume when air exits

  
• Structure of the lungs

  1. Trachea

  2. Bronchi

  3. Bronchioles

  4. Alveoli

  
• Trachea and bronchi

  • Lined with rings of cartilage to keep the pipes in shape and prevent obstruction
• Epiglottis

  A piece of tissue located at the top of the trachea that stops food and drink from entering the lungs

  
• Trachea, bronchi and bronchioles

  • Covered by ciliated cells that secrete mucus to trap dust and pathogens, which are then moved upwards and swallowed

  
• Ventilation of the lungs

  1. Inhalation

  2. Exhalation

  
• Inhalation

  1. Diaphragm muscles contract and straighten

  2. Intercostal muscles contract and pull the rib cage upwards and outwards

  3. Thorax expands so lungs can expand and draw in air
• Exhalation

  1. Diaphragm muscles relax and return to domed shape

  2. Intercostal muscles relax and ribs move downwards and inwards

  3. Thorax decreases in space so lungs decrease in volume and force air out
• Nose

  • Filters the air
  • Warms the air
  • Provides moisture to the air
  • Detects chemicals in the air
• Pleural membrane

  Smooth membrane lining the outside of the lungs and inside of the thorax, producing pleural fluid to reduce friction

  
• Breathing

  An involuntary action under the control of the medulla oblongata in the lower part of the brain
• At rest, we inhale and exhale about 16 times per minute, increasing to 20-30 breaths per minute during exercise
• Vital capacity

  The total air capacity of the lungs, about 5 litres in adults, with only 0.5 litres exchanged during breathing at rest

  
• Gaseous exchange in the alveoli

  Oxygen diffuses from the alveoli into the blood, and carbon dioxide diffuses from the blood into the alveoli
• Alveoli

  • Very thin (one cell thick) to reduce diffusion distance
  • Moist to allow oxygen to dissolve before diffusing
  • Surrounded by blood capillaries to maintain concentration gradient
  • Have a very large surface area for diffusion
  • Moist to aid diffusion of gases

  
• Carbon dioxide will diffuse out of the plasma of the blood into the alveoli and leave the body in the exhaled air
• Composition of inhaled and exhaled air

  • Oxygen (21% inhaled, 16% exhaled)
  • Carbon dioxide (0.04% inhaled, 4% exhaled)
  • Nitrogen (79% inhaled, 79% exhaled)
  • Water vapour (a little inhaled, 3% exhaled)
  • Other gases (1% inhaled, 1% exhaled)
• To test for the presence of carbon dioxide in exhaling air, one can breathe out through lime water which goes cloudy in the presence of carbon dioxide
• effects of smoking

  Short term effects: Bronchioles constrict, cilia stop beating, cilia produce more mucus

  Long term effects: Emphysema, chronic bronchitis, lung cancer, heart diseases
• Emphysema

  Condition which breaks down the alveoli, caused by substances in cigarettes weakening the alveolar walls, leading to reduced surface area for gaseous exchange and breathlessness

  
• Chronic bronchitis

  Inflammation of the bronchi caused by smoke stopping the cilia from beating, leading to irritant substances and excess mucus collecting in the bronchi
• Passive smoking

  Non-smoking family members of smokers have an increased chance of developing lung cancer as they still breathe in smoke
• Smoking increases the chance of blood clots and fat deposition in arteries, leading to coronary heart disease