Respiratory System

• Flow of air

  • Nose
  • Pharynx
  • Larynx
  • Trachea
  • Bronchi
  • Bronchioles
  • Alveoli
• Alveoli

  Responsible for the exchange of gases (gaseous exchange) between the lungs and the blood, via diffusion
• Alveoli

  • Their walls are very thin (one cell thick) which means there is a short diffusion pathway
  • An extensive capillary network surrounds the alveoli so they have an excellent blood supply
  • They have a huge surface area because there are millions of alveoli in each lung, which allows for a greater uptake of oxygen
• Diffusion

  The movement of gas molecules from an area of high partial pressure to an area of low partial pressure
• Inspiration/Inhalation

  Intercostal muscles contract pulling the ribs up and out, the diaphragm contracts causing it to flatten, the thoracic chest cavity gets larger causing a drop in lung pressure which allows air to rush in
• Expiration/Exhalation

  Intercostal muscles relax allowing the ribs to pull down and in, the diaphragm relaxes causing it to go into a dome shape, the thoracic chest cavity gets smaller causing an increase in lung pressure forcing air out of the lungs
• Diaphragm


  Sits underneath the lungs attached to the bottom of the rib cage, its purpose is to contract allowing more air into the lungs during inspiration/inhalation and to relax to help force air out of the lungs during expiration/exhalation
• Topics in the respiratory system unit

  • Lung volumes
  • Gas exchange
  • Regulation of pulmonary ventilation
  • Impact of poor lifestyle choices
• The body needs a continuous supply of oxygen to produce energy. When we use oxygen to break down food to release energy, carbon dioxide is produced as a waste product which the body must remove
• Respiration


  The taking in of oxygen and the removal of carbon dioxide, including ventilation, external respiration, transport of gases, internal respiration, and cellular respiration
• Rearrange the following words to show the correct passage of air: Larynx, Nose, Pharynx, Trachea, Bronchi, Bronchioles, Alveoli
• The alveoli are responsible for the exchange of gases (gaseous exchange) between the lungs and the blood, this occurs via diffusion which is the movement of gas molecules from an area of high partial pressure to an area of low partial pressure
• During inspiration, the intercostal muscles contract and pull the rib cage up and out, the diaphragm contracts causing it to flatten, the thoracic chest cavity gets larger causing a decrease in lung pressure which allows air to be sucked in
• During expiration, the intercostal muscles relax allowing the rib cage to fall down and in, the diaphragm relaxes pushing it up into a dome shape, the thoracic chest cavity gets smaller causing an increase in lung pressure forcing air out
• Muscles used during breathing

  • At rest: Diaphragm, External intercostals

  During exercise: Diaphragm, External intercostals, Sternocleidomastoid, Scalenes, Pectoralis major

  Expiration at rest: Passive - diaphragm and external intercostals relax, Internal intercostals, Abdominals
• Tidal volume


  The volume of air inspired or expired per breath
• Minute ventilation


  The volume of air inspired or expired per minute
• Residual volume is the volume of air that remains in the lungs after maximum expiration, it prevents the lungs from collapsing
• Lung volumes/capacities


  • Tidal volume
  • Inspiratory reserve volume
  • Expiratory reserve volume
  • Residual volume
  • Minute ventilation
• During exercise, tidal volume increases, inspiratory and expiratory reserve volumes decrease, and minute ventilation increases significantly
• A spirometer is used to measure the volume of air we breathe in and out, it traces the breathing movements and translates them into a graphical representation
• As exercise intensity increases, minute ventilation increases to meet the extra demand for oxygen
• Gaseous exchange is the process of getting oxygen into our lungs so it can diffuse into the blood, and removing carbon dioxide from the blood
• Partial pressure and diffusion are key concepts in describing the gaseous exchange process
• Oxygen has a higher partial pressure in the alveoli than in the capillary blood, so it diffuses from the alveoli into the blood, while carbon dioxide diffuses from the blood into the alveoli
• The difference in partial pressure is the concentration/diffusion gradient, and the bigger this gradient, the faster diffusion will occur
• Partial pressure


  The pressure exerted by a particular gas in a mixture of gases
• As air moves from alveoli to blood and then onto the muscles


  The partial pressure of oxygen needs to be successively lower
• Gaseous exchange in the lungs/alveoli

  1. Partial pressure of oxygen (PO2) in the alveoli (100 mmHg) is higher than the partial pressure of oxygen in the capillary blood vessels (40 mmHg)

  2. Oxygen has been removed by the working muscles so its concentration in the blood is lower, and therefore so is its partial pressure

  3. The difference in partial pressure is referred to as the concentration/diffusion gradient and the bigger this gradient, the faster diffusion will be

  4. Oxygen will diffuse from the alveoli into the blood until the pressure is equal in both
• Gaseous exchange in muscles

  1. The partial pressure of oxygen has to be lower at the tissues than in the blood for diffusion to occur

  2. In the capillary membranes surrounding the muscle the partial pressure of oxygen is lower than it is in the blood

  3. This lower partial pressure allows oxygen to diffuse from the blood into the muscle until equilibrium is reached

  4. Conversely, the partial pressure of carbon dioxide in the blood (40 mmhg) is lower than in the tissues (46 mmhg) so again, diffusion occurs and carbon dioxide moves into the blood to be transported to the lungs
• Composition of inspired, expired and exercised air

  • Inspired air at rest: Oxygen 21%, Carbon dioxide 0.03%, Nitrogen 79%, Water vapor varied
  • Expired air at rest: Oxygen 16.4%, Carbon dioxide 4.0%, Nitrogen 79.6%, Water vapor saturated
  • Expired air during exercise: Oxygen 14%, Carbon dioxide 6%, Nitrogen 79%, Water vapor saturated
• Neural and chemical regulation of pulmonary ventilation during exercise

  1. Neural control involves the brain and the nervous system, chemical control is concerned with blood acidity

  2. When blood acidity is high, the brain is informed and it sends impulses through the nervous system to increase breathing

  3. Sympathetic nervous system prepares your body for exercise so it will increase breathing rate

  4. Parasympathetic nervous system does the opposite and lowers breathing rate

  5. Respiratory system located in the medulla oblongata of the brain controls the rate and depth of breathing and uses both neural and chemical control

  6. The expiratory centre stimulates the expiratory muscles during exercise

  7. The respiratory centre responds mainly to changes in blood chemistry, during exercise blood acidity increases due to increased carbon dioxide and lactic acid

  8. The inspiratory centre is responsible for inspiration and expiration, it sends nerve impulses via the phrenic nerve to the inspiratory muscles to cause them to contract

  9. An increased concentration of carbon dioxide in the blood stimulates the respiratory centre to increase respiratory rate

  10. To achieve this, the respiratory centre sends impulses down the phrenic nerve to stimulate more inspiratory muscles: sternocleidomastoid, scalenes and pectoralis minor
• Components of the respiratory control system

  • Intercostal nerve
  • Phrenic nerve
  • Inspiratory centre
  • Chemoreceptors – detect an increase in blood acidity
  • Baroreceptors – detect a decrease in blood pressure
  • Proprioceptors – detect an increase in muscle movement
  • Increase breathing rate
  • Diaphragm and external intercostals
  • Abdominals and internal intercostals
  • Increase expiration
  • Respiratory centre – found in the medulla oblongata
  • Stretch receptors – prevent over-inflation of the lungs by sending impulses to the expiratory centre
  • Expiratory centre
• Lifestyle factors


  • Smoking
  • Exercise
• Improvements to efficiency of respiratory system after aerobic training

  • Increased surface area of alveoli
  • Increased capillary density around alveoli / muscle
  • Increased a-VO2 difference
  • Respiratory muscles (diaphragm, intercostals, sternocleidomastoid, scalenes, abdominals) strengthened
  • Increased depth of breathing / decreased breath frequency
  • Increased tidal volume / minute ventilation during maximal exercise
  • Increased vital capacity / inspiratory / expiratory reserve volume
  • Increased VO2 max
  • Greater amount of O2 diffused into blood / CO2 into alveoli
  • Greater gaseous exchange / increase pulmonary diffusion
  • Greater saturation of haemoglobin with oxygen
  • Greater amount of O2 diffused into muscle
  • Increased aerobic endurance
• Impact of smoking on the respiratory system

  • Irritation of the trachea and bronchi
  • Reduced lung function and increased breathlessness – caused by swelling & narrowing of lungs airways
  • Smoke damages the cells lining the trachea, bronchi and bronchioles, reducing the ability to clear mucus
  • Damage to the alveoli, reducing efficiency of gaseous exchange
  • Increased risk of COPD (chronic obstructive pulmonary disease)
  • Carbon monoxide reduces amount of O2 absorbed in blood, haemoglobin has greater affinity to CO than O2
  • Decreased gaseous exchange or diffusion gradient
  • Increased likelihood of respiratory diseases / damage to respiratory structures
  • Tar coats the airways / builds up in lungs and inhibits gaseous exchange
  • Narrowing of air passages causing increase in respiratory resistance
• Tobacco kills up to half of its users
• Tobacco kills more than 8 million people each year, with over 7 million from direct tobacco use and 1.2 million from second-hand smoke
• Around 80% of the world's 1.1 billion smokers live in low- and middle-income countries
• Every year around 78,000 people in the UK die from smoking, with many more living with debilitating smoking-related illnesses