Biology

• Respiratory surface


  The area where gaseous exchange with the environment actually takes place
• Properties of respiratory surface


  • Moist and permeable
  • Thin (less than 1 mm)
  • Large surface area
  • Good blood supply
  • Good ventilation mechanism
• Components of human respiratory system


  • Upper respiratory tract (nose, nasal cavity, pharynx)
  • Lower respiratory tract (larynx, trachea, bronchi, lungs)
• Nose


  • Composed of bones, cartilage and fatty tissues
  • Contains nostrils and nasal cavities
  • Lined by ciliated mucous membranes
• Nose hair, mucus and cilia


  Serve as a defence mechanism against harmful pathogens and particulate matter
• Pharynx


  Cone-shaped passageway leading from oral and nasal cavities to oesophagus and larynx
• Larynx


  • Enlargement in the airway at the top of the trachea and below the pharynx
  • Contains epiglottis and vocal cords
• Trachea


  Membranous tube reinforced with C-shaped cartilage
• Bronchi and bronchioles


  1. Trachea divides into primary bronchi

  2. Primary bronchi divide into secondary bronchi

  3. Secondary bronchi divide into tertiary bronchi

  4. Bronchioles are less than 1mm in diameter
• Alveoli


  • Air-filled chambers where gas exchange occurs
  • Walls are only 0.1 μm thick with a dense network of blood capillaries
• Lungs


  • Conical in shape with right lung having 3 lobes and left lung having 2 lobes
  • Spongy due to presence of alveoli
• Mechanism of breathing (ventilation)


  1. Inspiration (diaphragm contracts, rib cage moves up and out, pressure in lungs decreases, air rushes in)

  2. Expiration (diaphragm relaxes, rib cage moves down and in, pressure in lungs increases, air is expelled)
• Respiratory volumes


  • Tidal volume (amount of air inhaled/exhaled at rest)
  • Inspiratory reserve volume (extra air inhaled during deep breath)
  • Total lung capacity (6000ml)
• Surfactant lowers surface tension in alveoli, speeds up gas exchange, and helps kill bacteria
• Mouth to mouth artificial respiration (CPR) is a technique used to recover a person who has stopped breathing
• Respiratory Volumes


  • Tidal volume
  • Inspiratory reserved volume
  • Total lung capacity
• Breathing (inspiration and expiration) occurs in a cyclical manner due to the movements of the chest wall and the lungs
• The resulting changes in pressure, causes changes in lung volumes, i.e., the amount of air the lungs are capable of occupying
• Respiratory volume is the amount of air inhaled, exhaled and stored within the lungs at any given time
• Tidal volume


  The amount of air which is inhaled or exhaled at rest
• Inspiratory reserved volume


  The amount of extra air inhaled (above tidal volume) during a deep breath
• Total lung capacity


  The total amount of air the lungs can hold
• Mouth to mouth artificial respiration (Cardiopulmonary Resuscitation (CPR))


  1. Stretch out victim on his back and kneel close to his side

  2. Remove foreign objects if present from victim's mouth and throat by finger sweeping

  3. Lift up chin and tilt head back as far as possible

  4. Begin the resuscitation immediately

  5. Pinch the nostrils together

  6. Inhale deeply

  7. Place your mouth tightly around the victim's mouth (over mouth and nose of small children) and blow into the air passage with brief intervals

  8. Watch the victim's chest. When you see it rise, stop blowing, raise your mouth, turn your head to the side and listen for exhalation

  9. If patient is revived, keep him warm and do not move him until the doctor arrives, or at least for half or one hour
• Mouth to mouth artificial respiration is called resuscitation
• It is a technique used to recover a person who has stopped breathing
• In this technique, the rescuer presses his or her mouth against the mouth of the victim and allowing for passive inhalation, forces air into the lungs at intervals of several seconds
• Birds perform much better than man at high altitudes


  The efficiency of the birds' lungs allows them to extract considerably more oxygen from a given quantity of air than human lungs
• Efficiency of birds' lungs


  • They have haemoglobin with a very high affinity for oxygen
  • They have a very large number of capillaries in lungs
  • They have one-way flow of air through the lungs so there is no dead air (residual volume) in the bird's lung
  • Birds have several large air sacs in addition to their lungs
• Breathing centre


  Located in the medulla of the brain, it carries out involuntary control of breathing
• Inspiratory centre


  The ventral portion of the breathing centre that acts to increase the rate and depth of inspiration
• Expiratory centre


  The dorsal and lateral portions of the breathing centre that inhibit and stimulate expiration
• Through the cerebral cortex it is possible to consciously or unconsciously increase or decrease the rate and depth of the respiratory movement
• A person may also stop breathing voluntarily
• Occasionally people are able to hold their breath until the blood partial pressure of oxygen declines to a level low enough that they lose consciousness
• After consciousness is lost, the respiratory centre resumes its normal function in automatically controlling respiration
• Emotions acting through the limbic system of the brain can also affect the respiratory centre
• SCUBA


  Self-Contained Underwater Breathing Apparatus
• A typical aqualung contains compressed air or a mixture called Nitrox which consists of about 35 percent oxygen and 65 percent nitrogen
• This apparatus consists of a tank containing highly compressed air in which the pressure down to an ambient pressure so divers could breathe comfortably at any depth
• Transport of oxygen in blood


  1. Approximately 97% of oxygen is carried by the red blood cells as oxyhaemoglobin

  2. 3% is transported as dissolved oxygen in the plasma

  3. Oxygen binds with haemoglobin in the lungs in the presence of enzyme carbonic anhydrase

  4. Each molecule of haemoglobin can bind with four molecules of oxygen to form oxyhaemoglobin