Respiration in Humans

• Aerobic respiration


  Oxidation of food substances with the release of energy in living cells

  
• Anaerobic respiration


  Respiration that does not require oxygen to produce ATP
• Types of anaerobic respiration

  • Alcoholic fermentation
  • Lactic acid fermentation
• Alcoholic fermentation (in yeast)

  Glucose is converted into 2 molecules of ethanol and 2 molecules of CO2

  
• Lactic acid fermentation (in mammals)

  Glucose is converted into 2 molecules of lactic acid

  
• Anaerobic respiration in skeletal muscle

  Lactic acid builds up, causing fatigue, soreness/pain and stiffness
• Oxygen debt


  The amount of oxygen needed to remove lactic acid
• Removing oxygen debt


  1. Lactic acid is removed from muscles and transported to the liver

  2. Lactic acid is oxidized to produce energy in the liver

  3. Remaining lactic acid is converted back to glucose

  4. Glucose is transported back to the muscle and stored as glycogen

  
• Fermentation is important for the alcohol and baking industries
• Potassium hydroxide solution is used to absorb carbon dioxide in respiration experiments
• Limewater is used to test for the presence of carbon dioxide in respiration experiments

  
• Boiling the glucose solution first removes any carbon dioxide present
• The layer of oil serves to prevent air from entering the flask in respiration experiments
• The control experiment would involve a flask with no living organism
• Milton solution is used to sterilize the equipment in respiration experiments

  
• Cotton wool is used to allow air to enter the flask while preventing contamination in respiration experiments
• The purpose of the respiration experiments is to find out if heat is produced during respiration

  
• Parts of the respiratory system

  • External nostrils
  • Nasal passages
  • Pharynx
  • Larynx
  • Trachea
  • Bronchi
  • Bronchioles
  • Alveoli
  • Associated capillaries
• Functions of the respiratory system

  • Exchange oxygen and carbon dioxide
  • Regulate blood pH
  • Vocalization
  • Protect alveoli
  • Filter, warm and moisten air
  • Increase cross-sectional area from nose to bronchioles
• Inspiration (inhalation)


  1. Diaphragm contracts and flattens

  2. External intercostal muscles contract, internal intercostal muscles relax

  3. Ribs and sternum move upwards and outwards

  4. Volume of thoracic cavity increases

  5. Lungs expand to fill the enlarged space

  6. Air pressure in lungs decreases

  7. Air rushes into the lungs
• Expiration (exhalation)


  1. Diaphragm relaxes and arches upwards

  2. Internal intercostal muscles contract, external intercostal muscles relax

  3. Ribs and sternum move downwards and inwards

  4. Volume of thoracic cavity decreases

  5. Air is expelled from the lungs
• What happens during expiration

  1. Diaphragm relaxes and arches upwards

  2. Internal intercostal muscles contract while external intercostal muscles relax

  3. Ribs move downwards and inwards, sternum moves down to original position

  4. Volume of thoracic cavity decreases

  5. Lungs are compressed, air pressure inside increases

  6. Air pressure in lungs higher than atmospheric pressure, air forced out
• What happens during inhalation vs exhalation

  • Inhalation: Diaphragm contracts, lowers & straightens
  • Inhalation: External intercostal muscles contract, internal intercostal muscles relax
  • Inhalation: Rib cage raised upwards & outwards
  • Inhalation: Volume of thoracic cavity increases, air pressure in lungs decreases, air sucked in
  • Exhalation: Diaphragm relaxes, upwards & curves
  • Exhalation: External intercostal muscles relax, internal intercostal muscles contract
  • Exhalation: Rib cage lowered down & inwards
  • Exhalation: Volume of thoracic cavity decreases, air compressed in lungs, air forced out
• Alveoli


  • Provide large surface area for gaseous exchange
  • Walls covered with water layer to dissolve gases
  • Walls only one cell thick for quick diffusion
  • Richly supplied with capillaries for rapid gas transport
• Before reaching lungs, air is warmed, moistened and filtered
• Cilia


  Hair-like structures in mucous membrane that constantly move to transport mucus laden with foreign matter towards pharynx
• Exhaled air differs from inhaled air in terms of oxygen, carbon dioxide and other components
• Experiment to compare inspired and expired air

  1. Observe changes in 2 flasks after a few minutes

  2. Conclude if amount of carbon dioxide differs between inspired and expired air

  
• Experiment to show effect of exercise on breathing rate

  1. Count breaths per minute at rest

  2. Person does 5 mins vigorous exercise

  3. Count breaths per 30 secs for 10 mins

  4. Calculate breathing rate per minute

  5. Plot graph of breathing rate vs time
• Experiment to show effect of exercise on depth of breathing

  1. Person at rest breathes through tube connected to respirometer

  2. Person does 5 mins vigorous exercise

  3. Respirometer produces graph of results
• Tidal volume (TV)


  Air that moves into and out of lungs with each breath
• Inspiratory reserve volume (IRV)

  Air that can be inspired forcibly beyond the tidal volume
• Expiratory reserve volume (ERV)


  Air that can be evacuated from the lungs after a tidal expiration
• Vital capacity


  Total volume of air blown out after a deep breath
• Residual volume (RV)


  Air left in the lungs after strenuous expiration
• Smoking ads used to promote smoking as a cool and sporting lifestyle, but now there are restrictions on smoking
• Tobacco smoke causes inflammation of the airway lining, excessive mucus secretion, paralysis of cilia, airway blockage, and persistent cough
• Chronic bronchitis


  • Inflammation and excess mucus in bronchioles
• Emphysema


  • Destruction of alveoli walls, reduced surface area for gaseous exchange, loss of lung elasticity, difficulty breathing
• Chronic bronchitis and emphysema together are known as chronic obstructive pulmonary/lung diseases (COPD)