Mechanisms of Breathing

8.2 Mechanisms of Breathing
 
Breathing Mechanism of Insects
Inhalation
  • When inhaling air, the abdominal muscles will relax.
  • This will reduce the air pressure in the trachea and air enters into the trachea through the spiracle.
Exhalation
  • The abdominal muscles will contract when air is exhaled.
  • This will increase the air pressure in the trachea and subsequently forces air out of the spiracle.
 
Breathing Mechanism of Frogs
Inhalation
  • When the frog breathes through the nostrils, the mouth and glottis are closed and the floor of the buccopharyngeal cavity is lowered.
  • The low air pressure in the mouth cavity draws air into the buccopharyngeal cavity through the nostrils.
  • When the glottis opens, the nostrils close and the floor of the buccopharyngeal cavity is raised.
  • The increased air pressure pushes air into the lungs.
Exhalation
  • When the lungs contract, air is expelled from the lungs.
  • This is helped by the abdominal pressure and the elasticity of the lungs.
  • Some air is expelled through the nostrils while the rest is mixed with the air in the buccopharyngeal cavity.
 
 
Breathing Mechanism of Fish
Inhalation
  • When the mouth opens, the floor of the buccal cavity is lowered.
  • At the same time, the opercular cavity is enlarged and the operculum opening is closed.
  • This reduces the pressure in the buccal cavity.
  • Water from the outside which contains dissolved oxygen enters the mouth.
Exhalation
  • When the mouth is closed, the floor of the buccal cavity is raised.
  • Water enters through the gill lamella and gaseous exchange between blood and water occurs through diffusion.
  • At the same time, the operculum muscle relaxes and the opercular cavity becomes smaller.
  • The volume of the buccal cavity is reduced and the pressure in the buccal cavity becomes higher than the pressure outside.
  • The high pressure causes water to flow through the operculum opening.
 
 
Breathing Mechanism of Humans
Inhalation
  • The external intercostal muscles contract while the internal intercostal muscles relax.
  • This action causes the ribcage to move upwards and outwards.
  • At the same time, the diaphragm muscles contract and the diaphragm moves downwards to become flat and horizontal.
  • Both mechanisms cause the volume of the thorax cavity to increase and the pressure of the thorax cavity decreases.
  • The higher atmospheric pressure from outside forces air into the lungs.
Exhalation
  • The external intercostal muscles relax while the internal intercostal muscles contract.
  • This action causes the ribcage to move downwards and inwards.
  • At the same time, the diaphragm muscles relax and the diaphragm curves upwards to form a dome.
  • Both movements cause the volume of the thoracic cavity to reduce and the pressure of the thorax cavity to increase.
  • Air is pushed out of the lungs.
 
 
Compare and Contrast Breathing Mechanisms in Humans and Animals
Similarities
  • Humans and animals have special muscular structures to expand and contract the respiratory cavity.
  • The breathing mechanism involves changes in the volume and pressure in the respiratory cavity.
Differences

Mechanisms of Breathing

8.2 Mechanisms of Breathing
 
Breathing Mechanism of Insects
Inhalation
  • When inhaling air, the abdominal muscles will relax.
  • This will reduce the air pressure in the trachea and air enters into the trachea through the spiracle.
Exhalation
  • The abdominal muscles will contract when air is exhaled.
  • This will increase the air pressure in the trachea and subsequently forces air out of the spiracle.
 
Breathing Mechanism of Frogs
Inhalation
  • When the frog breathes through the nostrils, the mouth and glottis are closed and the floor of the buccopharyngeal cavity is lowered.
  • The low air pressure in the mouth cavity draws air into the buccopharyngeal cavity through the nostrils.
  • When the glottis opens, the nostrils close and the floor of the buccopharyngeal cavity is raised.
  • The increased air pressure pushes air into the lungs.
Exhalation
  • When the lungs contract, air is expelled from the lungs.
  • This is helped by the abdominal pressure and the elasticity of the lungs.
  • Some air is expelled through the nostrils while the rest is mixed with the air in the buccopharyngeal cavity.
 
 
Breathing Mechanism of Fish
Inhalation
  • When the mouth opens, the floor of the buccal cavity is lowered.
  • At the same time, the opercular cavity is enlarged and the operculum opening is closed.
  • This reduces the pressure in the buccal cavity.
  • Water from the outside which contains dissolved oxygen enters the mouth.
Exhalation
  • When the mouth is closed, the floor of the buccal cavity is raised.
  • Water enters through the gill lamella and gaseous exchange between blood and water occurs through diffusion.
  • At the same time, the operculum muscle relaxes and the opercular cavity becomes smaller.
  • The volume of the buccal cavity is reduced and the pressure in the buccal cavity becomes higher than the pressure outside.
  • The high pressure causes water to flow through the operculum opening.
 
 
Breathing Mechanism of Humans
Inhalation
  • The external intercostal muscles contract while the internal intercostal muscles relax.
  • This action causes the ribcage to move upwards and outwards.
  • At the same time, the diaphragm muscles contract and the diaphragm moves downwards to become flat and horizontal.
  • Both mechanisms cause the volume of the thorax cavity to increase and the pressure of the thorax cavity decreases.
  • The higher atmospheric pressure from outside forces air into the lungs.
Exhalation
  • The external intercostal muscles relax while the internal intercostal muscles contract.
  • This action causes the ribcage to move downwards and inwards.
  • At the same time, the diaphragm muscles relax and the diaphragm curves upwards to form a dome.
  • Both movements cause the volume of the thoracic cavity to reduce and the pressure of the thorax cavity to increase.
  • Air is pushed out of the lungs.
 
 
Compare and Contrast Breathing Mechanisms in Humans and Animals
Similarities
  • Humans and animals have special muscular structures to expand and contract the respiratory cavity.
  • The breathing mechanism involves changes in the volume and pressure in the respiratory cavity.
Differences