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

Mechanisms of Breathing

Mechanisms of Breathing

Chapter : Respiratory System in Humans and Animals

Topic : Mechanisms of Breathing

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