The tracheal system; spiracles, tracheae, tracheoles and air sacs (for some insects).

• Tracheoles penetrate the body tissues, which to allow a direct exchange of gases.
• Have many tracheoles; to increase the surface area for gases exchange.
• The tips of tracheoles contain fluid; dissolving the gases.
• Some insects have air sacs; speed up the movement of gases to and from tissues during vigorous movement of the body.

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• As insects inhale, abdominal muscles relax and spiracles open.
• It causes the air pressure inside the tracheae decreases, which draws the air into the tracheae through spiracles.
• As the insects exhale, the abdominal muscles contract, causing the air pressure in the tracheae to increase, pushing the air out through the spiracles.

• Respiratory structure: gills
• Gills are supported by the gill arch and protected by the operculum.
• Each gill has thin filaments.
• The filaments contain numerous lamellae.

• A large surface area of filaments and lamellae increases the efficiency of gases exchange in fish.
• The thin filaments are supplied with blood capillaries to transport respiratory gases efficiently.
• Countercurrent flow: the water flows over the gills in one direction, while the blood flows in the opposite direction.

• As the deoxygenated blood enters the blood capillaries, it encounters water with high oxygen content.
• The high concentration gradient of oxygen in the water allows the oxygen to diffuse into the blood capillaries to be brought to the whole parts of the body.

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During inhalation:

• The floor of buccal cavity lowers, opercular cavity enlarges, operculum closed; it lowers the pressure in the buccal cavity that allows water to draw into the mouth.

During Exhalation:

• The mouth is closed, the floor of buccal cavity rises; allows water to flow through the lamellae and gases exchange takes place.

Source:[respirationsystem.weebly.com]

• Skin
• Lungs

• Skin: thin, permeable to gas and moist; enables a rapid and efficient gases exchange.
• Lungs: moist, contain thin-walled sacs, and rich in blood capillaries for efficient transportation of gases.

During inhalation:

Air entering the buccopharyngeal cavity:

• Nostrils open, the floor of buccopharyngeal lowers and glottis close.
• It draws air into the buccopharyngeal cavity.

Air entering the lungs:

• Glottis open, nostrils close and the floor of buccopharyngeal raise.
• It increases the air pressure in the buccopharyngeal cavity that forces the air to enter the lungs.

During exhalation:

Air exits the lungs into the buccopharyngeal cavity:

• Lungs muscle contract, glottis open and buccopharyngeal floor lowers; drive the air out from the lungs.

Air exits the buccopharyngeal cavity:

• Glottis close, buccopharyngeal floor raise; air expelled out through the nostrils.

• The alveoli of the lungs

• Moist and thin-walled sacs of millions of alveoli, which surrounded by a rich network of blood capillaries.

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