How do fish breathe?

How do fish breathe?

Blood vessels in fishes' gills absorb oxygen and release carbon dioxide.

Biology

Keywords

fish, respiration, gill, gas exchange, exhalation, inhalation, oxygen, carbon dioxide, operculum, capillary, animal, vertebrates, biology

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Scenes

Inhalation:
- the mouth is closed
- the operculum rises
- the branchiostegal membrane is closed.

Therefore, the pressure in the gill cavity decreases and water flows in it through the mouth.

Exhalation:
- the mouth is open
- the operculum closes
- the branchiostegal membrane is open.

Therefore, the pressure in the gill cavity increases and water flows out behind the operculum.

The movement of the operculum ensures the change in pressure that is necessary for the inflow and outflow of water. The synchronized movement of the membrane and the mouth ensures that the water flows in one direction only.

  • - The blood vessels that supply the gill run here. Arteries, indicated with blue color here, carries blood rich in carbon dioxide from the body to the gills. Veins, indicated with red color, carry blood rich in oxygen from the gills to the body.

The blood in the vessels of the gill and the water move in opposite directions. Therefore, the partially oxygen-rich blood meets water with the highest oxygen content, from which it absorbs additional oxygen.

Blood already poor in oxygen thus meets water still rich in oxygen.

If the direction of the flow of blood and water was identical, the oxygen concentration of the water and the blood would become equal at the initial section of the vessel and the blood could carry a lot less oxygen. The reason for this is that the water already low in oxygen would not be able to transfer more oxygen to the blood already poor in oxygen.

The principle of countercurrent exchange is present in several vital functions, such as in urine and lymph production. The same principle is used in renal replacement therapy.

  • - The blood vessels that supply the gill run here. Arteries, indicated with blue color here, carries blood rich in carbon dioxide from the body to the gills. Veins, indicated with red color, carry blood rich in oxygen from the gills to the body.

Narration

The gill cover rises as the fish opens its mouth during inhalation. The pressure in the gill cavity therefore decreases and water flows in through the mouth. Water can only enter the gill cavity through the mouth, since the gill membrane serves as a valve that stops water from entering below the gill cover.

The mouth is closed, and the gill cover closes during exhalation. This leads to an increase in pressure in the gill cavity, which causes water to float out through the open gill membrane.

That is, during inhalation the mouth is opened, the gill cover rises, and the gill membrane is closed; during exhalation, the mouth is closed, the gill cover closes, and the gill membrane is opened.

The gill is the respiratory organ in fish. The gill arc contains the primary lamellae that hold the secondary lamellae. This structure increases the fish’s breathing surface, hence increasing the efficiency of gas exchange.

The secondary lamellae contain capillaries. The carbon dioxide content of the water that enters the gill is lower than that of the blood, while its oxygen content is higher. For this reason, gas exchange takes place; blood releases carbon dioxide and absorbs oxygen.

The principle of countercurrent exchange plays an essential role in gas exchange. Blood and water move in opposite directions, therefore, the partially oxygen-rich blood meets water with the highest oxygen content, from which it absorbs additional oxygen. On the other hand, blood that has already released a percentage of its carbon dioxide meets water with the lowest carbon dioxide content, to which it transfers additional carbon dioxide.

Fish also use their skin as a supplementary respiratory organs.

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