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Animation: Gas Exchange in Fish Gills

by Pearson
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>> The respiratory organs of aquatic animals are called gills, which in bony fish are covered by a stiff flap called the operculum. Here we've removed the operculum so that the gills are visible. Gills are outfoldings of the body's surface specialized for gas exchange. Because oxygen is far less plentiful in water than it is in air, the gills of active animals such as fishes must be very efficient to obtain enough oxygen. The gills in fish obtain oxygen from water as the water flows over the gills. Oxygen-rich water enters through the fish's open mouth, passes through slits in the pharynx, and flows across the gills, where oxygen diffuses from the water into the bloodstream. The oxygen-poor water then passes back out to the environment. A closer look reveals that the gills consist of multiple pairs of filaments supported by gill arches. As water flows through the gills, the filaments are surrounded by water. Notice that blood vessels run through the gill arch and branch into each filament. Red indicates that a blood vessel carries oxygen-rich blood. Blue indicates a vessel carrying oxygen-poor blood, blood whose oxygen has been depleted. Where is the oxygen-poor blood coming from? As blood circulates through the body tissues, oxygen is used; thus, the oxygen-poor blood comes from the body tissues, where it then returns to the heart, which pumps it to the gills. After the blood is recharged with oxygen in the gills, the blood continues on its journey and carries this oxygen to the body tissues. Next, let's take a closer look at a gill filament to see what happens to the oxygen-poor blood coming from the heart. Each gill filament bears many rows of plate-like lamellae that are the actual respiratory surfaces. Each lamella is full of tiny capillaries. Here we show the path of a single red blood cell as oxygen-poor blood coming from the heart flows through a larger vessel and then enters one of these capillary beds. Notice the color change of the cell from blue to purple to red as it travels through the capillary bed, picking up oxygen from the oxygen-rich water that flows through the gills. The red blood cell then enters the blood vessel at the other side of the capillary bed. Blood from that vessel flows into the larger vessel in the gill arch and then circulates to the body tissues. A process called countercurrent exchange makes fish gills highly efficient at extracting oxygen from the water. Countercurrent refers to the flow of two fluids, blood and water, in opposite directions. In our diagram, blood flows right to left through the capillaries. Water is moving in the opposite direction, left to right, as it flows through the gill filaments.
>> The respiratory organs of aquatic animals are called gills, which in bony fish are covered by a stiff flap called the operculum. Here we've removed the operculum so that the gills are visible. Gills are outfoldings of the body's surface specialized for gas exchange. Because oxygen is far less plentiful in water than it is in air, the gills of active animals such as fishes must be very efficient to obtain enough oxygen. The gills in fish obtain oxygen from water as the water flows over the gills. Oxygen-rich water enters through the fish's open mouth, passes through slits in the pharynx, and flows across the gills, where oxygen diffuses from the water into the bloodstream. The oxygen-poor water then passes back out to the environment. A closer look reveals that the gills consist of multiple pairs of filaments supported by gill arches. As water flows through the gills, the filaments are surrounded by water. Notice that blood vessels run through the gill arch and branch into each filament. Red indicates that a blood vessel carries oxygen-rich blood. Blue indicates a vessel carrying oxygen-poor blood, blood whose oxygen has been depleted. Where is the oxygen-poor blood coming from? As blood circulates through the body tissues, oxygen is used; thus, the oxygen-poor blood comes from the body tissues, where it then returns to the heart, which pumps it to the gills. After the blood is recharged with oxygen in the gills, the blood continues on its journey and carries this oxygen to the body tissues. Next, let's take a closer look at a gill filament to see what happens to the oxygen-poor blood coming from the heart. Each gill filament bears many rows of plate-like lamellae that are the actual respiratory surfaces. Each lamella is full of tiny capillaries. Here we show the path of a single red blood cell as oxygen-poor blood coming from the heart flows through a larger vessel and then enters one of these capillary beds. Notice the color change of the cell from blue to purple to red as it travels through the capillary bed, picking up oxygen from the oxygen-rich water that flows through the gills. The red blood cell then enters the blood vessel at the other side of the capillary bed. Blood from that vessel flows into the larger vessel in the gill arch and then circulates to the body tissues. A process called countercurrent exchange makes fish gills highly efficient at extracting oxygen from the water. Countercurrent refers to the flow of two fluids, blood and water, in opposite directions. In our diagram, blood flows right to left through the capillaries. Water is moving in the opposite direction, left to right, as it flows through the gill filaments.