Respiratory System Of FishGills mediate the gas exchange in fish. These organs, located on the sides of the head, are made up of gill filaments, feathery structures that provide a large surface for gas exchange. The filaments are arranged in rows in the gill arches, and each filament has lamellae, discs that contain capillaries. Blood enters and leaves the gills through these small blood vessels. Although gills are restricted to a small section of the body, the immense respiratory surface created by the gill filaments provides the whole animal with an efficient gas exchange. The surrounding water keeps the gills wet.

A flap, the operculum, covers and protects the gills of bony fish. Water containing dissolved oxygen enters the fish's mouth, and the animal moves its jaws and operculum in such a way as to pump the incoming water through the gills. As water passes over the gill filaments, blood inside the capillaries picks up the dissolved oxygen. Since the blood in the capillaries flows in a direction opposite to the flow of water around the gill filaments, there is a good opportunity for absorption. The circulatory system then transports the oxygen to all body tissues and picks up carbon dioxide, which is removed from the body through the gills. After the water flows through the gills, it exits the body behind the fish's operculum.

Oxygen and carbon dioxide dissolve in water, and most fishes exchange dissolved oxygen and carbon dioxide in water by means of the gills. The gills lie behind and to the side of the mouth cavity and consist of fleshy filaments supported by the gill arches and filled with blood vessels, which give gills a bright red colour. Water taken in continuously through the mouth passes backward between the gill bars and over the gill filaments, where the exchange of gases takes place. The gills are protected by a gill cover in teleosts and many other fishes but by flaps of skin in sharks, rays, and some of the older fossil fish groups. The blood capillaries in the gill filaments are close to the gill surface to take up oxygen from the water and to give up excess carbon dioxide to the water.

Most modern fishes have a hydrostatic (ballast) organ, called the swim bladder, that lies in the body cavity just below the kidney and above the stomach and intestine. It originated as a diverticulum of the digestive canal. In advanced teleosts, especially the acanthopterygians, the bladder has lost its connection with the digestive tract, a condition called physoclistic. The connection has been retained (physostomous) by many relatively primitive teleosts. In several unrelated lines of fishes, the bladder has become specialized as a lung or, at least, as a highly vascularized accessory breathing organ. Some fishes with such accessory organs are obligate air breathers and will drown if denied access to the surface, even in well-oxygenated water. Fishes with a hydrostatic form of swim bladder can control their depth by regulating the amount of gas in the bladder. The gas, mostly oxygen, is secreted into the bladder by special glands, rendering the fish more buoyant; the gas is absorbed into the bloodstream by another special organ, reducing the overall buoyancy and allowing the fish to sink. Some deep-sea fishes may have oils, rather than gas, in the bladder. Other deep-sea and some bottom-living forms have much-reduced swim bladders or have lost the organ entirely.

The swim bladder of fishes follows the same developmental pattern as the lungs of land vertebrates. There is no doubt that the two structures have the same historical origin in primitive fishes. More or less intermediate forms still survive among the more primitive types of fishes, such as the lungfishes Lepidosiren and Protopterus.

Earthworm: Respiration SystemEarthworms Do Not Have Lungs.

How Does Oxygen Enter an Earthworm’s Body?

Answer:

While earthworms do not have lungs, like you, they must have oxygen to live.

You have lungs that fill will air when you inhale. In your lungs, oxygen from the air is mixed

with blood, and then the blood carries oxygen to all the parts of your body.

Instead of lungs, earthworms have a thin permeable skin through which oxygen in air passes through.

The oxygen does not directly pass through the earthworm’s thin outer skin. Instead, the  oxygen must first mix with the moist slime on the earthworms skin. It is this mixture that passes through the skin as well as the very thin tissue of capillaries under the skin.

Blood in dorsal vessel moves toward the anterior (head) end. Blood in the ventral vessel moves toward the posterior (rear) end.

Every segment is separated by septae (a vertical wall of tissue). In each segment compartment, except for the first three on the anterior end and the last one on the posterior end, are two nephridia. The ends of these tube structures extend through the outside skin of the earthworm. Waste gases pass from the segment compartment outside the body.

Respiration

Earthworms have no special respiratory organs. Gases are exchanged through the moist skin and capillaries, where the oxygen is picked up by the hemoglobin dissolved in the blood plasma and carbon dioxide is released. Water, as well as salts, can also be moved through the skin by active transport.

 

The frog has three respiratory surfaces on its body that it uses to exchange gas with the surroundings: the skin, in the lungs and on the lining of the mouth.

While completely submerged all of the frog's repiration takes place through the skin. The skin is composed of thin membranous tissue that is quite permeable to water and contains a large network of blood vessels. The thin membranous skin is allows the respiratory gases to readily diffuse directly down their gradients between the blood vessels and the surroundings. When the frog is out of the water, mucus glands in the skin keep the frog moist, which helps absorb dissolved oxygen from the air.

A frog may also breathe much like a human, by taking air in through their nostrils and down into their lungs. The mechanism of taking air into the lungs is however sligthly different than in humans. Frogs do not have ribs nor a diaphragm, which in humans helps serve in expand the chest and thereby decreasing the pressure in the lungs allowing outside air to flow in.

In order to draw air into its mouth the frog lowers the floor of its mouth, which causes the throat to expand. Then the nostrils open allowing air to enter the enlarged mouth. The nostrils then close and the air in the mouth is forced into the lungs by contraction of the floor of the mouth. To elimate the carbon dioxide in the lungs the floor of the mouth moves down, drawing the air out of the lungs and into the mouth. Finally the nostrils are opened and the floor of the mouth moved up pushing the air out of the nostrils.

Frogs also have a respiratory surface on the lining of their mouth on which gas exchange takes place readily. While at rest, this process is their predominate form of breathing, only fills the lungs occasionally. This is because the lungs, which only adults have, are poorly developed.