Anatomy and Function of a Fish Respiratory, Circulatory, and Excretory Systems Part 3

Respiratory System The function of the respiratory system is to take oxygen into the body and pass carbon dioxide out of the body. The most important respiratory organs in fish are the gills. Inside the gills are respiratory organs which include: Gill fillaments Gill cover (operculum) Gill rakers Gas bladder

Functions of the Gill filaments, Gill rakers, and Operculum Contain blood vessels called capillaries. Blood in the capillaries picks up oxygen and gives off carbon dioxide.

Gill cover (operculum) Covers the gills. Protects the delicate gill filaments. Aids in moving water over the gill filaments. Gill Rakers: Not on notes Keep food in the mouth . Located in the mouth cavity.

How Water Moves Over Gills Water moves over the gills in a pumping action with two steps. The mouth cavity opens, making it larger and drawing in water. In this step, the gill covers are closed.

The mouth closes, making the mouth cavity smaller. The gill covers open and the water passes out through them. When swimming fast, some fish, such as sharks and tunas, just open their mouths and gill openings, letting water pass continuously through their gills.

As the water passes over the gills, blood in the capillaries of the gill filaments passes carbon dioxide into the water and picks up dissolved oxygen from the water. The blood then carries the oxygen to the body. Oxygen is essential in the body because it combines with food molecules to release energy for the body as needs.

Gas Bladder Gas bladder: Operates as a buoyancy-adjusting organ. In some species, it serves as an accessory respiratory organ(lung) when they crawl on land. Produces sound in some species. - Muscles in the wall of the bladder contract rapidly, producing a low-frequency(low-pitch) sound that is resonated and amplified in the bladder. (Not in notes)

Not On Notes Fish that have no gas bladder are always more dense than the surrounding water, so they sink if they stop swimming. Sharks, for example, must keep swimming to stay afloat. They use their tails and pectoral fins like airplane wings, adjusting the amount of lift to control the depth of their swimming.

How a fish regulates Buoyancy Some fish have a gas bladder lying below the kidneys. In some fish, the bladder is part of the respiratory system. In many fish, the gas bladder serves no respiratory function but regulates the fish’s buoyancy instead. It does this by making the fish’s density equal to the density of the surrounding water.

The fish sinks if its body density is greater than the density of water. The density of the gas bladder, filled mostly with oxygen and nitrogen gases, acts like an inflatable balloon inside the fish. The gas bladder reduces the density of the fish’s body until it is the same as the density of the water. In this way, the fish does not sink or rise, but floats within the water column.

When the fish swims into shallow water, its gas bladder expands because the pressure of water surrounding the fish is less. The fish compensates by absorbing some of the gas back into its body cells, bringing the gas bladder back to its original size.

When the fish swims deeper, its gas bladder gets smaller because of the increase in water pressure. Then more gas enters the bladder, enlarging it again. In this way, the fish remains neutrally buoyant, which means it is equal in density to seawater.

Because gases move slowly in and out of the bladder, fish caught at great depths(really deep water) are often bloated when brought to the surface. This is because the gas in the bladder expands rapidly when the fish moves from the high pressure of deep water to the lower atmospheric pressure outside of the water.

A fish pulled quickly to the surface cannot absorb the gases quickly enough and the bladder expands suddenly. Fish collectors must bring trapped fish to the surface slowly by stages to let the fish’s body absorb the gases from the bladder.

Circulatory System The circulatory system is a transportation system for body fluids that carry nutrients, oxygen, and hormones to cells and carbon dioxide and waste from cells. The circulatory components include: Heart Arteries Capillaries Veins Lymph ducts Blood Red blood cells White blood cells

Heart The heart pumps blood to all parts of the body. In the fish, it is a muscular organ of four chambers (2 main chambers: a thin walled atrium and a more muscular ventricle). Valves between the chambers allow the blood to flow in only one direction. When the heart muscle contracts, it forces blood into the arteries.

Arteries, Capillaries, and Veins A network of tubes called arteries, capillaries, and veins connects the heart with all parts of the body. Arteries: Carry blood from the heart to the capillaries. Capillaries: Thin walls let molecules move out of the blood vessel and into the fluids around the tissues Veins: Carry blood from the capillaries back to the heart.

Blood Blood is a liquid tissue made up of plasma and blood cells. Plasma contains water, carbon dioxide, hormones, nutrients, wastes, and other molecules. Blood carries nutrients and hormones to the cells. Blood also carries waste products away from cells.

Red Blood Cells There are two main types of blood cells. Red blood cells: Carry oxygen from the gills to other cells in the body. Hemoglobin, which contains iron, is found in red blood cells.

When hemoglobin combines with oxygen, it turns bright red. When hemoglobin releases its oxygen, it turns a very dark red.

White Blood Cells White blood cells fight disease. They often concentrate around infected wounds, killing bacteria and transporting wastes away from the wound. Dead cells in a wound form pus.

Oxygen Concentration in Blood: Blood that is low in oxygen and high in carbon dioxide is pumped by the heart to the gills, where it releases its carbon dioxide and picks up more oxygen through capillaries in the gill filaments.

From the gills, the blood (now rich in oxygen) flows through branching arteries to the brain, digestive system and other tissues and organs. From the digestive system, the blood absorbs nutrients and distributes them through the body. In each tissue and organ, some of the blood plasma passes through capillaries and flows around the cells.(Found twice on your notes. Disregard it the second time).

Carbon dioxide and waste products move from the cells into the plasma. The plasma then passes back into the capillaries and carries wastes away.

Lymph Ducts Lymph ducts pick up the liquid that passes out of the capillaries and collects in parts of the fish’s body. The lymph ducts return this liquid (called lymph) to the veins.

The circulatory system works like a canal system. It carries the oxygen and building materials needed to grow, maintain, and repair the body. It transports white blood cells to destroy disease invaders. It also carries wastes to the lungs, liver, and kidneys, which expel them.

Excretory System The excretory system removes wastes produced by the body. The excretory organs include: - Kidneys - Urinary duct - Bladder - Urogenital opening - Gill filaments

Kidneys Its chief organs are the kidneys, a pair of long, dark-red organs lying just under the vertebrae. In some fish, there may appear to be only one kidney. The kidneys remove some waste products from the blood.

Waste products filtered by the kidneys are formed in cells of the body. After filtering, usable materials such as sugars, salts, and water are absorbed back into the blood. The remaining waste products pass from the kidneys down the urinary duct.

Urinary Duct, Bladder, and the Urogenital Opening The urinary duct carries waste products from the blood to the bladder. The bladder stores the waste products until they are eliminated from the body. The urogenital opening lets waste products leave the body. This is the same opening through which materials pass from the urinary system and the reproductive system.

Gill Filaments The gills, though usually considered part of the respiratory system, are also excretory organs. The blood carries other waste products and excess salts to the gill filaments. Carbon dioxide and ammonia are excreted by the gills. Salt is also excreted by the gills if fish lives in saltwater.

Liver The liver also removes wastes from the blood, but is considered part of the digestive system, NOT the excretory system. The liver cleans blood after it has picked up digested products from the intestine. Wastes are converted into bile and stored in the gall bladder, where they wait to be poured back into the digestive tract to aid in digestion.

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The End!!! Anatomy of a Fish Part 4 is next!!