Excretion In Representative Animals

Excretion In Representative Animals

Excretion in Hydra:

Hydra does not have a specialized excretory structure. Its waste products are simply diffused into the outer isosmotic surrounding.

Excretion in Planaria:

Planarian is a flat worm. It has simple tubular excretory system called protonephrium.

1. Protonephrium:

A protonephridium is a network of closed tubules without internal openings.

2. Flame cells:

This tubular system spread throughout the body. Its branches are capped by cells called flame cells. Each flame cell has a tuft of cilla. The beating of cilia looks like a flickering flame. Thus it is called flame cell. The beating of these cilia propels the interstitial fluid into the tubular system.

3. Excretory duct:

The tubular system open into excretory duct. The excretory duct opens outside through nephridiopores. Fresh water flatworms excrete very dilute urine. The parasitic flatworms are isotonic to the host environment. Their flame cells dispose of nitrogenous wastes.

Excretion in Earthworm:

Excretory structures:

The excretory system of the earthworm is composed of another type of tubular excretory system called metanephridium. Each segment of the earth worm has a pair of metanephridia. The tubular system or metanephridium has internal ciliated openings called nephrostome. The tubule is immersed in the coelomic fluid. The tubule is enveloped by network of capillaries.

Mechanism of excretion:

The nephrostomes collect wastes from the coelomic fluid. The fluid moves through the tubule. The epithelium of tubules reabsorbs the salt from the fluid passing through the lumen (ustoS) of tubule. The epithelium sends these salts to blood vessels, surrounding the nephridium. The remaining waste is left as urine. This urine contains nitrogenous waste. The urine is finally removed through nephridiopores.

Excretion in Cockroach and Insects

Excretory structures:

The excretory system of Arthropods like insects is composed of tubular structure called Malapighian tubules. The malpighian tubules are suspended in the sinuses (haemocoel). The sinuses contain haemolymph (blood). The malpighian tubules open in the digestive system. The insects are the only animals in the animal kingdom in which excretory structure are associated with the digestive system.

Mechanism of excretion:

The malpighian tubules collect excretory product from the haemolymph. The solutes (including salts) passes through epithelium of the tubules form haemolymph. Finally these wastes enter into the lumen of the tubules. Then the fluid of the tubules is transported into the hind gut. It then enters into rectum.

Rectum reabsorbs most of the salts and water. Rectum finally excretes out the nitrogenous wastes in the form of uric acid. The adaptation of secretion of urea has made the insect most successful animals

on land with shortage of water.

Excretion in vertebrates

Evolution of Kidney:

1. The invertebrates like earthworm are the ancestors of the vertebrates. These invertebrates have segmentally arranged excretory structures called metanephridia. This character is also present in the primitive vertebrates like hagfishes.

2. However, evolution of kidney took place in other vertebrates and kidneys were formed. Kidneys contain numerous tubules called nephrons. The basic functional structure in kidneys is Nephron. The nephrons or tubules are not arranged segmentally. These are closely associated with the dense network

of capillaries.

Excretion in Man

Normal Mechanism

The life has chemical basis. It depends on metabolic pathways. Many wastes are produced during metabolic activities. These wastes are called metabolic wastes. There are following metabolic wastes in man:

➤ Urea: It is produced during metabolism of amino acids.

➤ Creatinine: It is produced from the muscle creatine

➤ Uric acid: It is produced from nucleic acids

➤ Bilirubin: It is end products of haemoglobin breakdown.

➤ Metobolites of various hormones.

➤ Toxins: These toxins are produced within the body or they are ingested into the body such as drugs, pesticides and food additives. The presence of waste in body causes serious hazards. So these

wastes are eliminated from the body by the excretory system.

Excretory organs

1. Skin:

The skin has sweat glands  and sebaceous glands. The sweat glands remove salts and sebaceous glands secret sebum. Sweat glands secrete salts and water for thermoregulation. While sebaceous glands secretes sebum for protection against. So skin does not come within the definition of excretory organs.

2. Kidney:

Liver and kidneys are the primary excretory structures.

3. Liver:

Liver is the central station of the metabolism. It is a central clearing house of the body. Therefore the liver play a pivotal role in homeostasis. It interacts  with most of the body organs system.

➤ Liver support the kidney for excretion.

➤ It detoxifies many chemical poisons.

➤ It produces ammonia, urea and uric acids from the nitrogen of amino acids.

In addition to synthesis of nitrogenous wastes, the liver also performs many functions, like synthesis, storage, conversion and recycling.