Excretory Products and their Elimination

Excretion is the process of elimination of metabolic waste from the body. This process is strictly found only in animals.

The excretory products include amino acids, urea, uric acid, carbon dioxide, water, and ammonia.

Some Molluscs and Echinoderms excrete waste products from the body in the form of amino acids.

Ammonia is the primary excretory product in animals, it is derived from the proteins present in the food we eat. It is the most toxic nitrogenous waste and is excreted by diffusion by most of the amphibians and aquatic animals.

Mammals excrete nitrogenous waste as urea. It is less toxic and comparatively less soluble in water.

Birds and reptiles excrete nitrogenous waste as uric acid.

Let us have a detailed look at the different excretory products and their elimination in different organisms.

Excretory Products of Different Organisms

The excretory products and organs of different organisms are mentioned below:

Organisms

Excretory Products

Excretory Organs

Paramecium, amoeba Ammonia

Contractile vacuole

Hydra

Ammonia General body surface

Ascaris

Ammonia

Renette cells

Periplaneta

Uric acid

Malphigian tubule

Palaemon

Uric acid

Antennary gland

Pheretima

Ammonia

Nephridial system

Spider

Uric acid

Coxal glands, Malpighian tubule

Taenia

Ammonia

Protonephridia

Leucon

Ammonia

General body surface

Human Excretory Organs

The human excretory system comprises of the following excretory organs:

  • A pair of kidneys

  • A pair of ureters

  • Urinary Bladder

  • Urethra

Kidneys

These are the primary excretory organs in humans located on the left and right side of the spine, near the liver. They are divided into the renal cortex, renal medulla, and renal pelvis. Renal pelvis carries urine from the kidney to the ureter. A nephron is the functional unit of a kidney.

Ureter

It is a thin tube that comes out of each kidney carrying urine to the urinary bladder.

Urinary Bladder

It is a sac-like structure that stores urine until micturition (expelling urine from the body).

Urethra

It is a tube-like structure that extends from the urinary bladder and helps in expelling urine outside the body. It is usually shorter in females and longer in males.

Other Excretory Organs

Besides the above mentioned excretory organs, humans have other excretory organs as well. These excretory organs include:

Skin

Skin is known to be the largest organ in the human body. It contains sweat glands and the sebaceous glands. The sweat glands produce sweat which contains sodium chloride, amino acids, water, and glucose.

The sebaceous glands excrete excess fat such as sterol and wax.

Lungs

Lungs facilitate gaseous exchange. They help in inhaling oxygen and eliminating carbon dioxide and water vapour from the body.

Around 18L of carbon dioxide per hour and 400ml water per day is eliminated from the body.

Salivary Glands

These glands participate in the excretion of heavy metal ions such as lead and mercury.

Gastrointestinal tract and Intestines

The intestines eliminate the nitrogenous waste in the form of faeces. Salts, glucose, calcium, iron, fibre is excreted through faeces.

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