EXCRETION

Excretion is the process by which wast products are removed from the body of living organisms.

Number of waste products are formed during the metabolic reactions. If these waste products are accumulated in the body they cause harm to the body. For the normal functions of the body these waste products should be removed from the body.

Following are important excretory products.

1. Carbon dioxide
2. Nitrogenous waste
3. Excess amount of water and salts

In unicellular organisms excretion of CO₂ takes place through the body surface by the process of simple diffusion.

In earth worm excretion of CO₂ takes place by the process of simple diffusion through the body surface.

In insects excretion of CO₂ takes place through trachea.

Excretions of CO₂ take place by gills in fishes.

In these animals excretion of CO₂ takes place through lungs.

Plants remove CO₂ through stomata. Other waste products are stored in different parts of the plant like leaf and seeds which detached from the plant after some time.

During the day time processes of photosynthesis and respiration take place in plants. The CO₂ produced by respiration is used during the process of photosynthesis. Oxygen is produced during the process of photosynthesis. During day time plants produce more O₂. During night only CO₂ is produced as the process of respiration takes place during night but there is no photosynthesis during night time.

Excretion of waste products takes place through the process of simple diffusion. Excess amounts of water and salts are excreted through contractile vacuoles.

Excretory organ of flat worms are flame cells, and tubules attached with them. The tubules are connected to the flame cell at one end while at other they collectively open into a common duct which opens outside through excretory pore.

Flame cell has structure of typical cell and contain nucleus and cytoplasm. It is rounded from the outside while its internal surface form a cavity with tuft of vilia . Flame cell appear like flicking flame of candle so it is called flame cell.

Flame cells absorb waste products and remove it through excretory pore.

Excretory organ of earth worm is nepheridia. Nepheridium is twisted tubule which opens at one end into the body cavity and at the other end to outside of the body. There is a pair of septal nepheridia in each segment. Nepheridia collect waste products from the body cavity and remove it from the body.

Excretory system of man consist of following parts.

1. A pair of kidney
2. A pair of ureter
3. Urinary bladder
4. Urethra

There is a pair of kidney in abdominal cavity, both are covered by a membrane called peritomium. Each kidney is bean shaped and dark brown in colour. Nephron is the functional unit of the kidney. There are about 1 million nephrons in each kidney.

Following regions can be seen in L-S of kidney.

It is darker region of the kidney.

It is inner lighter portion of the kidney.

These are conical structure in medulla.

It is funnel shaped part which arises from medulla and become narrow after some length then it is called ureter.

Nephron is a kidney unit receiving tissue fluid and modifying it into urine. Nephron consist of following parts.

1. Bowman's capsule
2. Glomerulus
3. Proximal convoluted tubule
4. Loop of haule
5. Distal comolillated tubule

Tissue filtrate is forced out from glomerulus into the cavity of Bowman's capsule. As fluid pass along the tubules all food and other useful substances are reabsorbed from tissue fluid leaving urine, which is brought to renal pelvic through collecting duct. From renal pelvic urine is carried to urinary bladder through ureter. Urine is stored in urinary bladder for some time and then removed from the body.

Defect can occur in the filtration process or the function of the tubules in changing the filtrate into urine or by accumulation of stones in kidney system.

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