Excretion is mainly responsible for the removal of waste products of the animal’s own metabolism. In vertebrates this is primarily carried out by the lungs, kidneys and skin.

Urine production per day increases on cold damp day as blood supply to the skin is decreased and to internal organs is increased to preserve the internal heat,so with more blood supply more urine is produced.

 Filtration of wastes from the blood in human body is carried out by kidney. Kidneys are essential to the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and regulation of blood pressure (via maintaining the salt and water balance).

 The amount of renal filterate formed by kidney tubules in a day is about 160 litres.

 In kidney, glomerulus is involved in urine formation by blood filtration..Glomerulus serves as the first stage in the filtering process of the blood carried out by the nephron in its formation of urine.

The plasma resembles in its composition with the filtrate found in the Bowman’s capsule except for the presence of proteins as proteins have high molecular weight. 

Maximum absorption of water in mammals is in kidney. Most of the water in the filtrate is reabsorbed because of renal processes which are independent of ADH action.

 Tubular portion of the nephrons is responsible for the absorption of water.

 The formation of nephric filterate in the glomerulus is a passive process , nonselective process in which hydrostatic pressure forces fluids through the glomerular membrane.

 Among these, spleen is not an excretory organ.It is involved in the production and removal of blood cells in most vertebrates and forming part of the immune system.

 Kidneys are not the only organs of excretion. Their work is supplemented by liver as urea production takes place in liver.

 An opening through which arteries and veins enter or leave the kidney is called hilum.

A man feels unpleasant due to excessive humidity and warmth. The reason is sweat does not evaporate due to humidity. 

 Besides urination, another important activity in which water is substantially lost from body is in the form of sweat.Maximum sweat rates of an adult can be up to 2–4 liters per hour or 10–14 liters per day (10–15 g/min•m²).

pH value of human urine is 6. Humans on average excrete 1.4 L of urine per person per day.

 The urine of a man suffering from diabetes insipidus is tasteless and watery due to deficiency of Anti Diuretic Hormone.

Apart from excretion, kidneys also perform osmoregulation. It is the physiological processes that an organism uses to maintain water balance; that is, to compensate for water loss, avoid excess water gain, and maintain the proper osmotic concentration (osmolarity) of the body fluids. 

Nitrogenous wastes are produced by the utilisation of proteins.They are further broke down to amino acids which undergo deamination to produce ammonia.It is the further converted to urea to be eliminated by kidneys.

Ultrafiltration takes place in glomerulus.The structures of the layers of the glomerulus determine their permeability-selectivity (permselectivity).

Flame cells function like a kidney, removing waste materials in flatworms.