Excretion is the process where all the unwanted wastes are removed from the body. In humans, it occurs in different body parts and carried through various internal organs.
A human body is a mysterious machine, where different life processes such as respiration, digestion, circulation, etc. occur simultaneously. Producing many waste products in our body in various forms that include water, carbon dioxide, and nitrogenous products like urea, ammonia, and uric acid, etc.
Moving on, the chemicals and other toxic compounds from medications and hormonal products are also produced which adds to these waste products. Simple diffusion is not sufficient to eliminate these wastes from our bodies. We need more complex and specific processes in order to eliminate waste products.
Blood contains both useful and harmful substances. And filtering the harmful substance is the function of the kidney. The kidneys separate useful substances by reabsorption and toxic substances by producing urine.
The kidney has a structural filtration unit called the nephron where the blood is filtered. Each kidney contains a million nephrons.
Kidney capillaries filter the blood and the essential substances like glucose, amino acids, salts, and the required amount of water get reabsorbed and the blood goes into circulation.
Nitrogenous waste and excess water are converted to urine in humans. Then urine thus produced is passed to the urinary bladder through the ureters. The urinary bladder is under the control of the Central Nervous System (CNS). The brain then signals the urinary bladder to contract and through the urinary opening called the urethra, we excrete the urine.