Excretion is a biological process and plays a vital role by eliminating toxic and other waste products from the body. In animals including humans, as the part of metabolism lots of waste products are produced. Animals excrete them in different forms such as by urine, sweat, feces, and tears. Among these the usual and the main form of excretion is urine.
Waste is excreted from the human body mainly in the form of urine. Our kidneys play a major role in the process of excretion. Constituents of normal human urine include 95 percent water and 5 percent solid wastes. It is produced in the nephron which is the structural and functional unit of the kidney. Urine formation in our body is mainly carried out in three phases namely glomerular filtration, reabsorption and secretion.
Glomerular filtration as the name suggests it occurs in the glomerulus where blood is filtered. This process occurs across the three layers- epithelium of Bowman’s capsule, endothelium of glomerular blood vessels, and a membrane between these two layers. Blood is filtered in such a way that all the constituents of the plasma except proteins reach the Bowman’s capsule. Therefore, this process is known as ultrafiltration. Around 99 percent of the filtrate obtained is reabsorbed by the renal tubules. This is known as reabsorption. This is achieved by active and passive transport.
The next step in urine formation is the tubular secretion. Here, tubular cells secrete substances like hydrogen ion, potassium ion, etc into the filtrate. By this process, the ionic, acid-base and the balance of other body fluids are maintained.
Osmoregulation is the process of regulating body fluids and its compositions. It maintains osmotic pressure of the blood and helps in the homeostasis. This is why it is recommended to consume more water about 2-3 liters which help in proper functioning of our kidneys. For example, we consume lots of water during summers but still, we urinate fewer times in summers than winters and the concentration of the urine is also more. The reason is that we lose lots of water from our body in summers through sweating. Thus, to maintain the fluid balance in the body our kidneys reabsorb more water.