Question

How is the structure of the kidney related to the function of excretion? Describe the formation of urine formation in humans.

Answer 1

Hint: Excretion is a biological process of eliminating toxins and other waste products from the body. In plants and animals, as part of metabolism, a lot of waste products are produced. In plants the waste products are excreted through transpiration. Animals excrete the waste products in different forms such as urine, sweat, faeces and tears. The main type of excretion is urine which is done by the kidney.

Complete answer:
Kidneys are bean shaped organs located at the upper and back side of the abdomen. The lower ribs protect the kidneys from damage. The kidney removes toxic waste products and excess water from the body in the form of urine. Urine formed in each kidney passes through the ureter and finally excreted through the urethra.
 Each kidney is made up of three regions- an outer cortex, medulla and renal pelvis in the region called the hilum of the kidney. The hilum is the concave part of the kidney where blood vessels and nerves enter and exit. It is also the exit point for the ureters. The renal cortex contains millions of nephrons which is the functional unit of the kidney. The medulla contains renal columns through which the blood vessels pass. On the outside of the kidney, the renal pelvis leads to the ureter. The ureters carrying the urine exit the kidney and empty into the urinary bladder.
Formation of urine happens in nephrons through three stages- Glomerular filtration, Reabsorption and Secretion. The initial step in the generation of urine is glomerular filtration. The impure blood entering the glomerular capillaries is filtered into Bowman's Capsule from where it enters the remaining part of nephron. The proteins and blood cells are retained in this process.
The essential nutrients, smaller proteins and amino acids in the filtrate obtained from the first step are reabsorbed by the adjacent capillaries in the renal tubules. This is done by active and passive transport.
The waste ions and hydrogen ions pass further down in the renal tubule. This phenomenon is called secretion. The secreted ions along with the remaining filtrate becomes urine. The urine then flows down to the bladder.

Note:
Urine is made of \[95\% \] water and \[5\% \] waste products. The nitrogenous wastes excreted in urine are urea, creatinine, ammonia and uric acid. Urine also secretes ions such sodium, potassium, hydrogen, and calcium. The other function of the kidney is regulation of osmotic pressure of blood through filtration and purification by a process known as osmoregulation.