Question

The main function of the kidney is
(a)Passive absorption
(b)Ultrafiltration
(c)Selective reabsorption
(d)All of the above

Answer 1

The kidneys are one of the most important organs of the human body which looks like a pair of beans, located below the ribs on both sides of the spine. The average length of a kidney is 10 to 16 cm they are made up of millions of basic functioning units called nephrons that take part in excretion.

Complete answer:
Ultrafiltration, passive absorption, and selective reabsorption in the kidney are carried out by the basic functional unit of the kidney known as the nephrons. Ultrafiltration happens in the middle of the Bowman's capsule and glomerulus of the nephron. All these 3 processes take place in the kidneys through the process of urine formation precisely in the nephron.

Additional Information: Passive absorption: Passive transport takes place in the kidney when the concentration of nitrogenous waste in the Bowman's capsule becomes minimal and the wastes in the glomerulus diffuse via the glomerular filtration membrane.
Ultrafiltration: The process of diffusion of blood along with the plasma through the barrier between glomerulus and Bowman's capsule. Due to the big size, red blood cells and plasma protein won’t pass through the ultrafiltration membrane.
Selective reabsorption: Reabsorption involves active and passive transport, where the water is absorbed by osmosis, Ions by active transport, and substances like glucose and amino acids by diffusion or facilitated diffusion. All these processes take place in the renal tubule of the kidney.
The kidney also synthesizes active vitamin D which helps in absorbing calcium from the food we eat. The kidney also helps in recycling useful components for red blood cell synthesis.
So, the correct answer is ‘All of the above’.

Note: -Pyelonephritis is a disorder when bacteria infect the kidney and causes back pain and fever. The mode of infection is when a healthy person comes in contact with an infected person’s urine or other physical contacts.
-Glomerulonephritis is an autoimmune disease where immune cells attack the kidney, causing inflammation and injury resulting in kidney failure and passage of blood and protein in the urine.
-Kidney stones also known as the nephrolithiasis is a condition where minerals in the urine form crystals which accumulate and block the urine flow.