Question

The diagram given is that of a structure present in a human kidney. Study the same and answer the questions that follow.

Mention the three main steps involved in the formation of the fluid from part 2.

Answer 1

Kidney is an organ found in the human body which forms a part of the human excretory system. Kidneys are bean-shaped organs reddish-brown in color. They perform the function of osmoregulation, the formation of urine, and acid-base balance. The smallest unit which is considered as the functional unit of the kidney is the nephron.

Complete answer: Human kidney is reddish-brown in color and is placed on the right and left retroperitoneal space. Kidneys consist of nephrons which are the smallest structural and functional unit of the kidney. The kidney is made up of two portions called the medulla and the cortex. The nephron is responsible for urine formation in the human body. The nephron is made up of two portions called the renal corpuscle and the renal tubule. The renal corpuscle consists of a bunch of capillaries called glomerulus which is surrounded by a cup-shaped structure called the bowman’s capsule. The renal tubule starts from the capsule and ends in the outer zone of the kidney that is the cortex. The renal tubule is composed of PCT, a loop of Henle, and DCT. Proximal convoluted tubule (PCT), distal convoluted tubule (DCT), and loop of Henle are found in the inner portion of the kidney called the medulla whereas the bowman’s capsule is found in the outer zone of the kidney that is the cortex. The formation of fluid called urine takes place in the renal tubule.

Three main steps of urine formation are-
1. Filtration occurs in the renal corpuscle which involves filtration of large protein molecules while small molecules are filtered to form ultrafiltrate which eventually forms the urine.
2. Reabsorption involves absorbing ions, molecules, and water into the peritubular capillary which are necessary for the body to maintain homeostasis.
3. Secretion is the reverse of reabsorption. It involves the secretion of creatinine, drugs, hydrogen ions, and urea from the blood into the collecting duct.

Urine is the end product of all three processes.

Note: The water and waste that is not reabsorbed by renal tubules form the urine. Sugar component glucose and blood are not found in urine. Dysfunction of the renal tubule cannot absorb glucose and hence it is present in the urine. This condition is called diabetes mellitus.