Question

One of the following is not the constituent of normal urine.
A. Uric acid
B. Urea
C. Creatinine
D. Lipoproteins

Answer 1

Urine is a pale-yellow color liquid waste excreted by the body. The kidney is an organ found in the human body which forms a part of the human excretory system. 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 Nephron is responsible for urine formation in the human body. Urine consists of 95% water and other constituents such as urea, chloride, sodium, potassium, creatinine, and other dissolved metabolites and ions. Normal urine does not contain lipoproteins as their size is large and is not filtered during the process of ultrafiltration. Therefore, lipoproteins are not a constituent of normal urine.

So, option D is the correct option.

Additional information:
A 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
2. Reabsorption
3. Secretion
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. Reabsorption involves absorbing ions, molecules, and water into the peritubular capillary which are necessary for the body to maintain homeostasis. 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.