Question

The cells of the proximal tubule develop microvilli and have a brushy border. The number of microvilli per square micron in a human being is
A. 150
B. 500
C. 3000
D. 3500

Answer 1

The Proximal Convoluted Tubule is a part of nephron. In the nephron, from Bowman’s capsule, PCT originated which is a thin tube. The nephron is found in the kidneys which act as an excretory organ. Nephron acts as a structural and functional unit of the kidney.

Complete answer: Kidney excretes excess and waste material like water, n-compounds and minerals in form of urine. It acts as a filtrate and has five parts; Malpighian body, PCT, Henley’s loop, DCT and Collecting duct. PCT is present in the cortical region of the kidney. The wall of PCT is made up of cuboidal epithelium. Microvilli are found in the cells of PCT. Microvilli form the brush border in PCT and due to which, the brush border surface area of PCT increases. It provides a maximum area for absorption of nutrients. 150 microvilli are found per square micron of PCT. PCT reabsorbs about 99% from the fluid filtered by the glomerulus. It includes sodium ions, glucose and water. The Malpighian body of nephron has Bowman’s capsule and glomerulus. The capsule is made by a double membrane of the epithelium. The glomerulus is a complex of capillaries of efferent and afferent arterioles. This filters the blood by causing pressure and separates large substances like amino acid, urea, uric acid and glucose. This is called glomerular filtrate. The glomerular filtrate is reabsorbed in PCT. Henley’s loop is a U-shaped tubule found in the medullary part of the kidney. It has ascending and descending arms. It reabsorbs potassium ions, chloride ions and water from the urine. This tubule determines the concentration of the urine. DCT is attached with the ascending arm of the loop of Henley. It is made up of cuboidal epithelium and has lesser microvilli than PCT. This tubule has a secretory function. The collecting duct is the terminal part of the nephron. The wall of the collecting duct is made up of cuboidal epithelium. Many collecting ducts combine to form a papillary duct.
Hence, the correct answer is option A.

Note: There are two types of nephrons:
i. Cortical nephrons have a small-sized Henley’s loop and it is found at the surface of the medulla. The malpighian body is found in the superficial region of the cortex.
ii. Juxtamedullary nephrons have Henley’s loop at the medullary region.