Question

The correct sequence of urine formation is-
a. Ultrafiltration $\rightarrow $ reabsorption $\rightarrow $ secretion
b. Reabsorption $\rightarrow $ secretion $\rightarrow $ Ultrafiltration
c. Reabsorption $\rightarrow $ ultrafiltration $\rightarrow $ secretion
d. Ultrafiltration $\rightarrow $ secretion $\rightarrow $ reabsorption

Answer 1

Hint: A nephron is the kidney 's essential structural and functional unit that controls water and soluble substances in the blood by moving through several stages that led to urine formation. The arrangement of the nephron is very important in formation of urine.

Complete answer:
> Option A is correct. There are three major areas of the renal tubule where urine is produced, such as the proximal convoluted tubule (or simply proximal tubule) that conducts the filtrate from Bowman's capsule; the Henle loop, an elongated, hairpin-shaped portion, and the distal convoluted tubule (or distal tubule) that conducts the filtrate to a collecting duct. Then, filtrate moves through the following structures- Bowman's capsule then proximal tubule, then a Henle loop to distal tubule to collect duct. Urine, the urinary system's watery discharge, is formed by a combination of three processes-filtration, accompanied by reabsorption, and then tubular secretion.

> Option B is incorrect. Reabsorption is the second stage in urine formation. Ultrafiltration procedure has resulted in the reabsorption of vital nutrients that can be processed into the procedure to be used by the body, additional secretion substances such as hydrogen ions, creatinine and medications can be extracted from the blood via the peritubular capillary network through the collection duct.

> Option C is incorrect. It is not possible to reabsorb before ultrafiltration because where non-filterable components such as cells and serum albumins escape through the efferent arteriole. These filterable components pile up to form the glomerular filtrate in the glomerulus. Nearly 20 percent of the total heart-pumped blood will reach the kidneys for filtration per minute.

> Option D is incorrect. Ultrafiltration is often accompanied by reabsorption where the fluid moves through the nephron components (the proximal / distal convoluted tubules, the Henle loop, the collection duct) as water and ions are separated as the osmolarity (ion concentration) fluid shifts. Secretion may occur in the collecting duct until the fluid exits the urine produced by the ureter. Finally, in order to avoid excretion by urine, contaminants such as hydrogen ions, creatinine, and medications may be eliminated from the blood.

Hence, The correct answer is option (A).

Note: About 1.5-2 litres of urine per day is formed from the 99% of the filtrate is reabsorbed by tubular resorption (back into the body) into the extracellular fluid. The fluid flow through the filtration membrane is regulated and determined by the ratio of the hydrostatic pressure in the capillaries and oncotic plasma protein pressure.