What is the first step of urine formation?Multiple choice question.Tubular reabsorptionTubular secretionGlomerular filtration

The first step of urine formation is Glomerular filtration.

Explanation:

Urine formation in the kidneys involves three main processes: glomerular filtration, tubular reabsorption, and tubular secretion.

1. Glomerular Filtration: This is the initial step where blood is filtered in the glomeruli, the tiny laundry-like structures in the nephron. The pressure in the glomeruli forces water, ions, and small molecules from the blood into the Bowman's capsule, forming a filtrate that will eventually be processed into urine.

2. Tubular Reabsorption: In this step, essential substances and water are reabsorbed back into the bloodstream from the filtrate as it passes through the renal tubules, reducing the volume of urine produced.

3. Tubular Secretion: This final step involves the secretion of additional waste products and excess ions from the blood into the tubular fluid, which will ultimately be excreted.

Thus, out of the options provided, glomerular filtration is indeed the correct answer as the first step in urine formation.