The filtrate formed by the nephrons in the kidney is not urine. The filtrate is first refined and concentrated by the processes of __________, which form the urine that leaves the body.

• A. filtration and secretion
• B. reabsorption and excretion
• C. filtration and reabsorption
• D. secretion and excretion
• E. reabsorption and secretion

Answer: (E)

Verified step by step guidance

1. Understand the function of the nephron: The nephron is the functional unit of the kidney, responsible for filtering blood and forming urine. It consists of several parts, including the glomerulus, proximal tubule, loop of Henle, distal tubule, and collecting duct.
2. Identify the initial process: Filtration occurs in the glomerulus, where blood plasma is filtered into the Bowman's capsule, forming the initial filtrate. This filtrate contains water, ions, glucose, amino acids, and waste products.
3. Recognize the role of reabsorption: As the filtrate moves through the nephron, essential substances like water, glucose, and ions are reabsorbed back into the bloodstream, primarily in the proximal tubule and loop of Henle. This process is crucial for conserving necessary nutrients and maintaining homeostasis.
4. Understand secretion: Secretion involves the active transport of additional waste products and excess ions from the blood into the nephron tubule. This process occurs mainly in the distal tubule and collecting duct, helping to fine-tune the composition of the urine.
5. Conclude with urine formation: After reabsorption and secretion, the remaining fluid in the nephron is concentrated and becomes urine. This urine is then transported to the bladder for excretion from the body.