How does filtration occur during the formation of urine in the kidneys?

• A. Blood pressure forces water and small solutes from the glomerulus into Bowman's capsule.
• B. Osmosis draws water from the collecting duct into the renal medulla.
• C. Active transport moves large proteins from the nephron back into the blood.
• D. Hormones trigger the reabsorption of glucose in the distal convoluted tubule.

Answer: (A)

Verified step by step guidance

1. Understand the process of filtration in the kidneys: Filtration occurs in the renal corpuscle, which consists of the glomerulus and Bowman's capsule. Blood pressure plays a key role in driving this process.
2. Identify the role of blood pressure: Blood pressure forces water and small solutes (such as ions, glucose, and amino acids) from the glomerulus into Bowman's capsule. This is the first step in urine formation and is known as glomerular filtration.
3. Clarify the role of osmosis: Osmosis is involved later in the nephron, particularly in the loop of Henle and collecting duct, where water is reabsorbed into the renal medulla. This is not part of the initial filtration process.
4. Explain active transport: Active transport is used for reabsorption of certain substances, such as glucose and ions, back into the blood from the nephron. However, large proteins are not filtered into the nephron due to their size and are retained in the blood during filtration.
5. Discuss hormonal influence: Hormones like antidiuretic hormone (ADH) and aldosterone regulate water and solute reabsorption in later stages of urine formation, but they do not directly affect the initial filtration process in Bowman's capsule.