The mechanism of urine formation in nephron involves

Options

A. Ultrafiltration
B. Secretion
C. Diffusion
D. Osmosis

Answer

### Step-by-Step Solution for the Mechanism of Urine Formation in Nephron

1. **Understanding the Excretory System**: The kidneys are the primary excretory organs in the human body. They play a crucial role in filtering blood and removing waste products.

2. **Nephron as the Functional Unit**: The nephron is the structural and functional unit of the kidney. Each kidney contains approximately one million nephrons, which are responsible for urine formation.

3. **Process of Urine Formation**: The mechanism of urine formation involves several key processes:
- **Ultrafiltration**: Blood enters the nephron through the afferent arteriole and is directed into the glomerulus, a network of capillaries. Here, blood is subjected to high pressure, which forces water, ions, and small molecules out of the blood and into the Bowman's capsule. This process is known as ultrafiltration.
- **Reabsorption**: After ultrafiltration, the filtrate (the fluid that has been filtered) moves through the renal tubule, where essential substances like glucose, certain ions, and water are reabsorbed back into the bloodstream.
- **Secretion**: Additional waste products and excess ions are secreted from the blood into the renal tubule to be included in the urine.
- **Excretion**: Finally, the remaining fluid, now called urine, is collected in the renal pelvis and transported to the bladder for excretion.

4. **Conclusion**: The primary mechanism of urine formation in the nephron is ultrafiltration, which is the first step in the urine formation process. Therefore, the correct answer to the question is **ultrafiltration**.

### Final Answer
The mechanism of urine formation in nephron involves **ultrafiltration**.

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