What are the main processes of urine formation ?

Explanation

To answer the question about the main processes of urine formation, we can break it down into three key steps:

### Step 1: Glomerular Filtration
The first process in urine formation is **glomerular filtration**. This process occurs in the glomerulus, a network of capillaries located at the beginning of the nephron. During glomerular filtration, blood is filtered under pressure, allowing water, ions, and small molecules to pass through the capillary walls into the Bowman's capsule, forming a filtrate. Larger molecules, such as proteins and blood cells, are typically retained in the bloodstream.

### Step 2: Selective Reabsorption
The second process is **selective reabsorption**. After the filtrate is formed, it passes through the renal tubule, where essential substances such as glucose, amino acids, and certain ions are reabsorbed back into the bloodstream. This process can occur actively (requiring energy) or passively (without energy) depending on the substances being reabsorbed. The goal of selective reabsorption is to retain valuable nutrients and maintain homeostasis.

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