Which useful substances are returned into blood by active absorption?

Explanation

**Step-by-Step Solution:**

1. **Understanding Glomerular Filtration**: The process begins in the Bowman's capsule where blood is filtered through a process called glomerular filtration. This occurs under high pressure, allowing various substances to pass from the blood into the nephron.

2. **Filtrate Formation**: During glomerular filtration, a large volume of fluid is filtered out from the blood, approximately 125 ml per minute, which totals around 180 liters per day. However, only about 1 to 1.5 liters are excreted as urine.

3. **Tubular Reabsorption**: The majority of the filtrate is reabsorbed back into the blood through a process known as tubular reabsorption. This occurs in different segments of the nephron, with the proximal convoluted tubule (PCT) being responsible for reabsorbing about 70-80% of the filtrate, including water and electrolytes.

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