Uriniferous tubules are mainly concerned with

Options

A. Concentration of urine
B. Passage of urine
C. Reabsorption of useful substances from glomerular filtrate
D. Removal of urea from blood

Answer

**Step-by-Step Solution:**

1. **Understanding the Structure**: The uriniferous tubules, also known as nephrons, are the functional and structural units of the kidney. Each kidney contains approximately one million nephrons.

2. **Function of the Kidney**: The primary role of the kidneys is to filter blood, removing waste products and excess substances, which are then excreted as urine.

3. **Process of Filtration**: The nephron receives impure blood from the renal artery. This blood contains waste products, including urea, which is a nitrogenous waste product formed from protein metabolism.

4. **Reabsorption and Secretion**: As the blood passes through the nephron, useful substances (like glucose, amino acids, and certain ions) are reabsorbed back into the bloodstream, while waste products, including urea, are secreted into the urine.

5. **Conclusion**: The main function of the uriniferous tubules is to remove urea and other waste products from the blood, which is then excreted as urine.

6. **Final Answer**: Therefore, the correct option is D: removal of urea from blood.

---