Haversian canals present in the long bones contain

Options

A. An artery and a vein
B. A nerve and lymphatic vessel
C. Few osteoblast in areolar tissue
D. All of these

Answer

### Step-by-Step Solution:

1. **Understanding Haversian Canals**: Haversian canals are part of the structural organization of long bones. They form a network that is essential for the nourishment and maintenance of bone tissue.

2. **Basic Unit of Bone - Osteon**: The basic structural unit of bone is called an osteon (or Haversian system). Each osteon consists of several components that work together to support bone health.

3. **Components of Osteon**:
- **Lamellae**: These are concentric rings of bone matrix that provide strength and structure to the bone.
- **Lacunae**: Small spaces between the lamellae that house bone cells (osteocytes).
- **Canaliculi**: Tiny channels that connect lacunae to each other and to the Haversian canal, allowing for nutrient exchange.

4. **Central Canal (Haversian Canal)**: The central canal, also known as the Haversian canal, runs longitudinally through the osteon. It contains several important structures:
- **Artery**: Supplies oxygen and nutrients to the bone.
- **Vein**: Drains waste products away from the bone.
- **Nerve**: Provides sensation and regulates bone metabolism.
- **Lymphatic Vessel**: Helps in the immune response and fluid balance.
- **Bone Cells**: Osteoblasts (bone-forming cells) are also present, packed within the connective tissue.

5. **Conclusion**: Therefore, Haversian canals in long bones contain:
- An artery and a vein
- A nerve and a lymphatic vessel
- Few osteoblasts packed in areolar tissue

6. **Final Answer**: Haversian canals present in the long bones contain all of the above-mentioned structures.