The correct option is Four glands.
Explanation
The parathyroid glands are small endocrine glands located in the neck, specifically on the posterior surface of the thyroid gland. They play a critical role in regulating calcium and phosphate levels in the blood.
Detailed Analysis:
- In humans, there are typically four parathyroid glands.
- They are arranged in two pairs: a pair of superior parathyroid glands and a pair of inferior parathyroid glands.
- These glands secrete Parathyroid Hormone (PTH), also known as parathormone, which increases blood calcium levels by acting on bones, kidneys, and the intestine.
- While anatomical variations can occur (resulting in fewer or supernumerary glands in rare cases), the standard physiological count is four.
Key Takeaway: Humans typically possess four parathyroid glands located on the back of the thyroid gland, which are crucial for maintaining calcium homeostasis.