Number of parathyroid glands in human:September 2005

**Core Concept**
The number of parathyroid glands in humans is a fundamental anatomical fact that is essential for understanding parathyroid function and its relationship to calcium metabolism.

**Why the Correct Answer is Right**
There are four parathyroid glands located in the neck, two superior and two inferior, which play a crucial role in regulating blood calcium levels through the secretion of parathyroid hormone (PTH). The parathyroid glands are embedded in the posterior aspect of the thyroid gland and are connected to it by fibrous tissue. The correct number of parathyroid glands is essential for surgical procedures, such as parathyroidectomy, which is sometimes performed to treat hyperparathyroidism.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because there are not three parathyroid glands. The typical anatomy of the human parathyroid glands consists of four glands.
**Option B:** This option is incorrect because there are not two parathyroid glands. The typical anatomy of the human parathyroid glands consists of four glands.
**Option C:** This option is incorrect because there are not five parathyroid glands. The typical anatomy of the human parathyroid glands consists of four glands.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that the number of parathyroid glands can vary slightly from person to person, but four is the typical number. This knowledge is crucial for surgeons performing parathyroid surgery.

**Correct Answer: D. Four.**