The correct answer is option C: Pituitary.

The pituitary gland is often referred to as the "master gland" because it plays a crucial role in regulating and controlling the functions of other endocrine glands throughout the body. Located at the base of the brain, it is a small pea-sized gland that is divided into two main parts: the anterior pituitary and the posterior pituitary.

1. Anterior Pituitary:
The anterior pituitary produces and releases several hormones that control various bodily functions. Some of the key hormones secreted by the anterior pituitary include:

- Growth Hormone (GH): Stimulates growth and development of bones and tissues.
- Adrenocorticotropic Hormone (ACTH): Stimulates the adrenal glands to produce cortisol, which helps regulate metabolism and response to stress.
- Thyroid-Stimulating Hormone (TSH): Controls the production and release of hormones from the thyroid gland, which plays a role in metabolism and energy levels.
- Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH): Regulate the production of sex hormones and control the reproductive functions in both males and females.

2. Posterior Pituitary:
The posterior pituitary does not produce hormones itself but stores and releases two important hormones that are synthesized in the hypothalamus, which is connected to the pituitary gland. These hormones are:

- Antidiuretic Hormone (ADH) or Vasopressin: Regulates water balance by controlling the amount of water reabsorbed by the kidneys.
- Oxytocin: Stimulates uterine contractions during childbirth and promotes milk ejection during breastfeeding.

The pituitary gland acts as a central control center that receives signals from the hypothalamus and releases appropriate hormones in response. It regulates various bodily functions including growth, metabolism, reproduction, and water balance.

In summary, the pituitary gland is known as the "master gland" because it controls the functions of other endocrine glands by secreting hormones that regulate their activity. Its role in maintaining overall hormonal balance makes it a vital part of the endocrine system.