The pituitary gland is a pea-sized structure sitting in a bony pocket at the base of your brain. Despite its tiny size (about 0.5 grams), it controls most of your body's other endocrine glands. That's why it's called the "master gland."

The pituitary has two distinct parts that work very differently:

Anterior Pituitary (Adenohypophysis): This is the true hormone factory. It produces six major hormones, all controlled by releasing hormones from the hypothalamus:

• Growth Hormone (GH): Stimulates growth of bones and tissues; affects metabolism
• Thyroid-Stimulating Hormone (TSH): Tells the thyroid to make thyroid hormones
• Adrenocorticotropic Hormone (ACTH): Stimulates the adrenal cortex to make cortisol
• Follicle-Stimulating Hormone (FSH): Controls egg/sperm production
• Luteinizing Hormone (LH): Triggers ovulation and testosterone production
• Prolactin: Stimulates milk production after childbirth

Posterior Pituitary (Neurohypophysis): This isn't really a gland — it's more like a storage warehouse. The hypothalamus makes hormones that travel down nerve fibers to be stored here and released when needed:

• Oxytocin: "The love hormone" — stimulates uterine contractions during labor and milk ejection during breastfeeding
• Antidiuretic Hormone (ADH/Vasopressin): Makes kidneys retain water; controls blood pressure

Your thyroid is a butterfly-shaped gland in your neck, wrapping around your trachea. It produces hormones that control your metabolic rate — how fast every cell in your body burns energy.

Thyroid Hormones:

• T4 (Thyroxine): The main product — has 4 iodine atoms; acts as a prohormone (converted to T3 in tissues)
• T3 (Triiodothyronine): The active form — more potent but present in smaller amounts

How It Works: TSH from the pituitary stimulates the thyroid to make T3 and T4. These hormones enter cells throughout the body and increase metabolic rate — affecting heart rate, body temperature, energy use, and protein synthesis. When thyroid hormone levels get too high, they inhibit TSH release (negative feedback).

Why Iodine Matters: Thyroid hormones are made from iodine. Without enough iodine in your diet, the thyroid can't make enough hormone, so it grows larger trying to compensate — this is called a goiter. That's why iodine is added to table salt.

Calcitonin: The thyroid also makes calcitonin, which lowers blood calcium by promoting calcium deposition in bones. It's less important in humans than in other animals.

Behind the thyroid are four tiny glands, each about the size of a grain of rice — the parathyroid glands. Despite their name and location, they have nothing to do with thyroid function. Their sole job is controlling calcium levels in your blood.

Parathyroid Hormone (PTH): When blood calcium drops, PTH is released and does three things to raise calcium back to normal:

1. Bones: Stimulates bone-dissolving cells (osteoclasts) to release stored calcium into blood
2. Kidneys: Reduces calcium loss in urine and activates vitamin D
3. Intestine: Via activated vitamin D, increases calcium absorption from food

Why Calcium Matters: Calcium isn't just for bones — it's essential for nerve signals, muscle contraction, blood clotting, and heart rhythm. Too little calcium causes muscle cramps and tingling; too much causes confusion, kidney stones, and weak bones.

The Balance: Calcitonin (from thyroid) lowers calcium; PTH raises it. They work as opposing forces to keep calcium in a tight range.

The adrenal glands sit on top of your kidneys like little hats. Each has two parts: an outer cortex and an inner medulla. The cortex has three distinct layers, each producing different steroids:

The pancreas is unique — it's both an exocrine gland (making digestive enzymes) and an endocrine gland. The endocrine part consists of tiny clusters called islets of Langerhans.

Two Opposing Hormones:

Insulin (from beta cells): Released when blood glucose rises after a meal. It acts like a key that unlocks cells to let glucose in. Without insulin, glucose builds up in blood while cells starve. It also promotes fat storage and protein synthesis.

Glucagon (from alpha cells): Released when blood glucose drops (like between meals or during fasting). It tells the liver to break down stored glycogen into glucose and release it into blood. It's like making a withdrawal from your energy savings account.

The Balance: These two hormones work in opposition to keep blood glucose stable. After eating → insulin dominates. During fasting → glucagon dominates. When this balance breaks down, diabetes results.

Diabetes: Type 1 is autoimmune destruction of beta cells (no insulin). Type 2 is insulin resistance (cells don't respond properly). Both lead to high blood glucose with devastating long-term effects on blood vessels, nerves, kidneys, and eyes.