American Medical Association Family Medical Guide - American Medical Association [598]
• Pituitary gland The pituitary is a pea-sized gland that is suspended from the base of the brain. The pituitary gland is the most important endocrine gland and is often called the master gland because it produces hormones that control other endocrine glands and many essential body processes.
• Hypothalamus The hypothalamus is a small structure at the base of the brain, below the thalamus (a structure deep inside the brain that processes sensory information) and above the pituitary gland. The hypothalamus coordinates production and release of hormones by the pituitary gland, the thyroid gland, the adrenal glands, the ovaries, and the testicles.
• Thyroid gland The thyroid is a butterfly-shaped gland at the base of the neck, directly below the larynx (voice box) and in front of the trachea (windpipe). The thyroid produces the hormones thyroxine and triiodothyronine, which have an important role in metabolism (the chemical processes that take place in the body), and calcitonin, which helps regulate the calcium level in the blood and enhances bone formation.
• Parathyroid glands The parathyroid glands are two pairs of pea-sized glands next to the thyroid gland. The parathyroid glands produce parathyroid hormone, which helps regulate the calcium level in the blood.
• Adrenal glands The adrenal glands are two small, triangular glands on top of the kidneys. The adrenal glands produce corticosteroid hormones, which have an important role in metabolism; epinephrine, which helps the body respond to stress or danger; aldosterone, which helps regulate blood pressure and the sodium and potassium levels in the blood; and testosterone, which stimulates development of male sexual characteristics.
The endocrine system The endocrine system is a group of glands and tissues that secrete hormones directly into the bloodstream to regulate many body processes. The major endocrine glands are the hypothalamus, the pituitary gland, the thyroid gland, the parathyroid glands, the adrenal glands, the pancreas, the ovaries (in women), and the testicles (in men).
• Pancreas The pancreas is a long, tapering gland near the back of the abdominal cavity, under the stomach. The pancreas secretes digestive enzymes, which help break down food, and produces insulin and glucagon, hormones that regulate the body’s use of sugar (glucose), fats, and proteins.
• Ovaries The ovaries are two egg-shaped glands on either side of a female’s uterus and directly below the fallopian tubes. The ovaries produce eggs and the female sex hormones estrogen and progesterone, which regulate the female reproductive system.
• Testicles The testicles are two egg-shaped glands suspended outside of a male’s body inside a pouch of skin and muscle called the scrotum. The testicles produce sperm and the male sex hormone testosterone, which regulates the male reproductive system.
Hormone levels in the blood vary in response to factors such as stress, infections or other diseases or conditions, and changes in the chemical composition of the blood. The amount of each hormone released into the bloodstream depends on the body’s changing needs and is regulated by feedback mechanisms. In some cases, the level of one hormone in the blood affects the level of another hormone. For example, the pituitary gland produces thyrotropin (also called thyroid-stimulating hormone, or TSH), which regulates the production of hormones by the thyroid gland. If the hypothalamus detects variations in the blood level of thyroid hormones, it signals the pituitary gland, which adjusts its production of thyrotropin. The change in thyrotropin levels causes the thyroid to modify its production of thyroid hormones.
Disorders of the Pituitary Gland
The pituitary gland is the most important endocrine gland. It is located at the base of the brain and secretes hormones that regulate the activity of the other endocrine glands and control many body processes. The pituitary is divided into three parts: the anterior (front) lobe, the intermediate (center) lobe, and the posterior