Cell Signaling via Hormones

You probably have a cell phone and you may have a computer; many of you contact the world and your friends with calls, texting, email, facebook, twitter, and old-fashioned talk. Within your body, your cells are connected in a much more intricate way, constantly signaling each other through the bloodstream, nerves, and direct or short distance contact. What goes on between your 10-100 trillion cells is amazing; no cell can live in isolation – survival depends on an elaborate intercellular communication network that coordinates the growth and metabolism of cells in diverse organs. In this column I will outline the function of endocrine glands that produce hormones, chemicals that circulate in the bloodstream and affect cells and organs throughout the body.

Endocrine Glands in the Brain
Hypothalamus: this tiny key gland, located near the center of the brain, regulates the anterior pituitary, increasing or decreasing its hormonal output. It regulates the autonomic nervous system, body temperature, and many other functions.
Anterior pituitary: this gland regulates growth hormone, the thyroid gland, the adrenal gland, the ovaries and testes, and milk synthesis in the breast
Posterior pituitary: this gland regulates uterine contraction, milk letdown, and kidney functions in men and women..
Pineal gland: located behind the eyes, the pineal regulates the sleep-wake cycle via the hormone melatonin. Bright light suppresses melatonin and wakes you up, darkness promotes melatonin secretion and puts you to sleep.


With all this happening in glands of the brain, it is clearly important to keep your brain safe and healthy. My advice – avoid brain injury by always wearing helmets for riding bikes or horses, and be very careful on motorcycles. Don’t hit soccer balls with your head, and don’t allow your children to do so. Football and boxing often injure the brain. Avoid drugs and excess alcohol. Treat high blood pressure, to avoid a stroke. Exercise daily and eat healthfully.

Some other Endocrine Glands
Thyroid Gland: located in the lower neck, the thyroid secretes hormones known as T3 and T4, that stimulate the body to consume oxygen, use energy, and thereby increase the rate of metabolism. They also promote protein synthesis. Calcitonin, produced by specialized cells in the thyroid gland, stimulates bone construction.
Adrenal Glands: Located above the kidneys, these glands put out cortisol, which stimulates glucose production, suppresses inflammation, and inhibits immune responses. They also produce aldosterone, which increases blood volume and blood pressure. The adrenals produce androgens, which give women increased facial hair, and become a source of estrogen for women after menopause. The inside of the adrenal glands produce epinephrine – the fight-or-flight hormone, which also increases blood pressure, heart rate and muscular readiness.
Pancreas: Located below the stomach and adjacent to the liver, this organ secretes insulin, which promotes the uptake of glucose from the bloodstream, enabling cells to use it for energy, and the liver to store it as glycogen. The pancreas also secretes glucagon, which acts in the opposite direction, increasing blood glucose levels when needed for activity.
Ovary: Estrogen, produced from pre-puberty to menopause, stimulates the growth of the uterus and its lining, as well as breast cells. It has many effects throughout the body and brain. Estrogen increases the secretion of cholesterol in bile, which is why women in their reproductive years are more prone to gall stones. Progesterone, produced by ovaries in the second half of the menstrual cycle, and during pregnancy, helps to sustain pregnancy. It also has favorable effects on the thyroid, bones, teeth, gums, joints and tendons.
Testis: Androgens from the testes, mainly testosterone, increase muscle mass and strength, deepen the voice and promote the growth of bodily hair. Testes also secrete some estrogen, which helps with bone strength.

There are other hormone secreting organs in the body as well, including the heart, kidneys, skin, gastrointestinal tract, and fat. Imagine all these hormones circulating in the bloodstream, influencing your trillions of cells. It gives me a feeling of awe - of evolution, of our closeness to other animals, who share these hormones, and of the wisdom of our bodies. Stay as healthy as you can, and your body should reward and amaze you with its intricate workings.
Sadja Greenwood, MD, MPH
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