As I’ve written before, the human body is nothing short of amazing. Good health depends on the strength and disease-free condition of all our tissues with freely-flowing fluids that circulate life-sustaining nutrients and oxygen.
Key to understanding human health is the endocrine system, a network of glands that manufacture and secrete hormones that control many bodily functions, including:
- Sensory perception
- Sexual development
Glands produce hormones that enter the bloodstream for transportation to the various tissues throughout the body. Hormones send chemical signals from one cell to another until they reach targeted tissues to communicate what they are supposed to do. When a gland stops producing the right amount of hormones – too much or too little – diseases develop that can be quite serious.
The main glands that secrete hormones are:
Pituitary – Called the “master control gland,” the pituitary gland controls other glands and manufactures the hormones that trigger growth.
Hypothalamus – regulates body temperature, hunger, moods, the release of hormones from other glands; controls thirst, sleep, and the sex drive.
Parathyroid – controls the amount of calcium in the body.
Pancreas – produces insulin that helps control blood sugar levels.
Thyroid – produces hormones associated with calorie burning and heart rate.
Adrenals – these twin glands (left and right) produce the hormones that control sex drive and cortisol, the stress hormone.
Pineal – produces melatonin which is linked to sleep.
Ovaries – secrete estrogen, testosterone and progesterone, the female sex hormones in women.
Testes – produce the male sex hormone, testosterone, and produce sperm in men.
The pituitary is small, about the size of a pea, and is located in a bony hollow (sella turcica) directly behind the bridge of the nose. The sella turcica shields the pituitary while limiting its ability to expand. A thin stalk connects the pituitary to the brain. It is called the master gland because it controls several other glands, among them the thyroid, adrenals, ovaries, and testicles.
The hypothalamus, sitting just above the pituitary, controls its glandular neighbor by transmitting chemical directives. Signals from the hypothalamus communications center travel in the form of hormones course through the bloodstream and nerves down the pituitary stalk, controlling the production and release of more hormones from the pituitary gland that, in turn, signal other glands and organs in the body.
The hypothalamus is in charge of temperature regulation, food intake, thirst and water intake, sleep and wake patterns, emotional behavior, and memory.
The hypothalamus or the pituitary can gauge how much stimulation a target gland needs by detecting the levels of hormones produced by target glands controlled by the pituitary.
The pituitary has two distinct divisions:
- Front (anterior) lobe – accounts for 80% of the pituitary gland’s weight
- Back (posterior) lobe
The anterior pituitary lobe makes and secretes six main hormones:
- Growth hormone (GH) – regulates growth and physical development and impacts body shape by stimulating muscle formation and reducing fat tissue
- Thyroid-stimulating hormone (TSH) – stimulates the thyroid gland to produce thyroid hormones
- Adrenocorticotropic hormone (ACTH or corticotropin) – stimulates the adrenal glands to produce cortisol and other hormones
- Follicle-stimulating hormone (FSH) and luteinizing hormone (LH or the gonadotropins) – stimulate the male testes to produce sperm, the female ovaries to produce eggs, and the sex organs to produce the sex hormones testosterone and estrogen
- Prolactin – stimulates the mammary glands of the breasts to produce milk
In addition, the anterior lobe also produces several other hormones: one causes the skin to darken (beta-melanocyte-stimulating hormone or BMSH) while others (enkephalins and endorphins) inhibit pain sensations. Still others (endorphins) assist in controlling the immune system.
The posterior pituitary lobe also secretes hormones that are usually produced in the hypothalamus and stored in the posterior lobe for release.
Hormones stored in the posterior lobe include:
- Vasopressin (the antidiuretic hormone) – helps the body conserve water and prevents dehydration
- Oxytocin – stimulates the release of breast milk and contractions of the uterus during labor
As mentioned before, the two pituitary lobes attach to the hypothalamus by a stalk that contains blood vessels and nerve cell projections (nerve fibers, or axons). The hypothalamus regulates the anterior lobe by releasing hormones through the connecting blood vessels and uses nerve impulses to control the posterior lobe.
After the hypothalamus transmits electrical messages to the pituitary gland, it responds by releasing the following hormones:
Antidiuretic hormone (ADH) – stimulates the kidneys to reabsorb fluid and produce less urine
Oxytocin – initiates labor, uterine contractions and milk ejection in mothers
The pituitary doesn’t secrete hormones consistently. Between active bursts released every 1-3 hours are periods of idleness. Some hormones, including adrenocorticotropic hormone (ACTH), growth hormone, and prolactin, follow a circadian rhythm with levels rising and falling predictably throughout a 24-hour cycle, usually peaking just before waking up and reaching their lowest levels just before going to sleep.
The pituitary gland is at risk of developing an adenoma or benign (harmless) tumor. These swollen tissues are not brain tumors but, rather, a non-cancerous growth. Some people live with pituitary tumors for years without experiencing any symptoms.
Most pituitary tumors are not inherited. About half of all cases involve a non-functioning tumor incapable of hormone production. Even so, these benign growths can cause headaches and visual problems. Pressure on the pituitary gland may cause it to stop producing the required amount of one or more of the pituitary hormones.