The Endocrine System: Hypothalamus, Pituitary, & Pineal Glands
Today, we begin our exploration of the endocrine system. In many ways, the endocrine system can be viewed as a partner, or complement, to the nervous system. Whereas the nervous system uses nerve impulses that last milliseconds to control short term events in the body, the endocrine system uses hormones that can sometimes take minutes, hours, or even days to take effect and control events. And sometimes those effects can last a lifetime.
Once you understand how important the endocrine system is in controlling every aspect of your life, from your moods to your sexuality to your energy levels to your ability to grow and be strong, you realize how important it is to keep it optimized. And yes, there are things you can do to keep it optimized.
The endocrine system is comprised of a group of ductless glands that secrete hormones directly into the spaces surrounding their cells. From there, the bloodstream picks them up and circulates them throughout the body -- ultimately reaching the organ or cells designed to respond to a particular hormone. It is the ductless nature of the glands that defines them as part of the endocrine system. As for hormones, they are the body's chemical messengers that tell the body what to do…and when. Hormones produced by the endocrine system are necessary for normal growth and development, reproduction, and maintaining bodily functions (homeostasis). In humans, the major endocrine glands are the hypothalamus, pituitary, pineal, thyroid, parathyroids, adrenals, the islets of Langerhans in the pancreas, the ovaries, and the testes.
Secretion of hormones in the endocrine system is controlled either by regulators in a particular gland that detect high or low levels of a biochemical and inhibit or stimulate secretion or by a complex mechanism involving the brain, the hypothalamus, and the pituitary.
It should be noted again that the nervous system and the endocrine system are complementary -- both in terms of form and function. Both systems share a primary function of coordinating the activities of the body's many systems. For example, the nervous system tells muscles when to contract and relax, whereas adrenalin tells the body how to respond to stress or threats. The primary difference is that nerve impulses execute their effect in milliseconds…and the effects tend to be short-lived. The endocrine system, on the other hand, takes substantially longer for hormones to wend their way from the gland that produces them, through the bloodstream, and ultimately to the organ or cells where they take effect. In addition, the actions of hormones are much longer lasting than the milliseconds of nerve impulses. Another way of putting this is to say that the nervous system directs the body's short term responses, whereas the endocrine system directs the body's longer term responses.
One other point of note is that both systems are mutually interconnected. For example, when the nervous system needs to control things longer term, it acts through the endocrine system by stimulating the release or inhibition of hormones themselves from the endocrine organs. On the other hand, adrenalin, released by the adrenal glands, acts upon the brain to stimulate the fight or flight response.
Before we continue, we need to lock down some important definitions.
- As mentioned above, endocrine glands (endo = "within") are glands that secrete directly into the spaces around the cells and whose products are picked up and circulated by the bloodstream.
- In contrast to the endocrine glands are the exocrine glands (exo = "out", krinein = "to secrete"). Unlike endocrine glands, exocrine glands secrete into ducts, which in turn, carry the secretions out of the glands and into the lumens (the inner cavities of a tubular organ such as blood vessels and the intestinal tract) or other body cavities or even out of the body. By an overwhelming majority, most glands in the body are exocrine glands, and most exocrine glands secrete their "products" outside of the body. These include sweat, oil, and mammary glands. (We will not be discussing the exocrine glands in this particular series of newsletters.)
- The endocrine system includes some organs that are wholly endocrine in function such as the pituitary gland, thyroid gland, parathyroid gland, adrenal glands, and pineal gland. (It is these glands in particular, along with the pancreas, that will be the focus of this series of newsletters.)
- Endocrine organs that have other functions as well as endocrine functions include the pancreas, liver, ovaries, stomach, hypothalamus of the brain, small intestine, kidneys, testes, and placenta. These are compound glands/organs. (Most of these will be covered when we explore their other functions.)
Endocrine gland locations
- The hypothalamus, pituitary gland, and pineal gland are located in the brain.
- The thyroid gland is located in the neck, with the four parathyroid glands situated behind it.
- The thymus is in the chest (will be covered when we discuss the immune system).
- The adrenal (AKA the supraneal) glands lie on top of the kidneys.
- The pancreas, stomach, ovaries, and testes are located in and beneath the abdominal cavity and have multiple functions -- some of which include endocrine functions.
As we mentioned earlier, the endocrine system releases chemical messengers called hormones (hormone = "urge on"), which act on other organs in different parts of the body. Effectively, hormones are the body's chemical messenger system -- they tell the body what to do and when. Some hormones promote or inhibit nerve impulses, while others (epinephrine and norepinephrine, for example) may act as neurotransmitters themselves in certain parts of the body. Then again, these hormones act as hormones (rather than as neurotransmitters) in other places. (This will be much easier to understand when we explore the adrenal glands in a subsequent newsletter.)
Also, as we mentioned earlier, hormones may take seconds, minutes, or hours to work their effects, and their duration of action may be short- or long-lived. How long?
Consider that once estrogen tells a fetus to become a girl, the effect lasts an entire lifetime -- unless a doctor intervenes at some point. In general, though, hormones regulate growth, development, reproduction, metabolism, mood, and tissue function.
General properties of hormones
Although they may reach all the cells of the body via the bloodstream, each of the 50+ hormones in the human body affects only a tiny handful of very specific cells. This selectivity is key to the functioning of the endocrine system. How is it accomplished?
- Target cells contain highly specific receptors, which are surface glycoproteins (proteins which include a carbohydrate and a simple protein).
- The geometry of the glycoprotein molecules allows only for very specific hormones to attach to the receptor in the target cell surface. Think of it as a lock and key mechanism. Exceptions include:
- Chemical mimics such as xenoestrogens (petroleum-based hormone lookalikes) and synthetic growth hormones in meat, etc. -- which can be potent in amounts as small as a billionth of a gram. These are never good.
- Plant mimics such as phytoestrogens consumed in the diet or in supplements, which can fill receptor sites, making them unavailable to the stronger natural hormones (or chemical mimics for that matter) in the human body. This effect can often be used to advantage to tone down overly strong hormonal responses in the human body.
Each target cell has up to 100,000 receptors for a given hormone. When there is an excess of that hormone, the number of receptors decreases, reducing sensitivity. This reduction of sensitivity is known as "down regulation." Also, as just explained, chemical and phyto mimics can fill receptor sites on a cell making those sites unavailable to the actual hormones -- thus down regulating the cell. Or in the case of some chemical mimics, up regulating them. (Note: cells contain receptors for multiple hormones, not to mention neuropeptides produced by the brain, and other kinds of receptors too. Thus a single cell may actually have millions of receptor sites on its surface.)
If an abnormally low number of hormone molecules is circulating, the number of receptor sites on individual cells will increase to raise the level of sensitivity and thus compensate. This is known as "up regulation."
Locally acting hormones:
These hormones do not enter the general circulation. There are two types -- one of which, in particular, is of special concern to us.
- Paracrine hormones (para = "near") act on cells next to the secreting cells without entering the bloodstream -- just passing through the interstitial fluid between cells.
- Autocrine hormones (auto = "self") act on the cell that secreted them. These can play a critical role in terms of our health. Cancer cells use autocrine signaling to trigger growth. This means that cancer cells are autonomous. They don't take orders from other cells in the body. They tell themselves what to do. That's one of their features that makes them so dangerous.
Now that we have a basic understanding of what the endocrine system is, what it does, and how it works, let's start making our way down through the body and begin by taking a look at the three endocrine glands in the human brain: the hypothalamus, the pituitary, and the pineal glands.
The hypothalamus is located below the thalamus and posterior to the optic chiasm. In humans, the hypothalamus is roughly the size of an almond. But within that small size, it contains a number of small nuclei with a variety of functions. One of the most important functions of the hypothalamus is to link the nervous system to the endocrine system via the pituitary gland. The hypothalamus actually controls the pituitary gland; and it integrates many messages from parts of the brain based on feedback from all over the body and tells the pituitary what to do.
Communication between the hypothalamus and the pituitary is effected through a portal blood capillary system, which connects the two glands over a very short distance. This provides a direct venous to venous connection. The advantage of this type of direct connection is that a portal flow allows blood-borne molecules from the hypothalamus to act on the pituitary before they are diluted with the blood in larger vessels, thus it takes very, very few molecules to direct the pituitary.
The hypothalamus synthesizes and secretes neurohormones, often called hypothalamic-releasing hormones, and these in turn stimulate or inhibit the secretion of pituitary hormones. Among other things, the hypothalamus, through its action on the pituitary, controls body temperature, hunger, thirst, fatigue, childbirth, emotions, growth, milk production, salt and water balance, sleep, weight, and circadian cycles. It is responsive to light (the length of the day for regulating both daily circadian and seasonal rhythms). It is also responsive to olfactory stimuli (including pheromones), steroids, neurally transmitted information (from the heart, stomach, and reproductive system, stress, changes in body temperature caused by infection, and blood-borne stimuli (including leptin and ghrelin (appetite regulating hormones), angiotensin, insulin, pituitary hormones, cytokines, and glucose, etc.)
For the most part, the hypothalamus functions pretty much problem free for the vast majority of people. However, any of the following can cause it to malfunction: anorexia, bulimia, malnutrition, too much iron, bleeding, head traumas, infections, inflammation, genetic disorders, tumors, radiation, and surgery.
At one time, the pituitary gland, also called the hypophysis, was once thought to be the "master gland" that controlled all the other endocrine glands. But, as mentioned above, we have since learned that the hypothalamus actually controls the pituitary gland; and it integrates many messages from parts of the brain based on feedback from all over the body and tells the pituitary what to do. In any case, the two glands are tightly integrated. Together, they regulate all processes having to do with primitive reactions, such as stress, rage, flight, body temperature, thirst, hunger, sexual activity, and survival in general. And between them, they secrete 16 hormones.
The pituitary is about 1 cm in diameter, and it lies in the sella turcica ("Turkish saddle") at the base of the brain, directly behind the optic chiasm. It is divided into two embryologically and functionally different parts: the anterior pituitary and the posterior pituitary. Embryologically refers to what tissue the gland developed "out of" starting as an embryo. The anterior pituitary evolved anatomically up from the floor of the mouth. The posterior pituitary, on the other hand, evolved downward from the base of the brain. In fact, the two parts of the pituitary don't even talk to each other.
The anterior pituitary gland is also called the adenohypophysis, and it makes up 75% of the pituitary gland -- the remaining 25% belonging to the posterior pituitary. Seven releasing hormones (including growth-hormone-releasing hormone and growth-hormone-inhibiting hormone) are secreted by the hypothalamus and are responsible for the release or inhibition of the anterior pituitary hormones. They are generally controlled by negative feedback mechanisms.
Once triggered by the hypothalamus, hormones released by the anterior pituitary flow into the general circulation for action in far parts of the body. Like the hypothalamus, anterior pituitary hormones are also controlled by negative feedback from the brain and the target organ. That is, when the target organ responds to the activating hormone from the pituitary, it will release its own hormone back into the blood, which will travel back to the brain through the circulatory system, which in turn triggers the hypothalamus to turn off production of the stimulating hormone in the anterior pituitary. For example, the pituitary stimulates the thyroid to release thyroid hormones, which travel throughout the bloodstream stimulating metabolism in select parts of the body as required. Through the negative feedback loop, the brain learns that the metabolism has been activated enough (in other words, that enough thyroid hormones have been released) and tells the hypothalamus/pituitary to stop stimulating the thyroid. This completes the negative feedback loop.
Principal anterior pituitary hormones
- Thyroid-stimulating hormone (TSH) stimulates the thyroid gland to release thyroid hormones, which tend to upregulate metabolism.
- Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) together stimulate the release of estrogen and progesterone, which cause the maturation of ova in the female and sperm cells in the male, as well as the release of testosterone.
- Prolactin (PL) stimulates the production of milk by the breasts. As a side note, prolactin can cross the placenta-blood barrier, causing "witch's milk," or milk production from a baby's nipples.
- Adrenocorticotropic hormone (ACTH) stimulates the release of adrenal cortical hormones by the adrenal glands.
- Melanocyte-stimulating hormone (MSH) causes increased skin pigmentation.
- Human growth hormone (hGH, or somatotropin) stimulates body growth and regulates metabolic processes. High hGH increases the growth of the skeleton during childhood, and it maintains muscle and skeletal size in the adult. Since hGH is probably the best known hormone produced by the pituitary -- and in the news constantly because of its illegal use among amateur and professional athletes looking for a competitive edge -- let's take a look at this particular hormone in a little more detail.
Human Growth Hormone
The rejuvenating powers of growth hormone (GH) are no secret to the wealthy and professional athletes: for the last 30-40 years, GH has been available from doctors, requires two injections a day, and costs up to $1,800 a month. Over the last few years, however, several alternatives for the rest of us have become available. And while I could never recommend the injections (for a variety of reasons), I can endorse the alternatives. Many fantastic claims are made for the effects of growth hormone, even claims of "almost" eternal youth. Would that it were so! Although the effects are more subtle for most people, they are nevertheless wide ranging:
- Fat loss (14 percent on average after six months, without dieting)
- Elimination of cellulite
- Higher energy levels and enhanced sexual performance
- Regrowth of heart, liver, spleen, kidneys, and other organs that shrink with
- Greater heart output and lowered blood pressure
- Improved cholesterol profile, with higher HDL ("good") cholesterol and
- lower LDL ("bad") cholesterol
- Superior immune function
- Increased exercise and athletic performance
- Better kidney function
- Stronger bones
- Faster wound healing and recovery from injury
- Younger, tighter skin
- Hair regrowth
The most important function of GH, however, is telling the liver to produce insulin-like growth factor 1 (IGF-1), the main key to anti-aging. Specifically, the benefits of GH can be measured in terms of how much it increases the body's production of IGF-1 (above a 20 percent increase starts to be significant
in terms of effectiveness).
There is some concern that, because it increases IGF-1 levels in the body, GH may increase the risk of prostate cancer. A simple reality check, however, calls these observations into question. First, both GH and IGF-1 levels decline as we age, yet the incidence of prostate cancer increases as these levels decline -- the exact opposite of the expressed concern. In addition, in numerous studies involving thousands of patients receiving growth hormone over many years, there were no observed increases in prostate cancer. In fact, based on real-life observation, there is evidence that growth hormone supplementation may reduce the risk of prostate cancer.
Supplementing with Growth Hormone
Most supplement formulas will increase IGF-1 levels by a minimum of 20 percent, with some even approaching 100 percent. But keep in mind that just one 30-minute aerobic session can easily increase IGF-1 levels by 100 percent, and a solid session of weight training can increase levels by an incredible 400--800 percent. Injections, on the other hand, which work directly on the liver (almost like a massive "pulse"), can increase IGF-1 production by only 20--40 percent. A downside to injections, in addition to cost, is that they can give too much GH to the body, shock the body, and can stop the pituitary from producing its own GH. This may explain why injectable GH produces more immediate results, yet ultimately plateaus in terms of effectiveness.
Incidentally, you can no longer actually buy true hGH or human growth hormone. Technically, only growth hormone actually taken from human beings can be called "human" growth hormone. Thirty years ago, the sole source of growth hormone was human cadavers, but that was abandoned when it turned out that growth hormone taken from people had a major downside (in addition to cost) -- it occasionally caused the human equivalent of mad cow disease.
Fortunately, at around the same time, recombinant DNA technology came into its own and scientists learned how to alter the DNA of a single-cell yeast plant, and more recently from bacteria, so that they could produce large amounts of growth hormone (molecularly identical to real hGH), safely and inexpensively. Because this growth hormone is identical to hGH, people often use the terms growth hormone and human growth hormone interchangeably, but it should be referred to as a "plant-based growth hormone."
Given this good, inexpensive source of growth hormone, another problem remained: the growth hormone molecule is so large (containing 191 amino acids) that it cannot be absorbed orally. That meant it could only be administered by injection, which required a doctor and was very expensive. Because of the cost, growth hormone injections became known as the secret youth formula of movie stars, athletes, and the very rich.
For most people, then, the best alternative to GH injections is the use of amino acid-based precursor formulas (also called a GH secretagogues). Typically, these formulas contain ingredients such as glutamine, tyrosine, GABA, arginine, and lysine. Although not as powerful as growth hormone injections, these formulas can be quite effective, provided your pituitary is functioning well, and they carry none of the downside of injections.
Things that sometimes go wrong with the anterior pituitary gland
Not surprisingly, since the pituitary is so involved with regulating growth, some of the key problems associated with a malfunctioning pituitary are related to growth. These include:
- Pituitary dwarfism: Low levels of hGH during the growth years causes bone-growth-plate closure before normal size is achieved. Also, many organs are smaller than normal, and the person has a childlike stature. Fortunately, injections of synthetic hGH produced by recombinant DNA technology in bacteria can prevent this if diagnosed in time.
- Pituitary giantism: Hyposecretion of hGH during childhood causes long bones and tall stature but otherwise normal proportions.
- Acromegaly: Usually caused by functioning pituitary tumors in the already normal adult, it causes thickening of bones of the face, hands, and feet (bones can get longer after the closure of growth centers) and thickening of the tongue, eyelids, and nose. Andre the Giant, the well known wrestler and actor, was one of the world's best known examples and was, in fact, often billed as The Eighth Wonder of the World. Another famous (possible example) might have been the biblical Goliath, who was slain by David with a slingshot. In fact, there is a very interesting theory, with real scientific basis, that proposes that Goliath's acromegaly might actually account for how he was slain by David. According to the theory, a pituitary tumor, because of the pituitary's placement right behind the optic chiasm, can sometimes place pressure on peripheral vision nerve fibers, resulting in tunnel vision. If Goliath had that condition, which sometimes does occur with acromegaly, he would have been blind to David, if David approached from the side, and a rock hurled from the side would hit the temple at the thinnest part of the skull, thus stunning the giant. Once stunned and on the ground, David would then be able to safely approach his now helpless victim and cut off his head. And thus the legend was born -- or so the theory goes.
Posterior pituitary gland
As I mentioned earlier, the posterior pituitary gland (AKA the neurohypophysis) is anatomically derived from a down growth of the brain and is not technically a gland since it does not synthesize hormones, but rather, stores and secretes two hormones actually made in the brain. These two hormones, oxytocin and vasopressin, are transported from the brain in small packets for storage in the posterior pituitary -- to be released as needed.
- Oxytocin (oxytocia = "rapid child birth"; AKA Pitocin) enhances the strength of uterine contractions and stimulates the ejection of milk after delivery. It may also foster maternal instincts and sexual pleasure during and after intercourse. Now synthesized and readily available, it is often given to women to help them have stronger contractions and expel the fetus in a more timely manner…when necessary.
- Vasopressin (Antidiuretic hormone, ADH) decreases urine production by increasing re-absorption by the kidneys, a useful trick when suffering from dehydration. The effect, though, is to raise blood volume and, therefore, to raise blood pressure. Alcohol inhibits ADH secretion, thus producing profuse urination after a drinking binge, which leads to severe dehydration, and the severe dehydration leads to the headache and thirst associated with a hangover.
The pineal gland is about the size of a grain of rice, is shaped like a tiny pine cone (hence its name), and is located in the center of the brain in a tiny cave, behind and above the pituitary gland. For years, mystics considered it to be the seat of the mystical third eye, whereas the medical community considered it vestigial and, thus, pretty much non-functioning. Since then, the mystics have not necessarily been refuted, but the medical community has been. The pineal gland is now known to be the major source of melatonin production in the body. It is full size in children, a size it maintains throughout adulthood -- although its weight can drop significantly starting with puberty. And it is not unusual for the gland to literally calcify in many adults. The gland most likely plays a significant role in sexual maturation, circadian rhythm and inducing sleep, and in seasonal affective disorder and depression. In animals, it plays a key role in hibernation.
The trigger for production and release of melatonin is total darkness -- any light in the room will inhibit this process. Today, however, living in a world with nightlights in the bedroom or streetlights sneaking through the window, we actually have an epidemic of people with insufficient melatonin production, even at a very young age. The problem doesn't just come from light falling on our eyes while we sleep, but from light falling on any part of the body. Even if you wear an eye-mask, if any light is falling on your arms or chest or feet, that's enough to slow melatonin production. Without artificial light, we would normally be in total darkness 8--12 hours a night, producing melatonin during all of those hours. Living in a city or suburban area may cut the hours of total darkness to six or less, and in many cases, zero. Melatonin levels also decline significantly as we age. Since its discovery in 1958, melatonin has been studied extensively and shown to be widely beneficial to the body. The benefits of supplementation to compensate for abnormally low production in the body include:
- Better Sleep -- Lowered levels of nighttime melatonin reduce the quality of sleep, resulting in the need for more sleep. If your pineal gland does not produce adequate melatonin early enough in the evening, both the quality and quantity of your sleep may suffer. Lack of melatonin may make it difficult for you to fall asleep or may cause you to wake up too soon. Too much melatonin and you will feel exhausted or "drugged" throughout the day. By taking melatonin instead of other sleep aids, rapid eye movement (REM) sleep (dreaming) is not suppressed nor does it induce "hangover" effects when used as directed.
- Enhanced Immune Function -- Many people report that supplementation with melatonin has significantly reduced their incidence of colds and infections. The exact way in which melatonin affects the immune system is not known. However, since much of the activity of the immune system takes place at night, some researchers have proposed that melatonin interacts with the immune system during sleep, helping to buffer the adverse effects of stress. It has been proposed by some that the increased incidence of cancer we see today is partially due to the extended time we are exposed to artificial lighting. This is reflected in the fact that melatonin levels in breast cancer and prostate cancer patients are half of normal.
- Powerful Antioxidant Capabilities -- Melatonin is one of the most powerful antioxidants produced in the body. In addition, since it is both water and fat-soluble, melatonin can reach almost every cell in the body. However, since it cannot be stored in the body, it must be replenished daily.
- Mood Elevator -- Nighttime melatonin levels are low in people with major depressive and panic disorders. Individuals with mood swings or who are melancholic also have lower melatonin levels. Both seasonal affective disorder (SAD) and cyclic depressions are related to the peaks and valleys of melatonin levels.
While the physiological function of the pineal gland remained unknown until recently, mystical traditions and esoteric schools, have long considered the pineal gland to be the connecting link between the physical and spiritual worlds…and the seat of extrasensory perception. I am not here to argue the spiritual qualities of the pineal gland, nor talk about its extrasensory capabilities, excepting one: its sensitivity to light.
As medically theorized, the pineal gland responds to the ebbs and flow of light entering our eyes during the day. In the evening, the pineal gland reacts to the diminishing levels of daylight and starts to produce melatonin, which is then released into the blood and flows through the body making us drowsy. Its secretion peaks in the middle of the night during our heaviest hours of sleep. In the morning, bright light shining through the eyelids reaches the pineal gland which reacts by switching off the production of melatonin, thus removing the desire to sleep. And we wake!
But this description is incomplete in one significant aspect. As it turns out, the pineal gland can be diminished not only by light shining on the eyelids, but by light shining anywhere on the body. Literally, light striking any part of your skin can reduce production of melatonin from the pineal gland. It seems the pineal can "see without eyes." How's that for ESP? Even more interesting is the fact that in some lower vertebrates the pineal gland actually has a well-developed eye-like structure and is considered by some scientists to be the evolutionary forerunner of the modern eye. In other vertebrates, though not organized as an eye, it functions as a light receptor -- effectively a third eye.
In any case, the key when it comes to the pineal gland and melatonin is that it's important to sleep in a darkened room, with no light coming through the curtains or night lights turned on in the room. And wearing eyeshades won't help as the pineal can sense any light shining on your skin. Failure to sleep in a darkened room will inhibit melatonin production, which presents a series of health problems, not the least of which is an inability to sleep deeply. But beyond that, if continued for too long, it will literally shut down the pineal and cause it to atrophy. At that point, your only choice will be to use melatonin supplements.
We'll pause here and pick up our discussion of the endocrine system in the next newsletter with an exploration of the thyroid and parathyroid glands. One of the interesting things you'll notice is that as we move down through the body, you'll find that you have progressively more options for altering the behavior of your endocrine glands. That said, you can nevertheless consider using the following supplements to assist the hyopthalamus, the pituitary, and the pineal glands in the optimal performance of their basic functions.
- hGH secretagogue -- available throughout the internet
- Timed release melatonin
- Hypothalamus PMG from Standard Process -- available throughout the internet
- Pituitrophin PMG from Standard Process -- available throughout the internet
Enjoy the following links to complete the entire newsletter series on the Endocrine System: