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How the Body Works: Overview of the Nervous and Endocrine Systems
Posted By Dr. Ben Kim
A thorough discussion of how your body works best begins with an overview of your nervous and endocrine systems, as these two organ systems act as co-directors of all of the activities that occur in your body.
To put it simply, your nervous and endocrine systems continuously monitor the well-being of each of the billions of cells in your body, and they continuously take action through messenger systems to keep all of your cells as healthy as possible.
A Key Difference in How Your Nervous and Endocrine Systems Work
Though your nervous and endocrine systems share the director's seat of your body, they fulfill their roles in completely different ways.
Your nervous system senses and controls every part of your body through its many nerves. Sensory receptors located throughout your body constantly send information through nerves to your brain; your brain digests this information; your brain then decides on appropriate action, and executes the action by sending additional information out to the target cells through other nerves.
For example, if you accidentally touch a hot pan, sensory receptors register pain almost instantaneously, this information travels through nerves to reach your brain, your brain understands that your hand is in danger of being injured in its current position, and your brain sends information down other nerves that tells your muscles to jerk your hand away from the pan.
As you almost certainly know from real life experience, transmission of information throughout your nervous system can occur within milliseconds. But it can also occur at a slower pace - good examples of slower and deliberate activity within your nervous system are all of the activities that must take place within your sensory receptors, nerves, brain, and muscles when you park your car in your driveway, type an e-mail, wash vegetables, take a shower, or hit a tennis ball.
Your endocrine system consists of a number of glands that produce and secrete hormones that make their way into your bloodstream. Once in your bloodstream, your hormones travel through your body and trigger specific actions whenever they encounter cells that display compatible receptors.
Because your endocrine system monitors and controls the well-being of your cells via your circulatory system, it generally works at a slower pace than your nervous system, sometimes taking hours to produce a desired effect as a hormone reaches its target destination and carries out its job.
For example, if your blood volume decreases for any reason (like dehydration), your endocrine system will sense this and call your kidneys, liver, lungs, adrenal glands, and blood vessels to action, with the end result being an increase in blood volume.
So your nervous system uses sensory receptors, nerves, and your brain to monitor and control the well-being of all of your cells, while your endocrine system uses your blood circulatory system to accomplish the same thing. Your nervous system operates at lightning speed, while your endocrine system generally works more slowly to create changes in your biochemistry.
Strands of One Big Web
Your nervous and endocrine systems are highly interdependent in behavior, much like all the strands of a spider web are intimately connected in stability and behavior.
The interdependent relationship between your nervous and endocrine systems begins in a tiny area of tissue in your brain called your hypothalamus.
Your hypothalamus is only about as large as a grape, and can be viewed as the micro-processing chip that controls almost all of your body's external and internal activities. Your hypothalamus receives information from all of the major areas of your brain, your major organs, and your eyes, and it registers sensations like pain, temperature, hunger, thirst, lust, stress, fear, and anger.
Once your hypothalamus registers incoming information and decides what your body needs to best survive and be healthy, it uses your autonomic nervous system to affect the behavior of all of your major organs. Examples of such effects are increased heart and lung rates, increased blood flow to your skeletal muscles or digestive organs, changes in how much light enters your eyes and how well your eyes can focus on distant objects, production of sweat or shivers, and arousal of sexual organs.
Your hypothalamus also produces a number of different hormones that directly impact your pituitary gland, which is about the size of a green pea, and is located just below your hypothalamus.
Amazingly, your pea-size pituitary gland is the chief gland of your endocrine system; it has two distinct portions that produce and secrete hormones that govern the activities and well-being of all of your organ systems. Actually, because your hypothalamus governs the activities of your pituitary gland, it may be more accurate to call your hypothalamus the master gland of your endocrine system. But technically, your hypothalamus is considered to be specialized neuroendocrine tissue because of its unique ability to affect both your nervous and endocrine systems.
Ultimately, what's important to know is this:
Together, your hypothalamus and pituitary gland have significant, ongoing influence over every other component of your endocrine system.
"Other components" includes your thyroid gland, parathyroid glands, pineal gland, adrenal glands, and all organs and tissues that secrete hormones - these organs and tissues include your kidneys, liver, stomach, small intestine, pancreas, heart, skin, thymus, and fat tissue. The ovaries, testes, and placenta also secrete hormones, and are considered to be important components of the endocrine system.
The Big Picture
In order get a sense of how your nervous and endocrine systems work together to keep you well, consider the example of hiking in a national park somewhere in Alaska late at night and coming upon a hungry grizzly bear.
As soon as your eyes detect the bear and your brain understands the bear's desire to make you her next meal, your hypothalamus uses your autonomic nervous system to immediately prepare your eyes to see better, your brain to think more quickly, and your heart, lungs, and large skeletal muscles to allow you to run faster or fight with more strength.
Interestingly, your autonomic nervous system accomplishes some of the above by stimulating the release of epinephrine and norepinephrine from the inner portion of your adrenal glands - this is yet another way in which your nervous and endocrine systems are intertwined in their roles as governors of all of your physiological activities.
Through your endocrine system, your hypothalamus stimulates the release of glucocorticoids (mainly cortisol) from the outer portion of your adrenal glands. Glucocorticoids increase the production of glucose, which ensures adequate availability of fuel to fight or run away from the bear.
Here are the main points to take away from this article:
All of your nervous and endocrine system's responses to physical danger also occur when you experience any type of emotional stress - to a lesser degree than in the example of encountering a grizzly, but ultimately, all of your cells are exposed to the same stress-related neurotransmitters and hormones whenever you are feeling emotionally stressed.
So the result of ineffectively managing emotional stress over a long period of time is premature aging and disease due to chronically being in fight-flight mode.
Also, in most cases, it doesn't make any sense to try to address just one particular problem within your nervous or endocrine systems with a specific remedy, like medication or a nutritional supplement. For example, multiple sclerosis, Alzheimer's, and Parkinson's disease are all systemic neurological challenges that are affected by every food that you eat, every hour of fatigue that you experience, and every emotion that courses through and touches every cell in your mind and body.
The same goes for almost all endocrine-related health challenges. For example, it's not possible to isolate the health status of your thyroid gland, to identify one, two, or five factors that are contributing to thyroid dysfunction. Every facet of your existence affects the health of your thyroid gland, and any diligent and well-thought out attempt to address real thyroid dysfunction must bring into consideration all main causes of disease and dysfunction.
Put another way, the health of every component of your nervous and endocrine systems depend on your overall health status and how healthy all of your organ systems are; the health of each of your body parts cannot be compartmentalized.
Of course, there can be focal causes of specific conditions, like the case of poor upper body posture creating shoulder impingement syndrome, or the case of an iodine deficiency resulting in enlargement of your thyroid gland (called a goiter).
So it does pay to have unusual symptoms of discomfort that you can't account for evaluated by a physician. But regardless of whether one specific cause is identified or not, you'll always stand a good chance of experiencing improvement by ensuring that you are earning good overall health through healthy living.
Next in this series on how your body works, we'll look at some concrete steps that you can take to help support the health of your nervous and endocrine systems.
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