By Mort Malkin
In the very first column of the B & B Trade, the complexity of the body — in both structure and chemistry — was set forth in plain language. In the most recent column, calcium in all its functions was outlined. The various influences of the dynamic were noted: calcium absorption from the gut, the narrow range of blood calcium, the role of bone as a calcium bank, and the influence of the thyroid and parathyroid glands. Oh yes, and the need for Vitamin D. All work together to hold a precarious balance.
Just as with calcium, the elements sodium & potassium have various functions and often balance each other. Potassium (K) is the principal element within cells, and sodium (Na) is the mainstay of the extracellular fluids. To maintain high sodium levels in the blood for an osmotic effect, the kidneys have the ability to reabsorb sodium from the renal tubules. Because a high blood potassium is dangerous, the kidneys can excrete it efficiently. Then, we have the sodium-potassium pump at the cell membrane to exchange the two elements during muscle contraction and other cell functions. The body has different ways to maintain optimum blood flow to all the different organs of the body, especially the heart itself, the brain, and the kidneys. Blood pressures must be kept in the Goldilocks zone of enough but not too much.
The brain, too, gets involved in the Goldilocks paradigm. We have the chemistry to address emergency situations, but we can’t live on adrenaline for an extended time. We must have space for rest and repair, too. Yes, there are some who seem to live at burn-out intensity and others who couldn’t care less if the sky starts to fall. But most of us live balanced between the two with approximately equal input from a) the catechol amines and b) acetyl choline and the glutamate-GABA axis. Although the neurochemistry is rather more complex, it’s basically an excitatory-inhibitory balance.
To help along the various balances in which we live our daily lives, we have a few endocrine glands available. From the top, the hypothalamus of the brain produces antidiurutic hormone (ADH) to prevent excessive excretion of water. The graybeards among us learned that ADH was a hormone of the posterior pituitary, but now we know it is produced in the brain and just stored in that part of the pituitary.
The anterior pituitary is more of a gland for all seasons and produces secretions to stimulate the thyroid, the adrenals, and the sex glands. It also produces, as well, growth hormone to act on muscles & bones and proteins in general.
Also in the brain is the pineal gland which secretes melatonin, a most interesting hormone. Melatonin is cyclical through the 24 hours of each day and influences sleep-wake cycles, mood, and immunity.
The thyroid gland, in health, keeps our metabolism on an even keel and our bones well mineralized, using two different hormones. Adjacent to the thyroid, the four small parathyroid glands insures adequate blood calcium levels, releasing the mineral from the bones as needed.
The thymus gland, located just behind the sternum (breast bone), promotes the maturation of a special class of white blood cells called t-cells. They are an important part of the immune system, but only a part.
Further south, the pancreas, a digestive gland, contains islands of cells that produce the hormones insulin and glucagon. Together, they maintain blood sugar concentration at just enough.
The adrenal glands are situated atop the kidneys like caps. Each is made up of a gland within a gland, separate embryologically and functionally. The adrenal medulla makes adrenaline to ready you for fight or flight and a little nor-adrenaline to help maintain blood pressure. Simple enough. The adrenal cortex is more complicated. The cortex produces three sets of hormones: cortisone to reduce inflammation and increase blood glucose, aldosterone to regulate sodium retention and potassium excretion, and a modest amount of androgen and estrogen (mostly androgen) in both men and women. The major amounts of sex hormones are produced by the testes and ovaries and thus, are mostly separate in men and women.
A few other tissues and organs produce secretions that are absorbed directly into the blood stream and so, must be classed as hormones. The kidneys produce erythropoietin to stimulate the bone marrow to form red blood cells. The kidneys also produce renin which raises blood pressure by acting on the lungs which, in turn, produce angiotensin converting enzyme (ACE). The heart makes (beside trouble) atrial naturetic factor (ANF) which inhibits both renin and aldosterone release. No one ever said the body’s chemistry would be simple.
Unsatisfied with the hormones of the specific endocrine tissues, every cell of the body can release prostaglandins which create an inflammatory effect that can be beneficial if kept less than exuberant.
To change gears, the first part of the small intestine (duodenum) produces cholecystokinin, which acts on the nearby organs of the digestive tract (pancreas, stomach, and gall bladder). Surprise — it also acts on the satiety center of the brain to suppress appetite. The message is to eat slowly so the cholecystokinin has a chance to work.
This miraculous, resilient body of ours wants to be in balance. It expects some ups and downs but is unhappy with extremes, especially long term extremes. The ancient Greek philosophers were right — everything in moderation (which translates to “perfection”).
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