The endocrine system is a collection of specialized cells, tissues, and glands that produce and secrete circulating chemical messenger molecules called hormones. Most hormones are secreted by endocrine glands - ductless organs that secrete their products into interstitial fluid, lymph, and blood. Hormones are bloodborne units of information, just as nerve impulses are units of information carried in nerves. Some hormones participate in feedback control loops regulating various bodily functions. We need these hormones to maintain allostasis. Other hormones produce specific effects, such as contractions of the uterus during childbirth, growth during childhood and the exciting development of sexual characteristics at puberty. We need specific hormones to be able to carry out each of these very specific functions. The endocrine system differs from the nervous system in that hormones of the endocrine system reach nearly every living cell (through circulation in the blood), each hormone acts only on certain cells (with target cells that have the appropriate receptor) and endocrine control tends to be slower than nervous system control. Due to these differences it’s understandable why the reflexes that prompt us to avoid a hot surface are controlled by the nervous system and that endocrine communication is highly effective for longer-term controls such as regulating blood pressure or the production of red blood cells. Hormones are generally classified into two basic categories based on their structure and mechanism of action: Steroid hormones are structurally related to cholesterol. They are all synthesized from cholesterol and all are lipid soluble. Nonsteroid hormones consist of, or at least partly derived from the amino acid building blocks of protein. In general, they are water soluble. The differences in lipid solubility explain most of the important differences in how the two categories of hormones work. Steroid hormones usually enter the cell, bind to an intracellular receptor and activate genes that produce new proteins. Nonsteroid hormones generally bind to receptors on the cell’s surface. Their binding either opens or closes cell membrane ion channels or activates enzymes within the cell. Negative and Positive Feedback Loops Feedback loops can enhance or buffer changes that occur in a system. Positive feedback loops enhance or amplify changes, this tends to move a system away from its equilibrium state and make it more unstable. Negative feedbacks tend to dampen or buffer changes; this tends to hold a system to some equilibrium state making it more stable. As messenger molecules, some hormones participate in internal allostatic control mechanisms and control vital physiological processes. It is essential to regulate carefully the rate at which each hormone is secreted so that its concentration in blood is just right to carry out its intended function. In a negative feedback loop involving a hormone, the endocrine gland is the control center and the hormone represents the pathway between the control center and the hormone’s target cells, tissues or organs. A negative feedback loop involving an endocrine gland and a hormone is a stable, self-adjusting mechanism for maintaining homeostasis of the controlled variable, because any change in the controlled variable sets in motion a response that reverses that change. Not all negative feedback loops are as simple as the one I described. In some cases the real control center is the brain, which activates an endocrine gland via nerves. The effect is the same. Additionally, a few hormones are secreted in response to specific environmental cues or for particular purposes such as puberty. This type of secretion is not part of a negative feedback loop. The pituitary gland- is a small endocrine gland located beneath the hypothalamus and connected to it by a stalk of tissue. The hypothalamus also produces hormones and monitors the pituitary gland. The pituitary gland is sometimes called “the master gland” because it secretes eight different hormones and regulates many of the other endocrine glands. The hypothalamus creates neuron cell bodies that make either antidiuretic hormones (ADH) or oxytocin - both nonsteroid hormones - and then sends the hormones down the axon for storage endings in the pituitary. ADH acts on the kidneys to regulate water balance and oxytocin causes uterine contractions and milk ejection in pregnant and lactating women. In both sexes, oxytocin contributes to feelings of sexual satisfaction. The anterior pituitary produces six key hormones:
Thyroid - The thyroid and parathyroid glands are anatomically linked. The thyroid gland is situated just below the larynx at the front of the trachea and the two lobes of the thyroid gland wrap part of the way around the trachea. The four small parathyroid glands are embedded in the back of the thyroid. The thyroid and parathyroid glands are both functionally linked- they help regulate calcium balance. In addition, the thyroid has a separate and important role in controlling metabolism. The thyroid gland produces two very similar hormones called thyroxine (T4) and triiodothyronine (T3). They’re identical except that thyroxine contains four molecules of iodine whereas T3 contains only three. The thyroid gland secretes mainly thyroxine but eventually most of it is converted to the more active T3 form of the hormone in the blood. These thyroid hormones regulate metabolism. Calcitonin, the other main hormone of the thyroid gland is produced by a separate group of thyroid cells. Calcitonin decreases the rate of bone resorption by inhibiting the activity of osteoclasts. It also stimulates the uptake of calcium by bone. The parathyroid glands produce only one hormone, parathyroid hormone which removes calcium and phosphate from bone, increases absorption of calcium by the digestive tract and causes the kidneys to retain calcium and excrete phosphate. Adrenal Glands- are two small endocrine organs located just above the kidneys. Each gland has an outer layer, the adrenal cortex, and an inner core, the adrenal medulla. The adrenal cortex produces small amounts of the sex hormones estrogen and testosterone and two classes of steroid hormones called glucocorticoids and mineralocorticoids. The adrenal cortex produces a group of glucocorticoids with nearly identical structures. Cortisol accounts for approximately 95% of these glucocorticoids. The other hormones produced by the adrenal cortex are the mineralocorticoids, the most abundant of which is aldosterone. The adrenal medulla produces nonsteroid hormones epinephrine (adrenaline) and norepinephrine (noradrenaline). These hormones play roles in metabolism and controlling blood pressure and heart activity. Pineal - The pineal gland is a pea-sized gland located deep within the brain, in the roof of the third ventricle. Its name derives from the fact that it is shaped like a small pine cone (hehe). More than 200 million years ago our pineal gland was photosensitive area or “third eye” located near the skin’s surface. Although it is now shielded from the sun by our thick skull, it still retains its photosensitivity because it receives input directly from the eyes via the optic nerve and nerve pathways in the brain. The pineal gland secretes the hormone melatonin in a cyclic manner coupled to the daily cycle of light and dark. Melatonin is sometimes called the “hormone of darkness” because its rate of secretion rises nearly 10 fold at night and then falls again during the daylight. Its secretion appears to be regulated by the absence or presence of visual cues. During the day, nerve impulses from the retina inhibit its release. AND we are just beginning to understand what melatonin does… Notes on the role of the pancreatic endocrine cells in the regulation of blood glucose: Within the pancreas, clusters of cells called the pancreatic islets produce and secret three hormones - glucagon, insulin, and somatostatin. Glucagon raises blood glucose levels, insulin lowers blood glucose levels, and somatostatin appears to inhibit the secretion of glucagon and insulin. Overall thoughts on the Endocrine System and its connection to Herbal Medicine: I’m fascinated by the thyroid. This organ plays an important role in determining our body temperature; the way we digest, metabolize and assimilate food; our body’s ability to make good-quality connective tissue, hair, skin and nails; and our mood. Thyroid fluctuations can affect many things including menopausal symptoms, fertility, and overall vitality. Your body can tilt towards hypothyroidism (underactive/low thyroid) or hyperthyroidism (overactive/high thyroid). Hypothyroidism is the most common thyroid imbalance in which things slow to nearly a halt resulting in colder body temperatures, weight gain, depression, sluggishness, poor digestion, brain fog, hair loss, dull skin, and horizontal ridges in the fingernails, among other things. It can look like anemia. Hyperthyroidism is characterized by an overdrive - you might feel like a hot furnace, become rail-thin, toss and turn at night, and feel extremely agitated and anxious. It wears on the whole body and can even make your eyes bug out in advance cases. Even though more and more people - particularly women - have thyroid imbalances, it’s hard to find good information about how to take care of the thyroid holistically. It’s important to get a full thyroid panel completed if you suspect issues. This will give you a better idea of what’s going on as well as rule out issues like anemia and lyme disease. Knowing exactly where you stand can help drive appropriate therapies. Herbal and lifestyle approaches to thyroid issues excel at addressing imbalances and are less apt to have negative side effects like some of the thyroid-focused supplements and pharmaceuticals. Also many underlying causes of thyroid problems relate to stress, grief, autoimmune disease, diet, a sedentary lifestyle, toxins and and emotional connections - consider the possible aggravating factors. Herbs that assist hypothyroid issues are iodine, kelp, selenium, ashwagandha, bacopa and guggul, and tyrosine. Avoid eating excessive amounts if you tend toward hyperthyroid disease. Lemon balm, motherwort and bugleweed are frequently used for hyperthyroid disease. Preliminary research suggests that these herbs inhibit parathyroid functions through a variety of mechanisms including binding to TSH receptors, inhibiting thyroid hormone production and preventing thyroid hormone conversion from T4 to T3. It’s interesting to me that lemon balm and motherwort are commonly used for conditions similar to hyperthyroid disease: insomnia, anxiety, agitation and stress-related cardiac overdrive including panic attacks and palpitations. Vitamin B, magnesium and bitters tend to be beneficial for healthy thyroid function regardless of whether your thyroid needs a boost or needs to be taken down a notch.
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AuthorThe adventures, studies, and musings of a student at the Vermont Center for Integrative Herbalism.
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