Thyroid Gland Overview - A Major Player in Regulating Your Metabolism
But a lot of things remain unclear about melatonin's connection to and impact on However, melatonin has a direct impact on thyroid. The thyroid, located in your neck, is a large endocrine gland that regulates your metabolism. It produces two main hormones to fulfill this role. Reprod Biol. ;6 Suppl The interaction of the thyroid gland, pineal gland and immune system in chicken. Dzerzhynsky ME(1), Gorelikova OI.
Hormones of the Thyroid The two main hormones the thyroid produces and releases are T3 tri-iodothyronine and T4 thyroxine. To a lesser extent, the thyroid also produces calcitonin, which helps control blood calcium levels.
Endocrine System Organs, Glands | Hormones and Metabolism
Diseases and Disorders of the Thyroid There are many diseases and disorders associated with the thyroid. They can develop at any age and can result from a variety of causes—injury, disease, or dietary deficiency, for instance. But in most cases, they can be traced to the following problems: Too much or too little thyroid hormone hyperthyroidism and hypothyroidism, respectively.
Abnormal thyroid growth Nodules or lumps within the thyroid Thyroid cancer Below are some of the most common thyroid disorders. To learn more, read our article about common thyroid problems. A goiter is a bulge in the neck.
A toxic goiter is associated with hyperthyroidism, and a non-toxic goiter, also known as a simple or endemic goiter, is caused by iodine deficiency. Hyperthyroidism is caused by too much thyroid hormone. People with hyperthyroidism are often sensitive to heat, hyperactive, and eat excessively. Goiter is sometimes a side effect of hyperthyroidism.
This is due to an over-stimulated thyroid and inflamed tissues, respectively. Hypothyroidism is a common condition characterized by too little thyroid hormone.
In infants, the condition is known as cretinism. Cretinism has very serious side effects, including abnormal bone formation and mental retardation. If you have hypothyroidism as an adult, you may experience sensitivity to cold, little appetite, and an overall sluggishness. Hypothyroidism often goes unnoticed, sometimes for years, before being diagnosed.
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. 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. 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. Chemical mimics such as xenoestrogens petroleum-based hormone lookalikes and synthetic growth hormones in meat, etc.
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 toreceptors 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. Or in the case of some chemical mimics, up regulating them.
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. These hormones do not enter the general circulation. There are two types -- one of which, in particular, is of special concern to us. 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: Hypothalamus 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 pheromonessteroids, 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 hormonesangiotensin, 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: Pituitary gland 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.
Thyroid Gland Overview
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: 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. 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.