Blood Lymph And Nerve Supply
The thyroid is supplied with arterial blood from the superior thyroid artery, a branch of the external carotid artery, and the inferior thyroid artery, a branch of the thyrocervical trunk, and sometimes by an anatomical variant the thyroid ima artery, which has a variable origin. The superior thyroid artery splits into anterior and posterior branches supplying the thyroid, and the inferior thyroid artery splits into superior and inferior branches. The superior and inferior thyroid arteries join behind the outer part of the thyroid lobes. The venous blood is drained via superior and middle thyroid veins, which drain to the internal jugular vein, and via the inferior thyroid veins. The inferior thyroid veins originate in a network of veins and drain into the left and right brachiocephalic veins. Both arteries and veins form a plexus between the two layers of the capsule of the thyroid gland.
What Conditions Are Related To Abnormal Thyroid Hormone Levels
Several conditions can result from or cause abnormal thyroid hormone levels. Thyroid disease is very common, with an estimated 20 million people in the United States having some type of thyroid condition. A person assigned female at birth is about five to eight times more likely to have a thyroid condition than a person assigned male at birth.
Thyroid conditions include:
- Thyroid cancer.
Issues with your pituitary gland or hypothalamus can also cause abnormal thyroid hormone levels since they help control thyroid hormone levels.
Which Hormones Does My Thyroid Gland Produce
The thyroid gland produces thyroxine , which is a relatively inactive prohormone. The highly active hormone is triiodothyronine . Collectively, thyroxine and triiodothyronine are referred to as the thyroid hormones. The thyroid gland produces just 20% of the high active T3, but it produces 80% of the prohormone T4. Once secreted by the thyroid, specific enzymes in other tissues like the liver or kidneys may transform T4 in to the active hormone T3.
In addition, there are other hormone-producing cells within the thyroid gland called C-cells. These cells produce calcitonin. Calcitonin plays a role in regulating calcium and phosphate levels in the blood, which is important for your bone health and maintenance.
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What Are The Risk Factors For Developing A Thyroid Condition
Thyroid conditions are common and can affect anyone at any age. However, some factors put you at a higher risk of developing a thyroid condition, including:
- Having a family history of thyroid disease.
- Having an autoimmune condition, such as Type 1 diabetes, rheumatoid arthritis or lupus.
- Taking a medication thats high in iodine.
Being older than 60, especially if youre a woman or a person who was assigned female at birth .
How Are Thyroid Hormone Levels Controlled
The production and release of thyroid hormone thyroxine and triiodothyronine is controlled by a feedback loop system that involves the following:
- Multiple hormones.
Your hypothalamus is the part of your brain that controls functions like blood pressure, heart rate, body temperature and digestion.
Your pituitary gland is a small, pea-sized gland located at the base of your brain below your hypothalamus. It makes and releases eight hormones.
Your pituitary gland is connected to your hypothalamus through a stalk of blood vessels and nerves. This is called the pituitary stalk. Through the stalk, your hypothalamus communicates with your pituitary gland and tells it to release certain hormones.
To start the feedback loop, your hypothalamus releases thyroid-releasing hormone which, in turn, stimulates your pituitary gland to produce and release thyroid-stimulating hormone . TSH then triggers your thyroid to produce T4 and T3. Of the total amount of hormones that TSH triggers your thyroid to release, about 80% is T4 and 20% is T3. Your thyroid also needs adequate amounts of iodine, a substance you get from the food you eat, to create T4 and T3.
This hormone chain reaction is regulated by a feedback loop so that when the levels of T3 and T4 increase, they prevent the release of TRH . When T3 and T4 levels drop, the feedback loop starts again. This system allows your body to maintain a constant level of thyroid hormones in your body.
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The Thyroid And Its Hormones
The thyroid gland, which consists of two lobes, is located in front of the windpipe , just below the voice box . The gland produces two structurally related hormones, thyroxine and triiodothyronine , that are iodinated derivatives of the amino acid tyrosine. Both hormones are collectively referred to as thyroid hormone. T4 constitutes approximately 90 percent of the hormone produced in the thyroid gland. However, T3 is a much more active hormone, and most of the T4 produced by the thyroid is converted into T3 in the liver and kidneys.
Thyroid hormone in general serves to increase the metabolism of almost all body tissues. For example, thyroid hormone stimulates the production of certain proteins involved in heat generation in the body, a function that is essential for maintaining body temperature in cold climates. Moreover, thyroid hormone promotes several other metabolic processes involving carbohydrates, proteins, and lipids that help generate the energy required for the bodys functions. In addition to those metabolic effects, thyroid hormone plays an essential role in the development of the central nervous system during late fetal and early postnatal developmental stages. Furthermore, thyroid hormone exerts an effect similar to that of GH on normal bone growth and maturation. Finally, thyroid hormone is required for the normal development of teeth, skin, and hair follicles as well as for the functioning of the nervous, cardiovascular, and gastrointestinal systems.
Preventing Thyroid Gland Disease
It is difficult to prevent thyroid gland disease, as it is not possible to modify some of the known risk factors, such as genetics. However, people can take certain measures to reduce the likelihood.
The main way to reduce the risk of developing hypothyroidism is to consume enough iodine. Because the body does not naturally produce iodine, people must eat food containing iodine or take dietary supplements. However, consuming too much iodine can aversely affect the T3 and T4 hormones.
People should also avoid smoking if they have concerns about thyroid disease, as cigarette smoke can affect iodine uptake.
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What Is Thyroid Hormone
Thyroid hormone is the hormone thats mainly responsible for controlling the speed of your bodys metabolism. In infants, thyroid hormone is critical for brain development. Your thyroid, a small, butterfly-shaped gland located at the front of your neck under your skin, makes and releases thyroid hormone. Its a part of your endocrine system.
Hormones are chemicals that coordinate different functions in your body by carrying messages through your blood to your organs, muscles and other tissues. These signals tell your body what to do and when to do it.
Metabolism is the complex process of how your body transforms the food you consume into energy. All of the cells in your body need energy to function.
Thyroid hormone actually represents the combination of the two main hormones that your thyroid gland releases: thyroxine and triiodothyronine . Theyre often collectively referred to as thyroid hormone because T4 is largely inactive, meaning it doesnt impact your cells, whereas T3 is active. Once your thyroid releases T4, certain organs in your body transform it into T3 so that it can impact your cells and your metabolism.
Your thyroid also releases a hormone called calcitonin to help regulate calcium levels in your blood by decreasing it. Calcitonin isnt grouped into the thyroid hormone name, and it doesnt impact your bodys metabolism like T3 and T4 do.
How The Parathyroid Glands Work
The parathyroid glands can usually be found on the thyroid glands posterior surface. Most people have four of them, although its not unheard of to have more .
Image from Human Anatomy Atlas.
Chief cells, the epithelial cells of the parathyroids, produce PTH , which plays an important role in regulating the bodys calcium levels.
When levels of calcium in the blood are low, the parathyroids secrete PTH. Basically, if you want to boost calcium levels in the blood, PTH is the best hormone for the job. It can do this in multiple ways.
PTHs cool calcium-related abilities include:
- Stimulating bone cells called osteoclasts to release bone-degrading enzymes, thus releasing calcium from the bone
- Signaling osteoblasts, which build up new bone tissue, to stop doing that for a bit, thus letting some calcium stay in the blood
- Helping tubules in the kidneys reabsorb calcium during urine production
- Kicking off calcitriol production.
Animation screenshot from Physiology & Pathology.
When blood calcium levels are sufficiently high, the release of PTH ceases.
In addition, the thyroid secretes calcitonin in response to high blood calcium. Basically, calcitonin counteracts what PTH does. Calcitonin signals osteoclasts to stop breaking down bone tissue, tells the kidneys to ease up on calcium reabsorption, and slows down the absorption of calcium in the intestines.
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The Parathyroid Glands And Their Hormones
The parathyroid glands are four pea-sized bodies located behind the thyroid gland that produce PTH. This hormone increases calcium levels in the blood, helping to maintain bone quality and an adequate supply of calcium, which is needed for numerous functions throughout the body . Specifically, PTH causes reabsorption of calcium from and excretion of phosphate in the urine. PTH also promotes the release of stored calcium from the bones as well as bone resorption, both of which increase calcium levels in the blood. Finally, PTH stimulates the absorption of calcium from the food in the gastrointestinal tract. Consistent with PTHs central role in calcium metabolism, the release of this hormone is not controlled by pituitary hormones but by the calcium levels in the blood. Thus, low calcium levels stimulate PTH release, whereas high calcium levels suppress it.
Many of the functions of PTH require or are facilitated by a substance called 1,25-dihydroxycholecalciferol, a derivative of vitamin D. In addition, numerous other hormones are involved in regulating the bodys calcium levels and bone metabolism, including estrogens, glucocorticoids, and growth hormone.
How Common Are These Conditions
- Diabetes: This condition is widespread. Almost 10% of people in the United States have diabetes and 27% have prediabetes.
- Thyroid disorders: About 20 million Americans have thyroid disease. Women are about five times more likely than men to develop the condition.
- Hypogonadism: About 40% of men over 45 have low testosterone. Levels of this sex hormone naturally drop as men age. Other factors, such as a mans diet, weight and other health problems also affect testosterone levels.
- PCOS: This common condition affects about 5% to 10% of adult women in the U.S. It is a leading cause of infertility.
- Osteoporosis: More than half of adults over age 50 have osteoporosis. It is more likely to occur in women than in men.
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The Pituitary And Its Target Organs
The pituitary has two distinct parts:
-
Front lobe, which accounts for 80% of the pituitary gland’s weight
The lobes are connected to the hypothalamus by a stalk that contains blood vessels and nerve cell projections . The hypothalamus controls the anterior lobe by releasing hormones through the connecting blood vessels. It controls the posterior lobe through nerve impulses.
The hormones produced by the pituitary are not all produced continuously. Most are released in bursts every 1 to 3 hours, with alternating periods of activity and inactivity. Some of the hormones, such as adrenocorticotropic hormone , growth hormone, and prolactin, follow a circadian rhythm: The levels rise and fall predictably during the day, usually peaking just before awakening and dropping to their lowest levels just before sleep. The levels of other hormones vary according to other factors. For example, in women, the levels of luteinizing hormone and follicle-stimulating hormone, which control reproductive functions, vary during the menstrual cycle.
Thyroid Follicles And Thyroid Function
The thyroid is highly vascular, meaning that it has a wealth of blood vessels. It is composed of follicles that absorb iodine, which is needed to produce thyroid hormones. These follicles store iodine and other substances necessary for thyroid hormone production. Surrounding the follicles are folliclar cells. These cells produce and secrete thyroid hormones into circulation via blood vessels. The thyroid also contains cells known as parafollicular cells. These cells are responsible for the production and secretion of the hormone calcitonin.
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Why You Need A Thyroid Gland
T3 and T4 travel in your bloodstream to reach almost every cell in the body. The hormones regulate the speed with which the cells/metabolism work. For example, T3 and T4 regulate your heart rate and how fast your intestines process food. So if T3 and T4 levels are low, your heart rate may be slower than normal, and you may have constipation/weight gain. If T3 and T4 levels are high, you may have a rapid heart rate and diarrhea/weight loss.
Listed below are other symptoms of too much T3 and T4 in your body :
-
Sweating or sensitivity to high temperatures
The Importance Of Thyroid Function
Your thyroid is a small, butterfly-shaped gland located at the base of the neck, just below the Adams apple. It is a crucial component to the function of many systems and organs, including the heart, brain, liver, kidneys and skin. With January being Thyroid Awareness Month, its important to understand how your thyroid gland functions and to be aware of the warning signs of a problem.
Thyroid gland function
The thyroid gland is part of the endocrine system, which is made up of glands that produce, store and release hormones into the bloodstream so the hormones can reach the bodys cells. Your thyroid gland uses iodine from the foods you eat to make two main hormones: triiodothyronine and thyroxine . It is important that the levels of these hormones are never too high or too low. The hypothalamus and the pituitary glands in the brain work together to maintain these levels.
The functionality of the thyroid gland will affect your bodys overall wellness. Your thyroid gland is responsible for manufacturing enough thyroid hormone to trigger your cells to perform and function at a certain rate. The thyroid hormones regulate vital functions like:
- Central and peripheral nervous system function
Thyroid problems
When the T3 and T4 hormone levels become too high or too low, your body will develop hyperthyroidism or hypothyroidism. Hyperthyroidism occurs when there is too much T3 and T4 in your system. Symptoms of hyperthyroidism include:
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The Gonads And Their Hormones
The gonads serve two major functions. First, they produce the germ cells . Second, the gonads synthesize steroid sex hormones that are necessary for the development and function of both female and male reproductive organs and secondary sex characteristics as well as for pregnancy, childbirth, and lactation. Three types of sex hormones exist each with different functions: estrogens , which exert feminizing effects progestogens , which affect the uterus in preparation for and during pregnancy and androgens , which exert masculinizing effects. In addition to the reproductive functions, sex hormones play numerous essential roles throughout the body. For example, they affect the metabolism of carbohydrates and lipids, the cardiovascular system, and bone growth and development.
Regulates The Release Of Hormones
Besides creating and releasing hormones, your endocrine system also regulates and controls how much of each hormone gets released. Numerous factors can impact your hormone levels, including how many are already in your blood, infections, stress, certain minerals in your blood, and more. The endocrine system will work to maintain the right balance. When something goes wrong with the endocrine system, it can lead to an endocrine disorder or other issues that affect your weight, mood, development, and more. This is why its so important to keep our systems, organs and glands as healthy as we can. Too little or too much of any hormone can be detrimental. Some ways you can support your endocrine system include:
- Eating a whole foods-based, nutrient-dense diet
- Getting enough exercise · Managing emotional stress
- Being mindful of any endocrine-related problems that run in your family
- Getting regular checkups
- Talking to us at Palmetto Endocrinology about supplements that may help
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The Adrenal Glands And Their Hormones
The adrenal glands are small structures located on top of the kidneys. Structurally, they consist of an outer layer and an inner layer . The adrenal cortex produces numerous hormones, primarily corticosteroids . The cortex is also the source of small amounts of sex hormones those amounts, however, are insignificant compared with the amounts normally produced by the ovaries and testes. The adrenal medulla generates two substancesadrenaline and noradrenalinethat are released as part of the fight-or-flight response to various stress factors.
The primary glucocorticoid in humans is cortisol , which helps control carbohydrate, protein, and lipid metabolism. For example, cortisol increases glucose levels in the blood by stimulating gluconeogenesis in the liver and promotes the formation of glycogen in the liver. Cortisol also reduces glucose uptake into muscle and adipose tissue, thereby opposing the effects of insulin. Furthermore, in various tissues, cortisol promotes protein and lipid breakdown into products that can be used for gluconeogenesis.
In contrast to the glucocorticoids, pituitary, or hypothalamic, hormones do not regulate aldosterone release. Instead, it is controlled primarily by another hormone system, the reninangiotensin system, which also controls kidney function. In addition, the levels of sodium and potassium in the blood influence aldosterone levels.
What Are Common Tests To Check The Health Of The Thyroid
The first-line test for checking the health of your thyroid is a blood test that measures your levels of thyroid-stimulating hormone . Its a screening test for both hypothyroidism and hyperthyroidism.
In general, the normal range for a TSH blood test is 0.5 to 5.0 mIU/L . However, this can vary from lab to lab and depending on certain factors, such as pregnancy and your age.
Your provider can also check the levels of T4 and T3 in your blood.
If your test results come back abnormal your provider may suggest having an imaging test such as a thyroid scan, which uses small amounts of a safe, radioactive material to create images of your thyroid, or a thyroid ultrasound.
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