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Which Two Hormones Are Secreted By The Thyroid Gland

Answer And Explanation: 1

Thyroid Gland, Hormones and Thyroid Problems, Animation

The correct answer: Hormones produced by the thyroid gland are:

  • Thyroxine

There are three hormones which are released by…

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The thyroid gland regulates blood calcium levels through calcitonin and is stimulated by TSH to form thyroid hormones. This lesson looks at the thyroid gland, thyroid hormones T3 and T4, TSH , and calcitonin.

Related to this Question

Feature: Myth Vs Reality

Thyroid disorders are relatively common, affecting as many as 20 million people in the United States. According to recent studies, one in ten Canadians have some type of thyroid condition and up to 50 per cent may be undiagnosed! Because thyroid disorders are common, there are also many common myths about them.

Should I Exercise If I Have A Thyroid Disease

Regular exercise is an important part of a healthy lifestyle. You do not need to change your exercise routine if you have a thyroid disease. Exercise does not drain your bodys thyroid hormones and it shouldnt hurt you to exercise. It is important to talk to your healthcare provider before you start a new exercise routine to make sure that its a good fit for you.

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Biochemistry Of Thyroid Hormone

Thyroxine and triiodothyronine contain iodine and are formed from thyronines, which are composed of two molecules of the amino acidtyrosine. Thyroxine contains four iodine atoms, and triiodothyronine contains three iodine atoms. Because each molecule of tyrosine binds one or two iodine atoms, two tyrosines are used to synthesize both thyroxine and triiodothyronine. These two hormones are the only biologically active substances that contain iodine, and they cannot be produced in the absence of iodine. The process leading to the eventual synthesis of thyroxine and triiodothyronine begins in the thyroid follicular cells, which concentrate iodine from the serum. The iodine is then oxidized and attached to tyrosine residues within thyroglobulin molecules. The iodinated tyrosine residues are then rearranged to form thyroxine and triiodothyronine. Therefore, thyroglobulin serves not only as the structure within which thyroxine and triiodothyronine are synthesized but also as the storage form of the two hormones.

Thenervous And Endocrine Systems

Thyroid hormones

The pituitary gland is located in a small bony cavity at the base of the brain. Astalk links the pituitary to the hypothalamus,which controls release of pituitary hormones. The pituitary gland hastwo lobes: the anterior and posterior lobes. The anterior pituitaryis glandular.

The endocrine system in females and males.Image from Purves et al., Life: The Science of Biology, 4thEdition, by Sinauer Associates and WH Freeman ,used with permission.

The hypothalamus contains neurons that controlreleases from the anterior pituitary. Seven hypothalamic hormones arereleased into a connecting the hypothalamus andpituitary, and cause targets in the pituitary to release eighthormones.

The location and roles of the hypothalamus andpituitary glands. Images from Purves et al., Life: TheScience of Biology, 4th Edition, by Sinauer Associates and WH Freeman ,used with permission.

is a peptide anteriorpituitary hormone essential for growth. GH-releasing hormonestimulates release of GH. GH-inhibiting hormone suppresses therelease of GH. The hypothalamus maintains homeostatic levels of GH.Cells under the action of GH increase in size andnumber . GH also causes increase in bone length andthickness by deposition of cartilage at the ends of bones. Duringadolescence, sex hormones cause replacement of cartilage by bone,halting further bone growth even though GH is still present. Toolittle or two much GH can cause dwarfism or gigantism, respectively.

The Posterior Pituitary

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How Does A Blood Test For Hypothyroidism Work

How to test for hypothyroidism?

Itâs important to note that there is no hypothyroidism test that can check thyroid hormones andâbased only on those test resultsâconclusively determine if someone has hypothyroidism. Thatâs because both thyroid hormone testing and a physicianâs evaluation of symptoms and medical history is required for a diagnosis.

A blood test for hypothyroidism is based on your levels of thyroid-stimulating hormone and the thyroid hormones T3 and T4. Because TSH signals the thyroid gland to produce more thyroid hormones, unusually high levels of TSH can mean that your thyroid isnât making enough hormones.

A thyroid lab test might also measure T3 and T4 to reveal just how low your thyroid hormone levels are, which can help your healthcare provider decide on a treatment strategy.

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Regulation Of Th Synthesis

The release of T3 and T4 from the thyroid gland is regulated by thyroid-stimulating hormone . As shown in Figure 2, low blood levels of T3 and T4 stimulate the release of thyrotropin-releasing hormone from the hypothalamus, which triggers secretion of TSH from the anterior pituitary. In turn, TSH stimulates the thyroid gland to secrete T3 and T4. The levels of TRH, TSH, T3, and T4 are regulated by a negative feedback system in which increasing levels of T3 and T4 decrease the production and secretion of TSH.

Figure 2. A classic negative feedback loop controls the regulation of thyroid hormone levels.

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What Does My Pituitary Gland Do

The pituitary gland is called the ‘master gland’ as the hormones it produces control so many different processes in the body. It senses the body’s needs and sends signals to different organs and glands throughout the body to regulate their function and maintain an appropriate environment.;It secretes a variety of hormones into the bloodstream which act as messengers to transmit information from the pituitary gland to distant cells, regulating their activity.;For example, the pituitary gland produces prolactin, which acts on the breasts to induce milk production. The pituitary gland also secretes hormones that act on the adrenal glands, thyroid gland’ data-content=’1456′ >thyroid gland, ovaries and testes, which in turn produce other hormones. Through secretion of its hormones, the pituitary gland controls metabolism, growth, sexual maturation, reproduction, blood pressure and many other vital physical functions and processes.;

How Can I Promote The Health Of The Thyroid Gland

Thyroid Gland: Thyroid Hormone Synthesis

Iodine is most essential to maintain a healthy thyroid. Iodine is the critical ingredient for the production of thyroid hormones. We dont need a lot of iodine, it is said that one teaspoon of iodine is enough for a lifetime. Nonetheless, the daily and constant supply of this micronutrient is important. Too much iodine at once is counter-productive and causes your thyroid to produce less hormones. The best way to get your daily dose of iodine is through eating healthy foods like seafood and dairy products. In addition, iodized salt is a good source and you can use it to season your food. Nowadays, iodine is added to salt to combat goitres .

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Disorders Of The Endocrine System

Iodine Deficiency, Hypothyroidism, and Hyperthyroidism

As discussed above, dietary iodine is required for the synthesis of T3 and T4. But for much of the worlds population, foods do not provide adequate levels of this mineral, because the amount varies according to the level in the soil in which the food was grown, as well as the irrigation and fertilizers used. Marine fish and shrimp tend to have high levels because they concentrate iodine from seawater, but many people in landlocked regions lack access to seafood. Thus, the primary source of dietary iodine in many countries is iodized salt. Fortification of salt with iodine began in the United States in 1924, and international efforts to iodize salt in the worlds poorest nations continue today.

Figure 3. Goiter

In areas of the world with access to iodized salt, dietary deficiency is rare. Instead, inflammation of the thyroid gland is the more common cause of low blood levels of thyroid hormones. Called hypothyroidism, the condition is characterized by a low metabolic rate, weight gain, cold extremities, constipation, reduced libido, menstrual irregularities, and reduced mental activity.

How Long Does It Take For Thyroid Medication To Work

The time it takes for the medication to work is unique to each person.Â;

Once you start your medication, it can take a few weeks to start noticing an improvement in your symptoms. However, some people see their symptoms get better almost right after starting.Â;

To see how your body responds to thyroid medication, you should retest your thyroid function about six weeks after starting or changing your prescription. Depending on your symptoms and lab results, your doctor may make changes to your dose. For example, if you are still having symptoms, you may need a higher dose of medication.

Sometimes, it can take several dosage changes, and even in medication, to get the results you need. However, once you find the right combination, its advantageous to stick with it unless something changes or your symptoms return.Â;

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How The Body Adjusts Thyroid Hormones

The body has a complex mechanism for adjusting the level of thyroid hormones. First, the hypothalamus, located just above the pituitary gland in the brain, secretes thyrotropin-releasing hormone, which causes the pituitary gland to produce thyroid-stimulating hormone . Just as the name suggests, TSH stimulates the thyroid gland to produce thyroid hormones. The pituitary gland slows or speeds the release of TSH, depending on whether the levels of thyroid hormones circulating in the blood are getting too high or too low.

Functions Of The Endocrine System


The Endocrine system controlsand regulates the complex activities of the body. The Endocrinesystem regulates the activities of the body by secreting complexchemical substances into the blood stream. Thesesecretions come from a variety of glands which control variousorgans of the body. The key functions are:

  • To regulate the metabolic functions of the body.
  • To regulate the rate of chemical reactions in various cells.
  • To influence the ability of substances to transport themselves through cell membranes.

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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 together 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 Is A T3 Test

T3 TestsT3 tests measure triiodothyronine levels in the blood. A Total T3 test measures the bound and free fractions of triiodothyronine. Hyperthyroid patients typically have an elevated Total T3 level. T3 tests can be used to support a diagnosis of hyperthyroidism and can determine the severity hyperthyroidism.

In some thyroid diseases, the proportions of T3 and T4 in the blood change and can provide diagnostic information. A pattern of increased T3 vs T4 is characteristic of Graves disease. On the other hand, medications like steroids and amiodarone, and severe illness can decrease the amount of thyroid hormone the body converts from T4 to T3 resulting in a lower proportion of T3.

T3 levels fall late in the course of hypothyroidism and therefore are not routinely used to evaluate patients with underactive or surgically absent thyroid glands.

Measurement of Free T3 is possible, but is often not reliable and therefore may not be helpful.

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Thyroid Hormones: T4 And T3

There are two main thyroid hormones produced by the follicles:;thyroxine , which contains four iodide ions and is represented by the structural diagram below , and triiodothyronine , which contains three iodide ions. T3 is much more powerful than T4, but T4 makes up about 90 per cent of circulating thyroid hormone, and T3 makes up only about ten per cent. However, most of the T4 is converted to T3 by target tissues.

Figure 9.5.3 This structural model represents a single molecule of thyroxine . The Is represent the four iodide ions it contains. The rings consist mainly of carbon atoms.

Like steroid hormones, T3 and T4 cross cell membranes everywhere in the body and bind to intracellular receptors to regulate gene expression.;Unlike steroid hormones, however, thyroid hormones can cross cell membranes only with the help of special transporter proteins. Once inside the nucleus of cells, T3 and T4 turn on genes that control protein synthesis. Thyroid hormones increase the rate of metabolism in cells,;allowing them to;absorb more carbohydrates, use more energy, and produce more heat. Thyroid hormones also increase the rate and force of the heartbeat. In addition, they increase the sensitivity of cells to fight-or-flight hormones .

Figure 9.5.4 The thyroid system is a negative feedback loop that includes the hypothalamus, pituitary gland, and thyroid gland. As this diagram shows, thyroid hormones increase the effect of catecholamines such as adrenaline, a fight-or-flight hormone.

Diagnostic Tests Of The Thyroid Gland

Thyroid Gland and Hormones

Doctors first examine the person and feel the person’s neck to see whether the thyroid gland is enlarged.

Depending on the results of the examination, other tests may also be needed. Additional testing may also be necessary in rare cases in which doctors cannot determine whether the problem lies in the thyroid or in the pituitary gland.

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Chapter14 What Types Of Glands Secrete Hormones Another Name For Pituitary Gland And Why

  • Where is the pituitary gland located? Name the two regions of the pituitary gland, and what hormones do they each secrete?
  • What controls the activity of the pituitary gland?
  • Chemical compositions of hormones. What type of composition can enter the cell nucleus and what type attaches to the cell receptor?
  • Negative and positive feedback – example of each.
  • Thyroid gland hormones – what causes the secretion of calcitonin and thyroxin? What effect does calcitonin have on blood calcium levels?
  • Which mineral is needed for proper functioning of the thyroid gland?
  • What causes hypothyroidism and hyperthyroidism?
  • How does PTH regulate calcium levels in blood?
  • Name the osteocytes that make and break bones by either adding calcium to bones or remove calcium from bones.
  • Name the hormones of the adrenal cortex and adrenal medulla.
  • What are the effects of cortisol on blood glucose? What is cortisol also known as?
  • When is aldosterone secreted? What is it also known as? What is its effect on blood pressure?
  • What are the effects of epinephrine and norepinephrine on HR and BP?
  • What are pancreatic cells also called?
  • Name the hormones produced by alpha and beta pancreatic cells. How do these two hormones regulate blood glucose?
  • Which gland produces melatonin? What is its effect?
  • Which gland produces thymosin? What is its effect on T cells?
  • Name the hormone released by the kidneys that help generate RBCs from the red bone marrow.
  • Spotlight On Aging: Thyroid Gland Changes In Older People

    Aging itself has only minor effects on the thyroid gland and thyroid hormones. As people get older, the thyroid gland shrinks and shifts lower in the neck. The level of the thyroid hormone triiodothyronine may fall slightly, but the speed of vital functions changes very little. However, thyroid disorders become more common with aging.

    Disorders that affect thyroid function, particularly hyperthyroidism and hypothyroidism, can be thought of as great masqueraders in older people. These disorders often cause symptoms that are easily mistaken for symptoms of other conditions or even as signs of getting old.

    Increased or decreased thyroid function can dramatically worsen the way an older person feels and can greatly diminish the ability to carry out daily activities. For these reasons, the great masqueraders must be unmasked and recognized for what they are so that they can be effectively treated.

    Screening older people for hyperthyroidism and hypothyroidism is helpful. Some experts recommend measuring the level of thyroid-stimulating hormone in the blood in people over 65 every 5 years.

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    What Hormones Does The Thyroid Gland Secrete

    The thyroid gland is found in front of the trachea in your neck. The gland is divided into 2 lobes and is connected in the middle by a thin bridge of thyroid tissue, known as the isthmus. Because of the 2 connected lobes, the thyroid has been described as being shaped like a butterfly, or a bow tie. The thyroid cartilage, which is the largest cartilage of the larynx lies just above the thyroid gland and is sometimes known as the Adams apple. A normal-sized thyroid gland cannot be seen in the neck and can barely be felt. It is only when certain conditions result in an enlarged thyroid gland , that a bulge may be seen or felt just underneath the Adams apple.

    What Does The Thyroid Do

    Regulation of Hormone Production

    Your thyroid has an important job to do within your body releasing and controlling thyroid hormones that control metabolism. Metabolism is a process where the food you take into your body is transformed into energy. This energy is used throughout your entire body to keep many of your bodys systems working correctly. Think of your metabolism as a generator. It takes in raw energy and uses it to power something bigger.

    The thyroid controls your metabolism with a few specific hormones T4 and T3 . These two hormones are created by the thyroid and they tell the bodys cells how much energy to use. When your thyroid works properly, it will maintain the right amount of hormones to keep your metabolism working at the right rate. As the hormones are used, the thyroid creates replacements.

    This is all supervised by something called the pituitary gland. Located in the center of the skull, below your brain, the pituitary gland monitors and controls the amount of thyroid hormones in your bloodstream. When the pituitary gland senses a lack of thyroid hormones or a high level of hormones in your body, it will adjust the amounts with its own hormone. This hormone is called thyroid stimulating hormone . The TSH will be sent to the thyroid and it will tell the thyroid what needs to be done to get the body back to normal.

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