Thyroid Gland

Dr. Nuha M.MalkawiDr. Nuha M.Malkawi 11

Dr. Nuha M. MalkawiDr. Nuha M. Malkawi


The thyroid gland is a The thyroid gland is a butterfly-shaped butterfly-shaped endocrine gland that is endocrine gland that is normally located in the normally located in the lower front of the neck lower front of the neck (The breathing airway, (The breathing airway, or trachea), and below or trachea), and below the larynx, or voice box.the larynx, or voice box.

الحنجرة


The thyroid’s job is to The thyroid’s job is to make thyroid make thyroid hormone, which is hormone, which is secreted into the secreted into the blood and then carried blood and then carried to every tissue in the to every tissue in the body. body.


FunctionFunctions: s:

The thyroid gland is to take iodine, The thyroid gland is to take iodine, found in many foods, and convert it found in many foods, and convert it into thyroid hormones: thyroxin (T4) into thyroid hormones: thyroxin (T4) and triiodothyronine (T3)and triiodothyronine (T3)..

The thyroid gland is controlled by The thyroid gland is controlled by the the pituitary gland which produces a which produces a hormone called Thyroid stimulating hormone called Thyroid stimulating hormone (TSH). Its level goes up hormone (TSH). Its level goes up when the level of thyroid hormones when the level of thyroid hormones comes down and vice versa.comes down and vice versa.


FunctionFunctions: s: The thyroid gland The thyroid gland Regulate body Regulate body

temperature and weight. affects body temperature and weight. affects body growthgrowth Thyroid hormone regulate Thyroid hormone regulate metabolismmetabolism which is the body's ability which is the body's ability to break down food and store it as to break down food and store it as energy and the ability to break down energy and the ability to break down food into waste products with a food into waste products with a release of energy in the process.release of energy in the process. Thyroid hormone is essential to help Thyroid hormone is essential to help each cell in each tissue and organ to each cell in each tissue and organ to work rightwork right. For example, thyroid . For example, thyroid hormone helps the body use energy, hormone helps the body use energy, stay warm, and keep the brain, heart, stay warm, and keep the brain, heart, muscles, and other organs working as muscles, and other organs working as they shouldthey should


The thyroid gland is composed of a mass of hollow The thyroid gland is composed of a mass of hollow spheres or spheres or folliclesfollicles. Each follicale has a lining one cell . Each follicale has a lining one cell thick, and contains a jelly –like colloidthick, and contains a jelly –like colloid((Colloid is a glycoproteinColloid is a glycoprotein))

lininglining


Steps Of Biosynthesis and Steps Of Biosynthesis and SecretionSecretion

Dietary Dietary iodine (Iiodine (I++)) is absorbed in the GI is absorbed in the GI tract, then taken up by the thyroid tract, then taken up by the thyroid gland (or removed from the body by gland (or removed from the body by the kidneys).the kidneys).

The transport of iodide into follicular The transport of iodide into follicular cells is dependent upon a sodium/iodine cells is dependent upon a sodium/iodine


Steps Of Biosynthesis and Steps Of Biosynthesis and SecretionSecretion Iodide (IIodide (I--)) taken up by the thyroid taken up by the thyroid

gland is oxidized by peroxide in the gland is oxidized by peroxide in the lumen of the follicle:lumen of the follicle:


Steps Of Biosynthesis and Steps Of Biosynthesis and SecretionSecretionFirst (Iodide oxidation): First (Iodide oxidation): Iodide (IIodide (I--)) taken up by the thyroid taken up by the thyroid

gland is oxidized by peroxide in the gland is oxidized by peroxide in the lumen of the follicle:lumen of the follicle:

• Oxidized iodine can then be Oxidized iodine can then be used in production of used in production of thyroid thyroid hormoneshormones..



Second (Iodination)Second (Iodination)

Iodide react with the tyrosine Iodide react with the tyrosine that is an integral part of the that is an integral part of the giant thyroglobulin molecule giant thyroglobulin molecule which is produce by The follicle which is produce by The follicle cells of the thyroid. cells of the thyroid.



Second (Iodination)Second (Iodination) Tyrosine Tyrosine binding with two atoms binding with two atoms

produces diiodotyrosine (DIT). produces diiodotyrosine (DIT). Thyroid peroxidase (TPO) is the Thyroid peroxidase (TPO) is the enzyme that catalyzes this reaction.enzyme that catalyzes this reaction.



Third (Coupling)Third (Coupling) The molecules must be combined to The molecules must be combined to

create the hormonescreate the hormones



Fourth (Pinocytosis)Fourth (Pinocytosis) The thyroid hormones are stored with The thyroid hormones are stored with

the thyroglobulin until they are needed.the thyroglobulin until they are needed.



Finally (Secretion)Finally (Secretion) The hormones are separated from the The hormones are separated from the

thyroglobulin and secreted into the thyroglobulin and secreted into the blood stream through proteolysis of Tg.blood stream through proteolysis of Tg.

Excess released iodotyrosines (MIT and Excess released iodotyrosines (MIT and DIT) are deiodinated in situ and the DIT) are deiodinated in situ and the resulting I- returns to be utilized in the resulting I- returns to be utilized in the intrathyroidal iodine cycle.intrathyroidal iodine cycle.


Biosynthesis and SecretionBiosynthesis and Secretion


TransportTransport

T3 & T4 leave the thyroid gland by T3 & T4 leave the thyroid gland by diffusiondiffusion

Both are transported in blood by Both are transported in blood by three three transport proteinstransport proteins, Thyroxine binding , Thyroxine binding globulin (TBG), transthyretin (TTRglobulin (TBG), transthyretin (TTR)) and Human Serum Albumin (HSA) and Human Serum Albumin (HSA)

A majority (99 %) of T4 & T3 is bound A majority (99 %) of T4 & T3 is bound to TBGto TBG

Both enter their target cells by Both enter their target cells by diffusiondiffusion


Their Their FunctionsFunctions

Most probably to ensure a Most probably to ensure a constant constant supplysupply of thyroid hormone to the cells of thyroid hormone to the cells and tissues by preventing urinary loss. and tissues by preventing urinary loss.

ProtectProtect the organism against abrupt the organism against abrupt changes in thyroid hormone production changes in thyroid hormone production

Degradation, protectDegradation, protect against iodine against iodine deficiency and target the amount of deficiency and target the amount of thyroid hormone delivery by ensuring a thyroid hormone delivery by ensuring a site-specific, enzymatic alteration of site-specific, enzymatic alteration of thyroxine-binding globulin thyroxine-binding globulin


Thyroid hormones regulationThyroid hormones regulation

The thyroid gland The thyroid gland concentrates iodine that concentrates iodine that the body absorbs from the body absorbs from various foods to make various foods to make thyroid hormones. The thyroid hormones. The thyroid gland makes thyroid gland makes mostly T4. Very little T3 is mostly T4. Very little T3 is made by the thyroid made by the thyroid gland. The liver and other gland. The liver and other organs convert T4 into T3. organs convert T4 into T3. Certain diseases and Certain diseases and drugs can affect the drugs can affect the conversion of T4 into T3.conversion of T4 into T3.



Increased levels of Increased levels of T3 and T4 prompt T3 and T4 prompt the hypothalamus the hypothalamus to slow down the to slow down the production of TRH, production of TRH, this resulting in a this resulting in a decreased activity decreased activity of TSH until the T3 of TSH until the T3 and T4 levels have and T4 levels have decreased again.decreased again.



Decreasing levels , Decreasing levels , our hypothalamus our hypothalamus to produce (TRH), to produce (TRH), which will signal the which will signal the pituitary gland to pituitary gland to produce TSH, which produce TSH, which will stimulate the will stimulate the thyroid´s production thyroid´s production of T3 and T4. of T3 and T4.


Thyroid Function TestsThyroid Function Tests

Blood tests to measure TSH, Blood tests to measure TSH, T4 and T3 are readily T4 and T3 are readily available and widely used available and widely used



Thyroid Antibody Tests Thyroid Antibody Tests

Two common antibodies that cause Two common antibodies that cause thyroid problems are directed thyroid problems are directed against thyroid cell proteins:against thyroid cell proteins:

Thyroid peroxidase (TPO) Thyroid peroxidase (TPO) Thyroglobulin. Thyroglobulin.

Measuring levels of thyroid antibodies Measuring levels of thyroid antibodies may help diagnose the cause of the may help diagnose the cause of the thyroid problems.thyroid problems.



Thyroid Antibody Tests Thyroid Antibody Tests

Thyroid antibody test is usually ordered Thyroid antibody test is usually ordered for patients who have a goiter, for patients who have a goiter, abnormal T3, T4 or TSH hormone abnormal T3, T4 or TSH hormone levels, or other indications of thyroid levels, or other indications of thyroid disesase or thyroid disease risk.disesase or thyroid disease risk.


Thyroid Function TestsThyroid Function TestsNon-blood testsNon-blood tests

Radioactive iodine uptakeRadioactive iodine uptakeRAIURAIU))))

By measuring the amount of radioactivity that By measuring the amount of radioactivity that is taken up by the thyroid gland (radioactive is taken up by the thyroid gland (radioactive iodine uptake, RAIU), doctors may determine iodine uptake, RAIU), doctors may determine whether the gland is functioning normally. whether the gland is functioning normally.

A very high RAIU is seen in individuals whose A very high RAIU is seen in individuals whose thyroid gland is overactive (hyperthyroidism).thyroid gland is overactive (hyperthyroidism).

While a low RAIU is seen when the thyroid While a low RAIU is seen when the thyroid gland is under active (hypothyroidism).gland is under active (hypothyroidism).


Is itIs it

HyperthyroidHyperthyroid

Hypothyroid Hypothyroid oror

EuthyroidEuthyroid


Wasting of Temporalis and shoulder muscleWasting of Temporalis and shoulder muscle Myxedema in limbsMyxedema in limbs


Fat accumulation Fat accumulation behind eyesbehind eyes

High TSHHigh TSH Patient Patient

previously had a previously had a thyroidectomythyroidectomy

Thyroid Gland

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