PBSci 7 - Thyroid gland

Thyroxine, Triiodothyronine, Calcitonin

The thyroid gland secretes 3 main hormones…

Thyroxine

What thyroid hormone is known as T4?

Triidothyronine

What thyroid hormone is known as T3?

Calcitonin

What thyroid hormone is important for the control of plasma Calcium ions (Ca 2+)?

Thyroxine, Triidothyronine

What thyroid hormones are important for growth and development?

Follicle

What is the functional unit of the thyroid gland?

Acinus

What is the other term for “Follicle” → Functional unit of thyroid?

Follicle

______ is a cavity surrounded by epithelial cells filled with a thick colloid called Thymoglobulin.

Thyroglobulin

It is the thick colloid that fills the follicle, also a large glycoprotein.

115 tyrosine residue

How many tyrosine residues are is contained by the Thyroglobulin molecule?

High blood supply

What feature is found in follicles of the thyroid gland in terms of blood supply?

Negative feedback

High levels of circulating T3 and T4, through ______ controls the Thyrotropin-Releasing Hormone (TRH) and Thyroid stimulating hormone (TSH) secretion

Thyrotropin-Releasing Hormone (TRH), Thyroid stimulating hormone (TSH) secretion

High levels of circulating T3 and T4, through negative feedback controls the ______

Hypothalamus-pituitary-thyroid axis

What regulates the thyroid hormone secretion?

Auto-regulation

This is the process of the thyroid gland regulates its own Iodine uptake and hormone synthesis based on blood Iodine levels.

Iodide

Captured ___ carried across the membrane by pendrine transport and oxidized by thryoid peroxidase enzyme, as the oxidizing agent.

Pendrin transport

What carries the captured iodide across the membrane?

Thyroid peroxidase enzyme

What oxidizes the captured iodide?

Tyrosil residue

Active iodine, after oxidation with TPO will be bound to ____ of thyroglobuline.

Monoiodotyrosin

A tyrosine with one iodine atom attached (at the 3' position).

Diiodotyrosin

A tyrosine with two iodine atoms attached (at the 5' positions).

Gastrointenstinal Tract

It is in this organ site wherein the iodine intake (as iodide) from diet are absorbed into the blood stream.

Blood

It is at this site is where Iodide is transported in plasma to the thyroid gland.

Thyroid Follicular Cell (Basolateral membrane)

It is the site where the Iodide goes after the blood via Na+/I- symporter (NIS).

Thyroid Follicular Cell (Apical membrane)

This is the site where the ff. are done…

• The iodide is transported into colloid via Pendrin

• Generation of H2O2 (Hydrogen peroxide) (via DUOX)

• Oxidation of Iodide by Thyroid Peroxidase Enzyme (TPO)

• Iodination of thyroglobulin tyrosyl residues

• Forms Monoiodotyrosine (MIT) and Diiodotyrosine (DIT)

• Coupling reactions (DIT+DIT → Thyroxine (T4), MIT+DIT → Triiodothyronine (T3).

  • Storage of iodinate thyroglobulin (w/ T3, T4) in colloid

Thyroid Follicular Cell (Colloid)

This is the site where endocytosis of iodinate thyroglobulin (stimulated by TSH), Proteolysis in lysosomes → Release of T3 and T4.

The site wherein the recycling of iodide leftover after MIT and DIT is formed is done.

Blood

It is the site where free T3 and T4 is secreted.

Then are bound to proteins.

Peripheral tissues

These are the sites where T4 conversion into active T3 by deiodonases (D1, D2) occurs.

Inactivation of T3 into reverse T3 by D3

Hypothalamus

This is the site that releases TRH.

Pituitary gland

This ist he site the releases TSH.

Hasimoto’s thyroiditis, Graves’ disease

This thyroid conditions is under the category of Autoimmune?

Subacute Thyroiditis

What thyroid condition is characterized by painful thyroid?

De Quervain's thyroiditis

What is the other term for subacute thyroiditis?

Papillary

What is the most common thyroid cancer (characterized by slow growth rate and generally good prognosis)?

Iodine deciency

What is the worldwide cause for hypothyroidism?

TSH test

What is the most sensitive test for thyroid function?

Free T4

If the TSH test is abnormal, add _____ to confirm whether hypothyroidism/hyperthyroidism.

Free T3

After free T4 is added to determine hypo/hyperthyroidism.

_____ is measured when hyperthyroidism is suspected but T4 is normal.

Autoantibodies

If autoimmune thyroid disease is suspected check ______

Decreased attention and memory

The following are symptoms of hypothyroidism

Cold intolerance, Dyspnea, Anorexia, Constipation, Menorrhagia/Amenorrhea, Arthralgias, Myalgias, Fatigue, Depression, Irritability,__________, Paresthesias

Myxedema signs

The ff. are signs of hypothyroidism:

Dry and yellow (carotenemic) skin, Weight gain, thinning and coarse hair, _______ (Puffy eyelides, hoarse voice, dependent edema, carpal tunnel syndrome, anemia)

Autoimmune

What is the most common cause of primary hypothyroidism?

Lymphocytic infiltration

What is a variant of autoimmune thyroiditis that can cause primary hypothyroidism?

External radiation

What treatment for head/neck cancers can cause primary hypothyroidism as a side effect?

Radioactive iodine (I-131) therapy

What treatment for hyperthyroidism can result in primary hypothyroidism?

Severe prolonged iodine deficiency

What nutritional deficiency is a cause of primary hypothyroidism?

Antithyroid medications (Lithium)

What class of drugs can cause primary hypothyroidism as a side effect?

Inherited enzymatic defects

What genetic conditions can cause primary hypothyroidism?

True idiopathic

What term describes primary hypothyroidism with no identifiable cause?

Cretinism

It is hypothyroidism during fetal life. Results in mental retardation, pot bellied, yellow skin (→ “Cretins”)

Baby is characterized to be heavier due to decreased Basal metabolic rate (BMR)

Cretinism

This condition is caused one or more of the ff. amidst pregnancy…

• Iodine deficiency

• presence of TSH receptor-blocking antibodies

• Insulin resistance

Endemic cretinism

This variant of cretinism is caused by an Iodine-deficient mother.

Myxedema

This condition is caused by hypothyroidism during adult years. As a result of antibodies against thyroid peroxidase/thyroglobulin.

Common in women.

Myxedema

Severe hypothyroidism in which there is accumulation of hydrophilic mucopolysaccharides in the skin and other tissues making face to swell and look puffy.

Increased deposition of Glycosamino glycans

Hashimoto’s thyroiditis

The autoimmune destruction of Thyroid gland. Resulting in Low T3 and T4, High TSH

L-thyroxine

Hashimoto’s Thyroiditis is treated with _____.

50-75

In mild cases of hashimoto’s thyroiditis - ____ µg/day

1.6

In moderate and severe cases of hashimoto’s thyroiditis - _____ µg/kg body weight

Non-toxic goiter

This thyroid condition may be endemic or sporadic. 

Characterized by Low T3 and T4, High TSH → Thyroid gland enlargement due to trapped iodide → Increased T3 synthesis → demands met → Patient euthyroid (normally functional thyroid).

150-200, Iodine

For patients with non-toxic goiter, treat with ______ µg of ____ daily

Thyroid nodule

This condition is due to an excess TSH release. Treated with T4 Therapy.

Papillary carcinoma of thyroid

This is the most common cancer in the thyroid gland. Caused by Excess TSH.

Hypothyroidism During Pregnance

This condition is caused by increase maternal TBG levels → Less Free T4. Treated with L-thyroxine

Hyperthyroidism

This condition is the result of ↑ T3 and T4 Production.

Thyrotoxicosis

This condition is the result of Ingesting too much Thyroid hormones.

Grave’s Disease

This is the most common cause of hyperthyroidism. An autoimmune disorder, wherein the patient produces TSH receptor-stimulating antibodies → mimicking action of TSH → No negative feedback.

Grave’s Disease

This condition is characterized by Increased T3, T4, and TSH Receptor Antibodies, with a Low TSH.

Grave’s disease

What is the condition associated with hyperthyroidism which exhibits enlarged thyroid (exophthalmos are evident)?

Propranolol

What is the drug used for immediate control of Grave’s disease?

Antithyroid drugs

What drugs are used for long term control of Grave’s disease

Radio iodine ablation

This treatment method is a safe treatment that selectively destroys thyroid cells and is used for conditions like hyperthyroidism (e.g., Grave’s disease) and certain thyroid cancers in post-menopausal women and elderly men

Thyroidectomy

This treatment is performed if there is a presence of large goiter and patient poorly complies with drug therapy.

Toxic-nodular goiter

This is a single adenoma or a multiple adenoma. Progressive (non-toxic → Toxic phase). Due to excess T3 and T4.

Treated with the same treatments of Grave’s disease.

Surgery is preferred.

Plummer’s disease

Single adenoma Toxic nodular goiter is the result of what disease?

Multinodular goiter

Multiple adenoma Toxic nodular goiter is termed as?

Subacute thyroiditis

This condition may be the result of a Viral infection → Enlarged and tender thyroid.

Initially, T4 and T3 are elevated and TSH is low, but as disease progresses T4 and T3 will drop and TSH will rise.

Acetaminophen (For Pain)

Silent thyroiditis

If the enlarged thyroid in subacute thyroiditis is NON TENDER it is called?

Thyroid storm

This is the extreme manifestation of thyrotoxicosis. Fatal and occurs in association with Grave’s/Toxic nodular goiter. It is due to Cytokine release and acute immunological disturbance.

Occurs in patients who are incompletely/not treated for thyrotoxicosis.

Exhibits fever, sweating, tachycardia, arrhythmia, diarrhea, delirium, pulmonary edema, stupor, coma, and death.

Neonatal hyperthyroidism

This condition occurs in neonates born to mothers with Grave’s disease.

Treated with Antithyroid drug therapy (e.g., Propylthiouracil, Methimazole) for up to 12 weeks.

1, Saturated Solution of Potassium Iodide

In cases of Neonatal hyperthyroidism, another treatment is ____ drop/day of _________