Thyroid Hormones and Anti-Thyroid Agents

Questions and Answers

What is the product of deiodination that is considered metabolically inactive?

rT3 (correct)

TSH

Which of the following can inhibit the conversion of T4 to T3?

Thyroid hormone replacement therapy

Starvation (correct)

Increased iodide intake

Physical exercise

How does Autoregulation affect thyroid hormone secretion?

It regulates iodide uptake independent of TSH. (correct)

It stimulates the release of TRH.

It causes an increase in TSH levels.

It increases the number of TSH receptors.

What role does TSH play in thyroid hormone synthesis?

Stimulates adenylyl cyclase. Signup and view all the answers

What is the effect of large amounts of iodine on hormone synthesis?

Inhibits iodide organification. Signup and view all the answers

Which thyroid hormone is almost completely absorbed with minimal interference by food or drugs?

T3 Signup and view all the answers

Enzyme inducers like rifampicin increase the metabolism of which thyroid hormones?

Both T3 and T4 Signup and view all the answers

Which of the following disorders is associated with thyroid stimulating immunoglobulin (TSI)?

Graves disease Signup and view all the answers

What is a common cardiac symptom of hypoproteinemia?

Arrhythmia Signup and view all the answers

Which of the following symptoms is NOT associated with respiratory issues due to hypoproteinemia?

Increased oxygen saturation Signup and view all the answers

Which condition is directly linked to increased peripheral vascular resistance (PVR)?

Chronic heart failure (CHF) Signup and view all the answers

What ocular symptom is related with hypoproteinemia?

Drooping eyelids Signup and view all the answers

Which cardiac effect is likely linked to a decrease in stroke volume (SV) due to hypoproteinemia?

Decreased pulse pressure Signup and view all the answers

What is a characteristic respiratory finding in hypoproteinemia?

Pleural effusion Signup and view all the answers

Which of the following symptoms is associated with periorbital edema?

Wide stare Signup and view all the answers

What is the result of increased heart rate (HR) in hypoproteinemia?

Increased arrhythmias Signup and view all the answers

What is the primary function of T4 and T3 hormones?

Support protein synthesis and enhance growth hormone effects Signup and view all the answers

Which hormone is crucial for calcium metabolism regulation?

Calcitonin Signup and view all the answers

What is a possible consequence of thyroid hormone deficiency during early life?

Irreversible mental retardation and dwarfism Signup and view all the answers

What condition is referred to as 'Goiter'?

Enlargement of the thyroid gland Signup and view all the answers

What does hyperactivity of the thyroid gland resemble?

Symptoms of sympathetic nervous system overactivity Signup and view all the answers

Which organ is NOT affected by thyroid hormones' regulation of resting metabolic rate?

Brain Signup and view all the answers

Which hormone is NOT directly synthesized by the thyroid gland?

Cortisol Signup and view all the answers

What is the approximate weight range of a normal adult thyroid gland?

15-25 g Signup and view all the answers

What is a characteristic of neonatal Graves disease?

It is self-limiting and usually resolves in 4-12 weeks. Signup and view all the answers

What is the primary cause of non-toxic goiter?

Inadequate thyroid hormone synthesis due to iodine deficiency. Signup and view all the answers

What is the best initial treatment for non-toxic goiter?

Prophylactic administration of iodine. Signup and view all the answers

What is the management approach for thyroid neoplasm?

Total thyroidectomy plus radioiodine therapy. Signup and view all the answers

Which medication can be added to treatment to prevent the conversion of T4 to T3 in neonatal Graves disease?

Prednisolone. Signup and view all the answers

What dietary source is recommended to manage iodine deficiency related to goiter?

Iodized salt. Signup and view all the answers

What is the main deficiency in hypothyroidism?

Lack of thyroid hormones Signup and view all the answers

Which condition is characterized by severe hypothyroidism at birth due to iodine deficiency?

Cretinism Signup and view all the answers

What is the initial treatment approach for drug-induced hypothyroidism?

Withdraw the drug and use levothyroxine Signup and view all the answers

What role does the hormone TSH play in hypothyroidism diagnosis?

Elevated levels indicate hypothyroidism Signup and view all the answers

Which of the following is NOT a cause of hypothyroidism?

Sepsis Signup and view all the answers

What is the typical levothyroxine dosage for adults managing hypothyroidism?

1.7 µg/kg/day Signup and view all the answers

Which of these conditions is an autoimmune disorder affecting the thyroid?

Hashimoto's thyroiditis Signup and view all the answers

What can result from untreated hypothyroidism in infants and children?

Growth and developmental retardation Signup and view all the answers

Study Notes

Introduction to Thyroid Hormones

The adult thyroid gland weighs 15-25 g and is located in front of the neck.
Major hormones produced include tetraiodothyronine (T4), triiodothyronine (T3), and calcitonin.
Iodine is crucial for the synthesis of T4 and T3, which are essential for growth, development, and metabolism.
Calcitonin regulates calcium metabolism.
Thyroid hormones are vital for the function and maintenance of all body tissues; deficiency can lead to irreversible mental retardation and dwarfism.
Thyroid hormones also influence other hormone secretions and degradation.

Regulation of Thyroid Hormone Secretion

Autoregulation: The thyroid gland autocompensates iodide uptake based on iodine levels, with excessive iodide inhibiting hormone synthesis.
Thyroid-Pituitary Feedback: Thyrotropin-releasing hormone (TRH) stimulates the synthesis of thyroid-stimulating hormone (TSH), which promotes the release of T4 and T3.
Abnormal Thyroid Stimulators: Graves' disease involves TSH receptor-stimulating antibodies which induce hormone secretion.

Pharmacokinetics of Thyroid Hormones

Absorption: T4 is well absorbed from the duodenum and ileum; food and certain drugs may impair its absorption. T3 has minimal interference during absorption.
Metabolism: Occurs predominantly in the liver; enzyme inducers may require dose adjustments for T4 to maintain effectiveness. In hyperthyroid patients, metabolic clearance increases.

Hypothyroidism Overview

Characterized by a deficiency of thyroid hormones, leading to a general slowdown of body functions; it can be reversible.
Symptoms in infants include growth retardation, potential dwarfism, and irreversible mental retardation.
Diagnosis involves laboratory tests showing low free T4 and elevated serum TSH.

Causes of Hypothyroidism

Drug-Induced: Medications blocking hormone synthesis (e.g., lithium, thioamides) can lead to mild to moderate hypothyroidism.
Dyshormoogenesis: Enzyme deficiencies impair T4 synthesis, often accompanied by goiter.
Destructive Factors: Radiation or surgical removal of the thyroid gland results in severe hypothyroidism without goiter.
Congenital Factors: Cretinism is caused by iodine deficiency and severe hypothyroidism is present.
Pituitary/Hypothalamic Disease: Absence of TSH leads to mild hypothyroidism.
Hashimoto's Thyroiditis: An autoimmune disorder causing thyroid destruction, initially presenting with goiter.

Management of Hypothyroidism

Drug-induced hypothyroidism managed by withdrawing the offending agent, supplemented with levothyroxine.
Levothyroxine dosages: infants receive 10-15 µg/kg/day while adults need 1.7 µg/kg/day.
During pregnancy, propylthiouracil (PTU) is preferred to avoid radioiodine exposure to the fetus.

Neonatal Graves' Disease

Occurs in newborns from maternal transmission of antibodies or genetic predisposition; usually self-limiting within 4-12 weeks.
Treatment can involve PTU, iodine, propranolol, and supportive care, with gradual withdrawal as the infant improves.

Non-Toxic Goiter

Characterized by thyroid enlargement without excessive hormone production, often due to inadequate thyroid synthesis.
Commonly caused by iodine deficiency; can also result from dietary goitrogens or neoplasms.
Treatment involves administering iodine prophylactically, with daily intake advised at 150-200 µg.

Thyroid Neoplasm

Thyroid tumors can be benign or malignant; biopsy is essential for diagnosis.
Management typically involves total thyroidectomy, radioiodine therapy, and lifelong levothyroxine replacement therapy.

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Description

This quiz covers the functions and effects of thyroid hormones, specifically T4 and T3, as well as the implications of anti-thyroid agents. It is designed to enhance your understanding of the thyroid gland's role in the endocrine system and conditions such as goiter. Prepare to test your knowledge on this crucial aspect of human physiology.