Mechanism of Action in Hypothyroidism

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Questions and Answers

What is the primary mechanism of action for T4 and T3 when they enter the cell?

They dissociate from thyroglobulin proteins and enter the nucleus. (correct)

They stimulate hormone release from the pituitary gland.

They alter membrane permeability of the cell.

They bind to mitochondrial receptors.

Which form of T3 receptor has a high abundance in the liver, kidney, and heart?

Alpha T3 receptor (correct)

Gamma T3 receptor

Beta T3 receptor (correct)

Delta T3 receptor

What physiological response occurs upon the activation of T3 receptors?

Formation of lipids

Increased RNA formation and protein synthesis (correct)

Inhibition of DNA replication

Reduction of cellular respiration

Which of the following statements about T4 and T3's affinity for nuclear receptors is true?

T4 shows about 10 times lower affinity for the receptor than T3. Signup and view all the answers

Where are T3 receptors predominantly found?

In the liver, kidneys, heart, and lungs Signup and view all the answers

What is the process called when T4 is converted to T3?

Deiodination Signup and view all the answers

What respiratory symptom is associated with hypoproteinemia?

Dyspnea Signup and view all the answers

Which cardiovascular effect is linked to increased PVR in hypoproteinemia?

Bradycardia Signup and view all the answers

What eye condition can result from hypoproteinemia?

Drooping eyelids Signup and view all the answers

Which symptom indicates decreased cardiac output in the context of hypoproteinemia?

Angina Signup and view all the answers

Which of the following is a respiratory consequence of hypoproteinemia?

Pleural effusion Signup and view all the answers

What cardiac condition is noted with decreased PVR in hypoproteinemia?

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

Which of these symptoms is associated with hypoproteinemia and observed around the eyes?

Retraction of the upper lid Signup and view all the answers

Which cardiovascular symptom would you expect in a patient experiencing tachycardia due to hypoproteinemia?

Heart palpitations Signup and view all the answers

What is the main reason to avoid radioiodine during pregnancy?

It crosses the placenta. Signup and view all the answers

What is the treatment regimen for neonatal Graves disease?

Daily doses of antithyroid drugs and supportive care. Signup and view all the answers

What is the characteristic feature of non-toxic goiter?

Absence of systemic effects and no excessive hormone. Signup and view all the answers

What is the best management for non-toxic goiter caused by iodine deficiency?

Increase dietary iodine intake. Signup and view all the answers

What condition can lead to the development of neonatal Graves disease?

Maternal hyperthyroidism and genetic transmission. Signup and view all the answers

What is the appropriate management for thyroid neoplasms?

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

What is the main onset of action time for the inhibition of hormone release via thyroglobulin proteolysis?

2-7 days Signup and view all the answers

Which of the following is a reason to use iodinated contrast media?

To inhibit conversion of T4 to T3 Signup and view all the answers

What is a potential side effect of iodinated contrast media?

Acneiform rash Signup and view all the answers

Why should iodide not be used alone in treating thyrotoxicosis?

The gland can escape from iodide blockade Signup and view all the answers

What is a contraindication for using iodide during treatment?

Pregnancy Signup and view all the answers

What is the primary mechanism of action for radioactive iodine in treating thyrotoxicosis?

Emission of beta rays Signup and view all the answers

What happens to the heart rate within 3 days after administering iodinated contrast media?

It returns to normal Signup and view all the answers

What is the half-life of radioactive iodine (^131^I)?

5 days Signup and view all the answers

What is the main concern when using radioactive treatment for hyperthyroidism in patients over 40 years old?

Risk of genetic damage Signup and view all the answers

Which beta blocker is widely recognized as the drug of choice for managing symptoms of thyrotoxicosis?

Propanolol Signup and view all the answers

What life-threatening condition is characterized by a sudden acute exacerbation of thyrotoxicosis symptoms?

Thyroid storm Signup and view all the answers

Which treatment is NOT indicated for a thyroid storm?

Surgical removal of the gland Signup and view all the answers

During pregnancy, what is the recommended surgical treatment for thyrotoxicosis?

Subtotal thyroidectomy Signup and view all the answers

What adjunct treatment should be used when patients are resistant to guanethidine and reserpine?

Beta blockers Signup and view all the answers

What is the main action of saturated potassium iodide in the treatment of thyrotoxicosis?

Decreases hormone release Signup and view all the answers

Which drug is included in the treatment regimen for thyroid storm to protect against shock?

Hydrocortisone Signup and view all the answers

Study Notes

Mechanism of Action of Thyroid Hormones

T4 and T3 dissociate from thyroglobulin proteins and enter cells by diffusion or active transport.
T4 is converted to T3 within cells, with T3 binding to specific alpha and beta thyroid hormone receptors primarily in liver, kidney, heart, lungs, skeletal muscles, pituitary gland, and intestines.
Activation of T3 receptors enhances RNA formation and protein synthesis, leading to physiological responses.
T4 has about 10 times lower affinity for receptors than T3.

Thyroid Hormones Chemistry

T4 (Thyroxine) transforms to T3 (Triiodothyronine) through deiodination.
Reverse T3 is another inactive form of thyroid hormone.
All forms of thyroid hormones are levo-isomers.

Clinical Manifestations in Hypothyroidism and Thyrotoxicosis

Respiratory System: Hypothyroidism leads to dyspnea and decreased vital capacity; thyrotoxicosis can cause pleural effusion and hypoventilation.
Cardiovascular System: Hypothyroidism results in decreased peripheral vascular resistance (PVR) and increased heart rate, stroke volume, and cardiac output; thyrotoxicosis exhibits increased PVR and bradycardia.
Ocular Symptoms: Thyrotoxicosis can cause upper lid retraction and exophthalmos; hypothyroidism may present with drooping eyelids and periorbital edema.

Hormonal Release and Management

Inhibition of hormone release results from suppression of thyroglobulin proteolysis.
Thyroid hormone therapy onset is within 2-7 days.
Must be combined with thioamides to prevent exacerbation of thyrotoxicosis.
Contraindications include use alongside radioactive iodine and during pregnancy.

Adverse Effects of Thyroid Medications

Uncommon effects include acneiform rash, swollen salivary glands, conjunctivitis, fever, metallic taste, bleeding disorders, and potential anaphylactoid reactions.

Iodinated Contrast Media

Examples: Ipodate, Io-panoic acid, and diatrizoate.
Inhibit conversion of T4 to T3, improving symptoms of thyrotoxicosis like heart rate normalization within 3 days.
Serve as non-toxic adjuncts in thyroid storm treatment.

Radioactive Iodine Therapy

^131I is used for treating thyrotoxicosis, rapidly absorbed and concentrated in the thyroid gland.
Its beta-ray emission induces thyroid cell necrosis and disruption; has a half-life of around 5 days.
Contraindicated in patients over 40 years old due to risk of genetic damage and leukemia, not recommended in pregnancy or nursing.

Use of Beta Blockers

Aid in managing symptoms of thyrotoxicosis mimicking sympathetic stimulation.
Propranolol is the preferred choice for reducing symptoms associated with hyperthyroid conditions.

Thyroid Storm

Represents a life-threatening exacerbation of thyrotoxicosis symptoms.
Treatment includes IV Propranolol, Diltiazem, saturated potassium iodide, iodinated contrast agents, and corticosteroids to protect against shock and inhibit T4 to T3 conversion.

Management of Thyrotoxicosis in Pregnancy

Surgical removal of part of the thyroid gland (subtotal thyroidectomy) is recommended during pregnancy.
Use of PTC and thyroid supplementation post-surgery while avoiding radioiodine due to placental crossing.

Neonatal Graves' Disease

May occur in newborns due to maternal antibodies or genetic transmission; typically self-limiting within 4-12 weeks.
Treatment involves PTC, iodine supplementation, and propranolol, with gradual withdrawal as the infant improves.

Non-Toxic Goiter

Characterized by thyroid enlargement without excessive hormone production, often due to iodine deficiency.
Treatment typically involves iodine supplementation via iodized salt or thyroxine to suppress TSH stimulation and address hypothyroidism.

Thyroid Neoplasm

Can be benign or malignant; biopsy is essential for diagnosis.
Management often entails total thyroidectomy followed by radioiodine therapy and lifelong levothyroxine replacement.

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Description

This quiz explores the mechanisms of action related to T4 and T3 hormones in hypothyroidism. It covers their binding to receptors and the significance of these processes in various organs. Test your knowledge on the intricate details of thyroid hormone activity.