Thyroid Flashcards
What is the embryological origin of the thyroid gland?
The thyroid gland arises from the primitive foregut around the 3rd week of gestation.
What is the thyroglossal duct?
An epithelial-lined tube connecting the thyroid gland to the foramen cecum during embryonic development
What is a thyroglossal duct cyst?
A congenital cervical anomaly resulting from the persistence of the thyroglossal duct
What is the treatment for a thyroglossal duct cyst?
Sistrunk operation: en bloc cystectomy and excision of the central hyoid bone to minimize recurrence.
What is a lingual thyroid?
A developmental abnormality where the thyroid gland fails to descend and remains at the base of the tongue.
What is ectopic thyroid tissue?
Thyroid tissue found outside its normal location
What is the pyramidal lobe?
A remnant of the thyroglossal duct found in about 50% of individuals
What is the normal weight of the thyroid gland?
Approximately 20 grams.
What is the histological structure of the thyroid gland?
The thyroid is divided into lobules containing 20-40 follicles
What are thyroid C cells?
Also known as parafollicular cells
What is the daily iodine requirement for the body?
0.1 mg per day.
How is iodine metabolized in the body?
Iodine is converted to iodide in the stomach and jejunum
What are the steps of thyroid hormone synthesis?
- Iodide trapping
What is the difference between T3 and T4?
T3 is more potent
What is the hypothalamic-pituitary-thyroid axis?
A regulatory system that controls thyroid hormone secretion via TRH (thyrotropin-releasing hormone) and TSH (thyroid-stimulating hormone).
What is the most sensitive test for thyroid function?
Serum TSH (normal range: 0.5-5 μU/mL).
What are free T4 and free T3?
Free T4 (12-28 pmol/L) and Free T3 (3-9 pmol/L) are the physiologically active forms of thyroid hormones.
What is the significance of thyroid antibodies?
Elevated in 80% of patients with Hashimoto’s thyroiditis.
What is the investigation of choice for discrete thyroid swellings?
Fine-needle aspiration cytology (FNAC).
What is radionuclide thyroid imaging used for?
Uses iodine-123 or iodine-131 to identify cold (20% risk of malignancy) and hot nodules (5% risk).
What is the purpose of thyroid ultrasound?
To distinguish solid from cystic nodules
What is a goiter?
Any enlargement of the thyroid gland
What is endemic goiter?
Caused by iodine deficiency
What are goitrogens?
Substances that interfere with thyroid function
What are the clinical features of nontoxic goiter?
Most patients are asymptomatic; large goiters may cause compressive symptoms like dyspnea and dysphagia.
What is Pemberton’s sign?
Dilated veins over the chest wall due to retrosternal extension of a large goiter
What diagnostic tests are used for goiter?
RAI uptake (patchy uptake in multinodular goiter)
What are the common causes of hyperthyroidism?
Graves’ disease
What is the classic triad of Graves’ disease?
- Thyrotoxicosis
What causes hyperthyroidism in Graves’ disease?
Stimulatory autoantibodies to the TSH receptor
What is Graves’ ophthalmopathy?
Characterized by exophthalmos
What is pretibial myxedema?
A dermopathy in Graves’ disease
What diagnostic tests confirm Graves’ disease?
Suppressed TSH
What are the treatment options for Graves’ disease?
- Antithyroid drugs
What are the common antithyroid drugs?
Propylthiouracil (PTU) and methimazole
What is radioactive iodine therapy (RAI) used for?
Indicated for older patients with small/moderate goiters
When is surgical treatment recommended for Graves’ disease?
For large goiters
What is toxic multinodular goiter?
Hyperthyroidism in older individuals with a history of nontoxic goiter; may present with atrial fibrillation or heart failure.
What is toxic adenoma?
Hyperthyroidism caused by a single hyperfunctioning nodule
What is thyroid storm?
A life-threatening condition of severe hyperthyroidism with fever
How is thyroid storm managed?
ICU care with beta-blockers
What is acute (suppurative) thyroiditis?
A rare infection of the thyroid
What is subacute thyroiditis?
Likely viral or autoimmune in origin
What is Hashimoto’s thyroiditis?
An autoimmune disorder causing destruction of thyroid cells
What is Riedel’s thyroiditis?
A rare condition where thyroid tissue is replaced by fibrous tissue
How is Riedel’s thyroiditis diagnosed?
Confirmed by open thyroid biopsy
How are thyroid hormones transported in the blood?
Thyroid hormones are transported in serum bound to carrier proteins; only 0.02% is free and physiologically active.
What is thyroid peroxidase (TPO)?
An enzyme that catalyzes iodide oxidation and iodination of tyrosine residues in thyroid hormone synthesis.
How is TSH secretion regulated?
By a negative feedback loop involving T4 and T3.
Where does peripheral conversion of T4 to T3 occur?
Primarily in the liver
What proteins bind thyroid hormones in the blood?
Thyroxine-binding globulin (TBG)
What is the half-life of T3 and T4?
T3 has a half-life of 1 day
Which thyroid hormone is more potent?
T3 is 3-4 times more potent than T4 per unit weight.
What regulates thyroid hormone synthesis?
Controlled by TSH
Where is the majority of the body’s iodine stored?
Over 90% of the body’s iodine is stored in the thyroid gland.
What stimulates thyroid hormone secretion?
TSH
