HRE TBL 2 - Thyroid, Parathyroid Function and Calcium Regulation

What is the embryological origin of the thyroid gland?

Endoderm from the floor of the primitive pharynx

What structure marks the origin site of the thyroid gland?

Foramen cecum

Which duct connects the thyroid gland to the tongue during development?

Thyroglossal duct

What is the most common congenital anomaly of the thyroid gland?

Thyroglossal duct cyst

Where is a thyroglossal duct cyst typically located?

Midline neck near the hyoid bone

What is the embryological origin of the superior parathyroid glands?

Fourth pharyngeal pouch

What is the embryological origin of the inferior parathyroid glands?

Third pharyngeal pouch

Which structure migrates with the inferior parathyroid glands?

Thymus

What is the embryological origin of C cells (parafollicular cells)?

Ultimobranchial body from the fourth pharyngeal pouch (neural crest derived)

What hormone is secreted by parafollicular cells?

Calcitonin

What is the function of calcitonin?

Lowers blood calcium levels

What is the most common location of ectopic thyroid tissue?

Lingual thyroid

Which nerve is closely associated with the inferior thyroid artery?

Recurrent laryngeal nerve

What arteries supply the thyroid gland?

Superior and inferior thyroid arteries (and sometimes thyroidea ima)

What veins drain the thyroid gland?

Superior, middle, and inferior thyroid veins

Which nerve innervates the cricothyroid muscle?

External branch of the superior laryngeal nerve

Which cells produce thyroid hormones?

Follicular cells

What is the role of thyroglobulin?

Protein scaffold for thyroid hormone synthesis

What enzyme catalyzes iodination in the thyroid?

Thyroid peroxidase

Which transporter imports iodide into follicular cells?

Sodium-iodide symporter (NIS)

What are the two major thyroid hormones?

T3 (triiodothyronine) and T4 (thyroxine)

Which thyroid hormone is more active?

T3

What is the primary carrier protein for thyroid hormones?

Thyroxine-binding globulin (TBG)

Which hormone stimulates thyroid hormone production?

Thyroid-stimulating hormone (TSH)

Where is TSH produced?

Anterior pituitary

What regulates TSH secretion?

Thyrotropin-releasing hormone (TRH) from the hypothalamus and negative feedback from T3/T4

What is the function of thyroid hormones?

Increase basal metabolic rate and stimulate growth and development

What are symptoms of hyperthyroidism?

Weight loss, heat intolerance, tachycardia, tremor

What is the most common cause of hyperthyroidism?

Graves’ disease

What autoantibody is present in Graves’ disease?

TSH receptor-stimulating antibody

What are symptoms of hypothyroidism?

Weight gain, cold intolerance, bradycardia, fatigue

What is the most common cause of hypothyroidism?

Hashimoto’s thyroiditis

Which antibodies are associated with Hashimoto’s?

Anti-TPO and anti-thyroglobulin antibodies

What is the histological feature of Hashimoto’s thyroiditis?

Lymphocytic infiltration with germinal centers and Hurthle cells

What are signs of a goitre?

Visible thyroid enlargement, dysphagia, hoarseness

What is subacute thyroiditis also known as?

De Quervain’s thyroiditis

What causes De Quervain’s thyroiditis?

Post-viral granulomatous inflammation

What lab result is seen in early De Quervain’s?

High T4, low TSH, elevated ESR

What thyroid cancer is most common?

Papillary thyroid carcinoma

What are psammoma bodies associated with?

Papillary thyroid carcinoma

Which thyroid cancer spreads hematogenously?

Follicular thyroid carcinoma

Which thyroid cancer arises from parafollicular cells?

Medullary thyroid carcinoma

Which thyroid cancer is associated with RET mutations?

Medullary thyroid carcinoma

What syndrome is linked to medullary thyroid carcinoma?

MEN 2A and 2B

What is the most aggressive thyroid cancer?

Anaplastic thyroid carcinoma

What does calcitonin serve as a tumor marker for?

Medullary thyroid carcinoma

What is the primary hormone regulating calcium homeostasis?

Parathyroid hormone (PTH)

Where is PTH secreted from?

Chief cells of the parathyroid gland

What stimulates PTH secretion?

Low serum calcium

What are the effects of PTH on bone?

Stimulates osteoclasts to increase calcium release

What are the effects of PTH on kidneys?

Increases calcium reabsorption and phosphate excretion

How does PTH affect vitamin D?

Stimulates conversion to active form (calcitriol) in kidneys

What is the active form of vitamin D?

Calcitriol (1,25-dihydroxycholecalciferol)

What is the function of calcitriol?

Increases calcium and phosphate absorption from the gut

Which organs regulate calcium metabolism?

Bone, kidney, intestine

What is the effect of calcitonin on bone?

Inhibits osteoclast activity

What are symptoms of hypercalcemia?

Stones, bones, groans, psychiatric overtones

What are symptoms of hypocalcemia?

Tetany, Chvostek’s sign, Trousseau’s sign

What causes primary hyperparathyroidism?

Parathyroid adenoma (most common), hyperplasia, carcinoma

What causes secondary hyperparathyroidism?

Chronic kidney disease or vitamin D deficiency

What lab findings are typical in primary hyperparathyroidism?

High calcium, high PTH, low phosphate

What lab findings are typical in secondary hyperparathyroidism?

Low/normal calcium, high PTH, high phosphate

What is tertiary hyperparathyroidism?

Autonomous PTH secretion after prolonged secondary hyperparathyroidism

How is hypoparathyroidism commonly caused?

Accidental removal during thyroid surgery

What lab findings are seen in hypoparathyroidism?

Low calcium, low PTH, high phosphate

How is hypocalcemia treated?

Calcium and vitamin D supplements

How is hypercalcemia treated?

IV fluids, bisphosphonates, calcitonin

What imaging is used to localize parathyroid adenoma?

Sestamibi scan

What syndrome involves failed development of parathyroids?

DiGeorge syndrome

What are signs of DiGeorge syndrome?

Hypocalcemia, cleft palate, congenital heart defects

What gene deletion causes DiGeorge syndrome?

22q11.2 deletion

Which hormone increases intestinal calcium absorption?

Calcitriol

Which hormone decreases serum calcium?

Calcitonin

What is pseudohypoparathyroidism?

PTH resistance at target organs

What lab findings are seen in pseudohypoparathyroidism?

Low calcium, high PTH, high phosphate

What is Albright hereditary osteodystrophy?

Short stature, round face, subcutaneous ossifications in pseudohypoparathyroidism

What is the function of TSH?

Stimulates thyroid growth and hormone secretion

What is the most accurate test for primary hypothyroidism?

TSH

What is the first step in thyroid hormone synthesis?

Iodide uptake via NIS

Where is the thyroid located anatomically?

Anterior to the trachea at levels C5-T1

What are the two lobes of the thyroid connected by?

Isthmus

What embryological structure does the thyroid descend through?

Thyroglossal duct

What causes a lingual thyroid?

Failure of thyroid migration

What is the significance of the pyramidal lobe?

Remnant of thyroglossal duct; normal variant

What is the role of TRH?

Stimulates TSH release from the anterior pituitary

What is the role of the hypothalamic-pituitary-thyroid axis?

Maintains homeostatic control of thyroid hormone levels

How do thyroid hormones exert their effects?

Bind to nuclear receptors and alter gene transcription

Which hormone has the longer half-life, T3 or T4?

T4

Which thyroid hormone is produced in greater quantity?

T4

Where is T4 converted to T3?

Peripheral tissues (e.g. liver, kidney)

What is reverse T3?

Inactive form of T3 produced during illness or stress

How does illness affect thyroid function tests?

Can cause low T3 syndrome (euthyroid sick syndrome)

What is the role of deiodinase enzymes?

Convert T4 to T3 or reverse T3

How is thyroid hormone stored in the gland?

Bound to thyroglobulin in the follicular lumen

What is Pendred syndrome?

Congenital disorder with thyroid goitre and hearing loss due to pendrin mutation

Which week of gestation does the thyroid gland begin to develop?

Week 4

At what week does the thyroid gland reach its final anatomical position?

Week 7

What is the first endocrine gland to develop in the embryo?

Thyroid gland

What does the thyroglossal duct normally do after development?

Atrophies and disappears

What happens if the thyroglossal duct fails to regress?

It forms a thyroglossal duct cyst