Thyroid Parathyroid

Question 1

What are the main hormones produced by the thyroid gland?

Answer 1

1. Triiodothyronine (T3) – Active form.
2. Thyroxine (T4) – Prohormone, converted to T3.
3. Calcitonin – Involved in calcium homeostasis.

Question 2

How are T3 and T4 transported in the blood?

Answer 2

• Thyroxine-Binding Globulin (TBG) – Binds most T3 & T4.
• Transthyretin (TTR, Thyroxine-Binding Prealbumin) – Binds T4.
• Albumin – Binds T3 & T4 weakly.
• Free fractions (FT3, FT4) – Biologically active.

Question 3

What is the hypothalamic-pituitary-thyroid (HPT) axis?

Answer 3

1. Hypothalamus secretes TRH → Stimulates pituitary.
2. Pituitary releases TSH → Stimulates thyroid.
3. Thyroid produces T3 & T4 → Regulates metabolism.

Question 4

What are the main physiological actions of thyroid hormones?

Answer 4

• ↑ Basal metabolic rate (↑ oxygen consumption, heat production).
• ↑ Cardiac output (↑ heart rate & contractility).
• ↑ Lipid metabolism (↓ cholesterol in hyperthyroidism, ↑ cholesterol in hypothyroidism).
• ↑ Bone turnover (enhances osteoclast activity).
• ↑ Gastrointestinal motility (can cause diarrhea in hyperthyroidism).

Question 5

What are the key static thyroid function tests?

Answer 5

1. TSH (Thyroid-Stimulating Hormone) – First-line test for dysfunction.
2. Free T4 (FT4) & Free T3 (FT3) – Measures active hormones.
3. Total T4 & Total T3 – Influenced by binding proteins.

Question 6

What are normal reference values for thyroid hormones?

Answer 6

• TSH: 0.5–4 mIU/L
• FT4: 10–20 ng/L
• FT3: 2–5 ng/L

Question 7

What are the key autoimmune thyroid markers?

Answer 7

• Anti-Thyroid Peroxidase Antibodies (ATPO) – Hashimoto’s thyroiditis.
• Thyroglobulin Antibodies (AAT) – Chronic autoimmune thyroiditis.
• TRAb (TSH Receptor Antibodies) – Graves’ disease (hyperthyroidism).

Question 8

What is thyroglobulin, and when is it measured?

Answer 8

A tumor marker used for thyroid cancer follow-up after thyroidectomy.

Question 9

What is calcitonin, and what does it indicate?

Answer 9

A marker for medullary thyroid carcinoma (MTC).

Question 10

What is the TRH Stimulation Test, and what does it assess?

Answer 10

• Inject TRH, measure TSH response.
• Normal: Increase in TSH.
• Pituitary failure: No TSH response (secondary hypothyroidism).
• Hypothalamic failure: Delayed but present TSH increase (tertiary hypothyroidism).

Question 11

What is the T3 Suppression Test (Werner Test) used for?

Answer 11

• T3 is given → Normally, TSH should be suppressed.
• No suppression in Graves’ disease → TSH remains high.

Question 12

What is the Querido Test (TSH Stimulation Test)?

Answer 12

• Inject TSH, measure T4 response.
• No T4 response → Primary hypothyroidism.
• Normal increase → Secondary/tertiary hypothyroidism.

Question 13

What are the key causes of hypothyroidism?

Answer 13

1. Primary hypothyroidism (Thyroid failure) → ↑ TSH, ↓ T3/T4.
   
   • Hashimoto’s thyroiditis (autoimmune destruction).
   • Iodine deficiency.
   • Post-surgical or radioactive iodine treatment.
2. Secondary hypothyroidism (Pituitary failure) → ↓ TSH, ↓ T3/T4.
3. Tertiary hypothyroidism (Hypothalamic failure) → ↓ TRH, ↓ TSH, ↓ T3/T4.

Question 14

What are the clinical signs of hypothyroidism?

Answer 14

• Weight gain, cold intolerance.
• Bradycardia, dry skin, constipation.
• Delayed reflexes (prolonged Achilles reflex time).

Question 15

What are the key causes of hyperthyroidism?

Answer 15

1. Graves’ disease (Basedow’s disease) – Autoimmune stimulation of TSH receptors.
2. Toxic multinodular goiter (Plummer’s disease) – Autonomous T3/T4 secretion.
3. Thyroid adenoma – Benign tumor secreting T3/T4.
4. Subacute thyroiditis – Temporary post-viral inflammation.

Question 16

What are the clinical signs of hyperthyroidism?

Answer 16

• Weight loss, heat intolerance.
• Tachycardia, sweating, tremors.
• Goiter, exophthalmos (Graves’ disease).

Question 17

What are the biochemical findings in hyperthyroidism?

Answer 17

• ↓ TSH, ↑ T3/T4.
• TRAb positive in Graves’ disease.

Question 18

What is the main function of the parathyroid glands?

Answer 18

Regulation of calcium & phosphate metabolism via Parathyroid Hormone (PTH).

Question 19

What are the effects of PTH?

Answer 19

• ↑ Calcium absorption in the intestines (via vitamin D activation).
• ↑ Bone resorption (stimulates osteoclasts).
• ↑ Renal calcium reabsorption & ↓ phosphate reabsorption.

Question 20

What is calcitonin, and how does it oppose PTH?

Answer 20

• ↓ Calcium absorption in the intestines.
• ↓ Bone resorption (inhibits osteoclasts).
• ↑ Renal excretion of calcium & phosphate.

Question 21

What are the key biochemical markers for calcium metabolism?

Answer 21

1. Total & Ionized Calcium.
2. Serum Phosphate.
3. Alkaline Phosphatase (ALP) – Bone turnover.
4. PTH levels (Bio-intact PTH assay).

Question 22

What are the biochemical findings in hyperparathyroidism?

Answer 22

• ↑ PTH, ↑ Calcium, ↓ Phosphate.
• ↑ Urinary cAMP (secondary messenger for PTH action).

Question 23

What are the biochemical findings in hypoparathyroidism?

Answer 23

• ↓ PTH, ↓ Calcium, ↑ Phosphate.
• ↓ Urinary cAMP.

Question 24

A patient has low TSH, high T3/T4, and positive TRAb. What is the diagnosis?

Answer 24

Graves’ disease (autoimmune hyperthyroidism).

Question 25

A patient has high PTH, high calcium, and low phosphate. What is the likely condition?

Answer 25

Primary hyperparathyroidism (parathyroid adenoma).