thyroid disorders

Question 1

what is the thyroid gland

Answer 1

The thyroid is a butterfly-shaped gland in the neck, just below the thyroid cartilage (Adams apple).
It is made up of a series of follicles, an outer layer of follicle cells surrounding a lumen of gelatinous colloid, including thyroglobulin, and associated parafollicular cells (C cells).
Thyroid hormones, thyroxine (T4) and triiodothyronine (T3) are produced and secreted by the follicles.
Calcitonin is produced by the parafollicular cells.

Question 2

Disorders of thyroid gland

Answer 2

Dysfunction can result in too much or too little thyroid hormone being produced.
Enlargement of the thyroid gland can occur (goitre) in both hypothyroidism and hyperthyroidism but is not always present.
Autoimmune destruction (Hashimoto’s thyroiditis), auto-antibodies (Grave’s disease), dietary iodine deficiency, inflammation, pituitary tumours, inherited disorders can all affect thyroid hormone production.

Question 3

what is Hypothyroidism
symptoms
treatmebt

Answer 3

The thyroid gland does not produce enough thyroid hormones.
Symptoms develop over a period of time so may be overlooked.

Symptoms in adults include:
Tiredness, sensitivity to cold, weight gain, slow movements and thoughts, slow heart rate, muscle aches and weakness, dry thickened skin, brittle hair and nails, loss of sex drive, depression, confusion and memory loss, irregular or heavy periods, growth and mental retardation in children.

treatment
Hormone replacement with levothyroxine (identical to endogenous T4).
Long half life means dose is not often critical.
T3 (liothyronine) can also be given as it is faster acting but has a shorter half life than T4.
If a dietary iodine deficiency is underlying cause of hypothryoidism, give iodine supplement.

Question 4

what is hyperthyroidism
symptoms
treatment

Answer 4

Occurs when the thyroid gland produces too much thyroid hormone.
Common, particularly in women where 2% of women have hyperthyroidism.

Symptoms in adults include:
Sensitivity to heat, weight loss, anxiety, rapid heart rate, atrial fibrillation, bulging eyes, hair loss, longer period cycles, hand tremor, thirst, hunger.

treatment
Inhibitors of thyroid synthesis e.g. carbinazole and propylthiouracil inhibit thyroid peroxidase and prevent iodination of thyroglobulin
Long term use of inhibitors of thyroid synthesis can lead to thyroid hypertrophy and goitre
Surgical resection of the thyroid
Thyroid ablation with radioactive iodine.

Question 5

what is Hashimoto’s disease
symptoms

Answer 5

Hashimoto’s thyroiditis can cause the thyroid gland to not make enough thyroid hormone.
It is an autoimmune disease.
It occurs when the body makes antibodies that attack the cells in the thyroid.
Symptoms may include an enlarged thyroid gland (goiter), tiredness, weight gain, and muscle weakness

symptoms
fatigue
sweating
enlarged thyroid
tremoring hand
change in bowel movement
intolerance to heat
changes in mood

Question 6

90% of secreted thyroid hormone from the thyroid gland is the less potent “prohormone” T4 and 10% is the more potent T3.

Both T3 and T4 circulate as a bound inactive form, binding to thyroxine-binding globulin or albumin to improve solubility and preventing urinary excretion.

T3 and T4 must dissociate from their transport proteins to exert their biological effects.

T4 must also be “activated” to T3 in peripheral target tissues (especially liver and kidneys) through the removal of one iodine

T3 and T4 act via the intracellular thyroid hormone receptor, a hormone responsive transcription factor.

Question 7

what causes goitre

Answer 7

If you are deficient in iodine, you cannot make enough thyroid hormone.
This would result in hypothyroidism.

Negative feedback mechanism would be suppressed due to deficiency of thyroid hormone.

As a result, TRH and TSH would continue to increase prompting the thyroid gland to produce more thyroid hormone.

Subsequently, the thyroid gland swells in size result in a condition called goitre.

Question 8

thyroid hormone secretion

Answer 8

Tyrosine-rich thyroglobulin synthesized and released into the lumen.
Iodide is actively taken up from the blood transported into the lumen.
Enzyme thyroid peroxidase converts iodide to free iodine.
Oxidised iodine atoms iodinate tyrosine in thyroglobulin (1 or 2 iodines per tyrosine).
Mono- or di-iodotyrosines couple together to form thyroxine (T4) or Tri-iodothyronine (T3).
Taken up by follicular cell, lysosomal enzymes break down thyroglobulin, which allows T4 and T3 to diffuse into bloodstream.