Hypothyroidism

Question 1

Describe the process of release thyroxine

Answer 1

Hypothalamus - TRH
Pituitary - TSH
Thyroid - thyroglobulin combines with iondine ion to form MIT and DIG which undergoes coupling reaction in presence of TPO to produce T4 and T3

Question 2

Describe the effect of primary hypothyroidism (myxodema)

Answer 2

Thyroid failure, autoimmune damage to the thyroid - less T4, TSH levels increase very high.

Symptoms: deep voice, depression, tiredness, cold intolerance, constipation, bradycardia, weight gain, loss of appetite.

Question 3

Describe what the Thyroid hormones are, and how they work

Answer 3

A healthy adult secretes both T4 and T3.

Thyroxine (T4) is a prohormone and get a converted to active T3 via deiodinase (majority of T3 is from T4 not from thyroid gland)

Thyroxine enters target cell, converted to T3, binds to thyroid hormone receptor in nucleus, then heterodimerses with retinoid X receptor, then this complex binds to thyroid response element that causes gene expression ,

Question 4

Describe the different hormone replacement therapies and adverse effects

Answer 4

1. Levothyroxine sodium (T4) (long half life 6days)
2. Liothyronine sodium (T3) (short half life 2 hours) - given in extreme condition myodema coma

Adverse effects: usually due to suppressed TSH

1. Skeletal - increased bone turnover, risk of osteoporosis
2. Cardiac - tachycardia
3. Metabolism - weight loss
4. Increased beta adernergic sensitivity - tremor and anxiety

Question 5

Describe role of TBG

Answer 5

Thyroxine binding globulin - T3 and T4 bound to plasma protein. Only free unbound thyroid hormone is available to tissue

Plasma binding protein increases in pregnancy and on prolonged treatment on oestrogen and phenothiazines. TBG falls in malnutrition and Liver disease