Thyroid Physiology

Question 1

The Thyroid Produces and Secretes 2 Metabolic Hormones

Answer 1

Thyroxine (T4 ) and triiodothyronine (T3)
Required for homeostasis of all cells
Influence cell differentiation, growth, and metabolism
Considered the major metabolic hormones because they target virtually every tissue

Question 2

Iodine Metabolism

Answer 2

Dietary Iodine is essential for the synthesis of thyroid hormones

Dietary sources of Iodine: salt, kelp, yogurt, milk, eggs, strawberries, cheese, seafood

Daily absorption of 100-200 mcg of dietary iodine is sufficient

Question 3

Thyroxine Binding Globulin (TBG) - Carrier

Answer 3

Binds in circulation
One of three proteins, along either TTR and albumin responsible for carrying T3 and T4
TBG has the highest affinity for T3 and T4, but is present in the lowest concentration

Question 4

Transthyretin (TTR) - Carrier

Answer 4

Transthyretin (TTR) is a serum and cerebrospinal fluid carrier of the thyroid hormone Thyroxine (T4)

Question 5

Actions of Thyroid in Growth and Development

Answer 5

Necessary for normal growth in infants and children as evidenced by growth retardation observed in thyroid deficiency

Normal levels of thyroid hormone are essential to the development of the fetal and neonatal brain

Thyroid deficiency in infants results in lethargy, mental retardation, poor tone and an enlarged tongue

Question 6

Pathophysiology of Grave’s Ophthalmopathy

Answer 6

Volume of extraocular muscles & retrobulbar connective & adipose tissue is increased
Occurs because of accumulation of glycosaminoglycans (GAG)—hyaluronic acid
GAG secretion is stimulated by activated T-cell cytokines:
The initial activation of the T-cells is by thyrotropin (TSH) receptor antigen
TSHR is greater in the retrorbital tissue in Grave’s patients
There is a correlation between the severity of ophthalmopathy and serum TSH receptor antibody concentrations