Thyroid Gland Flashcards
What does the thyroid gland produce?
Prohormone tetraiodothyronine (T4) and active hormone triiodothyronine (T3)
What is the function unit of the thyroid gland? Describe it
Thyroid follice; surrounded by a single layer of epithelial cells, follicular lumen itself is filled with colloid, and size of the epithelial cells and amount of colloid change with activity
What is colloid mostly composed of?
Newly synthesized thyroid hormones attached to thyroglobulin
How is T3 made?
80-90% is produced by peripheral conversion; 10-20% of circulating T3 comes from direct secretion from thyroid gland
What are some physiological states that are associated with a reduction in the conversion of T4 into T3?
Fasting, medical/surgical stress, catabolic diseases
What is the half life of T4?
6 days
What is the half life of T3?
1 day
Most circulating thyroid hormone is in what form?
T4
What are the main binding proteins that bind to T4 or T3?
Thyroxine-binding globulin (70%; higher affinity for T4 than T3), transthyretin (10-15%), albumin (15-20%)
Where is thyroxine-binding globulin synthesized?
Liver
What happens to T4 and T3 during hyperthyroidism?
Increased T4 and increased T3 resin uptake
What happens to T4 and T3 during hypothyroidism?
Decreased T4 and decreased T3 resin uptake
What happens to T4 and T3 during times of high thyroxine-binding globulin?
Increased T4 and decreased T3 resin uptake
What happens to T4 and T3 during times of low thyroxine-binding globulin?
Decreased T4 and increased T3 resin uptake
What happens to thyroxine-binding globulin and T3 during hepatic failure?
Decreased thyroxine-binding globulin and increased T3 resin uptake
