The Thyroid Gland Flashcards
What are the 2 active forms of thyroid hormone?
T3 triiodothyronine
T4 thyroxine
At what vertebral level does the thyroid gland sit at?
C5-T1
What 2 cells are found in the thyroid gland?
C (clear) cells
Follicular cells
What is the function of C cells?
Secrete calcitonin
What is the function of follicular cells?
Support thyroid hormone synthesis and surround hollow follicles
Manufacture thyroglobulin
Actively concentrate iodide
What is found in the centre of thyroid follicles?
Colloid
How is iodide transported into colloid?
Pendrin transporter
What inhibits iodide transport into thyroid gland?
Thiocyanates
Where is thyroid peroxidase found?
Colloidal side of cells
What is the role of thyroid peroxidase?
Catalyses the addition of iodide to tyrosine residues in thyroglobulin
What is made from the addition of one iodide to tyrosine?
MIT (monoiodotyrosine)
What is made from the addition of 2 iodide to tyrosine?
DIT (diiodotyrosine)
What is made from MIT+DIT?
T3
What is made from DIT+DIT?
T4
What plasma protein does T3 and T4 bind to?
Thyroxine-binding globulin
What is the typical half life for T3?
1 day
What is the typical half life for T4?
6 days
What deiodinates T4?
Deiododinase enzymes
What are the main functions of thyroid hormone?
Raises metabolic rate and promotes thermogenesis Increase hepatic gluconeogenesis Net increase in proteolysis Net increase in lipolysis Foetal brain development Critical for growth
What are the causes of hyperthyroidism?
Graves disease
Thyroid adenoma
What are the symptoms of hyperthyroidism?
Weight loss Heat intolerance Muscle weakness Increased HR Hyperexcitable reflexes
What are the causes of hypothyroidism?
Hashimoto’s disease
Idiopathic
Dietary iodine deficiency
What are the symptoms of hypothyroidism?
Weight gain Cold intolerance Slow speech Slow reflexes Fatigue Slow HR Weaker pulse
What is the term used for a thyroid gland enlargement?
Goitre
