Thyroid hormones Flashcards
Where is the thyroid gland located?
Two lobes located either side of the trachea just below the larynx
Which two hormones are involved in causing thyroid hormone to be released?
Thyrotropin releasing hormone
Thyroid stimulating hormone
What is most of the thyroid gland composed of?
Epithelial follicular cells surrounding a colloid
How is iodine transported into the colloid?
The follicular cells trap iodide via a Na I symporter & it is oxidised to iodine and transported into the colloid
How do T3 and T4 which are synthesised in the colloid diffuse into the blood?
- bound to thyroglobulin
- re-enter follicular cells and bind to lysozymes
- cleaved from thyroglobulin and are lipophilic so diffuse into the blood
How long can thyroid hormone be stored for?
2-3 months in the colloid
Out of t3 and t4, which is the main hormonal product of the thyroid gland and which is more biologically active?
T4 = main hormone T3 = biologically active
What happens to T4 in peripheral tissues?
It is converted to T3
What occurs when the conc of thyroid stimulating hormone is increased for prolonged periods?
follicular hyperplasia & hypertrophy is induced
- Goitre = enlarged thyroid gland
How do thyroid hormones affect metabolism?
- increases metabolic rate in tissues
- increase oxygen consumption and thermogenesis
- needed for growth and development
- development of CNS
What clinical signs would be expected with hyperthyroidism?
Weight loss
Polyphagia = excessive eating/appetite
What is the main difference between lipid soluble and water soluble hormones?
Lipid = bind to receptors in the cytoplasm or nucleus of the cell Water = bind to receptors on the surface of the cell
