thyroid hormones Flashcards
What is the endocrine system?
A collection of glands that secrete hormones directly into the bloodstream.
What are the three major groups of hormones?
- Peptides
- Steroids (lipid soluble)
- Amino acid derivatives
What regulates thyroid hormones?
The hypothalamic-pituitary-thyroid (HPT) axis.
What is the role of Thyroid-releasing hormone (TRH)?
Stimulates anterior pituitary thyrotrophs to secrete thyroid-stimulating hormone (TSH).
What is the composition of Thyroid-stimulating hormone (TSH)?
It is a dimeric glycoprotein hormone composed of two peptide chains: alpha subunit and TSH-specific beta subunit.
What is the primary effect of TSH on the thyroid gland?
Increases the overall activity of the thyroid.
What is goitre?
Hypertrophy of the thyroid gland caused by excessive TSH stimulation and/or dietary iodine deficiency.
Describe the anatomy of the thyroid gland.
Butterfly-shaped, wrapped around the trachea below the larynx, with two lobes connected by an isthmus.
What are thyroid follicles?
Structures consisting of a single layer of epithelial cells surrounding a colloid-filled lumen.
What hormone do parafollicular (C) cells secrete?
Calcitonin.
What is the primary action of calcitonin?
Inhibits bone resorption and promotes calcium excretion by the kidneys.
What are the main thyroid hormones?
- Triiodothyronine (T3)
- Thyroxine (T4)
What is the most potent active form of thyroid hormone?
Triiodothyronine (T3).
What is thyroglobulin (TGB)?
A glycoprotein containing high content of tyrosine, synthesized by thyroid follicular cells.
What is iodide trapping?
The process where thyroid follicles take in iodide from blood capillaries and store it for future use.
What enzyme is key in the synthesis of thyroid hormones?
Thyroid peroxidase (TPO).
What is the process of organification in thyroid hormone synthesis?
The incorporation of iodine into tyrosine residues on thyroglobulin.
What is the mechanism of action of T3 and T4?
They act in the nucleus as ligands for the thyroid hormone receptor (TR), altering gene expression.
What physiological effects do thyroid hormones have?
- Increase metabolic rate
- Modulate nervous system activity
- Promote growth and maturation
What is hypothyroidism?
An underactive thyroid condition characterized by various symptoms like weight gain and cold intolerance.
What is Hashimoto’s disease?
An autoimmune condition causing destruction of the thyroid gland, leading to hypothyroidism.
What is cretinism?
A condition resulting from congenital lack of thyroid hormones, leading to intellectual disability and impaired growth.
What is the treatment for hypothyroidism?
Lifelong replacement therapy with T4 (Levothyroxine).
What is hyperthyroidism?
An overactive thyroid condition characterized by excess circulating thyroid hormones.
What is Graves disease?
An autoimmune hyperthyroidism condition caused by thyroid-stimulating autoantibodies.
What are common treatments for hyperthyroidism?
- Anti-thyroid drugs (e.g., Carbimazole, PTU)
- Radioactive iodine ablation
- Surgical resection
True or False: T3 and T4 must dissociate from TBG to exert their biological effects.
True.
