Functions and Disorders of the Thyroid Gland Flashcards
What is the thyroid gland?
Shield shaped gland in neck, sits under Adam’s apple, in front of trachea, with parathyroid glands sitting above and below
What are the effects of iodine deficiency?
TSH drives thyroid to produce more thyroxine –> goitre
What are the actions of thyroid hormones?
growth, development, basal metabolic rate control, thermogenesis (brown adipose), active mental processes
What are thyroxine (T4) and triiodithyroxine (T3) made from?
iodinated tyrosine residues
Which of T4 and T3 is active?
T3 (has lost one iodine to become active)
Outline basic thyroid secretion
hypothalamus (TRH) –> anterior pituitary (TSH) –> thyroid (T4, T3) –> tissues
What is the structure of the thyroid gland?
made of many follicles, inside is colloid - hormones made here
Within the follicular colloid which molecule is processed with in the presence of H2O2 and thyroid peroxidase (TPO) ?
thyroglobulin
Thyroglobulin enters the follicular cell to be
cleaved to produce T4 and T3
DIT and MIT are recycled
How does TSH impact T4 and T3 synthesis?
speeds up the cycle by stimulating via cAMP/calcium action by binding a GPCR
Why must thyroxine be carried in the blood?
it’s not water-soluble
What are the proteins that carry thyroxine?
T4-binding globulin (70%)
transthyretin (20%)
albumin (10%)
How is T3 produced?
conversion of T4 via deiodinase 1 and 2
How is rT3 produced?
conversion of T4 via deiodinase 1 and 3
What are the clinical aspects of hyperthyroidism?
weight loss, appetite, fatigue, heat intolerance, sweating, GI disturbance
How does Graves’ Disease lead to hyperthyroidism?
Ab stimulate TSH receptor to produce T4/T3
What are the clinical features of Graves?
large smooth goitre
technetium scan - hotspots over thyroid
50% have ophthalmopathy (retracted eyelids, lid lag, proptosis, redness, gritty sensation, swelling, blurred vision, vision loss)
How does Graves lead to ophthalmopathy?
Ab binding to TSH receptors on orbital fibroblasts –> production og glycosaminoglycans and fat which causes swelling of muscles and tissues behind the eye
How is Graves treated?
Carbimazole - inhibits TSH synthesis radioiodine (high hypothyroidism risk) thyroidectomy beta blockers good for symptomatic control steroids for immunosuppression
What are the clinical features of multinodular goitre?
large, lumpy nodules
technetium scan show fewer hotspots
can block trachea if very big
increased thyroid hormones occur at later stages
How is multinodular goitre/single toxic nodule treated?
radioiodine
surgery (esp. if tracheal compression)
long-term carbimazole
How does thyroiditis lead to temporary hyperthyroidism?
autoimmune disruption of tissue in thyroid
Any TSH stored is released from colloid
treatment not required as thyroid gland not overactive, so TSH stops being released eventually
What are the clinical features of hypothyroidism?
weight gain, tired, cold intolerance, muscle stiffness, constipation, hyperlipidaemia, dry hair/skin
What are common causes of hypothyroidism?
hashimoto's (autoimmune) - Ab attack thyroid - permanent iatrogenic - post-op - radioactive iodine spontaneous atrophy temporary thyroiditis - viral, post-partum
What are some uncommon causes of hypothyroidism?
hypopituitarism (not enough TSH - secondary hypothyroidism)
congenital
iodine deficiency
drugs
What is used to treat hypoparathyroidism?
oral thyroxine
