The Thyroid Gland Flashcards
Diagram of the thyroid
Moves up when swallowing
30% of people have the extra pyramid
Colloid contains mucus and extracellular fluid
Diagram of thyroid gland
Parathyroid glands embedded in thyroid (produces calcium)
Left recurrent laryngeal nerve run close (supplies vocal chords)
Embryology of thyroid gland
Thyroid histology
Red blood vessels - red
White line/dots - where hormones are being made
Production of hormone in thyroid gland
TSH - thyroid stimulating horme
TG - Thyroglobulin (made by binding of TSH)
TPO - Thyroid peroxidase enzyme (made by binding TSH)
Chemical reactions in the thyroid gland
What happens during deiodination of triiodothyronine
Thyroxine (T4-prohormone) deiodinated to triiodothyronine (T3) - bioactive form
Deiodinated in a different position to produce reverse T3 (inactive)
T4 is converted by deiodinase enzyme
T3 - 80% from deiodination 20% from thyroidal secretion
T3 provides almost all the thyroid hormone activity
How is T3 and T4 transported in the blood
Bound to plasma proteins (inactive)
- Thyroid-binding globulin: TBG (70-80%)
- Albumin (10-15%)
- Prealbumin
Only 0.05% T4 and 0.5% T3 is unbound (bioacitve components
What does T3 do
Alter gene expression by binding onto thyroid hormone receptor
What is the TSH in newborns
Heel-prick test
What is untreated congenital hypothyroidism called
Cretinism
Why is thyroid essential for fetal
Growth and development
CNS
What action does thyroid homrones have
T4 - 7-9 days
T3 - 2 days
What is the Wolff Chaikoff effect
Ingest high levels of iodine to reduce thyroid hormone
How do you control thyroid hormone production
Negative feedback
Who is more predisposed to thyroid
Women 4:1
How does hypothyroidism arise
Hashimoto’s thyroditis disease
Graves’ disease (rarely)
Presence of one autoimmune disease increases risk of others
Symptoms of primary hypothyroidism
Eventual myxoedema coma
Cold intolerance
WHat is levothyroxine and how can it help
It replaces T4
Hyperthyroidism (by blocking the production of T3 and T4 and replacing it)
Common dose 100 mg
Administered orally
Might get weight loss or headache, heart attack and rapid HR
Why isn’t a T3 drug used
Because it has no effect
More expensive
Using a combination of T4/ T3 reports what
Improvement in wellbeing
May have complications of toxicity - palpitations, tremor, aniety - surpresses TSH
What are causes of hyperthyroidism
Graves disease - gland is smoothly enlarged and overactive
Toxic multinodular goitre
Solitary toxic nodule
Symptoms of hyperthyroidism
What happens in graves disease
Antibodies bind and sitmulate TSH receptor in thyroid
Other antibodies bind to muscles behind eye which causes exopthalmos - bulging of the eye, sore
Other antibodies stimulate growth of soft tissue of shins - pretibial myxoedema
