Endocrinology - Thyroid Flashcards
(37 cards)
What two processes must iodine undergo for thyroid hormone synthesis?
Oxidation and organification
Iodine needs to be oxidized to I2 and added to organic structures.
What role does Thyroid Peroxidase (TPO) play in thyroid hormone synthesis?
- catalyzes oxidation of iodine
- organification of iodine into MIT/DIT
- coupling of MIT/DIT into T3/T4
TPO antibodies are common in autoimmune thyroid disease.
What is thyroglobulin?
A thyroid hormone precursor protein produced by thyroid follicular cells containing numerous tyrosine molecules
It is involved in the synthesis of T3 and T4.
How is Triiodothyronine (T3) formed from Thyroxine (T4)?
Through the action of 5’ deiodinase
Most conversion occurs in peripheral tissues.
What is the Wolff-Chaikoff Effect?
A mechanism where excessive iodine inhibits thyroid peroxidase leading to decreased production of T3 and T4
It can lead to hypothyroidism in some cases.
What is the Job-Basedow phenomenon?
An iodine-induced hyperthyroidism; A condition of thyrotoxicosis that develops in iodine-deficient individuals with thyroid abnormalities after administering iodine
What is the function of Thyroxine-Binding Globulin (TBG)?
Carries thyroid hormones in the bloodstream
Most plasma thyroid hormone is T4, and almost all T4 is bound to TBG.
What happens to TBG production during pregnancy?
Increased production due to estrogen
This raises total T4 levels while TSH and free T4 remain normal.
List some major effects of thyroid hormones on metabolism.
• ↑ carbohydrate metabolism
• ↑ lipid metabolism
• ↑ basal metabolic rate
• ↑ Na/K ATPase pumps
• ↑ oxygen demand
• ↑ respiratory rate
• ↑ body temperature
Hypothyroid patients often experience weight gain, while hyperthyroid patients may lose weight.
What cardiac changes are associated with thyroid hormones?
Increased β1 receptors, cardiac output, and heart rate
Hypothyroid patients may experience bradycardia, while hyperthyroid patients may experience tachycardia or arrhythmias.
How do thyroid hormones affect bone density?
Increase bone turnover and stimulate bone resorption
Hyperthyroidism can lead to osteoporosis and hypercalcemia.
What are the effects of thyroid hormones on CNS development?
Required for CNS maturation
Childhood hypothyroidism can lead to conditions like cretinism.
Clinical features of hypothyroidism
- Lethargy and fatigue
- Weakness
- Cold intolerance
- Weight gain with loss of appetite
- Constipation
- Hyporeflexia
- Dry, cool skin
- Coarse, brittle hair
- Bradycardia
Major cause of congenital hypothyroidism
Thyroid dysplasia or aplasia
Why don’t most children with congenital hypothyroidism do not have symptoms at the time of birth?
The placenta supplies the fetus with maternal thyroid hormone (neonatal screening is required within 24-48 hours of birth)
Clinical features of congenital hypothyroidism
- abdominal distention
- umbilical hernia
- prolonged neonatal jaundice
- hypotonia
- decreased activity
- poor feeding
- adipsia (absent thirst)
- macroglossia
- hoarse cry
A complication of severe, untreated congenital hypothyroidism that leads to impaired development of the brain and skeleton resulting in short stature, delayed fontanelle closure, and permanent intellectual disability.
Cretinism
7 Ps of congenital hypothyroidism
- pot-bellied
- puffy face
- protruding umbilicus
- protuberant tongue
- poor brain development
- prolonged neonatal jaundice
Causes of acquired hypothyroidism
- Hashimoto thyroiditis
- iatrogenic
Best initial screening test for thyroid disorders
Thyroid function test (TSH and if abnormal T4)
Confirmatory test for primary hypothyroidism
Free T4
How is hypothyroidism is associated with infertility?
- Increased prolactin
- Low FSH/LH
- Disruption of menstrual cycle
- Low sperm count
A syndrome that causes abnormal findings on thyroid function tests in patients with severe illness which may be caused by cytokines, commonly causing decreased T3 levels with normal T4 and TSH. (Low T3 syndrome)
Euthyroid sick syndrome (non-thyroidal illness syndrome)
First line treatment of hypothyroidism
- Levothyroxine
