Endo 4 - Hypothyroid Disorders Flashcards
Which hormone switches on follicular cells in the thyroid gland?
TSH
What is Thyroxine important for?
keeping BMR high
What are the white bits seen near the thyroid on a scan?
Colloid, white bits where thyroxine is being released
What are some of the effects of hypothyroidism?
- reduced BMR
- cold intolerance
- bradycardia
- speech slows down
- tongue gets thick
- weight gain
- loss of appetite
- lethargy
- depression
- constipation
Will TSH be high or low?
High
What hormones are secreted by the thyroid?
T3 and T4
Is T3 or T4 the prohormone?
T4
Which hormone is the pharmacologically active one?
T3
Which form is mainly released by the thyroid?
T4
What converts t4 to t3?
Deiodinase
Describe the mechanism of action of thyroxine?
- Thyroxine enters the target cell
- t4 gets converted to t3 via deiodinase
- T3 binds to thyroid hormone receptor in the nucleus
- heterodimerises with a retinoid X receptor
- this then binds to the thyroid response element which causes changes in gene expression
What is the T4 replacement drug?
Levothyroxine Sodium
What is the t3 replacement drug?
Liothyronine Sodium
What is thyroxine replacement used for?
Autoimmune Primary Hypothyroidism
Iatrogenic primary hypothyroidism
How often is the drug taken?
Daily
What do you use to guide dosage?
Want to suppress TSH to within reference range
Describe the levels of TSH in someone with primary thyroid failure?
HIGH
Describe the levels of thyroxine in someone with primary thyroid failure>
Low
What is secondary hypothyroidism?
Problem with the pituitary
What measurement is used to guide the dosage in secondary hypothyroidism?
as there is no TSH production, you guide dosage using free T4 levels and keep within reference range
What is the clinical use of Liothyronine (t3)
Myxoedema coma
you give I.V. liothyronine as much faster than levothyroxine
When might you give combined t3 and t4?
Some patients do not feel better with just t4, so give t3 as well as more potent
What are some side effects of combined therapy of t3 and t4?
will suppress TSH completely, difficult to get right dosage
patients may complain about symptoms of thyrotoxicosis
Describe some adverse side effects of thyroid hormone over replacement?
- increased bone turnover
- reduced BMD
- risk of osteoporosis
- increased energy expenditure
- weight loss
- tachy
- tremor
- nervousness
What is the half life of t3?
2-5 days
What is the half life of t4?
6 days
What plasma protein is t3 and t4 bound to?
thyroxine binding globulin
What can cause an increase in the production of plasma proteins?
pregnancy
prolonged treatment with oestrogen
What can cause a decrease in the amounts of plasma proteins?
liver failure as most plasma proteins are made there
malnourishment
