Which three hormones does the thyroid produce?
- Thyroxine (T4)
- Triiodothyronine (T3)
The parathyroid glands are responsible for regulation of what in the body?
How much does the thyroid gland weigh?
How can the thyroid gland be imaged?
- Iodine uptake (it is highly vascular)
Describe the cells involved in the structure of the thyroid gland
Follicular cells surround colloid
Parafollicular C cells are dispersed rarely
What is a colloid?
Mixture of substances
How are T3 and T4 synthesised?
Iodine is taken up by follicle cells and attaches to tyrosine residues forming monoiodotyrosine (MIT) and di-iodotyrosine (DIT) units.
Coupling of units occurs with MIT + DIT forming T3 and DIT + DIT forming T4
Where are T3 and T4 stored until they are required?
Which two drugs are used most to treat hyperthyroidism?
- Propylthiouracil (PTU)
How do carbimazole and PTU function?
Inhibits binding of iodine to tyrosine residues preventing formation of T3 and T4
Which thyroid hormone comprises around 90% of all secreted thyroid hormones?
Which thyroid hormone is more potent?
Which enzyme is responsible for the conversion of T4 to T3?
Where does the conversion of T4 to T3 largely occur?
Liver and kidneys
Why do do pharmacotherapies for hyperthyroidism not work instantly?
They inhibit formation of T3/4
There is a large reservoir of these hormones already built up in the colloid
To have an effect these hormone stores must first be used up
What induces T3/4 release from follicle cells?
Which plasma proteins can T3/T4 bind to?
- Thyroxine binding globulin (70%)
- Transthyretin (20%)
- Albumin (5%)
Since T3 is the biologically active form, where does it act upon?
What effect does T3 have when bound to nuclear receptors?
Alters transcription of certain genes
Metabolic state correlates most directly with what?
(moreso that total concentration)
Why do thyroid hormones increase basal metabolic rate? (3)
- Increase no. and size of mitochondria
- Increase O2 use and rates of ATP hydrolysis
- Increase synthesis of respiratory chain enzymes
In which two ways is carbohydrate metabolism increased by thyroid hormones?
- Blood glucose levels increase as glycogenolysis and gluconeogenesis are stimulated
- Insulin-dependent glucose uptake into cells is increased
How is protein metabolism impacted by thyroid hormone release?
There is increased protein synthesis
How do thyroid hormones increase responsiveness to adrenaline and sympathetic neurotransmitters?
Increasing no. of receptors
In hyperthyroidism, there is cardiovascular responsiveness to rasied thyroid hormones. How can this be treated pharmacologically?
Why is propranolol the preferred beta blocker for cardiovascular responsiveness to thyroid hormones?
It reduces the symptoms of cardiovascular responsiveness
It has inhibitory action upon deiodinase enzymes blocking conversion of T4-T3 which provides a minimal but added therapeutic benefit
The thyroid stimulating hormone receptor is which type of receptor?
G protein coupled
When are thyroid hormones
a) Late at night
b) In the morning
How many type of deiodinase enzymes are there?
Where is type I deiodinase enzymes found?
Liver and kidney