Thyroid Hormone Function Flashcards
What are thyroid follicles?
Structural units of the thyroid gland made up of follicular cells creating a ring
What are colloids?
A glycoprotein in the centre of the thyroid follicles
What are follicular cells?
The cells which secrete thyroid hormone and form the ring of thyroid follicles
What are thyroid hormones?
Iodine containing hormones derived from two tyrosine amino acids linked with iodine
What are the three types of thyroid hormones produced?
T3, T4 and rT3
What does T4 stand for?
Thyroxine
What is thyroxine (T4)?
The precursor hormone that follicular cells produce
What happens to thyroxine (T4)?
It is converted to triiodothyronine (T3) or rT3
What is triiodothryonine?
The biologically active thyroid hormone
What is the more uncommon way of synthesising T3?
DIT+MIT
What is the more common way of synthesising T3?
DIT+DIT which form T4 which is then converted into T3 or rT3
What is rT3?
It is an isomer of T3 which is not very common and is unhelpful
What is the steps for the synthesis of thyroid hormones?
- Follicular cells produce enzymes and thyroglobulin for colloid
- I- is co-transported with Na+ into the colloid
- Enzymes add iodine to thyroglobulin to make T3 and T4
- Thyroglobulin is taken back into the cell and enzymes seperate T3 and T4 from protein
- Free T3 and T4 enter the circulation
What type of T3 and T4 are biologically active?
Free or unbound T3 and T4
How do T3 cells act?
By binding to thyroid receptors that regulate expression of thyroid responsive genes
What do thyroid hormones do?
- Increase mitochondrial activity and glucose oxidation
- Increase basal metabolic rate and heat production
What three thing stimulate thyroid hormone production?
- Low levels of thyroid hormones
- Low metabolic rate
- Decreased body temp
What is hyperthyroidism?
Too much thyroid hormones secreted
What is the most common disease associated to hyperthyroidism?
Grave’s disease
What causes Grave’s disease?
When the body produces thyroid stimulating immunoglobins which mimic the action of TSH resulting in too much T3 and T4
What are signs and symptoms of Grave’s disease?
- Muscle weakness
- Muscle tremor
- Rapid heartbeat
- Enlarged thyroid gland
What is primary hypothyroidism?
When the thyroid gland does not make enough thyroid hormones due to iodine deficiency
What is secondary hypothyroidism?
When the body does not produce enough TSH due to a tumour of the anterior pituitary
What is tertiary hypothyroidism?
When the hypothalamus does not make enough TRH
What are the signs and symptoms of hypothyroidism?
- Slow oxygen consumption
- Slow speech
- Slow heartbeat
What is the most common disease associated with hypothyroidism?
Goiter
