THYROID AND THYROID DISEASE Flashcards
What are the arteries which supply the thyroid gland and where do they branch from?
Superior thyroid artery is a branch of the external carotid
Inferior thyroid artery is a branch of the thyrocervical trunk
Thyroid ima artery is small and not always present. Either a branch of the aorta or the brachiocephalic trunk.
In the thyroid, what substance fills the follicles?
Colloid
What is the role of the c-cells (the parafollicular cells) of the thyroid gland?
To make calcitonin
On histological examination, what would the thyroid follicles of someone with underactive thyroid disease look like?
Flattened follicular epithelial cells with increased colloid
On histological examination, what would the thyroid follicles of someone with overeractive thyroid disease look like?
Tall columnar epithelial cells with reduced colloid
What is congenital hypothyroidism?
Failure of the gland to develop as a result of a genetic mutation such as PAX8.
What is a thyroglossal cyst?
Failure of thyroglossal duct to atrophy after the thyroid has migrated.
What are the functions of thyroid hormone?
Increase basal metabolic rate
Regulate long bone growth (with GH)
Neural maturation
Cardiovascular - positively chronotropic and inotropic
Increase body’s sensitivity to catecholamines (eg adrenaline)
CNS - regulates alertness
What are the two forms of thyroid hormone that are made by the thyroid follicles?
Thyroxine (T4) and Tri-iodothyronine (T3)
Which form of thyroid hormone is most abundant in the blood?
T4 - 60-150 nmol/L
T3 - 1.2-2.9 nmol/L
But most of this is bound to proteins
What is the normal range of TSH in the blood?
0.3-4.5 mU/L
When we measure levels of thyroid hormone in the blood what are we actually measuring?
The amount of free T4 (9-22 pmol/L)
Which form of thyroid hormone is the most bioactive?
T3
What effect does thyroid hormone have on insulin?
It is antagnostic
How does thyroid hormone affect growth hormone releasing hormone?
It decreases the secretion of GHRH
What hormones do thyroid hormones have an effect on?
Insulin
Growth hormone releasing hormone
Adrenaline
Thyroid releasing hormone
In which part of the cell does thyroid hormone have its affect?
DNA - binds to TR response elements
Over which tracheal cartilages is the thyroid gland found?
Second and third
What attaches the thyroid gland to the trachea?
Pretracheal fascia
Does the thyroid gland move with the trachea and larynx during swallowing?
Yes, unless the tongue is protruded.
What are the veins that drain the thyroid gland?
Superior thyroid vein
Middle thyroid vein
Inferior thyroid vein
What are the four groups of nodes that drain the lymphatics from the thyroid gland?
Prelaryngeal
Pretracheal
Paratracheal
Deep cervical
How many days worth of thyroid hormone is normally stored in the thyroid gland?
100 days - this means it takes a long time for an acquired hypothyroidism to manifest as symptomatic.
What is the amino acid used to make thyroid hormone?
Tyrosine