7 - General thyroid disorders Flashcards
Where is the thyroid located and what shape is it?
located in the neck and shield-shaped
What are the lobes of the thyroid?
left and right lobe and an isthmus (and some people have a pyramidal lobe - which is a part oft he extension from the back of the tongue from which the thyroid originated)
Where are the parathyroid glands found?
at the four corners of the thyroid
What are the parathyroid glands involved in?
the control of calcium (but functionally, they have nothing to do with the thyroid)
What is the origin of the thyroid?
back of the tongue
What is the foramen caecum?
simple at the back of the tongue (left by the disappearing thyroglossal duct)
What is the average thyroid weight?
20g
What important neve runs close thyroid gland and what does it supply?
recurrent laryngeal nerve
it innervates the larynx (voice box), allowing speech
What is the origin of the thyroid gland?
- midline outpouching of the floor of the pharynx (tube with no function that connects the tongue and the thyroid)
- the outpouching form a duct which elongates down: THE THYROGLOSSAL DUCT
- it migrates down the neck and splits into 2
- by week 7, it is in its final position
- the thryoglosaal duct disappears (leaving a dimple at the back of the tongue)
What does aberrant mean?
in the wrong place
What is a lingual thyroid?
where the thyroid tissue barely descends and can cause problems with breathing
Where os thyroxine produced and what is it essential for?
in thy thyroid
essential for normal brain development
What is usually the cause of cretinism?
low iodine levels
What cells are the site of thyroxine synthesis?
thyroid follicular cells
What is the effect of thyroxine?
affects the basal metabolic weight (affects every cell)
What is the difference between thyroglobulin and thyroxine binding globulin?
Thyroglobulin - not in the circulation
TBG - in the circulation
Thyroglobulin - stores thyroxine
TBG - binds to thyroxine
What do thyroid hormones do?
regulate growth, development and basal metabolic rate (general)
What is myxoedema?
primary hypothyroidism/ primary thyroid failure
What is the most common causes of myxoedema?
autoimmune damage to the thyroid
thyroidectomy (since thyroid tissue is removed)
What happens to the hormones levels in myxoedema?
- Thyroxine levels decrease
- TSH levels rise (to try and stimulate the production of more thyroxine)
- Eventually, TSH levels will fall because It becomes exhausted
- TRH levels will also increase, but only TSH is measured because TRH is undetectable in the blood
What is the negative feedback mechanism for of thyroxine on the pituitary and the hypothalamus?
- direct negative feedback effect on the pituitary to inhibit production of more TSH
- also affects the hypothalamus, where it inhibits the production of TRH (thyrotrophs)
What is hyperthyroidism (thyrotoxicosis)?
What happens to the levels of hormones?
overactive thyroid gland
over production of of thyroxine
TSH falls to zero
What is pretibial myxoedema?
What is it caused by?
(non pitting oedema) swelling on the shins pf patients with graves disease
caused by the growth of soft tissue
What is the different between myxoedema and pretibial myxoedema?
myxoedema - primary hypothyroidism
pretibial myxoedema - a feature of graves disease, which causes hyperthyroidism
