General thryoid disorders (7) Flashcards
where is the thyroid located
It is located in the neck
What is the origin of the thyroid?
Back of the tongue
Where is the foramen caecum?
Dimple at the back of the tongue (left by the disappearing THYROGLOSSAL DUCT)
What is the adult thyroid weight?
20g
How many lobes are there? Which is the largest?
2
Right lobe is larger than the left
What glands are found embedded in the thyroid?
Parathyroid glands
What important nerve runs close to the thyroid gland and what does it supply?
recurrent laryngeal nerve. innervates the larynx (voice box) allowing speech
what would happen if the recurrent laryngeal nerve was damaged
Damage can cause changes in quality of voice, or even difficulty talking Thus all thyroid surgeons mention this when obtaining consent for thyroidectomy.
where does the thyroid gland originate
base of the tongue where a midline outpouching forms of the floor of the pharynx
what is the thyroglossal duct
outpouching forms a ducht which elongates down.
what happens after the thyroglossal duct forms
it migrates down the neck and divides into 2 lobes
what is the foramen caecum
(at week 7) where the duct disappears leaving a dimple at the back of the tongue. the thyroid gland then develops.
what are the 3 problems that can occur with development of the thyroid
agenesis, incomplete descent and thyroglossal cyst
what is agenesis
complete absence of the thyroid
what is incomplete descent
it may not descend to the correct point in the neck. this may cause problems with delivery (i.e. base of tongue to trachea).
what is thyroglossal cyst
the thyroglossal duct may persist. cysts may form - presenting as a lump years later
what is lingual thyroid
where the thyroid tissue barely descends at all and remains very close to the back of the tongue - this can cause problems with breathing. (complete failure to descend from base of tongue )
what is thyroxine
Essential for normal brain development. Controls cellular activity
what is a cretin
an individual with irreversible brain damage caused by lack of thyroxine
what are the features of cretinism
lower IQ than normal. stunted growth.
how is cretinism prevented
all babies at 5-10 days have a heel prick test to acquire blood to test thyroid function (measuring TSH). If TSH is high thyroxine is given immediately.
Guthrie Test for Phenylketonuria is also done. The test isn’t done immediately after birth because the neonate may have the mother’s thyroxine
what is Thyroxine binding globulin
a specific plasma protein which binds 75% of thyroxine in the circulation
what are the roles of the thyroid gland
Normally responsible for the synthesis, storage and secretion of thyroid hormones
what is the role of thyroid hormones
regulate growth, development and basal metabolic rate
What is the epidemiology of Thyroid Disease
Affects 5% of the population. Female:Male ratio = 4:1. Overactive and underactive thyroid occurs at equal frequency
What is myxoedema - primary hypothyroidism
This is primary thyroid failure causes thyroxine levels to decline. Adenohypophysis detects this fall and secretes TSH. TSH level rise - to try and stimulate the production of more thyroxine. Eventually TSH levels will fall as it becomes exhausted
What are the two causes of myxoedema - primary hypothyroidism
Autoimmune damage to the thyroid and Thyroidectomy which is an operation that removes or damages the thyroid gland
What is the Hypothalamo-pituitary-thyroidal axis
The hypotalamus secretes TRH, which stimulates adenohypophysis to secrete TSH, which stimulates thyroxine release from thyroid. Thyroxine release has a direct negative feedback effect on the pituitary to inhibit TSH production. It also has an indirect negative feedback effect on the hypothalamus to inhibit TRH production. These negative feedback loops make sure that blood thyroxine concentration hardly changes
Why is only TSH measured when thyroxine is missing.
if you’re missing thyroxine you will have high TSH and TRH. Only TSH is measured because TRH is pretty much undetectable in the blood
What are the features of primary hypothyroidism (everything slows down)
Deepening voice. Depression and tiredness. Cold intolerance. Weight gain with reduced appetite. Constipation (bowels slow down). Bradycardia. Eventual myxoedema coma (brain stops functioning due to lack of thyroxine). Amenorrhoea may occur in late disease. Heart enlargement
What is the treatment of hypothyroidism
If not treated, cholesterol increases causing death from MI/stroke. Treatment involves giving thyroxine daily. Monitor TSH and adjust dose of thyroxine until TSH is normal
What is primary hyperthyroidism/thyrotoxicosis
Overactive thyroid gland makes too much thyroxine. TSH falls to zero - because there is no need to stimulate the production of thyroxine
What are the clinical features of primary hyperthyroidism/thyrotoxicosis
Myopathy. Mood swings. Feeling hot in all weather. Diarrhoea. Increased appetite but weight loss. Tremor of hands. Sore eyes. Goitre (enlarged thyroid). Sleep difficulties. Palpitations
What are the causes of primary hyperthyroidism/thyrotoxicosis
Graves’ disease triggers hyperthyroidism because the immune system produces an antibody which pretends to be TSH. The antibody binds to the TSH receptor and the thyroid gland becomes overactive. This can lead to goitre. Other antibodies bind to muscles behind the eye causing exophthalmos(swollen eye). Other antibodies stimulate the growth of soft tissue on the shin and causes pretibal myxoedema (hypertrophy).
what are the features of primary hyperthyroidism/thyrotoxicosis (everything speeds up)
Increases BMR. Raised body temperature. Weight loss due to increased calorie burning. Tachycardia
What is graves disease
Whole gland is smoothly enlarged and the whole gland is overactive
What is pretibal myxoedema
Its the swelling (non-pitting) that occurs on the shins of patients with Graves’ disease. Caused by the growth of soft tissue. This is different to myxoedema/hypothyroidism
