Functions and Disorders of the Thyroid Flashcards
thyroid gland = where is this found?
wrapped around your trachea and has a good blood supply.
where is the parathyroid glands and what do they do?
top and bottom of the thyroid and regulate calcium
thyroid hormones require what?
iodine
what happens in iodine deficiency?
peopel develop goitres in order to get as much iodine as possible and can also give this dificiency to offspring who will be intelleculy disabled due to not enough thyroid hormone
what do thyroid homrones do?
Essential for growth and development - active mental processing- intellictuly
Thermogenesis
Basal metabolic rate,
what are the 2 thyroid hormones? How are there made?
Thyroxine (T4) - inactive precursor
tri-iodothyronine (T3) - active
formed by splicing together tyrosine and adding iodine
what is reverse T3
inactive form of T3
How is the thyroid controlled?
Hypothalamus releases TRH (thyrotrophin releasing hormone). This stimulates the anterior pituitary to release TSH (Thyroid stimulating hormone) which is released into blood driving production of T4 and T3 from thyroid. T3 acts directly on its cells and T4 is converted into T3 before doing the same.
They also work in a negative feedback loop on the hypothalamus and the anterior pituitary
when normal what is there more of in the blood T4 or T3?
T4
when you have an iodine deficiency what gets released more T4 or T3?
T3
the thyroid follice - where do T4 and T3 vome from?
Between the colloid cells within the thyroid epithelial cells in the thyroid follicle .
How is thyroid hormones secreted?
Awful
Thyroid epithelial cells catch iodine which has been pumped in from blood though and pumps it into the colliod cells. The iodine is concentrated in the colloid.
The thyroid epithelial cells also have thyroglobulin which has lots of tyrosine residuals. These tyrosine residuals in the presence of TPO (tyrosine peroxidase) iodinates the tyrosine in the thyroglubulin. It does this by first making monoiodine, diodinine, T3 (caused by monoiodine and diodinine being spliced together) and T4 (caused by 2x diodinine being spliced together).
They are then brought into thyroid epithelial where it is degraded releasing T4 and T3 which can be secreted into the blood.
what controls T3 and T4 secretion
TSH
what happens to T3 and T4 once they are in the blood?
Transported bound to proteins - thyroxine binding globulin (TBG), transthyretin and albumin.
There is some free hormones
is T3 and T4 active when they are bound?
No
How is thyroid hormones brought into cells?
Active transport brings T3 and T4 into cells.
What happens to T3 in cells?
T3 can work directly and affect transcription through nuclear T3 receptors. This alters mRNA and metabolism, function, growth.
how is T4 made into T3 in cells?
Deiodinase 1 = turns T4 into T3 and reverse T3
Deiodinase 2 = turns into T3
Deiodinase 3 = turns into reverse T3
Can T3 be exported back into the blood and what cells do these?
Yes and kidney, liver, muscle cells do this
What are some clinical aspects of thyroid dysfunction?
Thyroid enlargements - goitre (diffuse or nodular
Increased hormone production Hyperthyroidism, or decreased hormone production Hypothyroidism.
Hyperthyroidism - what are the clinical features of this?
Height intolerance, sweating, anxiety, weight loss but increased appetite, fatigue, palpitations, tremor, muscle weakness, GI disturbances
What are causes of hyperthyroidism?
Graves disease
Multinodular Goitre
Single toxic nodule
Thyroiditits - viral, post partum
Other causes
What causes Graves disease?
Stimulating antibodies to the TSH receptors driving T4/T3 production causing the thyroid to hypertrophy (large smooth goitre).
what do 50% of graves patients get?
Ophthalmopathy
How do you diagnose graves?
Screening - historically you’d give people radioactive iodine to look at thryoid.
Does graves involve the full thyroid gland being active?
Yes
Graves Ophthalmopathy?
Retraction of the eyelids and proptosis (eyes pushed outwards), they get red, gritty, sore and swollen. Can affect eyesite.
What causes Graves Ophthalmopathy?
TSH receptors antibodies bind to TSH receptors on orbital fibroblasts leading to release of cytokines and stimulation of these fibroblasts, some of which can be made into adipocytes which cause swelling or they chuck out glycosaminoglycans which can bring in water.
How do you treat graves disease?
Carbimazole - inhibits thyroid hormone synthesis (TPO) and could decrease TSH receptor AB titre.
Radioiodine - high risk of hypothyroidism with standard dose and may worsen Ophthalmopathy.
Sub total or total thyroidectomy
Beta-blockers can be useful for control of symptoms.
How to treat Ophthalmopathy?
Steroids (immunosupression) may be used for treating active Ophthalmopathy.
Selenium supplementation (reduce inflammation)
Multinodular Goitre - what is active in these?
The nodules excrete alot but the patches around it dont as they have gotton the idea that there is too much T3 and T4 in the system
Do goitres get worse with age?
Yes
What causes nodular goitres?
Local growth factors
What happens to T3 and T4 when there is large levels of goitre?
they increase
How do you treat multi-nodular goitre/ toxic nodule?
Radioiodine - lower risk of hypothyroidism than graves as it will only concentrate on the nodules with increased T3, T4 and not the ones behaving normally.
No chance of remission with carbimazole you can’t get off it or you’ll get the giotre back
Surgery for patients with goitre/tracheal compression/deviation
Thyroiditis - viral or postpartum - are any tissues active?
No
What happens in thyroiditis
Pre-formed thyroid’s in the thyroid follicles are destroyed by inflammation and the thyroid hormones released into blood causing hyperthyrodism.
Then you get hypothyrodism because all the thyroid homrones are gone and the thyroid is damaged.
You then go back to normal (euthyroid) as the thyroid cells are made new.
What is the treatment for thyroiditis?
Normally nothing
What are the clinical features of hypothyrodism?
Weight gain, tiredness, cold itolerant, constipation, muscle stiffness, hyperlipidaemia, dry hair and skin. You might not get a goitre but you might
What are common causes of hypothyroidism?
Hashimoto thyroiditis
Iatrogenic (post surgery or radioactive iodine),
Spontaneous atrophic
Tempory thyroiditis - e.g. viral or postparum
What causes Hashimoto thyroiditis?
Antibodies attack thyroid making it permanently underactive. Runs in families
What are uncommon causes of hypothyroidism?
Hypopituitarism
Congenital (screening programme)
Iodine deficiency
Drug-induced
How do you treat hypothyrodism?
Oral T4 to normalise TSH and T4. Returns the patient to a clinical euthyroid state.
Some patients may get combined T4/T3 if they cant convert T4 to T3.
