3: Anatomy and physiology of the thyroid gland Flashcards
What is the master gland of the endocrine system?
Pituitary gland
In relation to the thyroid, which hormone is secreted by the hypothalamus and acts on the pituitary gland?
TRH
Thyrotrophin releasing hormone
Which hormone is secreted by the pituitary gland and acts on the thyroid?
TSH
Thyroid stimulating hormone
Which hormones are released by the thyroid gland?
Thyroxine (T4)
Tri-iodothyronine (T3)
Calcitonin
Which glands are found on the posterior aspect of the thyroid?
4 parathyroid glands
Which nerve could be damaged in thyroid surgery, almost certainly getting you sued?
Recurrent laryngeal nerve
Unilateral - swallowing issues
Bilateral - lack of phonation
Removal of the parathyroid glands during thyroid surgery may result in ___.
hypoparathyroidism
Thyroid pathologies have typical appearances on which imaging modality?
Ultrasound
The thyroid takes up ___. This allows it to be seen on radionucleotide imaging.
iodine
From wikiped:
Low uptake suggests thyroiditis, high uptake suggests Graves’ disease,[4] and unevenness in uptake suggests the presence of a nodule.
What carrier protein is found in the follicle of thyroid cells?
Thyroglobulin (which carries T3 and T4)
What is the fluid area found in the central of a follicle?
Colloid
Thyroglobulin is found in which part of a thyroid follicle?
Colloid
What binds to thyroglobulin to produce thyroid hormones?
Iodine
How are thyroid hormones transported from the colloid to the follicular cells once they have been produced?
Pinocytosis
How are thyroid hormones transported from the follicular cells into the bloodstream?
Exocytosis
Where are C cells found?
What do they produce?
Parafollicular
Calcitonin
Iodine binds to what part of thyroglobulin to form the precursors of thyroid hormones?
Tyrosine residue
What is the biggest cause of hypothyroidism (i.e lack of thyroid hormone production) globally?
Iodine deficiency
What antithyroid drugs are used to treat hyperthyroidism?
How do they work?
Carbimazole, propylthiouracil
Inhibit iodination of thyroglobulin
Why do anti-thyroid drugs have a long onset of action?
Prevent NEW thyroid hormones from being made
Still residual thyroid hormone floatin around, and it’s got a half life of around 10 days
Which thyroid hormone is
a) most commonly secreted
b) most potent?
a) T4
b) T3
T4 must be converted to __ before it can work.
T3
More potent
Where is T4 converted to T3?
Liver and kidneys
Thyroid hormones are (hydrophilic / hydrophobic).
Hydrophobic
How are thyroid hormones similar to steroids?
Hydrophobic
Pass through cell membrane
Act on nuclear receptors to alter metabolism
Require carrier proteins to travel in blood
Thyroid hormones are released from follicular cells in response to which hormone?
TSH
On which carrier proteins are thyroid hormones transported in the blood?
Thyroxine binding globulin (TBG)
Transthyretin
Albuminnnn
When thyroid hormones are bound to carrier proteins, they are ___.
inactive
Free thyroid hormones are (inactive / active).
active
Where are thyroid hormone receptors found?
Everywhere
hence systemic effects
How do thyroid hormones work normally?
Bind to nuclear receptors to alter gene transcription for genes controlling metabolism, growth, reproduction etc.
Thyroid hormones (increase / decrease) the basal metabolic rate.
increase basal metabolic rate
What process responsible for generating body heat are thyroid hormones responsible for?
Thermogenesis
What effect do thyroid hormones have on the metabolism of carbohydrates, lipids and protein?
Increase the metabolism of all three
Which hormone’s secretion itself requires the action of thyroid hormones?
Growth hormone
The development of which organ is especially dependent on thyroid hormones?
Brain
How exactly do thyroid problems cause autonomic symptoms?
Increase expression of adrenaline receptors
> autonomic symptoms (tachycardia, sweating, anxiety etc.)
The related actions of the hypothalamus, pituitary gland, thyroid gland and their hormones are collectively known as what?
H-P-T axis
The levels of T3 and T4 affect the secretion of TRH and TSH. What is this an example of?
Negative feedback
TSH receptors, found on thyroid ___ cells, are examples of which type of receptor?
follicular cells
G protein coupled receptors
G protein receptor function involves the conversion of ATP to ___, which causes an effect in the cell.
cAMP
Measuring thyroid hormones in sick patients is not advised - why?
Non-thyroid illness
STRESS increases the secretion of thyroid hormones which can be misinterpreted
Stress (increases / inhibits) thyroid hormone secretion.
inhibits secretion
What external factors influence the secretion of thyroid hormones?
Temperature
Circadian rhythm
Which family of enzymes deactivate thyroid hormones?
Deiodinase enzymes
Different types of deiodinase enzymes are found in (the same / different) tissues of the body.
different tissues, different enzymes
Which deiodinase enzyme converts T4 to T3 in liver and kidney cells?
D2
Where are thyroid hormone receptors found in a cell?
Within the nucleus
Different __ __ receptors are found in different parts of the body.
thyroid hormone
What, related to thyroid hormone receptors, can produce signs and symptoms of hyper and hypothyroidism?
Gene mutations
Producing RESISTANCE TO THYROID HORMONES
What is the appearance of hypothyroidism called in
a) adults
b) babies?
Myxoedema
Cretinism
a bit old-fashioned now
What is thyroid stimulating immunoglobulin an important part of?
Graves disease
behaves like TSH but isn’t regulated by negative feedback, so it produces hyperthyroidism
