Thyroid Flashcards
What is thyroxine derived from?
Tyrosine
What type of gland is the thyroid gland?
Ductless
Alveolar
How many lobes does the thyroid gland have and how are they connected?
2 lobes connected by the isthmus
What is an enlarged thyroid gland called?
Goitre
What is the secretory unit of the thyroid gland?
Thyroid follicle
What kind of epithelial are found lining the colloid centre?
cuboidal or columnar
What protein is found in the colloid?
Thyroglobulin (Tg)
Why are the epithelial cells of the thyroid gland polarised?
To allow the movement of things through the cells
What does the apical membrane face?
The colloid
What does the basolateral membrane face?
the extracellular fluid
What do the C cells of the thyroid secrete?
Calcitonin
What is the sequence of hormones released to produce thyroid hormone?
TRH -> TSH -> T3 + T4
When TSH binds to follicular cells, what does it promote?
iodine uptake
production and released of T3 and T4
promotion of gland growth
What are the acute effects of TSH stimulation?
synthesis and secretion of T3 and T4
What are the chronic effects of TSH stimulation?
growth and division of follicular cells
enlargement of thyroid gland
Which enzyme is required for thyroxine synthesis?
Thyroid peroxidase
What kind of molecule is thyroglobulin?
large glycoprotein
How is thyroglobulin synthesised?
peptide produced is glycosylated at ER
translocated to Golgi
packaged into secretory vesicles
stored as colloid
What are the full names of T3 and T4?
tri-iodothyronine
tetra-iodothyronine
Are thyroid hormones fat or water soluble?
Fat soluble
Where is Tg iodinated?
At the apical surface
Which of T3 or T4 is more potent?
T3 is more potent
Which of T3 and T4 has the longer half-life and why?
T4 has a longer half-life
has a greater affinity for TBG
What is the full name of TBG?
Thyronine Binding Globulin
What effect does oestrogen have on the thyroid?
increased synthesis of TBG
decreased clearance of T3 and T4
What happens to T4 in the peripheral tissues?
T4 is converted to T3 by deiodination
What is the treatment for hypothyroidism?
T4
How do thyroid hormones increase BMR?
increase number and size of mitochondria
increase oxygen consumption and heat generation
increase nutrient utilisation
What effects do thyroid hormones have on the nervous system?
increase myelination
increase reflex speed
increase mental activity
How do the thyroid hormone affect the heart?
They increase cardiac output.
What are the features of cretinism?
mental retardation
coarse features
short stature
delayed sexual development
What are the signs of hyperthyroidism?
heat intolerance increased perspiration weight loss tachycardia increased appetite nervousness or tremors
Define exopthalmus
Bulging of the eyes that can occur as a result of hyperthyroidism
What is main cause of hyperthyroidism?
Grave’s disease
Autoimmune production of an antibody that stimulates the TSH receptors.
What is the treatment for hyperthyroidism?
Carbimazole
How does carbimazole work?
It prevents iodination of the thyroid hormones by inhibiting the enzyme thyroid peroxidase.
What are the signs of hypothyroidism?
cold intolerance weight gain bradycardia constipation dry skin and brittle nails poor concentration
What is the main cause of hypothyroidism?
Hashimoto’s disease
Autoimmune production of antibodies that block the TSH receptors.
How does the thyroid develop in an embryo?
Develops near the tongue and migrates to the base of the neck.
When must a heel prick test be done by?
before the baby is 21 days old
Where are the T3 receptors?
In the nucleus
Name some causes of hypothyroidism other than autoimmune
post-surgery radioactive iodine anti-thyroid drugs eg. carbimazole lack of TSH production iodine deficiency
Name some causes of hyperthyroidism other than autoimmune
excessive T4 therapy
excess iodine
ectopic thyroid tissue
What is the term used to describe normal levels of the thyroid hormones?
Euthyroid
What is a hypopit?
When both the TSH and free T4 are low
What is the crisis version of hypothyroidism and what are the signs?
Myxoedema coma
low temperature
unconscious
barely responsive to pain
What is the crisis version of hyperthyroidism and what are the signs?
Thyroid storm
very high temperature
high blood pressure
deranged
The availability of thyroid hormone is tied to the availability of…
iodine
