Physiology Flashcards
(47 cards)
What three things does thyroid gland tissue secrete?
T3, T4 and calcitonin
What is required for the synthesis of thyroid hormones?
Iodine
What will happen if you live in an area where there is not enough iodine?
You won’t make enough thyroid hormones and hence will be hypothyroid
What is the difference, chemically, between T3 and T4?
1 iodine
Iodine is taken up by which cells?
Follicular cells
What does iodine attach to once it has been taken up? What does this form?
Iodine attaches to tyrosine units on thyroglobulin to form MIT and DIT units
How do carbimazole and PTU work?
They prevent iodination of tyrosine
What units need to be combined to form T3?
1 MIT and 1 DIT
What units need to be combined to form T4?
2 DITs
What happens to T3 and T4 molecules once they have been synthesised?
They are stored in colloid thyroglobulin until they are required
Which is the major biologically active thyroid hormone?
T3
Which thyroid hormone is produced in greater amounts?
T4
What happens to the majority of T4 produced?
It is converted to T3 in peripheral tissues
What chemical process changes T4 to T3?
5-monodeiodination (removal of 1 iodine)
What does 3-monodeiodination of T4 form?
rT3
Which family of enzymes regulates the conversion of T4 to T3?
Deiodinase enzymes
Where is deiodinase 1 found?
Liver and kidney
Which deiosinase enzyme is the major determinant of generating T3 from T4?
D2
Where is deiodinase 3 found?
Foetal tissue ad brain (except the pituitary gland)
What is the first step in releasing thyroid hormones?
TSH binds to its receptor on the surface of thyroid epithelial cells
What type of receptor is the TSH receptor?
GPCR
What happens when TSH has bound to its receptor?
GTP is converted to GDP and cAMP is produced
What allows T3 and T4 to be released from cells?
Increased cAMP
Where is most T3 and T4 found in the plasma? Why?
Bound to hormone binding proteins, since they are hydrophobic and lipophilic
