Lect 22 - Thyroid Flashcards
Jan 30, 2019
The colloid is made up of what type of macromolecule?
glycoprotein
Parafollicular cells are also called what?
C cells
TRH acts on which cells? Where are they located?
Thyrotrophs in the anterior pituitary
How many amino acids make up thyrotropin releasing hormone?
three
Thyrotropin releasing hormone is secreted ________.
constant
Which second messengers does TRH work through?
IP3/DAG/Ca
Which second messengers does TSH work through?
cAMP and PLC
What is the breakdown of T3, T4, and rT3 in the blood?
90% T4, 9% T3, and 1% rT3
How is iodine taken in through the diet?
by iodide or iodate
What is the daily requirement of iodine?
150 micrograms
If you have an iodine deficiency how does the body compensate?
Increasing TSH levels leading to goiter
About how many tyrosine molecules does thyroglobulin have?
~70
What protein works with iodine on the basolateral membrane of follicular lumen cells in the thyroid?
sodium-iodide symporter
Thyroglobulin is present on the follicular membrane bound to which enzyme?
thyroperoxidase
Iodine is oxidized by TPO in a process known as what?
Organification
Molecules of MIT and DIT are joined in a process known as what?
Conjugation
What is bad about cabbage?
It inhibits iodine trapping in the thyroid
What does TSH stimulation do in terms of thyroglobulin?
Taken up by lysoendosomes from the follicular lumen
What are three inhibitors of steps in the thyroid hormone synthesis pathway?
1) PTU
2) high iodine concentration (competitive inhibitor)
3) perchlorate/thiocyanate
The TSH-receptor complex is clinically significant in what way?
Antibodies in the body can attack it, either stimulating or inhibiting it
When autoantibodies inhibit the TSH-receptor complex, what is the disease called?
Hashimoto’s
When autoantibodies stimulate the TSH-receptor complex, what is the disease called?
Grave’s
A high iodine concentration is clinically helpful in inhibiting uptake of what?
radioactive iodine
How is T4 converted to T3?
5’-deiodinase
Thyroid hormone works synergistically with which hormones to promote bone formation?
growth hormone and somatomedin
What is another name for somatomedin C?
IGF-1 (insulin-like growth factor 1)
Thyroid hormone has tons of effects on target tissues. What are some of these effects?
1) increased insulin synthesis and increased blood glucose
2) decreased body weight
3) increased CO
4) increased BMR
5) increased oxygen consumption and blood flow to tissues
6) muscle protein breakdown
What are the effects of TH on the heart?
1) stimulation of beta-1 adrenoreceptors
2) increased activity of sodium-potassium ATPase
3) increased activity of SR calcium ATPase
4) increased CO thru increased SV and HR
The main effects of TH on muscle, fat, and liver are?
1) liver: increased glucose production
2) muscles: increased protein breakdown
3) fat: increased lipolysis
About what percentage of T3 and T4 is bound to thyroxine-binding globulin? What is the rest bound to?
70% bound to thyroxine-binding globulin; rest to albumin, transthyretin, and other binding proteins
What are the two main causes of hyperthyroidism?
1) Grave’s disease
2) Plummer’s disease aka toxic nodular goiter
What are three consequences of Grave’s disease?
1) exophthalmos
2) pretibial myxedema
3) thyroid storm
What is one treatment for Grave’s disease and how does it work?
iodide; works as a competitive inhibitor
What are three causes of hypothyroidism?
1) Hashimoto’s thyroiditis
2) thyroidectomy
3) iodide deficiency
What are two causes of hypothyroidism in newborns?
1) iodine deficiency in diet
2) placental transfer of TSH Abs
What is the cause of myxedema?
accumulation of GAGs (such as hyularonic acid)
An increase in TRH causes an increase in TSH as well as?
Prolactin
