pacj Flashcards
What do parafollicular cells/C cells produce?
Calcitonin
How is Iodide transported into the thyroid gland?
Iodide is actively transported into the
gland by a sodium-iodide symporter (NIS)
What inhibits and activates NIS gene?
Expression of the NIS gene is inhibited
by iodide and stimulated by TSH
What is the channel that iodide uses to go into the lumen called?
pendrin
What oxidizes Iodide?
Thyroid peroxidase
What is the incorporation of iodide into thyroglobulin called?
It is called iodination or organfication
What does a single, double, and addition iodination called?
Adding a single iodide tyrosine residue on thyroglobluin will form Monoiodotyrosine (MIT)
Adding another iodide molecule to the same tyrosine residue will form Diiodotyrosine (DIT)
Coupling two DIT molecules will form Tetraiodothyronine (T4)
Coupling a DIT molecule and an MIT molecule will form Triiodothyronine (T3)
This whole process is done by thyroid peroxidase
What is the electron acceptor for the iodiation?
The immediate oxidant (electron acceptor) for the reaction is hydrogen peroxide
(H 2 O 2 )
How is hydrogen peroxide generated in the follicular lumen?
Generation of H2O2 in the follicular lumen is catalyzed by dual oxidases (DUOX1, DUOX2.
What enzyme diodinates MIT and DIT?
iodotyrosine deiodinase
What are the receptors that T3 and T4 use to cross the membrane and flow into the blood?
T3 and T4 cross the membrane into the blood via monocarboxylate transporters MCT8 and MCT10.
What are the 4 proteins that T3 and T4 bind to while circulating in the blood?
- thyroxine-binding globulin (TBG) (70%)
- Transthyretin (TTR) (10% to 15% )
- Albumin (15% to 20%)
- lipoproteins. (3%)
What is Allan-Herndon-Dudley syndrome (AHDS)?
It is a syndrome where there is deficeny in the MCT8 receptor which doesn’t allow t3 and t4 to enter the brain
What transports T4 in cerebrospinal fluid?
Transthyretin transports T4 in cerebrospinal
fluid and provides thyroid hormones to the
CNS.
What is used to convert T4 to T3 in tissues with high blood flow?
type 1
deiodinase
What is used to convert T4 to T3 in the brain?
type 2 deiodinase
What is the function of type 3 deiodniase?
D3 is a high-affinity inner ring deiodinase that converts T4 to the inactive rT3.
How does T3 induce its direct affects on the CV system?
Direct inotropic effects result from
increased α-myosin heavy chain expression and inhibition of the plasma membrane Na + /Ca 2 + exchanger (NCX).
What are the affects of T3 on SERCA2 and phospholamban
Sarcoplasmic reticulum (SR) Ca 2+ ATPase (SERCA2) is increased by T3 and Phospholamban (PLB) is
decreased.
There is extra information in the slides but it is very logical, revising it quickly is advised
What is graves disease?
Autoimmune disorder that causes hyperthyroidisim
often accompanied by a diffuse goiter as a result of hyperplasia and hypertrophy of the gland.
How is thyrotoxicosis diagnosed?
Diagnose with thyroid function test. In thyrotoxicosis, serum levels of T3
and T4 are elevated and TSH levels low
What are the treatment options for hyperthyroidisim?
Anti-thyroid drugs: Drugs such as methimazole (Tapazole) and propylthiouracil (PTU) block the thyroid from making hormones.
* Radioactive iodine by mouth: The overactive thyroid cells absorb the
radioactive iodine, which damages the cells.
* The thyroid gland shrinks and thyroid hormone levels are reduced, usually leading to permanent destruction of the thyroid, which then causes hypothyroidism.
* Surgery: Surgical removal of the thyroid gland (thyroidectomy). This will correct hyperthyroidism, but it will usually cause hypothyroidism.
What is primary, secondary, and teritary hypothyroidism?
Primary hypothyroidism: T4 and T3 levels are
abnormally low and TSH is high. * Secondary and tertiary hypothyroidism: both
thyroid hormones and TSH are low.
