Endocrine-1 Flashcards
The coupling of the two outer rings of DIT
or of one outer ring of DIT with that of
MIT (each with the net loss of alanine)
leads to the formation of ___ and ___,
respectively.
T4 and T3
____________ (Tg) serves as the matrix for
the synthesis of T4 and T3 and as the
storage form of the hormones and iodide
Thyroglobulin
TRH is ____ amino acids long (_________) secreted by the hypothalamus. Its basic
sequence is pyro-glutamyl-histidine-proline amide
three (tripeptide)
The formation of thyroid hormones involve:
(1) active uptake of _______ by the follicular cells
(2) oxidation of iodide (I-) to hypoiodite (IO-) by H2O2 and ___________ (TPO) and formation of iodotyrosyl residues (MIT and DIT) of thyroglobulin (Tg) through aromatic iodination, (3) formation of iodothyronines from iodotyrosines through ________ reaction catalyzed by TPO and H2O2
(4) _______ of Tg & release of T4 & T3 into blood
(5) conversion of T4 to T3 by the action of _____
iodine
thyroperoxidase
coupling
proteolysis
5’-deiodinase
T4 is a prohormone and its peripheral
metabolism occurs in two ways:
outer ring deiodination -> T3
inner ring deiodination ->T4
conjugation of phenolic hydroxyl group and oxidative deamination of inner tyrosyl ring
Liotrix is a synthetically derived thyroid hormone replacement preparation. It consists of
Levothyroxine sodium and Liothyronine sodium in a __ to __ ratio by weight.
4 to 1
The phenyl-X-phenyl nucleus is essential for thyroid hormonal activities and should
have the following structural features:
Aliphatic Side Chain (R1)
Alanine-Bearing Ring (R3 and R5)
Phenolic Hydroxyl Group (R’4)
Bridging Atom (X)
Phenolic Ring (R’3 and R’5)
Antithyroid Drugs are potent inhibitors of ______________, which is responsible for the iodination of tyrosine residues of thyroglobulin (Tg) and the coupling of iodotyrosine residues to form iodothyronines
thyroperoxidase (TPO)
The most clinically useful thionamides are thioureylenes, which are five- or sixmembered heterocyclic derivatives of thiourea including what
Propylthiouracil (PTU)
1-methyl-2-mercaptoimidazole (Methymazole, MMI)
The grouping R-CS-N- has been referred to as _______, or if R is N, as it is in Thiouracil, PTU, and MMI, it is called a ________
thioamide
thioureylene tautomers (keto or enol)
SARs of the thiouracils and other related compounds as inhibitors of outer ring deiodinase states that the C-2 thioketo/thioenol group and an _________ N-1 position are essential for activity.
unsubstituted
Structural modifications leads to produce inactive ______ inhibitors N1-alkyl or aryl and Thiol alkylation or arylation
TPO
Thyroid Gland
neck surrounding trachea below the larynx
Thyroid Structure: follicles surround the colloid core storing __________, a substrate in thyroid hormone synthesis
thyroglobulin
What two things stimulate the release of T3 and T4 synthesis and release
TRH
TSH
____________ symporter (NIS) transports iodide into follicles
Sodium/Iodide
What is Organification
tyrosine residues are iodinated to form moniodotyrosine (MIT) and diiodotyrosine (DIT)
Thyroidal peroxidase:
inhibition by I-, thioamides
Inhibits T4→T3 conversion
* Methimazole (Tapazole)
* Propylthiouracil (PTU)
T3 not bound to T3 receptor dimer, suppresses what
thyroid hormone response element (TRE)
T3 bound to T3 receptor, activates thyroid
hormone response element promotes heterodimerization with
retinoid X receptor (RXR)
Primary Hypothyroidism:
Deficient thyroid hormone levels
TSH high; T4 low
Secondary (Central) Hypothyroidism:
Deficient TSH
TSH low; T4 low
Peripheral Hypothyroidism:
Deficient transport, metabolism or
action of thyroid hormones
Severe Hypothyroidism symptoms
myxedema (swelling of skin)
myxedema coma (water intox, shock, coma)