Thyroid Flashcards
– butterfly shaped, 2 lobes separated by Isthmus and straddles the trachea
Thyroid gland
Largest endocrine gland
Thyroid gland; (15-25g)
enumerate the principal cells of the thyroid gland
- Follicular epithelium; T3, T4
- Parafollicular cells: Calcitonin
What is the main function of the Thyroid gland?
produce thyroid hormones. Iodine storage
GIve the normal Thyroid iodide to plasma iodide ratio:
25-40:1
TRUE or FALSE: Iodine is needed for hormone synthesis
TRUE
Intake for Iodine:
normal intake -
hormone secretion deficiency -
- 1mg/week (150ug/day)
- <50ug/day
Enumerate the 3 components of the thyroid gland
- Follicles
- Colloid
- Thyroglobulin
Responsible for absorbing iodine (ring shape)
Follicles
Reservoir of materials for hormone production surrounded by follicle
Colloid
TRUE or FALSE: Colloid is rich in glycoprotein thyroglobulin
TRUE
this component is with tyrosyl groups (rich in tyrosine)
Thyroglobulin
TRUE or FALSE:
Follicle are the major component of colloid
FALSE; Thyroglobulin are th emajor component of colloid
TRUE or FALSE: Colloid are synthesized and secreted by follicles
FALSE; Thyroglobulin are the ones synthesized and secreted by follicles
which TG component reflects Thyroid mass, injury and TSH receptor stimulation?
Thyroglobulin
TRUE or FALSE: Presence of Thyroglobulin indicate tumor (malignant/benign)
TRUE
Which following conditions does thyroglobulin seen at increased levels?
increase in:
- Graves disease
- thyroiditis
- nodular goiter
The biosynthesis of T3 and T4 is controlled by?
Thyroid Stimulating Hormone (TSH)
Enumerate the biosynthesis of TH
- Iodide trapping/uptake
- Oxidation
- Iodination of tyrosyl residues by TPO
- Coupling/Condensation reaction
- Thyroglobulin is then moved to the colloid for storage
- Exocytosis of colloid droplets
Iodide trapping/uptake is controlled by?
Na-Iodide symporter
what is the lumen Iodide to follicular iodide ratio?
5:1
Conversion of iodide to elemental iodide is catalyzed by which enzyme?
Thyroid peroxidase (TPO)
Where does the iodothyronine formed?
optical barrier, follicular cells = Monoiodothyronine & Diiodothyronin
DIT + DIT by TPO
T4; Thyroxine
MIT + DIT
T3; Triiodothyronine
Transport:
T4 binding proteins
Circulating T4 plasma protein (%)
Free T4 (%)
99.95% T4 =Plasma protein,
0.05% = Free
T4 percentages:
TBG
TBPA
TBA
- 75% of T4
- 15=20% of T4
- 9% of T4
TBG is measured by what method?
Immunoassay
Which substances affect the TBG & T4 binding?
- Salicylates
- phenytoin
- penicillin
- heparin
t3 binding protein percentage:
0.5% Free
t3 binding protein percentage:
TBG
TBPA
TBA
- 99.5%
- very low
- none
_______ affinity of T3 binding protein
_______ Free T3 in plasma
_______ biological activity of T3 & T4
- decrease
- increase
- increase
Discuss the hormone loop
Metabolism →, detected by Hypothalamus →, Stimulate the pituitary gland →, TSH to target oragen (Thyroid) →, T3, T4 →, Target organ (adrenal medulla) →, Epinephrine & norepinephrine →, increase Metabolism
Enumerate the three Thyroid autoantigens
- Thyroperoxidase
- Thyroglobulin
TSH receptor
What are the Physiologic actions of Thyroid?
- Basal metabolic Rate
- Tissue growth
- CNS development
- ANS
- CV & Respiratory systems
- GIT
- Skin
- Lactogenesis
Responsible for deiodination
Iodothyronine-5’-deiodinase
Which type is abundant for T3 circulation?
Type 1
Location of Type 1 and Type 2 iodothyronine-5’-deiodinase
Type 1 - Liver & Kidney
Type 2 - Brain
Which type maintains T3 levels in the CNS?
Type 2
Main serum carrier of T3 and T4
Thyroglobulin
Method of choice for TBG level detection
immunoassay
used to confirm results of FT3 and FT4 or abnormalities in the relationship of total thyroxine and THBR test
TBG test
Hyperthyroidism vs Euthyroidism
Hyperthyroidism - increased thyroxine levels
Euthyroidism - increased binding with TBG and Thyroxine
Total serum of T3 and T4 are dependent upon ________
amount of TBG
Enumerate the conditions associated with increase and decrease TBG levels
increased: Hypothyroidism, pregnancy, estrogen, euthyroidism
Decreased: anabolic steroids and nephrosis
