Steroid Hormones & thyroid function Flashcards
(31 cards)
name of the process that makes T1 & T2 & describe it. & where process is done
a) Organification of thyroglobulin: bind oxidised I2 to thyroblobulin
b) Thyrosine + I2 (TPO*) => T1
T1 + I2 (TPO) => T2
*TPO= Thyroid peroxidase (oxidise)
c) follicle cells
name of the process that makes T3 & T4 & describe it. & where process is done
a) Coupling of iodotryrosine
b) T1 + T2 => T3
T2 + T1 => rT3
T2 + T2 => T4
c) Thyroglobulin / colloid region
Hashimoto disease has autoimmune Ab that target _
TPO (anti-TPO Ab => hypothyroidism)
Which of the following thyroid hormones has the highest biological activity?
T3 (tri-iodothyronine)
* Note: bc T4 converted to active form by de-iodase = T3
Which of the following thyroid hormones is more abundant?
T4 (tetra-iodothyronine aka thyroxine)
4 phases of T3/T4 synthesis
- Trapping of iodine
- Adding Iodine to tyrosine (via organification w/ TPO)
- Coupling of 2 iodonated tyrosine residues
- lysosomes digest thyroglobulin and release T3 & T4
What is iodine trapping?
- TSH strongly regulates iodine trapping
- Symport mechanism: 2Na+ & I2 (-ve) go in follicle cell from plasma
Regulation of thyroid hormones is based on
Free T4 and free T3
What is TBG? & significance if inc. or dec.
a) thyroxine-binding globulin: binds to thyroid hormones in circulation
b) inc. TBG = early liver disease
c) dec. TBG = late liver disease
the effect of T3 on target cells
- T3 diffuses to the nucleus
- binds to thyroid receptor hormone
- hormone-receptor complex binds to thyroid response element
- initiate transcription & translation
Describe the negative Fb loop for T3 & T4
- TRH: thyrotrophin releasing hormone produced by hypothalamus
- TSH produced by Ant. PT gland
- Thyroid gland produce T3* & T4
- Inc. T3 & T4 inhibits production of TRH & TSH
difference b/w 1º & 2º disease & e.g of each
1º: disease in same organ (e.g. in thyroid gland)
2º disease in another organ => affects that organ (e.g. in hypothalamus/PT gland)
Describe Grave’s disease (aka _) (include blood test expectations)
a) hyperthyroidism
- caused by Thyroid Stimulating Ig (TSI) Ab or anti-TSH receptor => similar effect to TSH => excess production of T3 & T4 by thyroid gland
- blood test show: elevated T3 & T4 & Low TSH (-ve Fb)
Describe Hashimoto’s disease (aka _) (include blood test expectations)
a) hypothyroidism
- caused by TPO autoAb => dec. production of T3 & T4
b) blood test show: Low T3 & T4 & High TSH
trophic hormone
a hormone which stimuates another organ to release a hormone
Steroid hormone structure & 4-5 e.g.
a) 3x 6C + 1x 5C rings
b) - Sex steroids (androgens, testosterone)
- Progestogens (Progesterone)
- Glucocorticoids (Cortisol)
- Mineralcorticoids (aldosterone)
- Vitamin D (based on its structure)
Most abundand steroid hormone & starting compound for synthesis of all steroid hormones is
pregnenolone
What dictates whether a tissue responds to steroid hormones or not? & e.g. (2)
- Hormone receptors: FSH/LH/ACTH
- Enzyme profile: 18-hydrolase required for aldosterone synthesis - found in zona glomerulosa cells (outer zone) of adrenal cortex
steroid hormones for male sexual development
- Androgens
- Didehydroepiandrosterone
- Testosterone
steroid hormones for female sexual development
- Oestrogens
- Progesterone (maintain prego)
- Estradiol
Give an e.g. for each group: (a) Glucocorticoid & (b) mineral corticoid
a) cortisol
b) aldosterone
inc. cortisol = [inc./dec.] weight
inc
According to circadian release of cortisol, cortsol is [Hi/lo} early in the morning & [Hi/Lo] @ night
a. Hi
b. Lo
Hormonal regulation of cortisol
- injury, fear stress => Corticotrophin Releasing Hormone (CRH) in hypothalamus
- => Adrenocorticotropic hormone (ACTH) in Ant. PG
- => Cortisol in adrenal cortex
- Inc. [Cortisol] => -ve Fb => dec. CRH & ACTH
