Thyroid Flashcards
describe the signalling pathway of TRH
IP3 and DAG increase the release of TSH
describe the signalling pathway of TSH
cAMP
describe the daily requirements of iodine
- daily requirements = 150 micrograms from diet
- ingested in form of idodide (I-) or iodate (IO3)
- pregnant women and lactating females have higher iodine requirements
- deficiency will initially compensate by increased TSH levels which leads to goiter
- if intake is < than 50 micrograms, compensation will fail
describe the location and amounts of iodine in the body
describe structure of thyroglobulin
- large glycoproteins
- contains ~70 tyrosine molecules
describe synthesis of thyroglobulin
- made in epithelial cells
- synthesized in ribosomes
- transport to Golgi
- discharged into follicle lumen
- synthesis and storage of TH remains here
list the 8 steps in TH synthesis
- synthesis and extrusion of TG into the lumen
- Na/I symporter on the basal membrane
- oxidation of I- to I0 to fuse with TG via TPO (inhibited by PTU)
- Organification of I2 to MIT and DIT via TPO (inhibited by PTU)
- Coupling MIT and DIT via TPO
- endocytosis of TG that contain DIT, MIT, T3, T4
- hydrolysis of T3, T4 off the TG via proteolyase
- Deiodination of MIT and DIT via deiodinase
describe the effect of T3/T4 at the target tissue
- 5’ deiodinase converts T4 into T3 (10x more potent)
- T3 enters the nucleus and modulates gene expression
- increases basal metabolic rate
describe the locations of T3 and T4 in the body
- 70% of T3 and T4 bound to thyroxine-binding globulin (TBG)
- pregnancy and estrogen increase levels of TBG
- liver disease decreases levels of TBG
- rest bound to blood proteins
increase in ___ negatively feedbacks thyrotrophs (TSH) and hypothalamus (TRH)
T3
- T4 doesn’t regulate thyroid hormones
describe hyperthyroidism diseases
- thyroid enlargement (Grave’s disease)
- overactive lump (Plummer’s disease)
describe Grave’s disease
- antibody for TSH receptor upregulates production of T3/T4
- decreases TRH and TSH since T3 negative feedback
describe the signs of Grave’s disease
- thyroid enlargement
- opthalmopathy
- pretibial myxedema
- non-pitting edema
- untreated can lead to thyroid storm
- bulging eyes
describe causes of hypothyroidism
- due to low levels of TH in blood
- Hashimoto’s thyroiditis
- thyroidectomy
- iodide deficiency
- secondary
- insufficient pituitary action
- resistance of organs to TH
describe hypothyroidism in newborns
- may be due to
- iodide deficiency (not common in 1st world)
- placental transfer of TSH antibodies
- symptoms
- respiratory problems, jaundice, poor feeding, umbilical hernia, reduction of bone development
describe amenorrhea in hypothyroidism
- decrease in thyroid hormone increases TRH levels which stimulates prolactin
- prolactin inhibits GnRH, which leads to amennorhea