Thyroid Flashcards
What does the follicle consist of?
Cuboid epithelial follicle cells surrounding a colloid-filled lumen
What is the purpose of the Thyroid Follicle?
Thyroid hormone synthesis
How are iodide ions absorbed into the Thyroid follicle?
Via a Sodium Iodide Transporter (NIS)
What type of transporter is an NIS?
Symporter (travels across membrane in same direction as transported molecule)
Where in the follicle cell is Tg synthesised?
Rough ER
What is Tg?
Thyroglobulin
Which molecule mediates the process of Tg Iodination?
Thyroid Peroxidase (TPO)
Where is the Iodinated Tg stored?
Colloid
Which organelles break down the iodinated Tg?
Lysosomes
Which molecules are freed from the proteolysis of iodinated Tg?
T3, T4, MIT, DIT
What happens to the MIT and DIT after proteolysis?
They are deiodinated and returned for reuse in the lumen
By what process do T3 and T4 enter the bloodstream?
Diffusion
Which form is the majority of thyroid hormone transported as?
T4 (roughly 10x more than T3)
What are the main characteristic differences between T3 and T4?
T3 is more active, and has a shorter half-life (~1 day); T4 is less active, and has a longer half-life (~5-7 days)
What is the primary functional unit of the Thyroid Gland?
Thyroid Follicle
Which organ secretes TRH?
Hypothalamus
What is TRH?
Thyrotropin-Releasing Hormone
Which part of the pituitary gland does TRH stimulate?
Thyrotoph (anterior pituitary gland)
Which hormone does the Thyroptroph secrete?
TSH (Thyroid secreting hormone)
What effect does TSH have on the Thyroid gland?
Causes cAMP levels to rise, stimulating active transport of Iodide, and synthesis of Tg in rough ER
What does TPO do?
Mediates conversion of Iodide to Iodine, and coupling of Iodine to Tyrosine and Thyroglobulin (colloid)
What type of Endocrine feedback loop is the Thyroid involved in?
Negative feedback loop
What form of Thyroid hormone is used at cellular level?
T3 (more active, and so has higher affinity for Thyroid hormone receptors)
How does thyroid hormone affect a cell?
It binds to nuclear receptors TRalpha and TRbeta, forming a hormone receptor complex, which binds to DNA in Thyroid Response Elements region
