Question

Tony had his thyroid gland surgically removed when he was in his late twenties; now he is in his sixties. He takes Synthroid (thyroxine) pills daily and periodically has his blood levels checked for T4 and TSH.

E. Is thyroxine hydrophilic or hydrophobic? How is that related to whether or not Tony could take it as a pill (orally) instead of having to inject it?

H. How does the thyroxine in his pills affect his blood levels of TSH?

I. If the dose of his thyroxine pills is too low, what would happen to his blood levels of T4 and TSH?  

J. If the dose of his thyroxine pills is too high, what would happen to his blood levels of T4 and TSH?

Answer 1

Ans E) The thyroxine is hydrophobic because it is lipid soluble. Since it is hydrophobic in nature, it is easily able to diffuse through the plasma membrane and hence can interact with the receptors present intracellularly. Since the plasma membrane has lipid bilayer made of phospholipid, it can enter the cell and bind to intracellular receptors. Hence, since it is a hydrophobic drug it is better that it is injected so that it is absorbed and delivered fast. One of the problems with the hydrophobic drugs is that it has low solubility when route of administration is oral. Hence to increase its solubility it is better to inject it rather than consuming orally.

Ans H) The TSH hormone helps in regulating the concentration of thyroid hormone. When there is thyroxine present in the pills, it decreases the concentration of the TSH in the blood level. Hence, when there is increase in thyroxine in the body from the pill, it tends to also decrease and stimulate the decrease its concentration in blood.

Ans I) When the dose of thyroxine pill is too low, it means the blood level of T4 and TSH is high and hence it helps in regulating the functions. Since the TSH is responsible for increase in the thyroxine production, hence it will be low.

Ans J) When the dose of the thyroxine of pill is too high, it means that it concentration in the blood will be too high. When it is too high, it would decrease the concentration of T4 and TSH in the blood stream so that there is a steady maintenance of the same.