Question

Why thyroxine is a hormone, not an enzyme?
A. It is secreted in small quantity
B. It is not a polypeptide
C. It has no special effect
D. It is directly poured into the blood

Answer 1

Animals have three types of gland: exocrine, endocrine, and heterochrony.
The hormone is informational molecules secreted by the endocrine cells in one part of the body in response to changes in the external and internal environment and carried by the blood to another part where they stimulate or inhibit specific physiological processes for the benefits of the body as a whole.

Complete answer: Endocrine glands lack ducts and pass their secretions into the surrounding blood for transport to the site of action.
Their secretions are known as a hormone or internal secretions.
The thyroid gland is an endocrine gland secret three hormones thyroxine or tetraiodothyronine (T4), triiodothyronine (T3), and calcitonin.

So the correct answer is option is D. It is directly poured into the blood

Additional information: Thyroid glands originate from the endoderm of the embryo. It surrounds the front of the larynx and upper part of the trachea in the neck.
1. Thyroxine and triiodothyronine (T3) hormones are iodinated forms of the amino acid tyrosine. They are stored in the colloid that fills the follicles and is released to the blood when needed.
2. Thyroxin also controls the working of kidneys.
3. Its deficiency decreased in urine output
4. Increased secretion of thyroxin hormones results in goiter.

Note: The thyroxine hormone is produced by the thyroid gland which is endocrine in nature which means that they are directly released into the blood. Hence thyroxine is a hormone, not an enzyme.