A researcher is interested in studying the synthesis of peptide and steroid hormones. She harvests 5 samples of cells from different hormone-producing organs of the body and allows each sample of cells (Cell Types 1-5) to synthesize its hormones for a period of time. Afterwards, she measures the intracellular concentration of the hormones synthesized in each Cell Type. The results are displayed in the corresponding chart. Based on the information provided, where would Cell Type 2 possibly be found in the human body?
Correct Answer: A. Testes
This is a great example of a conceptual question on the DAT. There are many pieces of information here, but if we take it one step at a time, it really isn’t that bad.
First, we have to explain why Cell Type 2 has such a low intracellular concentration compared to the other Cell Types. Recall that steroid hormones are lipid-soluble, which means they freely diffuse through the cell membrane.
In contrast, peptide hormones are stored in granules and are only released when stimulated. So from this information, we can deduce that Cell Type 2 must be synthesizing a steroid hormone, and the other Cell Types must be a variant of a peptide hormone.
As Cell Type 2 was synthesizing its steroid hormone, it was just freely diffusing out, and not building up in concentration inside the cell, so when the researcher measured the intracellular concentration, she barely found any steroid hormone at all. In contrast, Cell Type’s 1, 3, 4, and 5 were synthesizing peptide hormones and building up their concentrations because they store peptide hormones in granules.
Lastly, the question asks where Cell Type 2 possibly came from. Cell Type 2 would need to be harvested from a part of the body that produces steroids, of which there are three main centers, and those are:
1. Adrenal cortex, which produces mineralocorticoids and glucocorticoids like aldosterone and cortisol. It also is a secondary site for androgen synthesis.
2. Testes, which mainly secrete testosterone in relation to hormone synthesis.
3. Ovaries, which mainly secrete estrogen and progesterone in relation to hormone synthesis.
Note: The placenta also produces steroid hormones during pregnancy.
Thus, the correct answer to this question is [A], the testes, as it is the only organ listed that synthesizes steroid hormones.
All of the other answer choices describe organs that do not produce steroid hormones, and are therefore incorrect.
B. Adrenal medulla – Composed mainly of chromaffin cells, which synthesize catecholamines (epinephrine, norepinephrine, and dopamine) from tyrosine.
C. Anterior pituitary – Produces FSH, LH, ACTH, TSH, Prolactin and GH. (Remember the acronym FLAT PiG).
D. Pineal gland – The pineal gland is responsible for synthesizing melatonin.
E. Pancreas – Synthesizes several important peptide hormones, including insulin, glucagon, and somatostatin.