Steroids are nonpolar, which means that they are able to pass easily through cell membranes, but require a transport protein through the hydrophilic blood in order to do so. The steroid hormone then enters the nucleus and attaches to the DNA in order to increase the desired product at the level of transcription.

Luteinizing hormone is responsible for the secretion of testosterone from leydig cells in the testes.

FSH is responsible for the proliferation of sertoli cells, which nurture sperm cell precursors. hGH is responsible for body growth, and is not responsible for testosterone formation. Oxytocin is responsible for increasing uterine contractions during pregnancy.

Insulin is responsible for lowering blood sugar levels, and is therefore released when the body's blood sugar levels are too high. Glucagon is released in response to low blood sugar levels, and acts to increase sugar concentrations.

Thyroid hormones (T3 and T4) are released to increase the body's metabolic rate, but are not directly influenced by blood sugar levels.

The question tells us that slowed output of thyroid hormones can lead to obesity. One can safely assume that receptor insensitivity will have a similar effect. In either scenario, the T3 and T4 hormones are unable to elicit the proper response form the body. Similar to individuals with hypothyroidism, individuals with insensitive receptors would show slowed metabolism and increased weight gain.

Oxytocin is responsible for lactation in nursing women. When the nipple is stimulated, oxytocin is released from the posterior pituitary to cause lactation. During labor, release of oxytocin causes positive feedback on the hypothalamus, which causes further oxytocin release.

Luteinizing hormone and follicle-stimulating hormone are released from the anterior pituitary and function to regulate the menstrual cycle. Vasopressin is released from the posterior pituitary and helps to regulate blood pressure and water balance.

Testosterone is well known to be responsible for male secondary sexual characteristics. It also plays a key role in behavior, such as aggression. For example, during mating season in gorillas the testosterone levels in males raise significantly and lead to confrontations between males.

Progesterone and estrogen are responsible for female secondary sexual characteristics, while cortisol plays a role in the body's response to long-term stress.

In order for menstruation to occur, progesterone levels must decrease. When fertilization does not occur, the corpus luteum ceases progesterone production, initiating menstruation. The corpus luteum then transitions into the corpus albicans and removed from the ovary in preparation for the new menstrual cycle.

Epinephrine, released from the adrenal gland, is important for the fight-or-flight response. During moments of stress, heart rate increases, pupils dilate, and blood vessels constrict in order to prepare for danger. All of this is controlled by epinephrine and norepinephrine, and is part of the sympathetic nervous system.

To answer this question, you must have an understanding of the differences between endocrine, paracrine, and autocrine functioning. This example, in which a molecule exhibits autocrine behavior, means that a cell releases a hormone that acts on itself. In paracrine signaling, the molecule does not act on the same cell, but does diffuse through tissue to reach nearby target cells. Finally, endocrine signaling refers to hormone molecules that are released and transported through the bloodstream to act on more faraway target cells in distant regions.

The two hormones known for their effect on plasma calcium levels are calcitonin and parathyroid hormone (PTH). When calcium levels are high, calcitonin is released by the thyroid gland to stimulate the uptake of serum calcium into bone. This effectively decreases calcium levels in the blood. PTH has the opposite effect and is released by the parathyroid gland.

The three remaining answer choices are not known for their effect on calcium levels in the blood.