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.

Growth hormone is released from the anterior pituitary, and has numerous effects on the body. One of its primary effects is to stimulate release of insulin-like growth factors (IGFs) from the liver. These compounds circulate in the blood and directly stimulate bone and cartilage growth.

The release of thyroid-stimulating hormone (TSH) causes the release of T3 and T4, which help speed up metabolism. Glucagon serves to increase blood glucose level. Epinephrine is released in response to short term stress, and stimulates the sympathetic nervous system.

Progesterone is a steroid hormone that supports gestation in mammalian pregnancy. After the eighth week of pregnancy, it is produced by the placenta and helps to decrease the maternal immune response to prepare for pregnancy.

Melatonin is a hormone used to regulate circadian rhythm and sleep cycles. Glucocorticoids, such as cortisone and cortisol, prepare the body for long term stressors. Prolactin stimulates the production of milk in mammals. Growth hormone promotes the enlargement of various organs and stimulates cell division.

Vitamin D is the only vitamin that can be produced endogenously via UV activation of 7-dehydrocholesterol in the skin. All other vitamins must be obtained from outside sources, namely the digestion of other organic matter.

Insulin works by stimulating adipocytes (fat cells), hepatocytes (liver cells), and skeletal muscle to translocate glucose transporter-rich vesicles to the cell membrane. This allows the diffusion of glucose from the blood into these tissue types after a carbohydrate-rich meal. Without insulin, even if an individual has high blood glucose levels, these three cell types would essentially be deprived of the circulating glucose.

Glucagon works against insulin by increasing blood glucose levels as they decrease via gluconeogenesis and glycogenolysis.

To answer this question, it is necessary to understand the prefixes "hyper" and "hypo." "Hyper" refers to excessive synthesis, while "hypo" refers to reduced synthesis.

Growth hormone is responsible for stimulating cell growth and division throughout the body. Hyposecretion would cause a deficiency and reduce the effectiveness of growth hormone, potentially causing pituitary dwarfism. Hyposecretion of growth hormone in adults leads to poor protein synthesis, which significantly impacts the muscles and skin.

Enlargement of the face and extremities is an adult condition known as acromegaly. The underlying cause is hypersecretion of growth hormone. In children, this condition can lead to gigantism if untreated. The hormone thyroxine is not involved. Parathyroid hormone elevates blood calcium levels, so hypersecretion would cause high blood calcium. Insulin functions to reduce blood glucose levels. Since diabetes is classified by high blood glucose, insulin must lose functionality to cause this disease. This means that it would be hyposecreted, rather than hypersecreted.

Antidiuretic hormone (ADH) is secreted by the posterior pituitary and acts on the kidney tubules, increasing the water retention in blood and decreasing the water volume in urine. It works by increasing the number of aquaporins (water channels in the plasma membrane) in the collecting duct of the kidney nephrons. Water flows down its osmotic gradient out of tubule, and into the blood for circulation.

Aldosterone also functions to regulate water volume in the blood, and is associated with the renin-angiotensin-aldosterone system (RAAS). Aldosterone functions by increasing sodium reabsorption. This increases the solute concentration in the blood, passively causing water to diffuse out of the filtrate and into the blood. Though aldosterone and antidiuretic hormone have similar functions, aldosterone is secreted by the adrenal cortex, not the pituitary.

Oxytocin stimulates uterine contractions and milk release in the mammary glands. Glucagon and insulin are involved in the regulation of blood sugar levels.

After a large meal the body must quickly remove glucose from the blood. Insulin facilitates the entry of glucose into a variety of body cells, particularly hepatocytes in the liver. Once inside the cell, glucose is either stored as a polymer (glycogen) or reduced into carbon dioxide and water to produce a usable form of energy (ATP) for the cell. Glycogen is stored in the liver until blood glucose levels become low, at which point it can be converted back to glucose and released to maintain homeostasis. This process, known as glycogenolysis, is stimulated by the release of glucagon. Together, insulin and glucagon create a negative feedback loop to regulate glucose in the blood.

Thyroxine (T4) regulates metabolic rate, and is released from the thyroid. Adrenocorticotropic hormone (ACTH) is released from the anterior pituitary and stimulates the release of glucocorticoids (like cortisol) from the adrenal glands. The release of epinephrine is tightly linked to the sympathetic nervous system, and is involved in the immediate stress response.

Glucocorticoids are produced from the adrenal gland. Their primary effect increases energy and glucose metabolism by making more glucose available from non-carbohydrate sources. Glucocorticoids stimulate gluconeogenesis.

One way this is accomplished is through activation of the glucocorticoid receptors within skeletal muscle, which signal the breakdown of muscle proteins to their corresponding amino acids. The amino acids are then transported to the liver and kidneys where they are converted to glucose, which is released into the bloodstream. 

The ability to make glucose from muscle proteins can provide additional fuel when the body needs more glucose (under stress conditions) than the liver can mobilize from the glycogen it has stored. The process, however, can be detrimental if stimulated for extended periods of time.