Tyrosine and iodine are both precursors for synthesis of T4. Selenium is essential for conversion of T4 to T3, and iron is the cofactor for conversion of phenylalanine into tyrosine.

Calcitonin is produced by the parafollicular (c cells) of the thyroid as a response to elevated blood calcium levels. Calcitonin reduces plasma calcium by inhibiting osteoclast activity and stimulating osteoblasts to deposit more bone. Parathyroid hormone has the opposite effect - it acts to increase calcium levels when serum calcium decreases. While they may ultimately affect serum calcium levels, thyroid hormone and cortisol are not directly involved in calcium homeostasis.

Thyroid-stimulating hormone (TSH) is produced in the anterior pituitary. Somatostatin, dopamine, and gonadotropin releasing hormone are all hypothalamic hormones. Somatostatin is also secreted by the pancreas, and slows down digestive processes. To remember the hormones of the anterior pituitary, use the following mnemonic: FLAT PEG, Follicle-stimulating hormone, Luteinizing hormone, Adrenocorticotropic hormone, Thyroid-stimulating hormone, Prolactin, Endorphins, Growth hormone.

Epinephrine is the only hormone of those listed that is produced by the adrenal medulla. The adrenal medulla is the center of the adrenal gland. Antidiuretic hormone is produced by the posterior pituitary. Calcitonin is produced by the thyroid. Thyroid-stimulating hormone is secreted from the anterior pituitary, as is follicle-stimulating hormone. 

Oxytocin is produced by the hypothalamus, and is released by the posterior pituitary. Women experience an increased level of oxytocin during labor, after birth, and while breastfeeding. It helps to increase uterine contractility, aiding in the delivery process and preventing hemorrhage after birth. Progesterone and estrogen are hormones released from the ovary. Estrogen is has many effects on the body, one of which is the development of sex characteristics in females. Progesterone is important in regulation of the uterine lining. Prolactin is made by the anterior pituitary gland and functions in the production on breast milk. 

All of these are correct effects of parathyroid hormone. The kidneys resorb calcium and as a result, less is released into the urine. The intestines absorb additional calcium from food and calcium is released from the bone through the work of osteoclasts. 

Thyroid-stimulating hormone (TSH) is produced by the anterior pituitary. TSH causes the thyroid to release thyroid hormones (T3 and T4). A TSH blood test is often ordered to diagnose hypoactive thyroid. 

Aldosterone is a hormone secreted by the adrenal glands. Serum aldosterone levels vary throughout the day. Aldosterone presence is highest in the morning. Of the answer choices, 7 AM is the best choice. A physician may have the patient come to the office at a specific time of day for this reason.

The pineal gland is responsible for regulating melatonin. It is not known at this time to secrete any other hormone. Melatonin is thought to play a critical role in the regulation of the circadian rhythm. Cortisol is secreted by the adrenal cortex and is involved in regulating the stress response. Vitamin D become activated in three steps. First, ultraviolet light in the skin begins the process, then the process continues in the liver, and is completed in the kidney. The active form of vitamin D increases calcium absorption in the gut, decreases calcium loss in urine, and increases calcium mobilization from bone. Vasopressin is also known as antidiuretic hormone, and functions in water retention. Leptin is a hormone secreted by adipose tissue that tells the body that it is full, and not hungry.

Endocrine glands secrete hormones into the blood. The endocrine glands include the ovaries, testes, hypothalamus, thyroid, pituitary, adrenal glands, pancreas, the pineal gland, and others. Salivary glands are considered exocrine glands. Exocrine glands secrete substances through ducts to the body surface or into body cavities, such as the mouth in the case of salivary glands.