Made up of glands and organs, the endocrine system works to keep the body in homeostasis, or balance. This system of ductless glands release hormones directly into the blood stream, sending these messenger cells throughout the body, continuously updating the body's status to their target cells. Think of the endocrine system as a thermostat, it's constantly making adjustments to keep your body in balance.
Pituitary Gland
A marble-sized gland at the base of the brain, the pituitary is controlled by the hypothalamus gland. During exercise the pituitary gland releases the human growth hormone. This hormone tells the body to increase bone, muscle and tissue production. The pituitary gland controls the thyroid and adrenal glands.
Thyroid Gland
When you begin to exercise the thyroid gland, at the base of the neck, sends out hormones to regulate the body's temperature, heart rate and blood pressure. The level of alertness and concentration necessary to work at an intense level also come from the thyroid gland hormones.
Adrenal Glands
Located on top of the kidneys the adrenal glands are responsible for the release of cortisol into the blood stream. Cortisol levels control blood pressure, glucose and acts as an anti-inflammatory agent. A second hormone released by the adrenal glands during exercise is aldosterone. This hormone is responsible for regulating hydration, how much fluid is lost due to sweat. Finally, the fight or flight hormone, adrenaline, is produced during exercise. Adrenaline regulates the speed of the heart as well as the strength of its contractions and causes stored carbohydrates to rapidly turn over into energy.
Pancreas
Insulin and glucagon, hormones that control sugar levels in the body, are secreted by the pancreas. Exercise improves insulin sensitivity, reducing the reliance on insulin injections.

What does this mean for the cancer survivor? After radiation therapy you may experience isolated growth hormone deficiencies, and will be at increased risk for hypothyroidism, thyroid nodules or thyroid cancer. Some chemotherapies cause diabetes. Hormonal therapy can cause sterility, testosterone deficiencies and premature menopause.