Unlike the nervous system, the endocrine system operates in a less rapid and more long-lasting manner. It is important to note that when the endocrine glands and the hormones that they secrete do not work properly, a variety of disorders can arise. Acting as the body’s messengers by transferring important information and instructions from one set of cells to another, hormones regulate the mood, body development, sexual function, pregnancy, other reproductive processes, and much more.

The glands that make up the (human’s) endocrine system are the hypothalamus, pituitary, thyroid, parathyroid, adrenals, pineal body, pancreas, ovaries, and testicles. Of note is that by anatomical design, part of the pancreas is exocrine, as its bulk is connected to the digestive system and secretes digestive enzymes into the intestine. Endocrine glands are not the only ones secreting hormones in our body. Some non-endocrine organs, such as the brain, heart, lungs, kidneys, liver, thymus, skin, and placenta, also produce (a small amount of) hormones.

The shape of each hormone molecule is specific and can bind to certain cells only. These unique binding sites on the target cells are called hormone receptors. Many hormones come in antagonistic pairs with opposite effects on the target organs. For example, glucagons and insulin have opposite effects on the liver’s control of sugar level in the blood. Insulin lowers the blood sugar levels by instructing the liver to take glucose out of circulation and store it, whereas glucagons instruct the liver to raise the blood sugar level by releasing some of the stored glucose. Many hormonal regulations depend on feedback loops to maintain balance and homeostasis.