Anatomy of the Endocrine System

By Mary Green

The endocrine system consists of a collection of glands that regulate a number of vital functions of our body. All of these glands coordinate with each other in order to regulate various life processes. Here is a rundown of the endocrines glands that form this system and their functions.

Adrenal glands (suprarenal glands)

Located atop the kidneys, adrenal glands are just two or three inches long and weigh less than an ounce, but are responsible for the secretion of more than 35 different hormones which maintain the body’s salt and water balance, affect kidney function and help the body cope with and respond to stress. During stressful situations, adrenaline is released by the adrenals and proteins are converted into energy by the cortisol released from the cortex (outer layer) of these glands, leading to the release of the body’s stored sugar. This sugar substance is known as glycogen, and it generates energy that accelerates our heart, respiratory rate and blood pressure. In this way, our body gets the fuel required for the quick response in a crisis. The adrenal glands also produce androgens, male sex hormones that promote the development of male characteristics, and estrogen, which is an essential hormone for female body metabolism.


Hypothalamus

The hypothalamus, located just above the brain stem, serves as the link between the endocrine system and the nervous system via the pituitary gland by controlling the pituitary through the stimulation or suppression of hormone secretions. It activates and controls involuntary functions such as body temperature, hunger, thirst and fatigue.


Pituitary gland

No larger than the size of a pea, the pituitary is often referred to as the “master” gland because it secretes hormones that regulate the function of other endocrine glands (the thyroid, adrenals and reproductive glands). It also produces hormones that stimulate the growth of bones and tissues, affect sexual development, encourage reabsorption of water by the kidneys and even trigger uterine contractions during and after labor.


Pineal body (pineal gland)

Located deep in the center of the brain, the pineal gland is involved in several body functions, including secretion of the hormone melatonin, which helps maintain a person’s wake/sleep cycles and regulate reproductive hormones and the conversion of nervous system signals to endocrine signals.


Pancreas

Located in the abdomen, the pancreas is both a digestive organ and an endocrine gland. The “islets of Langerhans” are the regions of the pancreas that contain its hormone-producing cells. The two primary endocrine functions of these cells are to keep the body supplied with fuel for energy by maintaining a steady level of the glucose (sugar) in the bloodstream with the hormones insulin and glucagon and to help in food digestion by secreting digestive enzymes.


Parathyroid glands

Each the size of a grain of rice, the body’s four parathyroid glands have a very rich blood supply, which comes in handy since they monitor the calcium level in the blood. As blood filters through the parathyroids, they detect the amount of calcium and make more parathyroid hormone (PTH) when calcium levels are too low. Once PTH is released, it circulates to the cells of the bones and causes them to release calcium into the bloodstream. When calcium levels are too high, the parathyroids make less PTH or cease producing it until normal levels are restored. Calcium is the element that allows the normal conduction of electrical currents along nerves—it’s how our nervous system works, how one nerve “talks” to the next, and is the primary element which causes muscles to contract. The parathyroids also help the lining of the intestines become more efficient at absorbing calcium in the diet.


Thymus gland

While not technically considered a part of the endocrine system, the thymus is included here because it has an endocrine-like function: it produces humoral factors, which are hormones that stimulate the development of antibodies. The thymus is situated in the upper part of the chest, behind the breastbone and in front of the trachea. The thymus controls the body’s immunity by releasing humoral factors that stimulate the production of T-lymphocytes, which are white blood cells that fight invading bacteria, viruses, foreign tissue and abnormal cell growths such as cancer. These T-cells circulate through the bloodstream and collect in the lymph organs – the spleen and lymph nodes – for future use.


Thyroid gland

The butterfly-shaped thyroid takes iodine and converts it into two hormones (T3 and T4), which are transported throughout the body and enter cells to regulate blood pressure, body temperature, heart rate, metabolism and how the body reacts to other hormones. The thyroid gland also produces calcitonin, which stimulates bone cells to add calcium to bone, as well as regulating calcium metabolism.


Ovaries

The ovaries, the female gonads, have two main reproductive functions in the body: they produce oocytes (eggs) for fertilization and the reproductive hormones estrogen and progesterone. Estrogen is involved in the development of female sexual features such as breast growth, the accumulation of body fat around the hips and thighs, and the growth spurt that occurs during puberty. Both estrogen and progesterone are also involved in the regulation of the menstrual cycle and prepare the lining of the uterus for pregnancy in the event of the released egg being fertilized.


Testes

The testes, also known as testicles or male gonads, have two functions: to produce sperm and to produce hormones, particularly testosterone, which regulate body changes associated with sexual development, including enlargement of the penis, the growth spurt that occurs during puberty, and the appearance of other male secondary sex characteristics such as deepening of the voice, growth of facial and pubic hair, and the increase in muscle growth and strength.