Do you know which organ system in our bodies produces 'hormones'? It is the endocrine system. We need to have the right amount of each hormone for our body to function properly. Too much or too little - both are harmful. In this lesson, let us learn more about this important organ system of our body.
Learning objectives
The endocrine system is made up of glands that produce and secrete hormones, chemical substances produced in the body that regulate the activity of cells or organs. Hormones are the body’s chemical messengers. They carry information and instructions from one set of cells to another. The endocrine system influences almost every cell, organ, and function of our bodies.
There are two major categories of glands in the body – exocrine and endocrine.
| Exocrine glands | Endocrine glands |
| Exocrine glands have ducts that carry their secretory products to a surface. These glands include the sweat, sebaceous, and mammary glands and, the glands that secrete digestive enzymes. | The endocrine glands do not have ducts to carry their product to a surface. They are called ductless glands. The secretory products of endocrine glands are called hormones and are secreted directly into the blood and then carried throughout the body where they influence only those cells that have receptor sites for that hormone. |
What does the endocrine gland do?
The hypothalamus is located in the lower central part of the brain. This part of the brain is important in the regulation of satiety, metabolism, and body temperature. In addition, it secretes hormones that stimulate or suppress the release of hormones in the pituitary gland. Many of these hormones are releasing hormones that are secreted into an artery (the hypophyseal portal system) that carries them directly to the pituitary gland. In the pituitary gland, these releasing hormones signal secretion of stimulating hormones. The hypothalamus also secretes a hormone called somatostatin, which causes the pituitary gland to stop the release of growth hormone.
The pituitary gland is located at the base of the brain beneath the hypothalamus and is no larger than a pea. It is often considered the most important part of the endocrine system because it produces hormones that control many functions of other endocrine glands. When the pituitary gland does not produce one or more of its hormones or not enough of them, it is called hypopituitarism.
The pituitary gland is divided into two parts: the anterior lobe and the posterior lobe.
The anterior lobe produces the following hormones, which are regulated by the hypothalamus:
The posterior lobe produces the following hormones, which are not regulated by the hypothalamus:
The hormones secreted by the posterior pituitary are actually produced in the brain and carried to the pituitary gland through nerves. They are stored in the pituitary gland.
The thyroid glands can be found at the front of the neck. It sits low in the throat, between the windpipe and is brownish-red in color with blood vessels running through it. It secretes thyroid hormones – thyroxine and triiodothyronine. These hormones control the rate at which cells burn fuel from food to make energy. The higher the level of thyroid hormone in the bloodstream, the faster chemical reactions happen in the body. Thyroid hormones are important because they help kids’ and teens’ bones grow and develop, and they also play a role in the development of the brain and nervous system.
The parathyroid glands consist of four small glands that are located behind the thyroids in the neck. They release parathyroid hormone which controls the level of calcium in the blood with the help of calcitonin which the thyroid makes. Sometimes, when the gland produces excess parathyroid hormones, it can have negative effects such as brittle bones and kidney stones.
The adrenal glands sit atop the kidneys and are no larger than a walnut. The adrenal glands have two parts, each of which makes a set of hormones and has a different function:
The outer part is the adrenal cortex. It makes hormones called corticosteroids that help control salt and water balance in the body, the body’s response to stress, metabolism, the immune system, and sexual development and function.
The inner part is the adrenal medulla. It makes catecholamines such as epinephrine. Also called adrenaline, epinephrine increases blood pressure and heart rate when the body is under stress.
The pancreas is exocrine as well as an endocrine gland that sits behind the stomach. It has two primary roles to play:
Insulin is produced by the β cells in the pancreas and it helps in regulating the blood glucose levels in the body from getting too high. The lack of insulin causes type 1 and type 2 diabetes.
The hormone glucagon is produced by the α cells of the pancreas and it helps the body to prevent the glucose levels from dropping low. Lack of glucagon leads to hypoglycemia. Another key difference between the two is insulin becomes active when the blood glucose levels are high, and glucagon becomes active only when blood glucose levels are low.
The pineal body also called the pineal gland, is in the middle of the brain. It secretes melatonin, a hormone that may regulate when you sleep at night and when you wake in the morning. It produces a hormone known as melatonin which influences the body’s internal clock and helps the body know when it is time to sleep.
The gonads are the main source of sex hormones. In males, the male gonads or testes are in the scrotum. They secrete hormones called androgens, the most important of which is testosterone. Testosterone results in the changes associated with puberty like penis and height growth, deepening voice, and growth in facial and pubic hair.
Ovaries, located in the pelvis, are the female gonads. They make eggs and secrete the female hormones estrogen and progesterone. Estrogen is involved when a girl starts puberty. During puberty, a girl will have breast growth, start to accumulate body fat around the hips and thighs, and have a growth spurt. Estrogen and progesterone are also involved in the regulation of a girl’s menstrual cycle. These hormones also play a role in pregnancy.
