The Endocrine System

The endocrine system plays an important role in reproduction. Male and female bodies have different reproductive glands and hormones with their own distinct functions. Hormones control the growth of the body during childhood and guide sexual development during teenage years.

Hormones continue governing sexual reproduction into older adulthood.

Components of the endocrine system include:

Hypothalamus Pituitary gland Pineal gland Thyroid and parathyroid Adrenal glands Pancreas Testes and ovaries

Many hormones affect the body during pregnancy, the time in which a fetus develops inside a woman's body. Hormones help the fetus inside the woman's body develop its structures and organs. Hormones alter the shape of a pregnant woman's body and organs. They also aid in the healthy functioning of the fetus, which can't support itself. The human chorionic gonadotropin (hCG) hormone increases the size of the uterus to accommodate a growing fetus. The increase in hCG can cause nausea and vomiting, a condition referred to as morning sickness.

An estrogen (female sex hormone) called progesterone maintains the size of the uterus throughout pregnancy.

The endocrine system is the system of the body responsible for growth and development. The system is made up of: Glands - organs that create and release chemical substances into the blood Hormones - the chemical substances created by glands Organs are groups of tissues that work together to perform a task. Tissues are groups of similar cells that work together. Cells are the basic structural and functional units of life

Chemical substances are fixed combinations of chemical elements. A chemical element is a substance composed of one atom, the smallest form of matter. An example of a chemical element is oxygen, an essential gas needed for breathing. Chemical substances always have the same structure: water, for example, has two hydrogen atoms and one oxygen atom. Adding or subtracting atoms would change the chemical substance. Molecules are stable chemical substances with two or more atoms.

Glands are organs that create and release special chemical substances into the blood. Glands are composed of epithelial tissue, a type of tissue that is able to secrete (make and release) and absorb certain substances.

Different glands have different physical structures. Healthy glands are always producing and storing hormones, which they release in specific amounts. You will learn about hormones next.

The endocrine system uses hormones to carry out several important functions, including:

Growth and development Metabolism regulation Stress response Mood regulation Reproduction

Metabolism is the process by which chemicals and other molecules change into different substances. Metabolism is responsible for two important functions in the human body: Assisting in digestion, the process of converting food into nutrients and waste Constructing the building blocks of new cells

Hormones govern the rate of metabolism and its processes in the body. Under certain conditions, glands will release hormones that instruct cells to speed up or slow down metabolism.

Hormones control a person's growth and development throughout life. As a fetus (unborn child) grows inside a woman's body during pregnancy, hormones instruct its cells to develop into organs and physical structures. Hormones also control the fetus's development into a male or female.

Hormones have the ability to accelerate or stunt growth and development after birth as well. If growth hormones are not released correctly in the years following birth, people may not grow to their full potential.

Perimenopause is the stage in a woman's life during which ovaries begin to secrete lower levels of estrogens. Those lowered levels have a significant impact on the body. For example, menstruation, the monthly cycle of shedding lining from the uterus, becomes more irregular and eventually stops. Menopause is the time of life when a woman completely stops releasing ova. Estrogen levels become further unbalanced as menstruation stops, and that can affect a woman's mood and cause hot flashes, which are sudden, unexplained feelings of heat.

Postmenopause describes the time of life after menopause is complete. Hormone levels eventually stabilize, but a woman can no longer become pregnant.

Hormones also affect mood, which is a person's emotional state. Some glands in the endocrine system release hormones in response to exposure to light. During winter months, when daylight is not as plentiful, those hormones are released less frequently, which may negatively affect mood.

Sex hormones also affect mood. Female bodies experience a monthly reproductive cycle that is governed by hormones. As hormone levels shift throughout the month, a woman's mood also can shift.

Different hormones - and different levels of hormones - are released at different stages of a person's life.

Some of the stages of life in which hormonal changes occur include: Puberty Pregnancy Menopause Older adulthood

Puberty is the time of life when children mature into adults who can sexually reproduce. The sex hormones, androgens and estrogens, guide that transformation. Androgens cause boys to grow facial hair and pubic hair. They cause the voice to deepen, and they initiate rapid growth of muscles, bones, and male sexual organs. Estrogens cause girls to develop breasts, pubic hair, and wider hips. Both classes of sex hormones initiate the development of sex cells, specifically sperm in males and ova (eggs), in females.

Sperm and ova contain genetic information that creates a new life when the two types of sex cells are combined. Genetic information is the chemical programming that guides a new life's development. Puberty begins in the early teenage years, when the pineal gland reduces melatonin production. Before then, melatonin prevents other hormones from initiating sexual development.

Stress is mental or physical strain, which might include a sense of fear or anxiety. When the brain perceives stress, it sends signals to the endocrine system as a way to respond to what it views as potential danger. In response to that sense of danger, the endocrine system activates the fight-or-flight response, a response to stress that alters the body's priorities temporarily. Hormones reduce the body's perception of pain, increase the focus of the senses, and divert energy toward muscles (soft tissues that contract for movement) and away from the processes of other organs.

That response is important during times of stress and danger, but prolonged exposure to the fight-or-flight response can impair organ function and cause more stress, creating a damaging cycle of stress responses.

The testicles are two glands located in the scrotum, a sac between the legs of the male body. The testicles are part of both the endocrine and reproductive systems. The reproductive system is the body system that creates new life. The testicles produce hormones called androgens, which guide the development of male characteristics. One type of androgen is testosterone, a hormone that matures the male sex organs and increases both muscle strength and bone density. Women do not have testicles, so they naturally have lower levels of testosterone and other androgens.

The ovaries are two glands in the female body that are attached to the uterus, the female sex organ in which a fetus develops during pregnancy. The ovaries are analogous to the testicles in the male body; they aren't the same glands, but they perform similar functions. Like the testicles, ovaries are part of the endocrine and reproductive systems. Ovaries produce estrogens, which are female sex hormones. An example of an estrogen is estradiol, a hormone with many functions, including increasing bone strength. Estrogens mature the female sex organs and increase the storage of fat in the body. They affect mood if they are not maintained at regular levels. Men do not have ovaries, so they naturally have lower levels of estrogens.

The adrenal glands are glands located on the top of each kidney. The kidneys are two bean-shaped organs, located in the abdominal area, that filter waste and toxins from blood. Both adrenal glands create hormones that regulate the body's response to stress and assist the kidneys. For example, the adrenal glands create epinephrine and aldosterone. Epinephrine (also called adrenaline) is a hormone that activates the fight-or-flight response. Aldosterone is a hormone that helps the kidneys supply blood with enough necessary nutrients.

The pancreas is a long, flat gland located behind the stomach. The pancreas produces several hormones. One of the most important is insulin, a hormone that regulates the level of sugar in the blood by encouraging muscles and other tissues to absorb sugar. In addition to its role in the endocrine system, the pancreas also secretes enzymes (molecules that speed up chemical reactions) that digest food in the duodenum. The duodenum is the first part of the small intestine. The small intestine is a narrow tube in which food is broken down and absorbed into the body.

The thalamus is a structure located in the brain, the primary organ of the nervous system. The nervous system is the system that coordinates all actions of the body. The thalamus is made up of two lobes connected to the center of the brain. Lobes are rounded subsections of a biological structure. The hypothalamus is a section of the brain located beneath the thalamus. The word hypothalamus means "below the thalamus." The hypothalamus is not a gland, but part of the brain that links the nervous system to the endocrine system and regulates hormone activity in the body. It does that by releasing its own hormones, which stimulate the gland connected to it, the pituitary gland.

The pituitary gland is the "master" gland that controls how all other glands in the endocrine system release hormones. The pituitary gland is located in the brain, beneath the hypothalamus. The pituitary gland creates and releases hormones that instruct the other endocrine glands to create and release hormones. In addition to controlling the other glands of the endocrine system, the pituitary gland releases somatotropin, also called human growth hormone (HGH), which encourages the growth of cells throughout the body.

Many hormones are released less frequently as people age. Decreases in the levels of growth hormone reduce muscle mass and strength, so the body becomes weaker and more difficult to repair. Lower levels of testosterone in both sexes cause a decrease in bone strength, which further weakens the body.

The secretion of melatonin, the hormone produced by the pineal gland, also slows in old age and, as a result, the elderly might sleep less at night.

The pineal gland is a small gland located behind the thalamus in the brain. Its primary product is melatonin, a hormone that controls the body's sleep cycle. The pineal gland secretes more melatonin after the sun sets and the body is no longer exposed to sunlight. Increased melatonin levels cause sleepiness, so the pineal gland and melatonin work together to regulate a human's sleep cycle. Serotonin is a neurotransmitter that affects the brain's feelings of sleepiness. Neurotransmitters are chemicals in the brain that send signals between brain cells. Because serotonin affects the brain's feelings of happiness and well-being, the pineal gland also plays a part in regulating mood.

The thyroid is an endocrine gland located at the base of the throat that produces hormones that control metabolism and cell development. Thyroxine is one of the hormones produced by the thyroid. It can increase heart rate and the rate at which the body changes nutrients from food into energy. That energy can fuel muscles or grow and repair other cells. On the surface of the thyroid are four parathyroid glands, which secrete a parathyroid hormone. The hormone that regulates calcium levels in the body.

Hormones are the chemical substances created by glands. Hormones can bind to a cell and instruct it to perform a specific action. The endocrine system uses hormones to guide the growth and development of the human body.

When glands release hormones into the bloodstream, they circulate through the body until they find target cells, which are cells that contain the correct receptors for that hormone. Hormone receptors are molecules that bind with a hormone and then instruct the cell to perform an action, such as grow or divide.