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The Endocrine System

What Does The Endocrine System Do?

Many of our body’s functions – growth, metabolism, sexual development and function, among others – are controlled by the endocrine system, which consists of glands that make and secrete regulatory chemicals called hormones.

Hormones are secreted into the bloodstream in one part of the body and travel through the bloodstream to control what happens in another part.

Endocrine System

What Makes Up The Endocrine System?

The Endocrine system consists of the hypothalamus, pituitary, thyroid, parathyroids, adrenals, pineal body, and the reproductive glands (the ovaries and the testes). The pancreas is also part of this hormone-secreting system, even though it is also associated with the digestive system because it produces and secretes digestive enzymes.

Although the endocrine glands are the body’s main hormone producers, some non-endocrine organs — such as the brain, heart, lungs, kidneys, liver, thymus, skin, and placenta — also produce and release hormones.

Hypothalmus

Hypothalamus and PituitaryThe hypothalamus is part of the brain that lies just above the pituitary gland. It releases hormones that start and stop the release of pituitary hormones.

The hypothalamus controls hormone production in the pituitary gland through several “releasing” hormones. Some of these are growth hormone-releasing hormone, or GHRH (controls GH release); thyrotropin-releasing hormone, or TRH (controls TSH release); corticoptropin-releasing hormone, or CRH (controls ACTH release).

Pituitary

Even though it is no larger than the size of a pea, the pituitary gland is sometimes called the “master gland” because of its great influence on the other body organs.

Located just below the hypothalmus, the pituitary gland is divided into two parts, front (anterior) and back (posterior).

The anterior pituitary produces several hormones:

  • Prolactin or PRL – PRL stimulates milk production from a woman’s breasts after childbirth and can affect sex hormone levels in the ovaries in women and the testes in men.

  • Growth hormone or GH – GH stimulates growth in childhood and is important for maintaining a healthy body composition. In adults it is also important for maintaining muscle mass and bone mass. It can affect fat distribution in the body.

  • Adrenocorticotropin or ACTH – ACTH stimulates production of cortisol by the adrenal glands. Cortisol, a so-called “stress hormone, helps maintain blood pressure and blood glucose levels, and is vital to survival.

  • Thyroid-stimulating hormone or TSH – TSH stimulates the thyroid gland to make thyroid hormones, which, in turn, control (regulate) the body’s metabolism, energy, growth and development, and nervous system activity.

  • Luteinizing hormone or LH – LH regulates testosterone in men and estrogen in women.

  • Follicle-stimulating hormone or FSH – FSH promotes sperm production in men and stimulates the ovaries to release eggs (ovulate) in women. LH and FSH work together to allow normal function of the ovaries or testes.

The posterior pituitary produces two hormones:

  • Oxytocin – Oxytocin causes milk in nursing mothers and contractions during childbirth.

  • Antidiuretic hormone or ADH – ADH, also called vasopressin, regulates water balance. If this hormone is not secreted properly, this can lead to problems of sodium (salt) and water balance, and could also affect the kidneys so that they do not work as well.

In response to over- or underproduction of pituitary hormones, the target glands affected by these hormones can produce too many or too few hormones of their own. For example, too much growth hormone can cause gigantism, or excessive growth, while too little GH may cause dwarfism, or very short stature.

Thyroid

ThyroidThe thyroid, located in the front part of the lower neck, below the Adam’s apple, is shaped like a bow tie or butterfly and produces the thyroid hormones thyroxine and triiodothyronine. These hormones control the rate at which cells burn fuels from food to produce energy. As the level of thyroid hormones increases in the bloodstream, so does the speed at which chemical reactions occur in the body.

Thyroid hormones also play a key role in bone growth and the development of the brain and nervous system in children. The production and release of thyroid hormones is controlled by thyrotropin, which is secreted by the pituitary gland.

Parathyroid

ParathyroidAttached to the thyroid are four tiny glands that function together called the parathyroids. They release parathyroid hormone, which regulates the level of calcium in the blood with the help of calcitonin, which is produced in the thyroid.

In response to too little calcium in the diet, the parathyroid glands make parathyroid hormone, or PTH, that takes calcium from bones so that it will be available in the blood for nerve conduction and muscle contraction.

Adrenals

AdrenalsThe body has two triangular adrenal glands, one on top of each kidney. The adrenal glands have two parts, each of which produces a set of hormones and has a different function.

The outer part, the adrenal cortex, produces hormones called corticosteroids that influence or regulate 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, the adrenal medulla, produces catecholamines, such as epinephrine. Also called adrenaline, epinephrine increases blood pressure and heart rate when the body experiences stress. (Epinephrine injections are often used to counteract a severe allergic reaction.)

Pineal Gland

Pineal GlandThe pineal body, or pineal gland, is located in the middle of the brain.

It secretes a hormone called melatonin, which may help regulate the wake-sleep cycle of the body.

Scientists are still learning how the pineal gland works.

Reproductive Glands

The reproductive glands are the testes (in males) and the ovaries (in females).

  • Testes

    TestesMales have twin reproductive glands, called testes, that produce the hormone testosterone. Testosterone helps a boy develop and then maintain his sexual traits. During puberty, testosterone helps to bring about the physical changes that turn a boy into an adult male, such as growth of the penis and testes, growth of facial and pubic hair, deepening of the voice, increase in muscle mass and strength, and increase in height.

    Throughout adult life, testosterone helps maintain sex drive, sperm production, male hair patterns, muscle mass, and bone mass.

  • Ovaries

    OvariesThe two most important hormones of a woman’s twin reproductive glands, the ovaries, are estrogen and progesterone. These hormones are responsible for developing and maintaining female sexual traits, as well as maintaining a pregnancy.

    Along with the pituitary gonadotropins (FH and LSH), they also control the menstrual cycle.

    The most common change in the ovarian hormones is caused by the start of menopause, part of the normal aging process. Loss of ovarian function means loss of estrogen, which can lead to hot flashes, thinning vaginal tissue, lack of menstrual periods, mood changes and bone loss, or osteoporosis.

Pancreas

PancreasThe pancreas is an elongated organ located toward the back of the abdomen behind the stomach. The pancreas has digestive and hormonal functions. One part of the pancreas, the exocrine pancreas, secretes digestive enzymes.

The other part of the pancreas, the endocrine pancreas, secretes hormones called insulin and glucagon. Insulin is a hormone that helps glucose move from the blood into the cells where it is used for energy.

The pancreas also secretes glucagon when the blood sugar is low. Glucagon tells the liver to release glucose, which is stored in the liver as glycogen, into the bloodstream. These hormones regulate the level of glucose (sugar) in the blood.

5 Interesting Facts About The Endocrine System

  1. The endocrine system has no ducts. The hormones it produces are released directly into the bloodstream which carries it to another part of the body.

  2. The endocrine system is responsible for producing about 30 distinct hormones. All these hormones have very distinct jobs to do.

  3. The rush of adrenaline one gets when facing adventure or fear is the result of the adrenal glands production of epinephrine hormone, or adrenaline as we otherwise know it.

  4. We must be grateful to the pineal gland for our sweet sleep. It secretes melatonin which regulates our sleep.

  5. The endocrine system is responsible for the production of insulin. The failure to produce insulin will result in diabetes.

How Does The Endocrine System Work?

Once a hormone is secreted, it travels from the endocrine gland through the bloodstream to target cells designed to receive its message. Along the way to the target cells, special proteins bind to some of the hormones. The special proteins act as carriers that control the amount of hormone that is available to interact with and affect the target cells.

Also, the target cells have receptors that latch onto only specific hormones, and each hormone has its own receptor, so that each hormone will communicate only with specific target cells that possess receptors for that hormone. When the hormone reaches its target cell, it locks onto the cell’s specific receptors and these hormone-receptor combinations transmit chemical instructions to the inner workings of the cell.

When hormone levels reach a normal or necessary amount, further secretion is controlled by important body mechanisms to maintain that level of hormone in the blood. This regulation of hormone secretion may involve the hormone itself or another substance in the blood related to the hormone.

For example, if the thyroid gland has secreted adequate amounts of thyroid hormones into the blood, the pituitary gland senses the normal levels of thyroid hormone in the bloodstream and adjusts its release of thyrotropin, the pituitary hormone that stimulates the thyroid gland to produce thyroid hormones.

Another example is parathyroid hormone, which increases the level of calcium in the blood. When the blood calcium level rises, the parathyroid glands sense the change and decrease their secretion of parathyroid hormone.

This turnoff process is called a negative feedback system.

What Can Go Wrong With Your Endocrine System?

These are some possible endocrine disorders:

Adrenal insuffiency

This condition is characterized by decreased function of the adrenal cortex and the consequent underproduction of adrenal corticosteroid hormones. The symptoms of adrenal insufficiency may include weakness, fatigue, abdominal pain, nausea, dehydration, and skin changes. Doctors treat adrenal insufficiency by giving replacement corticosteroid hormones.

Cushing Syndrome

Excessive amounts of glucocorticoid hormones in the body can lead to Cushing Syndrome. In children, it most often results when a child takes large doses of synthetic corticosteroid drugs (such as prednisone) to treat autoimmune diseases such as lupus. If the condition is due to a tumor in the pituitary gland that produces excessive amounts of corticotropin and stimulates the adrenals to overproduce corticosteroids, it’s known as Cushing Disease.

Symptoms may take years to develop and include obesity, growth failure, muscle weakness, easy bruising of the skin, acne, high blood pressure, and psychological changes. Depending on the specific cause, doctors may treat this condition with surgery, radiation therapy, chemotherapy, or drugs that block the production of hormones.

Type 1 Diabetes

Type 1 Diabetes is usually diagnosed in children and young adults, and was previously known as juvenile diabetes. In Type 1 Diabetes, the body does not produce insulin. Insulin is a hormone that is needed to convert sugar (glucose), starches and other food into energy needed for daily life.

Type 1 Diabetes can cause long-term complications, including kidney problems, nerve damage, blindness, and early coronary heart disease and stroke.

Type 2 Diabetes

Unlike people with Type 1 Diabetes, people with Type 2 Diabetes produce insulin; however, either their pancreas does not produce enough insulin or the body cannot use the insulin adequately. This is called insulin resistance. When there isn’t enough insulin or the insulin is not used as it should be, glucose (sugar) can’t get into the body’s cells. When glucose builds up in the blood instead of going into cells, the body’s cells are not able to function properly.

Type 2 Diabetes is the more common type. Anyone can get Type 2 Diabetes. However, those at highest risk for the disease are those who are over 45, are obese or overweight, have had gestational diabetes, have family members who have Type 2 Diabetes, have prediabetes, are inactive, have low HDL cholesterol or high triglycerides levels or have high blood pressure.

Growth Hormone problems

Too much growth hormone in children who are still growing will make their bones and other body parts grow excessively, resulting in gigantism. This rare condition is usually caused by a pituitary tumor and can be treated by removing the tumor.

In contrast, when the pituitary gland fails to produce adequate amounts of growth hormone, a child’s growth in height is impaired. Hypoglycemia (low blood sugar) may also occur in kids with growth hormone deficiency, particularly in infants and young children with the condition.

Hyperthyroidism

Hyperthyroidism is a condition in which the levels of thyroid hormones in the blood are excessively high. Symptoms may include weight loss, nervousness, tremors, excessive sweating, increased heart rate and blood pressure, protruding eyes, and a swelling in the neck from an enlarged thyroid gland (goiter).

Hypothyroidism

Hypothyroidism is when the levels of thyroid hormones in the blood are abnormally low. Thyroid hormone deficiency slows body processes and may lead to fatigue, a slow heart rate, dry skin, weight gain, constipation, and, in kids, slowing of growth and delayed puberty.

How Do Your Keep Your Endocrine System Healthy?

To keep your Endocrine system healthy, follow these 3 rules:

  1. Eat a healthy diet in order to maintain a healthy weight and balance hormones.

  2. Be aware of your family history. Monitor your endocrine system if endocrine disorders such as diabetes or hypothyroidism run in your family.

  3. Reduce stress to avoid extended chemical secretions that can result in disorders or a weakened immune system.

This article is part of a series called “Your Body: An Owner’s Manual” which explains how your body systems work and how to maintain them. The first article in the series included a picture of my wife, fitness coach Kathie Lamir, who exemplifies a healthy body. Pictures of Kathie were so well received that I have included one with each article in the series

Fitness Trainer Kathie Lamir

Your Body: An Owner’s Manual

There was a time when I didn’t know much more about the human body than that my wife’s was beautiful!

Fitness Guru Kathie LamirSee what I mean?

How strange, I thought. We only get one body. It has to last a lifetime. And the better it works, the better we feel. Why wouldn’t we want to know everything about how it works and how to maintain it?

Yet most of us don’t. We know more about the insides of our car than how our body functions.

Maybe that’s because cars come with owner’s manuals, but your body doesn’t.

Well, problem solved.

This article introduces a 12-part series that will explain how your body works. This series is the instruction manual for your body that you never got.

This initial article will briefly describe the 11 human body systems.

Articles about each of the body systems will follow, one a day. Each article will answer these questions . . .

  1. What Does The System Do?

  2. What Makes Up The System?

  3. How Does The System Work?

  4. What Can Go Wrong With The System?

  5. How Do You Keep The System Healthy?

And each article will include “5 Interesting Facts About The System.”

Before starting this discussion of our body systems, however, you must understand that dividing your body into 11 systems for the purpose of studying them does not mean that they are independent systems. Far from it, they are interconnected and dependent on each other.

In fact, some body parts are part of multiple systems. For example, the long bones (like the femur) are not only part of the skeletal system, but they are also part of the circulatory system because they manufacture blood cells. And the ovaries are part of the endocrine system as well as the reproductive system. More about all of this later . . .

These are the 11 main human body systems, presented in alphabetical order.

Circulatory System

The circulatory system is made up of your heart, blood vessels and blood. Your heart pumps oxygen-rich blood from your left ventricle into your biggest artery, the aorta. From there, the aorta branches into smaller arteries, which then branch into even-smaller arteries that travel all over the body. When blood reaches the smallest blood vessels, called capillaries, an exchange occurs. Oxygen, nutrients and hormones are deposited into the cells and waste material from the cells, such as carbon dioxide, is collected for the return trip to the heart.

Veins carry the blood back to the heart where it enters the right atria, passes through the right ventricle and is sent to your lungs where, in capillaries in the lungs, the waste carbon dioxide is deposited and oxygen is picked up. The newly oxygenated blood returns to the heart and, this time, it enters the left atria. From there it goes to the left ventricle and, from there, it is pumped again .

Click here to learn more about your circulatory system.

Digestive System

Your digestive system consists of organs that break down food into the protein, vitamins, minerals, carbohydrates and fats that your body uses for energy and for building and repairing cells and tissues.

Food passes from your mouth down through a muscular tube called the esophagus, and into the stomach, where food continues to be broken down. The partially digested food passes into the small intestines where it is broken down into nutrients which enter the bloodstream through tiny hair-like projections called villi. The liver, the gallbladder and the pancreas produce enzymes and substances that help with digestion in the small intestine.

The last section of the digestive tract is the large intestine, which includes the cecum, colon, and rectum. Indigestible remains of food are eliminated through the anus.

Click here to learn more about your digestive system.

Endocrine System

The endocrine system is made up of a group of glands that produce the body’s long-distance messengers, or hormones. Hormones are chemicals that control body functions such as metabolism, growth, and sexual development. The glands, which include the pituitary gland, thyroid gland, parathyroid glands, adrenal glands, pineal body, pancreas, ovaries, and testes, release hormones directly into the bloodstream, which transports the hormones to organs and tissues throughout the body.

Click here to learn more about your endocrine system.

Immune System

The immune system is our body’s defense system against infections and diseases. Organs, tissues, cells, and cell products work together to respond to dangerous organisms (like viruses or bacteria) and substances that may enter the body from the environment.

An anatomic response physically prevents threatening substances from entering your body. Examples of the anatomic system include the mucous membranes and the skin. If substances do get by, the inflammatory response goes on attack.

The inflammatory system works by excreting the invaders from your body. Sneezing, runny noses, and fever are examples of the inflammatory system at work.

When the inflammatory response fails, the immune response goes to work. This is the central part of the immune system and it is made up of white blood cells, which fight infection by gobbling up antigens. About a quarter of white blood cells, called the lymphocytes, migrate to the lymph nodes and produce antibodies which fight disease.

Click here to learn more about your immune system.

Lymphatic System

The lymphatic system has three main purposes. It removes excess fluid and waste products from the spaces between the cells and returns them to the blood stream. It aids the immune system in destroying and removing waste, debris, dead blood cells, pathogens, toxins, and cancer cells. And it also absorbs fats and fat-soluble vitamins from the digestive system and delivers these nutrients to be used by the cells of the body.

Click here to learn more about your lymphatic system.

Muscular System

The muscular system is made up of tissues that work with the skeletal system to control movement of the body. Some muscles—like the ones in your arms and legs—are voluntary, meaning that you decide when to move them. Other muscles, like the ones in your stomach, heart, intestines and other organs, are involuntary. This means that they are controlled automatically by the nervous system and hormones—you often don’t even realize they’re at work.

Muscles also generate heat to help regulate your body’s temperature and maintain your posture.

Click here to learn more about your muscular system.

Nervous System

The nervous system is the control system and the network of communication for your body.

Think of your brain as a central computer that controls all voluntary and involuntary bodily functions.

Your “computer” acts through a network that relays messages back and forth from the brain to different parts of the body.

This “network” consists of the spinal cord and nerves. The spinal cord runs from the brain down through the back to nerves which branch out to every organ and part of your body.

When a message comes into the brain from anywhere in the body, the brain tells the body how to react. For example, if you accidentally touch a hot stove, the nerves in your skin shoot a message of pain to your brain. The brain then sends a message back telling the muscles in your hand to pull away. Fortunately, all of this occurs lightning fast.

Click here to learn more about your nervous system.

Reproductive System

The reproductive system allows humans to produce children. Sperm from the male, which is produced in the testes, fertilizes the female’s egg, or ovum, in the fallopian tube. The fertilized egg travels from the fallopian tube to the uterus, where the fetus develops over a period of nine months.

Click here to learn more about your reproductive system.

Respiratory System

The respiratory system brings air into the body and removes carbon dioxide. It includes the nose, trachea, and lungs.

When you breathe in, air enters your nose or mouth and goes down a long tube called the trachea. The trachea branches into two bronchial tubes, or primary bronchi, which go to the lungs. The primary bronchi branch off into even smaller bronchial tubes, or bronchioles. The bronchioles end in the alveoli, or air sacs. Oxygen follows this path and passes through the walls of the air sacs and blood vessels and enters the blood stream. At the same time, carbon dioxide passes into the lungs and is exhaled.

Click here to learn more about your respiratory system.

Skeletal System

The skeletal system has a number of functions, some obvious and some less so. Of course, it supports your body and gives it structure.

However, in addition, your skeletal system works with the bones to allow movement, protects your internal organs, produces blood (in the bone marrow) and stores minerals such as calcium and phosphorous which it releases into the blood when necessary.

Click here to learn more about your skeletal system.

Urinary System

The urinary system eliminates waste from the body, as urine. The kidneys remove waste from the blood. The waste combines with water to form urine. From the kidneys, urine travels down two thin tubes called ureters to the bladder. When the bladder is full, urine is discharged through the urethra.

Click here to learn more about your urinary system.

Oh . . . if you want to learn more from the world’s greatest personal trainer, my wife Kathie Lamir, this is her website.