The Endocrine System for Dummies

Written by Lisa Victoria Larsen

The endocrine system is in charge of creating and releasing the hormones that is needed to maintain countless bodily functions. The tissues of the endocrine system includes your hypothalamus, pituitary gland, pineal gland, thyroid gland, parathyroid glands, adrenal glands, pancreas and reproductive organs.

Hormones are chemicals. They carry instructions through your blood to your organs, skin, muscles and other tissues. There are more than 50 different hormones and they affect almost every aspect of your body. They tell your organs what to do and when to do it.

Glands are tissues that create and release substances. They send hormones directly into your bloodstream.

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The endocrine system controls the metabolism, internal balance (homeostasis), growth, development, reproduction, sleep, mood, energy, digestion, blood sugar, sexual drive, blood pressure, and the nervous system.

• Metabolism provides energy for essential body functions like breathing, digestion, circulating blood, regulating body temperature and growing and repairing cells.

  
  

  It refers to the chemical processes that happens in your body when you eat, drink, rest, and breathe. The process is complex, regulating conversion of the things you digest to combine calories and oxygen to create and release energy. And it never stops. We have this thing called Basal Metabolic Rate (BMR), which refers to the absolute minimum amount of energy you need to exist. This amount is individual. There is a difference between a fast metabolism and a slow metabolism. People with fast metabolisms burns many calories even while resting. The ones with a slow metabolism needs fewer calories to keep everything going. A fast BMR does not necessarily lead to a thinner body. They just need more energy to maintain their essential body functions.
  

  Many factors can weigh in on how well your metabolism works. For instance:
  

  - Muscle mass; People with more muscle mass tend to have faster metabolisms, and it takes more energy to build and upkeep muscle mass than fat.
  

  - Age; When getting older, muscle mass tends to get smaller. This slows down our metabolism.
  

  - Gender; Men usually have faster metabolisms than women because they have more muscle mass, bigger bones and less body fat. Women generally needs more body fat to reproduce.
  

  - Genes; What you inherit from your parents can be a factor when it comes to your ability to build and store muscle mass.
  

  - Activity; Exercise in all forms cause your body to burn more energy than it does resting. This includes walking, sports, raising small kids etc.
  

  - Smoking; One reason people who quit smoking may gain weight is that nicotine speeds up your metabolism. Although it may be very negative for other health issues like cancer, high blood pressure, coronary artery disease.

• Homeostasis is, in simple terms, a self-regulating process. It involves three mechanisms; a receptor, a control center and an effector. These three work together to keep your body in balance, noticing changes in your body and then starting processes to regulate your system. It refers to any automatic process that anyone needs to stay balanced on the inside, and the body does this to make sure that everything works the right way and we stay alive. It really is quite complex.

  In a state of homeostasis, your levels are rising and falling as responses to changing enviroments, for instance blood sugar, blood pressure, energy level, acid levels, oxygen, proteins, temperature, hormones and electrolytes. When the system is disturbed, your body will react to create balance again.

  This can be made possible by the nervous system, the hormonal system or electrical currents. Allostasis is another term that is used to describe our body's ability to foresee, adapt and deal with future events of balance. It really is preparing for needs and managing resources so that your body can adjust before the problems arise.
  

  - The receptor of homeostasis; these are cells, tissues and organs that track your system and spots any changes. When the change comes, they notify the control center.

  - The control centers are often found in the brain, and are the determinators of what is "your normal" and what to do to achieve this. The control center will notify the effector.

  
  

  - The effector is your cells, tissues and organs that then will react to the signals and start the correcting process to achieve the wanted balance.

• Growth; three different ways that we grow are through cell count increase, cell mass increase and a rise of non-cellular particles that circles the cell. We grow from birth until death in one way or another. It is a biological process that happens as a result of formation of new cells and packing proteins or other materials into cells that already are there. The growth is not constant in every part of the body, as it is different rates of maturing in different tissues and regions of the body. Human growth hormones (HGH) are produced in your brain's pituitary gland, which controls your height, bone lenght and muscle growth. These hormones increase during childhood and peaks at puberty. Throughout life, the hormones regulates fat, muscle mass, tissue and bones, in addition to insulin and blood sugar levels. These hormones tells your liver to produce a substance called insulin-like growth factor (IGF-1). Acromegaly is a condition that is caused by excess levels of growth hormones, typically as a result of a pituitary tumour.

• Development; human organs and organ systems develop in a process called organogenesis. The pituitary gland sends out two hormones concerning development, follicle stimulating hormone (FSH) and luteinizing hormone (LH). These make sure that we develop male or female reproduction abilities.

  The thyroid is another important gland when it comes to development. Without thyroid hormones, your body's development will not be normal. The thyroid is the body's first endocrine gland to develop in the gestation process. In adults, thyroid hormones can influence mood and behavior. Thyroid dysfunction can affect neurotransmitter systems and lead to psychiatric disorders.

  Adrenocorticotropic hormone (ACTH) controls the coordinated development of the vasculature and endocrine tissue mass. ACTH is a tropic hormone that indirectly affects target cells by first stimulating other endocrine glands. ACTH stimulates the adrenal glands to produce cortisol, the stress hormone, which again plays a role in glucose metabolism and immune function.

• Reproduction; the main hormones of reproduction are estrogen, testosterone and progesterone. They are responsible for puberty, menstruation, menopause, sex drive, sperm production and fetal egg production. They are produced in the female ovaries and male testes. Other hormones that play a part in this are human chorionic gonadotropin (HcG), prolactin, luteinizing hormone (LH) and follicle stimulating hormone (FSH), which are produced, stored and stimulated by the pituitary gland.

  Estrogen causes eggs to mature in the ovaries when women hits puberty. These are then released during the menstrual cycle. In males, testosterone stimulates sperm production in the testes.

  
  

  In males, the endocrine regulation is as follows: - The hypothalamus releases gonadotropin-releasing hormone (GnRH), which stimulates the pituitary gland to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH).

  - FSH and LH travel through your blood and bind to receptors in the testes. - FSH stimulates the production of sperm cells (spermatogenesis). LH stimulates production of testosterone in the testes. - Together, FSH and LH controls the function of the testes. - Your adrenal glands also produce a hormone (DHEA), which your body transforms into testosterone. - Testosterone also signals your body to make new red blood cells, ensures that you bones and muscles stay strong, and enhances libido (the sex drive).

  In females, the endocrine regulation is as follows: - The hypothalamus releases gonadotropin-releasing hormone (GnRH), which stimulates the pituitary gland to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH).

  - FSH and LH travel through your blood and bind to receptors in the ovaries. - FSH and LH promote ovulation and stimulate secretion of estradiol (an estrogen) and progesterone from the ovaries. - Estrogen and progesterone circulate in the bloodstream, almost entirely bound to plasma proteins. Only unbound estrogen and progesterone appears to be biologically active. - They stimulate the uterus, vagina and breasts to prepare for pregnancy.

• Sleep interacts with the endocrine system over a wide range of hormones. But what is really sleep? It is a state in which the consciousness is lost and motoric function is reduced. It also comprises different stages of brain waves of different patterns, with the most well known being rapid eye movement (REM) and non-rapid eye movement (NREM) sleep. NREM is characterized by orderly synchronized brain activity, with the brain moving from phases of light to deep sleep. Deeper sleep means slower brain waves. While your muscles are relaxed, they are not paralyzed. On the other hand is REM, which occurs after slow-wave sleep is completed. In the REM stage, the brain shows very disorderly brain waves, similar to the awake brain. Skeletal muscles are paralyzed. Sleep is regulated by the circadian system and the sleep pressure system. Sleep pressure is the need to sleep of any organism at a given moment. Both these systems work in parallel and are responsive to the hours in a day and the organism's homeostatic processes.
  

  Circadian rhytms are shifted by external cues like light and dark, exercise, food intake, temperature and various chemicals/medicines. The master circadian clock is the suprachiasmatic nucleus (SCN) of the hypothalamus.

  The SCN enables the body to sleep in long periods related to external light and dark, which are translated into biological day and night, and also regulates the daily rhythm of hormonal secretion and other biological processes.

  The sleep pressure system determines how much sleep each person needs to return to the normal state.

  When it comes to keeping track of the day-night cycle, the SCN helps with the secretion of high cortisol early in the morning, to be ready and alert for the activity of the wake cycle.
  

  Several hormones are involved in sleep and our circadian rhythm. Growth hormone levels are increased during deep sleep and are vital for cell growth and repair. Growth hormones in turn, affects the regulation and metabolism of glucose, lipids and proteins. Melatonin levels are high during the biological night versus day. It plays an important role in regulating human sleep patterns. Basically it tells your body when to sleep. Melatonin also controls more than 500 genes in the human body, including the genes involved in the immune system. Thyroid stimulating hormone (TSH) concentrations reach their maximum and minimum in the middle of the biological night and afternoon. T3 and T4 concentrations are not associated with circadian rhytmicity.

• Mood is affected by almost all of your hormones in one way or another. The hormones that perhaps impacts your mental health more than others are serotonin, dopamine, thyroid hormones and sex hormones. - Serotonin is a chemical that carries messages between nerve cells in the central nervous system in the brain and throughout your body. It's techically a monoamine neurotransmitter known as hydroxytryptamine (5-HT), which also acts as a hormone. Most of the serotonine found in your body is in your gut. Actually, about 90% of it is found in the cells lining your gastrointestinal tract. It's made from the essential amino acid tryptophan. An essential amino acid means it can't be made by your body. It has to be obtained by the food you eat. Serotonin is often called one of the "feelgood" chemicals. When it's at a normal level, you feel more focused, emotionally stable, happier and calmer. Low levels are associated with depression. - Dopamine is also a monoamine neurotransmitter. It plays a role in the "fight-or-flight" response. It also causes blood vessels to relax or constrict. Dopamine increases salt and urine removal from your body, as well as reduces insulin production in the pancreas. Dopamine is another "feelgood" chemical, being a part of your reward system. This system is designed from an evolutionary standpoint, to reward you when doing the things you need to do to survive, like eat, drink, reproduce and overcome obstacles. As humans, we are hard-wired to seek out situations that releases dopamine in our system. It makes us feel good and we seek more of that feeling. This is why junk food and sugar is so addictive. They trigger the release of a large amount of dopamine into your brain and gives a feeling that you want to repeat. Dopamine makes you experience happiness, motivation, alertness and focus. - Thyroid hormones commonly affect your mood, and the more severe the thyroid disease, the more severe the mood changes. It can cause anxiety, nervousness, irritability, depression, unusual tiredness, loss of apetite, lack of concentration, short temper and anger. - Sex hormones have both organizational and activational effects in the central nervous system.

• Energy levels are heavily dependent on our hormones. And with so many hormones involved, it can be difficult to isolate exactly which ones are responsible for changes in the energy level. Here are a few to consider when detangling your decreased energy health;

  - Thyroid hormones; they are responsible for maintaining balance in the body, affecting temperature, metabolism, heart rate, mood, and energy levels. When you experience hypothyroidism, which is abnormally low thyroid hormones, many body systems slow down, leading to fatigue and low energy. Less energy consumed can lead to weight gain, slower digestion leads to constipation, and the decreasing serotonin levels may result in depression. - Adrenal hormones; cortisol responds to the body's energy needs by regulating metabolism and hunger. Chronic stress can disrupt this system and damage your body's ability to function optimally. - Estrogen and progesterone; when these levels fluctate or drop sharply, many women experience uncomfortable symptoms like hot flashes, mood swings, vaginal dryness, and bone thinning/increased fracture risk. Both low and high estrogen levels may also effect your energy levels significantly. For women, hormone levels can shift dramatically during perimenopause and menopause, whereas men typically experience a slow and gradual decline beginning around age 30. So both men and women can develop symptoms and see their energy levels decline as they approach middle age. Unfortunately, imbalances in a variety of hormones often have similar symptoms. Additionally, an imbalance of one hormone may cascade into more complex conditions since many hormones directly impact each other.

• Digestion hormones regulate the system that produces them, functioning largely independent from the rest of the endocrine system. When food enters the stomach, the wall where the stomach joins the small intestine, gastrin is released, which promotes the flow of acid from the gastric glands in the stomach. These glands also release pepsinogen which is the inactive form of the protein digesting enzyme pepsin, but this process is primarily under nervous control. The entry of the acidified stomach contents into the first part of the small intestine releases secretin (a digestive hormone) and cholecystokinin. Secretin promotes the discharge of fluid and bicarbonate ions from the pancreas and promotes the secretion of bile from the liver, which aids in the digestion of fats.

• Blood sugar is influenced by several hormones. These are: - Insulin; Enhances entry of glucose into cells and storage of glucose as glycogen, or conversion to fatty acids. It also enhances synthesis of fatty acids and proteins and suppresses breakdown of protein into amino acids and triglycerids into free fatty acids. - Amylin; Suppresses glucagon secretion after eating and slows gastric emptying. It also reduces food intake. - GIP; Induces insulin secretion, inhibits apoptosis of the pancreatic beta cells and promotes their proliferation. It also stimulates glucagon secretion and fat accumulation. - Glucagon; Enhances release of glucose from glycogen and synthesis of glucose from amino acids or fats.
  

  - Asprosin; Enhances release of liver glucose during fasting. - Somatostatin; Suppresses release of insulin, pituitary tropic hormones, gastrin and secretin. It also decreases stomach acid production by preventing the release of other hormones (gastrin and histamine), thus slowing down the digestive process. - Epinephrine; Enhances release of glucose from glycogen and fatty acids from adipose tissue. - Cortisol; Enhances gluconeogenesis and antagonizes insulin.
  

  - ACTH; Enhances release of cortisol and fatty acids from adipose tissue. - Growth hormone; Antagonizes insulin. - Thyroxine; Enhances release of glucose from glycogen and absorption of sugars from intestine.

• Sexual drive: Libido naturally varies from person to person. It can also change throughout life. However, the sex hormones testosterone and estrogen, together with the neurotransmitters dopamine and oxytocin regulates libido.

• Blood pressure is regulated by the hormone aldosterone (ALD) by managing the levels of salt (sodium) and potassium in your blood and impacting blood volume. Your blood pressure can also be impacted by several other hormones: - Adrenal glands; if the adrenal glands make too much aldosterone, cortisol or adrenaline-like hormones, it can cause high blood pressure.
  

  - Thyroid gland; high blood pressure can be caused by an underactive or overactive thyroid gland. - Pituitary gland; sometimes problems with the adrenal glands and thyroid gland are due to problems with the pituitary gland. If the pituitary gland sends too much signal to the adrenal galnds or thyroid gland, it can result in high blood pressure. - Parathyroid glands; if the parathyroid glands make too much parathyroid hormone, it can cause high blood pressure. - Pancreas; high blood pressure in adults with obesity may be partially due to elevated insulin levels and insulin resistance.

• The nervous system is designed to protect us from danger through its interpretation of, and reactions to, stimuli. But a primary function of the sympathetic and parasympathetic nervous systems is to interact with the endocrine system to elicit chemicals that provide another system for influencing our feelings and behaviours. When the hormones released by one gland arrive at receptor tissues or other glands, these recieving receptors may trigger the release of other hormones, resulting in a series of complex chemical chain reactions. The endocrine system works together with the nervous system to influence many aspects of human behaviour, including growth, reproduction and metabolism. And the endocrine system also plays a vital role in emotions.