Hormones are chemical messengers. They travel through the blood, passing signals to organs and tissues. For the most part, hormones work slowly, affecting growth and development, mood, sexual function, and metabolism. Hormone levels can spike and fall, which leads to a variety of health, emotional, and other problems. Some hormones are linked to personality traits and behaviors, while others signal specific reactions that keep the body functioning normally.
Various glands and organs within the endocrine system produce hormones, including the hypothalamus, pineal, and pituitary glands in the brain, the thyroid and parathyroid in the neck, as well as the pancreas, adrenal glands, testes, and ovaries. The thymus is also part of the endocrine system. It is located behind the breast bone and helps establish a healthy immune system in fetal development and childhood. Although it grows rapidly during fetal development, growth slows down after birth until puberty, when it begins to shrink.
Several other organs produce hormones or store and release them when necessary. The stomach and small intestine make and secrete leptin and ghrelin, two hormones that affect appetite and satiety. Body fat or adipose tissue exists throughout the body, including surrounding some organs. It produces several hormones responsible for controlling blood pressure, insulin sensitivity, and more. The heart also releases peptide hormones that help lower elevated blood pressure.
The placenta is an endocrine organ that develops while a woman is pregnant. It produces several hormones, including estrogen, progesterone, and human chorionic gonadotropin (hCG). These hormones help sustain a healthy pregnancy; they stimulate the development of breast milk, prevent uterine contractions until labor, and increase the fats and sugars in the blood so the developing fetus gets the nourishment it needs.
Adrenaline is one of the most important hormones, produced in the adrenal glands located above the kidneys. Adrenaline is responsible for the fight-or-flight response and is released during times of stress. It prompts the contraction of blood vessels to get more blood to the major organs and to open airways to bring in more oxygen. The body's pain threshold rises, and there is an increase in strength and awareness of one's surroundings. Once triggered, these effects can last for up to an hour.
Cortisol hormones are also connected to the stress response. This steroid hormone is also produced in the adrenal glands, but its secretion is controlled by the pituitary gland and the hypothalamus. Most cells are sensitive to cortisol, which means it has system effects, not all of which are stress-related. Cortisol helps control blood sugar, reduces inflammation, and regulates metabolism. It is also essential to fetal growth in pregnancy.
The body could not grow without the human growth hormone or GH produced by the pituitary gland. It affects how tall children grow and lowers body fat and increases muscle mass throughout childhood and puberty. GH also affects metabolism in both children and adults. Synthetic GH can treat deficiencies that cause short stature or muscle wasting and syndromes such as Prader-Willi and Turner.
The pancreas produces insulin and controls the absorption of glucose, which gives cells the energy they need to function; it can also be converted to fat if necessary. Diabetes occurs when the body does not make enough insulin or is unable to use it properly. Type 1 is present from birth, when the pancreas is unable to produce insulin. In type 2 diabetes, the pancreas is unable to produce enough insulin to meet the demands of the body. Type 2 usually develops in adulthood and is often the result of lifestyle choices. In either case, without insulin hormones, blood sugar levels rise, and cells are unable to use it for energy effectively.
Melatonin is one of the primary hormones responsible for sleep. It is created in the brain by the pineal gland and released cyclically — more melatonin is produced at night, telling the body that it is time to go to sleep. In other animals, melatonin stimulates the growth of the winter coat and signals the start of hibernation. Melatonin is not necessary for sleep, but it is believed to improve this vital stage.
Several hormones influence mood, but the main one is serotonin. It impacts the whole body and influences everything from sleep to digestion to eating but is very prominent in brain function. Serotonin is a natural mood regulator. Normal levels link to emotional stability, calm, and happiness. Low levels of serotonin can cause depression, anxiety, and even OCD.
We have listed only a few of the most recognizable hormones. Experts believe there are more than 70 in all, affecting everything from metabolism to circadian rhythm to sexual arousal. Hormones and their effects are very complex. Considering how important they are to maintaining normal body function, it is easy to see how problems in the endocrine system can have significant consequences.
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