Hormones

Hormones are substances in the blood that are produced by cells of an endocrine gland or by nerve cells in response to a specific nervous or chemical stimulus. They affect the metabolic function of those cells that have the appropriate receptor for the hormone. Hormones are synthesized in one type of cell and then released to direct the function of other cell types. All multicellular organisms (including plants) produce hormones. The best known hormones are those produced by endocrine glands of vertebrate animals, but hormones are produced by nearly every organ system and tissue type in a human or animal body. Hormones are chemical substances made by endocrine glands. These glands pass the hormones directly into the bloodstream, which carries them around the body. In this way, a hormone can cause a change in the body at some distance from the gland where it was made. Hormones are at the center of control for a myriad of biochemical reactions and metabolism. A great number of hormones have been identified in the human body and have been found to be secreted by a number of different organs. Hormones regulate the digestive system, growth, hunger, thirst, blood glucose and cholesterol levels, fat burning and storage, absorption and excretion, internal clocks such as day and night cycles, menstrual cycles, and sex drive. Human hormones, such as human growth hormone (hGH), prolactin (hPRL), placental lactogen (hPL) or growth hormone variant (hGH-V) are homologous protein hormones which are potent endogenous chemical substances asserting specific biological activities on their respective target organs. The biological activities of these hormones are not the same and they differ depending on the hormone and/or the hormone target organ. For example, human growth hormone, which is a protein of the anterior lobe of the pituitary gland, promotes and regulates body growth and morphogenesis, fat mobilization and inhibitions of glucose utilization.

The endocrine system

The endocrine system is a system of ductless glands that regulates bodily functions via hormones secreted into the bloodstream. The endocrine system includes the pituitary gland, thyroid gland, parathyroid glands, adrenal gland, pancreas, ovaries, and testes (see testis). The thymus gland, pineal gland, and kidney are also sometimes considered endocrine organs. The endocrine system (along with the nervous system) controls and regulates the complex activities of the body. The Endocrine system regulates the activities of the body by secreting complex chemical substances (hormones) into the blood stream. The endocrine system is composed of a number of tissues that secrete their products, called endocrine hormones, into the circulatory system; from there they are disseminated throughout the body, regulating the function of distant tissues and maintaining homeostasis. The regulation of body functions by the endocrine system depends on the existence of specific receptor cells in target organs that respond in specialized ways to the minute quantities of the hormonal messengers. Hormones that are produced in the endocrine glands in one part of the body travel through the bloodstream until they encounter special receptors with which they interact to initiate essential biological responses in specific target tissues. Hormones are slow-acting and their effects tend to persist in the body for long periods of time. Hormones are also specific. Each hormone has a unique chemical conformation that matches a particular receptor protein at its target cell. The amounts of hormones are maintained by feedback mechanisms that depend on interactions between the endocrine glands, the blood levels of the various hormones, and activities of the target organ. Hormones act by regulating cell metabolism.

Natural hormones produced by human body

Types of hormones

Hormones differ in how they affect their target cells, and can be classified into three main categories: amine, peptide, and steroid.

Amine hormones - Amine hormones are made from single amino acids. Three major amine hormones (dopamine, norepinephrine, and epinephrine) are known collectively as the catecholamines. The catecholamines are synthesized through enzymatic modification of the amino acid tyrosine. The amine hormones such as the catecho-lamines, melatonin and serotonin are formed by side-chain modifications of either a single tyrosine or tryptophan molecule while the eicosanoid family of hormones are formed from lipids. Amine hormones are soluble and are transported in blood plasma in solution.

Peptide hormones - Peptide hormones are a class of peptides that are secreted into the blood stream and have endocrine functions in living animals. Peptides are simple, small proteins. Peptide hormones are synthesized in the rough endoplasmic reticulum. Usually, a peptide hormone is first synthesized as part of a larger preprohormone. The first step is cleavage of the signal sequence in the rough ER to form a prohormone. Peptide hormones are hydrophilic hormones (that is they are polar and can dissolve in water). Peptide hormones are water soluble.

Steroid hormones - The steroid hormones are synthesized by chemical modification of cholesterol. Steroid hormones are not water-soluble and therefore must be bound to plasma proteins to be transported to their target tissue. The protein binding complicates the activity of steroid hormones, delaying the time to stimulate a biological response. Examples of steroid hormones are testosterone and cortisol. Sterol hormones such as calcitriol are a homologous system.

Lipid and phospholipid hormones - Lipid and phospholipid hormones are derived from lipids such as linoleic acid and phospholipids such as arachidonic acid. The main class is the eicosanoids. Eicosanoids are a large group of molecules derived from polyunsaturated fatty acids. The principal groups of hormones of this class are prostaglandins, prostacyclins, leukotrienes and thromboxanes.

Functions and health benefits of hormones

Antidiuretic hormone (vasopressin) - Antidiuretic hormone affects blood pressure by stimulating capillary muscles and reduces urine flow by affecting reabsorption of water by kidney tubules. Antidiuretic hormone causes kidneys to retain water and, along with aldosterone, helps control blood pressure

Corticotropin (ACTH) - ACTH stimulates the adrenal glands to release glucocorticoid hormones. These hormones are anti-inflammatory in nature, reducing edema and other aspects of inflammation. Corticotropin controls the production and secretion of hormones by the adrenal cortex.

Luteinizing hormone - Luteinizing hormone and follicle-stimulating hormone control reproductive functions, including the production of sperm and semen, egg maturation, and menstrual cycles; control male and female sexual characteristics (including hair distribution, muscle formation, skin texture and thickness, voice, and perhaps even personality traits).

Oxytocin - Oxytocin helps to cause labor and contractions in the body when the body is receptive to its influence. It has stimulant effects on the smooth muscle of the uterus and mammary glands. Oxytocin is involved in reproductive behaviour in both men and women.

Prolactin - Prolactin is involved in breast development and regulates the production of breast milk. Prolactin contributes to the development of the fully mature nonpregnant gland. It also has hormone regulating functions during the menstrual cycle.

Thyroid-stimulating hormone - Thyroid-stimulating hormone stimulates the release of thyroid hormone from thyroglobulin. It also stimulates the growth of thyroid follicular cells.

Parathyroid hormone - Parathyroid hormone controls the distribution of calcium and phosphate in the body. Parathyroid hormone also functions in neuromuscular excitation and blood clotting.

Thyroid hormone - Thyroid hormone is essential for normal metabolic processes and mental and physical development. Thyroid hormone regulates the rate at which the body functions (metabolic rate).

Aldosterone - Aldosterone is responsible for preserving salts in our body, keeping fluids in, and maintaining our blood pressure. It helps regulate the body's electrolyte balance by acting on the mineralocorticoid receptor (MR).

Cortisol - Cortisol is important for maintaining blood sugar levels, maintenance of body fluids and electrolytes, and protecting the body from stress. Cortisol has anti-inflammatory action, maintains blood sugar level, blood pressure, and muscle strength.

Dehydroepiandrosterone (DHEA) - Dehydroepiandrosterone is a steroid precursor produced by the adrenal gland and converted to testosterone or the estrogens by the body's tissues. DHEA appears to facilitate improved cholesterol profiles, loss of body fat, increased muscle gain.

Epinephrine - Epinephrine helps the liver release glucose (sugar) and limit the release of insulin. It also makes the heart beat faster and can raise blood pressure. It is the most common neurotransmitter in the nervous system, in particular at ganglion cells of the sympathetic nervous system.

Insulin - Insulin is necessary for glucose to be able to enter the cells of the body and be used for energy. Insulin controls the amount of sugar in the blood by moving it into the cells, where it can be used by the body for energy.

Erythropoietin - Erythropoietin is important for the normal production of new red blood cells. Erythropoietin stimulates red blood cell production.

Renin - Renin is an enzyme secreted by the kidneys that converts angiotensinogen into angiotensin II. Renin is part of a very complicated biochemical pathway in the body called the renin-angiotensin system. This is a necessary system since it works to elevate or decrease blood pressure in times of need.

Angiotensin - Angiotensin is a family of peptides (smaller than proteins) that act as vasoconstrictors to narrow blood vessels. Angiotensin controls blood pressure.

Estrogen - Estrogen stimulates the development of secondary sexual characteristics and induces menstruation in women. Estrogen is important for the maintenance of normal brain function and development of nerve cells.

Progesterone - Progesterone, along with estrogen, prepares the uterus (womb) for a possible pregnancy each month and supports the fertilized egg if conception occurs. Progesterone also helps prepare the breasts for milk production and breastfeeding.

Testosterone - Testosterone stimulates blood flow, growth in certain tissues, and the secondary sexual characteristics. Testosterone is required for sperm production, the development of the male reproductive organs, and the emergence of male secondary sexual characteristics.

Cholecystokinin - Cholecystokinin is a peptide hormone of the gastrointestinal system responsible for stimulating the digestion of fat and protein. It also acts as a hunger suppresant.

Leptin - Leptin plays a role in body weight regulation by acting on the hypothalamus to suppress appetite and burn fat stored in adipose tissue. Leptin works by inhibiting the actions of neuropeptide Y and agouti-related peptide and by increasing the actions of alpha-melanocortin stimulating hormone.