Human Endocrine System

The human endocrine system is a messenger system that regulates distant target organs through feedback loops of hormones released by the internal glands of an organism directly into the circulatory system. In invertebrates, the hypothalamus is the neural control node for all endocrine systems. 

The endocrine system is a system of glands and organs that is located all around the body. It functions similarly to the nervous system in that it controls and regulates all of the body's functions.

Although the nervous system communicates through nerve impulses and neurotransmitters, the endocrine system communicates through chemical messengers known as hormones.

The thyroid gland and the adrenal glands are the two main endocrine glands in humans. The study of the endocrine system and its disorders is known as endocrinology. Endocrinology is a subspecialty of internal medicine.

Functions of Human Endocrine System

The endocrine system regulates a variety of body functions through hormone release.

Hormones are produced by the endocrine system's glands and pass through the bloodstream to different organs and tissues in the body. Hormones then instruct these organs and tissues about how to act.

The Endocrine System is in control of the following bodily functions:

• Metabolic rate

• Development and growth of a human being

• Reproduction and sexual function

• Heart Rate

• Blood pressure 

• The appetite that is the need to eat

• Controls cycles of sleep and wakefulness

• Controls the temperature of the body

Human Endocrine Glands

The human endocrine system is made up of a complex network of glands that secrete different hormones in the human body. Hormones are produced, stored, and released via the endocrine glands in human beings. Each gland produces one or more hormones that target specific organs and tissues in the body.

The List of All Important Endocrine Glands in Human Body are as follows:

1. Hypothalamus

• The hypothalamus is a part of the brain that houses a number of small nuclei that perform various functions. 

• One of the hypothalamus' most essential functions is to connect the nervous and endocrine systems via the pituitary gland. 

• The limbic system includes the hypothalamus, which is situated under the thalamus.

• The hypothalamus is in charge of regulating certain metabolic processes as well as other autonomic nervous system behaviours. 

• It produces and secretes certain neurohormones known as releasing hormones or hypothalamic hormones, which stimulate or inhibit the pituitary gland's hormone secretion. 

• Body temperature, appetite, essential aspects of parenting and attachment behaviours, thirst, fatigue, sleep, and circadian rhythms are all regulated by the hypothalamus.

2. Pituitary Gland (Human Body Master Gland)

• The pituitary gland which is the master gland of the human body, also known as the hypophysis, is a small endocrine gland that weighs about 0.5 grams and is about the size of a pea.

• Since it regulates the activities of many other endocrine glands, the pituitary gland is known as the master gland of the human body.

• It's a protrusion at the base of the brain that protrudes from the bottom of the hypothalamus.

• The hypophysis is found in the center of the middle cranial fossa, on the hypophyseal fossa of the sphenoid bone, and is enclosed by a narrow bony cavity (sella turcica) filled by a dural fold (diaphragma sellae).

• The anterior pituitary, also known as the adenohypophysis, is a lobe of the pituitary gland that controls stress, development, reproduction, and lactation.

• Melanocyte-stimulating hormone is synthesized and secreted by the intermediate lobe.

• The neurohypophysis, or posterior pituitary, is a lobe of the pituitary gland that is functionally linked to the hypothalamus by the median eminence by a narrow tube known as the pituitary stalk, also known as the infundibulum.

• The pituitary gland secretes hormones that regulate development, blood pressure, energy balance, all sex organ functions, thyroid gland function, and metabolism, as well as some aspects of pregnancy, childbirth, breastfeeding, water/salt concentration in the kidneys, temperature regulation, and pain relief.

3. Pineal Gland

• The pineal gland, also known as the epiphysis cerberin, is a small endocrine gland found in most vertebrates' brains.

• Melatonin, a serotonin-derived hormone produced by the pineal gland, regulates sleep patterns in both circadian and seasonal cycles.

• The pineal gland is tucked in a groove where the two halves of the thalamus meet in the epithalamus, near the middle of the brain, between the two hemispheres.

• The pineal gland is a neuroendocrine secretory circumventricular organ with capillaries that are largely permeable to blood solutes.

• Melatonin production is the pineal gland's primary role. Melatonin functions in the central nervous system in a variety of ways, the most important of which is to help regulate sleep patterns. Darkness stimulates melatonin development, while light inhibits it.

4. Thyroid Gland

• The thyroid gland is a two-lobed endocrine gland in the neck that produces thyroid hormone.

• A thin band of tissue called the thyroid isthmus connects the lower two-thirds of the lobes.

• The thyroid gland is found below Adam's apple in the front of the neck.

• The spherical thyroid follicle, lined with follicular cells (thyrocytes) and occasional parafollicular cells that surround a lumen containing colloid, is the functional unit of the thyroid gland.

• The thyroid gland produces three hormones: triiodothyronine (T3) and thyroxine (T4) are the two thyroid hormones that are created from iodine and tyrosine, and calcitonin, a peptide hormone.

• Thyroid hormones affect metabolic rate and protein synthesis, as well as growth and development in infants.

• Calcium homeostasis is supported by calcitonin.

• Thyroid hormones modulate DNA transcription by crossing the cell membrane and binding to nuclear thyroid hormone receptors TR-ɑ1, TR-ɑ2, TR-β1, and TR-β2, which bind with hormone response elements and transcription factors.

• Thyroid hormones also function within the cell membrane or cytoplasm through reactions with enzymes such as calcium ATPase, adenylyl cyclase, and glucose transporters, in addition to their actions on DNA.

5. Parathyroid Gland

• Humans and other tetrapods have tiny endocrine glands in their necks called parathyroid glands.

• Humans have four parathyroid glands, which are normally found on the back of the thyroid gland in different places.

• In response to low blood calcium, the parathyroid gland produces and secretes the parathyroid hormone, which plays an important role in controlling the amount of calcium in the blood and bones.

• The primary function of the parathyroid glands is to keep calcium and phosphate levels in the body within a small range so that the nervous and muscular systems can work properly. This is accomplished by the parathyroid glands secreting parathyroid hormone (PTH).

6. Thymus Gland

• The immune system's thymus is a specialized primary lymphoid organ. Thymus cell lymphocytes or T cells grow within the thymus. 

• T cells play a crucial role in the adaptive immune system, which allows the body to respond to foreign invaders. 

• The thymus is found in the anterior superior mediastinum, behind the sternum, and in front of the heart in the upper front portion of the chest. 

• It consists of two lobes, each with a central medulla and an outer cortex, and is encased in a capsule.

7. Adrenal Gland

• The adrenal glands, also known as suprarenal glands, are endocrine glands that contain adrenaline and the steroids aldosterone and cortisol, among other hormones. Above the kidneys are the adrenal glands.

• An outer cortex that produces steroid hormones and an inner medulla make up each gland. The zona glomerulosa, zona fasciculata, and zona reticularis are the three major areas that make up the adrenal cortex.

8. Pancreas

• The pancreas is a digestive and endocrine system organ found in invertebrates.

• The pancreas is the largest endocrine gland in the human body.

• It is a gland that is found in the abdomen behind the stomach in humans.

• The pancreas performs both endocrine and digestive exocrine functions. It is an endocrine gland that regulates blood sugar levels by secreting the hormones insulin, glucagon, somatostatin, and pancreatic polypeptide.

• It works as an exocrine gland in the digestive system, secreting pancreatic juice into the duodenum through the pancreatic duct.

9. Gonads

• A gonad, also known as a sex gland or reproductive gland, is a mixed gland that contains an organism's gametes (sex cells) and sex hormones.

• Two key hormones are released by the female ovaries, which are found in the pelvic cavity. Under the influence of follicle-stimulating hormone, the ovarian follicles begin to secrete estrogens at puberty.

• Estrogens promote the production of secondary sexual characteristics and the maturation of the female reproductive system. Progesterone is produced in response to high luteinizing hormone levels in the blood. It helps to regulate the menstrual cycle by interacting with estrogens.

• In response to luteinizing hormone, the male testes begin to release testosterone at puberty.

• Testosterone aids in the maturation of male reproductive organs, as well as the development of secondary sex characteristics such as increased muscle and bone mass and hair growth.

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Endocrine System Hormones

In this section, we will learn about some of the hormones in the human body which are secreted by endocrine glands.

1. Adrenaline

• Adrenaline known as epinephrine is secreted by the adrenal gland.

• Adrenaline's main effects involve rising heart rate, blood pressure, widening lungs for air passage, enlarging the pupil in the eye, redistributing blood to muscles, and changing the body's metabolism to maximize blood glucose levels, mainly for the brain.

2. Aldosterone

• Aldosterone is a steroid hormone secreted by the adrenal gland.

• The primary function of aldosterone is to control salt and water in the body, thus influencing blood pressure.

3. Cortisol

• Cortisol is a steroid hormone secreted by the adrenal gland.

• Cortisol controls a variety of vital functions in the body, including metabolism and immune response. It also plays a vital role in assisting the body's stress response.

4. Dehydroepiandrosterone Sulfate (DHEA)

• Dehydroepiandrosterone sulfate (DHEA) is secreted by the adrenal gland.

• DHEA is a male sex hormone that both men and women produce. DHEA is required for the production of both the male and female sex hormones testosterone and estrogen. It also plays a role in the maturation of male sexual characteristics during puberty.

5. Estrogen

• Estrogen is secreted by the ovaries in females.

• Estrogens are involved in ovarian function, such as the maturation of ovarian follicles, as well as vaginal and uterus maturation and maintenance. Estrogens also play a key role in the regulation of gonadotropin secretion. 

6. Follicle Stimulating Hormone (FSH)

• The pituitary gland secretes Follicle Stimulating Hormone (FSH).

• FSH aids in the regulation of the menstrual cycle in women and promotes the development of eggs in the ovaries. Women's FSH levels fluctuate during the menstrual cycle, with the maximum levels occurring right before the ovary releases an egg. This is referred to as ovulation. FSH aids in the regulation of sperm production in males.

7. Glucagon

• Glucagon is secreted by the pancreas.

• Glucagon induces glucose synthesis, prevents glucose degradation, and facilitates the conversion of glycogen to glucose in the liver.

8. Insulin

• The ꞵ cells of the pancreatic islets of Langerhans secrete the peptide hormone called Insulin.

• Insulin regulates blood glucose levels by facilitating cellular glucose absorption, controlling carbohydrate, lipid, and protein metabolism, and promoting cell division and growth through its mitogenic effects.

9. Luteinizing Hormone (LH)

• The pituitary gland secretes Luteinizing hormone (LH).

• LH is important for sexual development and function. LH aids in the regulation of the menstrual cycle in women. It also causes an egg to be released from the ovary. This is referred to as ovulation.

10.  Melatonin

• Melatonin is secreted by the pineal gland.

• Melatonin is a hormone of darkness that mediates dark signals and provides night information, rather than being an asleep hormone. It's also thought to be an endogenous synchronizer, stabilizing and reinforcing the body's various circadian rhythms.

11.  Oxytocin

• Oxytocin is secreted by the pituitary gland.

• The function of oxytocin in female reproduction is well-known. It is released in significant quantities during labor and after nipple stimulation. The use of oxytocin as a medicinal agent during labor and childbirth is one of the oldest uses of oxytocin as a medicine.

12.  Parathyroid hormone

• Parathyroid hormone is secreted by the Parathyroid gland.

• The parathyroid hormone causes the bones to release calcium into the bloodstream, the intestines absorb calcium from food, and the kidneys conserve calcium.

13.  Progesterone

• The corpus luteum in the ovary secretes the Progesterone hormone.

• Progesterone is important for sustaining the early stages of pregnancy and the menstrual cycle. It may also play a role in the progression of some cancers.

14.  Prolactin

• Prolactin is secreted by the pituitary gland.

• Prolactin is involved in hundreds of physiologic activities, but two of the most important are milk production and the growth of mammary glands in breast tissues. Prolactin encourages the development of mammary alveoli, which are the components of the mammary gland where milk is produced.

15.  Testosterone

• Testosterone is secreted by multiple glands, ovaries, testes, and adrenal.

• Testosterone is a sex hormone with many functions in the body. It's thought to control libido, bone density, fat distribution, muscle mass and strength, and red blood cell and sperm production in men. A small amount of testosterone in the bloodstream is transformed into estradiol, an estrogen-like substance.

16.  Thyroid hormone

• The thyroid gland secretes the thyroid hormone.

• Thyroid hormones have an effect on every cell and organ in the body. They influence weight loss or benefit by regulating the rate at which calories are burned. The heartbeat can be slowed or sped up by thyroid hormone.

Disorders of the Endocrine Glands

When our thyroid gland produces more thyroid hormone than is needed, we will have hyperthyroidism. A variety of factors, including autoimmune diseases, can cause this.

• When our thyroid does not produce enough thyroid hormone, we will have hypothyroidism. It can be caused by a variety of factors, much like hyperthyroidism.

• High levels of the hormone cortisol cause Cushing syndrome.

• When our adrenal glands don't produce enough cortisol or aldosterone, we get Addison disease.

• Diabetes is a disorder in which blood sugar levels are uncontrollably high. Diabetes patients have an excessive amount of glucose in their blood (high blood sugar). Type 1 diabetes and type 2 diabetes are the two forms of diabetes.

In this article, we studied different glands of the human endocrine system, also we got to know the master gland and largest endocrine gland in the human body, hormones in the human body, and the conditions which affect the human endocrine system.

Conclusion

The endocrine system is a complex system of glands and organs that aids in the regulation of many bodily functions. This is achieved by the endocrine system's release of hormones, or chemical messengers. The endocrine system consists of glands that generate and secrete hormones, which are chemical compounds generated in the body that control cell or organ function. Hormones control body growth, metabolism (the body's physical and chemical processes), and sexual development and function. Hormones are released into the bloodstream and have the potential to affect one or more organs in the body.