The human endocrine system

The endocrine system

The endocrine system is the collection of glands of an organism that secrete hormones directly into the circulatory system to be carried towards distant target organs. 

The phenomenon of biochemical processes’ serving to regulate distant tissues by means of secretions directly into the circulatory system is called endocrine signaling.

The endocrine system is the collection of glands that produce hormones that regulate metabolism, growth and development, tissue function, sexual function, reproduction, sleep, and mood, among other things.

The endocrine system is made up of the pituitary gland, thyroid gland, parathyroid glands, adrenal glands, pancreas, ovaries (in females) and testicles (in males), the Mayo Clinic notes.undefined The word endocrine derives from the Greek words “endo,” meaning within, and “crinis,” meaning to secrete, according to Health Mentor Online.

 In general, a gland selects and removes materials from the blood, processes them and secretes the finished chemical product for use somewhere in the body.

The endocrine system includes all of the glands of the body and the hormones produced by those glands. The glands are controlled directly by stimulation from the nervous system as well as by chemical receptors in the blood and hormones produced by other glands. 

By regulating the functions of organs in the body, these glands help to maintain the body’s homeostasis. Cellular metabolism, reproduction, sexual development, sugar and mineral homeostasis, heart rate, and digestion are among…


The endocrine system is made up of glands that produce and secrete hormones, chemical substances produced in the body that regulate the activity of cells or organs. 

These hormones regulate the body’s growth,metabolism(the physical and chemical processes of the body), and sexual development and function.

 The hormones are released into the bloodstream and may affect one or several organs throughout the body.Hormones are chemical messengers created by the body.

 They transfer information from one set of cells to another to coordinate the functions of different parts of the body.

Simply put, the endocrine system is a network of glands that secrete chemicals called hormones to help your body function properly. Hormones are chemical signals that coordinate a range of bodily functions.

The endocrine system works to regulate certain internal processes. (Note:endocrine shouldn’t be confused with exocrine. Exocrine glands, such as sweat and salivary glands, secrete externally and internally via ducts. 

Endocrine glands secrete hormones internally, using the bloodstream.
Although we rarely think about the endocrine system, it influences almost every cell, organ, and function of our bodies. 

The endocrine system plays a role in regulating mood, growth and development, tissue function, metabolism, and sexual function and reproductive processes.

In general, the endocrine system is in charge of body processes that happen slowly, such as cell growth. Faster processes like breathing and body movement are controlled by the nervoussystem. But even though the nervous system and endocrine system are separate systems, they often work together to help the body function properly.

The foundations of the endocrine system are the hormones and glands. Asthe body’s chemical messengers,hormones transfer information and instructions from one set of cells to another. Many different hormones move through the bloodstream, but each type of hormone is designed to affect only certain cells.

Anatomy of the Endocrine System

Anatomy of the endocrine system

Hypothalamus

The hypothalamus is a part of the brain located superior and anterior to the brain stem and inferior to the thalamus.

 It serves many different functions in the nervous system, and is also responsible for the direct control of the endocrine system through the pituitary gland.

 The hypothalamus contains special cells called neurosecretory cells neurons that secrete hormones:

• *.Thyrotropin-releasing hormone (TRH)
• *.Growth hormone-releasing hormone (GHRH)
• *.Growth hormone-inhibiting hormone (GHIH)
• *.Gonadotropin-releasing hormone (GnRH)
• *.Corticotropin-releasing hormone (CRH)
•  *.Oxytocin
• *.Antidiuretic hormone (ADH)

All of the releasing and inhibiting hormones affect the function of the anterior pituitary gland. TRH stimulates the anterior pituitary gland to release thyroid-stimulating hormone. GHRH and GHIH work to regulate the release of growth hormone GHRH stimulates growth hormone release, GHIH inhibits its release.

 GnRH stimulates the release of follicle stimulating hormone and luteinizing hormone while CRH stimulates the release of adrenocorticotropic hormone. The last two hormones oxytocin and antidiuretic hormone are produced by the hypothalamus and transported to the posterior pituitary, where they are stored and later released.Pituitary Gland.

 The pituitary gland, also known as the hypophysis, is a small pea-sized lump of tissue connected to the inferior portion of the hypothalamus of the brain.

 Many blood vessels surround the pituitary gland to carry the hormones it releases throughout the body. Situated in a small depression in the sphenoid bone called the sella turcica, the pituitary gland is actually made of 2 completely separate structures: the posterior and anterior pituitary glands.1.
Posterior Pituitary:


The posterior pituitary gland is actually not glandular tissue at all, but nervous tissue instead. The posterior pituitary is a small extension of the hypothalamus through which the axons of some of the neurosecretory cells of the hypothalamus extend.

 These neurosecretory cells create 2 hormones in the hypothalamus that are stored and released by the posterior pituitary:
*.Oxytocin triggers uterine contractions during childbirth and the release of milk during breastfeeding.
*.Antidiuretic hormone (ADH) prevents water loss in the body by increasing the re-uptake ofwater in the kidneys and reducing blood flow to sweat glands.

Anterior Pituitary:

 The anterior pituitary gland is the true glandular part of the pituitary gland. The function of the anterior pituitary gland is controlled by the releasing and inhibiting hormones of the hypothalamus. The anterior pituitary produces 6 important hormones:

• *.Thyroid stimulating hormone (TSH), as its name suggests, is a tropic hormone responsible for the stimulation of the thyroid gland.
• *.Adrenocorticotropic hormone (ACTH) stimulates the adrenal cortex, the outer partof the adrenal gland, to produce its hormones.
• *.Follicle stimulating hormone (FSH) stimulates the follicle cells of the gonads toproduce gametes—ova in females and sperm in males.
• *.Luteinizing hormone (LH) stimulates the gonads to produce the sex hormones—estrogens in females and testosterone in males.
• *.Human growth hormone (HGH) affects many target cells throughout the body by stimulating their growth, repair, and reproduction.
• *.Prolactin (PRL) has many effects on the body, chief of which is that it stimulates themammary glandsof the breast to produce milk.

Pineal Gland

The pineal gland is a small pinecone-shaped mass of glandular tissue found just posterior to the thalamus of the brain. 

The pineal gland produces the hormone melatonin that helps to regulate the human sleep-wake cycle known as the circadian rhythm. 

The activity of the pinealgland is inhibited by stimulation from the photoreceptors of the retina.

 This light sensitivity causes melatonin to be produced only in low light or darkness. Increased melatonin production causes humans to feel drowsy at nighttime when the pineal gland is active.

Thyroid Gland

The thyroid gland is a butterfly-shaped gland located at the base of the neck and wrapped around the lateral sides of the trachea.

 The thyroid gland produces 3 major hormones:

• *.Calcitonin
• *.Triiodothyronine (T3)
• *.Thyroxine (T4)
•  

Calcitonin is released when calcium ion levels in the blood rise above a certain set point. Calcitonin functions to reduce the concentration of calcium ions in the blood by aiding the absorption of calcium into the matrix of bones. 

The hormones T3 and T4 work together to regulate the body’s metabolic rate. Increased levels of T3 and T4 lead to increased cellular activity and energy usage in the body.

Parathyroid Glands

 The parathyroid glands are 4 small masses of glandular tissue found on the posterior side of the thyroid gland. The parathyroid glands produce the hormone parathyroid hormone (PTH), which is involved in calcium ion homeostasis.

 PTH is released from the parathyroid glands when calcium ion levels in the blood drop below a set point. PTH stimulates the osteoclasts to break down the calcium containing bone matrix to release free calcium ions into the bloodstream. PTH also triggers the kidneys to return calcium ions filtered out of the blood back to the bloodstream so that it is conserved.

Adrenal Glands

The adrenal glands are a pair of roughly triangular glands found immediately superior tothe kidneys. The adrenal glands are each made of 2 distinct layers, each with their own unique functions: the outer adrenal cortex and inner adrenal medulla.

*.Adrenal cortex: 

The adrenal cortex produces many cortical hormones in 3 classes:

•  glucocorticoids
•  mineralocorticoids, and
• androgens.
•  

Glucocorticoids have many diverse functions, including the breakdown of proteins and lipids to produce glucose.

 Glucocorticoids also function to reduce inflammation and immune response.

Mineralocorticoids, as their name suggests, are a group of hormones that help to regulate the concentration of mineral ions in the body.

Androgens, such as testosterone, are produced at low levels in the adrenal cortexto regulate the growth and activity of cells that are receptive to male hormones. 

In adult males, the amount of androgens produced by the testes is many times greater than the amount produced by the adrenal cortex, leading to the appearance ofmale secondary sex characteristics.

Adrenal medulla:

 The adrenal medulla produces the hormones epinephrine and norepinephrine under stimulation by the sympathetic division of the autonomic nervous system. 

Both of these hormones help to increase the flow of blood to the brain and muscles to improve the “fight-or-flight” response to stress. 

These hormones also workto increase heart rate, breathing rate, and blood pressure while decreasing the flow of blood to and function of organs that are not involved in responding to emergencies.

Pancreas

The pancreasis a large gland located in the abdominal cavity just inferior and posterior to thestomach. The pancreas is considered to be a heterocrine gland as it contains both endocrine and exocrine tissue. The endocrine cells of the pancreas make up just about 1% of the total mass of the pancreas and are found insmall groups throughout the pancreas called islets of Langerhans. Within these islets are 2 types of cells alpha and beta cells. 

The alpha cells produce the hormone glucagon, which is responsible for raising blood glucose levels. Glucagon triggers muscle and liver cells to break down the polysaccharide glycogen to release glucose into the bloodstream.

 The beta cells produce the hormone insulin, which is responsible for lowering blood glucose levels after a meal. Insulin triggers the absorption of glucose from the blood into cells, where it is added to glycogen molecules for storage.

Gonads

The gonads ovaries in females and testes in males are responsible for producing the sex hormones of the body.

 These sex hormones determine the secondary sex characteristics of adult females and adult males.

*Testes:

 The testes are a pair of ellipsoid organs found in the scrotum of males that produce the androgen testosterone in males after the start of puberty. 

Testosterone has effects on many parts of the body, including the muscles, bones, sex organs, and hair follicles. This hormone causes growth and increases in strength of the bones and muscles, including the accelerated growth of long bones during adolescence.

 During puberty, testosterone controls the growth anddevelopment of the sex organs and body hair of males, including pubic, chest, and facial hair. 

In men who have inherited genes for baldness testosterone triggers the onset of androgenic alopecia, commonly known as male pattern baldness.

*.Ovaries: 

The ovaries are a pair of almond-shaped glands located in the pelvic body cavity lateral and superior to the uterus in females. The ovaries produce the female sex hormones progesterone and estrogens.

 Progesterone is most active in females during ovulation and pregnancy where it maintains appropriate conditions in the human body to support a developing fetus. 

are a group of related hormones that function as the primary female sex hormones. 

The release of estrogen during puberty triggers the development of female secondary sex characteristics such as uterine development, breast development, and the growth of pubic hair. Estrogen also triggers the increased growth of bones during adolescence that lead to adult height and proportions.

Thymus

The thymus is a soft, triangular-shaped organ found in the chest posterior to the sternum. The thymus produces hormones called thymosins that help to train and develop T-lymphocytes during fetal development and childhood.

 The T-lymphocytes produced in the thymus go on to protect the body from pathogens throughout a person’s entire life. 

The thymus becomes inactive during puberty and is slowly replaced by adipose tissue throughout a person’s life.Other Hormone Producing Organs In addition to the glands of the endocrine system, many other non-glandular organs and tissues in the body produce hormones as well.

*Heart: The cardiac muscle tissue of the heart is capable of producing the hormone atrial natriuretic peptide (ANP) in response to high blood pressurelevels. ANP works to reduce blood pressure by triggering vasodilation to provide more space for the blood to travel through. ANP also reduces blood volume and pressure by causing water and salt to be excreted out of the blood by the kidneys.

*.Kidneys: The kidneys produce the hormone erythropoietin (EPO) in response to low levels of oxygen in the blood. EPO released by the kidneys travels to the red bone marrow where it stimulates an increased production of red blood cells.

 The number of red blood cells increases the oxygen carrying capacity of theblood, eventually ending the production of EPO.

*.Digestive System: The hormones cholecystokinin (CCK), secretin, and gastrin are all produced by the organs of the gastrointestinal tract. CCK, secretin, and gastrin all help to regulate the secretion of pancreatic juice, bile, and gastric juice in response to the presence of food in the stomach. CCK is also instrumental in the sensation of satiety or “fullness” after eating a meal.

*Adipose: Adipose tissue produces the hormone leptin that is involved in the management of appetite and energy usage by the body.

 Leptin is produced at levels relative to the amount of adipose tissue in the body, allowing the brain to monitor the body’s energy storage condition. When the body contains a sufficient level of adipose for energy storage, the level of leptin in the blood tells the brain that the body is not starving and may work normally.

 If the level of adipose or leptin decreases below a certain threshold, the body enters starvation mode and attempts to conserve energy through increased hunger and food intake and decreased energy usage. Adipose tissue also produces very low levels of estrogens in both men and women.

 In obese people the large volume of adipose tissue may lead to abnormal estrogen levels.*.Placenta: In pregnant women, the placenta produces several hormones that help to maintain pregnancy. 

Progesterone is produced to relax the uterus, protect the fetusfrom the mother’simmune system, and prevent premature delivery of the fetus.

 Human chorionic gonadotropin (HCG) assists progesterone by signaling the ovaries to maintain the production of estrogen and progesterone throughout pregnancy.

*.Local Hormones: 

Prostaglandins and leukotrienes are produced by every tissue in the body (except for blood tissue) in response to damaging stimuli.

 These two hormones mainly affect the cells that are local to the source of damage, leaving the rest of the bodyfree to function normally.

Prostaglandins cause swelling, inflammation, increased pain sensitivity, and increased local body temperature to help block damaged regions of the body from infection or further damage. 

They act as the body’s natural bandages to keep pathogens out and swell around damaged joints like a natural cast to limit movement.

Leukotrienes help the body heal after prostaglandins have taken effect by reducing inflammation while helping white blood cells to move into the region to clean up pathogens and damaged tissues.

The endocrine system helps control the following processes and systems:

• *.Growth and development
• *.Homeostasis (the internal balance of body systems)
• *.Metabolism (body energy levels)
• *.Reproduction
• *.Response to stimuli (stress and/or injury)

The endocrine system completes these tasks through its network of glands, which are small but highly important organs that produce, store, and secrete hormones.The glands of the endocrine system are:

• *.Hypothalamus
• *.Pineal Gland
• *.Pituitary Gland
• *.Thyroid
• *.Parathyroid
• *.Thymus
• *.Adrenal
• *.Pancreas
• *.Ovaries
• *.Testes

These glands produce different types of hormones that evoke a specific response in other cells, tissues, and/ororgans located throughout the body.

 The hormones reach these faraway targets using the blood stream. Like the nervous system, the endocrine system is one of your body’s main communicators. But instead of using nerves to transmit information, the endocrine system uses blood vessels to deliver hormones to cells.