Endocrine Glands: Endocrine System, Functions and Hormones

Endocrine glands are said to be ductless glands of the endocrine system that secrete their hormones, products into the blood. Rather than a duct, endocrine glands secrete their own substances directly into the bloodstream. 

The nine major glands of the endocrine system comprise the pituitary gland, pineal gland, ovaries, pancreas, thyroid gland, testis, hypothalamus, adrenal glands, parathyroid gland. The pituitary glands and the hypothalamus are the neuroendocrine organs. Of all endocrine systems, the hypothalamus is the neural node in the vertebrates. 

Key Terms: endocrine system, endocrine system, gland parathyroid, hypothalamus gland, endocrine glands

What is the Endocrine System?

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Endocrine system is a system of organs and glands that locates all around the body. It regulates and controls all the functions of the body. The nervous system communicates through the neurotransmitters and nerve impulses, the endocrine system communicates through hormones also known as chemical messengers. 

The hormones are chemicals that affect a lot of the functions of the body from growth, reproduction, hunger to more complex functions like behavior and human emotions. Through nine primary glands, these hormones are produced in our body. The organs along with these nine glands provide auxiliary functions that make up the endocrine system. Some of the glands are specific to either female (ovaries) and male (testis)

The pituitary glands and the hypothalamus are the neuroendocrine organs. Of all endocrine systems, the hypothalamus is the neural node in the vertebrates. In humans, the two main endocrine glands are the adrenal gland and the thyroid gland. The disorders and the study of the endocrine system are known as endocrinology, Of internal medicine, endocrinology is a subspeciality.

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Functions of Human Endocrine System

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Through the release of hormones, the endocrine system regulates various functions of the body. The endocrine glands produce hormones that regulate the functions of tissues and cells. Hormones then instruct these tissues and organs about how to act. The functions of the Human Endocrine system are mentioned in the below points:

• Growth and development of human beings
• Metabolic rate
• Sexual and Reproductive function.
• Blood Pressure
• Heart Rate
• Appetite needed to eat
• Controls cycles of wakefulness and sleep
• Controls body temperature

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Human Endocrine Glands

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The Human Endocrine system is made of the complex gland of the network that excretes different hormones in the human body. Hormones are stored, released, and produced along with the endocrine glands in human beings. Each gland creates one or more hormones that select particular tissues and organs in the human body. The nine major endocrine glands are mentioned below:

Hypothalamus

Hypothalamus is an important regulator of the autonomic nervous system as well as certain metabolic processes. It connects the endocrine and nervous systems through the pituitary gland. The limbic system includes the hypothalamus which is located under the thalamus. Hypothalamus secretes and produces certain neurohormones known as hypothalamic hormones or releasing hormones that inhibit or stimulate the secretion of the pituitary gland's hormone. Appetite, important aspects of attachment and parenting behaviors, Body temperature, fatigue, sleep, circadian rhythms, thirst, etc all are regulated by the hypothalamus.

Pituitary Gland

Pituitary Gland is also known as hypophysis is the master gland of the human body. It is a small endocrine gland that weighs the size of a pea. Pituitary glands regulate the activities of different endocrine glands that are thyroid, adrenal glands. It excretes hormones that function blood pressure, development, all sex organ functions, energy balance, metabolism, thyroid gland function, as well as some other aspects of breastfeeding, childbirth, pregnancy, salt/water concentration in kidneys, pain relief, and temperature regulation. Pituitary glands consist of anterior portion produces posterior portion and hormones that have many neural links. It secretes prolactin that stimulates milk production.

Pineal Gland 

Between two halves of the brain, the pineal gland is located. The other name for the pineal gland is the epiphysis cerebrum. The pineal gland produces Melatonin, a serotonin-derived hormone that functions sleep patterns in both seasonal and circadian cycles. It affects the wake cycle/ body's sleep. 

Thyroid Gland

At the front of the neck, the thyroid gland is found. It is a two-lobed endocrine gland located in the neck that produces thyroid hormone. The Thyroid isthmus, a thin bank tissue connects the bottom two-thirds of the lobes. The functional unit of the thyroid gland is the spherical thyroid follicle linked with occasional parafollicular cells and follicular cells that are surrounded by a lumen containing colloid. Thyroxine ( T4), Triiodothyronine (T3 ) are the hormones produced by the thyroid gland. These two glands are created from tyrosine, calcitonin, and iodine. The thyroid gland affects the protein synthesis and metabolic rate as well as development and growth in infants. 

Parathyroid Gland

The small endocrine gland located in the neck is known as the Parathyroid gland. It consists of four small glands located behind the thyroids in the neck. The parathyroid gland affects the level of calcium in the human body by producing a hormone known as Parathyroid Hormone. Parathyroid controls the amount of calcium in bones and blood. The main function of the parathyroid glands is to keep phosphate and calcium in the body within a little range so that the muscular and nervous system can work properly. 

Adrenal Glands

They are also called suprarenal glands. It is an endocrine gland that consists of steroids aldosterone, cortisol, and adrenaline among other hormones. The adrenal glands are located up to the kidney. More than 150 hormones are produced by adrenal glands that regulate various functions in the body. The adrenal gland is an outer cortex that produces the inner medulla and steroid hormones. Zona fasciculata, zona reticularis, and zona glomerulosa are the major three areas that make up the adrenal cortex.

Thymus Gland

The thymus is found behind the sternum, anterior superior mediastinum, and in the front of the heart. The thymus is said to be a specialized primary lymphoid organ. The thymus gland consists of two lobes: the outer cortex and the center of the medulla. The thymus cell T cells or lymphocytes grow within the thymus.

Pancreas

The pancreas is an endocrine and digestive system organ that is found in vertebrates. It is an endocrine gland that is located behind the stomach. The pancreas controls blood sugar levels by excreting the hormones such as glucagon, insulin, pancreatic polypeptide, somatostatin. It works in the digestive gland as an exocrine gland by excreting pancreatic juice into the duodenum by the pancreatic duct.

Gonads

Gonads are a mixed gland that consists of sex hormones and organism's gametes. It is also known as the reproductive or sex gland. Female ovaries release two hormones that are found in the pelvic cavity. Ovaries produce estrogen which is important for female sex characteristics and reproduction. Testis produces testosterone which is important for male sex characteristics. Thus, it results in increased bone mass, hair growth, and muscle.

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Endocrine System: Hormones

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The human body hormones that are secreted by the endocrine glands are mentioned below:

Adrenaline: Adrenaline is secreted by the adrenal gland known as epinephrine. It affects blood pressure, rising heart rate, redistributing blood to muscles, widening lungs for passage of air.

Aldosterone: It is a steroid hormone that is excreted by the adrenal gland. The main function of aldosterone is to control water and salt in the body.

Cortisol: Cortisol controls different key functions in the body including immune response and metabolism. In assisting stress response of the body, Cortisol plays an important role. 

Dehydroepiandrosterone Sulphate (DHEA): It is a male sex hormone that is produced by both men and women. During puberty, it plays an important role in the maturation of male sexual characteristics

Estrogen: In females, estrogen is secreted by ovaries. It involves ovarian functions such as the uterus and vaginal maturation, maturation of ovarian follicles, and maintenance.

Follicle Stimulating Hormone: Follicle Stimulating Hormone is secreted by the pituitary gland. It helps in the promotion of the development of eggs in the ovaries and regulates the women's menstrual cycle.

Glucagon: Glucagon is secreted by the pancreas. It prevents degradation of glucose, induces synthesis, and facilitates the liver transformation of glycogen to glucose.

Insulin: Insulin controls blood sugar by controlling protein metabolism, lipid, carbohydrate, facilitating cellular glucose absorption, and promoting growth and cell division through mitogenic effects.

Luteinizing Hormone: It is excreted by the pituitary gland. It is important for sexual development and function. It regulates women's menstrual cycle.

Melatonin: It is a hormone responsive to darkness that provides night information and conciliates. It is excreted by the pineal gland.

Oxytocin: Oxytocin is used as a medicinal agent during childbirth and labor.

Parathyroid hormone: It causes the intestine to absorb calcium from food, kidneys to conserve calcium, and bones to release calcium into the bloodstream.

Progesterone: Progesterone is important for sustaining and sustaining the early stages of pregnancy. 

Prolactin: Prolactin motivates the development of mammary alveoli. 

Testosterone: It is secreted by the testes, adrenal, ovaries. It is a sex hormone with different functions in the human body. 

Thyroid hormone: It has an effect on every organ and cell in the human body. The thyroid hormone is excreted by the thyroid gland.

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Factors Affecting Human Endocrine System

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• We will have hyperthyroidism when the thyroid gland produces more thyroid hormones than required. Various factors including autoimmune diseases can cause this.
• We will have hyperthyroidism when our thyroid does not create more thyroid hormone than required. It can be caused by many factors, like hyperthyroidism.
• Cushing syndrome is produced by excess levels of the hormone cortisol.
• We get Addison disease when our adrenal glands do not produce much aldosterone or cortisol.
• Diabetes is said to be a disorder in which levels of blood sugar are uncontrollably high. 

Thus, the endocrine system is said to be a complex system of organs and glands that aids in the regulation of many functions of the body. This can be obtained by the endocrine system's release of chemical messengers or hormones. The endocrine system secretes and generates hormones, which are chemical compounds that are generated in the body that control organ or cell function.

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Things to Remember

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• Endocrine glands are ductless glands of the endocrine system that secrete their hormones into the bloodstream.
• The nine major glands of the endocrine system comprise the pituitary gland, pineal gland, ovaries, pancreas, thyroid gland, testis, hypothalamus, adrenal glands, parathyroid gland.
• Endocrine system regulates and controls all the functions of the body.
• Hormones are chemicals that affect a lot of the functions of the body from growth, reproduction, hunger to more complex functions like behavior and human emotions. 
• The Endocrine system manages important functions such as growth and development of human beings, metabolism, sexual and reproductive function, sleep cycle, body temperature etc. 
• Diseases caused due to hormone deficiency: Hyperthyroidism, Cushing Syndrome, Addison Disease, Diabetes, etc. 

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