Endocrine System - Functions, Organs, Conditions

Human endocrine system - Functions & Overview

Edited By Irshad Anwar | Updated on Jul 02, 2025 05:22 PM IST

The endocrine system releases several hormones and controls many functions of the body, such as metabolism, growth, and mood. This is an important topic in Class 12 Biology of the chapter on Chemical Coordination and Integration. This major topic in Biology is also important for students who are preparing for exams like NEET, AIIMS, nursing and paramedical courses. This article includes the definition of the endocrine system, its parts, structure and functions.

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Definition of Endocrine System
Parts and Organs of the Endocrine System
Hormonal Regulation
Structure of the Endocrine System
Functions of the Endocrine System

Human endocrine system - Functions & Overview

Definition of Endocrine System

The endocrine system is defined as the system of glands that secrete their secretion directly into the bloodstream and not through a duct. These endocrine glands control the body system and produce hormones that help regulate all the body functions of our cells and tissues.

Hormones are defined as the chemicals that affect the body's functions, which range from hunger to reproduction to even the growth of the body. The hormones also control the emotions and behaviour of a human being. When we talk about the exocrine glands in our bodies, they secrete their secretion in the ducts. These usually contain earwax and sebaceous glands that usually secrete oil, and sweat glands that usually secrete sweat.

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Parts and Organs of the Endocrine System

The endocrine system consists of a network of glands and organs that produce hormones to regulate various body functions. These glands are scattered throughout the body and are responsible for controlling processes like growth, metabolism, reproduction, and stress response. Key components include the hypothalamus, pituitary gland, thyroid, parathyroid, adrenal glands, pineal gland, pancreas, ovaries, and testes, all with unique roles in maintaining balance and coordination in the body.

There are several diverse glands in the endocrine system, each having specific kinds of hormones secreted.

Hypothalamus

Located in the brain, below the thalamus.
The hypothalamus acts as a link between the endocrine and nervous systems.
Produces hormones that regulate the pituitary gland, such as releasing and inhibiting hormones.
Controls body functions like temperature, thirst, hunger, and emotions.
Helps regulate sleep cycles and the body's internal clock.

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Pituitary Gland

The pituitary gland is a pea-shaped gland at the base of the brain, below the hypothalamus.
Divided into anterior and posterior lobes, each releasing different hormones.
The anterior lobe of the pituitary produces growth hormone (GH), thyroid-stimulating hormone (TSH), and adrenocorticotropic hormone (ACTH).
The posterior lobe of the pituitary stores and releases hormones produced by the hypothalamus, which include oxytocin and antidiuretic hormone (ADH).
Coordinates the functions of other endocrine glands.

Thyroid Gland

The thyroid gland is found in the neck, surrounding the trachea.
Produces hormones such as thyroxine (T4) and triiodothyronine (T3), which regulate metabolism.
Regulates energy production, heart rate, and digestion.
Requires iodine to manufacture thyroid hormones.
It aids in the proper growth and development of the brain, particularly in children.

Parathyroid Gland

These are four small glands located at the back of the thyroid gland.
The parathyroid hormone, PTH, regulates calcium and phosphorus in the blood.
This hormone maintains the proper functioning of muscles, nerves, and bones.

Adrenal Glands

Two triangular glands sit on top of each kidney.
Adrenal glands consist of two parts adrenal cortex and adrenal medulla.
The adrenal cortex secretes cortisol, which regulates metabolism and stress, and aldosterone, which controls salt and water balance.
The adrenal medulla secretes adrenaline, also known as epinephrine, and noradrenaline, which enables the body to respond to stress.
Involved in the fight or flight reaction.

Pineal Gland

Pineal Gland is a tiny, pea-sized gland located in the brain between the two hemispheres.
Produces melatonin, a hormone which helps control the sleep-wake cycles.
Regulates seasonal biological rhythms in some animals.

Pancreas

A long, flat organ located behind the stomach.
The pancreas is both an endocrine and exocrine gland.
It produces insulin, which lowers blood sugar, and glucagon, which raises blood sugar.
It maintains blood sugar levels within a normal range.
It also produces digestive enzymes to help break down food.

Ovaries

Two almond-shaped organs are located in the pelvic cavity.
Ovaries produce female sex hormones like estrogen and progesterone.
It regulates the menstrual cycle and ovulation.
Facilitate pregnancy and secondary sexual development, for example, growth of mammary glands in females.

Testes

Two oval-shaped structures contained within the scrotum
Produced testosterone, which is the most important male sex hormone.
Regulate male sexual organ development and accessory reproductive structures, including changes in deep voice and pubic and facial hair growth
Fundamental in the formation of sperm as well as in fertility.

Endocrine Glands

Hormonal Regulation

Hormones regulate various physiological activities.

Metabolism

Thyroid hormones control the rate of metabolism

Growth and Development

Growth and development is controlled through the growth hormone

Stress Response

The reaction of the body to stress is controlled by the adrenal hormones

Structure of the Endocrine System

The endocrine system is distributed throughout the body and is different from all other systems. The parts of the endocrine system can act independently in regulating various functions of the body. For instance, the pineal gland within the brain synthesizes melatonin depending on the level of light it detects. The reproductive glands, however, respond to totally different signals, showing the vast difference in their functions.

The hypothalamus and thyroid control other glands to keep the body going. Many glands release numerous hormones at the same time, which work differently and create different effects. All these make the endocrine system one of the more complex systems in the human body.

Functions of the Endocrine System

Endocrine glands are a group of ductless glands that control the body. They usually act on the body by secreting some of the chemical substances that are termed hormones. Hormones usually act on all the nearby tissues of the body from where they are secreted, and they are transported through the bloodstream to act on the specific target organs. Human endocrine systems use hormones to keep track of all the coordinated systems in the body. These glands are located in the human system and in many different locations. Endocrine glands usually coordinate with the neural system of the human body and help with control and coordination activities.

Also Read:

Pancreas Function in the Human Body	Difference between Endocrine and Exocrine gland
Hormone Receptors	Adrenal Insufficiency
Disorders of Pituitary Gland	Mechanism of Hormone Action

Frequently Asked Questions (FAQs)

1. What are the names of the hormones that are secreted by the posterior pituitary?

The two main hormones that are secreted by the posterior pituitary are:Vasopressin is also known as an antidiuretic hormone Oxytocin.

2. What is the function of oxytocin?

The primary function of oxytocin is to act on the uterine muscles and initiate muscle contraction during pregnancy. So it serves as a hormone used during the foetal ejection complex.

3. What is pineal gland?

It is a tiny gland that is located in the midbrain. Its function is not clearly known but it is seen to regulate The Mating behaviours and also the day night Rhythm cycle of a human.

4. What are prostaglandins?

Prostaglandins are defined as a hormone that is usually synthesised by various tissues in the cells. These hormones are known to produce their effect on smooth muscle and on many various glands. Erythropoietin is a hormone that is produced by the kidney cell and functions in the production of the red blood cells.

5. What is the endocrine system and its function?

The endocrine system consists of glands that release hormones, which are chemical messengers regulating and coordinating processes such as metabolism, growth, and reproduction.

6. What are 7 endocrine organs?

Among the seven major endocrine organs, the major endocrine organs consist of the pituitary gland, thyroid gland, parathyroid glands, adrenal glands, pancreas, ovaries in females, and testes in males.

7. What are the 4 main organs of the endocrine system?

The four main endocrine glands are the pituitary, thyroid, adrenal, and pancreas, all playing a central role in hormone regulation in the body.

8. What is the endocrine system and how does it differ from the nervous system?

The endocrine system is a network of glands that produce and secrete hormones directly into the bloodstream. Unlike the nervous system, which uses electrical impulses for rapid communication, the endocrine system uses chemical messengers (hormones) for slower, longer-lasting effects throughout the body.

9. What is the difference between endocrine and exocrine glands?

Endocrine glands secrete hormones directly into the bloodstream, affecting distant target cells. Exocrine glands, on the other hand, release their products through ducts onto external or internal body surfaces, such as sweat glands or salivary glands.

10. How does the endocrine system contribute to homeostasis?

The endocrine system contributes to homeostasis by regulating various bodily functions through hormone secretion. It helps maintain balance in metabolism, growth, development, reproduction, and responses to stress and environmental changes. The system's feedback mechanisms ensure that these processes remain within optimal ranges.

11. How do growth factors differ from hormones?

While both growth factors and hormones are signaling molecules, growth factors typically act more locally and specifically. They stimulate cell growth, proliferation, and differentiation, often binding to receptors on nearby cells. Hormones, in contrast, are generally produced by endocrine glands and act on distant target cells throughout the body.

12. How do endorphins function in the body?

Endorphins are naturally occurring opioid peptides that function as neurotransmitters and hormones. They are released in response to pain, stress, or intense physical activity. Endorphins bind to opioid receptors in the brain, reducing pain perception, inducing feelings of pleasure or euphoria, and potentially modulating appetite and immune response.

13. Why are hormones often called "chemical messengers"?

Hormones are called "chemical messengers" because they are molecules produced by endocrine glands that travel through the bloodstream to target specific cells or organs, delivering instructions for various bodily functions. This chemical communication allows for precise regulation of physiological processes.

14. How do target cells recognize specific hormones?

Target cells recognize specific hormones through specialized protein structures called receptors. These receptors are located either on the cell surface or within the cell, depending on the hormone type. The hormone binds to its specific receptor like a key fitting into a lock, triggering a cellular response.

15. How does negative feedback control hormone levels in the body?

Negative feedback is a self-regulating mechanism where the effect of a process inhibits its cause. In hormone regulation, when hormone levels rise, they signal the gland to reduce or stop hormone production. This helps maintain hormone levels within a normal range, preventing overproduction and ensuring homeostasis.

16. Why is the pituitary gland often called the "master gland"?

The pituitary gland is called the "master gland" because it produces hormones that control several other endocrine glands, including the thyroid, adrenals, and gonads. Its hormones influence growth, metabolism, reproduction, and other vital functions, making it a central regulator of the endocrine system.

17. How do lipid-soluble and water-soluble hormones differ in their mechanisms of action?

Lipid-soluble hormones (e.g., steroid hormones) can pass through cell membranes and bind to receptors inside the cell, directly influencing gene expression. Water-soluble hormones (e.g., peptide hormones) cannot enter cells and instead bind to receptors on the cell surface, triggering intracellular signaling cascades.

18. What is the role of the hypothalamus in the endocrine system?

The hypothalamus is a crucial link between the nervous and endocrine systems. It receives signals from the brain and body, and in response, produces releasing and inhibiting hormones that control the pituitary gland. This allows the hypothalamus to regulate various bodily functions, including temperature, hunger, and sleep.

19. How does the thyroid gland regulate metabolism?

The thyroid gland produces thyroxine (T4) and triiodothyronine (T3), which regulate metabolism by increasing the rate of cellular energy production. These hormones affect nearly every cell in the body, influencing heart rate, body temperature, and how quickly the body uses energy from food.

20. How do growth hormones affect the body throughout life?

Growth hormones, produced by the pituitary gland, stimulate cell growth and reproduction. In children, they promote linear growth and organ development. In adults, growth hormones continue to regulate metabolism, bone density, and muscle mass, playing a crucial role in maintaining overall health and tissue repair.

21. What is the function of melatonin in the body?

Melatonin, produced by the pineal gland, regulates the sleep-wake cycle (circadian rhythm). It is secreted in response to darkness, helping to induce sleep and synchronize the body's internal clock with the external environment. Melatonin also has antioxidant properties and may influence immune function.

22. How do stress hormones prepare the body for "fight or flight"?

Stress hormones, primarily cortisol and adrenaline, prepare the body for "fight or flight" by increasing heart rate, blood pressure, and blood glucose levels. They also redirect blood flow to essential organs and muscles, enhance focus, and temporarily suppress non-essential functions like digestion and immune response.

23. What is the difference between autocrine, paracrine, and endocrine signaling?

Autocrine signaling occurs when a cell produces hormones that act on itself. Paracrine signaling involves hormones affecting nearby cells. Endocrine signaling, the primary mode of the endocrine system, involves hormones traveling through the bloodstream to affect distant target cells.

24. What is hormone synergism and why is it important?

Hormone synergism occurs when two or more hormones work together to produce an effect greater than the sum of their individual effects. This is important because it allows for more precise and efficient regulation of complex physiological processes, such as growth, metabolism, and reproduction.

25. What is the role of leptin in appetite regulation?

Leptin is a hormone produced by fat cells that helps regulate energy balance by inhibiting hunger. It signals the brain about the body's energy stores, suppressing appetite when fat stores are sufficient. Leptin resistance can lead to continued hunger signals despite adequate energy stores, contributing to obesity.

26. How does the renin-angiotensin-aldosterone system (RAAS) regulate blood pressure?

The RAAS regulates blood pressure and fluid balance. When blood pressure drops, the kidneys release renin, which triggers a cascade leading to the production of angiotensin II. This hormone constricts blood vessels and stimulates aldosterone release, which increases sodium and water retention, ultimately raising blood pressure.

27. How do hormones influence mood and behavior?

Hormones can significantly influence mood and behavior by affecting neurotransmitter levels and neural activity in the brain. For example, cortisol can impact stress responses and memory, while sex hormones like estrogen and testosterone can influence aggression, libido, and emotional processing.

28. What is the role of insulin in glucose regulation?

Insulin, produced by the pancreas, regulates blood glucose levels by promoting the uptake of glucose into cells, especially in muscle and fat tissue. It also stimulates the liver to store excess glucose as glycogen and inhibits the breakdown of stored fats. This helps maintain blood glucose within a normal range.

29. How do endocrine disruptors affect the body?

Endocrine disruptors are chemicals that interfere with the normal functioning of the endocrine system. They can mimic or block natural hormones, alter hormone production or breakdown, or modify hormone receptor function. This can lead to developmental issues, reproductive problems, metabolic disorders, and increased cancer risk.

30. How does the endocrine system change with age?

As we age, the endocrine system undergoes various changes. Hormone production may decrease or become less efficient, and target tissues may become less responsive to hormones. These changes can affect metabolism, bone density, muscle mass, and reproductive function, contributing to the aging process.

31. How does the endocrine system interact with the immune system?

The endocrine and immune systems interact closely. Hormones like cortisol and adrenaline can suppress immune function, while others like growth hormone and prolactin can enhance it. Conversely, immune cells can produce hormones and cytokines that affect endocrine function, creating a bidirectional communication network.

32. What is the significance of hormone half-life?

Hormone half-life refers to the time it takes for half the amount of a hormone to be eliminated from the body. This is important because it affects how long a hormone's effects last and how frequently it needs to be secreted. Hormones with shorter half-lives allow for more rapid adjustments in body functions.

33. What is the role of hormones in maintaining calcium homeostasis?

Calcium homeostasis is maintained through the interplay of parathyroid hormone (PTH), calcitonin, and vitamin D. PTH increases blood calcium levels by promoting bone resorption and calcium reabsorption in the kidneys. Calcitonin decreases blood calcium by inhibiting bone resorption. Vitamin D enhances calcium absorption in the intestines.

34. How do sex hormones influence secondary sexual characteristics?

Sex hormones, primarily estrogen, progesterone, and testosterone, influence the development of secondary sexual characteristics during puberty. These include changes in body hair, voice pitch, muscle mass, and fat distribution. They also play crucial roles in reproductive function and behavior throughout adulthood.

35. What is the function of antidiuretic hormone (ADH)?

Antidiuretic hormone, also known as vasopressin, regulates water balance in the body. It is released by the posterior pituitary in response to dehydration or increased blood osmolarity. ADH acts on the kidneys to increase water reabsorption, concentrating urine and helping to maintain blood volume and pressure.

36. What is the role of ghrelin in hunger regulation?

Ghrelin, often called the "hunger hormone," is produced primarily in the stomach. It stimulates appetite and food intake, increases gastric acid secretion, and promotes fat storage. Ghrelin levels typically rise before meals and fall after eating, playing a key role in meal initiation and energy balance.

37. What is the function of erythropoietin (EPO)?

Erythropoietin is a hormone primarily produced by the kidneys in response to low oxygen levels. It stimulates the production of red blood cells in the bone marrow, increasing the oxygen-carrying capacity of the blood. This helps maintain adequate oxygen supply to tissues, especially during conditions like anemia or high altitude exposure.

38. How do thyroid hormones affect fetal development?

Thyroid hormones are crucial for fetal development, particularly brain development. They promote neuronal growth, differentiation, and myelination. Adequate maternal thyroid function is essential during early pregnancy when the fetal thyroid is not yet functional. Thyroid hormone deficiency during pregnancy can lead to developmental delays and cognitive impairment.

39. What is the role of oxytocin in social bonding and childbirth?

Oxytocin, often called the "love hormone," plays a crucial role in social bonding, trust, and empathy. During childbirth, it stimulates uterine contractions and milk ejection during breastfeeding. Oxytocin release is also associated with physical touch, promoting parent-child bonding and romantic attachments.

40. What is the function of parathyroid hormone-related protein (PTHrP)?

PTHrP is similar to parathyroid hormone but has distinct functions. It plays a crucial role in fetal development, particularly in bone and cartilage formation. In adults, it regulates calcium transfer in the placenta and mammary glands during pregnancy and lactation. It's also involved in smooth muscle relaxation and cell proliferation.

41. How do hormones regulate the menstrual cycle?

The menstrual cycle is regulated by a complex interplay of hormones. Gonadotropin-releasing hormone (GnRH) from the hypothalamus stimulates the pituitary to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH). These hormones then stimulate the ovaries to produce estrogen and progesterone, which prepare the uterus for potential pregnancy and regulate the cycle's timing.

42. What is the role of glucagon in glucose regulation?

Glucagon, produced by the pancreas, works opposite to insulin in regulating blood glucose. When blood sugar levels drop, glucagon stimulates the liver to convert stored glycogen back into glucose and release it into the bloodstream. It also promotes the breakdown of fats and proteins for energy, helping to maintain stable blood glucose levels.

43. What is the function of atrial natriuretic peptide (ANP)?

Atrial natriuretic peptide is a hormone released by heart muscle cells in the atria in response to high blood pressure or volume. ANP promotes sodium and water excretion by the kidneys, relaxes blood vessels, and inhibits the renin-angiotensin-aldosterone system. These actions help lower blood pressure and reduce blood volume.

44. How does the pineal gland contribute to circadian rhythms?

The pineal gland produces melatonin in response to darkness, helping to regulate the sleep-wake cycle. Melatonin secretion increases at night and decreases during the day, synchronizing various physiological processes with the 24-hour light-dark cycle. This helps maintain circadian rhythms, influencing sleep patterns, body temperature, and other daily biological cycles.

45. What is the role of inhibin in reproductive function?

Inhibin is a hormone produced by the gonads (ovaries in females, testes in males) that plays a crucial role in regulating the production of follicle-stimulating hormone (FSH). It acts through negative feedback on the pituitary gland, inhibiting FSH release. This helps control the development of eggs in females and sperm production in males.

46. How do hormones influence bone metabolism?

Several hormones influence bone metabolism. Parathyroid hormone and vitamin D promote calcium release from bones and increase calcium absorption. Calcitonin inhibits bone resorption. Growth hormone and sex hormones (estrogen, testosterone) stimulate bone formation. Thyroid hormones also play a role in bone turnover and maintenance.

47. What is the function of cholecystokinin (CCK)?

Cholecystokinin is a hormone released by the small intestine in response to food. It stimulates the release of digestive enzymes from the pancreas and bile from the gallbladder. CCK also acts as a hunger suppressant, contributing to the feeling of fullness after eating. It plays a role in digestion, appetite regulation, and gut motility.

48. How does cortisol affect the immune system?

Cortisol, often called the "stress hormone," has complex effects on the immune system. In short-term stress, it can enhance immune function. However, chronic elevation of cortisol tends to suppress the immune system by reducing inflammation, decreasing the production and activity of various immune cells, and inhibiting the release of inflammatory mediators.

49. What is the role of gastrin in digestion?

Gastrin is a hormone produced by G cells in the stomach and duodenum. It stimulates the secretion of gastric acid by parietal cells in the stomach, promotes the growth of the gastric mucosa, and enhances the motility of the gastrointestinal tract. Gastrin release is triggered by the presence of food in the stomach, particularly proteins.

50. What is the function of secretin?

Secretin is a hormone produced by S cells in the duodenum in response to acidic chyme entering from the stomach. It stimulates the pancreas to release a bicarbonate-rich fluid that neutralizes stomach acid in the small intestine. Secretin also inhibits gastric acid secretion and gastrin release, slows gastric emptying, and stimulates bile production by the liver.

51. How does the endocrine system regulate fluid balance?

The endocrine system regulates fluid balance through several hormones. Antidiuretic hormone (ADH) increases water reabsorption in the kidneys. Aldosterone promotes sodium retention and potassium excretion. Atrial natriuretic peptide increases sodium and water excretion. These hormones work together to maintain proper blood volume and osmolarity.

52. What is the role of prolactin beyond lactation?

While prolactin is best known for its role in milk production, it has numerous other functions. It influences reproductive behavior, immune system regulation, and osmoregulation. Prolactin also plays a role in metabolism, potentially affecting insulin sensitivity and fat storage. In some species, it's involved in parental behavior and stress responses.

53. How do hormones influence hair growth and loss?

Several hormones influence hair growth and loss. Androgens, particularly dihydrotestosterone (DHT), can cause hair