Hormones- Definition, Anatomy, Function, Types, and Disorders

Hormones: Definition, What They Are, Function, Types, Causes, Symptoms, Treatment

Edited By Irshad Anwar | Updated on Jul 02, 2025 06:50 PM IST

Hormones are chemical messengers secreted by endocrine glands that regulate various physiological processes in the body. They control functions like growth, metabolism, reproduction, and mood. Hormones travel through the bloodstream to target specific organs and tissues, ensuring proper coordination within the body. In this article, hormones, types of hormones, functions of hormones, major endocrine glands, mechanisms of hormone action, important hormones, roles of hormones, hormonal diseases., chemical messengers, and hormone action and receptors are discussed. Hormones is a topic of the chapter Chemical Coordination and Integration chapter of Biology.

This Story also Contains

What are Hormones?
Types of Hormones
Functions of Hormones
Major Endocrine Glands
Mechanisms of Hormone Action
Important Hormones
Roles of Hormones
Hormonal Diseases
Why are Hormones called Chemical Messengers?
Mechanism of Hormone Action and Receptors

What are Hormones?

Hormones are chemical messengers synthesised from the endocrine glands. They travel in blood to reach target organs and tissues to control various physiological processes to maintain homeostasis.

Types of Hormones

The types of hormones include:

Peptide Hormones:

Consisting of amino acids. Examples: Insulin, glucagon, and growth hormone.

Steroid Hormones:

Consisting of cholesterol. Examples: Cortisol, aldosterone, estrogen, and testosterone.

Amino Acid-Derived Hormones:

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Consisting of single amino acids. Examples: Thyroxine, epinephrine, and norepinephrine.

Glycoprotein Hormones:

Protein hormones with carbohydrate groups. Examples: Follicle-stimulating hormone, luteinizing hormone.

Functions of Hormones

The functions of hormones include:

Regulation of Metabolism:

Insulin and glucagon act on the levels of blood sugar, while thyroid hormones act on metabolic rate.

Growth and Development:

Growth hormone acts on growth in the tissues. Estrogen and testosterone act as sex hormones in reproductive growth and development.

Homeostasis:

Aldosterone holds homeostasis in sodium and potassium balance. Antidiuretic hormone maintains the balance of water in the body.

Stress Response:

Cortisol and adrenaline control the stress response in the body.

Reproduction:

Hormones like FSH and LH maintain the menstrual cycle in females and spermatogenesis in males.

Endocrine Glands and the Hormones Secreted Hormones are produced and secreted by endocrine glands which are present in different parts of the body.

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Major Endocrine Glands

The major endocrine glands are:

Pituitary Gland:

It is also known as the master gland, and it controls other endocrine glands. This gland produces hormones like growth hormone, prolactin, and oxytocin.

Thyroid Gland:

It produces thyroid hormones T3 and T4, which maintain the metabolic rate.

Adrenal Glands:

They secrete hormones like cortisol, adrenaline, and aldosterone.

Pancreas:

Produces hormones like insulin and glucagon that regulate blood sugar levels.

Gonads:

Ovaries in females produce oestrogen and progesterone while testes in males produce testosterone.

Human Kidney

Mechanisms of Hormone Action

The mechanisms of hormones are:

Release Feedback Loops:

Negative feedback loops regulate most of the release of hormones to maintain homeostasis. For example, the level of the thyroid hormone is maintained by the hypothalamic-pituitary axis using a negative feedback loop.

Response to Stimuli:

Stress, increased blood sugar, change in ion concentration, etc can lead to the secretion of hormones.

Important Hormones

Some important hormones include:

Cortisol

Function: Sometimes called the "stress hormone," cortisol enables the body to appropriately respond to stressful situations, increasing heart rate and blood sugar levels, and the amount of energy available.

Estrogen

Estrogen is the most common female sex hormone that performs the functions of the secondary sexual development of females, cycling of female genitalia, preparing the uterus for impregnation, and maintaining female reproductive health. Estrogen levels dramatically change during menopause, leading to a host of symptoms.

Melatonin

This gene regulates the circadian rhythm, and sleep, and maintains the normal sleep-wake cycle and is, therefore, commonly referred to as the body's inner clock.

Progesterone

Function: This is one of the major female sex hormones involved in the menstrual cycle, preparing the uterus for the implantation of a fertilized ovum, and maintaining embryogenesis.

Testosterone

Function: It is the primary male sex hormone responsible for the changes one undergoes at puberty and the growth of muscle mass, bone, and facial hair. It is also essential for male sexual development and general health.

Roles of Hormones

Hormones carry out a range of crucial roles in the body, which include:

Food Metabolism:

Hormones initiate metabolic processes through the regulation of the breakdown of food and the speed at which it is used by the body.

Growth And Development:

The hormones maintain growth development during the pubertal period and in adulthood.

Thirst And Hunger:

They influence appetite and the desire to drink fluids.

Thermoregulation:

Maintenance of body temperature through metabolic actions.

Maintenance And Regulation

Affecting mood, emotions, and cognitive abilities.

Sex Development And Reproduction:

Control of reproductive processes as well as secondary sexual traits.

Hormonal Diseases

The hormonal diseases are brought about by disorders or malfunctioning of the endocrine glands, similar to that of the hypothalamus, adrenal, and pituitary glands. Some of the well-known diseases include

Hyperthyroidism:

It is a condition where too much production of thyroid hormone occurs, with symptoms like weight loss and an increase in heartbeats.

Osteoporosis

It is a condition characterized by reduced bone mass, usually due to hormonal imbalance.

Diabetes:

Abnormality in insulin production or action which misregulates the sugar level in the blood. The cause of these diseases can either be genetic, environmental, or even nutrition-related.

Why are Hormones called Chemical Messengers?

Hormones are chemicals that convey information from one part of the body to another. They are secretions of certain cells found only in the hypothalamus and some glands which then travel in the blood to reach their target tissues to exert their action. They assist in the regulation of physiological processes and homeostasis.

Mechanism of Hormone Action and Receptors

Hormones exert their action by combining with specific receptors on target cells.

Hormone Receptors

Cell Surface Receptors: These are for peptide hormones and amino acid-derived hormones. The receptors trigger an intracellular cascade once there is a binding between the hormone and the receptor.
Intracellular Receptors: These belong to steroid and thyroid hormones. They reside in the cell, and the hormones diffuse through the plasma membrane to elicit their response, mostly changes in gene expression, upon binding.

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Difference between Endocrine and Exocrine Glands	Difference between Thyroid and Parathyroid
Pancreas Function in the Human Body	Disorders of Pituitary Gland
Adrenal Insufficiency	Hormone Receptors

Frequently Asked Questions (FAQs)

1. What are hormones?

Hormones are messenger chemicals resulting from endocrine glands that govern different physiological activities.

2. What are some of the types of hormones existing?

There are peptide, steroid, amino acid-derived, and glycoprotein hormones.

3. How does this series of hormones involved in metabolic processes function?

It is through any of the many hormones taking control, including insulin and glucagon, both of which take part in controlling the sugar level in the blood, while the thyroid hormones themselves manage the metabolic rate.

4. What was the role of hormones in growth and development?

Growth hormones and sex hormones act on tissue growth, reproductive development, and function.

5. How about their stress reaction?

Cortisol and adrenaline are some of the playing hormones in the body's reaction to stress.

6. How do hormones interact with the immune system?

Hormones and the immune system have a complex, bidirectional relationship. Many hormones, such as cortisol and estrogen, can modulate immune function. For example:

7. How do endocrine disruptors affect hormone function?

Endocrine disruptors are chemicals that interfere with the endocrine system. They can:

8. What is the role of hormones in aging?

Hormones play a significant role in the aging process. As we age, the production of many hormones declines, leading to various physiological changes:

9. How do hormone imbalances occur, and what are their potential consequences?

Hormone imbalances can occur due to various factors, including gland dysfunction, tumors, medications, stress, or aging. An excess or deficiency of hormones can lead to a wide range of symptoms and health issues. For example, an overactive thyroid gland (hyperthyroidism) can cause weight loss, anxiety, and rapid heartbeat, while an underactive thyroid (hypothyroidism) can lead to weight gain, fatigue, and depression.

10. What is hormone replacement therapy, and when is it used?

Hormone replacement therapy (HRT) involves supplementing or replacing hormones that the body is no longer producing in sufficient quantities. It's commonly used to treat symptoms of menopause in women by replacing estrogen and sometimes progesterone. HRT can also be used for other conditions such as hypothyroidism (thyroid hormone replacement) or growth hormone deficiency. While HRT can be effective in managing symptoms and health risks associated with hormone deficiencies, it also carries potential risks and should be used under careful medical supervision.

11. What is the concept of hormone resistance, and how does it occur?

Hormone resistance occurs when target cells become less responsive to a hormone, despite normal or elevated hormone levels. This can happen due to:

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

Negative feedback is a regulatory mechanism where the end product of a process inhibits its own production. In hormone regulation, when hormone levels rise, they signal the gland that produced them to reduce or stop secretion. This helps maintain hormone levels within a narrow, optimal range. For example, when blood glucose levels rise, insulin is released, which lowers glucose levels, in turn signaling a decrease in insulin production.

13. How do hormones contribute to energy homeostasis?

Hormones play a vital role in maintaining energy homeostasis by regulating appetite, metabolism, and energy storage. Key hormones involved include:

14. How do hormones regulate blood pressure?

Hormones play a significant role in regulating blood pressure through various mechanisms:

15. What is the role of hormones in thermoregulation?

Hormones play a significant role in thermoregulation, the process by which the body maintains its core temperature. Key hormones involved include:

16. How do hormones regulate growth and development throughout life?

Hormones regulate growth and development from conception through adulthood:

17. What is the role of hormones in bone metabolism?

Hormones are crucial regulators of bone metabolism, influencing bone formation, remodeling, and mineral homeostasis. Key hormones involved include:

18. How do hormones influence fetal development?

Hormones play crucial roles in fetal development, influencing organ formation, growth, and sexual differentiation. Key hormones include:

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

Endocrine glands secrete hormones directly into the bloodstream, which then travel to target cells throughout the body. Exocrine glands, on the other hand, release their products through ducts to specific areas, such as sweat glands secreting onto the skin surface or salivary glands releasing saliva into the mouth.

20. How do hormones achieve specificity in their actions?

Hormones achieve specificity through target cell receptors. Each hormone has a unique molecular structure that fits into specific receptors on target cells, much like a key fitting into a lock. Only cells with the appropriate receptors will respond to a particular hormone, allowing for precise control of biological processes across different tissues and organs.

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

Lipid-soluble hormones, such as steroid hormones, can pass through cell membranes and bind to receptors inside the cell. They typically alter gene expression, leading to the production of new proteins. Water-soluble hormones, like peptide hormones, cannot enter cells directly. Instead, they bind to receptors on the cell surface, triggering intracellular signaling cascades that lead to rapid cellular responses.

22. What is the role of second messengers in hormone action?

Second messengers are molecules inside the cell that relay and amplify the signal from a hormone binding to a cell surface receptor. When a hormone (the first messenger) binds to its receptor, it triggers the production or release of second messengers, such as cyclic AMP (cAMP) or calcium ions. These second messengers then activate various cellular processes, allowing a single hormone molecule to have a significant impact on cell function.

23. What is the difference between paracrine and autocrine signaling in hormone action?

Paracrine signaling occurs when a hormone affects nearby cells in the same tissue, while autocrine signaling involves a cell producing a hormone that acts on itself. Both of these local signaling methods differ from the typical endocrine signaling where hormones travel through the bloodstream to distant target cells. Paracrine and autocrine signaling allow for more rapid and localized responses in specific tissues.

24. How do growth hormones work, and what factors can affect their production?

Growth hormones, primarily produced by the pituitary gland, stimulate cell reproduction and regeneration. They work by binding to receptors on target cells, promoting protein synthesis and cell division. Growth hormone production is influenced by factors such as sleep, exercise, nutrition, and stress. During puberty, sex hormones also interact with growth hormones to stimulate the growth spurt. Disorders affecting growth hormone production can lead to conditions like dwarfism or gigantism.

25. What is the hypothalamic-pituitary axis, and why is it important?

The hypothalamic-pituitary axis is a complex interplay between the hypothalamus and the pituitary gland, two key structures in the endocrine system. The hypothalamus produces releasing and inhibiting hormones that control the pituitary gland's hormone secretion. This axis is crucial for maintaining homeostasis and regulating various bodily functions, including growth, stress response, and reproduction.

26. How do hormones contribute to the body's stress response?

Hormones play a crucial role in the body's stress response through the hypothalamic-pituitary-adrenal (HPA) axis. When stressed, the hypothalamus releases corticotropin-releasing hormone (CRH), which stimulates the pituitary to secrete adrenocorticotropic hormone (ACTH). ACTH then prompts the adrenal glands to produce cortisol, the primary stress hormone. This cascade helps the body respond to stress by increasing heart rate, blood pressure, and blood glucose levels.

27. How do environmental factors influence hormone production and function?

Environmental factors can significantly impact hormone production and function. Factors such as light exposure, diet, stress, and environmental toxins can alter hormone levels. For example, exposure to artificial light at night can disrupt melatonin production, affecting sleep patterns. Endocrine disruptors in the environment, like certain plastics or pesticides, can mimic or interfere with natural hormones, potentially leading to developmental or reproductive issues.

28. What is the difference between tropic and non-tropic hormones?

Tropic hormones are those that stimulate other endocrine glands to produce and secrete their hormones. For example, thyroid-stimulating hormone (TSH) from the pituitary gland stimulates the thyroid to produce thyroid hormones. Non-tropic hormones, on the other hand, act directly on target tissues to produce effects. For instance, insulin acts directly on various cells to regulate glucose uptake and metabolism.

29. What are hormone receptors, and why are they important?

Hormone receptors are specialized proteins on or within target cells that bind specific hormones. They are crucial for hormone action because they allow cells to recognize and respond to hormones. The presence or absence of specific receptors determines which cells will be affected by a particular hormone, enabling precise control of physiological processes. Receptor dysfunction can lead to hormone resistance or hypersensitivity.

30. What is the concept of hormone pulsatility, and why is it important?

Hormone pulsatility refers to the rhythmic, pulsatile release of hormones rather than a constant secretion. Many hormones, such as growth hormone and gonadotropin-releasing hormone (GnRH), are released in pulses. This pulsatile release is important because:

31. What is the difference between classical and non-classical hormone actions?

Classical hormone actions refer to the traditional model where hormones bind to specific receptors and trigger well-defined cellular responses. These actions typically involve changes in gene expression and protein synthesis, and their effects can take hours or days to manifest. Non-classical hormone actions, also known as rapid or membrane-initiated actions, occur much faster (within seconds to minutes) and often involve changes in ion channels or enzyme activities without directly affecting gene expression. Both types of actions are important for the overall physiological effects of hormones.

32. What is the role of hormones in maintaining circadian rhythms?

Hormones play a crucial role in regulating circadian rhythms, our body's internal 24-hour clock. The primary hormone involved is melatonin, produced by the pineal gland in response to darkness. Melatonin helps regulate sleep-wake cycles. Other hormones, such as cortisol, also follow circadian patterns, with levels typically peaking in the morning to help us wake up and declining in the evening to prepare for sleep.

33. What is the role of hormones in sexual development and reproduction?

Hormones are crucial in sexual development and reproduction. During puberty, sex hormones (estrogen, progesterone, and testosterone) drive the development of secondary sexual characteristics. In adults, these hormones regulate reproductive functions:

34. How do hormones regulate metabolism?

Hormones play a crucial role in regulating metabolism by controlling the rate at which the body uses energy. Key metabolic hormones include:

35. How do hormones influence behavior and mood?

Hormones significantly influence behavior and mood by interacting with the nervous system. For example:

36. How do hormones regulate fluid and electrolyte balance?

Hormones play a crucial role in maintaining fluid and electrolyte balance in the body. Key hormones involved include:

37. What are hormones and how do they differ from other signaling molecules?

Hormones are chemical messengers produced by endocrine glands that travel through the bloodstream to target specific cells or organs. They differ from other signaling molecules like neurotransmitters in that they can affect distant parts of the body and have longer-lasting effects. Hormones regulate various physiological processes, including growth, metabolism, and reproduction.