WHAT IS HORMONE

Hormones

Introduction

Hormones are chemical substances produced by special cells or glands in our body. They travel through the blood or act on nearby cells and tissues to control and coordinate many important activities. They act as messengers and carry signals to different parts of the body. Hormones help control many important functions such as growth, development, metabolism, digestion, reproduction, sleep, mood, blood pressure, blood sugar, water balance and responses to stress. They are released into the blood and help different organs work properly and maintain balance in the body.

The organs that produce and release hormones are called endocrine glands. Together, these glands form the endocrine system.

Examples of important endocrine glands include the pituitary gland, thyroid gland, adrenal glands, pancreas, ovaries, testes, pineal gland, parathyroid glands, hypothalamus, and thymus.

What Are Hormones

A hormone is a chemical substance produced by specialized cells and released into the body to send a message to specific target cells or organs. Hormones generally work in very small amounts, but their effects can be significant.

For example:

• The pancreas produces insulin.

• Insulin helps body cells take up glucose from the blood.

• The thyroid produces thyroxine (T4) and triiodothyronine (T3).

• These hormones help regulate metabolism.

• The adrenal glands produce adrenaline, which helps the body respond quickly to stressful or dangerous situations.

The Endocrine System

The endocrine system is a network of glands and tissues in the body that produce and release hormones. These glands release hormones directly into the bloodstream, which carries them to different parts of the body. The endocrine system helps control and coordinate important body functions such as growth, development, metabolism and reproduction.

Major endocrine organs and glands

1. Hypothalamus

2. Pituitary gland

3. Pineal gland

4. Thyroid gland

5. Parathyroid glands

6. Thymus

7. Adrenal glands

8. Pancreas

9. Ovaries

10. Testes

11. Kidneys

12. Heart

13. Liver

14. Gastrointestinal tract

15. Adipose tissue

Functions of Hormones

Hormones perform many functions in the human body.

1. Growth and development

Growth-related hormones help children and adolescents grow and develop normally.

Growth hormone (GH) plays an important role in the growth of bones and other tissues.

2. Metabolism

Hormones control how the body uses and stores energy.

Thyroid hormones, for example help regulate metabolic activity.

3. Blood sugar regulation

The hormones insulin and glucagon help maintain the level of glucose in the blood.

• Insulin generally lowers blood glucose.

• Glucagon generally raises blood glucose.

4. Reproduction

Hormones control reproductive development and reproductive functions.

Important reproductive hormones include:

• Estrogen

• Progesterone

• Testosterone

• Follicle-stimulating hormone (FSH)

• Luteinizing hormone (LH)

5. Stress response

Hormones help the body respond to physical or emotional stress.

Important hormones include:

• Adrenaline

• Noradrenaline

• Cortisol

6. Water and mineral balance

Hormones help maintain appropriate levels of water and minerals such as sodium and calcium.

Examples include:

• Antidiuretic hormone (ADH)

• Aldosterone

• Parathyroid hormone (PTH)

7. Sleep and biological rhythms

Melatonin, produced mainly by the pineal gland helps regulate the body's sleep-wake cycle.

8. Mood and behaviour

Hormones can influence mood, motivation, stress responses and other aspects of behaviour.

Examples include:

• Cortisol

• Estrogen

• Testosterone

• Thyroid hormones

However, mood and behaviour are controlled by many interacting systems, especially the nervous system so no single hormone determines a person's personality or emotions.

Types of Hormones

Hormones can be classified in different ways.

A. Peptide and Protein Hormones

These hormones are made from chains of amino acids. They act by binding to receptors on the surface of target cells.

Examples:

• Insulin

• Glucagon

• Growth hormone

• Prolactin

• ADH

• Oxytocin

B. Steroid Hormones

Steroid hormones are made from cholesterol. Many steroid hormones can enter cells and influence gene activity through intracellular receptors.

Examples include:

• Cortisol

• Aldosterone

• Estrogen

• Progesterone

• Testosterone

C. Amino-Acid-Derived Hormones

These hormones are derived from amino acids such as tyrosine or tryptophan.

Examples include:

• Thyroxine (T4)

• Triiodothyronine (T3)

• Adrenaline

• Noradrenaline

• Melatonin

5. Major Hormones of the Human Body

A. Hypothalamus

The hypothalamus is a region of the brain that connects the nervous system with the endocrine system. It controls many functions of the pituitary gland.

Important hypothalamic hormones include:

• Thyrotropin-releasing hormone (TRH)
• Stimulates the pituitary gland to release thyroid-stimulating hormone.
• Corticotropin-releasing hormone (CRH)
• Stimulates the release of ACTH, which ultimately helps regulate cortisol production.
• Gonadotropin-releasing hormone (GnRH)
• Controls the release of FSH and LH.
• Growth hormone-releasing hormone (GHRH)
• Stimulates growth hormone release.
• Somatostatin
• Inhibits the release of several hormones, including growth hormone.
• Dopamine
• Acts as a neurotransmitter and also inhibits prolactin secretion from the pituitary.

Pituitary Gland Hormones

The pituitary gland is a small gland located at the base of the brain. It is sometimes called the "master gland" because it regulates several other endocrine glands.

However, the pituitary itself is controlled extensively by the hypothalamus.

Growth Hormone (GH)

Function:

• Supports growth of bones and tissues.

• Helps regulate protein, fat, and carbohydrate metabolism.

Thyroid-Stimulating Hormone (TSH)

Function:

• Stimulates the thyroid gland to produce thyroid hormones.

Adrenocorticotropic Hormone (ACTH)

Function:

• Stimulates the adrenal cortex to produce hormones, particularly cortisol.

Follicle-Stimulating Hormone (FSH)

Function:

• Supports development of ovarian follicles in females.

• Helps support sperm production in males.

Luteinizing Hormone (LH)

Function:

• Helps regulate ovulation and ovarian hormone production.

• Stimulates testosterone production in the testes.

Prolactin

Function:

• Promotes milk production after childbirth.

• Also has other roles in reproductive and metabolic processes.

Antidiuretic Hormone (ADH)

ADH is made in the hypothalamus and stored and released by the posterior pituitary.

Function:

• Helps the kidneys conserve water.

• Contributes to regulation of blood volume and blood pressure.

Oxytocin

Oxytocin is also made in the hypothalamus and released by the posterior pituitary.

Functions:

• Helps produce contractions of the uterus during childbirth.

• Helps with milk ejection during breastfeeding.

• Also has roles in social bonding and other behaviours.

Thyroid Gland Hormones

The thyroid gland is located in the front of the neck.

Thyroxine (T4)

Functions:

• Helps regulate metabolism.

• Supports growth and development.

• Supports normal brain development.

• Influences heart rate and body temperature.

Triiodothyronine (T3)

T3 is the more biologically active thyroid hormone.

Functions:

• Regulates metabolic activity.

• Supports normal growth and development.

• Influences the function of many organs.

Calcitonin

Produced by specialized cells of the thyroid.

Function:

• Helps regulate calcium levels in the blood.

• It generally opposes the action of parathyroid hormone on blood calcium.

Parathyroid Hormone

The parathyroid glands are usually four small glands located behind the thyroid gland.

Parathyroid Hormone (PTH)

Functions:

• Raises blood calcium when it becomes too low.

• Helps regulate calcium and phosphate balance.

• Acts on bones and kidneys and indirectly affects calcium absorption from the intestine.

Calcium is important for healthy bones, muscles, nerves, and many cellular processes.

Adrenal Gland Hormones

There are two adrenal glands, located above the kidneys.

They have two major regions:

• Adrenal cortex

• Adrenal medulla

Cortisol

Cortisol is produced by the adrenal cortex.

Functions:

• Helps the body respond to stress.

• Influences blood glucose levels.

• Affects metabolism.

• Helps regulate immune and inflammatory responses.

Aldosterone

Functions:

• Helps the kidneys retain sodium.

• Promotes potassium excretion.

• Helps regulate blood volume and blood pressure.

Adrenaline (Epinephrine)

Produced mainly by the adrenal medulla.

Functions:

• Increases heart rate.

• Helps increase blood flow to muscles.

• Helps make energy available quickly.

• Prepares the body for rapid action during stress.

Noradrenaline (Norepinephrine)

Functions:

• Helps regulate blood pressure.

• Contributes to the body's response to stress.

• Acts as both a hormone and a neurotransmitter.

Pancreatic Hormones

The pancreas has both digestive and endocrine functions.

Important hormones include:

Insulin

Function:

• Helps cells take up glucose from the blood.

• Helps lower blood glucose levels.

• Promotes storage of energy after meals.

Glucagon

Function:

• Helps raise blood glucose when it becomes low.

• Stimulates the liver to release glucose into the bloodstream.

Somatostatin

Function:

• Helps regulate and inhibit the release of several hormones.

• Helps regulate digestive activity and pancreatic secretions.

Pineal Gland Hormone

Melatonin

Melatonin is produced mainly by the pineal gland in the brain.

Functions:

• Helps regulate the sleep-wake cycle.

• Helps coordinate biological rhythms with the light-dark cycle.

Melatonin production generally increases in darkness and decreases with light exposure.

Reproductive Hormones

Estrogen

Estrogens are a group of hormones produced mainly by the ovaries in females, although smaller amounts are produced in other tissues and in males.

Functions:

• Supports development of female reproductive characteristics.

• Helps regulate the menstrual cycle.

• Supports bone health.

• Plays important roles in reproductive and other body functions.

Progesterone

Produced mainly by the ovaries after ovulation and by the placenta during pregnancy.

Functions:

• Helps prepare and maintain the uterine lining for pregnancy.

• Supports pregnancy.

• Helps regulate the menstrual cycle.

Testosterone

Testosterone is produced mainly by the testes in males. Smaller amounts are also produced by the ovaries and adrenal glands.

Functions:

• Supports development of male reproductive characteristics.

• Supports sperm production.

• Helps maintain bone and muscle tissue.

Hormones Related to Pregnancy

Human Chorionic Gonadotropin (hCG)

Produced by the developing placenta during early pregnancy.

Functions:

• Helps maintain hormone production needed to support the early pregnancy.

• It is the hormone detected by most pregnancy tests.

Human Placental Lactogen (hPL)

Produced by the placenta.

Functions:

• Helps prepare the breasts for breastfeeding.

• Alters maternal metabolism during pregnancy to help provide nutrients to the developing fetus.

Relaxin

Produced during pregnancy.

Functions:

• Helps prepare the reproductive system for childbirth.

• Contributes to changes in ligaments and the cervix during pregnancy.

Hormones Produced by the Kidneys

The kidneys also have important endocrine functions.

Erythropoietin (EPO)

Function:

• Stimulates the bone marrow to produce red blood cells when oxygen levels are low.

Renin

Function:

• Helps regulate blood pressure and fluid balance through the renin-angiotensin-aldosterone system.

Calcitriol

Calcitriol is the active form of vitamin D and is produced by the kidneys from vitamin D precursors.

Functions:

• Helps increase calcium and phosphate absorption from the intestine.

• Supports healthy bones and mineral balance.

Hormones Produced by the Heart

Atrial Natriuretic Peptide (ANP)

Produced mainly by the atria of the heart.

Functions:

• Helps reduce blood volume and blood pressure.

• Promotes sodium and water excretion by the kidneys.

B-type Natriuretic Peptide (BNP)

Produced mainly by the heart's ventricles when they are stretched.

Function:

• Helps regulate blood volume and blood pressure.

Hormones Produced by the Digestive System

The digestive tract produces several hormones that regulate digestion and appetite.

Gastrin

Function:

• Stimulates the stomach to produce acid.

• Supports digestive activity.

Secretin

Function:

• Stimulates the pancreas to release bicarbonate.

• Helps neutralize stomach acid entering the small intestine.

Cholecystokinin (CCK)

Functions:

• Stimulates the release of digestive enzymes.

• Helps the gallbladder release bile.

• Contributes to feelings of fullness after eating.

Ghrelin

Produced mainly by the stomach.

Function:

• Stimulates hunger and influences energy balance.

GLP-1

Produced mainly in the intestine after eating.

Functions:

• Stimulates insulin release when blood glucose is elevated.

• Helps slow stomach emptying.

• Contributes to feelings of fullness.

GIP

Produced by cells of the small intestine.

Function:

• Helps stimulate insulin release after food intake.

• Participates in regulation of glucose and energy metabolism.

Hormones Produced by Fat Tissue

Fat tissue is not simply an energy-storage tissue. It also acts as an endocrine organ.

Leptin

Functions:

• Helps regulate appetite and energy balance.

• Provides information to the brain about energy stores.

Adiponectin

Functions:

• Participates in regulation of glucose and fat metabolism.

• Is involved in maintaining metabolic health.

Important Hormones at a Glance

Hormone	Main Source	Major Function
Growth hormone	Pituitary	Growth and tissue development
TSH	Pituitary	Stimulates thyroid hormone production
ACTH	Pituitary	Stimulates cortisol production
FSH	Pituitary	Reproductive functions
LH	Pituitary	Ovulation and sex hormone production
Prolactin	Pituitary	Milk production
ADH	Hypothalamus/posterior pituitary	Water conservation
Oxytocin	Hypothalamus/posterior pituitary	Uterine contractions and milk ejection
T3	Thyroid	Metabolism and development
T4	Thyroid	Metabolism and development
Calcitonin	Thyroid	Calcium regulation
PTH	Parathyroid	Raises blood calcium
Cortisol	Adrenal cortex	Stress and metabolism
Aldosterone	Adrenal cortex	Salt, water and blood pressure regulation
Adrenaline	Adrenal medulla	Rapid stress response
Insulin	Pancreas	Lowers blood glucose
Glucagon	Pancreas	Raises blood glucose
Melatonin	Pineal gland	Sleep-wake rhythm
Estrogen	Mainly ovaries	Reproductive development and cycle
Progesterone	Mainly ovaries	Menstrual cycle and pregnancy
Testosterone	Mainly testes	Male reproductive development and sperm production
EPO	Kidneys	Red blood cell production
Renin	Kidneys	Blood pressure and fluid regulation
ANP	Heart	Helps lower blood volume and pressure
Gastrin	Stomach	Stimulates stomach acid
Secretin	Small intestine	Stimulates bicarbonate release
CCK	Small intestine	Digestive enzyme and bile release
Ghrelin	Mainly stomach	Hunger regulation
Leptin	Fat tissue	Energy balance and appetite regulation
hCG	Placenta	Supports early pregnancy
GLP-1	Intestine	Glucose regulation and fullness

How Hormones Work

Hormones do not affect every cell in the body equally. They act mainly on cells that have the appropriate receptors.

A simple sequence is:

Endocrine gland → Hormone released → Bloodstream → Target cell → Receptor → Cellular response

For example:

Pancreas → Insulin → Blood → Muscle/fat/liver cells → Insulin receptor → Increased glucose uptake and storage

This is similar to a key fitting into a specific lock: a hormone can produce its main effects only in cells that have the appropriate receptor.

Hormones and Homeostasis

One of the most important roles of hormones is maintaining homeostasis.

Homeostasis means keeping the body's internal conditions within a suitable range despite changes in the environment.

Examples include:

• Maintaining blood glucose levels.

• Maintaining body temperature.

• Maintaining water balance.

• Maintaining calcium levels.

• Regulating blood pressure.

• Controlling energy use.

Hormonal systems often work through negative feedback.

Example: Thyroid hormone regulation

The hypothalamus releases TRH → the pituitary releases TSH → the thyroid produces T3 and T4.

When thyroid hormone levels become sufficient, they provide feedback that reduces further stimulation from the hypothalamus and pituitary.

This helps prevent excessive hormone production.

Hormones and the Nervous System

The endocrine system and nervous system work closely together.

The nervous system usually sends signals rapidly through nerve cells, while hormones can produce effects that last longer.

The hypothalamus is an important connection between these two systems.

For example, during stress, the brain can activate hormonal pathways that cause the adrenal glands to release cortisol and adrenaline.

Imbalanced of Hormones

Hormones need to be produced and regulated appropriately. Too much or too little of a hormone can affect normal body functions.

Examples include:

• Too little thyroid hormone
• May lead to hypothyroidism, which can cause symptoms such as tiredness, feeling unusually cold, and slowed body processes.
• Too much thyroid hormone
• May lead to hyperthyroidism, which can cause symptoms such as rapid heartbeat, heat intolerance, and weight changes.
• Problems with insulin production or action
• Can contribute to diabetes, a group of conditions involving abnormal blood glucose regulation.
• Excess growth hormone
• In children, excessive growth hormone can cause unusually rapid growth; in adults it can cause acromegaly.
• Insufficient ADH
• Can cause excessive water loss through urine, as occurs in diabetes insipidus.
• Hormonal disorders should be evaluated by qualified healthcare professionals because symptoms can have many different causes.

Conclusion

Hormones are essential chemical messengers that coordinate a wide range of processes in the human body. They help control growth, metabolism, blood glucose, water balance, stress responses, sleep, reproduction, development, and many other functions.

The endocrine system includes major glands such as the hypothalamus, pituitary, thyroid, parathyroids, adrenal glands, pancreas, pineal gland, ovaries, and testes, as well as hormone-producing organs such as the kidneys, heart, stomach, intestines, liver, and fat tissue.

A healthy body depends not simply on having hormones, but on maintaining the right amounts, timing, receptors, and feedback mechanisms. Hormones therefore play a central role in maintaining the body's internal balance, or homeostasis.

Quick Summary

Hormones = Chemical messengers

Endocrine glands → Hormones → Bloodstream → Target cells → Receptors → Body response

Major examples:

Insulin → Blood glucose

T3/T4 → Metabolism

Growth hormone → Growth

ADH → Water balance

Cortisol → Stress and metabolism

Adrenaline → Rapid stress response

Estrogen/Progesterone/Testosterone → Reproductive functions

Melatonin → Sleep-wake cycle

PTH → Calcium balance

EPO → Red blood cell production