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Hormones - Functions, Types, and Mechanism of Action

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Hormones are a group of signaling molecules secreted by glands that do physiological activities and maintain homeostasis in the body. Read further to know more.

Written by

Dr. Asna Fatma

Medically reviewed by

Dr. Basuki Nath Bhagat

Published At September 22, 2022
Reviewed AtJanuary 12, 2024


Hormones are the body’s chemical messengers; they travel in the bloodstream to various organs and tissues. These hormones carry out multiple physiological functions in the body. Endocrine glands are majorly responsible for the production of hormones. There are different types of hormones for specific functions in the body, and different endocrine glands produce them. Any imbalance in the levels of hormones can lead to serious health issues.

What Are Hormones?

Hormones are a group of signaling molecules in multicellular organisms that are transported to distant cells and organs through complex biological processes to regulate physiology and behavior in the body. These hormones act as chemical messengers in the body that are carried by the bloodstream to different parts of the body, which interpret these messages and act on them accordingly. Hormones carry out their functions by evoking responses from specific organs or tissues that are adapted to react to them. Hormones work slowly over time and affect the body’s growth, development, metabolism, sexual functioning, and mood. When the endocrine glands underproduce (or do not produce at all) or overproduce a hormone, multiple diseases are caused.

What Do Hormones Do?

Hormones are vital for the proper functioning of the body, and they carry out a lot of crucial functions in the body. The various functions of the hormones include:

  • Communication between organs and tissues.

  • Growth and development.

  • Behavioral activities.

  • Metabolism of food (the chemical process of changing food into energy).

  • Digestion.

  • Respiration.

  • Sensory perception.

  • Sleep.

  • Excretion.

  • Lactation.

  • Stress induction.

  • Sexual functioning.

  • Reproduction.

  • Cognitive functions (Brain functions involved in reasoning, information manipulation, and knowledge gain) and mood changes.

  • Maintaining body temperature and thirst.

How Do the Hormones Work?

The blood carries the actions of hormones throughout the body. But specific hormones affect specific cells, which have receptor sites for that hormone. The mechanism of action of hormones is in the form of a lock and key mechanism. If the hormone fits the receptor site like a key, then only there will be an effect. If the hormone and the receptor site do not match, then there will be no outcome. The target tissue is sometimes localized and limited to a certain gland or organ. In some cases, the target tissues are diffused and present throughout the body; therefore, many areas are affected.

Hormones bring about their characteristic effect by modifying cellular activity. In addition, protein and steroid hormones react with the receptor differently. The protein hormones react with the receptor on the cell's surface, and the resulting hormone action is relatively fast. The steroid hormones react with the receptor inside the cell; this process is relatively slow because it involves protein synthesis.

What Are the Types of Hormones?

Hormones can be chemically classified into four groups:

  • Amino Acid Derived: These are hormones that are modified amino acids.

  • Polypeptides and Proteins: These hormones are a chain of amino acids; the chain may be less or more than one thousand amino acids long.

  • Steroids: These hormones are lipids synthesized from cholesterol; four interlocking carbohydrate rings characterize steroids.

  • Eicosanoids: These hormones are lipids synthesized from fatty acid chains of the plasma membrane.

Hormones activate the target cells by different mechanisms, depending upon the chemical nature of the hormone. Therefore, based on these criteria, hormones are classified as:

  • Lipid-Soluble: Basically, steroid and thyroid hormones are lipid-soluble hormones. These hormones diffuse through the cell membrane of the target cells and then bind to the receptor protein, activating a DNA (deoxyribonucleic acid) segment that turns on specific genes.

  • Water-Soluble: Proteins, polypeptides, and amino acid hormones are water-soluble hormones. These hormones bind to the receptor protein on the cell's plasma membrane. The receptor protein, in turn, stimulates the production of secondary messengers.

Where Are the Hormones Produced?

Specialized cells or glands in different body tissues are responsible for producing hormones. The endocrine system, which creates and releases hormones into the bloodstream, includes these glands and tissues. Hormones are essential for controlling several physiological functions and preserving homeostasis. The following are some of the main glands and tissues that make hormones:

  • Hypothalamus: Although it is not a gland, the brain's hypothalamus is an important organ for regulating hormones. It creates hormones that regulate the pituitary gland's secretion, including hormones that release and inhibit.

  • Hypophysis or Pituitary Gland: Often called the ‘master gland’ this gland sits at the base of the brain and secretes a range of hormones that control growth, metabolism, reproduction, and other endocrine glands.

  • Thyroid Gland: The thyroid is a gland in the neck that secretes the thyroid hormones triiodothyronine and thyroidine, which control growth, metabolism, and energy production.

  • Parathyroid Glands: The parathyroid glands secrete parathyroid hormone (PTH), which controls blood and bone calcium and phosphorus levels in the thyroid gland.

  • Adrenal Glands: Sitting atop each kidney, the adrenal glands secrete hormones like adrenaline, which is involved in the ‘fight or flight’ response, and cortisol, which controls metabolism and the stress response.

  • Pancreas: The organ behind the stomach that makes insulin and glucagon, which control blood sugar and metabolism, is the pancreas.

  • Ovaries: In females, the ovaries generate progesterone and estrogen, which control secondary sexual traits, pregnancy, and the menstrual cycle.

  • Testes: In men, testosterone production from the testes controls the development of sperm, muscle mass, and secondary sexual traits.

  • Pineal Gland: Melatonin, which is produced by the pineal gland in the brain, controls the circadian rhythm, or the cycle of sleep and wakefulness.

  • Thymus: The thymus, a gland in the chest, secretes hormones that affect how the immune system develops and operates.

What Are the Major Hormones in the Body and Their Function?

Hormones in the Body - Chemical Class - Steroids

Hormones in the Body - Chemical Class - Peptide

Hormones in the Body - Chemical Class - miscellaneous


Hormones are the body's chemical messengers carried through the blood to the different parts of the body to carry out specific functions. Hormones are responsible for various bodily actions, from growth and development to reproduction, stress response, and more. Therefore, hormones are crucial for a healthy body and life; any imbalance in the levels of the hormones can cause various disorders. Conditions like hypothyroidism, hyperthyroidism, Cushing’s disease, Conn’s disease, infertility, complete androgen insensitivity, depression, and more. Therefore, maintaining the correct level of hormones in the body is crucial.

Dr. Basuki Nath Bhagat
Dr. Basuki Nath Bhagat

Family Physician


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