Hormones- Properties, functions and classification


Hormones are chemical messengers produced in small amounts by endocrine glands. They are secreted into the bloodstream to control metabolism and biological activities in target cells or organs.

Hormones, which are produced by various tissues and glands in the body, play a pivotal role in the endocrine system. Researchers have identified over 50 types of hormones in the human body. These hormones exert control over several key aspects of our physiology, including:

1. Metabolism: Hormones such as insulin, glucagon, thyroid hormones, and adrenaline regulate metabolism by influencing the breakdown, utilization, and storage of nutrients. They help maintain energy balance and regulate processes like glucose metabolism, lipid metabolism, and protein synthesis.

2. Sexual function: Sex hormones, including estrogen, progesterone, and testosterone, are instrumental in sexual development and reproduction. They affect the development and function of sexual organs, the menstrual cycle, sperm production, and secondary sexual characteristics.

3. Mood: Hormones, along with neurotransmitters, have a significant impact on mood regulation. Serotonin, dopamine, and norepinephrine, among others, influence emotional well-being, motivation, and feelings of pleasure. Hormonal imbalances can contribute to mood disorders like depression and anxiety.

4. Sleep-wake cycle: Hormones like melatonin, produced by the pineal gland, regulate the sleep-wake cycle. Melatonin helps synchronize the body's internal clock, promoting sleepiness at night and wakefulness during the day. Disruptions in hormone production can lead to sleep disorders and disturbances in circadian rhythms.

5. Development and growth: Hormones play a vital role in the development and growth of the body. Growth hormone (GH) stimulates tissue growth, bone development, and muscle mass. Thyroid hormones contribute to proper growth, brain development, and overall metabolism. Sex hormones are responsible for the development of secondary sexual characteristics and reproductive system maturation.

6. Internal balance (homeostasis): Hormones help maintain internal balance and homeostasis in the body. They regulate processes like blood sugar levels (insulin and glucagon), electrolyte balance (aldosterone), fluid balance (antidiuretic hormone), and stress responses (cortisol). Hormonal regulation ensures that various systems work harmoniously and maintain optimal conditions for proper bodily function.

These functions highlight the critical role hormones play in controlling and coordinating essential physiological processes, ensuring overall health and well-being.

Characteristics or properties of hormones:

1. Low molecular weight: Hormones are typically small molecules.
2. Soluble organic molecules: They are soluble in body fluids.
3. High rate of diffusion: Hormones can diffuse rapidly through the bloodstream.
4. Readily oxidized: Hormones can be easily oxidized, but their effects are not constant.
5. Effective in low concentration: Hormones can have significant effects even at low concentrations.
6. Travel in blood: Hormones are transported through the bloodstream to reach their target cells or organs.
7. Target site different from production site: Hormones act on specific target cells or organs that are different from where they are produced.
8. Specific to a particular target: Each hormone has a specific target tissue or organ on which it exerts its effects.
9. Non-specific for organisms: Hormones can influence body processes in other individuals of the same species.

Functions of hormones:

1. Regulatory and homeostasis functions: Hormones help regulate various physiological processes and maintain internal balance (homeostasis) in the body.

2. Maintenance of cellular consistency: Hormones contribute to maintaining the internal environment of cells within certain parameters.

3. Permissive functions: Hormones facilitate the movement of substances into and out of cells.

4. Integrative function: Hormones often balance or integrate the activities of different systems in the body.

5. Developmental function: Hormones play a role in the development and growth of an organism, including fetal development.

Classification of hormones:

Hormones can be classified based on their chemical nature or the mechanism of their action.

A. Classification based on chemical nature:

1. Protein hormones: Examples include insulin and glucagon.

2. Steroid hormones: Examples include sex hormones (estrogen, progesterone, testosterone) and glucocorticoids (cortisol).

3. Amino acid derivatives: Examples include epinephrine and norepinephrine.

B. Classification based on mechanism of hormone action:

1. Group I hormones (lipophilic hormones): These hormones are lipophilic (lipid-soluble) and often derived from cholesterol. They bind to intracellular receptors. Examples include steroid hormones like estrogen, androgen, glucocorticoids, and thyroxine.

2. Group II hormones (water-soluble hormones): These hormones bind to cell surface receptors and stimulate the release of secondary messengers to initiate biochemical functions. There are three types based on the secondary messengers involved:

   i. Secondary messenger is cAMP: Examples include adrenocorticotropic hormone, follicle-stimulating hormone, luteinizing hormone, and glucagon.

   ii. Secondary messenger is phosphatidylinositol/calcium or both: Examples include acetylcholine, vasopressin, insulin, and growth hormones.

   iii. Secondary messenger is cGMP: An example is atrial natriuretic peptide (ANP).

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