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

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.

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:

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.

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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