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

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.

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

The mechanisms of hormone 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.

Feedback Mechanism

Learn about feedback mechanisms here:

• Thyroid Mechanism Of Action:

Thyroid secretes thyroxine. Its production is in turn regulated by a hormone called Thyrotropin Releasing Hormone produced from the hypothalamus and another hormone called Thyroid Stimulating Hormone produced from the anterior pituitary.

• Positive Feedback:

Low thyroxine levels will stimulate the production of TRH and TSH, which increase the level of thyroxine secretion.

• Negative Feedback:

When there is a high amount of thyroxine in the blood, it acts as negative feedback to suppress the formation of TRH and TSH to prevent overstimulation and maintain the optimum quantity of thyroxine.

Hormone Clearance

Hormones are generally cleared from the blood by the liver, kidneys, or other organs to avoid overstimulation.

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.

Mechanism Of Hormone Action

The mechanism is described below:

• Peptide Hormones:

The hormone binds to cell surface receptors and activates second messenger systems which modulate cellular function.

• Steroid Hormones:

The hormones diffuse into the cell and then bind to intracellular receptors which directly influence DNA transcription and protein synthesis.

• Amino Acid-Derived Hormones:

Depending on their nature, they act via cell surface or intracellular receptors.

Endocrine Gland Disorders

Hormone imbalance can lead to many disorders.

Hypothyroidism:

The production level of thyroid hormone is decreased; symptoms include fatigue, weight gain, and depression.

Hyperthyroidism:

This excess synthesis of the thyroid hormone causes symptoms such as weight loss, tachycardia, and anxiety.

Diabetes Mellitus Type 1 Diabetes:

Autoimmune destruction of cells of the pancreas that produce insulin.

Type 2 Diabetes:

There is insulin resistance, which later leads to a decrease in its production.

Adrenal Disorders

• Cushing's Syndrome:

Overproduction of cortisol is a classic manifestation of the disease; this includes weight gain, hypertension, and high blood sugar levels, or a combination of these features.

• Addison's Disease:

It is a deficiency of the production of hormones from the adrenal glands; symptoms and signs are related to fatigue, muscle weakness, and low blood pressure.

Conclusion

The range of physiological activities that the body has to control extends from metabolism to reproduction and is serviced by hormones. The precise action and interaction allow all of the body's systems to function in harmony.

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