Hormone In The Endocrine System

Hormones As Chemical Signals

Hormones are traditionally defined as chemical signals, transported to their target tissues in the blood today, however, that definition is often expanded to include all chemical messengers that bind to target cells with high affinity. So far, more than 100 hormones have been identified in the human body, and this rises to more than 200 if hormone-like substances are included .

Hormones exert their physiological effects by binding to specific receptors associated with their target cells . Many drugs have been designed to target these receptor sites, either to mimic the actions of hormones or to act as competitive antagonists to physically block the receptor, preventing the natural hormone from binding and exerting its effect. Hormones can be broadly divided into three major classes:

• Peptide hormones
• Amino acid-derived hormones.

Peptide hormones

These are the largest hormones, with relatively high molecular weights. They are proteinaceous chemical signals, comprising chains of amino acids of varying lengths. Examples include:

• Somatotropin
• Insulin
• Ghrelin .

Some peptide hormones are initially produced as inactive forms called prohormones a good example is insulin, which is first synthesised as a much larger molecule, called proinsulin, and then cleaved into its active, shorter form before being released into the blood.

Steroid hormones

• Oestrogen
• Testosterone
• Cortisol.

Amino acid-derived hormones

A Diseases And Disorders Of The Pituitary Gland

Hypersecretion

• The hypersecretion of the anterior pituitary hormones can result in gigantism and acromegaly.
• These conditions are the result of over secretion of the growth hormone-releasing hormone by the hypothalamus.
• Gigantism can be observed in the form of large bones and increased height. Acromegaly is characterized by large extremities as a result of the thickening of the bones and soft tissues.

Hyposecretion

• The hyposecretion of the pituitary gland can result in a number of disorders like ischaemic necrosis, dwarfism, and Frohlichs syndrome.
• Ischaemic necrosis is characterized by the deficient stimulation of target glands and hyposecretion of all the glands controlled by the pituitary gland.
• Dwarfism is a commonly understood disorder as a result of the deficiency of the growth hormone in childhood.
• The hyposecretion of the ADH can result in a rare condition called diabetes insipidus, characterized by the loss of reabsorption of water by the renal tubules in the kidney.

What Are Some Examples Of Hormones

Some examples of hormones are:

Growth hormone: This is released from the pituitary gland. It is essential for normal physical growth in children and for some functions in adults, such as fat and muscle mass.

Thyroxine: The thyroid gland converts iodine from the diet into thyroxine. This controls many functions of the metabolism, including temperature, heart rate and growth.

Cortisol: This is released from the adrenal glands . It is important for controlling blood pressure and for dealing with the body’s response to stress.

Insulin: This is produced by islet cells in the pancreas. It controls blood sugar levels.

Oestrogen and progesterone: These hormones, released from the ovaries, are responsible for female body characteristics and for storing and releasing eggs.

Testosterone: This is released from the testes. It produces male body characteristics and sperm.

Find out more about the main endocrine glands and their hormones.

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Problems Of The Endocrine System

Numerous problems can occur in the endocrine system. These can be considered as excessive or deficient hormone production. Endocrine organs are also prone to tumours which can over produce hormones. Some problems of the endocrine system include:

• Diabetes too much sugar in the blood caused by problems with insulin production. This includes type 1 diabetes and type 2 diabetes .
• Menstruation abnormalities irregular menstruation or lack of menstruation. Some causes of this include polycystic ovarian syndrome , pituitary adenoma or primary ovarian failure .
• Thyroid problems when the gland is overactive or underactive . Thyroid nodules are common but thyroid cancers are rare.
• Parathyroid problems an enlargement or one of more of the parathyroid glands can lead to high calcium levels in the blood .
• Pituitary adenomas these are tumours of the pituitary gland that can make too much of a certain hormone or cause deficiencies of hormones. These tumours can be small or large .
• Neuro-endocrine tumours these are rare to tumours of certain endocrine glands . These can include too much adrenaline released by the adrenal gland , or too much hormone 5HIAA from a carcinoid tumour which causes diarrhoea and flushing.

What Conditions Are Caused By Hormone Issues

Dozens of medical conditions are caused by hormone issues. For most hormones, having too much or too little of them causes symptoms and issues with your health. These imbalances often require treatment. Some of the most common hormone-related conditions include:

• Hereditary gene mutations that cause problems with the structure and/or function of an endocrine gland.

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Types Of Endocrine Disorders

There are many different types of endocrine disorders. Diabetes is the most common endocrine disorder diagnosed in the U.S.

Other endocrine disorders include:

Adrenal insufficiency. The adrenal gland releases too little of the hormone cortisol and sometimes, aldosterone. Symptoms include fatigue, stomach upset, dehydration, and skin changes. Addison’s disease is a type of adrenal insufficiency.

Cushing’s disease. Overproduction of a pituitary gland hormone leads to an overactive adrenal gland. A similar condition called Cushing’s syndrome may occur in people, particularly children, who take high doses of corticosteroid medications.

Gigantism and other growth hormone problems. If the pituitary gland produces too much growth hormone, a child’s bones and body parts may grow abnormally fast. If growth hormone levels are too low, a child can stop growing in height.

Hyperthyroidism. The thyroid gland produces too much thyroid hormone, leading to weight loss, fast heart rate, sweating, and nervousness. The most common cause for an overactive thyroid is an autoimmune disorder called Grave’s disease.

Hypothyroidism. The thyroid gland does not produce enough thyroid hormone, leading to fatigue, constipation, dry skin, and depression. The underactive gland can cause slowed development in children. Some types of hypothyroidism are present at birth.

Precocious puberty. Abnormally early puberty that occurs when glands tell the body to release sex hormones too soon in life.

The Thyroid And Its Hormones

The thyroid gland, which consists of two lobes, is located in front of the windpipe , just below the voice box . The gland produces two structurally related hormones, thyroxine and triiodothyronine , that are iodinated derivatives of the amino acid tyrosine. Both hormones are collectively referred to as thyroid hormone. T4 constitutes approximately 90 percent of the hormone produced in the thyroid gland. However, T3 is a much more active hormone, and most of the T4 produced by the thyroid is converted into T3 in the liver and kidneys.

Thyroid hormone in general serves to increase the metabolism of almost all body tissues. For example, thyroid hormone stimulates the production of certain proteins involved in heat generation in the body, a function that is essential for maintaining body temperature in cold climates. Moreover, thyroid hormone promotes several other metabolic processes involving carbohydrates, proteins, and lipids that help generate the energy required for the bodys functions. In addition to those metabolic effects, thyroid hormone plays an essential role in the development of the central nervous system during late fetal and early postnatal developmental stages. Furthermore, thyroid hormone exerts an effect similar to that of GH on normal bone growth and maturation. Finally, thyroid hormone is required for the normal development of teeth, skin, and hair follicles as well as for the functioning of the nervous, cardiovascular, and gastrointestinal systems.

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The Endocrine System And Homoeostasis

An average adult human with a weight of 70kg is thought to comprise around 30-40 trillion cells . For each cell to function effectively, it must be maintained at the correct temperature and pH, and provided with a steady stream of nutrients and oxygen. At the same time, the local environment of each cell needs any waste metabolites, such as carbon dioxide and urea, to be efficiently removed.

Homoeostasis can be broadly defined as the ability to maintain a relatively stable internal environment it is essential to good health and survival . A multitude of variables in the body are susceptible to continual and significant fluctuation, and most of the major organ systems of the body are dedicated to keeping these variables within their normal physiological ranges.

The internal biochemical processes necessary for life are primarily driven by biological catalysts known as enzymes, which generally fall into two categories:

Anabolic and catabolic enzymes can only function efficiently in narrow ranges of temperature and pH they also require a steady supply of the substrate molecules on which they act . As an example, for aerobic cellular metabolism to occur, the respiratory enzymes in cells require a steady stream of glucose and oxygen.

The homoeostatic mechanisms that ensure a stable environment in the body rely on a process called negative feedback, which is discussed below.

Set points, negative feedback and the role of hormones

Effects of variables outside of their normal range

Testing For Endocrine Disorders

If you have an endocrine disorder, your doctor may refer you to a specialist called an endocrinologist. An endocrinologist is specially trained in problems with the endocrine system.

The symptoms of an endocrine disorder vary widely and depend on the specific gland involved. However, most people with endocrine disease complain of fatigue and weakness.

Blood and urine tests to check your hormone levels can help your doctors determine if you have an endocrine disorder. Imaging tests may be done to help locate or pinpoint a nodule or tumor.

Treatment of endocrine disorders can be complicated, as a change in one hormone level can throw off another. Your doctor or specialist may order routine blood work to check for problems or to determine if your medication or treatment plan needs to be adjusted.

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The Exposure Patterns Of Nms

To define whether NMs are harmful to the endocrine system, we need to consider the exposure patterns of NMs, including exposure routes, dose, and duration. Indeed, the same NMs may have different effects on endocrine functions depending upon the exposure.

The entry route is a major factor which affects the endocrine-disrupting effects of NMs. For vertebrate animals, the exposure routes used in experiments include inhalation, oral entry , intraperitoneal injection, and intravenous injection . Among them, intravenous injection results in greater uptake than other routes . Inhaled or oral NMs can be partially eliminated while some can be absorbed into the bloodstream. Then they may be transported to organs including endocrine organs via circulation . EDs can pass through the liver, wherein they are metabolically detoxificated . Since it is difficult for NMs to enter the body by dermal exposure , few studies explore the adverse effects on endocrine organs or their functions after dermal exposure of NMs.

For invertebrate animals, NMs are often added into the environment. For example, aquatic animals are exposed to NMs in the water and flies are cultured in molasses culture medium supplemented with NMs.

Matthew A. Wallig, in, 2018

Hormones And Endocrine Function

Hormones are are the bodys chemical messengers, sending signals into the bloodstream and tissues. Hormones work slowly, over time, and affect many different processes, including growth and development, metabolism how your body gets energy from the foods you eat- sexual function, reproduction, and mood. When glands do not produce the right amount of hormones, diseases develop that can affect many aspects of life.

Some factors that affect endocrine organs include puberty, aging, pregnancy, the environment, genetics and certain diseases and medications, including naturopathic medicine, herbal supplements, and prescription medicines such as opioids or steroids. Hormones are vital to your health and well-being.

Hormone stability can be a delicate balancing act, which is why you want to work with a hormone specialist. If you suspect hormone or endocrine-related problems get help from an endocrinologist near you.

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Common Endocrine System Disorders

There are eight main glands that run through your body as part of the endocrine system. The glands produce hormones which run through your bloodstream to your organs and tissues. The hormones move slowly but they do have an effect on the entire body, including:

• Development and growth
• Metabolism which includes breathing, digestion, maintaining body temperature, elimination, and blood circulation
• Sexual function
• Procreation
• Disposition

Hormone levels can go high or low due to various conditions such as infection, stress, etc., leading to endocrine system diseases.

The Major Endocrine Glands

Fig 1 shows the position of the major endocrine glands in the body however, it is important to be aware that many other organs and tissues have a secondary endocrine function, including the heart, kidneys, bone and adipose tissues .

The hypothalamus

The hypothalamus is a vital region of the brain, which plays an important role in:

• Thermoregulation
• Coordination of the autonomic nervous system
• Generating a range of hormones that regulate the activity of endocrine glands.

Indeed, the hypothalamus can be thought of as the key crossover point between the nervous system and the endocrine system.

The pituitary gland

The pituitary gland is a pea-sized structure, typically weighing around 500mg it is located at the base of the brain, just behind the nasal cavity, where it is protected by the sphenoid bone of the skull . It has two major regions:

As the pituitary gland regulates hormone release from other endocrine glands, it is often referred to as the master gland. This is something of a misnomer as the release of stimulating hormones from the pituitary gland is, itself, under the control of hormones produced by the hypothalamus this will be explored in Part 2.

Thyroid gland and associated parathyroids

The thyroid is a bilobed organ that resembles a bow tie in shape it typically weighs 25-30g and is located just below the larynx . The thyroid itself has two major populations of endocrine cells:

Pancreas

• Alpha cells, which produce glucagon
• Beta cells, which produce insulin.

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The Most Common Kinds Of Hormones In The Body

Now you know the three major types of hormones, its time to break them down and learn about the most common hormones the endocrine system secretes:

• Adrenocorticotropic Hormone is a hormone found in the adrenal glands. It stimulates the said gland to secrete hormones that respond to stress.
• Human Growth Hormone plays an important role in the growth of muscles, limbs, and internal organs
• Thyroid Stimulating Hormone is responsible for stimulating the thyroid gland to produce thyroid hormones too little production leads to hypothyroidism, while excessive production causes hyperthyroidism.
• Follicle Stimulating Hormone is essential when it comes to fertility because it stimulates sperm production among men and egg production among women
• Prolactin stimulates the corpus luteum to produce two of the most important female hormones: estrogen and progesterone. Lack of these can make you infertile, develop secondary male characteristics, or develop serious hormonal imbalance issues.
• Luteinizing Hormone works alongside PRL to prepare the uterus for pregnancy or to stimulate ovulation
• Oxytocin causes smooth muscles in the uterus to relax during pregnancy. OT also stimulates breast milk production in mothers.

Its the endocrine systems job to maintain healthy levels of the different types of hormones. Failure to do so can cause systemic effects.

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Luteinizing Hormone And Follicle

LH and FSH control the production of the sex hormones. Synthesis and release of LH and FSH are stimulated mainly by gonadotropin-releasing hormone and suppressed by estrogen and testosterone. One factor controlling GnRH release is kisspeptin, a hypothalamic peptide that is triggered by increased leptin levels at puberty. Two gonadal hormones, activin and inhibin, affect only FSH activin is stimulative, and inhibin is inhibitory.

Several other hormones are produced by the anterior pituitary. These include pro-opiomelanocortin , alpha- and beta-melanocyte-stimulating hormone , beta-lipotropin , the enkephalins, and the endorphins. POMC and MSH can cause hyperpigmentation of the skin and are only significant clinically in disorders in which ACTH levels are markedly elevated . The function of β-LPH is unknown. Enkephalins and endorphins are endogenous opioids that bind to and activate opioid receptors throughout the CNS.

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Examples Of Peptides And Proteins In The Body

Proteins and peptides make up our tissues and muscles and are ever-present in the communication between cells. Examples are:

• DNA

Steroid hormones are responsible for:

• Easing bodily inflammations
• Regulating metabolic rates
• Balancing salt and water levels
• The development of sexual traits, such as facial hair for men and chest growth among women

How Can Chemicals Affect The Endocrine System

Scientific research on human epidemiology, laboratory animals, and fish and wildlife suggests that environmental contaminants can disrupt the endocrine system leading to adverse-health consequences. It is important to gain a better understanding of what concentrations of chemicals found in the environment may cause an adverse effect. Various types of scientific studies are necessary to resolve many of the scientific questions and uncertainty surrounding the endocrine disruptor issue. Many such studies are currently underway by government agencies, industry, and academia.

Learn more with EDSP about concerns and examples of endocrine disruption.

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How Does The Hormonal System Work

When a hormone is released from a gland, it travels in the bloodstream through the body. It passes by most cells, but eventually reaches its target.

When it reaches its target, it attaches to a particular type of cell, known as a receptor cell. The hormone then tells the receptor cell to do something. It can make cells grow faster, release another hormone, absorb sugar from the blood, withhold water from the kidneys, or one of many other important functions in the body.