What are The Hormones?

What are The Hormones?

Hormones are a class of signaling molecules released by a specific group of cells, called endocrine cells.

In human physiology, they commonly regulate metabolic processes and behavioral changes.  There are three major classes of hormones: peptide, steroid, and amino acid derivatives. They can be the products of single cells (such as parathyroid hormone) or involved in excretion.

In addition to their main cellular function as signal transduction agents, some hormones have important anti-inflammatory functions that may contribute to homeostasis and disease resistance. The term hormone is often synonymous with gonadotropin, but not all hormones are gonadotropins. For example, growth hormone is a cytokine that stimulates growth and cell reproduction in somatic cells.

Hormones are produced in endocrine glands, though they are also synthesized by many other tissues within the body. Endocrine glands are specialized for the synthesis of specific hormones with different effects depending on their chemical nature and cross-reactivity.

Some hormones may have autocrine or paracrine functions when produced at a site different from where exert their primary function. For example, TSH is released by the anterior pituitary to stimulate the thyroid gland; gut hormone peptides (glucagon, OXM) act on intestinal epithelial cells; growth hormone can act on any cell that expresses its receptor, and some adult liver cells produce erythropoietin.

It is important to note that cells do not create hormones; they produce hormones, which are transported in the blood (endocrine system) or other body fluids (paracrine/autocrine).

Hormones act by binding to specific receptor proteins, which can be located on the plasma membrane of cells. This may be at a surface membrane site called a zymogen granule, or inside the cell on the cytoplasmic surface of the cell membrane. Hormone-receptor interactions cause changes within the target cell triggering various intracellular action pathways that ultimately result in altered gene expression.

What is homeostasis?

Homeostasis is an organism’s regulatory process that maintains stability while adjusting its internal processes to maintain optimal conditions. Organisms are inherently unstable, so processes are crucial for them to maintain their stability.

Some of the major controls on organismal homeostasis include homeostatic thirst, hunger, osmotic pressure, blood sugar levels, oxygen levels, pH, body temperature, and blood pressure. A dynamic equilibrium between physiological processes is essential to maintaining homeostasis.

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Homeostatic mechanisms control vital functions such as breathing rate, body temperature, and acidity of the blood (pH). They also control unnamed complex functions such as bone strength and rates of aging; these mechanisms include enzyme systems such as hormone receptors, nutrients such as vitamins and minerals (particularly calcium), and other molecules like water.

While older viewpoints recognized a hierarchy of needs (such as Maslow’s need hierarchy), more current systems focus on the complex interactions of numerous variables.

Homeostasis is the process that regulates the internal environment in order to maintain a stable, constant condition of its physiological parameters, while an organism’s surroundings are constantly changing.

Through homeostasis, organisms are able to maintain some degree of control over their external conditions so that they can survive within a range of external conditions or fluctuating environmental factors.

The concept was originally described by French physiologist Claude Bernard in 1865 and has been extensively characterized since then by biologists and chemists.

4 types of hormones:

1)amino acid hormones

2)peptide hormones (made from amino acids and dextrin.)

3)steroid hormone (made from cholesterol).

4)other hormones (like insulin, calcitonin, parathyroid hormone).  They’re simple molecules. Amino acid is the simplest of all.  It only contains a few elements: Hydrogen, Nitrogen, Carbon, and Oxygen.  The most interesting of these is Nitrogen which makes amines.

Peptides have more complexity:

they have a head made of amino acids and a tail at the other end which attaches to some receptor site in your body so the effects can be carried out on them.  The more complex peptides have more chains of amino acids.  To make a peptide hormone, a polypeptide hormone precursor will be cleaved to produce the active hormone.

Steroids are basically fat-soluble molecules, except for oxygen and hydrogen atoms which contribute to the more complex structure of these hormones.  These elements add up another 4 chemical groups: OH/O, NH, CH3, and COOH on top of the basic carbon-oxygen-hydrogen skeleton making steroids one of the more complex hormones.  In steroids, all hydrogens attached to carbons are usually lost during the biosynthesis of the active form of these hormones from cholesterol.

Insulin and parathyroid hormone (PTH) aren’t really considered as hormones by some people.

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Insulin is a peptide hormone, but the active form of this hormone isn’t made from a prohormone.  It’s just produced in beta cells and secreted into the bloodstream.

what are hormones made of Amino acids are the simplest of all?  They only contain a few elements:

Hydrogen, Nitrogen, Carbon, and Oxygen. Peptides have more complexity – they have a head made of amino acids and a tail at the other end which attaches to some receptor site in your body so the effects can be carried out on them. Steroids are basically fat-soluble molecules with the addition of 4 chemical groups – OH/O, NH, CH3, and COOH on top of the basic carbon-oxygen-hydrogen skeleton making steroids one of the more complex hormones.

Insulin isn’t really considered a hormone by some people because it’s not like other hormones like a steroid that is cleaved from cholesterol.. it is just produced in beta cells and secreted into the bloodstream.

where are hormones produced:

hormones are made all over the body.  The largest producer of hormones in our bodies is gonads (testes and ovary). A single gonad makes about 500-1000 IU of steroid hormones a day! A single adrenal gland can make about 0.5-1 milligram of steroid hormones a day.

The largest producer of peptide hormones is the thyroid gland which can make about 25-40 mg of T3 and T4 in a day. The adrenal cortex makes small amounts of steroids and peptides, while the medulla makes epinephrine and norepinephrine.  All these structures are interrelated so when one structure releases hormones, it will cause changes in other organs that produce or respond to its respective hormones.

Hormones controlling other hormones:

There’s also a group of hormones called tropic hormones (like ACTH and GH). They aren’t really considered a classical hormone because they don’t have receptors, but instead, interact with other cells by binding to the cell membrane instead. But let’s start this off by saying how do hormones work.

hormones are the chemicals released by endocrine glands (like gonads, thyroid, adrenal cortex) or cells in organs (pancreas).  When they interact with their target cell, it causes the effect on that cell which causes changes in overall organ function and/or metabolism of the whole body.  One example is thyroid hormone T3 which increases the metabolic rate of our bodies so we burn more energy.

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When one gland releases its respective hormones, it will affect other organs that produce or respond to its respective hormones.  TH is produced by the hypothalamus and pituitary gland. When you’re cold, your hypothalamus sends a signal to the pituitary gland to release TH causing an increase in the metabolic rate of your body to make you feel warm.

hormones are changing all the time for example circadian rhythms (24 hours cycle) of hormone secretion like cortisol is controlled by the hypothalamus, while thyroid hormones like T3 and T4 follow 24 hours secretion pattern that even controls other endocrine glands which have own rhythm of hormone release.

The brain releases some neuropeptides in response to stress via the hypothalamic-pituitary-adrenal axis. These neuropeptides also affect the activity of both the anterior pituitary gland and adrenal cortex so they can be considered tropic hormones too.

are hormones proteins:

No.  Hormones are kind of “complex” chemical structures that can’t be made from amino acids.

The hormone structure is very complex and different from protein because it has carbon-oxygen-hydrogen atoms along with nitrogen, oxygen, or sulfur and other elements like phosphate and sulfate. So you can say humoral (chemical) signals like hormones don’t really qualify as proteins since proteins are made up of amino acids which contain hydrogen, nitrogen, oxygen, and carbon only.

What about insulin?

Insulin isn’t considered as a hormone either because it’s not like other hormones as I’ve said before that they’re cleaved from cholesterol to become active form.. but insulin is just produced by the beta cells in the pancreas and secreted into the bloodstream.

Insulin is more like an enzyme or catalyst that increases the transport of sugar (in the form of glucose) from your digestive tract into cells to produce energy for body functions. It’s considered a “protein” because it has amino acid chains, but its function is very different than proteins derived from amino acids.. so if insulin doesn’t qualify as protein then why should peptide hormones like ACTH be classified as protein since they also lack essential elements found in other hormones.


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