What do You Mean by Histamine and Its Functions?
There are many biochemical compounds synthesized and stored in different cells of our physiology. One such naturally produced compound is histamine. This is a biochemical substance produced by the local cells in different tissues regarding an immune response. The production of this compound shows the presence and signifies the outcome of inflammation in an affected part of our body. In this section, we will learn about the definition of histamine meaning and its action. We will also discuss the function of histamine elaborately.
What is Histamine?
Every living organism has an immunological system that protects it from the different foreign particles or parasitic invasions. One such function of the immunological system is to produce histamine. Let us learn what this biochemical compound is.
The word ‘histamine’ means a biochemical compound secreted by the mast cells and basophils as a local response to an invasion of parasites or to protect cells from any foreign body. If we concentrate on the spit meaning of this word, we will find that it is an ‘amine’ generated in the cells or tissues or ‘histo’.
As the histamine meaning suggests, it is an amine compound that is formed due to the decarboxylation of histidine, an amino acid. In the animal kingdom, you will find myriads of compounds that match the prototypical formula of histamine. In fact, its presence has been noticed in insect venoms and plants. The name ‘amine’ comes from the derivation of ammonia (NH3).
How Histamine was Discovered?
In the year 1907, the histamine structure was recognized and synthetically manufactured in the laboratories. Its functions in human physiology were then established. This compound was found in the tissues when there is an immune response occurring due to the presence of a foreign body or microbe. This is the natural way of our body reacting against something unnatural entered in the tissues.
The function of histamine is to trigger the immune response actions and to make our body prepared for such incidents. Due to its formation, many cytological actions are initiated that help our body to cope with an immunological action and fight to eliminate the foreign body present in our system. This is why you can find histamine in different forms in almost all animals. Now that we have understood the histamine meaning, let us find out what its functions are.
Functions of Histamine
As we all know that histamine produced by an immune response in the local cells due to the presence of an unwanted particle or microbial invasion, let us find out what this biochemical compound does after secretion.
Vasodilatation
The primary histamine function is to dilate the blood capillaries and cause an escalation of blood flow. The blood pressure eventually reduces due to the enhanced lumen size of the blood vessels and vascular hyper-permeability. The endothelial cells of the capillaries bind with histamine to become dilated and become more permeable to the blood cells. In fact, the smooth muscles present in the blood vessels start to relax and cause a fall in blood pressure in the localized area.
Nasal Mucosal Effect
Due to the secretion of histamine, the nasal mucosal blood vessels become more permeable. It causes the excess passage of fluid escaping in the nasal passage. This happens when an allergic reaction triggers due to the occurrence of foreign bodies in the nasal mucosa. The role of histamine is to provide protection to the eyes and nose by secreting fluid produced due to the localized neural stimulation in this region.
Regulation of Sleep-Wake Cycle
Histamine is also responsible for the regulation of the sleep-wake cycle of a human being. It acts as a neurotransmitter connecting with the hypothalamus of a mammalian brain. When the neurological system of a human is asked what is the function of histamine, you will find that it is a part of the histamine system of a brain that controls the sleep and wake cycles of a human being. During wakefulness, this neurotransmitter is fired rapidly. When you are lethargic, the transmission reduces.
Gastric Acid Production and Release
The production and presence of histamine also cause the formation of gastric acid in the stomach. This biochemical stimulator escalates the absorption rate of water and carbon dioxide in the blood circulation system for the production of carbonic acid. This acid is then released into the stomach causing hyperacidity in the digestive system. This histamine action causes the escalation of acidity. Ranitidine is one of the prime antagonists that doctors prescribe to stop this uptake cycle.
Protection
The prime histamine function is to protect our body from foreign bodies, venom, or any kind of microbial invasion. It also protects us from convulsion, denervation super sensitivity, stress, and ischemic lesions. In fact, it also controls the learning and forgetting of memories.
Conclusion
Study the histamine structure and find out the meaning of the name first. Proceed to learn the basic functions of histamine in our body. It will become clearer to understand how this biochemical compound functions in our body.
FAQs on Histamine
1. What is histamine and from which amino acid is it derived?
Histamine is a naturally produced organic nitrogenous compound involved in local immune responses, regulating physiological functions in the gut, and acting as a neurotransmitter. It is synthesised in the body through the decarboxylation (removal of a carboxyl group) of the amino acid histidine.
2. What are the primary functions of histamine in the human body?
Histamine has several key functions throughout the body. Its primary roles include:
- Inflammatory Response: It is released by mast cells and basophils during an allergic reaction or injury, causing inflammation.
- Vasodilation: It dilates blood vessels, increasing blood flow to an area, which aids the immune response but can also lower blood pressure.
- Gastric Acid Secretion: It stimulates the parietal cells in the stomach to secrete gastric acid, which is essential for digestion.
- Neurotransmission: In the brain, it acts as a neurotransmitter that helps regulate the sleep-wake cycle and promotes wakefulness.
3. How does histamine cause vasodilation and inflammation?
When released in response to injury or allergens, histamine binds to receptors on the surface of endothelial cells lining the blood capillaries. This binding causes the smooth muscles in the vessel walls to relax, leading to vasodilation (widening of blood vessels). It also increases the permeability of these capillaries, allowing fluid and immune cells to move from the bloodstream into the surrounding tissues. This influx results in the classic signs of inflammation: swelling (edema), redness, and heat.
4. What is the role of histamine in causing allergic reactions like hay fever?
In an allergic reaction, the immune system mistakes a harmless substance like pollen for a threat. This triggers mast cells in the nasal passages to release large amounts of histamine. The histamine then causes local blood vessels to dilate and become leaky, leading to symptoms like a runny nose, watery eyes, and nasal congestion. It also stimulates nerve endings, causing itching and sneezing, which are characteristic of hay fever.
5. Is histamine classified as a hormone or a neurotransmitter?
Histamine is versatile and functions as both, depending on its location and target. It is primarily known as a local chemical messenger or 'autocoid' because it acts on nearby cells rather than being transported through the bloodstream from a gland like a traditional hormone. However, in the central nervous system, particularly the hypothalamus, it functions as a true neurotransmitter, carrying signals between neurons to regulate processes like alertness and the sleep-wake cycle.
6. Why do antihistamine medications help reduce allergy symptoms?
Antihistamine medications work by acting as receptor antagonists. They do not stop the production of histamine, but instead, they block it from binding to its specific receptors (primarily H1 receptors) on target cells. By occupying these receptors, antihistamines prevent histamine from initiating the inflammatory cascade that causes allergy symptoms like swelling, itching, and fluid leakage. This effectively suppresses the body's reaction to the allergen.
7. Besides allergies, what is histamine's function in the central nervous system?
Within the central nervous system (CNS), histamine plays a crucial role as a neurotransmitter that regulates arousal and wakefulness. Histaminergic neurons originating in the hypothalamus fire rapidly during waking hours and slow down during periods of relaxation or sleep. This is why some older antihistamines, which can cross the blood-brain barrier, cause drowsiness as a side effect—they block this wakefulness-promoting action in the brain.
8. How does histamine contribute to the production of gastric acid in the stomach?
In the stomach lining, histamine is released by specialised cells called enterochromaffin-like (ECL) cells. It then binds to H2 receptors on nearby parietal cells. This binding stimulates the parietal cells, activating a process that leads to the secretion of hydrochloric acid (HCl) into the stomach. This mechanism is a vital part of the digestive process, helping to break down food and kill ingested pathogens.
