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Have you ever been around sick people and not gotten ill? We know that sickness spreads really easily between people, however a lot of times we are protected from it by our own bodies. While the human body needs to be a comfortable environment for the cells that comprise it, it also needs to fend off many other organisms that would like to take advantage and hijack our bodies for their own benefit. We call these harmful organisms pathogens and the body must protect itself against
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Jetzt kostenlos anmeldenHave you ever been around sick people and not gotten ill? We know that sickness spreads really easily between people, however a lot of times we are protected from it by our own bodies. While the human body needs to be a comfortable environment for the cells that comprise it, it also needs to fend off many other organisms that would like to take advantage and hijack our bodies for their own benefit. We call these harmful organisms pathogens and the body must protect itself against
The defences employed by the body to protect itself against foreign organisms may be either specific or non-specific. Specific defences do what they say on the tin, specifically targeting a particular pathogen.
The adaptive immune system is the quintessential example of a specific defence of the human body against pathogens. This uses specialised white blood cells to generate an immune response tailor-made to destroy a particular pathogen. This response is then memorised, allowing the body to respond more rapidly to future attacks by the same pathogen.
This is the type of immune response used in vaccines, so if you want to know more, check out our article on Vaccination.
Non-specific defences, on the other hand, do not bother to identify exactly what they are defending against. Instead, they focus on either preventing organisms from gaining entry to the body, removing them once they have entered, or blindly attacking anything they identify as foreign. Non-specific defences occur throughout many layers within the body, beginning with the skin, and working inwards. It is these layers that this article will explore.
You might think that your body does little to protect you from infection before you get sick, but that is absolutely not true. There are many organs in our bodies that have a defensive function among other things. We will explore a few of these organs and see how they contribute to keeping us healthy.
The skin is the human body's largest organ, forming a tough outer barrier. This not only keeps all of our component bits and bobs in the right place inside us but also keeps foreign material and organisms out. The skin is formed from tightly bound together epithelial cells, topped off with a layer of dead cells, forming a tough, nigh impenetrable barrier.
However, this does not mean that the skin is impervious to foreign organisms, as they may still be able to take hold in intact skin, or the skin may be damaged, creating an entry point.
The skin also secretes a number of antimicrobial compounds, known as antimicrobial peptides and lipids. These prevent infection by cleaving the membrane of bacterial cells, thereby killing them and forming a structural part of the skin's defensive layer.
A lipid that plays both a structural and chemical role in the defence of the body is sebum. This mix of lipids acts to form a seal around the hair within a hair follicle, preventing the entry of foreign organisms.
Another feature of the skin that acts as a defence against foreign pathogens is the skin's pH. Fatty acids, lactic and trans-urocanic acids are secreted onto the skin, maintaining the pH at 5.4-5.9. This pH makes the skin an inhospitable environment for foreign organisms. The pH disparity between the skin and the blood's pH of 7.4 provides another chemical layer of defence.
Along with its chemical and physical properties, the skin also contains cells designed to target foreign organisms for destruction. These are the cells of the innate immune system, and we will explore these further later on in the article.
Any area in which foreign substances enter the body is also a possible way foreign organisms may enter the body. This includes the respiratory tract.
The inside of the nose, like the rest of the airways, is lined with mucus. This thick, viscous fluid traps debris and foreign organisms, preventing them from progressing deeper into the body. The nose is also lined with hairs, which, combined with the mucus, strengthen the physical barrier against entry into the body. When you then blow your nose, or it runs, the debris is removed from the body.
These are the tubes that conduct air from the outside environment down into the alveoli of the lungs. Like the nose, they contain mucus along with hair-like projections. The mucus is produced by cells known as goblet cells, which secrete mucus into the airways.
The hair-like projections of the trachea and bronchi are significantly smaller than the hairs found within the nose. They are known as cilia, and the cells from which they grow as ciliated cells. These hairs gradually waft mucus up to the top of the airway, where it eventually is either removed from the body or swallowed into the stomach.
As you may know, the stomach is lined with cells known as parietal cells, which secrete concentrated hydrochloric acid. This acid chemically destroys the pathogens that enter the body.
Apart from generic physical and chemical barriers, the human body has a series of specialised cells that are part of the non-specific defence system. These are part of the innate immune system, the portion of the immune system which presents a non-specific defence against foreign bodies and organisms. This is mediated both by chemical processes and cells.
Inflammation is a natural immune defence process characterized by redness, heat, swelling, pain, and sometimes loss of function in the affected area. Inflammation is initiated by the release of chemical signals, such as cytokines, which attract immune cells to the site of injury or infection.
Inflammation happens because the damaged cells activate and release chemical signals that attract cells from the immune system, like neutrophils. On top of that, the chemical signals allow fluid to escape the blood vessels so that those cells can more easily enter the damaged area. That is why swelling happens during inflammation, and why some people can experience pain if the fluid build-up presses on their nerve endings.
Fever is also a generic defence mechanism to help your body fight off infection which consists in elevating body temperature. Bacteria and viruses that infect humans thrive at a certain temperature, mostly the average 37ºC of the human body. When their host gets hotter, they struggle to survive and reproduce as effectively. The extra heat also helps activate the immune system.
Phagocytosis is the process by which specialised cells of the body engulf and destroy pathogens and other small foreign particles. During phagocytosis, the foreign body is wrapped up by the phagocytosing cell's plasma membrane, forming a type of vacuole known as a phagosome. Once the phagosome is floating within the cytoplasm of the cell, the foreign body is digested and destroyed.
This destruction occurs through the fusion of granules containing enzymes, antibiotic proteins and many reactive oxygen species with the phagosome.
The body contains a number of cells which have specifically evolved to counteract the presence of foreign bodies and organisms. Phagocytes are cells whose whole function is to destroy pathogens through phagocytosis. Their surface is covered in receptors, which recognise the presence of a foreign object or organism and trigger phagocytosis. There are three main subtypes of phagocytes; neutrophils, macrophages and dendritic cells.
Neutrophils circulate within the blood, ready to respond to the presence of foreign material. When an infection is recognised within a tissue, neutrophils infiltrate the tissue in large numbers to counteract this infection.
Macrophages, on the other hand, are cells which are permanent residents of the tissues in which they are found. They lie in wait in these tissues, ready to counteract any invaders.
Dendritic cells act as triggers for the adaptive immune response and their purpose is to destroy foreign bodies. They do this by breaking the pathogens apart and presenting specific, recognisable sections of them, known as antigens, to the adaptive immune system.
Specific and non-specific defence mechanisms work in parallel to avoid or eliminate infections in the human body. Even though they are team mates, they are quite different systems that complement each other.
Table 1. Differences between specific and non-specific defence mechanisms of the human body. | ||
---|---|---|
Specific Defense Mechanisms | Non-Specific Defense Mechanism | |
Definition | The immune system's targeted response to specific antigens | The immune system's non-targeted response to any foreign substance |
Recognition | Recognizes and responds to specific antigens | Does not recognize specific antigens, but reacts to any foreign substance |
Components | Includes B and T cells, antibodies, and memory cells | Includes physical barriers, such as skin and mucous membranes, as well as white blood cells like neutrophils and macrophages |
Human development | Takes time to develop in the organism | Present from birth |
Response time | Takes time to develop a targeted response, but has memory for future encounters | Immediate response, but no memory for future encounters |
Effectiveness | Highly effective against specific antigens, but may not be effective against all foreign substances | Less effective than specific defence mechanisms, but can respond to a wider range of foreign substances |
Examples | Antibody production, T cell activation | Inflammation, phagocytosis |
Hopefully, you now understand why you don't get ill every time you come across a sick person. Remember, non-specific defences do what they say on the tin, they are non-specific and don't target any particular pathogen.
Non-specific defences, on the other hand, do not bother to identify exactly what they are defending against. Instead, they focus on either preventing organisms from gaining entry to the body, removing them once they have entered, or blindly attacking anything they identify as foreign.
The stomach acid functions as a chemical barrier against infection.
Things like skin, mucous in airways, hairs in airways, stomach acid and the innate immune response protect the body against pathogens.
They prevent foreign materials and organisms out.
The Skin
Flashcards in Non Specific Defences of the Human Body14
Start learningWhat is a non-specific defence of the human body?
A defence against foreign material and organisms that acts upon any material or organism recognised as foreign.
What is a specific defence of the human body?
A defence against foreign material and organisms that provides a response tailored to a specific organism or foreign material.
What organ is the largest in the human body and also the first line of defence in the non-specific defences of the human body?
The Skin
What are the chemical defences of human skin?
A relatively low pH and the production of antimicrobial proteins and lipids.
How does the nose prevent the entry of foreign organisms and material to the body?
Mucus and hair block and capture foreign materials and organisms, ready for removal when the nose is blown.
What physically captures foreign materials and organisms in the airway?
Mucus
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