Explore the body's defenses and learning materials.
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Human Body Defense System
The human body's defense system, or immune system, is a complex network of cells, tissues, and organs that protects the body from infection by germs such as bacteria, viruses, fungi, and parasites, as well as from abnormal cells such as cancer cells.
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External Body Defense System
The external immune system is the body's first line of defense, tasked with preventing the entry of pathogens such as microorganisms or viruses that can cause disease.
The external immune system functions as both a physical and a chemical defense. It is also called the innate immune system because humans are born with it.
Human physical defenses consist of the integumentary system (body covering) consisting of skin and mucous membranes. This defense plays a vital role in preventing bacteria, viruses, and other microorganisms from entering the body.
1.) Integumen The skin serves as the body's first line of defense because it is composed of tightly packed epithelial cells. Healthy, normal skin is impermeable to bacteria and viruses.If we make an analogy, the skin is like a sturdy house wall, made up of tightly packed bricks, and is difficult for animals or humans to penetrate.
2.) Mucous Membrane The mucous membrane is a layer that lines the digestive tract, respiratory tract, reproductive tract, and excretory tract. This membrane can produce mucus, a thick fluid that plays a role in coagulating microorganisms and foreign objects that enter the body. Microorganisms and foreign objects that are successfully coagulated will be expelled through the cough or sneeze reflex.
Chemical defenses utilize chemical compounds. These chemical defenses include lysozyme, sebum, and stomach acid. These defenses act to inhibit the growth of microorganisms and even kill them. 1.) Lysozyme Lysozyme is an antimicrobial protein found in tears, saliva, sweat, and breast milk. This compound helps reduce the risk of bacterial infection by destroying the peptidoglycan layer of bacterial cell walls. 2.) Sebum Sebum is an oil produced by oil glands in the skin. This natural oil plays a crucial role in preventing bacterial growth. 3.) Gastric Acid (HCL) Gastric acid, also known as HCl, is an acidic compound that is responsible for killing pathogens that enter the body through food.
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Internal Body defense system
The body's internal defense system is activated to prevent pathogens that have already entered the body's tissues from spreading and causing further damage. This internal defense is carried out by several types of leukocytes, which recognize pathogens by their characteristic particles called antigens.
An antigen is a compound in the form of proteins, glycoproteins, lipids, and polysaccharides. The internal defense system can recognize foreign components or various other substances produced by a pathogen. Leukocytes that enter the body determine whether the foreign object is an antigen, its level of danger to the body, and what to do with the foreign component.
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Nonspecific Internal Body Defense
The nonspecific defense system is known for its rapid response and works against all pathogens without exception. The following are the types of nonspecific immune responses in the human body.
1.) Phagocytosis Phagocytosis is the process by which several types of leukocytes engulf pathogens that enter the body's tissues. Phagocytic leukocytes include neutrophils (approximately 60-70%), monocytes (5%), and eosinophils (1.5%). a.) Macrophages Macrophages are a type of leukocyte derived from monocytes and successfully enter tissue. Monocytes generally remain in the bloodstream only briefly before entering the tissue to develop into macrophages.
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Nonspecific Internal Body Defense
2.) Microphages Microphages are a type of granular leukocyte consisting of neutrophils, basophils, and eosinophils. Microphages' defense mechanism begins with the reception of chemical signals from cells destroyed by microbes. Eosinophil microphages have a specific role, namely phagocytizing large parasites, such as protozoa. Furthermore, eosinophils can also produce enzymes that can destroy parasitic cells.
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Nonspecific Internal Body Defense
2.) Fever Fever is not a disease, but rather one of the body's mechanisms to signal that the body's defense system is working against pathogens in the body. After receiving this signal, several types of leukocytes will immediately produce pyrogen molecules (substances that stimulate the onset of fever) which function as the body's thermostat (body temperature regulator). 3.) Inflammation Tissue damage due to wounds or trauma from accidents, infections, surgical effects, or tissue transplants can provide a pathway for microbes to enter the body. The inflammatory process occurs when arterioles (before capillaries) and venules (after capillaries) dilate in the injured area.
Histamine, a chemical produced by the body in response to tissue damage, is known to be involved in the mechanism of inflammation. Basophil leukocytes and mast cells in the connective tissue surrounding the wound release histamine as a chemical signal that can stimulate the enlargement and increased permeability of the surrounding capillaries. Leukocytes and damaged tissue cells also release prostaglandins, increasing blood flow to the injured area.
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Nonspecific Internal Body Defense
4.) Interferon Secretion Interferon is a protein compound secreted by several body cells infected with a virus. This compound can induce cells surrounding the infected cell to become resistant to the virus.Interferon is the first line of defense when a virus enters the body. Interferon's structure consists of a glycoprotein produced by macrophages.
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Nonspecific Internal Body Defence
5.) Antimicrobial Protein - Various proteins play a role in nonspecific defense by killing microorganisms and preventing their reproduction.
- Important proteins are interferons and complement/enhancing proteins.
- Interferons were first identified in 1957 in virus-infected cells. These cells release a substance that helps other cells become immune to the virus.
6.) Complement - It is a group of proteins consisting of at least 20 proteins.
- Complement proteins circulate in the blood in an inactive form.
- Complement proteins work by forming 'holes' in unwanted cells and killing them.
- Specific defense/immune response must be complemented by the presence of antigens, defense cells, and specific antibodies produced against the invading antigens.
- An antigen is a protein or polysaccharide molecule located on the cell membrane of microbes, foreign cells, or cancer cells that the body recognizes as foreign (non-self).
- Antibodies can remember antigens they have previously encountered and will react quickly when that antigen is encountered (Ig).
- In addition to the body's natural immunity, immunity can also be achieved through vaccination/immunization.
- In vaccination, immunity occurs by introducing a weakened pathogen, which will not cause disease but can initiate the body's long-term ability to respond to the actual pathogen.
- Vaccination is effective against diseases caused by viruses (polio, smallpox, measles).
- When an antigen enters the body naturally (flu) or artificially (vaccination), the body creates its own immunity → active immunity.
- In active immunity, the body is stimulated to produce its own antibodies.
Immunity can also occur when antibodies are introduced from outside the body → passive immunity. Examples of passive immunity: - antibodies transferred from the mother to the fetus through the placenta.
- antibody injections given to travelers against various pathogens.
Passive immunity is temporary.
The main function of antibodies is as protective proteins that recognize and fight harmful foreign substances such as bacteria, viruses, and toxins by attaching to antigens (markers of foreign substances) and neutralizing them.
Antibody Mechanism of Action: - Neutralization: Antibodies bind to antigens on pathogens or toxins, preventing them from infecting host cells or disrupting their normal function.
- Complement System Activation: Binding of antibodies to antigens can activate the complement system, a network of proteins that can destroy bacterial cells by creating holes in the cell wall (lysis).
- Opsonization: Antibodies can mark pathogens, making them more easily recognized and ingested by phagocytic cells (such as macrophages), thus destroying them.
- Antibody-Dependent Cellular Cytotoxicity (ADCC): Antibodies can trigger certain immune cells to attack and destroy infected or cancerous cells.
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Human Body Defense System learning video
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