Host defense mechanism

 HOST DEFENSE MECHANISM

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Introductionn

The first wonder of this world is the human body structure which have a lot of complex things that are still not discover by the science. One of the unique thing that a human body have is "Defense Mechanism" against any foreign agent by the help of three different mechanisms

• Natural barriers
• Nonspecific immune responses
• Specific immune responses

1) Natural Barriers

These are the epithelial surfaces which are present physically in our body and act as a defense barrier against the infection.

• Skin
• Act as a mechanical barrier to microbes.
• Provide bactericidal secretions.
• Some parasites like Human Papillomavirus can invade normal skin.

• Mucous membranes
• They are bathed in secretions that have antimicrobial properties.
• Secretion's like tears, prostatic fluid, cervical mucus etc.
• It act as a defense barrier by splitting the muramic acid linkage in gram positive bacterial cell wall.

• Respiratory tract
• The respiratory tract has upper airway filters which transports the microbes away from lungs.
• Coughing also helps to remove organisms.
• This mechanism of defense get fails because of the continuous consumption of cigarette, smoke etc.

• Gastrointestinal tract
• It act as a barrier because of having acidic pH of stomach and antibacterial activity of pancreatic enzymes, bile and intestinal secretions.
• Peristalsis movement of intestines also helps to remove microbes.
• This mechanism of defense get fails when expose to the infections like Salmonella, Campylobacter and C. difficile.

• Genitourinary tract
• It include the length of urethra (20cm), hypertonic state of kidney, urea secretion in urine and acidic pH of urine.
• It also facilitate the harmless removal of bacteria by the help of Tamm-Horsfall mucoprotein which is produce and excrete by kidneys.

2) Nonspecific Immune Responses

It can be defined as the defense system with which you were born and it protects you from all the antigens.

• Antibacterial substances 
• Beta lysin
• Lukins
• Plakins
• Lactic acid
• Interferons

• Cellular factors
• It act as barrier by the accumulation of Phagocytic cells at the site of infection.
• Phagocytes engulf the organisms and destroy them
• Fibrin deposition entangles the organisms.

• Inflammation
• Occurs due to the tissue injury and initiated by the entry of pathogen.
• It leads to the increase in vasodilation, vascular permeability and cellular infiltration which leads to the plasma pour out and dilutes the toxic products present at the site of infection.

•  Fever
• In this barrier the body temperature increases and destroy the infecting organism.
• It stimulates the production of interferons.
• It helps to recover from viral infection.

3) Specific Immune Responses

• It can be defined as the response of our body in which it produces specific types of antibodies to kill the specific type of antigens.
• In specific defense the immune system forms a chemical memory of the invading microbe.
• If the microbe enters again, the body reacts quickly to kill the microbe.
• The major players in this defense system are
• Macrophages (WBCs that kills microbes)
• T cells (identify and destroy the microbes)
• B cells (activates the T-cell via antigen)
• Antibodies (a protein made by human body that destroy the invasive microbes)

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