Covers innate immunity as the body's non-specific, genetically determined first line of defence, then its physical barriers in skin and mucous membranes, with organ-by-organ protective mechanisms. Also explains how normal microbiota resist pathogens, and how inflammation works, including its cardinal signs and the role of fever.
Topic 27 of 113 in the MU Sofia syllabus for Microbiology (Medicine, Year 3). The free AceMed note covers it in 5 sections, about 613 words (5 min of reading), with 15 flashcards.
In this note
Natural Resistance. Protective Role of Skin and Mucosas. Protective Role of Human Body Microbiota. Protective Role of Inflammation.
Natural Resistance (Innate Immunity)
Protective Role of Skin and Mucosas (Physical Barriers)
Protective Role of Human Body Microbiota (Normal Flora)
Protective Role of Inflammation
Natural Resistance (Innate Immunity)
Natural Resistance (or Innate Immunity) is the immunity that an individual has due to their genetic makeup.
It is the immunity that is quick to respond and is present/active from birth.
Innate immunity is the non-specific, immediate response to pathogens.
It lacks immunologic memory, is short-lasting, and does not improve upon subsequent exposures.
It comprises physical, chemical, molecular, and cellular defences.
Major components include skin and mucous membranes, phagocytic leukocytes (neutrophils and macrophages), specialised lymphocytes (NK cells), and several plasma proteins including proteins of the complement system.
It can distinguish between self and non-self.
The response is rapid and prevents the establishment of infection.
Innate mechanisms are the primary immune defenses.
Protective Role of Skin and Mucosas (Physical Barriers)
The skin and mucous membranes act as barriers, preventing bacteria from entering the body.
They are the main factors in the first line of defence against infection.
These anatomical structures attempt to prevent microorganisms from colonizing the skin and mucosa.
Skin:
Acts as a mechanical barrier, with keratin and an acidic environment (pH 3-5), deterring microbial invasion.
Secretions like sweat, flushing, skin shedding, and organic acids provide additional protection.
Sebaceous glands produce fatty acids that are bactericidal.
Secretes antimicrobial proteins like lysozyme and psoriasin.
Mucous Membranes:
Contain normal microbiota, which competes with pathogens.
Mucus traps microorganisms, and cilia help expel them.
Specific examples:
Gastrointestinal tract: Peristalsis, gastric acid (low pH), bile acids, digestive enzymes, and gut flora provide protection. Peristalsis is a physiological defence mechanism.
Respiratory airways and lungs: Mucociliary elevator, surfactant, and defensins. The mucociliary escalator is a physiological defence mechanism.
Nasopharynx: Mucus, saliva, lysozyme.
Eyes: Tears. Tears are also a physiological defence mechanism.
Oral cavity: Lysozyme.
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