Human Defense Mechanisms

Chapter 6 This chapter outlines the concepts of innate immunity, inflammation, and wound healing. Innate immunity refers to the body's initial defense mechanisms against invasion and injury. Inflammation is the body's response to injury and infection, aimed at protecting and healing the body. Wound healing involves several phases, including hemostasis, inflammation, tissue formation, and remodeling. Bullet points Human Defense Mechanisms  The human body has defense mechanisms to protect against injury and infection  Innate immunity refers to the initial response to invasion and injury  Adaptive immunity develops over time and provides long-term protection against specific invaders Innate Immunity  Innate barriers form the first line of defense at the body's surfaces  Inflammation is the second line of defense activated to protect the body from further injury and fight infection Inflammation and Wound Healing  Inflammation is a part of the second line of defense in innate immunity  Wound healing occurs in four phases: Hemostasis, Inflammation, Proliferation and New Tissue Formation, Remodeling and Maturation  Dysfunctional wound healing can occur Pediatric and Geriatric Considerations  The newborn child and the elderly have age-related factors affecting their innate immunity Comparison between Innate and Adaptive Immunity  Innate immunity is the first line of defense against infection, while adaptive immunity is the third line of defense  Innate immunity provides immediate response, while adaptive immunity has a delay between exposure and maximal response  Innate immunity is broadly specific, while adaptive immunity is also broadly specific but with a very specific response toward the target  The cells involved in innate immunity include epithelial cells, mast cells, granulocytes, lymphocytes, monocytes/macrophages, natural killer cells, platelets, and endothelial cells Innate Immunity - First Line of Defense  Physical and biochemical barriers form the first line of defense at the body's surfaces  Physical barriers include epithelial cells of the skin and linings of the gastrointestinal, genitourinary, and respiratory tracts  Barriers may remove pathogens through mechanical means Protective Mechanisms of Innate Barriers  Beneficial microorganisms called the "normal microbiome" can protect us from pathogenic microorganisms  Other protective mechanisms include production of mucus, hair-like cilia, low temperature, and low pH Cell-Derived Chemicals  Epithelial cells secrete substances like mucus, perspiration, saliva, tears, and earwax to protect against infection  These secretions contain substances like lysozyme, fatty acids, lactic acid, and antimicrobial peptides that kill or inhibit bacteria, fungi, and viruses  Examples of antimicrobial peptides include defensins and collectins The Normal Microbiome  The body's surfaces can house a group of beneficial microorganisms called the "normal microbiome"  These microorganisms help protect against pathogenic microorganisms The Microbiome  The human body is colonized by a variety of microorganisms known as the normal microbiome  Microbiome is found on body surfaces such as the skin, mucous membranes, GI tracts, respiratory tract, urethra, and vagina  Microbiome consists of bacteria and fungi specific to each location and individual  Microorganisms in the microbiome have a commensal or mutualistic relationship with the body Benefits of the Normal Microbiome  Facilitates digestion of fatty acids and large polysaccharides  Synthesizes essential metabolites like vitamins K and B  Produces antibacterial substances toxic to pathogenic microorganisms  Competes with pathogens for nutrients and blocks their attachment to the epithelium  Induces the growth of gut-associated lymphoid tissue, aiding in adaptive immunity  Contributes to brain-gut axis communication, affecting cognitive function, behavior, and stress responses Alterations in the Microbiome  Prolonged use of broad-spectrum antibiotics can disrupt the normal microbiome and lead to overgrowth of pathogenic microorganisms  Physical integrity of the skin and mucosal epithelium protect the microbiome from immune responses  Some members of the normal microbiome can become opportunistic pathogens in immunocompromised individuals Inflammation as a Protective Response  Inflammation is a protective response that aids in recovery from injury and disease  Inflammatory mediators are released in response to cellular or tissue damage  Leukocytes, plasma proteins, and biochemical mediators migrate to damaged tissue to destroy invaders and promote healing  Uncontrolled or chronic inflammation is involved in many diseases Mast cell degranulation and arteriolar vasodilation  Erythema (redness) and warmth are observed Increase in capillary permeability  Edema (tissue swelling) occurs Tissue and cell injury  Activation of clotting (neutrophils)  Cellular infiltration  Pathogenic phagocytosis invasion  Thrombosis (clots wall off injury)  Pus formation Release of products that stimulate cellular nerve endings  Pain is experienced Acute Inflammatory Response  Inflammation is initiated by cellular injury and can be complicated by infection  It involves mast cell degranulation, activation of plasma protein systems, and activation of macrophages  These systems are interdependent, resulting in the development of microscopic and clinical hallmarks of inflammation Vascular Response  Triggers for inflammation include infection and tissue damage  Classic signs of inflammation include redness, heat, swelling, pain, and loss of function