Chapter 12Summarize what the three lines of defense are.- The host defenses are a multilevel network of innate, nonspecific protections and specific immunities referred to as the first, second, and third lines of defense.- The interaction and cooperation of these three levels of defense normally provide complete protection against infection.- The first line of defense includes any barrier that blocks invasion at the portal of entry.o This nonspecific line of defense limits access to the internal tissues of the body.o However, it is not considered a true immune response because it does not involve recognition of a specific foreign substance, but it very general in action.- The second line of defense is a more internalized system of protective cells and fluids that includes inflammation and phagocytosis.o It acts rapidly at both the local and systematic levels once the first line of defense has been circumvented.- The highly specific third line of defense is acquired on an individual basis as each foreign substance is encountered by white blood cells called lymphocytes.o The reaction with each different microbe produces unique protective substances and cells that can come into play if that microbe is encountered again.o The third line of defense provides long-term immunity.- Human systems are armed with various levels of defense that do not operate in a completely separate fashion; most defenses overlap and are even redundant in some of their effects.Identify three components of the first line of defense.- The inborn, nonspecific defensed can be divided into physical, chemical, and genetic barriers that impede the entry of not only microbes but any foreign agent, whether living or not.- Physical barriers are the most common type of barrier in the first line of defenses.o The skin and mucous membranes of the respiratory and digestive tracts have several built-in defenses.  The outermost layer (stratum corneum) of the skin is composed of epithelial cells that have become compacted, cemented together, and impregnated with an insoluble protein, keratin.- The result is a thick, tough layer that is highly impervious and waterproof.- Few pathogens can penetrate this unbroken barrier. In addition, outer layers of skin are constantly sloughing off, taking associated microbes with them. Other cutaneous barriers include hair follicles and skin glands.- The hair shaft is periodically shed, and the cells are desquamated.- The flushing effect of sweat glands also helps remove microbes.o The mucous membranes of the digestive, urinary, and respiratory tracts and of the eye are moist and permeable. They do provide barrier protection but without a keratinized layer. The mucous coat on the free surface of some membranes impedes the entry and attachment of bacteria. Blinking and teat production (lacrimation) flush the eye’s surface with and rid it of irritants. The constant flow of saliva helps carry microbes into the harsh conditions of the stomach. Vomiting and defecation also evacuate noxious substances or microorganisms from the body.o The respiratory tract is constantly guarded from infection by elaborate and highly effective adaptions. Nasal hair traps larger particles. The copious flow of mucus and fluids that occurs in allergy and colds exerts a flushing action. In the respiratory tree (primarily the trachea and bronchi), a ciliated epithelium (called the ciliary escalator) conveys foreign particles entrapped in mucus toward the pharynx to be removed. Irritation of the nasal passage reflexively initiates a sneeze, which expels a large volume of air at high velocity. Similarly, the acute sensitivity of the bronchi, trachea, and larynx to foreign matter triggers coughing, which ejects irritants.o The genitourinary tract derives partial protection via the continuous trickle of urine through the ureters and from periodic bladder emptying that flushes the urethra. Vaginal secretions provide cleansing of the lower reproductive tract in females.o The composition of resident microbiota and its protective effect are also a physical property of first line defenses. Even though the resident biota does not constitute an anatomical barrier, its presence can block the access of pathogens to epithelial surfaces and can createand unfavorable environment for pathogens by competing for limited nutrients or by altering the local pH. The presence of a robust commensal biota ‘trains’ host defenses in such a way that commensals are kept in check and pathogens eliminated.- The skin and mucous membranes offer a variety of chemical defenses.o Sebaceous secretions exert an antimicrobial effect, and specialized glands of the eyelids lubricate the conjunctiva with an antimicrobial secretion.o An additional defense in tears and saliva is lysozyme, an enzyme that hydrolyzes the peptidoglycan defense in the cell wall of bacteria.o The high lactic acid and electrolyte concentrations of sweat and the skin’s acidic pH and fatty acid content are also inhibitory to many microbes.o Likewise, the hydrochloric acid in the stomach renders protection against many pathogens that are swallowed, and the intestine’s digestive juices and bile are potentially destructive to microbes.o Even semen contains and antimicrobial chemical that inhibits bacteria, and the vagina has a protective acidic pH maintained by normal biota.- Genetic differences in susceptibility can exist within members of one species.o Often these differences arise from mutations in the genes that code for components describes in this chapter and the next, such as complement proteins, cytokines, and T-cell receptors.Define marker, and discuss its importance in the second and third lines of defense.- Immunology encompasses the study of all features of the body’s second and third lines of defense.o Be aware that immunology is central to the study of fields as diverse as cancer and allergy.o In the body, the mandate of the immune system can be easily stated. A healthy functioning immune system is responsible for the following: Surveillance of the body. Recognition of foreign material. Destruction of entities deemed to be foreign.o Because infectious agents could potentially enter through any number of portals, the cells of the immune system constantly move about the body, searching for potential pathogens.o This process is carried out primarily by white blood cells, which have been trained to recognize