Describe the important anatomical features of the skin Chapter 16 The skin together with the hair nails and sweat and oil glands forms the integument The outermost portion of the skin is the epidermis which is further subdivided into four or five distinct layers o On top is a thick layer of epithelial cells called the stratum corneum about 25 cells thick The cells in this layer are dead and have migrated from the deeper layers during the normal course of cell division They are packed with a protein called keratin which the cells produce in very large quantities o Keratin gives the cells their ability to withstand damage abrasion and water penetration the surface of the skin is termed keratinized for this reason Cells emerge from the deepest levels of the epidermis Because this process is continuous the entire epidermis is replaced every 24 45 days Millions of cells from the stratum corneum slough off every day and attached microorganisms slough off with them The skin is also brimming with antimicrobial substances Small molecules called antimicrobial peptides have been identified in epithelial cells These are positively charged chemicals that act by disrupting negatively charged membranes of bacteria o There are many different types of these peptides and they seem to be chiefly responsible for keeping the microbial count of skin relatively low Sweat is also inhibitory to microorganisms because of both its low pH and its high salt concentration o Lysozyme is an enzyme found in sweat and tears and saliva that specifically breaks down peptidoglycan which is a unique component of bacterial cells walls o Below the stratum corneum are three or four more layers of epithelial cells The lowest layer the stratum basale or basal layer is attached to the underlying dermis and is the source for all of the cells that make up the epidermis o The dermis underneath the epidermis is composed of connective tissue instead of epithelium This means that it is a rich matrix of fibroblast cells and fibers such as collagen and it contains macrophages and mast cells The dermis also harbors a dense network of nerves blood vessels and lymphatic vessels The roots of hairs called follicles are in the dermis Sebaceous oil glands and scent glands are associated with the hair follicle Separate sweat glands are also found in this tissue o The sebaceous glands secretion called sebum has a low pH which makes the skin inhospitable to most microorganisms The sebum is oily due to its high concentration or lipids The lipids can serve as nutrients for normal microbiota but breakdown of the fatty acids contained in lipids leads to toxic by products that inhibit the growth of microorganisms not adapted for the skin environment This mechanism helps control the growth of potentially pathogenic bacteria All of these glands have openings on the surface of the skin so they pass through the epidermis as well List the natural defenses present in the skin LISTED ABOVE List the types of normal biota presently known to occupy the skin Microbes that live on the surface as normal biota must be capable of living in the dry salty conditions they find there Microbes are rather sparsely distributed over dry flat areas of the body such as on the back but they can grow in dense populations in moist areas and skin folds such as the underarm and groin areas The normal biota also live in the protected environment of the hair follicles and glandular ducts Predominant bacterial genera are Streptococcus Staphylococcus Propionibacterium and Corynebacterim The fungus Malassezia is also present in high numbers It came as a surprise that two dominant genera on human skin are Pseudomonas and Janthinobacterium both gram negative rods Another important finding is a rich diversity of microbe many of them well known to be pathogenic living under the skin List the possible causative agents modes of transmission virulence factors diagnostic technique and prevention treatment for the highlighted condition maculopapular rash disease There are a variety of microbes that can cause the type of skin eruptions classified as maculopapular a term denoting flat to slightly raised colored bumps Measles Measles is also known as rubeola Be very careful not to confuse it with the next maculopapular disease rubella o Signs and Symptoms The initial symptoms of measles are sore throat dry cough headache conjunctivitis lymphadenitis and fever In short time unusual oral lesions called Koplik s spots appear as prelude to the characteristics red maculopapular exanthema that erupts on the head and then progresses to the trunk and extremities until most of the body is covered The rash gradually coalesces into red patches that face to brown In a small number of cases children develop laryngitis bronchopneumonia and bacterial secondary infections such as ear and sinus infections Occasionally 1 in 100 cases Measles progresses to pneumonia or encephalitis resulting in various central nervous system changes ranging from disorientation to coma o Permanent brain damage or epilepsy can result A large number of measles patients experience secondary bacterial infections The most serious complication is subacute sclerosing panencephalitis SSPE a progressive neurological degeneration of the cerebral cortex white matter and brain stem o Its incidence is approximately one case in a million measle infections and it afflicts primarily male childten and adolescents o The pathogenesis of SSPE appears to involve a defective virus one that has lost its ability to form a capsid appears to involve a defective virus one that has lost its ability to form a capsid and be released from an infected cell o Instead it spreads unchecked through the brain by cell fusion gradually destroying neurons and accessory cells and breaking down myelin o The disease causes profound intellectual and neurological impairment o The course of the disease invariably leads to coma and death in a matter of months or years The measles virus is a member of the Morbillivirus genus It is a single stranded enveloped RNA virus in the family Paramyxoviridae o Pathogenesis and Virulence Factors The virus implants in the respiratory mucosa and infects the tracheal and bronchial cells From there it travels to the lymphatic system where it multiplies and then enters the bloodstream Viremia carries the virus to the skin and to various organs The measles virus induces the cell membranes of adjacent host cells to fuse into large syncytia