<Li> An acidic pH (around 5.0) and low amounts of water make it hostile to many microorganic pathogens . </Li> <Li> The presence of non-pathogenic microorganism on the epidermis surface help defend against pathogenic one by limiting food availability and through chemical secretions . </Li> <Ul> <Li> Psychological stress, through an increase in glucocorticoids, compromises the stratum corneum and thus the barrier function . </Li> <Li> Sudden and large shifts in humidity alter stratum corneum hydration in a way that could allow entry of pathogenic microorganisms . </Li> </Ul> <Li> Psychological stress, through an increase in glucocorticoids, compromises the stratum corneum and thus the barrier function . </Li>

Which of the following structures is not part of the epidermis