epidermis, but it is also present in cells progressing toward the surface and within the nonnucleated cells of the keratinized layer. The arrows indicate the melanin pigment in keratinocytes of the stratum spinosum and in the stratum
Dermis, skin, human, H&E and elastin stain ×200; inset ×450.
This figure is included because it shows certain features of the dermis, the connective tissue layer of the skin. The dermis is divided into two layers: the papillary layer (PL) of loose connective tissue and the reticular layer (RL) of more dense connective tissue. The papillary layer is immediately under the epidermis. It includes the connective tissue papillae that project into the undersurface of the epidermis. The reticular layer is deep to the papillary layer. The boundary between these two layers is not demarcated by any specific structural feature except for the change in the histologic composition of the two layers.
This specimen was stained with H&E and also with a procedure to display elastic fibers (EF). They are relatively thick and conspicuous in the reticular layer (see also inset), where they appear as the dark-blue profiles, some of which are elongate, whereas others are short. In the papillary layer, the elastic fibers are thinner and relatively sparse (arrows). The inset shows the typical eosinophilic staining of the thick collagenous fibers in the reticular layer. Although the collagenous fibers at the lower magnification of this figure are not as prominent, it is nevertheless possible to note that they are thicker in the reticular layer than in the papillary layer. The papillary layer is evidently more cellular than the reticular layer. Many of the small dark-blue profiles in the reticular layer represent oblique and cross sections through elastic fibers (see inset) and not nuclei of cells.
KEY CC, clear cells EF, elastic fibers PL, papillary layer RL, reticular layer arrows, middle figure pigment in different layers of epidermis; Lower figure delicate elastic fibers
Skin possesses three types of glands: eccrine, apocrine and sebaceous. Eccrine sweat glands are distributed over the entire body surface except for the lips, glans penis, prepuce, clitoris, and labia minora. They are especially numerous in the thick skin of the hands and feet. Evaporation of the secreted sweat on the skin surface cools the body. Apocrine sweat glands are localized in the axilla, areolae, perineal and perianal area, prepuce, scrotum, mons pubis, and labia majora. Many of the epithelial cells in the secretory segment of these glands exhibit an apical bleb-like protrusion that was earlier thought to represent their mode of secretion, i.e., pinching off of the bleb as the secretory product, thus the name apocrine. It is now known that secretion occurs as a merocrine process. The secretion is a clear, viscous product that becomes odife-rous through the action of resident microbes on the skin surface. In the human, its role is unclear, but it is generally believed that the secretion may act as a sex attractant (pheromone). Apocrine glands are present at birth but do not fully develop and become functional until puberty. In the female, these glands undergo changes that parallel the menstrual cycle. ORIENTATION MICROGRAPH: The adjacent orientation micrograph of the skin of the axilla shows both the large, branched tubular apocrine glands (A) and the smaller, simple tubular eccrine glands (E) in the hypodermis (H). Also evident is a tangentially cut hair follicle (HF). The overlying dermis (D) consists of dense connec-tive tissue and includes part of a sebaceous gland (SG). AAEESGDHFHA A E E SG D HF H
Apocrine sweat gland, skin, human, H&E, ×33. image are two sweat glands (SwG) also surrounded by dense connective tissue. Note the considerable difference in diameter and lumen size of the