Epidermis sweat glands

Figure 3.9 The structure of mammalian skin (A) epidermis, (B) dermis, (C) sebaceous gland, (D) capillary, (E) nerve fibers, (F) sweat gland, (G) adipose tissue, (H) hair.

Beneath die basement membrane of the epidermis is the dermis, a thick, tough, collagen-rich connective tissue. Blood vessels and nerve endings are found in this layer, as are roots of hairs and oil and sweat glands.1 ... 

Structure of skin. Skin is composed of two layers, the epidermis and the dermis, separated by a basement membrane zone. Hypodermis, composed of adipose tissue, sweat glands, and pacinian corpuscles, is not part of the skin.45... 

In discussing skin structure, we limit ourselves to those features of the membrane which are pertinent to drag delivery in particular, to the stratum corneum (SC), the outermost layer wherein skin s barrier function principally resides. Macroscopically, skin comprises two main layers the epidermis and the dermis ( 0.1 and 1 mm in thickness, respectively) (see Figure 8.1). The dermal-epidermal junction is highly convoluted ensuring a maximal contact area. Other anatomical features of the skin of interest are the appendageal structures the hair follicles, nails and sweat glands. 

Structures and substances that originate in the dermis such as hairs, sebaceous gland secretions and the ducts of the sweat glands pass through the epidermis to reach the surface of the body. 

Appendageal structures commonly found within the skin are the hairs, hair follicles, associated sebaceous glands, apocrine and eccrine sweat glands, and arrector pili muscles. Hairs are formed by epidermal invaginations. These keratinized structures traverse the dermis and may extend into the hypodermis. The free part of the hair above the surface of the skin is the hair shaft, and the part deep within the dermis is the hair root, which forms an expanded knob-like structure called the hair bulb. This is composed of a matrix of epithelial cells in different stages of differentiation. Hair is composed of three concentric epithelial cell layers the outermost thin cuticle, a densely packed keratinized cortex, and a central medulla of cuboidal cells. The hair follicle consists of four major components (1) internal root sheath (internal root sheath cuticle, granular layer, pale epithelial layer) (2) external root sheath (several layers similar to the epidermis) (3) dermal papilla (connective tissue) and (4) hair matrix (comparable to the stratum basale of the epidermis). 

Epidermis of skin, sweat glands, hair, and nails... 

Skin repair after a peel to the reticular dermis is slower, as all the basal layer keratinocytes have been destroyed and the skin can only rely on the differentiated keratinocytes of the pilosebaceous units and the intradermal excretory ducts of the sweat glands. To repair the dermis, the sebocytes in the pilosebaceous units must dedifferentiate, and horizontal growth is required to close the skin quickly. Next comes a phase of vertical growth whose purpose is to regenerate a physiologically sound epidermis that will maintain homeostasis and restore the vital barrier function after the keratinocytes have differentiated into corneocytes. 

Hershey et al, since 1954 (H17, H18, H19, H20) have reported on several glycolytic, pentose shunt, and Krebs cycle enzymes in human epidermis measured by Lowry s microtechniques. They have also compared enzyme activities in various structures of the skin (e.g., hair follicle, sweat gland, sebaceous gland, dermis, and epidermis), and have reported on their susceptibility to heat inactivation. 

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