Structure and function of the skin.

The skin is a complex, dynamic organ of many cell types and specialized structures serving multiple functions crucial to heath and survival. One of the largest and most versatile of organs, the skin provides a number of unique functions:

1/ It protect deeper cells from the environment (ie, desiccation, chemical and mechanical injury, microbial, fungal and parasitic invasion, damaging effects of ultraviolet light)

2/ It regulates and helps maintain body temperature.

3/ It serves as a neuroreceptor organ in monitoring diverse environmental stimuli.

4/ It processes antigenic substances presented to it.

5/ It provides cosmetic adornment as an organ with specialized keratinized structures – hear and nails – that serve some protective function as well.

These functions may be correlated with specific structures and properties of epidermal and dermal regions. The stratified squamous epithelium differentiates to form the stratum corneum of anucleate cornified cells. In aggregate, these constitute a relatively impermeable protective barrier to inward penetration of liquids, irritating chemicals, allergens, and microorganisms. These tightly packed lamellae of cornified surface cells – in conjunction with the brown pigment melanin, produced by specialized cells in the epidermis, the melanocytes – play an impotent role in protection against the carcinogenic and aging effects of ultraviolet radiation. The skin plays an impotent role in immunologic defense by virtue of the Langerhans cells, serving as the most peripheral outpost of the immune system. Langerhans cells present antigen as the first step necessary for delayed hypersensitivity reactions. Cytokine mediators such as interleukin – 1 produced by keratinocytes aid these cell-mediated immune reaction in skin.

The connective tissue, which makes up preponderance of the dermis, is composed of collagen and elastic fibers and ground substance. The dermis provides nourishment to the epidermis and interacts with the epidermis during embryogenesis. Two components of the dermis – its unique circulatory system and specialized cutaneous appendages, the eccrine sweat glands – play a vital role in the body’s thermoregulatory function. Furthermore, the extensive innervation of the skin and its appendages make the skin impotent neuroreceptor sense organ interacting with the environment, registering such sensations as pain, itch, vibration, heat, and cold. The dermis also contains complex tubular structures in the axillas and the genitocrural and mammary areas, ie, the apocrine sweat glands, which secrete a viscous fluid which, when acted upon by resident bacteria, emits distinctive body odors.

Дата добавления: 2015-08-03