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Skin Anatomy
By peace | November 25, 2006
The skin is one of the largest organs of the body and has many different functions. The skin functions in thermoregulation, protection, metabolic functions and sensation. The skin is divided into two main regions, the epidermis, and the dermis, each providing a distinct role in the overall function of the skin. The dermis is attached to an underlying hypodermis, also called subcutaneous connective tissue, which stores adipose tissue and is recognized as the superficial fascia of gross anatomy.
The skin forms the outer covering of the body. It is a strong elastic covering that encloses the body and protects it from damage by injury or infection. An average man is covered by approxiamtely 18 square feet of skin which weighs about 4.1kg.
The skin varies in thickness from 0.05mm to 5mm. As in other mammals, human skin is composed of an outer layer, the epidermis, and an underlying layer of fibrous tissue called the dermis. Beneath the dermis is the subcutaneous fat. The thickest skin is found on the sole of the foot and palm of the hand, some of the thinnest skin is found on the eyelid.
The epidermis is constantly growing from the bottom upwards and the dead skin cells (stratum corneum) are shed (usually invisibly) from the surface. This whole process normally takes about 52-75 days but can be much quicker in some skin diseases such as psoriasis.
In the deeper parts of the dermis are hair follicles, from which hair grows. It varies in thickness from about 0.005mm in the fine ‘lanugo’ hair covering a fetus to 0.2mm in beard hair. It varies in length from 1mm or less to 1.5m in extreme instances.
Oil glands (sebaceous glands) are found attached to hair follicles, Sweat glands are found in the dermis with ducts passing to the surface through the epidermis. In certain areas such as the axilla and groin there are specialised sweat glands called apocrine glands which develop after puberty. In addition there are specialised sense organs and nerves, blood vessels and other tissues such as muscle, which make the skin one of the most complex organs in the body.
Sweat glands occur in varying numbers over most of the body. For example, there are approximately 3000 square inches in the palm of the hand and sole of the foot, compared with 500 square inches in the badck. Specialised sweat glands are found in the armpit and genital area.
Sensations of pain, touch and temperature are conveyed to the brain from nerve endings in the skin. Some sensory nerve endings are highly specialised in shape and form, and their distribution varies gratly in the body. Finger tips and lips have a great many nerve endings. In other areas, like the forearm and abdomen, nerve endings are more sparse.
There are two main kinds of human skin; Glaborous skin (non-hairy skin) and hair-bearing skin. Glaborous skin is found on the palms and soles and is characterised by a thick epidermis with dermatoglyphics (fingerprints). Hairy skin differs from site to site, for example, the scalp versus the arm. It also contains a wide range of other structures depending on the part of the skin examined. Hair grows in different densities, patterns and colour over the skin. It is not found on the palm or the sole. Alongside some of the roots of the hair are sebaceous glands which produce a hair-bearing areas, and on the face, especially beside the nose.
Nails are a highly specialised and much changed form of the epidermis. They are semi-transparent and the underlying tissue, rich in blood vessels, shines through.
Topics: All Posts, Children, Man's health, Physiology, Woman's Health |
January 25th, 2008 at 2:04 pm
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