Hypodermis, also known as subcutaneous tissue, has important functions. Hypodermis layer lies immediately below the dermis.
Subcutaneous tissue layer has many types of cells in it like fibroblasts, fat cells (adipocytes) and leukocytes. Fibrous bands and elastins are found in this region of integumentary system, anchoring the cutaneous layer (skin) to the deep fascia fat. Sudoriferous glands (sweat glands), papilla region of hair root and pacinian corpuscle (a type of nerve ending) are found in the junction of dermis and hypodermis.
Blood vessels and lymphatic vessels traverse this region, carrying the blood and lymph to the dermis. At the junction of dermis and subcutaneous tissue, arteries form deep cutaneous plexus. Its function is to supply oxygen and nutrients to the tissues in the hypodermis, dermis, hair follicles, sebaceous glands and sweat glands.
The thickness of hypodermis varies considerably in respect of body area, nutritional status, age and gender of the individual. In thin areas of the skin like eyelids, genitals, and nipples, it is nearly absent. With aging drastic changes take place in the hypodermis. It begins to thin out and disintegrate causing deep wrinkles, folds and sagging of the facial skin.
The fat storing cells, adipocytes, are grouped together in lobules separated by connective tissue. Hormones in adults have effect on the pattern of hypodermis fat distribution function. In men fat tends to accumulate over the abdomen, torso and shoulders and in women fat accumulates on the breasts, waist, hips, buttocks and thighs. In weight loss there is usually changes in the amount of lipid content of the adipocytes and not in their number.
The adipose fat also functions as a cushion and padding against pressure and friction, absorbing shocks from impacts to the skin. Fats stored in this layer also functions as energy reserve and the fat is put back into circulation when needed. Another function is in providing thermal insulation to the inner body to slow down heat loss. This helps in the regulation of body temperature. Children and elderly people have less storage of adipose fat in their subcutaneous tissue and are more sensitive to cold.
Panniculus carnosus, a layer of flat sheets of striated muscle is found in hypodermis. Their function in humans is seen in some muscles of facial expression, dartos muscle (dartos fascia or tunica dartos) lying beneath the skin of scrotum, palmaris brevis muscle in the ulnar side of hand and platysma muscle found in the neck.
Image source: http://en.wikipedia.org/wiki/File:Skin.png
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Current topic in dynamic skin care: Functions of hypodermis layer.