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Skin appendages
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Hairs, sweat glands, sebaceous glands and nails are structures associated with the skin. They have their roots in the dermis or even in the hypodermis.
Thus, body hair is anchored in the dermis whereas the hair on the head, surrounded by a sheath of connective tissue, is anchored 4 mm down in the hypodermis.
The skin is home to a variety of glands of which the main function is to synthesise substances which, depending on their nature, cool down the organism, protect the skin or make it more supple, lubricate the hair, or eliminate mineral elements or cholesterol. Among these glands are the sweat glands and the sebaceous glands.
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Schematic representation of sweat gland coiled secretory portion
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There are two types of sweat glands: eccrine
(from the Greek ex, out of, and krinein, to secrete) and apocrine
(from the Greek apo, far from). The former are the more numerous (2 to 5 million). They form coiled secretory portion at the dermis-hypodermis junction and the secreting duct opens as pores in the skin. Very abundant on the soles of the feet, the palms of the hands and the armpits (600/cm2), they secrete from birth a transparent fluid composed mainly of water, lactic acid, urea, toxins arising from metabolism and even defensins, substances which fight against bacteria. The main function of this eccrine sweat is to cool the organism: it eliminates by perspiration the excess heat produced after effort; it is also involved during times of rest to maintain the thermal equilibrium with the ambient environment (when it is very hot for example). The eccrine glands produce on average 200 ml of sweat per day. During major physical effort or when it is very hot this production can reach 10 litres per day.
The apocrine sweat glands are situated in specific areas: the armpits, the eyelids, the pubic area and the genitals. They are inactive until puberty. They are stimulated by the emotions and stress. Their secretion is more opaque, thicker, richer in fats, cholesterol and fatty acids
in particular. Their output is extremely limited, a few microlitres per day. Unlike the eccrine glands, they do not open directly onto the surface of the skin. Flowing into the epithelial sheath of the hair, then to the surface of the skin via the openings of the hair follicles, apocrine sweat may become unpleasant smelling due to the combined action of the oxygen in the air with the enzymes produced by the microflora.
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Each hair of the body, which has much the same biological machinery as the hair on the head, has a sebaceous gland attached to it. They look like a group of cells, the sebocytes, the function of which is to produce lipids which are the constituents of sebum. The sebum is transferred by the sebocytes into the duct of the sebaceous gland and is then secreted onto the surface of the skin where, with sweat, it helps form the hydrolipidic film. The sebum is a lubricant, which protects the skin from drying, out, from small scratches and harsh treatment and also possesses antifungal properties.
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The nail is a hard horny layer formed from flat keratinised
cells which are stuck together. It covers and protects the last phalanges of the fingers and toes. Hard, flexible, translucent, smooth and shiny, they are continually growing, on average by 0.1 mm/day (4 times slower than the hair). The nail can be considered as the remains of a defence system because it allows scratching, cutting or tearing. It plays a role in prehension, and enables tiny objects to be grasped, splinters to be removed, etc. When broken or soft, it may reflect a lack of vitamins or trace elements.
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The Hair follicle
is a complex structure which includes the Hair in its connective tissue sheath, the arrector muscle, the sebaceous gland
and in certain regions an apocrine sweat gland.
To improve your knowledge on hair
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