germinativum (the basal Iayer). For further details, see later this chapter (The functions of the skin,

Horny). This layer is the most superficial layer and is in contact with the external world. The eliding is now converted into keratin (essentially, keratin is a fibrous protein), the cells by now have become dead and their cellular outlines have become obscure. The most superficial portion of the stratum come is regularly. Cast off (it is estimated, that a healthy adult loses about 1 gm of stratum corium per day). The functions of the stratum cornea have been described later in this chapter. Is should be remembered that keratin is a very tough material, remarkably resistant to many forms of injuries the epidermis contains no blood vessels, us nutrition being derived from the capillaries of the dermis. Melanocytes, which are responsible for the synthesis of melanin, the pigment, are present in the str. germinativum (the basal Iayer). For further details, see later this chapter (The functions of the skin, color) Dermis The bulk of the dermis is made up of collage nous fibers. The superficial portion of the dermis makes inroads into the epidermis, and these inroads are called property of the skin. The dermal capillaries, especially those of the papillae are responsible for the nutrition of the epidermis. Dermis also contains nerve fibers and lymphatics. Histological. the dermis is often divided into two layers, via, the papillary or superficial layer (adjacent to the epidermis) and the reticular or deeper layer Harris the hairs develop from me epidermis Part of the hair, remains buried within the epidermis and me rest shoots out from the skin fig. 8.5.7) The hairs are of three types. (I) lanugos hair, (ii) vellums hair and (iii) the terminal body, including its scalp and eyelids. They begin to develop at around 3rd month of intrauterine life shortly before birth most of the lanugos hairs are shed. However, the tangos hairs of the scalp and eyelids persist A few months alter birth these too are shed off and are replaced by the vellums hair. The vellums hair (from vellum = fleece) covers al Iain skin, SO that the vellums is the body knar of al the infants and children The terminal hair begins to grow a] tie age Of puberty They replace the vellums hairs In seem cases the replacement may not be completed before the age of 40 years Tar mina hairs form the scalp hairs, body hairs, maxillary hairs and genital hairs (but not the downy facial hairs of the adult women) of the adult and are coarse and pigmented. Baldness in adult males, characteristically, recession of hairs co-cur in the is temporal regions, and also a patch of baldness develops in the region of vortex in many males, these three areas ultimately unite to produce the characteristic baldness (alopecia) of the males. This type of baldness is due to the male hormone testosterone. However, heredity strongly influences the form of alopecia. This type of baldness is not seen in women Shaving and growth of hair In spite of the almost universal belief that repeated shaving promotes more hair growth and specialty makes the hairs coarser and tougher, there is no firm proof of it Arrestor pylori (fig 8.5.2) are attached with the hair follicle. When they contract, the hairs stand out and become erect. The contraction of These muscles is due to the sympathetic stimulation Excitement and panic thus can cause erection of hair Sweat glands are of two types, via (I) the echini and (ii) the porcine glands Echini glands are me common sweat glands, occurring at over the body, but their population is most dense over the thick skin. An echini gland (fig. 8.5.3) is basically a simple tubular structure, which, at the beginning. In the deeper part of the dermis, is highly coiled like a resting snake. The rest of the duct is practical straight, coursing through the superficial part of the dermis, men through the epidemic. Ultimately opening through the pore into the exterior. Sweat is synthesized by the coiled portion of the sweat gland When it is synthesized, the sweat Is isotonic, but as it is carried forward to the exterior, its Na is partly reabsorbed In a subject, in whom profuse sweating is occurring but no replenishment of Na is taking place, the sweat becomes progressively less and less saline (re. us Na toncemrabon progressively falls) due to the action of the hormone altfosterune For the functions of sweat see temperature regulation, later this chapter Aponte glands are found m the pubic region, maxilla and around the nipple of the breast They have, apparently, some relationship with reproductive physiology They begin lo function vgorosry with he onset of puberty but their atlrvity dense at old age) Their secretion by Itself is not odorous. but bacterial decomposition makes it odorous To some attend the odors rather charade relic of an ndfcidual In general, the odor is unpleasant, but sexual activity is related to the odor of the opposite sex It is presale that appoint glands help to gently an animal by another anuran predator (e g beer for a goat or deer), friendly