Knowing the percentage of hairs normally found in the three growth phases, it is possible to establish whether an individual has some illness that has brought about an increase in hair loss. With this method, known as a tricogram, it can be determined whether the three stages are regular or, in the event of a problem, which is over- or under-represented. To perform the test a sample of at least 100 hairs are taken and observed under the microscope. The number of hairs in each phase is then determined. An increase in the telogen phase will consequently be indicative of a real increase in hair loss.
Hair loss or thinning is known as alopecia. There are three types:
1. Noncicatricial or dysfunctional alopecia
2. Cicatricial or destructive alopecia
3. Hair breakage alopecia
Dysfunctional alopecias are the most frequent forms, with both common baldness (androgenic alopecia) and temporary hair loss (telogen effluvium) belonging to this category. The latter condition very often occurs after giving birth. Destructive alopecias are those conditions of the scalp that may be either congenital or acquired. This group also includes all those alopecias caused by any trauma leading to scarring of the scalp. Hair breakage alopecias can also be either congenital or acquired. Acquired forms include the tricoressi nodosa that can follow aggressive cosmetic treatments like, for example, excessive heat or over-energetic brushing.
The skin is supplied with three types of glands, all of which are formed from the epidermis during foetal development.
These are defined as holocrine glands due to the secretions they produce. The secretions are particularly thick and rich in organic substances and their production brings about the destruction of the gland cells themselves. With the exception of the palms and the soles of the feet, sebaceous glands are present all over the skin. They are always connected to a hair follicle, but in some areas like those around the anus, genitals, eyelids, and lips, they are directly connected with the skin surface because in these regions an adequate protection and lubrication must be guaranteed. This applies to man as much as to other mammals.
The sebaceous glands are not uniformly distributed over the body, some areas-the face, the back, and the torso-s-are particularly richly endowed, so much so that their density can reach over 200 glands per crrr', In other areas, such as the front of the leg, they are at their least dense and are found at less than 40 glands per crrr'. This non-uniform distribution of the sebaceous glands is the main difference responsible for both the different skin types and so-called combination skin.
The sebaceous glands are defined as being ramified-alveolar because their structure resembles a bunch of grapes, each grape (alveolus) connected by a stem to the main branch of the bunch. The entire gland, like the hair follicle, is surrounded by a connective sheath that invaginates to surround even the individual alveoli. A few alveoli become surrounded by the connective sheath and form a lobe, as if several alveoli were held together by a thin membrane. The alveolus is the secretory unit of the gland. The cells that constitute the outer layer of this region and are in contact with the connective sheath divide and multiply, progressing toward the centre of the alveolus and beginning sebum production.
Each alveolus ends in a small excretory duct that collects the sebum produced by the rupture of the mature cells. The alveolar ducts unite at the excretory duct of the different lobes, the lobe ducts coming together to form the common excretory duct, which opens into the hair follicle at the base of the infundubulum. This way hairs are already covered with sebum before they emerge from the skin surface. In areas where the sebaceous glands are not associated with a hair follicle the excretory duct opens directly onto the skin surface. In these areas the sebaceous glands are larger and at times modified to such an extent that they constitute different entities. This is true in the case of the Meibomian glands of the eyelids, which when inflamed produce a hard filtrate in the shape of an ear of com so giving rise to styes.
Sebum is a product of the sebaceous glands. Production of sebum is not constant, and it changes with different stages of life. In the foetus the sebaceous glands begin secreting sebum during the fourth month. This occurs to such an extent that at birth a newborn baby is often covered by a vernix caseosa, which is in fact a layer of sebum that protects the foetus from the amniotic fluid. Later when the baby is no longer being breastfed and, therefore, no longer receiving the maternal hormones that stimulate the glands, the sebaceous glands enter a state of quiescence which only ends when the child reaches puberty and the sexual glands have developed and begun to secrete sex hormones-predominantly androgens in the male and estrogens in the female. In both sexes it is the androgenic hormones that stimulate both the sebaceous glands and hair growth. The production of sebum, beginning again at puberty and continuing until adulthood, is always higher in males than in females. In females there is a reduction in sebum production after the menopause caused by the progressive inactivation of the ovaries, which consequently stop synthesizing androgens. In later years both men and women produce less sebum even though the sebaceous glands enlarge (become hypertrophic) and their openings often dilate.
Sebum represents about 95% of the lipids in our skin. On synthesis it has a different composition from that when it reaches the skin surface. The hair follicle contains many bacteria that possess a variety of enzymatic activities (particularly lipases) able to hydrolyse and, therefore alter, the complex molecules contained in the newly synthesized sebum. The composition of sebum on the skin surface:
Sebum is fundamental in all mammals because it represents the best protection for their fur. Man has lost most of his covering of hair and so sebum, though still important, is less so than for other mammals. However, even in man sebum continues its role of protecting the skin. By emulsifying itself, that is, mixing with the water derived from sweating or transpiration, sebum forms a film over the skin that is able within certain limits to protect it from harmful chemical substances and from the action of pathogenic microorganisms.
Sebum contributes to the skin's emollience (softness) by retaining water. The hairs are also protected by sebum without which they would appear opaque and dull. The presence of sebum around the anus, genitals, eyes, and lips has protective, emolient, and antimicrobic functions.
Our website is not responsible for the information contained by this article. Articleinput.com is a free articles resource thus practically any visitor can submit an article. However if you notice any copyrighted material, please contact us and we will remove the article(s) in discussion right away.
Note: This article was sent to us by: Andrew John Peterson at 03132010
1. Functional activation of cloned cells
All articles are property of their respective authors. Please read our Privacy Policy!
© 2009 ArticleInput.com.