The human body's largest organ is the integumentary system,
which includes the skin, hair, nails, glands and nerve receptors. The
integumentary system works to waterproof, cushion and protect the body from
infection, according to the National Institutes of Health. Most skin is
waterproof because of keratin, a fibrous protein, and it also is made up of
water, other proteins, lipids and different minerals and chemicals. Skin
excretes wastes, regulates temperature and prevents dehydration by controlling
the level of perspiration. It also houses sensory receptors that detect pain,
sensation and pressure.
The skin is also the body's initial defense against
bacteria, viruses and other microbes. Skin and hair provide protection from
harmful ultraviolet radiation, and the skin guards against sunburn by secreting
melanin, according to the American Academy of Dermatology (AAD). Human skin
color is determined by the interaction of melanin, carotene and hemoglobin.
Storage of water, fat, glucose and vitamin D is also a
function of the integumentary system, according to the AAD.
Three layers of tissue
Human skin is composed of three layers of tissue: the
epidermis, dermis and hypodermis, according to the Cleveland Clinic and about
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Epidermis
The epidermis is the top layer of skin and does not contain
blood vessels. While it is only about one-tenth of a millimeter thick, the
epidermis is made of 40 to 50 rows of stacked cells called squamous cells or
keratinocytes, according to the Cleveland Clinic.
Keratinocytes produce keratin, a fibrous, waterproofing
protein. The majority of the skin on the body is keratinized, meaning it's
waterproof, with the exception of the lining of skin on the inside of the mouth,
according to the Cleveland Clinic. Keratin is also a key component of hair and
nails.
The epidermis also consists of melanocytes, which produce
melanin, the dark pigment that gives skin its color; Merkel cells, which are
thought to be involved in touch reception; and Langerhans cells, which help the
immune system fight antigens (foreign bodies), according to Penn Medicine.
Only the deepest layer of the epidermis receives nourishment
from the layer beneath it. Cells that are pushed away from this layer
eventually die. When they reach the skin surface, they are sloughed off or
shed. The skin sheds millions of dead keratinocytes every day.
Dermis
The dermis is the middle layer of skin, and it actually has
two layers, according to the AAD. The papillary layer consists of the loose
connective tissue, while the reticular layer is the deep layer of the dermis
and consists of dense connective tissue. These layers provide elasticity,
allowing for stretching while also working to fight wrinkling and sagging.
The dermal layer provides a site for the endings of blood
vessels and nerves, according to the AAD. The structures for hair are in this
layer of skin.
Lymph vessels, which supply the clear fluid containing white
blood cells of the immune system, are also housed in this layer, to help ward
off infections and other foreign bodies. The dermis, the AAD noted, is also
home to the sweat glands and oil glands, which are attached to hair follicles.
Hypodermis
The hypodermis — also called subcutaneous tissue — is the
deepest layer of the skin. It helps insulate the body and cushion internal
organs, the Cleveland Clinic noted. The hypodermis is composed of connective
tissue called adipose tissue, which stores excess energy as fat. Blood vessels,
lymph vessels, nerves and hair follicles also run through this layer of skin.
Diseases of the integumentary system
Dermatologists specialize in treating diseases, disorders
and injuries of the skin, hair and nails. They treat common conditions such as
acne and warts; chronic skin conditions such as eczema and psoriasis; and more
serious diseases like skin cancer, according to the AAD. A residency in
dermatology involves one year as an intern in either surgery or internal
medicine, followed by a three-year residency.
After this, many dermatologists pursue further training
through one- or two-year fellowships in specialized fields, such as cosmetic
surgery, laser medicine or immunodermatology, the AAD noted.
Skin cancer
There are three main types of skin cancer, the most common
of which is basal cell carcinoma, said Dr. Charles E. Crutchfield III, a
clinical professor of dermatology at the University of Minnesota Medical
School, and medical director of Crutchfield Dermatology. More than 2 million
cases of this skin cancer are diagnosed in the United States every year,
according to the AAD. This type of cancer is skin colored or has a slight pearl
color to it. It rarely metastasizes (i.e., it rarely spreads to other parts of
the body), but it can be very problematic if it's not treated, Crutchfield
cautioned. According to the AAD, basal cell carcinoma can destroy skin tissue
and bone.
The second most common skin cancer is squamous cell
carcinoma. This is a rough-surfaced skin-colored lesion. Squamous cell skin
cancer causes death in about 10 percent of affected patients.
The most serious skin cancer is melanoma, which looks like a
dark, changing, bleeding skin spot, Crutchfield said. Melanoma is fatal in as
many as 35 percent of patients diagnosed with this form of skin cancer.
Warts
Warts are rough bumps caused by a viral infection. They
commonly occur on the hands and feet. Sometimes, tiny black dots will be
visible in a wart, Crutchfield noted. "Those are blocked blood vessels,
which is a common occurrence with a papilloma viral infection." The best
treatment for warts is to cause a mild irritation of the wart — usually by
freezing, liquid irritation and lasers — so the immune system can recognize the
viral infection and get rid of it.
Eczema
Also known as dermatitis, eczema looks like red, itchy,
flaky skin. It can occur anywhere. Sometimes, it happens by itself, and other
times, it is caused by outside factors such as poison ivy, according to
Crutchfield. Dermatitis is best treated with topical anti-inflammatory creams
and ointments. For mild cases, over-the-counter medications work well, but a
prescription may be required for more severe cases.
Acne
Acne, a disorder of the hair and oil glands, is among the
most common conditions treated by dermatologists, Crutchfield said. "It is
under the control of hormonal changes, hence the initial flare during
adolescence," he said.
Acne presents itself as red bumps and pimples on the face,
chest and back, Crutchfield said. Treatments include vitamin A products
(retinols), salicylic acid (to unplug pores), benzoyl peroxides (to decrease
bacteria) and antibiotics (to reduce inflammation).
Vitiligo
Vitiligo is a condition in which the cells that produce skin
color — melanocytes — no longer function properly. Some are attacked by the
immune system. Sometimes, the cells mysteriously die or stop working,
Crutchfield noted. "When this happens, the person with vitiligo can get
multiple patches of white skin. One of the best treatments for vitiligo is specialized
light treatment from a doctor."
Psoriasis
Psoriasis is an inflammatory skin condition in which red,
itchy plaques commonly occur on the knees and elbows. Crutchfield explained
that the nails can have pits and the scalp can be red and itchy, flaky and
inflamed. "About 3 percent of all people have psoriasis to some degree,
and it does run in families many times," he noted. Some patients with
psoriasis can also develop arthritis, called psoriatic arthritis. The best
treatment for psoriasis are topical medicines, light treatments and, in severe
cases, systemic prescription medicines.
Moles
Moles are normal parts of the skin. Moles can be flat or
raised, and they can be red, brown, black or skin-colored. If a mole start
changing — in size, color or shape, or if it bleeds and doesn't heal on its own
in three weeks — it should be evaluated by a doctor to make sure it is not
turning into a skin cancer, Crutchfield said. if you want
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September 18, 2017
