"Integumentary" redirects here. For the part of the female reproductive system of seed plants, see Ovule.
Integumentary system
Cross-section of all skin layers
Identifiers
MeSH D034582
TA A16.0.00.001
TH H3.12.00.0.00001
FMA 72979
Anatomical terminology
[edit on Wikidata]
The integumentary system comprises the skin and its appendages acting to protect the body from various
kinds of damage, such as loss of water or damages from outside. The integumentary system
includes hair, scales, feathers, hooves, and nails. It has a variety of additional functions; it may serve to
waterproof, and protect the deeper tissues, excrete wastes, and regulate body temperature, and is the
attachment site for sensory receptors to detect pain, sensation, pressure, and temperature. In most land
vertebrates with significant exposure to sunlight, the integumentary system also provides for vitamin
D synthesis.
Contents
1Skin
2Epidermis
3Dermis
4Hypodermis
5Functions
6Clinical significance
7References
8External links
Skin[edit]
The skin is the largest organ of the body. In humans, it accounts for about 12 to 15 percent of total body weight
and covers 1.5-2m2 of surface area.[1]
3D still showing integumentary system.
The human skin (integument) is composed of at least two major layers of tissue: the epidermis and dermis.
(The hypodermis or subcutaneous layer is not part of the skin [citation needed].) The epidermis is the outermost layer,
providing the initial barrier to the external environment. It is separated from the dermis by the basement
membrane. The epidermis contains melanocytes and gives color to the skin. The deepest layer of epidermis
also contains nerve endings. Beneath this, the dermis comprises two sections, the papillary and reticular
layers, and contains connective tissues, vessels, glands, follicles, hair roots, sensory nerve endings, and
muscular tissue.[2] The deepest layer, the hypodermis, is primarily made up of adipose tissue. Substantial
collagen bundles anchor the dermis to the hypodermis in a way that permits most areas of the skin to move
freely over the deeper tissue layers.[3]
Epidermis[edit]
Main article: Epidermis
Epidermis and dermis of human skin
The epidermis is the top layer of skin made up of epithelial cells. It contains blood vessels. Its main functions
are protection, absorption of nutrients, and homeostasis. In structure, it consists of a keratinized
stratified squamous epithelium; four types of cells: keratinocytes, melanocytes, Merkel cells, and Langerhans
cells. The major cell of the epidermis is the keratinocyte, which produces keratin, a fibrous protein that aids in
skin protection. An overwhelming amount of keratin can cause disease by giving rise to eruptions from the skin
that will protrude outwards and lead to infection. [citation needed] Keratin is also a waterproofing protein. Millions of
dead keratinocytes rub off daily. The majority of the skin on the body is keratinized. The only skin on the body
that is non-keratinized is the lining of mucous membranes, such as the inside of the mouth. Non-keratinized
cells allow water to "stay" atop the structure.
The protein keratin stiffens epidermal tissue to form fingernails. Nails grow from a thin area called the nail
matrix at an average of 1 mm per week. The lunula is the crescent-shape area at the base of the nail, lighter in
color as it mixes with the matrix cells. Also, the stratum corneum is the top part of the epidermis.
Dermis[edit]
Main article: Dermis
The dermis is the middle layer of skin, composed of dense irregular connective tissue and areolar connective
tissue such as a collagen with elastin arranged in a diffusely bundled and woven pattern. The dermis has two
layers. One is the papillary layer which is the superficial layer and consists of the areolar connective tissue. The
other is the reticular layer which is the deep layer of the dermis and consists of the dense irregular connective
tissue. These layers serve to give elasticity to the integument, allowing stretching and conferring flexibility,
while also resisting distortions, wrinkling, and sagging.[2] The dermal layer provides a site for the endings of
blood vessels and nerves. Many chromatophores are also stored in this layer, as are the bases of integumental
structures such as hair, feathers, and glands.
Hypodermis[edit]
Main article: Hypodermis
The hypodermis, otherwise known as the subcutaneous layer, is a layer beneath the skin. It invaginates into
the dermis and is attached to the latter, immediately above it, by collagen and elastin fibers. It is essentially
composed of a type of cell known as adipocytes specialized in accumulating and storing fats. These cells are
grouped together in lobules separated by connective tissue.
The hypodermis acts as an energy reserve. The fats contained in the adipocytes can be put back into
circulation, via the venous route, during intense effort or when there is a lack of energy-providing substances,
and are then transformed into energy. The hypodermis participates, passively at least, in thermoregulation
since fat is a heat insulator.
Functions[edit]
The integumentary system has multiple roles in maintaining the body's equilibrium. All body systems work in an
interconnected manner to maintain the internal conditions essential to the function of the body. The skin has an
important job of protecting the body and acts as the body's first line of defense against infection, temperature
change, and other challenges to homeostasis. [4][5] Functions include:
Protect the body's internal living tissues and organs
Protect against invasion by infectious organisms
Protect the body from dehydration
Protect the body against abrupt changes in temperature, maintain homeostasis
Help excrete waste materials through perspiration
Act as a receptor for touch, pressure, pain, heat, and cold (see Somatosensory system)
Protect the body against sunburns by secreting melanin
Generate vitamin D through exposure to ultraviolet light
Store water, fat, glucose, vitamin D
Maintenance of the body form
Formation of new cells from stratum germinativum to repair minor injuries
Protect from UV rays.
Regulates body temperature
It distinguishes, separates, and protects the organism from its surroundings. Small-bodied invertebrates of
aquatic or continually moist habitats respire using the outer layer (integument). This gas exchange system,
where gases simply diffuse into and out of the interstitial fluid, is called integumentary exchange.
