Theintegumentary system is the set of organs forming the outermost layer of an animal's body. It comprises theskin and its appendages, which act as a physical barrier between the external environment and the internal environment that it serves to protect and maintain the body of the animal. Mainly it is the body's outer skin.
The integumentary system includesskin,hair,scales,feathers,hooves,claws, andnails. It has a variety of additional functions: it may serve to maintain water balance, protect the deeper tissues, excrete wastes, and regulatebody temperature, and is the attachment site forsensory receptors which detect pain, sensation, pressure, and temperature.
The skin is one of the largest organs of the body. In humans, it accounts for about 12 to 15 percent of total body weight and covers 1.5 to 2 m2 of surface area.[1]
3D still showing human integumentary system
The skin (integument) is a composite organ, made up of at least two major layers of tissue: theepidermis and thedermis.[2] The epidermis is the outermost layer, providing the initial barrier to the external environment. It is separated from the dermis by thebasement membrane (basal lamina andreticular lamina). The epidermis containsmelanocytes and gives color to the skin. The deepest layer of the epidermis also containsnerve endings. Beneath this, the dermis comprises two sections, the papillary and reticular layers, and containsconnective tissues, blood vessels, glands, follicles,hair roots, sensory nerve endings, and muscular tissue.[3]
Between the integument and the deep body musculature there is a transitional subcutaneous zone made up of very loose connective andadipose tissue, thehypodermis. Substantialcollagen 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.[4]
Theepidermis is the strong, superficial layer that serves as the first line of protection against the outer environment. The human epidermis is composed ofstratified squamous epithelial cells, which further break down into four to five layers: thestratum corneum,stratum granulosum,stratum spinosum andstratum basale. Where the skin is thicker, such as in the palms and soles, there is an extra layer of skin between the stratum corneum and the stratum granulosum, called thestratum lucidum. The epidermis is regenerated from the stem cells found in the basal layer that develop into the corneum. The epidermis itself is devoid of blood supply and draws its nutrition from its underlying dermis.[5]
The predominant cellkeratinocyte, which produceskeratin, a fibrous protein that aids in skin protection, is responsible for the formation of the epidermal water barrier by making and secretinglipids.[6] The majority of the skin on the human body is keratinized, with the exception of the lining ofmucous 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 formfingernails. Nails grow from a thin area called thenail matrix at an average of 1 mm per week. Thelunula is the crescent-shape area at the base of the nail, lighter in color as it mixes with matrix cells. Onlyprimates have nails. In other vertebrates, the keratinizing system at the terminus of each digit produces claws or hooves.[2]
The epidermis of vertebrates is surrounded by two kinds of coverings, which are produced by the epidermis itself. Infish and aquaticamphibians, it is a thin mucus layer that is constantly being replaced. In terrestrial vertebrates, it is thestratum corneum (dead keratinized cells). The epidermis is, to some degree, glandular in all vertebrates, but more so infish andamphibians. Multicellular epidermal glands penetrate the dermis, where they are surrounded by blood capillaries that provide nutrients and, in the case of endocrine glands, transport their products.[7]
The dermis is the underlying connective tissue layer that supports the epidermis. It is composed of dense irregular connective tissue andareolar connective tissue such as a collagen withelastin arranged in a diffusely bundled and woven pattern.
The dermis has two layers: the papillary dermis and the reticular layer. The papillary layer is the superficial layer that forms finger-like projections into the epidermis (dermal papillae),[5] and consists of highly vascularized, loose connective tissue. The reticular layer 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.[3] The dermal layer provides a site for the endings of blood vessels and nerves. Manychromatophores are also stored in this layer, as are the bases of integumental structures such ashair,feathers, andglands.
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, which are 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.
The integumentary system has multiple roles inmaintaining 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.[8][9]
Its main functions include:
Protect the body's internal livingtissues and organs
Protect against invasion by foreign organisms, includinginfectious organisms
It distinguishes, separates, and protects the organism from its surroundings.
Small-bodied invertebrates of aquatic or continually moist habitatsrespire using the outer layer (integument). This gas exchange system, where gases simply diffuse into and out of theinterstitial fluid, is calledintegumentary exchange.
^Martini, Frederic; Nath, Judi L. (2009).Fundamentals of anatomy & physiology (8th ed.). San Francisco: Pearson/Benjamin Cummings. p. 158.ISBN978-0321505897.
^abKardong, Kenneth V. (2019).Vertebrates : comparative anatomy, function, evolution (Eighth ed.). New York, NY. pp. 212–214.ISBN978-1-259-70091-0.{{cite book}}: CS1 maint: location missing publisher (link)
