The integumentary system varies greatly from animal to animal. In most animals, there is a layer or more of epithelial cells constituting the integument, called the epidermis, an underlying nutritive layer, called dermis and a waterproof cover, the cuticle.
However, the integument can be only one cell thick in unicellular organisms, such as bacteria and protozoa, being the cell membrane itself. Among vertebrates, there are also a variety of attachments, such as fur, scales, horns, claws and feathers.
The integumentary system has several functions, the main ones being: protect the body of the invasion of microorganisms and of the dehydration, also controlling the body temperature and receiving the external stimuli through sensory receptors.
Also read about the Integumentary System The Human skin.
Integumentary System of Vertebrates
There is a great diversity of integuments among vertebrates, related to the adaptation of these animals to the environment in which they live. Just remember the many white fur of the Arctic bear, the hull of armadillos and turtles, the feathers of the chickens or an eagle, or even the scales of so many species of fish, to see the variety of this system.
Skin Layers
Cross-section of the skin seen under a microscope. The epidermis is the darkest part (the outermost stratum corneum is flaking off) and the dermis is the lightest.
The epidermis cells originate in the basal part and move upwards, becoming flatter. When they reach the most superficial layer (stratum corneum) the cells are dead and are composed largely of keratin. In terrestrial vertebrates, this layer of cells is periodically shed, as in reptiles that change skin, or continuously in plaques or scales as in mammals.
The dermis is made up of connective tissue, blood and lymph vessels, nerve endings and smooth muscle fibers. It is a layer of variable thickness, whose irregular surface with protrusions (dermal papillae), inserts into the recesses of the epidermis.
Skin Appendices
glands
are glands exocrine as they secrete their products to the surface of the epidermis. They can be tubular or bag-shaped, secrete continuously, periodically or only once, they can be found grouped, alone, or branched.
There are several types of substances that can be secreted, thus: poison glands secrete toxins, sebaceous ones secrete oil, the ceruminous ones secrete wax, the mammary ones the milk, the odoriferous different substances of odor, the mucous ones that release the mucus. In aquatic animals, there are mucous glands to lubricate the body and reduce friction with water. In deep-sea fish, there are epidermal glands modified into structures called photophores, which produce light.
Horns and Antlers
They are very hardened corneal projections found in mammals. They are made up of a cone of keratinized cells and fibers, which grow from the epidermis. The fibers, similar to a thick strand of hair, grow from the dermal papillae, whose cells produce a kind of cement that binds the fibers together, holding them together. In buffaloes, goats and other ruminants hollow horns are found, which are extensions of the frontal bone of the skull, covered by a horny layer. In deer, the antlers they are bone structures without any epidermal coverage, only in young people it is covered with skin, which gives a velvety texture.
Pigment Cells
In fish, amphibians and reptiles there are chromatophores which are branched cells, responsible for rapid color changes. In birds and mammals, the melanocytes, branched cells producing melanin granules that are transferred to the cells of the skin's granular layer.
Claws, Nails and Hoofs
They are keratinized corneal structures, modified according to the animal. At claws they are curved and sharp and are present in many vertebrates; it is believed to have been the first type of nail that emerged, the nails and hooves being derived from it. At nails they are present in mammals and help animals to grasp objects or food. You hooves they are like thicker nails, curved around the end of the finger.
Feathers and Hair
The feathers are made up of a type of keratin, believed to have evolved from reptile scales. They are unique structures for birds and are changed periodically. These structures are extremely light, not hampering flight. There are different types of feathers: the contour ones help to define the body shape and during flight and the feathers under the body act as insulators.
Invertebrate Integumentary System
in most arthropods the body is segmented, with rigid plates connected by flexible membranes composing the exoskeleton, consisting of fibers of chitin. There is an epidermis whose basement membrane secretes the cuticle. In some species the cuticle suffers sclerotization, giving a consistency similar to keratin. In crustaceans there is incorporation of calcareous substances to the cuticle. There is also a layer of wax that makes the surface of the body waterproof, thus preventing dehydration of these animals.
the epidermis of molluscs it has many functions as in higher animals. O ciliated epithelium helps snails move and bivalves feed. Cephalopods (octopus and squid) have luminous glands and pigment cells which favors them to change color quickly. At shells are composed of an outer layer of calcium carbonate, a middle layer of calcite and a innermost pearlescent (also called mother-of-pearl) secreted by the mantle epithelium (fold of the epidermis). THE Pearl it forms when a foreign body invades the shell, being enveloped by nacre and growing with the animal.
In the integumentary system of Cnidarians in addition to epithelial cells, there may be different types: spiny, pigment and sensory cells with hair. The outer surface may contain flagella or microvilli, some have polyps and others have an outer limestone skeleton.
At sponges have a simple epithelium called pinacoderm, some have calcium carbonate spikes just below the epithelium in the mesoglea.
