The following points highlight the ten main functions of the integument in vertebrates. The functions are: 1. Protection 2. Temperature Control 3. Food Storage 4. Secretion 5. Excretion 6. Sensation 7. Respiration 8. Locomotion 9. Dermal Endoskeleton 10. Sexual Selection.
Function # 1. Protection:
The integument forms a covering of the body and is protective. It protects the body against entry of foreign bodies and against mechanical injuries. It protects the tissues against excessive loss of moisture, this is very important because both aquatic and terrestrial animals are dependent upon water in their bodies for various metabolic activities.
The integument forms protective derivatives, such as scales, bony plates, layer of fat, feathers and hair which reduce the effect of injurious contacts. In some animals the skin shows protective colouration which makes the animals resemble their environment, thus, making them almost invisible to their enemies. Poison glands of toads, slippery skin of aquatic animals and an armour of spines of some mammals are protective devices of the integument.
The skin forms a covering which prevents the passage of water and solutes in one of the following ways:
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(a) By formation of cuticle in Protochordata and embryos of fishes and amphibians,
(b) By secreting a coat of mucus in fishes and aquatic amphibians, and
(c) By formation of keratin layers in the epidermis of tetrapoda.
Keratin is formed from the cytoplasm of degenerating cells of the epidermis which finally form a layer of horny stratum corneum.
Function # 2. Temperature Control:
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Heat is produced constantly by oxidation of food stuffs in tissues. This heat is distributed evenly by the circulating blood. The body heat is lost constantly with expired breath, with faeces and urine, and from the surface of the skin. The integument regulates heat and maintains a constant temperature in endothermal animals.
In birds the heat is regulated by adjustment of feathers which retain a warm blanket of air, when feathers are held close to the body they remove warm air and body cooled, when feathers are fluffed out they keep the warm air enclosed. In mammals constant evaporation of sweat regulates the body heat. In cold weather contraction of skin’s blood capillaries reduces the loss of body heat. In some animals fat in the skin prevents loss of heat because it is a non-conductor of heat.
Function # 3. Food Storage:
The skin stores fat in its layers as reserve food material which is used for nourishment in times of need. In whales and seals the fat of the skin forms a thick layer, called blubber which is not only reserve food but also maintains the body temperature.
Function # 4. Secretion:
The skin acts as an organ of secretion. Glands of the skin are secretory. In aquatic forms there are secretory mucous glands whose secretions keep the skin moist and slippery. In mammals sebaceous glands secrete oil which lubricates the skin and hairs.
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Mammary glands produce milk for nourishment of the young. In birds uropygial glands secrete oil for preening the feathers. Odours of scent glands attract the opposite sex. Lacrymal glands’ secretion wash the conjunctiva of eyeball in mammals. Ear wax (cerumen) secreted by the glands of auditory meatus greases the eardrums and avoids insects to enter the canal.
Function # 5. Excretion:
The integument acts as an organ of excretion. Shedding of the corneal layer during ecdysis removes some waste substances. In mammals metabolic waste (salts, urea and water) is removed from the blood by means of sweat. Chloride secreting cells are found in gills of marine fishes.
Function # 6. Sensation:
The skin is an important sense organ because it has various kinds of tactile cells and corpuscles which are sensory to touch, temperature changes, heat, cold, pressure and pain.
Function # 7. Respiration:
In amphibians, the moist skin acts as an organ of respiration, in frogs the respiratory function of the skin is greater than that of the lungs.
Function # 8. Locomotion:
Derivatives of the integument bring about locomotion in some animals, such as the fins of fishes aid in locomotion in water, the web of skin in the feet of frogs and aquatic birds aid in swimming, feathers of the wings and tail of birds are used for flying, and extensions of the integument forming “wings” of flying lizards, extinct pterodactyls, flying squirrels and bats.
Function # 9. Dermal Endoskeleton:
The skin contributes to the endoskeleton. It forms the dermal bones of vertebrates and also forms parts of the teeth. Endoskeleton of head protects the brain and sense organs. In the body it protects the soft, tender viscera.
Function # 10. Sexual Selection:
The skin acts as an organ of sexual selection. It provides the feathers of birds which often have brilliant colours which are for sexual attraction. Some integumentary glands of mammals produce odours far attracting the opposite sex. Antlers of male deer distinguish it from female.
Besides the above functions, mammalian skin synthesises the vitamin D with the help of Sebum of sebaceous glands. Brood pouches beneath skin in some fishes and amphibians protect unhatched eggs. Nasal glands of tetrapods keep the nostrils free of dirt and water. Skin also has the power of absorption of oils, ointments, etc.