The below mentioned article provides a study note on integument in mammals.
The integument or skin in mammals as well as in all vertebrates is continuous with the mucous membrane of mouth, rectum, urinogenital organs, nostrils and eyelids. The skin is made up of two distinct and embryo-logically different layers.
The outer layer is epidermis and it is ectodermal in origin and the inner layer is dermis which is mesodermal in origin. The two layers are separated by a basement membrane (Fig. 10.4).
The outer layer or the epidermis is again divided into a number of distinct strata. The innermost layer of the epidermis is called stratum germinativum or Malpighian layer. This layer is made up of tall and columnar cells arranged perpendicular to the dermis.
The cells divide mitotically and continually. The new cells thus formed tend always to reach the surface and on their sojourn become flattened and show poor stain ability.
The layer formed by these flat cells is known as transitional layer. The outermost layer of the epidermis is called stratum corneum or horny layer. The cells of this layer are flat and dead. The chief constituent of these cells is keratin which is a very hard, tough and insoluble protein.
The epidermis in certain parts of the body of man is a bit different. In the thick skin on the soles of the feet and palms of the hands the transition from Malpighian layer to corneal layer is not so abrupt. The transitional layer in these parts of the body is further subdivided into an inner stratum granulosum and an outer stratum lucidum.
The thickness of the epidermal part of the skin remains fairly constant because the rate of proliferation of the stratum germinativum is nearly equal to the loss of corneal cells. The dermis or corium is thicker than the epidermis and is made up of connective tissue fibres, smooth muscle fibres, blood vessels, nerves and glands.
In whales and seals the fat forms a thick layer, called blubber which acts as food reservoir and also helps in maintaining body temperature. The pigments of the skin or melanin in mammals never remain confined in specialised cells but they remain in the cells of the deepest layer of the epidermis.
Functions of the Integument in Vertebrates:
1. Protection:
i) The integument or skin protects the body from the entry of foreign bodies and prevent from the mechanical injuries.
ii) The hard dermal and epidermal scales that protect the skin from surface abrasion and also the soft tissues which lie beneath it.
iii) Hair, bristles and spines are employed for offensive and defensive purposes.
iv) The impervious integument helps the body from loss of water.
2. Thermoregulation:
The integument of warm-blooded animals regulates the body temperature. Feathers of birds, sweat glands and blubber of mammals help in the regulation of body temperature. Deep covering of the hairs help in the conservation of heat, specially during winter.
3. Storage of food:
In whales, seals and sea cows, a sub- dermal fat layer forms a thick layer, called blubber, which acts as food storage.
4. Excretion:
The integument of some aquatic vertebrates (e.g., aquatic amphibians) serves as an organ for excretion. During ecdysis the waste material which is stored in the corneal layer of the skin is shed. Sweat of the sweat glands aids in removing nitrogenous wastes from the body.
5. Respiration:
The moist skin of common eel, mud skippers and swamp eels sub-serve respiration. The skin of amphibians is moist and highly glandular that help air in contact with the skin to be interchanged and thus performs accessory respiration. In plethodontid salamanders, the lungs are absent, so rely totally on cutaneous respiration.
6. Secretion:
The skin acts as an organ of secretion. The different glands are located in the skin those help the vertebrates in different ways for survival. Fishes possess numerous mucous glands in the skin that secrete abundant mucous.
The slimy mucus of the fish on the skin reduces resistance during swimming. The poison glands of fishes, amphibians and snakes are used for protection and predation. Mammary glands, scent glands, and sebaceous glands are present in the skin and serve different functions.
7. Locomotion:
Various types of integumentary derivatives sub-serve different types of locomotion’s. The fins of fishes, web in aquatic amphibians, terrapins and aquatic birds, scutes in snakes, adhesive pads in climbing lizards, feathers in birds and patagium in flying lizards help in different modes of locomotion.