Derivatives Of Integument
Derivatives Of Integument
Different structures are derived from the skin of various animals which are known as derivatives of integument. Depending upon the layer of skin from which these structures are derived , derivatives of integument can be studied under following headings:- Epidermal Derivatives and Dermal Derivatives.
- Epidermal glands
- Epidermal scales and scutes
- Digital structures like claws , nails and hoofs
Each of them are described below:-
- Epidermal glands
Epidermal glands are derived from the stratum germinativum of epidermis. Though they are derived from the epidermis , they may invade deep inside the dermis. The various epidermal glands present in different vertebrates are:-
- Mucus gland: Mucus glands are present in fish and in many amphibians. These glands secrete mucus which makes their body moist, soft and slippery. Mucus also has bactericidal and fungicidal effects.
- Poision glands: Many fish and amphibians have poision glands present in their skin. Fish like puffer fish (Tetrodon), lion fish(Pterios), stone fish(Synanceia) etc and amphibians like golden dart frog(Phyllobates) have poision glands in their skin. Due to the presence of poision glands , these animals escape from being eaten by predators.
- Luminescent glands: Luminiscent glands or photophore are light emitting glands present in some deep sea fish like Angler fish , Lantern fish etc. The light emitted from these glands helps to attract the prey.
- Uropygral glands: Uropygral glands or preen glands are present in birds. They are present dorsally at the base of their tail feather. The oily secretion from these glands make their feather soft and water proof. It also helps to attract the opposite sex.
- Femoral glands: Femoral glands are present in some male lizards like Uromastix. These glands secrete a sticky secretion which becomes hard on exposure to air and form a spine like structure. This structure helps to tightly grab the female’s body during copulation. Femoral glands are present at the base of their thigh region.
- Sweat glands: Sweat glands are slender,thin and coiled glands present in many mammals. They are responsible for production of sweat which helps in cooling of the body. Sweating process also helps to excrete some metabolic waste.
- Sebaceous glands: They are branched and tubular glands present in different mammals . These glands secrete an oily secretion called sebum that makes the hair and skin soft , moist and water proof. Sebum also has bactericidal and fungicidal effects.
- Scent glands / Odoriferous glands: Scent glands are modified sweat or sebaceous glands. The smell or secretion from these glands helps to attract the opposite sex. Scent glands are present in the head region near by the eyes in many deer species. In Musk deer , scent glands are present in the navel i.e present in the abdominal region. In many carnivores and rodents , scent glands are present around their anal region.
- Mammary glands: Mammary glands are the characteristic feature of mammals. They are highly developed in females to suck milk for their youngs. Mammary glands are provided with nipples in all the mammals except in Monotremes (Eg: Platypus) which lack nipples.
- Epidermal Scales and Scutes
Epidermal scales and scutes are hard structure derived from the stratum germinativum of epidermis. They are hard due to the deposition of sclero protein(fibrous protein) called keratin.
Most of the reptiles have a continuous layers of the epidermal scales in their body. Scutes are the structure similar to scales but they are not continuous or overlapping unlike the scales. Scutes are present in the cells of turtles , skin of crocodile while scales are present in lizards and snakes among the reptiles.
Scales are also present in birds but they are limited in the lower part of their legs and feet. The beak present in them also modified epidermal scales. Scales are present in some mammals. The scale present in armadillous(Dasypus) and scaly anteater(Manis) are epidermal scales. In rodents like rat , mouse, shrew etc. , patches of epidermal scales are present in their tail region.
- Digital Structures
Digital structures are hard , cornified (having keratin protein) present at the tip of digits(fingers) in reptiles , birds and mammals. It includes structure like claws, nails, hoofs .
All the digital structures are made up of same basic plans. They consists of two parts; Unguis and Sub unguis. Unguis is the upper hard and exposed part while Sub unguis is the lower comparatively soft and hidder part.
Claws: Claws are elongated ,pointed and sharp structures present at the tip of digits in reptiles , birds and in many mammals. They consist of a hard and dorsally situated unguis and comparatively soft and ventrally situated sub unguis.
Nails: Claws are modified into nails in primates. Nails consist of a large broad , flat and comparatively hard unguis and relatively soft and reduced subunguis.
Hoofs: Hoofs are present in ungulates(hoofed mammals).In hoofs, the unguis is present dorsally above the digits while sub unguis is present below the digits and it touches the ground.
Horns are present in hoofed mammals. They are present on the head region and are used for offence and defence. Horns are again of following types:-
- True horns : True horns or hollow horns are pointed and permanent structures arising as a bony projection from the frontal bone of skull. They are unbranched structures and are covered by hard epidermis. They grow throughout the life and are never shed. They are present in both sexes in animals belonging to family Bovidae (cattle, goat, sheep, bison etc.)
- Prong horns: Prong horns are also true horns arising as a bony projection from the frontal bone of skull but they consist of 1 to 3 short branches or prongs at their end and these prongs are shed each year. They are also covered by hard epidermis. Such prong horns are present in antilopes(Antilocapra).
- Antlers : They are hard , solid and branched structures made up of thick connective tissue and are arised from the frontal bone of skull. They are hard due to the deposition of calcium salts. They are annual growths and not permanent structures. After the end of breeding season , Antlers are shed and new antlers develop following year. They are present usually only in males belonging to deer family (Cervidae).
- Giraffe horns : Giraffe horns are short , cylindrical and unbranched structures arising from the frontal bone of skull. They are permanent structures which grow throughout the life and are never shed. They are present in both sexes in giraffe.
- Hair horns or fiber horns : Hair horns or fiber horns are present in both sexes of rhino. They are solid and pointed structures developed from the nasal bone of skull. They are formed by the fusion of thick hairy and keratinized epidermal fibers. Such hair horns are two in number in African species of rhinocerous and one in Asian species.
Feathers are light , strong , elastic and water proof structures present in birds and are derived from the stratum corneum of epidermis. They are dry, non living and keratinized structures and are variously coloured due to presence of pigments like carotenoids and melanins. Feathers are shed and are replaced periodically.
Feathers form a protecting covering , help in temperature regulation , make their body light and help in flying. A typical bird consist of three main types of feathers which are:
- Contour feathers(flight feathers)
- Plumules / Down feathers(Insulation)
- Filoplumes(Sensory feather)
Hair are present in mammals. They may cover the entire body as found in furred animals or they may occur only at certain parts of the body as found snout region in whales and dolphins.
Like scales and feathers , hair are also cornified (having keratin protein) epidermal derivatives. They get lost and replaced periodically.
Hair is derived from the stratum germinativum of epidermis and consist of two basic parts : the lower root and the upper shaft . Stratum germinativum of epidermis invade deep into the dermis forming a structure called hair follicle into which the root of the hair lies. Root consist of actively dividing cells but beyond the root , the cells gradually die as a result the exposed part of the shaft consist of only dead cells. Just below the root , there is swollen structure called hair papilla or dermal papilla containing the blood vessels and nerve fibers.
Function: Hair help in insulation of the body and reduce the forces of impact during injury. Hair present in the nostril area and in auditory canals present entry of dust and small organisms. Hair present in the eye lashes and eye brows protect the eyes. Similarly , hair present in the snout region are touch sensitives.