integumentary system of vertebrates


Jaw less fishes like Lampreys and hag fishes have thick skin. Many types of epidermal glandular cells are present which secrete a protective cuticle. In hag fishes multicellular slime glands produce large amount of mucous slime that covers the body surface. They protect the animal from external parasites. Thus hag fishes are called slime eels.

The skin of cartilaginous fishes like sharks is multilayered and contains mucous and sensory cells. The dermis contains bony placard scales called dentives. Dentives contain blood vessels and nerves and are similar to vertebrate teeth and grow throughout life. Like teeth once denticles reach maturity wear down and are lost. Denticles give cartilaginous fishes a sand paper texture. The skin of boy fishes contains scales composed of dermal bone. 

A thin layer of dermal tissue overlaid by superficial epidermis normally covers scales. As scales are not shed, they grow at margins and over the lower surface. In many bony fishes growth lines are present that indicate the fish age. The dermis is richly supplied with capillary beds for respiration. Epidermis also contains many mucous glands. Mucus production helps to prevent bacterial and fungal infections and it reduces friction as the fish swims. Some species have granular glands which secrete on irritation or to some species poisonous alkaloid. Many Teliost (bony fishes) that live in deep aquatic habitats have photophores that facilitate species recognition or act like lures and warming signals.

The skin of Amphibians consists of stratified epidermis and dermis containing mucous glands, serous glands and pigmentation cells. Considering them phylogenetically they are transitional between aquatic and terrestrial vertebrates. The earliest amphibians were covered with dermal bone scales like their fish ancestor. The problems faced by amphibian due to terrestrial environment are (i) desiccations the damage caused by the ultra violet rays and (ii) physical abrasion. Evolution resulted in increased amount of Keratin production in the inner layers of skin which napped to protect the cells from UV rays. Mucus produced by mucus glands performs three functions (i) prevents desiccation (ii) facilitates gas exchange and (iii) makes the body slimy. Some poison glands are found in the dermis which produce unpleasant tasting or toxic fluid which acts as a predator deterent. Sensory nerves penetrate the epidermis as free nerve endings.

Skin of reptiles reflects their adaptation to their terrestrial mode of life. Outer epidermal layer (stralum corneum) is thick, lacks gland and is modified into Keratinized scales, suctes (thick scales) in turtles, beaks in turtles, rattles on snake and claws, plagues and spiny crests on most other reptiles. This layer resist abrasion, inhibits dehydration and protects the animals. During molting the older outer layer separates from new epidermis. Diffusion of fluids aids separation.

Skin of birds consists of outer epidermis of ectodermal in origin and inner dermis of mesodermal origin. Epidermis consists of outer epitrichuim, middle stratum corneum and an inner stratum germinativum or stratum Malipighium. Dermis consists of muscle fibres, nerve fibres, blood capillaries and connective tissue. Epidermis and Dermis and no pigmented cells but pigments occur on scales and feathers.

The skin of birds lacks sweet or other types of cutaneous glands except uropygial or preen gland. Skin of Mammals is thick and covered with hair. Skin consist of two main layers (1) the epidermis, ectodermal in origin and dermis which mesodermal in origin. From skin arise hairs, claws, nails and glands. Epidermis consists of outer stratum corneum. This layer has hard Keratin. Below it is stratum lucidum followed by thin layer of stratum gramulosum. Innermost layer of epidermis is stratum malpighium or stratum germinativum made of columnar cells. At the base of epidermis are pigment cells. Dermis is thick, tough, flexible and elastic covering whole body. Dermis is formed of connective tissue fibres, unstriped muscles, blood capillaries, nerves and fat cells. Some of the epidermal glands like sweet glands, sebaceous glands etc are found in dermis.

Comments

Post a Comment

Popular posts from this blog

What is the Dynamic Theory of Profit

Image
Clark's Dynamic Theory of Profit And Its Criticism The Dynamic Theory of Profit is associated with the name of an American Economist, J. B. Clark. In the world of reality, according to J. B. Clark, profit arises only in a dynamic economy. An economy is said to be dynamic when there is a change in population growth or change in the method of production or a change in the consumer’s wants, etc. A society which is without these changes is called a static society. In a static society, only monopoly profits continue to exist. All other economic profits are gradually eliminated by competition. In a dynamic society, an entrepreneur is always confronted with continuous unpredictable changes in demand for his product. The variation in demand may take place due to changes in fashions, tastes, the standard of living, distribution of income, population, new inventions, international repercussions, technological advances, etc. A prudent entrepreneur will always keep an eye on future demand
Read more

Compare the anatomy of Bifacial and Isobilateral leaves

BIFACIAL LEAF: It is also called dorsiventral leaf. This leaf is more strongly illuminated on upper surface than on lower surface. This unequal illumination induces a difference in the internal structure between upper and lower sides. Its internal structure shows: (1)        Upper Epidermis This is single layer of cells with thick cuticle which checks excessive evaporation of water from the surface. It does not contains chloroplasts, stomata are also absent. (2)        Lower Epidermis This is also single layer but with a thin cuticle. It bears many stomata, two guard cells of which contain some chloroplast, none are present in the epidermal cells. Internal to each stomata is large cavity called respiratory cavity. Lower epidermis of leaf is meant for exchange of gases (oxygen and carbon dioxide) between the atmosphere and the plant body. Excess water also evaporates from lower epidermis. (3)        Mesophyll The ground tissue lying between upper epidermis and th
Read more

osmoregulation in terrestrial and aquatic animals

Mechanism of osmoregulation is very important for all groups of animals whether inhibting land or water. Unlike plant cells, animal cells when placed in hypotonic solution burst due to the continuous absorption of water. On the contrary they would shrink and die if constantly placed in hypertonic solution. Normally uptake and loss of water are in balance for proper survival of cell. (1)        Osmoregulation in terrestrial animals: Terrestrial animals are more likely to loose water by evaporation through their permeable surfaces exposed to amsophere. Among various animal groups only Arthropods and vertebrates became the most successful land dwellers. They have developed number of strategies to maintain osmoregulation of their body fluid. (a) Water proof external coverings: To prevent water loss through external surfaces, vertebrates like reptiles, birds and mammals have water proof keratinized epidermis. Similarly the insects have developed external water proof layer called
Read more