THE SKIN
- The skin is an external protective layer of an organism. The skin spread all over the surface of the body such as Nostrils, Eyelids, Genitals. Outer membrane of Eardrum is also skin, conjunctiva of eyelids also skin.
- The evolution of skin in vertebrate is transition from the aquatic to the terrestrial are correlated.
STRUCTURE OF SKIN AND FUNCTION OF SKIN;
- The vertebrate skin can be derived into three strata, They are Epidermis, Dermis and Hypodermis.
- The Epidermis is made up of Ectoderm and the dermis or corium are made of mesoderm.
EPIDERMIS;
- Epidermis is the thin outer most layer of the skin, which is made up of four different cell types in five layers.
- The epidermis is made up of four different cell types in five layers, They are
- The deepest layer ''Stratum Basale''
- Stratum Spinosum,
- Stratum granulosum,
- Stratum lucidum
- Stratum corneum
THE DEEPEST LAYER STRATUM BASALE,
- Stratum Basale is the outermost layer attached to the dermis , this deepest layer stratum basale which is base layer contains single row of keratinocytes.
- The keratinocytes are rapidly dividing all the time and pushing the new cell to form the layer above.
- These continuous pushing of keratinocytes help in regenerating the dead cells or injured area as the Name suggests the keratinocytes are made of enormous keratin.
- In aquatic fishes the Keratinized layer forms the cuticle.
- The Stratum Basale not only contains the keratinocytes, But its also contain Melanocytes which produce melanin and tactile cells which act as a sensory receptor for touch.
STRATUM SPINOSUM,
- The stratum spinosum is an pricky layer, because the cells looks spiky.
- Stratum spinosum is a thick layer formed by full of cells , Which looks likes a web like system full of intermediate filament attach the other cells and forms tight junction called desmosomes.
- The cell stratum spinosum also contains dendritic cells which ingest foreign substances and activates immune system.
STRATUM LUCIDUM;
- The stratum lucidum is otherwise called clear layer. It is 2-3 cell layers thick.
- The flattend keratinizationed cells form the below layer caller stratum granulosum and now completely keratinized or dead cells and completly flattened and clear layer.
- These keratinocyte cell are aggregatedinto arrays called tonofilaments.
STRATUM CORNEUM:
- The stratum corneum is also known as horny layer. It is a outermost layer thick upto 20-30 cell layers which is full of dead and no nucleus in it.
- In stratum corneum the cells are dead in different manner that is the cell plasma membrane with the thick keratin protein give protection to organism.
- In aquatic fishes the keratinized layer forms the cuticle , but in amniotic animals the stratum corneum is cuticle these are also called cornified cells.
DERMIS
- In skin integument the dermis is situated below the epidermis layer and above the hypodermis layer.
- The dermis packed with outer loose layer and inner dense layer the dermis is full of connective tissue muscles, capillaries. blood vessels, collagen fiber, Nerves and glands and etc,
- In amphibian and reptiles the collagen fibre which store energy and dissipate energy and transmits forces, are arranged regularly and in aves and mammals the collagen fibre arranged irregularly.
- In some parts of animals such as comb of cock and face and buttocks of monkeys are looks bright red blood circulatory area..
HYPODERMIS
- The hypodermis is the deepest layer of skin in this layer also contains the , muscle fibre, blood vesseles, Nerves collagen etc.
- An the hypodermis refion under the skin is purpose of storing the fat under the Adipose tissues( helps store fat).
SOME IMPORTANT FUNCTIONS OF SKIN INCLUDES:-
- PROTECTION - Against entry of foreign bodies and mechanical injuries, forms protective derivatives such as Nail, Hair, Scales, Bony plates, feather and in organisms,.
- TEMPERATURE CONTROL- Protection from loss of water and maintain homeostasis.
- FOOD STORAGE- stores the food under the skin and also used to fat from the food to control body heat.
- SECRETION- Sweat glands, oily glands from the skin helps kills the bacteria in the skin, and stop cell dehydration,
- EXCRETION- Some animals excrete the waste though their skins they excrete the salt, nitrogenous wastes through sweet.
and Respiration in some animals such as frog skin as cuticle respiration, Locomotion in fishes through the fins, the fins are modifications of skin and Sexual attraction in Aves skin provides feathers which has amazing colours helps the bird to attract their opposite sex, these help them to selects their potential mates.
