Integumentary System

Introduction

The integument or the skin forms the external covering of a vertebrate. It is continuous with the mucous membrane lining the mouth, rectum, nostrils, eyelids, and the opening of urinogential ducts. The skin comes in contact with the environment, and the type of environment whether terrestrial or equatic, influences the character of the skin. The vertebrate skin differs from that of invertebrates in having two layers, an outer epidermis derived from the ectoderm, an and inner dermis or corium formed from the mesenchyme of the dermatomes, the relative amount of the two layers veries with the environment.

Function of the Intigumentary System

1. The integument forms a covering of the body and is protective, it protects teh body against entry of foreign bodies and against mechanical injuries.
2. heat is produced constantly by oxidation of tissues,this heat is distributed evenly by the circulating blood. The integument regulates heat and maintains a constant temperature in endothermal animals.
3. 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 thik layer called blubber which is not only reserve food but also maintains the body temperature.
4. The integument acts as an organ of excretion. Shedding of the corneal layer during ecdysis removes some waste substance, in mammals metabolic waste is removed from the blood by means of sweat.
5. The skin is an important sense organ because it has verious kinds of tactile cells and corpuscles which are sesory to touch, temperature changes, heat, cold, pressure and pain.
6. 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.
7. The skin contributes to the skeleton, it forms the dermal bones of vertebrates and also forms parts of the teeth.
8. The skin acts as an organ of sexual selection, it provies 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.

Derivatives of the Integument

Both layers of integument have given reise to various types of derivates. The epidermis gives rise to integumentary glands, epidermal scales, horns, tips of digits, different corneal structures, feathers, and hairs. The dermis forms dermal scales of fishes and of some reptiles.

Epiersmal Derivates

A. Epidermal glands

1. Unicellular glands
2. Tubular glands
3. Alveolar or saccular glands

According to function the epidermal glands of vertebrates are of the following types:

1. Mucous glands
2. Luminescent organs or Photophores
3. Multicellular mucous glands
4. Femoral glands
5. Urophygial glands
6. Sudorific or sweat glands
7. Sebaceous glands
8. Mammary glands

B.Epidermal scales

After the evolutionary loss of dermal scales of fishes, amniotes developed an entirely new type of scale derived from the epidermis. The skin of vertebrates is rarely naked, it is usually provided with protective scales, bony plates, feathers or hairs.

C. Corneal structures

Some epidermal scales of the tail of rattle-snake are modified to form a rattle, it consists of a series of old dried scales.

D. Horns

These are found in ungulate mammals only, five types of horns are recognized

1. Rhinoceros or keratin fibre horn
2. Pronghorn
3. Antlers
4. Giraffe horns
5. Hollow horns

E.Digital tips

In amniota the distal ends of digits have claws, nails or hoofs formed from the horny layer of the epidermis . They grow parallel to the surface of the skin and are built on the same plan.

F. Feathers

Feathers are found only in birds and are modified reptilian scales, they are formed from the epidermis in which the stratum corneum is highly specialized. Feathers are light, strong, elastic, waterproof and show many colours due to pigmentss and structural arrangement. They form a protective covering, regulate body temperature, and support the body in flight.

G. Hair

Hair is found only in mammals, it protects at an acute angle from the skin. Hair covers the entire integument in most, but in others only traces are left, such as whales have only a few coarse hairs on the snout.