The 2 most important types of derivative of Skin are listed below:
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1. Soft derivative:
It consists of cutaneous gland of different types –
I. Sweat gland:
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It is concerned with regulation of body temperature. They are most numerous on palm, soles, forehead and arm pit.
Mammary gland:
Characteristics of mammals these are modified apocrine sweat glands in eutheria and modified sebaceous gland in prototheria. They are present in both females and males but are functional in females only after the birth of child.
II. Sebaceous gland:
Associated with hair follicles theses, secrete over or sebum which keep the hair and skin smooth, soft, supple and water proof. Over secretion of sebaceous gland is called seborrhoes. Noticeable on the faces of some person’s emotional stress may increase the flow of sebum.
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Modified sebaceous glands
(i) Meibomian glands:
Also called tarsal gland on the edges of eyelids, these glands keep thin film of oil over the cornea.
(ii) Zeis gland:
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Associated with follicles of eye lashes there secretion keeps eye lashes smooth and oily. (Infection of zeis gland causes a stye or hordeolum)
(iii) Ceruminous gland:
Present in external ear canal. Secretion of this gland, called earwax/cerumen, prevents the dust particles from entering the ear passage and for absorbing the reflected soundwaves within the ear canal.
III. Perineal glands:
Also called scent glands/inguinal glands are found in the dermis of perineum around the genital organs. They secrete pheromones.
IV. Lacrymal glands:
Located at the superior lateral portion of each eye orbit this gland secretes tear, containing watery solution which consists of salts, some mucous and a bactericidal enzyme (lysozyme), which clears, lubricates and moistens the eyeballs.
2. Hard derivatives:
It consists of hairs, claws, nails, hoofs, horns, scales and feathers.
Hair:
Presence of hair on the body is one of the chief characteristics of mammals. A hair develops as a thickening of the stratum germinativum of the epidermis.
They ate fine cornfield or keratinized filaments that develop from tubular pits called hair follicles. At the lower end of the hair follicles is present a hair papilla made of connective tissue, blood capillaries and nerve fibres.
An oil or sebaceous gland opens into hair follicle. Base of hair or bulb introduces new cells for growth of hair.
Arrector pili muscles (smooth muscle) can move the hair. As its smooth fibre connects each hair follicle with the basement membrane of the epidermis so its contraction squeezes the oil out of the oil gland and brings about movement of the hair.
Besides bulbs, hair has two parts – root (which is deep situated in the dermis) and shaft (outside the skin and visible).
Hair is sensitive to touch thus they help in perceiving mechanical stimuli. Eyelashes of eyelids serve to protect the eyes. Hair of nostrils and ear canal prevents the entry of dust particles; harmful microorganism etc. and hair on head may have a protective role.