BIOLOGY - IX

SKIN - STRUCTURE AND FUNCTION 

Preview 

* Skin is the largest organ of the body.

* Skin is defined as the outermost productive covering of the body, stretched all over it in the form of a layer.

* Structurally, skin consists of two main layers : an outer epidermis and an inner dermis .* Epidermis shows 3 regions--

a) the outermost cornified layer(stratum corneum)

b) the middle granular layer.

c) the inner malphighian layer(germinative layer)

* Cells of cornified layer are dead and made of a horny protein keratin.

* Cells of granular layer and malphighian layers are living.

* The dark coloured pigment, melanin, which determine skin colour is present in the malphighian layer. Melanin acts as a screen against ultra-violet light .

* Dermis, below the epidermis, is a much thicker layer than the epidermis.

*  While epidermis consist of stratified epithelium, dermis consists of elastic connective tissue.

* Blood capillaries , hair follicles, sweat glands, oil glands (sebaceous glands) and nerve endings are present in the dermal layer.

* Skin performs following functions:

a) protection 

i) it protects the underlying tissues from mechanical injury.

ii) It protects the body from harmful ultraviolet rays (present in sunlight)

iii) it prevents the entry of harmful germs into the body.

iv) it prevents dedication (as the loss of water by evaporation is prevented).

b) Temperature regulation

 The skin helps to keep the body temperature constant.

c) Perceive changes in the surroundings

The skin contains numerous sense organs which are sensitive to temperature, touch and pain. The organism, thus, is made aware of the changes in its surroundings.

d) Synthesis of vitamin D

 by the action of sunlight.

e) The skin takes part in the excretion process. Elimination of water and salts take place during sweating through the skin.

Definition 

a) Cornified layer: 

b) Dermis: 

c) Epidermis: 

d) Keratin: 

e) Malphighian layer: 

f) Melanin:  

 Questions

1) Define skin.

2) List the function of skin

3) List four ways in which the skin serves as a protective body covering .

4) Name the two main layers of skin.

5) Name the three regions of skin epidermis.

6) Name the pigment which impart skin its colour.

7) Mention the roles of the following:

a)  Blood capillaries

b) Oil glands(sebaceous glands)

c) sweat glands 

8) Name any two glands found in human skin.

9) What is keratin ? Where it is found in the skin ?

9) Fill in the blanks:

a)  The three regions of the skin epidermis____, _____, ____  and ____.

b) Cells in the coniferous layers are ____ and are made up of____.

c) The cells in the____ layer divide constantly.

d) Dermis is made up of____ tissue.

e) Sweat glands are present in___''