Std 9 Modified Skin Notes PDF

SMT SULOCHANADEVI SINGHANIA SCHOOL, THANE STD 1X SUB: BIOLOGY TOPIC – SKIN -- THE JACK OF ALL TRADES Skin is the largest organ of our body. It accounts for 15% of an adult human’s total body weight. Skin is the outerm...

SMT SULOCHANADEVI SINGHANIA SCHOOL, THANE STD 1X SUB: BIOLOGY TOPIC – SKIN -- THE JACK OF ALL TRADES Skin is the largest organ of our body. It accounts for 15% of an adult human’s total body weight. Skin is the outermost covering of the body and is stretched all over to form a layer. Skin is an impermeable barrier. Functions of Skin /Integument - 1. Protection – is the primary function in which – a. Protect underlying tissues from mechanical shocks. b. Holds the body fluids inside and prevents excessive loss of water by evaporation. c. Prevents entry of harmful substances /disease causing germs. d. Protects the body against excess ultraviolet light which is potentially very harmful. 2. Sensation – as the skin is a sense organ and receives sensation for touch, pain, pressure, heat etc. 3. Temperature regulation – by preventing loss of heat in cold weather and facilitates loss of heat in hot weather. 4. Storage of food – by skin in the form of a layer of fat contained in special cells. 5. Excretion – by eliminating water in the form of sweat, salts, urea. 6. Synthesis of Vitamin D- when skin is exposed to sunlight. 7. Skin on the fingers and palms forms ridges and grooves which provides more efficient grip. Vertical section of Human skin  Structure of the skin – Skin Proper is made up of – A. Epidermis – made up of - a. Cornified layer b. Granular layer c. Germinative layer B. Dermis – made up of – Elastic fibres , Blood vessels , Nerves. A. Epidermis- Location - Outer thinner part Structure - Formed of stratified epithelium piled up layer after layer. Epidermis is thick and hard on palms, soles and heels, devoid of blood vessels. The epidermis is divided into three regions – a. Outer Cornified layer, b. Middle Granular layer c. Inner Malpighian layer a. Cornified layer – Stratum corneum Location - Outer most layer Structure - Layer of flattened dead cells, made up of horny protein –Keratin. The cells are continually worn out or shed and replaced from beneath by those arising from the deeper Malpighian layer. Found in – Nails, Hair, horns, Hoofs and Silk Function - i. Tough and offer resistance against mechanical damage ii. Bacterial infection iii. Loss of water by evaporation b. Granular layer- Location- Middle layer Structure - Thin consists of two or three sub- layers of flattened cells Function – To give way to the outer cornified layer. c. Malpighian layer /Stratum Malpighi/ Germinative layer – Location- Innermost region of the epidermis. Structure - Cells can actively divide to produce new cells which press and shift outward to replace worn out cells of the outermost cornified layer. Function - Colouration of the skin is due to pigment – Melanin, in the cells of Malpighian layer. Continued exposure to sunlight, the face and body parts are tanned, but revert to original conditions when exposure is cut down. GR --- The skin pigment acts like an umbrella. Ans- To protect inner parts of the body from harmful effects of ultraviolet rays of sunlight. Abnormal Conditions of Skin Pigmentation – a. Leucoderma /Vitiligo – Skin pigmentation is lost in from of small /large patches from different parts of the body. Cause- Not exactly known. b. Albinism – Complete loss of pigmentation of the skin all over the body including hair, eyebrows, eyelashes and even Iris. The skin of a person appears pinkish as the underlying blood capillaries are exposed. Cause- A recessive trait due to inheritance. Dermis Location- Inner to epidermis Structure - Thick layer of connective tissue made up of elastic fibres, tough and flexible. The dermis of skin is very thick on palms and soles, very thin on the eyelids. The dermis contains structures – blood vessels, nerve fibres, sensory receptors, hair follicles, sweat gland. Outer region of the dermis lies next to the epidermis, raised into numerous small processes – papillae, contain the blood capillaries and nerve endings. The nerve ending and sense organs concerned with sensations of touch and pain. The sharp sense of touch in the skin of finger tips enables blind to read the Braille character. Sensory receptors in the deeper parts concerned with the sensations of pressure, pain, heat, cold. GR. The layer beneath the dermis contains numerous fat cells. Ans- As it is subcutaneous fat which not only serves as food reserve, but also as a heat insulating layer and shock absorber. Label the parts:-