•The integumentary system includes skin and its appendages (hair,nails, sweat glands and sebaceous glands).
•The meaning of word integumentary "covering".
• Skin is also referred to as the cutaneous membrane, an outermost protective covering of the body.
•integumentary system covers 3,000 square inches of surface area in average adult.
Skin
Skin is the largest organ of human body.
•It is also known as the integument.
•It has a surface area of 1.8m and comprises of 16% of the total body weight)
• Skin performs various functions out of which, the most important one is its action as a barrier to the external environment during selective inward and outward movement of water, electrolytes, etc.
• It also provides protection by restricting the entry of microbes, UV rays, harmful chemicals and mechanical wear and tear).
•The skin is made up of three distinct structural layers, viz.,
epidermis,
dermis, and
hypodermis.
• The derivatives of skin include nails, hair. sebaceous gland, and sweat glands,")
Structure of skin
Skin is the thick, protective covering of body which comprises of the
following layers:
1) Epidermis: It is the outermost covering of stratified squamous epithelial tissue, lacking blood vessels. The major portion of epidermis is made up of keratinocytes (cells).
• it is made up of keratinized stratified squamous epithelium.
• the epidermis is a layer that gives strength to the skin.
• various in thickness from a few cell eyelids to dozens of cell thick (palm and soles of feet)
•it does not have any vascularisation.
sweet relies on absorption Oxygen and nutrients from the blood vessels of dermis deep to it.
• the nails are made in the epidermis.
a) Stratum basale :-
It has four types of cells are :-
i) keratinocyte cell -
keratin is a protein made up of these cells.
• keratin is waterproof and strong
ii) Merkel cells :-
• use a sensory receptor for the sense of light touch.
iii) Macrophages :-
It help to inject Debris.
iv) Melanocytes :-
•Produce melanin
•Everyone has the same number of melanocytes.
•But they don't all make some amount of pigment so people have different skin colour.
b ) Stratum spinosjm
•they are not attached to each other by desmosomes which are pointy/ spiny.
•The cells are still alive but no longer divide in this layer.
•They are not dead just in menopause.
• also contain lengerhan's white blood cells that function in the immune response.
•They are made in red bone marrow.
• the stratum spinosum provide the strength to the epidermis.
c) Stratum Granulosum :-
• A more new cells are made in streatham basil the state I'm spinosum layer is pushed up to become the s.granulosum layer.
• the cell in the sratum granulosum begin to die because they are now too far from nutrient source in dermis.
• The cell now have a grainy appearance so this layer is called s.granulosum.
d) Stratum corneum :-
• as more new cells are made in s basal the cell are all pushed up again and the s.granulosum layer becomes the s.cornium.
• In this layer the dead cell fill up with keratin.
• The cellar lose the nucleus and fuse to squamous sheets, which are said from the surface in about two weeks, this process is called deshquamation.
Main difference of thick skin and thin skin related to thickness of the stratum corneum.
• it takes about 15-30 days cell to move from the s.basale to s.corneum and another to week for it to shed.
• We lose half a million cell per hour 1.5 gram a day.
• that can be major source of dust in the house.
2.) Dermis :-
In dermis there is a two layers are :-
i) papillary layer (pimple has bumps this is more superficial layer.
ii) Reticular layer.
i) papillary layer :-
• papillary layer papillary means pimple.
• papillary layer of dermis; loose connective tissue.
• has ridges to increase surface area for contact with epidermis because the blood vessels and nutrients from them are only in the dermis.
• the papillary layer in the dermis is what forms our fingerprints.
• surgeons make in incision on the body based on the lines of cleavage of the skin formed by the papillary layer of the dermis.
ii) Reticular layer
• Dense irregular connective tissue.
• Gives the dermis its strength.
• Remember the epidermis is the the strongest layer of the skin stratum spinosum is the strongest layer of the epidermis. But the reticular layer of the dermis is the strongest layer of the dermis.
• the dermis and lost lots of collagen and elastin.
The dermis where is most of the body collagen is found.
• Stretch marks are caused from tiny tears in the collasion of the dermis.
• leather is made of the dermis.
• the dermis is also the area where all the skin glands of the body are locate.
• The blood vessels in the dermis are what gives a pink colour.
iii) Hypodermis
• this is the fat layer it layer tremendously in thickness shins=thin buttocks= thick.
• it also contain fibrous tissue blood vessels and nerves and sits on the top of the muscle.
Function
• stores fat
• Cushions
• Insulation from cold because of heat produced by the layer blood vessels in this layer.
FUNCTION OF THE SKIN
i) protection = physical barrier that protects underlying tissue from injury ultraviolet light and bacterial invasion.
• mechanical barriers part non specific immunity (skin tears and saliva)
ii) Regulation of body temperature = high temperature or strenuous exercise sweat is evaporated from the skin surface to cool it down.
• vasodilation (increase blood flow) and ra vasoconstriction (decrease in blood flow) regulate body temperature.
iii) Sensation - nerve ending and receptor cells that detect extremely to temperature, pain, pressure and touch.
iv) Excretion
• sweat removes water and small amount of salt, uric acid and ammonia from the body surface.
v) Blood reservoir -
• dermis houses and extensive network of blood vessels carrying 8 - 10% of blood total blood flow in a resting adult.
vi) Synthesis of vitamin D ( cholecalciferol)
• UV rays in sunlight stimulate the production of vitamin D. enzyme in the kidney and liver modify and convert to final form.
• Calcitriol aids in absorption of calcium from foods and is considered a hormone.
Accessory Structure of skin
Accessory structure of skin derived from the epidermis these are necessary structure also known as appendages of skin.
These include
1. Nails
2. Hair
3. Sweat gland
4. Sebaceus gland
Structure of Nails
1) Nail plate
• it is translucent(transparent) part which is commonly referred to as nail.
• it is horney layer of skin, devoid of living cell
• it is strong and flexible.
• The keratin sheets are closely linked.
• the lipid contact of nails 0.15 - 0.75% which is lower than that in horny layer of the skin while the sulphur content in approx 3% which is higher than that of the skin keratin.
• nail matrix produce cells that becomes the nail plate.
2) Nail bed
• nail require substantial amount of moisture to remain healthy.
• the water content in nail is maintained by nail bed.
• it also plays an important role in the growth of nail in proper direction along the nail wall.
3) Lunula
• It is the path of matrix that is visible
• It is crescent-shaped milky white area at the root of nail and is is not fully keratinised.
• It is software as compared to the other nail part.
4) Nail wall
• It is dead part of the skin that surrounds the nail
• The eponychium is that part of the skin which touch the root of the nails.
• It main function is to protect the newly formed nail.
FUNCTION OF NAIL
• Nail primarily act as a barrier to the loss or influx of water.
• They protect the nerve ending.
• they receive the stimulus of touch and pressure or pain through the receptor present on the site.
HAIR:-
• the hair follicle is a sensing reative and multilayer skin.
• hair growth is a distant and multi phased process that include a continuous cycle of growth reabsorption rest and renewal.
Structure
• Hair follicles are found during first trimester of pregnancy.
• They are formed by the the epidermal dermal interaction.
• Externally the hair follicle is divided into 3 segment.
i) infundibulum - it extends from the surface opening of the follicle to the level of the opening of its sabaceous gland.
ii) Isthmus - extends from the infundibulum to the level of in short of the arrector pili muscles.
iii) Inferior Segment
• the part in which the growing follicle is nearly uniform in diameter at its base where it expands to form the bulb.
• the base of the bulb is invaginated by the top of vascularized loose connective tissue called dermal papilla.
A cross-sectional structure of hair and hair follicles
a) sebaceous glands :- this gland secretes sebum does helping in lubrication and production of scalp and hair.
b) Arrector pili :- these muscles are involuntary muscles controlled by autonomic nervous system.
c) Hair shaft :- it refers to the part of the hair present outside the skin surface.
The part of their within the skin surface is called hair root.
d) hair bulb :- A bulb like structure present at the end of hair root is called hair bulb.
FUNCTION -
• The hair on the head protect the scalp from ultraviolet light from a cushion around the head and insulate the skull.
• eyebrows protect the eyes from the small foreign particle and insects.
• body hair help in evaporation of perforation and drain the external water from the body.
Sweat Glands :-
sweat gland comprises of a small tube like structure which originates in the form of a coil in the deep dermis or superficial subcutaneous layer of the skin.
Sweat :-
Sweat mainly contain water about 99% and other constituents like salt (Mainly sodium chloride) ascorbic acid or (vitamin c).
Function of sweat gland
These glands actively participate in the thermoregulation.
Sweat has antimicrobial properties.
Sebaceous glands ( holocrine glands)
are associated with hair follicles and secret Sebum that waterproof and most prized the hair shaft.
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