Anatomy&Physiology of Skin

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Anatomy andAnatomy andPhysiology of skinPhysiology of skin

Anatomy andAnatomy andPhysiology of skinPhysiology of skin


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Basic structure and function


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SKIN

Largest, Thinnest, Important organ. Self-Repairing and protective boundary.

Surface area: 2m (approx).

Depth 0.5 -4.0mm: thickness dependson location.

It is classified into:-1. EPIDERMIS2. DERMIS


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EPIDERMIS Epithelial layer derived fromectodermal germ layer. Superficial and thinner layer. Includes Also hairs, sweat glands,

sebaceous glands. Avascular tissue, made up of

keratinocytes that germinate in the

lowest layer and migrate towards thesurface whilst changing in character. 4-5 layers depending on location. Protective and regulatory functions.


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THICK AND THINSKIN

-The hairless skin covering the palms ofhands, soles of feet and other bodysurface subjected to friction is calledthe thick skin.

-Hairs are not found in thick skin.

-Each of 5 strata of epidermis arepresent.-Outermost stratum- stratum corneum is

especially noticeable in thick skin.

-In thick skin underlying dermal papillaeare raised in curving ridges to formFINGER PRINTS or FOOTPRINTS.

-These helps in pick up and manipulatesmall objects with hands and provide

slip resistance to soles of feet.


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THIN SKIN

- Most of the body surface iscovered by thin skin.

- Number of cell layers of epidermisare less than that of thick skin.

- One or more strata may be absent.

- Raised curved papillae are notpresent.


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CELL TYPES

K

ERATIN

OC

YTES

become filled witha tough, fibrous protein calledkeratin.

-More than 90% of epidermal cells.-Principal structure element of outer

skin. MELANOCYTES contribute color to

the skin.

-Decrease the amount of UV rays thatcan penetrate into deeper layers ofskin.

- More than 5% of epidermal cells.- Melanocytes may be completely

absent from skin called VITILIGO.


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- LANGERHANS CELLS dendritic cells,branched cells that play role inimmunity.

- These cells originate in bone marrow

but migrate to deep cell layers ofepidermis early in life.

- Merkel cells: touchsensitive.

- Merkel discs: tactile disc.


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CELLLAYERS1. STRATUM BASALE ( base layer ) :-

-primary layer-Single layer of columnar cells.-Cells of deepest stratum of epithelial undergo

MITOSIS.-As a result cells transfer or migrate from basallayer to the other layer until they are shedfrom the skin surface.

-contains stem cells connected to the papillary

layer of the dermisregenerating layercontains some sensory cells (Merkelsdiscs)contains melanocytes (25%)


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2. STRATUM SPINOSUM(spiny layer)

-Formed from 8-10 layers of irregularlyshaped cells with very prominent bridgesor desmosomes.

-The desmosomes appear to pull points of

the plasma membrane of adjoining cellstoward are another.-This gives cells of this layer a spiny or

prickly appearance, prickly layer.

- Rich in RNA.- The term stratum germinativum (growth

layer) is often used to describe thestratum basale and stratum spinosum

together.


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3. STRATUM GRANULOSM(granular layer) :-

granular layer contain keratohylin-a precursor to

keratin. Process of surface keratinformation begins

cells take on protective function in

this layer degeneration of cell nucleus begins-some cell death occurs.

Cells are arranged in a sheet.


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4. STRATUM LUCIDUM(clear layer)

friction layer.The kertinocytes in this layer are

flats, closely packed and clear.

Typically nuclei are absent.Filled with a substance called ELEIDIN,

which will be transformed to keratin.This layer is absent in thin skin but is

apparent in section of thick skin.3 -5 cells deephigh friction, non-haired areas -eg

soles,


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5. STRATUM CORNEUM(horny layer)

- Superficial layer.- composed of very thin squamous cells.- Continually being shed and replaced.- Cytoplasm in these cells has been replaced by a dense

network of keratin fibers.

-The process by which cells in this layer are formedfrom cells in deeper layer of epidermis and thenfilled with keratin and moved to the surface is calledas KERATINIZATION.

-The stratum corneum is sometimes called the barrierarea of the skin because it function as a barrier to

water loss and to many microorganism and harmfulchemicals. Once this barrier layer is damaged, theeffectiveness of skin as a protective covering isgreatly reduced.

- Sometimes certain diseases of skin cause thethickening of this layer more than normal limits

called hyperkeratosis.


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EPIDERMALGROWTH ANDREPAIR

- Turnover time and regeneration time areterms used to describe the period requiredfor a population of cells to mature andreproduce.

- Lost cells are replaced by mitotic activity.- New cells are formed at the same ratethat old keratinized cells flake off fromthe stratum corneum, to maintain a

constant thickness of the epidermis. Current research suggest that regenerationtime required for completion of mitosis, isabout 35 days.


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The process can be accelerated byabrasion of skin surface, which

tend to peel off a few of the celllayers of stratum corneum.

If the abrasion continues over a

prolonged time, the increase inmitotic activity and shortenedturnover time will result in anabnormally thick stratum corneum

and development of callus. Normally about 10% to 12% of allcells in the stratum basal entermitosis each day.


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DERMAL-EPIDERMALJUNCTION

Area between the epidermis anddermis.

The junction glues the 2 layers

together and provides mechanicalsupport for the epidermis. Partial barrier for passage of somecells and large molecules.

Any detachment of large area ofepidermis from dermis is an extremelyserious condition that may result indeath.


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DERMIS- Deeper and thicker layer.- Derived from mesoderm.- Dense and vascular connective tissue layer- Thickness 4mm- Thinnest on eyelids and penis where thickness

is about 0.5mm.- Provide mechanical strength to skin.-A specialized network of nerves and nerve

endings in dermis is called as somatic sensory

receptors, which gives the sensory informationsuch as pain, pressure touch and temperature.- It is rich in vascular supply.-Plays important role in regulation of body

temperature.


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RETICULAR LAYER Consists of dense reticulum or network of

fibers. Most of the fibers are of collagenous type

which gives the toughness to skin. Elastic fibers are also present. It is point of attachment for skeletal &

smooth muscle fibers It helps in giving facial expression &

voluntary movement of scalp. In this area arrector pili muscles are

present, Contraction of these muscle makethe hair stand on end-as in extreme fear& cold we called it as Goosebumps.


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DERMALGROWTH AND

REPAIR Dermis does not continually shed and

regenerate. In wound healing, the regeneration of dermis

takes. In dermis, fibroblast quickly reproduce & formdense mass of new connective tissue fiber.

If the dense mass is not replaced by normal

tissue, it remain as a scar. If the elastic fibers in the dermis arestretched too much these fibers will weaken &tear that will result as a stretch marks


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Physiology of Skin

PROTECTIVE FUNCTIONSSkin forms the covering of all the

organs of the body & protectsthese organs from the followingfactors:

Bacteria and toxic substances.

Mechanical blow. U.V. rays.


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Protection from Bacteria andToxic Substances

Skin covers the organs of the bodyand protects the organs from having

direct contact with external

environment.

The keratinized stratum corneum

layer of epidermis is responsible for

the protective function of skin. This

layer also offers resistance to the

skin against toxic chemicals like

acids and alkalies.


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Protection from Mechanical Blow

The skin is not tightly placed over

the underlying organs or tissues.

It is some what loose and movesover the underlying subcutaneous

tissues. So the mechanical impact

of any blow to the skin is nottransmitted to the underlying

tissues.


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Protection from U.V. Rays.

Exposure to sunlight causes increased production of

melanin pigment in skin. This absorb U.V. rays.

At the same time the thickness of stratum corneum

is increased. This layer also absorbs U.V. rays.


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General sensation

Skin is considered as the largest sense

organ in the body. It has many nerveendings which are specialized to formcutaneous receptors .


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Storage

The dermis as well as thesubcutaneous tissue can store fats,water ,salts, glucose and suchother substances.

It can also store the blood by thedilation of blood vessels.


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Vitamin D productionThe first step in the production of vitamin D in the

body occurs when the skin in exposed to U.V. light.7- dehydrocholestrol

Cholecalciferol ( Vit D3 )

25- hydroxyl cholecalciferol

1,25-hydroxycholecalciferol

Active form


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ExcretionThrough sweat and insensibleperspiration, salts and metabolitesare excreted to some extent.

Excess sweating may lead to lowblood Na levels (hyponatremia)


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Secretion

Sweat

Sebum


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Absorption

Water absorption causing swelling ofthe stratum corneum.

Lipids are easily permeable to skin likevitamins.

Some drugs in transdermal patchs eg.Hormone replacement therapy during themenopause

Some toxic chemicals eg. mercury


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IMMUNITY

The epidermis containsspecialised immune cells calledLANGERHANS CELLS.

They phagocytose interdusingAntigens & travel to lymphoidtissue where they present

Antigen to T-lymphocytesthus stimulating an immuneresponse.


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REGULATION OF BODY

TEMPERATURE A Set point of body temp. is 37c . It

may increase to 37.6C by lateafternoon & decrease to 36.2C byearly morning.

The homeostatic regulation of bodytemp. in two ways:

By liberating sweat at its surfaceBy adjusting the flow of blood indermis


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HEAT PRODUCTION

BY MEANS OF

Metabolism of foodsDuring exercise

S

hivering


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HEATLOSS

Heat loss can be regulated by alteringthe flow of blood in the skin .

If heat must be conserved, dermal bloodvessels constrict to keep the warm bloodcirculating in body.

Heat can be transferred to the externalenvironment through the physical process


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EVAPORATION

Evaporation of waterconstitute one

method by whichheat is lost from thebody, especially fromthe body


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RADIATION

Heat radiate from the body surfaceto nearby object that are coolerthan skin.

CONDUCTION Conduction means the transfer of

heat to any substance actually incontact with the body; To clothingor jewelry, Even to cold foods.


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CONVECTION

It is transfer of heat away from a surfaceby movement of heated air or fluidparticles.

For examples:-If you have ever stepped fromyour shower into even slightly moving air

from an open window.


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HOMEOSTATIC REGULATION OF

HEATLOSS Temperature receptors in a part of the

brain called Hypothalamus detectchanges in the body the bodys internal

temperature. Above the set point i.e.370 C.

The hypothalamus acts as an integratorand sends a nervous signal to the sweat

glands and blood vessels of the skin. Sweat glands increase their output

sweat and blood vessels increase theirdiameter.


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Skin Color Melanin: The main determinant of

skin color is the quantity of themelanin deposited in the cells ofthe epidermis.

Two groups of melanin are made bythe melanocytes of the body.

Eumelanin: true black substance. Pheomelanin: dusky back substance.


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FACTORS AFFECTING SKINCOLOR

GE

NE

Sprolonged exposure ACTH

to sunlight

Melanocytes synthesis of

melanin

type & quality of melanin deposited inepidermis

Unoxgen. Hb skin color vol. Of blood

F ti f ki


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Functions of skin

Function Example Mechanism

Protection From microorganism

From dehydrationFrom u.v. rays

From mechanicaltrauma

Surface film/

mechanical barrier.Keratin

Melanin

Tissue strength

Sensation PainHeat &coldPressureTouch

Somatic sensoryreceptors.

Permit movement andgrowth without injury

Body growth andchange in body contoursduring movements

Elastic and recoilproperties of skin andsubcutaneous tissue.

Endocorine Vitamin D production Activation of precursorcompound in skin cell byU.V. rays

Excretion WaterUreaAmmoniaUricacid

Regulation of sweatvolume and content

Immunity Destruction of microbes Phagocytic cells andlangerhans cells

Temperature regulation Heat loss or retention Regulation of blood flowto skin and evaporation

of sweat.


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Thank You

Anatomy&Physiology of Skin

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