Integumentary System (2)

8/7/2019 Integumentary System (2)

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Integumentary System

Dr. Abdul Ahad Shaikh


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Introduction

The skin and its accessory structures make upthe integumentary system

A surface area of 1.5 - 2 square meters

Weighs approximately 4-5 kg (9-11 lbs.) Forms the boundary between our internal and

the external environment

It is a malleable, tough, organ that is constantly

regenerating Without skin we would succumb to infection,

water loss, or heat loss


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Functions

ProtectionChemical barrier

Physical or Mechanical barrier

Biological barrier

Body Temperature Regulation

Cutaneous Sensation

Metabolic Functions

Blood Reservoir

Excretion


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Protection

Chemical barrier Skin secretions create an acid mantle

that retard bacteria reproduction

Sebum from sebaceous glands isbactercidal

Skin cells secrete a natural antibiotic

called human defensin

Melanin shields the skin from UV

radiation


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Protection

Physical or mechanical barrier Hard keratinized cells provide a continuous

barrier

Glycolipids of the epidermis block the

diffusion of water and water solublesubstances from between cells

Substances that do penetrate the skin in

limited amounts include

Lipid soluble substances; oxygen, carbon dioxide

and fat soluble vitamins (A, D, E, and K)

Natural and manufactured solvents, salts, and

drugs


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Protection

Biological barrier Langerhans cells of the epidermis

present foreign substances

(antigens) to the white blood cells

(lymphocytes) which in turn activate

our immune system

Macrophages of the dermis dispose

of viruses and bacteria that havepenetrate the epidermis but they also

work as presenters


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Body Temperature Regulation

The body works best when itstemperature remains within homeostatic

limits

Cooling occurs through radiation of heatand evaporation of water from the

surface of the skin

Heating occurs from metabolism, activity

and shivering

Extremes of environmental temperature

threaten homeostatic balance


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Cutaneous Sensation The skin is richly supplied with cutaneous

sensory receptors

Cutaneous receptors are classified as

exteroreceptors because they respond to

external stimuli

Cutaneous receptors include

Meissners corpuscles (light touch)

Pacinian corpuscles (deep pressure

Root hair plexuses (displacement of

hair shaft)

Free nerve endings (pain)


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Metabolic Functions

Sunlight bombarding modifiescholesterol molecules in the epidermal

cells are converted to a precursor of

vitamin D

Keratinocyte enzymes can disarm

many cancer causing carcinogens

Keratinocytes can also activate steroid

hormones


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Blood Reservoir

The skin can hold about 5% of thebodys entire blood volume

Blood volume can be diverted from the

skin to other organs in need

Blood volume can be diverted to the

skin for temperature regulation


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Excretion

Limited amount of nitrogen-containing

wastes (ammonia, urea, and uric acid)

are eliminated from the body in sweat

Sweating also excretes water and salt


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omeos a c m a ances o e

Skin

Homeostatic imbalances of the skin

range from mild to life-threatening

Homeostatic imbalances are readily

visible

There are over 1000 different conditions

and ailments affecting the skin


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Burns Burns are a devastating threat to the

individual because of their effect on theskin

The threat to life severe burns is loss of

body fluids contain protein and electrolytes Fluid loss can cause dehydration and

electrolyte imbalances

These in turn can lead to renal shutdownand circulatory shock

The amount of fluid volume lost is

estimated using the rule of nines


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Burns

Estimating the area of a burn using the rule of 9s


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Primary germ layer

Epidermis, hair, nails, skin gland- Ectoderm

Dermis (connective tissue)- Mesoderm


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Structure of the skin

The superficial portion of the skin is the

epidermis and is composed of epithelial

tissue

The deeper layer of the skin is dermis and

is composed of connective tissue

Deep to the dermis is the subcutaneous

layer or hypodermis (not a part of skin)


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Skin (Integument)


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Epidermis

A thick keratinized layer of stratified

squamous epithelium

Consists of four distinct cell types

Arranged in four or five distinct celllayers


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Cells of the

Epidermis

Keratinocytes

Melanocytes

Merkel cells Langerhans

cells


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Cells of the Epidermis


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Keratinocyte

Principle cell

of the

epidermis

Seen heremigrating

upward

through

various layersof the

epidermis


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Keratinocytes

Most of the epidermal cells are keratinocytes The chief role of keratinocytes is to produce

keratin, the tough fibrous protein that gives the

epidermis its protective qualities

Tightly connected by desmosomes

Keratinocytes arise from constant cell mitosis at

the deepest layer of the epidermis

Keratinocyte cells manufacture keratin during theirmigration to the skin surface

Keratins (cytokeratins) are polymers of type I and

type II intermediate filaments, found in the

genomes of vertebrates,


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Keratinocytes (continued)

As cells migrate to the surface their contentsbecome dominated by keratin

The cells will deform to become flattened,

dead structures that are keratin filled

Million of cells on the free surface rub off daily

A totally new epidermis every 25-45 days

Cell reproduction is higher in areas subject to

friction (hands, feet)


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Melanocytes

Spider

shaped

cells found

in Stratumbasale or

basal layer


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Melanocytes

Specialized epithelial cells that synthesizethe pigment melanin

Cells are found in the deepest layer of the

epidermis

Melancytes have many branching processes

that touch all keratinocytes in the basal layer

Processes carry melanin to keratinocytes

Melanin granules accumulate on the super-

ficial side of the nucleus of the ketatinocytes


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Melanocytes Melanin granules form a pigment shield that protects

the nucleus from ultraviolet (UV) radiation in sunlight

All humans have the same amount of melanocytes

Racial differences in skin coloring is thought to reflect

the kind and amount of melanin made and retained

Production of melanin is stimulated by DNA damageinduced by UVB-radiation

The photochemical properties of melanin make it an

excellent photoprotectant.

It absorbs harmful UV-radiation and transforms theenergy into harmless heat through a process called

"ultrafast internal conversion". This property enables

melanin to dissipate more than 99.9% of the

absorbed UV radiation as heat


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Langerhans

Cells

Star shaped

cells amongkeratinocytes


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Merkel

Cells

Spiky shaped

hemispheres

found at theepidermal -

dermal

junction


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Merkel Cells

Each Merkel cell is associated with adisc shaped sensory nerve ending

The combined structure is called a

Merkel disc Merkel discs function as a sensory

nerve receptor for touch


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Epidermal

layers

Four layers

in thin skin Covers most

of the body


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Epidermal

Layers Five layers

found in

thick skin

Stratum

lucidum is

extra layer

Found onfingertips,

palms and

soles of

feet


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Stratum

basale Deep layer

attached to

underlying

dermis

Singe row

of

youngest

cells

Ongoing

cell mitosis


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Deepest epidermal layer firmly attached to

the dermis

Consists of a single row of the youngestkeratinocytes

Cells undergo rapid division, hence its

alternate name, stratum germinativum

Stratum Basale (Basal Layer)


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Stratum Basale (Basal Layer)


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Stratum

spinosum Several cell

layers thick

Cells

contain a

web-like

system of

filaments

Abundant

Langerhans

cells in this

layer


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Cells contain a weblike system of

intermediate filaments attached to

desmosomes

Melanin granules and Langerhans cells

are abundant in this layer

Stratum Spinosum (Prickly Layer)


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Stratum

granulosum

Area of 3-5

cell layers

Ketatinocytes

flatten and

begin to

disintegrate

Release ofglycolipid

slows water

loss

Cell binding


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Thin; three to five cell layers in which

drastic changes in keratinocyte

appearance occurs

Keratohyaline and lamellated granules

accumulate in the cells of this layer

Stratum Granulosum (Granular Layer)


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Stratum

lucidum Consist of

a few rows

of clear,

flat, deadcells

Present

only in

thick skin


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Thin, transparent band superficial to the

stratum granulosum

Consists of a few rows of flat, dead

keratinocytes

Present only in thick skin

Stratum Lucidum (Clear Layer)


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Stratum

corneum Broad zone

20-30 cell

layers thick

3/4 of

epidermal

thickness

Protectsskin from

abrasion &

penetration


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Outermost layer of keratinized cells

Accounts for three quarters of the epidermal

thickness

Functions include:

Waterproofing

Protection from abrasion and penetration

Rendering the body relatively insensitive tobiological, chemical, and physical assaults

Stratum Corneum (Horny Layer)


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Dermis

Second major skin region containing

strong, flexible connective tissue

Cell types include fibroblasts,macrophages, and occasionally mast cells

and white blood cells

Composed of two layers papillary and

reticular


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Layers of the Dermis: Papillary

Layer Papillary layer Areolar connective tissue with collagen

and elastic fibers Its superior surface contains peglike

projections called dermal papillae

Dermal papillae contain capillary loops,

Meissners corpuscles, and free nerve

endings


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Layers of the Dermis: Reticular

Layer Reticular layer Accounts for approximately 80% of the

thickness of the skin Collagen fibers in this layer add strength

and resiliency to the skin

Elastin fibers provide stretch-recoil

properties


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Hypodermis

Subcutaneous layer deep to the skin

Composed of adipose and areolar

connective tissue


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Skin Color

Three pigments contribute to skin color

Melanin yellow to reddish-brown to black

pigment, responsible for dark skin colors

Freckles and pigmented moles result

from local accumulations of melanin

Carotene yellow to orange pigment, most

obvious in the palms and soles of the feet Hemoglobin reddish pigment responsible

for the pinkish hue of the skin


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Sweat Glands

Different types prevent overheating of thebody; secrete cerumen and milk

Eccrine sweat glands found in palms, soles

of the feet, and forehead Apocrine sweat glands found in axillary and

anogenital areas

Ceruminous glands modified apocrine

glands in external ear canal that secretecerumen

Mammary glands specialized sweat glands

that secrete milk


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Sebaceous Glands

Simple alveolar glands found all over the

body

Soften skin when stimulated by hormones Secrete an oily secretion called sebum


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Structure of a Nail

Scalelike modification of the epidermis on

the distal, dorsal surface of fingers and

toes

Figure 5.4


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Hair

Filamentous strands of dead keratinized

cells produced by hair follicles

Contains hard keratin which is tougher andmore durable than soft keratin of the skin

Made up of the shaft projecting from the

skin, and the root embedded in the skin

Consists of a core called the medulla, a

cortex, and an outermost cuticle

Pigmented by melanocytes at the base of

the hair


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Hair Follicle

Root sheath extending from the epidermal

surface into the dermis

Deep end is expanded forming a hair bulb A knot of sensory nerve endings (a root

hair plexus) wraps around each hair bulb

Bending a hair stimulates these endings,

hence our hairs act as sensitive touch

receptors


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Hair Follicle


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Hair Follicle

Date post:	09-Apr-2018
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Integumentary System (2)

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