Download Integumentary system

The integumentary system (skin) Roles:

protection

maintenance of normal body temperature

storage (of fat)

synthesis (of vitamin D)

excretion (of salts, water and wastes in sweat)

sensory perception
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General Structure of the skin

Three distinct regions or layers compose the skin:

Epidermis squamous ET.

Dermis - inner layer;
keratinized
epithelium
(hair
follicles), glandular epithelium (sweat, sebaceous glands),
dense irregular CT (collagen), smooth muscle tissue
(arrector pili muscles), nervous tissue (Meissner's &
Pacinian Corpuscles), and blood vessels.

Hypodermis (Subcutaneous) layer - adipose tissue;
distinct layer beneath skin.
outermost
layer;
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keratinized
stratified

Each skin layer has its own unique function:

Epidermis - protection;

Dermis - nourishment of epidermis;

Subcutaneous layer - insulation.
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Cells of the Epidermis




Keratinocytes – produce the
fibrous protein keratin that give
the epidermis its protective
properties
Melanocytes – produce the brown
pigment melanin
Langerhans’ cells – epidermal
macrophages that help activate the
immune system
Merkel cells – function as touch
receptors in association with
sensory nerve endings
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Figure 5.2b
Layers of the epidermis


Stratum basale - innermost layer;

single layer of cuboidal youngest keratinocytes.

This layer is constantly undergoing cell division and
produces new cells; also called stratum germinativum

contains melanocytes
Stratum spinosum - several spiky-like layers.

The cells divide relatively fast.
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Layers of the epidermis


Stratum granulosum

It is composed of 3-5 layers of flattened granular cells
(filled with keratin); abundant granules

at the upper border of this layer the cells begin to die.
Stratum lucidum - composed of flattened dead
keranocytes.

transparent band superficial to the stratum
granulosum

Present only in thick skin
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Layers of the epidermis

Stratum corneum

Outermost layer of keratinized cells, consists of 2030 layers of cells

Accounts for three quarters of the epidermal
thickness

Protective layer
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http://sprojects.mmi.mcgill.ca/dermatology/epidermis.htm
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
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

reticular
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Layers of the Dermis: Papillary Layer

Papillary layer – 20% of the dermis

Areolar connective tissue with collagen and elastic
fibers

Its superior surface contains finger-like projections
called dermal papillae

Dermal papillae contain capillary loops, Meissner’s
corpuscles, and free nerve endings
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Layers of the Dermis: Reticular Layer

Accounts for approximately 80% of the thickness
of the skin

Composed of dense irregular CT

Collagen fibers in this layer add strength and
resiliency to the skin

Elastin fibers provide stretch-recoil properties

Contains the Pacinian corpuscle
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
Meissner's Corpuscle's located in dermal papillae;
found in the fingertips, palms, soles, eyelids, tip of
tongue, nipples, clitoris, tip of penis.


Light touch
http://www.siumed.edu/~dking2/intro/IN038b.htm
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Pacinian corpuscle's located in deep dermis and subcutaneous
regions;
 Populate areas in the joints, tendons, muscles, mammary
glands, and external genitalia.
 Pressure

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http://www.siumed.edu/~dking2/intro/IN039b.htm
Hypodermis

Subcutaneous layer deep to the skin

Composed of adipose and areolar connective tissue
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Sweat Glands - Eccrine Glands (also called merocrine)

Structure - coil in deep dermis; duct in dermis

Characteristics - respond to elevated temperature /
exercise; no odor in secretion; function throughout life; not
associated with hair follicles;

Location - all over body

Secretion - water plus salts and wastes (urea and uric acid),
oddorless

Mode of secretion – exocytosis (merocrine)
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Apocrine glands

Structure - ducts terminate into hair follicles.

Characteristics - respond to stress / emotions; odor in
secretion; begin to function at puberty & continue
through life; associated with hair follicles.

Location - armpits; genital areas;

Secretion - milky protein and fat-rich substance.
Odorless but when combined with molecules on skin,
takes the typical “sweat odor”

Mode of secretion – exocytosis (merocrine)
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Modified Apocrine Glands

Ceruminous glands - external ear; secretion earwax;

Mammary glands - breasts; milk.
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Sebaceous Glands

Location - found nearly all over skin; associated
with every hair follicle

Secretion - sebum (i.e. oil and fragmented cells).
Sebum is secreted into hair follicle;

Mode of secretion – holocrine (cells burst)


Secretion is stimulated by hormones especially
androgens.
Function oily substance keeps skin & hair soft and
moist and waterproof.
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
http://www.sweatmanagement.ca/UnderstandSW.asp
Hair Function and Distribution


Functions of hair include:

Helping to maintain warmth

protection
Hair is distributed over the entire skin surface except:

Palms, soles, lips, nipples and portions of the
external genitalia
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Hair parts

The shaft, which projects from the skin

Root or base is in deep dermis


Papilla – a small nipple of dermal tissue that enters into the
hair bulb from the connective tissue sheath and provides
nutrition to the growing hair.
Arrector Pili Muscle - a bundle of smooth muscle
associated with every hair follicle; causes hair to stand on
end ("goose bumps") when frightened or cold.
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Hair root

A hair has three concentric
layers of keratinized cells:
 Medulla,
consists of
large cells and air spaces.
 The
cortex, a bulky
layer surrounding the
medulla, consists of
several layers of flattened
cells.
 The outermost cuticle is
formed from a single
layer of cells that overlap
one another from below
like shingles on a roof
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 5.5c, d
Hair structure - Follicle

A structure formed from both epidermis and dermis.

The follicle is the point from which the hair grows. It is
well supplied with minute blood vessels, and the blood
passing through them nourishes the growing region

The follicle is composed of:

A connective tissue root sheath derived from the
dermis

A basement membrane (glassy membrane)

Inner epithelial root sheath derived from the
epidermis
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Hair bulb

The hair bulb lies inside the hair follicle.

It is a structure of actively growing cells. New cells are
continuously produced in the lower part of the bulb.

As they grow and develop they steadily push the
previously formed cells upwards.
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Nails
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Nails are derivates of the stratum corneum undergoing
keratinization (active mitosis in lunula).

Functions: protection of digit ends.

Body the visible attached portion;

Free edge – the portion that grows away from the body;


Root – the part that is in the skin and adheres to an
epithelial nail bed;
Nail matrix – the part of the nail bed containing germinal
cells responsible for nail growth.
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Structure of a Nail
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Figure 5.6