The human body skin detailed description.

The skin is the body’s largest organ, serving as a protective barrier between the internal organs and the external environment. It plays a crucial role in various physiological processes, including temperature regulation, sensation, and immune defense. Here’s a detailed overview of the skin, its structure, functions, and common conditions.

Structure of the Skin
The skin is composed of three primary layers:

Epidermis: The outermost layer, which provides a waterproof barrier and creates our skin tone.
Stratum Corneum: The outermost sublayer, consisting of dead, flattened cells that are shed regularly.
Stratum Lucidum: Found only in thick skin areas like the palms and soles.
Stratum Granulosum: Where cells begin to die and form a waterproof barrier.
Stratum Spinosum: Provides strength and flexibility to the skin.
Stratum Basale: The deepest sublayer, where new skin cells are generated.
Dermis: Located beneath the epidermis, it contains tough connective tissue, hair follicles, and sweat glands.
Papillary Layer: The upper layer, which contains capillaries and sensory neurons.
Reticular Layer: The deeper layer, which provides strength and elasticity due to its dense concentration of collagen and elastin fibers.
Hypodermis (Subcutaneous Layer): The deepest layer, made of fat and connective tissue, which insulates the body and absorbs shock.
Functions of the Skin
The skin performs several vital functions:

Protection: Acts as a barrier against mechanical impacts, pathogens, and harmful substances.
Regulation: Helps regulate body temperature through sweat production and blood flow.
Sensation: Contains sensory receptors that detect touch, pressure, pain, and temperature.
Excretion: Removes waste products through sweat.
Synthesis: Produces vitamin D when exposed to sunlight.
Immune Defense: Contains cells that detect and fight off pathogens.
Skin Types and Characteristics
Skin types vary based on genetics and environmental factors:

Normal Skin: Balanced, neither too oily nor too dry, with few imperfections.
Oily Skin: Characterized by excess sebum production, leading to a shiny appearance and potential for acne.
Dry Skin: Lacks moisture, often feeling tight and rough, with a tendency to flake. Combination Skin: Features both oily and dry areas, typically with an oily T-zone (forehead, nose, and chin) and dry cheeks.
Sensitive Skin: Prone to redness, irritation, and reactions to products or environmental factors.
Common Skin Conditions
Acne: A condition where hair follicles become clogged with oil and dead skin cells, leading to pimples, blackheads, and cysts.
Eczema (Atopic Dermatitis): A chronic condition causing red, itchy, and inflamed skin. Psoriasis: An autoimmune disorder that results in the rapid buildup of skin cells, forming scales and red patches.
Rosacea: A condition that causes redness and visible blood vessels in the face.
Vitiligo: A disorder where the skin loses its pigment cells, resulting in white patches.

1. Human Anatomy & Physiology
FIFTH EDITION
Elaine N. Marieb
PowerPoint
®
Lecture Slide Presentation by Vince Austin
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Chapter 5
The Integumentary System

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Skin (Integument)
•Consists of three major regions
•Epidermis – outermost superficial region
•Dermis – middle region
•Hypodermis – deepest region

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Skin (Integument)
Figure 5.3

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Epidermis
•Composed of keratinized stratified squamous
epithelium, consisting of four distinct cell types and
four or five layers
•Cell types include keratinocytes, melanocytes,
Merkel cells, and Langerhans’ cells
•Outer portion of the skin is exposed to the external
environment and functions in protection

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Cells of the Epidermis
•Keratinocytes – produce the fibrous protein keratin
•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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•Deepest epidermal layer firmly attached to the dermis
•Consists of a single row of the youngest keratinocytes
•Cells undergo rapid division, hence its alternate name,
stratum germinativum
Layers of the Epidermis: Stratum Basale
(Basal Layer)

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Figure 5.2
Layers of the Epidermis: Stratum Basale
(Basal 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
Layers of the Epidermis: Stratum Spinosum
(Prickly Layer)

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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
Layers of the Epidermis: Stratum Granulosum
(Granular Layer)

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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
Layers of the Epidermis: Stratum Lucidium
(Clear Layer)

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•Outermost layer of keratinized cells
•Accounts for three quarters of the epidermal
thickness
•Functions
•Waterproofing
•Protection from abrasion and penetration
•Renders the body relatively insensitive to biological,
chemical, and physical assaults
Layers of the Epidermis: 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, Meissner’s
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 Structure
Figure 5.3

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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 the body;
secret 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 and secrete cerumen
•Mammary glands – specialized sweat glands that
secret milk

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Sebaceous Glands
•Soften skin when stimulated by hormones
•Simple alveolar glands found all over the body
•Secrete an oily secretion called sebum

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Hair
•Helps maintain warmth, alerts the body to presence of
insects on the skin, and guards the scalp against
physical trauma, heat loss, and sunlight
•Filamentous strands of dead keratinized cells
produced by hair follicles
•Contains hard keratin, which is tougher and more
durable than the 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

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Hair
•Pigmented by melanocytes at the base of the hair
Figure 5.6a

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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
Figure 5.6c

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Types of Hair
•Vellus – pale, fine body hair found in children and the
adult female
•Terminal – coarse, long hair of eyebrows, scalp,
axillary, and pubic regions

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Hair Growth
Hair grows at different rates on different individuals.
Hair spends 2 to 6 years in the growth phase where
keratinized cells accumulate from the hair follicle.
After this they spend several months in the resting
phase.
Following the resting phase, the hair will fall out and be
replaced by another hair.
Some people are better able to grow long hair than
others based on this phenomenon.

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Hair Thinning and Baldness
•Alopecia – hair thinning in both sexes
•True, or frank, baldness – genetically determined and sex influenced condition (i.e., male pattern baldness)
•Androgens seem to play a key role in male patterened baldeness.
•This occurs in women too. Men tend to move toward “horseshoe” pattern while women usually more
uniform thinning on the top of the head

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Nails
-Plates of tightly pack, hard, keratinized epidermal cells.
-Form a clear and solid covering over dorsal surfaces of
distal portions of digits
-Nails consist of:
Nail body: portion of nail that is visible
Free edge: portion that may extend past distal end
Nail Root: portion buried in a fold of skin

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…continued
-Most of nail body appears pink due to underlying
capillaries
-Free edge is white because of absence of underlying
capillaries
-Lunula: crescent shaped white portion at proximal end
of nail

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Structure of a Nail
•Scalelike
modification
of the epidermis
on the distal,
dorsal surface
of fingers
and toes
Figure 5.7

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Functions of the Integumentary System
•Protection – chemical, physical, and mechanical
barrier
•Body temperature
•Regulated by dilation (cooling) and constriction
(warming) of dermal vessels
•Sweat glands increase secretions to cool the body
•Cutaneous sensation – exoreceptors sense touch and
pain

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Functions of the Integumentary System
•Metabolic functions – synthesis of vitamin D in
dermal blood vessels
•Blood reservoir – skin blood vessels store up to 5%
of the body’s blood volume
•Excretion – limited amounts of nitrogenous wastes
are eliminated from the body in sweat

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Skin Cancer
•Basal cell carcinoma
•Squamous cell carcinoma
•Melanoma

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Basal Cell Carcinoma
•Least malignant and most common skin cancer
•Stratum basale cells proliferate and invade the dermis
and hypodermis
•Slow growing and do not often metastasize
•Can be cured by surgical excision in 99% of the cases

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Squamous Cell Carcinoma
•Arises from keratinocytes of stratum spinosum
•Arise most often on scalp, ears, and lower lip
•Grows rapidly and metastasizes if not removed
•Prognosis is good if treated by radiation therapy or
removed surgically

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Melanoma
•Cancer of melanocytes is the most dangerous type of
skin cancer
•Melanomas have the following characteristics
(ABCD rule):
•A: Asymmetry; the two sides of the pigmented area
do not match
•B: Border is irregular and exhibits indentations
•C: Color (pigmented area) is black, brown, tan, and
sometimes red or blue
•D: Diameter is larger than 6 mm (size of a pencil
eraser)

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Melanoma
•Treated by wide surgical excision accompanied by
immunotherapy
•Chance of survival is poor if the lesion is over 4 mm
thick

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Burns
•First-degree – only the epidermis is damaged
•Symptoms include localized redness, swelling, and
pain
•Second-degree – the epidermis and upper regions of
dermis damaged
•Symptoms mimic first degree burns, but blisters also
appear
•Third-degree – involve entire thickness of the skin
•Burned area appears gray-white, cherry red, or
black, and there is no initial edema nor pain (since
nerve endings are destroyed)

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Rule of Nines
•Estimates the severity
of burns
•Burns considered
critical if:
•Over 25% of the body
has second-degree
burns
•Over 10% of the body
has third-degree burns
•There are third-degree
burns on face, hands,
or feet
Figure 5.9a

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Developmental Aspects of the Integument: Fetal
•Epidermis develops from ectoderm
•Dermis and hypodermis develop from mesoderm
•Lanugo – downy coat of delicate hairs covering the
fetus
•Vernix caseosa – substance produced by sebaceous
glands that protects fetus’s skin in the amnion

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•Skin and hair become oilier and acne may appear
•After one reaches the 20s and 30s, skin shows the
effects of cumulative environmental assaults
•Scaling and dermatitis become more common
Developmental Aspects of the Integument:
Adolescent to Adult

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•Epidermal replacement of cells slows and skin
becomes thinner
•Skin becomes dry and itchy
•Subcutaneous fat layer diminishes, leading to
intolerance of cold
•Decreased elasticity and loss of subcutaneous tissue
leads to wrinkles
•Decreased numbers of melanocytes and
Langerhans’cells increase the risk of skin cancer
Developmental Aspects of the Integument:
Old Age