What is it?
The skin and its derivatives (sweat and oil
glands, hair and nails) serve a number of
functions, mostly protective.
• Epidermis – outer layer
– Stratified squamous
– Often keratinized
(hardened by keratin)
– Dense connective tissue
• 16% of your total body weight
• First line of defense against microorganisms
• Irradiated by sunlight
• 1.5-2 M squared in area
• There are 2 major components: 1)
cutaneous membrane (skin) and 2)
accessory structures (nails, hair and
• Or cornification, is the formation of
protective , superficial layers of cells filled
Functions of SKIN or
1. Protection- of underlying tissues and organs
from fluid loss, abrasion and impact and
chemical attack and microbial infection.
2. Excretion- of salts, water and organic wastes
and by integumentary glands.
3. Maintenance- of body temperature…via
evaporation or insulation( Keratin)
4. Synthesis of Vitamin D3, a steroid, a hormone
necessary for normal calcium absorption.
5. Detection of touch, pressure, pain…general
senses that are relayed to the central nervous
SKIN: 2 TISSUES
• 1. Epidermis- Contains either 4 or 5 layers
depending on if THIN or THICK skin.
• THIN: covers most of body ( 4 layers)(.08mm)
• THICK: soles of feet, palms of hands (.5mm) (5
• Stratum: 1. germantivum(basale) 2. spinosum,
3.granulosum, 4. Lucidum (only in thick skin),
• Example: Stratum germativum (basale)for 1st
1) Papillary Layer- Consists of Areolar
Tissue. Contains capillaries, lymphatics, and
sensory neurons that supply the surface of the
skin. Projections: Dermal Papillae.
2) Reticular Layer- deep to the PL,
Contains blood vessels, deep pressure receptors
called* Pacinian corpuscles and Macrophages.
Also tissue : consists of interwoven layer of
connective tissue; containing collagen and
elastin fibers. Appendage structures extend into
• Thicker than epidermis
• Contains connective tissue; elastic fibers,
collagen, nervous tissue, smooth muscle and
blood;receptors and glands are found here.
• A basement membrane separates the
epidermis from dermis.
• loosely woven fibers
• rich blood supply
• irregular surface (fingerprints)
• dense irregular CT
• cleavage lines
• less scarring
• flexure lines—less sliding
Layers of Epidermis
Layers of Epidermis
• Stratum basale (germinativum)
• Stratum spinosum (prickly layer)
• Stratum granulosum (granular)
• Stratum lucidum (clear layer)
• Stratum corneum (horny layer)
Cell and Layers of the Epidermis
• Single layer cells on basement membrane
• Cell types in this layer
• undergo mitosis to replace epidermis
• distribute melanin through cell processes
• melanin picked up by keratinocytes
– merkel cells are touch receptors
• form Merkel disc
• Pigment (melanin) produced by
• Color is yellow to brown to black
• Melanocytes are mostly in the stratum
• Amount of melanin produced depends upon
genetics and exposure to sunlight
• These are found mostly
in the stratum basale
• Everyone has the same
number of melanocytes.
• The darker skin a
person has depends on
how much melanin a
produces and the size of
the granules. This is
determined by one’s
• UV rays can stimulate
Here’s How it Works
• Melanocytes deeper in the epidermis are
stimulated to produce new melanin
granules. These new granules are
transferred to keratinocytes in the upper cell
layers of the skin. These granules become
positioned in the outer portions of the cells
above the cell nuclei, thus providing
If Melanocytes on Bottom,
How Does Skin Get Tan on
• Melanocytes have extensions that transfer
the granules to surface cells by a process
known as Cyocrine Secretion.
• Contain special white blood cells from the
lymphatic system. Help protect body from
• Produces lipid-filled vesicles that
release a glycolipid by exocytosis
to waterproof the skin
• Thin translucent zone seen only in
thick skin ( palms and soles of
• Cells have no nucleus or organelles
• The most superficial layer of epidermis
• 20- 30 layers thick
• Cornified, ABSOLUTELY dead
• ABSOLUTELY flattened
• These take up 75% of the epidermis.
• They exfoliate continuously.
Cutaneous Glands- the EXOCRINE glands,
including sweat and sebaceous glands.
• Both of these glands are formed in epidermis and
pushed down during development and remain
almost entirely in dermis.
• Sebaceous- OIL glands. Usually empty into
hair follicle, sometimes directly skin.
---SEBUM=oil and skin cells, germicide.
• Named after
• Theses are sensory
receptors that detect
More Than One Kind….
Sebaceous (Oil) Glands
Secrete oil or sebum
Everywhere except palms, soles
Usually secretes into hair follicle
Lubricates hair and skin
• softens dead cells--pliability
• slows water loss
Stimulated by hormones
with hair follicle
Sebaceous Eccrine glands , that
glands is SUDORIFEROUS
or SWEAT GLAND
associated empties onto Skin
with hair follicle
• Sweat Glands- Eccrine and Apocrine
• Eccrine- more numerous, ubiquitious, used to
regulate body temperature.Empty onto skin.
• Apocrine- found auxillary, and pubic areas only.
Develop during puberty under influence of
testosterone. Contain protein and fat. Do not
regulate body temp. Activated by stress and sexual
foreplay. Empty onto hair follicle.. usually.
Apocrine Vs. Eccrine Glands
What Did You Say???
• Ceruminous glands- This are
modified (eccrine) sweat glands in the
passageway of the external ear. Their
secretions combine w/ sebaceous glands
forming CERUMEN….or earwax.
Together w/ tiny hairs traps foreign
• Located under the dermis
• Mostly adipose
– energy reservoir
– thermal insulation
• Hypodermic injections
– highly vascular
Common Cancers: Skin Cancer
• Risk factors
– Exposure to UV light
• Detection and treatment
– Types: basal and squamous cell carcinomas (95% of
skin cancers), melanoma is most dangerous
– Melanoma: asymmetry, border irregularity, color
change, diameter greater than ¼ inch
– Surgical removal
– Early detection: 96% survival 5 years out
• Skin cancer is the most common type of cancer in
humans. Cause is unknown, but most important
risk factor is over exposure to UV light. Frequent
irritation to skin by infections, chemicals or
physical trauma seem to be a predisposing. Also
Risk factors: living at high altitudes, fair skinned
people, having a lot of moles, a family history of
the disease and if you had one or more severe
sunburns as a child
Skin Cancer: RFs
• over exposure to UV light.
• Frequent irritation to skin by infections, chemicals or
• living at high altitudes,
• fair skinned people,
• having a lot of moles
• family history of the disease
• one or more severe sunburns as a child
Skin Cancer: 3 Types
• Basal – arise from the layer stratum basale. Least
malignant, most common. Cannot form keratin (
soft). Looks like a mound. No boundary between
epidemis and dermis.
• Squamous – arise from statum spinosum.
Characterized by pearly beaded edge. These will
metastasize into the lymph nodules if left
untreated and can be lethal.
• Melanoma- rarest but most deadly. Develops
from pigmented moles. 5% survival rate.
ABCD Test For
A – Asymmetrical; the two sides of the
pigmented spot do not match.
B- BORDERS-irregular boarders; not
smooth with indentations apparent
C- COLOR- pigment contains areas of
D- DIAMETER- larger than ¼ inch
• Hot water, sunlight, radiation, electric shock or acids
• Death from fluid loss and infection
• Degrees of burns
– 1st-degree = only the epidermis (red, painful and edema)
– 2nd-degree = epidermis and part of dermis (blistered)
• epidermis regenerates from hair follicles and sweat glands
– 3rd-degree = epidermis, dermis and more is destroyed
• often requires grafts or fibrosis and disfigurement may occur
• Treatment – IV nutrition and fluid replacement,
debridement and infection control
Hair and Hair Follicles
HAIR STRUCTURE ( flexible epithelial
• contains a MATRIX- the growth zone ..a zone of
stratum basale, hair bulb at inferior end of follicle.
(ACTIVELY DIVIDING Epithelial Cells—alive)
• Root- Part of hair enclosed in follicle—now
keratinized and dead
• Shaft- Hair part that projects from surface of the
scalp or skin.
• Composed of:
• Inner Epidermal Sheath ( epithelial tissue)
• Outer DERMAL Connective Tissue
• Nipple-like PAPILLA (provides blood
supply to matrix in hair bulb)
• Arrector pili ( small bands of smooth
muscle) that connect follicle to dermal
tissue. ---goose bumps.
The part of the hair covered by the follicle is
called the ROOT.
Hair exposed is called the SHAFT.
Hair is formed from STRATUM BASALE
Cells in GROWTH ZONE of MATRIX of
HAIR BULB. This is nurished by
DERMAL Papilla .
HAIR YOU SEE IS DEAD
• SOFT KERATIN in the Medulla
• HARD KERATIN in the Cortex and Cuticle
• Hardest and Outermost is the CUTICLE
Associated Hair Structures
• Hair follicle
– Dermal and epidermal sheath
surround hair root
• Arrector pilli ( when erect
pull hair straight and causes
– Smooth muscle
• Sebaceous gland
• Sweat gland