Chapter 4: Skin &
Body Membranes
Functions of the Skin
 Thermoregulation
 Protects
body from mechanical
damage (bumps/cuts), chemical
damage, UV radiation, bacteria
 Mini-excretory system to urea, salt
and water
 Sensory receptors
 Manufactures protein and vitamin D
Structure of the Skin

1. Epidermis:
stratified squamous
epithelium that can
keratinize. Cells are
called keratinocytes.
– Outermost layer:
avascular
– Keratin: fibrous protein
component of nails,
hair, calluses, and skin
surface
5 layers of epidermis

1. Stratum Basale
or germinativum
–
–
–
–
Deepest layer
Gets nutrients
Cells divide here
New melanocytes
and keratinocytes
push up to become
part of S.spinosum
and S.granulosum
 2.
Stratum spinosum
– Keratinocytes provide a waterproof layer
 3.
Stratum granulosum
– 3-5 rows of flat cells
– Cells fill with keratin granules
– (cells die as they leave this row)
5 layers (cont)
 4.
Stratum lucidum
– Only found in palms and soles of feet
– Clear flat, dead cells
5 layers (cont)

5. Stratum
corneum
– Outermost layer
20-30cell layers
thick.
– Full of keratin
– Shed and replaced
every 25-45 days.
Skin color
 Melanin:
produced as body’s natural
sunscreen
– Protects against UV rays by shielding
the DNA in the pigment
– Colors range from yellow to black and
are formed in the S. basale. (Freckles
and moles)
Skin color
 Carotene-
orange yellow
pigment deposited in the S.
corneum.
 Other colors
– Cyanosis: poorly oxygenated
blood causes blue skin
– Erythema: redness if embarrassed,
fever, hypertension, allergy
– Pallor or blanching: from fear, anger,
anemia or low blood pressure
Skin color (cont)
 Other
colors
– Jaundice: yellow from liver disorder,
excess bilirubin in the blood.
– Bruises- site where blood has escaped
Dermis (your “hide”)
Dense connective
tissue.
 Collagen:
toughness & skin
hydration
 elastic fibers:
elasticity/
stretching
 Your leather
shoes!
Regions of the Dermis
 1.
Papillary layer: fingerlike
projections called dermal papillae.
– Form fingerprints, genetically
determined
– Contain capillary loops which provide
nutrients to epidermis above.
Papillary layer
 Contains
pain receptors (free nerve
endings) and touch receptors
(Meissner’s corpuscles)
Regions of dermis (cont)
 2.
Reticular layer
– Deepest skin layer
– Contains blood vessels and capillaries
(Maintains body temperature)
– Sweat and oil glands
– Deep pressure receptors called Pacinian
corpuscles
Subcutaneous Layer
 Aka:
Hypodermis (below dermis)
 Absorbs shock and insulates deeper
tissue
 Mostly adipose
Did you get it?
 Create
a simple diagram showing all
the 3 major layers of the skin.
Within each layer, label the sublayers
as well.
Accessory Organs
1. Sebaceous Glands
 Exocrine
gland
 Sebum (oil)
lubricates skin
and kills
bacteria
 arrector pili
squeezes
gland and
forces oil out
Acne
 Sensitive
to male hormones
– Acne at puberty
 Ducts
become blocked and secretions
accumulate
 Inflammation (pimple) bacterial infection
2. Sweat
Glands

sudoriferous
– 2.5 million/person
A. Eccrine Glands
 Discharge
onto
skin through tube
 All over body
 Water, salt, urea,
uric acid, vitamin
C, lactic acid
(mosquitoes),
ammonia are
produced
 Heat regulation
B. Apocrine
 Secretes
follicle
into hair
– Axilllary and
genital areas
 Fun
Fact: Odor
caused by bacteria!
Accessory Structures
 Hair
– Produced in hair
follicles
– Hair papilla
– Formed by
stratum basale
cells
– Root/shaft

Hair Shaft
– Dead, keratinized
cells
– 3 layers
 Cuticle-
surface
 Cortex- provides
stiffness
 Medulla- core, soft
 Hair
(cont)
– Hormones account for hair development
in scalp, pubic regions
– arrector pilli muscles (smooth muscle):
connect each side of hair to dermal
tissue
 Hair
color
– Produced by melanocytes
 Type
of hair depends on shaft
 flat:
curly/kinky
 Round: straight
Nails
 Protect
tips of fingers/ grasp objects
 Structure
– Scale-like modification of the epidermis
– Dead cells filled with keratin
– Colorless (except for lunula) pink from
blood vessels underneath
Homeostasis
 Injury/repair
– Scab: blood clot (temporary fix)
– Keloid: thickened area of scar tissue,
covered by a shiny
smooth epidermal surface
(harmless)
Development of skin
 Lanugo:
hairy covering of fetus,
shed by birth
 Vernix caseosa: white, cheesy
covering of fetus produced by oil
glands to protect skin
 Optimal appearance of skin- 20-30
Old Age
 Amount
of subcutaneous fat
decreases (cold intolerance)
 Less oil production and fewer
collagen fibers (dryness/bruises)
 By 50, # hair follicles dropped by
30%.
 Melanin decreases/absent (gray or
white)
Skin Cancer
 1.
Basal cell carcinoma: from S.
basale
– Least malignant, most common
– Slow growing, 99% curable if surgically
removed
Skin Cancer
 2.
Squamous cell carcinoma: from
S. spinosum. Forms an ulcer often
on the head
– Will spread to lymph nodes
– Prognosis is good if radiation or surgery
Skin cancer (cont)
 3.
Melanoma: cancer of the
melanocytes
– Often deadly
– Forms where pigment is present (moles)
– Spreads to surrouding lymph and blood
vessels
– Wide surgical excision and
chemotherapy