Chapter 4
Skin and Body Membranes
Anatomy
Essentials of Human Anatomy & Physiology, 7th ed.
by Elaine N. Marieb
Skin and Body Membranes: Integumentary System, Anatomy
 Skin = cutaneous membrane =
integument = epidermis + dermis
 Integumentary System = Skin + skin
derivatives
Skin derivatives
 Sweat glands
 Oil glands
 Hairs
 Nails
Skin = Integument
• Covers 15-20 ft.2
• Weighs ~ 9 lbs.
• Every square inch contains
~ 15 feet of blood vessels,
12 feet of nerves, 650 sweat
glands, 100 oil glands,
1500 sensory receptors,
over 3 million cells.
• Entire epidermis regenerates
every 25-45 days!
Skin and Body Membranes: Integument
 Epidermis – outer layer
 Stratified squamous epithelium
 Avascular
 Often keratinized
(hardened by keratin)
• Dermis
 Dense irregular
connective tissue
Skin and Body Membranes: Integument
Deep to dermis is the hypodermis
Not part of the skin
Anchors skin to underlying organs
Composed mostly of adipose tissue
Skin and Body Membranes: Integumentary System, Anatomy
Figure 4.4
Layers of
Epidermis
Skin and Body Membranes: Layers of Epidermis
Stratum basale (deepest layer)
• Cells undergoing mitosis
• Lies next to dermis
• Contains two cell types:
keratinocytes & melanocytes
Stratum spinosum (spiny layer)
• Keratinocytes mature, filling cells with
keratin protein
• Phagocytic white blood cells – Langerhans cells
Stratum granulosum (granular layer)
• 3-5 rows of flattened keratinocytes (produce keratin)
Skin and Body Membranes: Layers of Epidermis
Stratum lucidum (clear layer)
• Occurs only in thick, glaborous (hairless) skin
Stratum corneum (outermost layer)
• Shingle-like dead cells filled with keratin
• 5-50 cell layers thick, depending upon location
The stratum corneum
is thickest in the soles
of the feet.
It’s thinnest
in the
eyelids.
Skin and Body Membranes: Epidermis
Melanin
• The pigment, melanin, is produced by
melanocytes in the stratum basale.
• Color is yellow to brown to black
• Melanocytes have cellular extensions,
called dendrites that weave between the
cells of the stratum basale and spinsoum.
The keratinocytes absorb melanin from the
dendrites, and skin is evenly
colored…usually.
• Amount of melanin produced depends upon
genetics and exposure to sunlight
Skin and Body Membranes: Integumentary System, Anatomy
Figure 4.4
Dermis
• Dense, irregular
connective
tissue
• Thickness varies
• Two layers:
papillary &
reticular
Skin and Body Membranes: Dermis
Papillary layer
• Most superficial dermal layer
• Capillaries which provide nutrients to the
avascular epidermis through diffusion
• Sense receptors: pain receptors
(free nerve endings) & touch receptors
(Meissner’s corpuscles)
• Projections called dermal papillae
Skin and Body Membranes: Dermis, papillary layer
As the epidermis layers superficially to
the dermis, the pattern of dermal
papillae is amplified. Your fingerprints,
handprints, and footprints are the
pattern of your dermal papillae!
Skin and Body Membranes: Dermis
Reticular layer
• Thicker than papillary layer
• Blood vessels (arterioles, venules) help
maintain body temperature homeostasis
• Sweat and oil glands
• Deep pressure receptors – Pacinian corpuscles
• Connective tissue fibers: Collagen & Elastin
Skin and Body Membranes: Integumentary System, Anatomy
Skin and Body Membranes: Dermis, reticular layer
Separation of
bundles of
collagen fibers
form lines of
cleavage in the
skin. (Langer’s
cleavage lines)
Why do surgeons
make incisions
along these
lines?
Skin and Body Membranes: Integumentary System, Anatomy
Figure 4.4
Skin and Body Membranes: Integumentary System, Anatomy
Appendages of
the Skin:
Hair & Nails
Skin and Body Membranes: Skin appendages, hair
Hair
• Produced by
hair bulb matrix
• Consists of hard
keratinized
epithelial cells
• Melanocytes
provide pigment
for hair color
• Composed of a
root & shaft
Figure 4.7c
Skin and Body Membranes: Skin appendages, hair
Root the part of
hair enclosed in
the follicle.
Shaft the part of
hair projecting
from the surface
of the scalp or
skin
Skin and Body Membranes: Skin appendages, hair
Shaft
 Central medulla
 Cortex surrounds
medulla
 Cuticle on outside of
cortex (heavily
keratinized)
Figure 4.7b
Skin and Body Membranes: Skin appendages, hair
The shape of the hair shaft determines the
macroscopic appearance of the hair.
Flat shaft = curly/kinky hair
Oval shaft = wavy hair
Round shaft = straight hair
Skin and Body Membranes: Skin appendages, hair
Associated Hair Structures
 Hair follicle
• Dermal and epidermal
sheath surround hair root
 Arrector pili muscle
• Smooth muscle that
surrounds hair follicles
and contracts when cold
or frightened
 Sebaceous gland
 Sweat gland
Skin and Body Membranes: Integumentary System, Anatomy
Figure 4.4
Skin and Body Membranes: Skin appendages, nails
Nails
 Heavily keratinized, scale-like modifications of
the epidermis.
 Only two layers of epidermis extend beneath
the nail bed: stratum basale &
stratum spinosum
Skin and Body Membranes: Skin appendages, nails
Slide 4.22
Nail Structures
 Free edge
 Body
 Root of nail
 Nail folds -skin
folds that border
nail
 Cuticle -thick
proximal nail fold
 Lunula –white
crescent
Figure 4.9