The skin, or cutaneous mem-
brane, covers the external sur-
face
of the
body.
The
skin
is
the largest organ of the body in
terms of both surface area and weight. In adults, the
skin covers an area of about 2 square meters (22 square
feet) and weighs 4.5-5 kg (10-11 lb), about 16% of total
body weight.
Let’s take a closer look at the structure of the skin.
cutaneous mem-
brane
(ku-TA-ne-us)
Pertaining to the skin.
epidermis
(ep-i-DERM-is;
epi-
=
"above") The super-
ficial, thinner layer
of the skin, which is
composed of epithe-
lial tissue.
Skin Is a Multilayered
Organ
The skin consists of two main parts
(see Figure 4.1a):
Epidermis
is
the
superficial,
thinner
portion,
which
is
composed of
epithelial tissue.
Dermis is the deeper, thicker
connective tissue
portion.
Deep to the dermis, but not part
of the skin, is the subcutaneous
(subQ) layer. This layer consists
of areolar connective tissue and
adipose tissue. Fibers that extend
from the dermis anchor the skin
to the subcutaneous layer, which,
in turn, attaches to underlying tis-
sues and organs. The subcutane-
ous layer serves as a storage depot
for fat and contains large blood
vessels that supply the skin.
The
epidermis
is composed of
keratinized stratified squamous
epithelium. It contains four prin-
cipal types of cells: keratinocytes,
dermis
A layer of
dense irregular con-
nective tissue lying
deep to the epidermis.
subcutaneous
(subQ) layer
(sub -
ku-TA-ne-us) The layer
beneath the skin. Also
called
hypodermis
(hl-po-DER-mis).
areolar connec-
tive tissue
(a-RE-o-
lar) A type of fibrous
connective tissue in
which the fibers are
arranged in a loose
net or mesh.
b.
Hair
• Threads of fused, dead, keratinized
epidermal cells.
• Base is surrounded by living hair
follicle, nerve endings, blood vessels,
oil glands, and smooth muscle.
• Guard skin and scalp from sun injury,
protect eyes and nose from foreign
particles, and assist in temperature
regulation.
Hair shaft
Hair follicle
Dermal root sheath
Dorsal view
Nail body
Lunula
Cuticle
Nail root
c.
Nails
• Made of plates of packed, hard,
dead keratinized epidermal cells.
• Consists of visible nail body,
embedded nail root, and free
edge, which extends past the
digit.
• Nail matrix proximal to the root
contains dividing cells that allow
nail to grow.
• Help us grasp and manipulate
small objects, protect ends of
fingers and toes, and scratch
various parts of the skin.
Sagittal section showing internal detail
Free edge
of nail
The Integumentary System Is Composed of Skin, Glands, Hair, Nails, and Nerve Endings
93
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