White Plains High School
Anatomy and Physiology
Integumentary System Part 1
Chapter 5
Pages 149-153
Goals:
o List the layers of each tissue
o Describe the function of each tissue
o Describe the factors that contribute to skin color
Pertinent Vocabulary
Superficial fascia (hypodermis)
Epidermis
Keratinocytes
Keratin
Melanocytes
Melanin
Epidermal dendritic cells
Merkel cells
Stratum basale
Stratum greminativum
Stratum spinosum
Stratum granulosum
Stratum lucidum
Stratum corneum
Dermis
Papillary layer
Friction ridges
Reticular layer
Tension lines
Carotene
Fun Facts: The skin covers 1.1 to 2.2 square meters weighs between 4-5 kg (8-11 lbs) and
about 11% of your body weight. It varies from 1.5 to 4 mm in thickness. Its major roles
are as a barrier to infection, moisture loss and homeostasis.
The Integumentary system (skin) is made up of two layers:
o The epidermis
o The dermis
The hypodermis or superficial fascia is a layer under the dermis and is not considered
part of the skin but serves to separate the skin from the underlying muscle. This layer
contains fat tissue and is loosely anchored to the skin. This allows the skin to slide while
the fat serves as an insulator and a cushion. This layer is the major site of fat
accumulation. Its distribution changes based on gender, in females the fat accumulation is
in the thighs and breast while in the male it forms the so called “beer belly”.
A) Epidermis
This is the outer most layer and consists of a stratified squamous epithelium. Four cell
types populate the epidermis:
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Keratinocytes
Melanocytes
Epidermal dendritic cells (Langerhan’s cells)
Tactile cells (Merkel cells)
1) Keratinocytes
These cells produce keratin, a protein made of intermediate fibers. These cells attach to
each other by desmosomes. Recall that these structures help hold cells together where
there are strong shearing forces. These cells are found in the lowest level of the
epidermis, the stratum basale (basal cell layer). These cells divide and give rise to the
major epithelial cell type in the epidermis.
2) Melanocytes
These cells produce melanin and are found occupying the stratum basale. Melanin is
formed in the Golgi bodies of these cells and the accumulated melanin is stored in
intracellular vesicles called melanosomes. The melanocytes are “spider” shaped. Actin
filaments transport the melanosomes to the distal portions of the melanocyte where the
melanin is secreted. (Recall the unit on intracellular transport) The melanin is then taken
up by the keratinocytes.
3) Epidermal dendritic cells (Langerhan’s cells)
These cells originate in the bone marrow and migrate to the epidermis. They play an
important role in the skin’s immune response.
4) Merkel (tactile) cells
These cells are found at the dermal/epidermal junction (stratum basale) and serve as a
touch receptor. This is a disk shaped cell whose distribution varies around the body.
These cells are distributed and help give rise to five layers which make up the epidermis.
These are:
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Stratum basale
Stratum spinosum
Stratum granulosum
Stratum lucidum
Stratum corneum
1) Stratum basale (basal layer)
This is the deepest epidermal layer. Cells in the lowest level undergo constant mitosis in
an effort to replace cells lost in the upper layers. 10 to 25% of the cells in this layer are
melanocytes.
2) Stratum spinosum (prickly layer)
This layer is several cells thick. The cells are filled with intermediate fibers which attach
to the desmosomes. The desmosomes appear on the cells surface like spikes giving rise to
the name prickly.
3) Stratum granulosum
This layer is 3 to 5 layers thick and is where keratinization occurs. Here the cells begin
to flatten and the organelles begin to break down. Two types of granules (non membrane
bound inclusions) are found in this cell type:
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Keratohyaline granules which contain keratin
Lamellated granules contain glycolipids and serve as a
water proofing
4) Stratum lucidum
Seen only where the epidermis is very thick, typically the feet and palms of the hand. It is
a histological term for a clear area of cells seen between the stratum granulosum and the
stratum corneum.
5) Stratum corneum (horny layer)
This is the outermost layer and is between 20 to 30 cells thick. It protects against
abrasions and is made up of dead cells. The glycolipids from the lamellated granules
waterproof this layer. It is estimated that you shed about 18 pounds of this layer in your
lifetime.
B) The Dermis
This layer consists of connective tissue and resident cell types of macrophages,
fibroblasts and masts cells. This is the layer that becomes leather. Interspersed in this
layer are blood vessels, nerve tissue, hair follicles, oil and sweat glands. The dermis
consists of two layers:
 Papillary layer
 Reticular layer
1) The Papillary Layer
This consists of areolar connective tissue and lies just below the stratum basale. The
loose nature of this layer allows the cells of the immune system to act quickly on any
breach of the epidermal cells. (recall tissue healing). Projecting from this layer are
dermal papillae which go up into the epidermis. These carry nerve and capillary networks
and touch receptors known as Meissner’s corpuscles.
The dermal papillae make up the dermal ridges and by extension help form the
epidermal ridges. These are prominent on the hands and feet and form friction ridges
and improve gripping. On the fingers these are known as finger prints.
2) The Reticular Layer
This layer accounts for about 80% of the thickness of the dermis. It is made up of dense
irregular connective tissue with scattered fat deposits. The collagen fibers run is planes
and are responsible for the furrow in the brow and neck. If this area is stretched as occurs
in pregnancy or obesity, the dermis becomes torn and gives rise to the so called “stretch
marks or cellulite”
Skin Color
There are 3 pigments that contribute to your skin color:
 Melanin
 Carotene
 Hemoglobin
1) Melanin is the only pigment produced in the skin. Melanin is a polymer of the amino
acid tyrosine.
The color ranges from yellow to tan to reddish brown to black. Tyrosinase is the enzyme
responsible for making the melanin. This is formed in the melanocytes.
All humans have the same number of melanocytes; racial differences are due to the type
of melanin formed. Those groups with dark brown to black skin have the darker forms
and retain it longer. Freckles are locale accumulations of melanin. Exposure to
ultraviolet light stimulates melanin production.
2) Carotene is a yellow to orange pigment and can accumulate in the stratum corneum. Is
often seen in the palms and soles of the feet where this epidermal layer is thickest.
3) Hemoglobin reflects through the skin of lightly pigmented individuals.
Skin conditions can be a sign of underlying health issues.
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Redness erythema - blushing fever
Pallor – pale
Jaundice- liver issues
Bronzing- Addison’s disease, deep tan
Bruises – blood accumulating in the dermis