Integumentary system: Is composed of the skin, hair, oil and sweat glands, nails and sensory
receptors. The integumentary system helps maintain a constant body temperature, protects
the body, and provides sensory information about the surrounding environment.
Skin is composed of a complex system of cell layers, nerves and glands that protect and
connect us to the outside world.
Skin is the body’s largest organ
If you took it off and laid it flat the surface area would cover 2 square meters.
Skin weighs roughly 8 pounds
Skin loses about 30,000-40,000 dead skin cells from the surface roughly every minute.
28 day turnaround (adult)
Our skin reflects our age and health
Skin is an indicator of clinical conditions and dysfunction
o Paleness is a sign of shock
o Redness is a sign of fever
o Rashes are a sign of allergies
o Paleness is a sign of loss of blood
Also known as the cutaneous membrane
Thin skin: four strata or layers- stratum basale, stratum spinosum, stratum granulosum, and a
thin stratum corneum.
Thick skin: Where exposure to friction is greatest such as in the fingertips, palms, and soles, the
epidermis has 5 layers- stratum basale, stratum lucidum, and a thick stratum corneum.
This is called thick skin.
Feature Thin Skin Thick Skin
Distribution All parts of body except Areas such as palms,
areas such as palms, palmar palmar surface of digits and
surface of digits, and soles soles
Epidermal thickness 0.10-0.15mm (0.004- 0.6-4.5mm (0.024-0.18),
0.006in) due mostly to a thicker
Epidermal strata Stratum lucidum essentially Stratum lucidum present;
lacking; thinner strata thicker strata spinosum and
spinosum and corneum corneum
Epidermal ridges Lacking due to poorly Present due to well-
developed, fewer, and less- developed and more
well-organized dermal numerous dermal papillae papillae organized in parallel rows
Hair follicles and arrector Present Absent
Sebaceous glands present Absent
Sudoriferous glands fewer More numerous
Sensory receptors Sparser Denser
-contain melanin that protects underlying cells from UV
-Melanin is transferred to the keratinocytes
-Everyone is born with the same # of menalocytes, but we produce different amounts of
-Protects germinal layer against UV
-Increased UV=Increased melanin (tanning)
-Melanin (dark granulates in melanosomes)
Skin Colour: Expression, of 3 pigments
Hemoglobin: Red. Hemoglobin is an iron binding protein that binds O 2n blood cells.
Albinism: no melanin produced
Vitilago: complete loss of melanin (auto-immune disease)
Freckles: Localized concentration of melanocytes
Melanoma: Very high increased concentration of melanocytes Structure of the Skin
The superficial, thinner portion, which is composed of epithelial tissue.
Thickest on the palms and soles of feet
Thinnest on the eye lids
Composed of keratinized stratified squamous epithelium.
Contains 4 principal cell types: keratinocytes, melanocytes (those two are most
common), Langerhans cells, and Merkel cells.
About 90% of epidermal cells are keratinocytes (arranged in 4 or 5 layers and produce
keratin), 8% of epidermal cells are melanocytes (which develop from the ectoderm of a
developing embryo and produce the pigment melanin.
A small fraction of epidermal cells are Langerhans cells (also called epidermal dendritic
cells) migrate to the epidermis layer where they participate in immune responses
mounted against microbes that invade the skin and are easily damaged by UV light.
Merkel cells- least numerous of the epidermal cells. They are located in the deepest
layer of the epidermis. They contact the flattened process of a sensory neuron (nerve
cell), a structure called a Merkel (tactile) disc. They detect touch sensations.
Stratum Basale (dividing):
-Deepest layer of the epidermis, composed of a single row of cuboidal or columnar
-Some cells in this layer are stem cells that undergo cell division to produce keratinocytes.
-Also known as the stratum germinativum to indicate its role in forming new cells.
Stratum Spinosum (spiny):
-Superficial to the stratum basale
-Mainly consists of numerous keratinocytes arranged in 8-10 layers.
-Cells in the more superficial layers become somewhat flattened.
-The keratinocytes are produced by the stem cells in the basal layer. They have the same
organelles as cells of the stratum basale and come retain their ability to divide.
-Although the bundles of keratin are rounded, they shrink and pull apart when prepared for
microscopic examination so that they appear to be covered with thorn like spines (thus the
-Langerhan cells and projections of melanocytes are also present in the stratum spinosum. Stratum Granulosum (granular):
-Consists of three to five layers of flattened keratinocytes that are undergoing apoptosis (an
orderly, genetically programmed cell death in which the nucleus fragments before the cells die,
balance between cell production & cell loss).
-The nuclei and other organelles of these cells begin to degenerate as they move farther from
the source of nutrition (the dermal blood vessels)
-A distinctive feature of cells in this layer is the presence of darkly staining granules of a protein
called keratohyalin (which assembles keratin intermediate filaments into keratin)
-Also present in the keratinocytes are membrane-enclosed lamellar granules, which fuse with
the plasma membrane and release a lipid-rich secretion. This secretion s deposited in the space
between cells. The lipid-rich secretion acts as a watery repellant sealant , retarding loss and
entry of water and foreign materials. As their nuclei break down during apoptosis, the
keratinocytes of the stratum granulosum can no longer carry on vital metabolic reactions, and
-Thus the stratum granulosum marks the transition between the deeper, metabolically active
strata and the dead cells of the more specific strata.
Stratum Lucidum (clear):
-Present only in the thick skin of areas such as the fingertips, palms, and soles.
-It consists of 4-6 layers of flattened clear, dead keratinocytes that contain large amounts of
keratin and thickened plasma membranes.
-This probably provides an additional level of toughness in this region of thick skin.
Stratum Corneum (cornified):
-Consists on average of 25 to 30 layers of flattened dead keratinocytes, but can range in
thickness from a few cells in thin skin to 50 or more layers in thick skin.
-The cells are extremely thin, flat, plasma-membrane-enclosed packages of keratin that no
longer contain a nucleus or any internal organelles.
-Constant exposure of skin to friction stimulates increased cell production and keratin
production that results in the formation of a callus, an abnormal thickening of the stratum
COME, LET’S GO SUN BATHE.
-epidermal peg surrounded by dermal papilla
-Down growths of epidermis into the dermis Dermal papilla: Fingerlike projections of the papillary region of the dermis that may contain
blood capillaries or corpuscles of touch
Feature Sebaceous (oil) Eccrine sweat Apocrine sweat Ceruminous
glands glands glands glands
Distribution Largely in lips, Throuhgout skin Skin of axillae, External auditory
glans penis, labia of most regions groin, areolae, canal
minora, and of body, bearded regions
tarsal glands; especially skin of of face, clitoris,
small in trunk forehead, palms, and labia minora
and limbs; and soles.
absent in palms
Location of Dermis