What Is the Integumentary System?

In addition to the skin, includes the hair and nails, organs that grow out of the skin.
Because the organs of the integumentary system are mostly external to the body, they
serve vital physiological functions. They provide a protective covering for the body,
sense the environment, and help the body maintain homeostasis.

(BOOK). Integumentary means “covering”. It is made up of skin (cutaneous membrane)

and its appendages: hair, nails, sebaceous glands, and sweat glands. Integumentary
system covers an average adult = 3,000 square inches of surface area.

The Skin

- The body’s largest organ.

-The average square inch of skin has 20 blood vessels, 650 sweat glands, and more
than a thousand nerve endings.

- It also has an incredible 60 thousand pigment-producing cells. All of these

structures are packed into a stack of cells that is just 2 mm thick, or about as thick as
the cover of a book.

-The skin is consists of two distinct layers: the epidermis and dermis (as shown in the
diagram below).

(BOOK) Skin function:

 a covering for the underlying, deeper tissues, protects from dehydration , injury,
and germ invasion.
 Help regulate body temperature; controls the size of blood vessels in the dermal
layer of the skin.
 Helps manufacture vitamin D. ultraviolet light is necessary for the first stage of
vitamin D formation.
 A site for nerve endings. A square inch of skin contains 72 feet of nerves and
hundreds of receptors.
  Has a tissue that temporarily stores fat, glucose, water, and salts. later will be
absorbed by the blood and transported to other parts of the body
 Reduces harmful ultraviolet radiation from sunlight.
 Has a special property that permits the absorption of certain drugs and other
chemical substances; drugs for rashes, or medications via patches that can be
absorb through the skin.

STRUCTURE OF THE SKIN

1. Epidermis ( outermost layer)

-This layer is thinner than the inner layer (the dermis).

-The epidermis consists mainly of epithelial cells, called

keratinocytes, which produce the tough, fibrous protein keratin.

-The innermost cells of the epidermis are stem cells that divide
continuously to form new cells.

-The newly formed cells move up through the epidermis toward

the skin surface, while producing more and more keratin.

-The cells become filled with keratin and die by the time they reach
the surface, where they form a protective, waterproof layer.

- As the dead cells are shed from the surface of the skin, they are
replaced by other cells that move up from below.

-Also contains melanocytes, the cells that produce the brown

pigment melanin, which gives skin most of its color. Although the
epidermis contains some sensory receptor cells — called Merkel cells —
it contains no nerves, blood vessels, or other structures.

2. Dermis (Innermost layer)

- Thicker layer of skin.
- It consists mainly of tough connective tissue, and is attached to the epidermis by
collagen fibers.
- The dermis contains many structures, including blood vessels, sweat glands, and
hair follicles, which are structures where hairs originate; and
- the dermis contains many sensory receptors, nerves, and oil glands.

(BOOK)

1. Epidermis (outermost) – a cover that is made up of epithelial cells, with no blood

vessels present (avascular).
2. Dermis (innermost) – or true skin, it’s made up of connective tissues and is
vascular. Thickness varies: is thinnest on the eyelids and thickest on the palms of
the hands and soles of the feet.

- Surface layer (*stratum corneum) consists of dead cells in keratin.

- keratin - a protein that renders the skin dry and provides a waterproof
covering, thus resisting evaporation and preventing excessive water loss. Also
serves as a barrier against ultraviolet light, bacteria, abrasions, and some
chemicals.
 Epidermal Cells:
a. Keratinocytes- comprise most of the epidermis and produce
the protein keratin
b. Merkel cells - the sensory receptors for touch.
c. Melanocytes – makes the protein melanin(protects skin against
ultraviolet rays)
d. Langerhans cells (not the one in pancreas)-
macrophages(WBC, cleans the body of unwanted microscopic
particles, e.g, bacteria and dead cells), effective in the defense
of skin against microorganisms.

Epidermal Layers:

1. Stratum Germinativum (stratum basale) – a continuous

cell division; the deepest epidermal layer.
- consist of layer cells (mostly
keratinocytes).
- grow upward and becomes part of the
superficial layers, the stratum spinosum.
- melanocytes and merkel cells are also
found here.
2. Stratum Spinosum - 8-10 cell layer thick. Contains
melanocytes, keratinocytes, and Langerhans cells.
Spinosum meaning “Little spine” under microscope.
3. Stratum granulosum – keratinization(keratinocyte cells
change shape, lose nucleus, lost most of their water, and
become mainly hard protein/keratin) process begins and the
cells begin to die.
4. Stratum Lucidum - foundonly on the palms of the hand and
the soles of the feet. Cells appear clear.
5. Stratum Corneum- dead, flat, scalelike keratinized cells,
which slough(shed/remove) off daily.

(BOOK) Skin Color – contributes of 3 pigments to skin color: Melanin, Carotene, and
hemoglobin.

_alteration in skin color may indicate disease conditions or emotional states.

Sebaceous glands- microscopic organs in the skin that secrete an oily substance
called sebum that lubricates and waterproofs the skin.

- The glands are part of the pilosebaceous unit, which comprises the hair follicle,
hair shaft, and erector pili muscles (responsible for goosebumps).

-work in tandem with the sweat-producing eccrine glands to regulate body

temperature. In hot conditions, the excreted sebum mixes with sweat to slow the rate of
evaporation. In cold temperatures, the sebum will contain more lipids to shield the hair
and skin from moisture that can facilitate heat loss.

-In addition to maintaining moisture and regulating temperatures, sebum contains

squalene and other substances that prevent bacteria, fungi, and other microorganisms
from causing infection.

(BOOK) Sebaceous Glands- protected by a thick, oily substance known as sebum,

secreted by the sebaceous glands.
 Sebum – contains amino acids, lactic acids, salt, and urea.

- lubricates the skin, keeps it soft and pliable.

(BOOK)Sweat Glands (sudoriferous)- distributed over entire skin surface. Is tubular,

with a coiled base and tubelike duct that extends to form a pore in the skin. Perspiration
is excreted through the pores.

-under nervous system, these glands can be activitaed by several factors

including heat, pain, fever, and nervousness.

- present in large numbers ( under arms, on the palm of the hands, soles of the
feet, and forehead).

- perspiration is excreted through the pores.

Nail

Melanocytes- Produce 2 classes of melanin: Pheomelanin (red to yellow) and

Eumelanin (dark brown to black).

- people with whiter skin have great proportion of Pheomelanin on their skin

- Photosensitive – makes skin burn because of drugs

 -to older adults melanin collects in spots called “aging”/”liver” spots.

- The environment can modify/affect skin color (e.g., exposure to sunlight(

increase in eumelanin)

- prolonged exposure under the ultraviolet rays is dangerous, it may lead to the
development of skin cancer.

Carotene - yellow to orange pigment found in certain plants.

- - some Asians has yellowish tinge because/due to the variations in melanin as well as
the carotene.

- pinkish color to some fair-skinned people is due to the presence of oxygen in the
hemoglobin of the RBC, within the dermal capillaries.

Hair

-Hair is a fiber found only in mammals. It consists mainly of keratin-producing

keratinocytes. Each hair grows out of a follicle in the dermis. By the time the hair
reaches the surface, it consists mainly of dead cells filled with keratin

-Hair serves several homeostatic functions.

-Head hair is important in preventing heat loss from the head and protecting
its skin from UV radiation.

-Hairs in the nose trap dust particles and microorganisms in the air, and prevent
them from reaching the lungs.

-Hair all over the body provides sensory input when objects brush against it, or
when it sways in moving air.

-Eyelashes and eyebrows protect the eyes from water, dirt, and other
irritants.(picture below)

Nails

-Fingernails and toenails consist of dead keratinocytes filled with keratin.

-The keratin makes them hard but flexible, which is important for the functions
they serve.
 -Nails prevent injury by forming protective plates over the ends of the fingers
and toes.

-They also enhance sensation by acting as a counterforce to the sensitive

fingertips when objects are handled; and

- In addition, the fingernails can be used as tools.

References: https://www.ck12.org/book/CK-12-College-Human-Biology/section/12.2/