3.2 Notes
Integument – another name for skin
Integumentary System – body system that involves the skin, hair, and nails
The skin is an epithelial tissue membrane (epithelial tissue with an underlying layer of
connective tissue), more specifically a cutaneous membrane (covers body surfaces that are
exposed to the external environment). The thin, outer, epithelial layer is the epidermis
(developed from the ectoderm). The thicker, underlying connective tissue layer is the dermis
(developed from the mesoderm). The epidermis and the dermis meet at the dermal-epidermal
junction. Below the dermis (deeper in the body) is the hypodermis, or subcutaneous layer
(also known as the superficial fascia).
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Functions of the Skin
1. Protection
2. Sensation
3. Excretion
4. Vitamin D Production
5. Immunity
6. Homeostasis
7. Heat Production
8. Heat Loss
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Epidermis
Cell types:
keratinocytes – epidermal cell responsible form producing keratin; makes up
90% of epidermal cells
melanocytes – specialized cell in the stratum basale that produces melanin
(brown pigment in skin and hair)
 Albinism- condition when a person cannot produce melanin
Cell layers:
strata – layer of the skin
1.
2.
3.
4.
5.
Stratum corneum (horny layer)
Stratum lucidum (clear layer)
Stratum granulosum (granular layer)
Stratum spinosum (spiny layer)
Stratum basale (base layer)
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In the deepest layer of the epidermis, the stratum basale, mitosis (cell division) occurs.
The stratum basale is a single layer of columnar cells. Cells are produced in this layer
and migrate from the stratum basale through the other layers until they are shed from the
surface.
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When the cells that are produced in the stratum basale reach the stratum spinosum (8-10
layers of irregularly shaped cells), proteins are synthesized that are required for the
production of keratin.
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Then the cells move to the stratum granulosum where the process of keratinization
begins. Cells in this layer are arranged in a sheet of two to four layers and have started to
degenerate. They are filled with keratohyalin (protein that is required for keratin
production). The stratum granulosum may be absent in thin skin.
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After the stratum granulosum, cells enter the stratum lucidum. The stratum lucidum is
layer of closely packed keratinocytes that are filled with eleidin (a soft gel-like
substance that is an intermediate of keratohyalin and keratin). This layer blocks water
penetration or loss. It is not present in thin skin.
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The most superficial layer of the epidermis is the stratum corneum. It is a layer of
squamous cells. These cells are dead and continually being shed and replaced. The
cytoplasm in these cells have been replaced by keratin. The process by which these cells
were produced from the underlying layers is called keratinization. It is referred to as
barrier layer of the skin because it is a barrier to water loss. This layer blocks many
things from entering the body such as microorganisms. If this layer is damaged, most
contaminants can easily pass through the underlying layers and enter the body.
- Cells push upward from the stratum basale into each successive layer, die,
become keratinized, and eventually desquamate (fall away), as did their
predecessors.
Dermal-epidermal junction
– composed chiefly of an easily identified basement membrane (where the outer
epithelial tissue layer and the underlying connective tissue layer meet), specialized
fibrous elements, and a unique polysaccharide gel that “glues” the epidermis to the
dermis
Dermis (corium)
– “true skin”; composed of a thin papillary and a thicker reticular layer; serves as
protection from mechanical injury and compression; provides a reservoir storage area for
water; contains muscle fibers, hair follicles, sweat and sebaceous glands, blood vessels

Papillary layer – thin superficial layer of the dermis that is composed of loose
connective tissue elements and thin collagenous and elastic fibers; it forms bumps,
called dermal papillae which are arranged in rows, which form ridges and project
into the epidermis; the papillary layer gets its name from these papillae
o The epidermis conforms tightly to these papillae ridges and as a result the
epidermis also has these ridges on its surface; they are well defined on the tips
of fingers and toes (fingerprints)
o Some dermal papillae contain capillaries that provide nutrients to the
epidermis, others contain nerve endings involved in sensing touch and pain

Reticular layer – thick layer of the dermis consisting of a much more dense
reticulum (network of collagenous fibers with some elastic fibers)
o this contributes to skins toughness as well as its stretchability
o serves as a point of attachment for numerous skeletal muscles (skeletal
muscles of face and scalp) and smooth muscle fibers (hair follicles)
o contains blood and lymphatic vessels, sweat and oil glands, hair follicles, and
nerve endings
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unlike the epidermis, the dermis does not continually shed and regenerate
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it does regenerate, but only occurs rapidly when healing a wound
Hypodermis (Subcutaneous layer, Superficial fascia)
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includes fibrous connective tissue and adipose tissue
Sweat glands (Sudoriferous glands)
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distributed in the dermis over the entire body, with larger concentrations located in the
axilla (armpit), palms of the hands, soles of the feet, and on the forehead
o there are two types of sweat glands:

eccrine glands
 more numerous and widespread sweat glands of the body
 open directly to the skin
 sweat consists of 99% water
 secretory portion is located in the hypodermis

apocrine glands
 genital and armpit areas
 apocrine glands are larger than eccrine glands
 secrete a milky fluid consisting of sweat, fatty acids, and proteins
 ducts empty into hair follicles
Sebaceous glands
-
secrete oily substance (sebum) for the hair and skin
located all over the body except for palms of the hands and soles of the feet
most empty into a hair follicle, though some secrete directly to the skin (prevents water
loss from the epidermis)
keeps skin and hair soft and contains chemicals that kill bacteria, also has an antifungal
effect
very active during adolescence
Hair
- hair shaft – the part of the hair you see (dead keratinized cells)
- hair root – the part of the hair under the skin
- hair bulb – found at the base of the hair root; where nutrients are obtained from dermal
papillae and new cells are formed
- the inner core of the shaft is the medulla, surrounding that is the cortex, and the covering
layer is the cuticle
o as new cells are formed, the old cells are pushed upward, keratinized, and die
o melanin provide for the color of hair, as less melanin is produced, hair becomes
gray or white
o follicle shape is genetically determined
 a round hair follicle produces straight hair
 an oval follicle produces wavy hair
 a flat-shaped follicle produces curly hair
Nails
-
heavily keratinized epidermal cells compose fingernails and toenails
o the visible part of nails is the nail body
o the rest of the nail is the nail root
o the fold of skin that covers the root is the cuticle
o under the nail lies a layer of epithelium called the nail bed
o the proximal end of the nail bed is called the nail matrix, or growth zone
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nails grow by mitosis (just like epidermis and hair)