The Integumentary System
Introduction to the Integumentary System
The integumentary system is considered an organ because it is made up of different tissues. Actually, it
contains all four of the primary tissues; epithelium, connective, muscle and nervous. The integument is
comprised of: 1) the cutaneous membrane (skin); and 2) associated structures (hair, glands and nails).
The most superficial portion of the integumentary system is comprised of stratified squamous
(keratinized) epithelial tissue which makes the epidermis (epi - above or upon). Deep to this is a
combination pf areolar and dense irregular connective tissue that makes up most of the dermis. The
associated structures include exocrine glands (sebaceous and sweat), hair and hair follicles, and finger
and toe nails.
Gross Anatomy of the skin, hair, glands and nails
The Integumentary system includes the skin and the associated accessory structures hair, glands and nails.
Note that the skin is a type of membrane, which can be referred to as the cutaneous membrane. Ask
yourself, what is a membrane? It is like a formula:
Membranes in Anatomy = Epithelial Tissue
Connective Tissue
When examining models, drawings or slides of the skin, keep in mind that it will always be superficial
epithelium and deep connective tissue. Review the characteristics of epithelial and connective tissue and
see these qualities apply when examining the skin and its function . Examine the accessory structures of
the skin (hair, glands and nails) remembering that they are all derived from epithelial tissue but originate
in the dermis portion of the skin.
As usual , epi- means above , upon or on top. Sometimes a source of confusion is the naming of the
apocrine sweat gland; the ‘apo’ part means apical or top portion, such that it infers the secretion is made
by cleaving off the top of the cell. However, it is believed that this type of gland actually secretes by means
of merocrine mode. It is interesting to note that the integumentary system contains all four tissue types.
General Functions of Integumentary System
A. Gives Physical Protection
B. Prevents Pathogen Invasion
C. Restricts Desiccation (Dehydration)
D. Provides Sensory Perception
E. Vitamin D Production
, 2
A. The Epidermis – The most superficial layer of the skin is made of epithelial tissue . It is classified as
stratified squamous keratinized (dry) epithelium . The epidermis has either 4 (thin skin) or 5 (thick skin)
distinct layers or ‘strata’ that can be identified. Below is a description of each of the possible layers, from
the deepest layer to the most superficial.
1. Stratum Basale (Germinativa) – composed essentially of a single row of cells that make the deepest
layer of the epidermis. Roughly the cells in this layer are about 80-90% keratinocytes and 10-20%
melanocytes. The keratinocytes have mitotic potential which means they can divide and rapidly reproduce
in order to continue replacing themselves. These are the ‘stem cell’ of the bulk of the epidermis – the
name germinativa means ‘to germinate’, like a seed beginning to grow. These cells are sitting directly on
the basement membrane, which is attached to connective tissue directly deep to it. The melanocytes
located in this layer are the cells that produce the dark pigmented molecule melanin. When melanin
granules are released into the tissue in response to UVA light stimulation, the skin becomes darker. The
melanin provides protection to the nucleus (where the DNA resides) of keratinocytes against UVA
irradiation, to prevent UVA related cellular damage.
2. Stratum Spinosum – can be several cell layers thick. Mostly spindly keratinocytes with some scattered
Langerhans cells that provide immunological protection. The term spinosum means ‘spiny’; the spiny
appearance of the cells in this area is somewhat due to the histological preparation. Some cells are
beginning to die here, due to distance away from nutrients and oxygen in the blood supply of the dermis.
3. Stratum Granulosum - from 3 to 5 layers of flattened keratinocytes containing darkly staining
keratohyaline and lamellated granules, these are very effective waterproofing hydrophobic substances
that provide the protection against dehydration of the body at the surface of the skin.
4. Stratum Lucidum - a thin translucent band of a few cells, this layer is only found in thick skin, that is, the
skin found on the palms of the hands and soles of the feet. Lots of keratin here in this layer. Cells in this
layer are dead, as they are too far away from the capillaries in the underlying connective tissue.
Introduction to the Integumentary System
The integumentary system is considered an organ because it is made up of different tissues. Actually, it
contains all four of the primary tissues; epithelium, connective, muscle and nervous. The integument is
comprised of: 1) the cutaneous membrane (skin); and 2) associated structures (hair, glands and nails).
The most superficial portion of the integumentary system is comprised of stratified squamous
(keratinized) epithelial tissue which makes the epidermis (epi - above or upon). Deep to this is a
combination pf areolar and dense irregular connective tissue that makes up most of the dermis. The
associated structures include exocrine glands (sebaceous and sweat), hair and hair follicles, and finger
and toe nails.
Gross Anatomy of the skin, hair, glands and nails
The Integumentary system includes the skin and the associated accessory structures hair, glands and nails.
Note that the skin is a type of membrane, which can be referred to as the cutaneous membrane. Ask
yourself, what is a membrane? It is like a formula:
Membranes in Anatomy = Epithelial Tissue
Connective Tissue
When examining models, drawings or slides of the skin, keep in mind that it will always be superficial
epithelium and deep connective tissue. Review the characteristics of epithelial and connective tissue and
see these qualities apply when examining the skin and its function . Examine the accessory structures of
the skin (hair, glands and nails) remembering that they are all derived from epithelial tissue but originate
in the dermis portion of the skin.
As usual , epi- means above , upon or on top. Sometimes a source of confusion is the naming of the
apocrine sweat gland; the ‘apo’ part means apical or top portion, such that it infers the secretion is made
by cleaving off the top of the cell. However, it is believed that this type of gland actually secretes by means
of merocrine mode. It is interesting to note that the integumentary system contains all four tissue types.
General Functions of Integumentary System
A. Gives Physical Protection
B. Prevents Pathogen Invasion
C. Restricts Desiccation (Dehydration)
D. Provides Sensory Perception
E. Vitamin D Production
, 2
A. The Epidermis – The most superficial layer of the skin is made of epithelial tissue . It is classified as
stratified squamous keratinized (dry) epithelium . The epidermis has either 4 (thin skin) or 5 (thick skin)
distinct layers or ‘strata’ that can be identified. Below is a description of each of the possible layers, from
the deepest layer to the most superficial.
1. Stratum Basale (Germinativa) – composed essentially of a single row of cells that make the deepest
layer of the epidermis. Roughly the cells in this layer are about 80-90% keratinocytes and 10-20%
melanocytes. The keratinocytes have mitotic potential which means they can divide and rapidly reproduce
in order to continue replacing themselves. These are the ‘stem cell’ of the bulk of the epidermis – the
name germinativa means ‘to germinate’, like a seed beginning to grow. These cells are sitting directly on
the basement membrane, which is attached to connective tissue directly deep to it. The melanocytes
located in this layer are the cells that produce the dark pigmented molecule melanin. When melanin
granules are released into the tissue in response to UVA light stimulation, the skin becomes darker. The
melanin provides protection to the nucleus (where the DNA resides) of keratinocytes against UVA
irradiation, to prevent UVA related cellular damage.
2. Stratum Spinosum – can be several cell layers thick. Mostly spindly keratinocytes with some scattered
Langerhans cells that provide immunological protection. The term spinosum means ‘spiny’; the spiny
appearance of the cells in this area is somewhat due to the histological preparation. Some cells are
beginning to die here, due to distance away from nutrients and oxygen in the blood supply of the dermis.
3. Stratum Granulosum - from 3 to 5 layers of flattened keratinocytes containing darkly staining
keratohyaline and lamellated granules, these are very effective waterproofing hydrophobic substances
that provide the protection against dehydration of the body at the surface of the skin.
4. Stratum Lucidum - a thin translucent band of a few cells, this layer is only found in thick skin, that is, the
skin found on the palms of the hands and soles of the feet. Lots of keratin here in this layer. Cells in this
layer are dead, as they are too far away from the capillaries in the underlying connective tissue.
