Key terms
or Questions you
have.
Integumentary System
I. General Information
A. Organ system consists of a group of organs working together to perform a
specific activities.
B. Integumentary System: inte- =whole; gument = body covering= Composed of
organs such as skin, hair, and nails.
C. Skin (Cutaneous membrane) is the largest organ of the body in surface area and weight. (22
square feet; 10 pounds)
D. Functions: Regulate body temperature, protection, detect sensations, excretion, absorption, and
synthesis of vitamin D.
II. Structure of the Skin
A. Superficial layer – epithelial tissue (epidermis)
B. Deep layer – connective tissue makes up the dermis
C. Subcutaneous (subQ) layer or (Hypodermis) – Deep to the dermis but not part of the skin.
1. Also called hypodermis
2. This layer consists of areolar and adipose tissues.
3. Anchoring fibers that extend from the dermis attach the skin to the subQ layer.
4. The deep layer of the subQ layer is attached to underlying tissue and organs
5. The subQ and dermis layers contain nerve endings called lamellated (pacinian)
corpuscles, which are sensitive to pressure.
III. Epidermis
A. Composed of keratinized stratified squamous epithelium
B. Contains four types of cells
1. Keratinocytes
a). 90% of epidermal cells are keratinocytes
b). Arranged in four or five layers
c). Produce keratin a tough protein that helps protect skin
i. protection from heat, microbes, and chemicals
d). Produce lamellar granules, which release a water-repellent sealant.
2. Melanocytes
a). 8% of the epidermal cells are melanocytes
b). Produce the pigment melanin (melano means black)
c). Cytoplasmic extensions of the melanocytes extent between the keratinocytes.
d). Melanocytes transfer melanin to the keratinocytes
e). Melanin – is a yellow-red or brown-black pigment that gives skin color
f). Melanin absorbs damaging ultraviolet (UV) light
g). Melanocytes are more susceptible to UV damage than keratinocytes are
3. Langerhans cells
a). Participate in immune responses against microbes that invade skin
b). Langerhans cells, macrophages, and B cells help other immune cells fight
microbes.
c). Langerhans cells are damaged by UV light.
4. Merkel cells
a). Contact the flattened process of a sensory neuron called tactile (Merkel) disc.
b). Merkel cells and tactile discs detect touch sensations
C. Five Layers of the Epidermis
1. Stratum basale
a). Single row of cuboidal or columnar keratinocytes
b). Some stem cells are found in the stratum basale
2. Stratum spinosum
a). Superficial to the stratum basale
b). Eight to ten layers many-sided keratinocytes fitted closely together
c). More superficial layers become flattened as cell migrate to the surface
3. Stratum granulosum
a). Superficial to the stratum spinosum
b). Located in the middle of the epidermis
c). Three to five layers of keratinocytes that are undergoing apoptosis.
i). Apoptosis – Genetically programmed cell death (nucleus fragments
before cell dies)
d). Nuclei and cell organelles degenerate/dissolve
e). Keratinocytes contain mostly keratin and lamellar granules (No organelles)
f). Lamellar granules release lipids (oils) as a water-repellent sealant.
4. Stratum lucidum
a). Superficial to the stratum granulosum
b). Present only in thick skin: fingertips, palms, and soles of foot.
c). three to five layers of flattened clear, dead keratinocytes
d). Keratinocytes in this layer contain only keratin.
5. Stratum Corneum
a). Superficial to the stratum lucidum
b). 25 to 30 layers of flattened dead keratinocytes
c). These cells are continuously shed and replaced by migrating keratinocytes
from below.
d). Multiple layers of cells in the stratum corneum protect deeper layers from
injury.
f). Constant friction to this layer will cause a callus.
i. Callus – abnormal thickening of the stratum corneum
D. Keratinization
1. Newly formed cells in the stratum basale are pushed to the surface
2. As the cells move from one layer to another, keratin increases
3. Keratinized cells slough off when they reach the out layer of the stratum corneum.
4. Cells that are sloughed off are replaced by more keratinocytes from lower layers
5. It takes four weeks for a keratinocytes to form and migrate through the five layers.
6. Dandruff-excessive amount of keratinized cells shed from the skin of the scalp
IV. Dermis
A. Layer of skin between epidermis and subQ (Hypodermis) layer
B. Composed of connective tissue containing collagen and elastic fibers
C. Dermal papillae
1. Superficial layer of dermis (top 1/5 of dermis)
2. Papillae (nipple-shaped) structure
a). Contains capillary loops – capillaries
b). Corpuscles of touch – tactile receptor
c). Meissner corpuscles - nerve endings that are sensitive to touch
d). Free nerve endings – receive sensations of warmth, coolness, pain, tickling,
and itching.
D. The deeper part of the dermis
1. Attached to the subQ (Hypodermis) layer
2. Consists of dense irregular connective tissue containing:
a). Collagen, coarse elastic fibers
b). Adipose cells, hair follicles, nerves, oil glands, and sweat glands are found
in-between the elastic fibers.
c). Function of collagen and elastic fibers:
i). Extensibility – ability to stretch
ii). Elasticity – ability to return to original shape after stretching
iii). Striae – Stretch marks (cause by extreme stretching
pregnancy and obesity
V. Skin Color
A. Three pigments that give color to skin
1. Melanin – Causes skin color: pale yellow, red, tan, and black.
a). Melanocytes – cells that produce melanin and transfer it to keratinocytes
b). Most plentiful in epidermis of penis, nipples, area around nipples, face, and
limbs.
c). Number of melanocytes is about the same in all people groups
d). Differences in skin color are due to amount of melanin produced by cells.
e). Age (liver) spots – Freckle-like blemish; light brown to black in color
i. Age spots are areas of skin where melanin accumulate
ii. Nevus (Mole) – round, flat, or raised area of overgrown melanocytes
-Moles are usually non-cancerous (Benign)
2. Hemoglobin
1. Oxygen carrying protein that gives albinos’ skin color range from pink to red.
3. Carotene
a). Yellow-orange pigment that fives egg yolk and carrots color.
b). Associated with vitamin A (pigments for vision)
c). Meals high in carotene can cause the skin to turn orange.
VI. Accessory Structures of the Skin
A. Hair
1. Called pili - a thread of fused, dead keratinized cells that consist of a shaft and root
2. Present on most skin surfaces except on palms, fingers, soles, and toes
3. High growth areas are: scalp, eyebrows, and around external genitalia
4. Genetic traits and hormone levels determine thickness and pattern of hair distribution.
5. Structures of the hair
a). Shaft – Superficial portion, which extends above the skin
b). Root - Deeper portion, which extends below epidermis and into the dermis
c). Hair follicle – Surrounds the root
d). Hair root plexuses – Nerve endings that are sensitive to touch
e). Papilla of the hair – contain blood vessels that provide nourishment
f). Matrix – produces new hairs by cell division when old hairs are shed
g). Arrector pili – smooth muscle associated with hair
i. Extends from the upper dermis to the hair follicle
ii. Arrector pili contracts raising hair perpendicular to skin
iii. This action causes “goose bumps”
6. Color of hair
a). Melanin is secreted by melanocytes located in the matrix of the hair bulb
i. Dark hair contains true melanin
ii. Blond and red hair are caused by variants of melanin
iii. Gray hair is caused by a decline in melanin production
iv. White hair results from trapped air bubbles in the hair shaft
B. Glands of the skin
1. Sebaceous Glands or oil glands
a). Connected to hair follicles
b). Oil gland opens into the hair follicle or opens directly on skin’s surface.
c). No sebaceous glands on the palms of hands or soles of feet
d). Sebum – Oily substance secreted by sebaceous glands
i). Keeps hair from drying out
ii). Slows evaporation of water from skin
iii). Softens skin
iv). Inhibits bacterial growth
e). Blackheads – blocked sebaceous glands with accumulated sebum
i). Sebum is nutritive to certain bacteria causing pimples or boils form
ii). The color of blackheads is due to melanin and oxidized oil not dirt
2. Sudoriferous Glands or Sweat Glands
a). Three to four million in the skin
b). Two kinds
i.) Eccrine Sweat Glands
-more common than apocrine gland
-Most numerous in the skin of forehead, palms, and soles
- Gland is deep in dermis and opens by pores in the skin
-Glands produce 600mL day (over ½ a liter of sweat)
-Sweat contains water, ions, Na+, Cl-, urea, uric acid,
ammonia, amino acids, glucose, and lactic acid.
-Sweat helps cool the body through evaporation
ii. Apocrine Sweat Glands
-Sweat glands located in axilla (armpit), groin, areolae areas,
and bearded regions ooh h face in males.
-Glands mostly located in the subQ (hypodermis) layer of skin
-Secreted fluid has oils and proteins that make it more viscous
-Secreted during emotional stress (cold sweats)
3. Ceruminous Glands
a). Located in the skin of external auditory canal of ear
b). Cerumen (Earwax) – made up of ceruminous and sebaceous fluid
c). Prevents foreign debris from entering the ear canal
C. Nails
1. Made of tightly packed, hard, dead, keratinized cells of the epidermis.
2. Components of nails
a). Nail body – visible part of the nail
b). Free edge – Part of nail that is clipped – part extends past end of finger or toe
c). Nail root – Part of nail not visible, covered by cuticle
d). Lunula – whitish crescent next to cuticle
e). Nail Matrix – Where the nail grows (1mm per week)
f). Cuticle – composed of stratum corneum
g). Function – Helps grasp object, protects ends of fingers, allows scratching