Integumentary System
Anatomy and Physiology | Tutorial Notes
Tissues
Learning objectives
After study of this chapter, the student will:
1. Describe the structure of layers of the skin.
2. Summarize the factors that determine skin color.
3. Describe the accessory structures associated with the skin.
4. Explain the functions of each accessory structure of the skin.
5. List various skin functions and explain how the skin helps regulate body temperature.
6. Describe wound healing.
7. Distinguish among the types of burns, including a description of healing with each type.
8. Summarize life-span changes in the integumentary system.
tutorial outline
I. Layers of Skin
A. Epidermis – Stratified Squamous Epithelium
B. Dermis – Dense Irregular Connective Tissue, Smooth Muscle Tissue, Nervous Tissue
C. Subcutaneous Layer – Areolar Connective Tissue, Adipose, Blood Vessels
· Not included as a layer of skin
II. Epidermis
A. Avascular
B. Composed of stratified squamous epithelium
C. Thickness of skin varies from region to region
1. Epidermis is thickest on soles of feet and palms of the hand
2. Epidermis is thinnest on eyelids
D. Epidermis contains 4 – 5 layers, depending on the thickness
Arranged from Deep skin to superficial surface:
1. Stratum Basale
i. Stratum basale is the deepest layer of epidermis, 1 – 2 Cell Layers thick
iii. Composed of basal keratinocytes (stem cells of the epidermis)
iv. Keratinocytes of stratum basale divide to form the keratinocytes of the stratum spinosum.
v. Melanocytes within the stratum basale produce the pigment melanin.
§ Melanin provides skin color
§ Melanin absorbs UV radiation in sunlight, protecting cells from UV damage, which causes mutations in the DNA of skin cells
§ Differences in skin color result from the differences in the amount of melanin produced by the melanocytes.
2. Stratum Spinosum
i. Stratum spinosum has a prickly appearance
ii. Keratinization begins in the stratum spinosum
§ Keratinization = cells begin to accumulate a hardened, water insoluble protein, called keratin.
3. Stratum Granulosum
i. Stratum granulosum is composed of keratinocytes that have migrated upwards from the stratum spinosum.
ii. Keratinocytes in this layer bind keratin filaments together and become known as granular cells.
4. Stratum Lucidum
i. Stratum Lucidum is a thin clear layer of dead cells visible only in areas of thick skin (palms of hands and soles of feet)
5. Stratum Corneum
i. Stratum cornuem is the outermost layer of epidermis
ii. Stratum corneum contains 15 – 20 layers of flattened dead keratinized cells.
iii. The dead cells eventually shed.
E. Functions of the Epidermis
1. retards water loss
2. protects body from mechanical injury
3. provides protection from harmful chemicals
4. prevents pathogens from entering the body
III. Dermis
A. Dermal papillae
1. Dermal papillae form the border between dermis and epidermis
2. Dermal papillae increase surface area where the epidermis receives oxygen and nutrients from dermal capillaries
3. Fingerprints are formed from the ridges of the dermal papillae
B. Components within the Dermis
1. Dermis contains areolar connective tissue and dense irregular connective tissue
2. Smooth muscle fibers associated with hair follicles and glands
3. Facial muscles are anchored into the dermis
4. Dermal blood vessels supply nutrients to all skin cells.
5. Nerve cell processes are scattered throughout dermis.
6. Sensory Receptors of the dermis include:
· Lamellated (Pacinian) corpuscles – respond to heavy pressure
· Tactile (Meissner’s) corpuscles – light touch and texture
· Free Nerve endings – respond to temperature and tissue damage
§ Free nerve endings extend into epidermis
7. Accessory structures: sweat glands, sebaceous glands, hair follicles
IV. Accessory Structures of the Skin
A. Nails
1. Protective coverings on the ends of fingers and toes
2. Nail Plate – the hard and translucent portion of the nail that overlies the skin
3. Nail Bed – portion of skin underneath the nail plate
4. Lunula – half-moon shaped region at the base of the nail plate. Most active growing region.
B. Hair Follicles
1. Hair is present on all skin surfaces except the palms, soles, lips, nipple, and parts of the external reproductive organs.
2. Hair follicle – tube-like depression, which contains a group of epidermal stem cells at the base.
3. Hair root – portion of hair extending from the surface into the dermis (and sometimes the subcutaneous layer)
4. Hair shaft – composed of dead, keratinized cells
5. Hair papilla – contains blood vessels to nourish the hair
6. Arrector pili muscle - attaches to hair follicle
· Mammals with fur – arrector pili muscles raises its fur for insulation
· For some animals (e.g. cats) arrector pili muscles raises its fur to exaggerate the animal’s size
· In humans, arector pili muscles are responsible for goosebumps
C. Sebaceous glands
1. Holocrine glands – gland releases entire cells
2. Usually associated with hair follicles
3. Secrete sebum – mixture of fatty material and cell debris
4. Sebum keeps hairs and skin soft, pliable, and waterproof
D. Sweat (sudoriferous) glands
1. Eccrine (merocrine) glands
· Most numerous sweat glands
· Most abundant on forehead, neck and back
· Respond to elevated body temperature
· Also release sweat that appears on the palms and soles when a person is emotionally stressed.
·
2. Apocrine sweat glands
· Located in axillary and groin areas
· Sweat develops a scent as its metabolized by bacteria
· Become active at puberty
· Wet certain areas of the skin when a person is emotionally upset, frightened, or in pain.
· Active during sexual arousal.
E. Ceruminous Glands - modified sweat glands that secrete ear wax
F. Mammary Glands – modified sweat glands that secrete milk
V. Functions of the skin
• Protective covering, barrier against harmful substances and microorganisms
• Prevents some water loss
• Contains sensory receptors
• Excretes some wastes
• Helps produce Vitamin D
• Helps regulate body temperature
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