1. The Integumentary System
Integumentary system
- The skin and its derivatives (sweat and oil glands, hairs, and nails)
- Provides external protection for the body.
Functions of the Integumentary System
1. Protection
a. Chemical Barriers (skin secretion and melanin)
i. Skin secretions (acid mantle)
1. Low pH and sebum slow bacterial growth on skin surface
2. Human defensin – natural antibiotic
3. Cathelicidins – proteins that prevent Strep A infection in wounded skin
ii. Melanin – chemical pigment that prevents UV damage
b. Physical/Mechanical Barriers – continuity of the skin and hardness of keratinized cells
i. Continuity prevents bacterial invasion
ii. Glycolipids prevent diffusion of water and water-soluble substances between cells
iii. Substances that are able to penetrate the skin:
1. Lipid-soluble substances (i.e., oxygen, carbon dioxide, steroids, and fat-soluble vitamins)
2. Oleoresins of certain plants (ex. Poison ivy and poison oak)
3. Organic solvents (ex. Acetone, dry cleaning fluid, and paint thinner)
4. Salts of heavy metals (ex. Lead, mercury, and nickel)
5. Penetration enhancers
c. Biological Barriers – Langerhans’ cells, macrophages, and DNA
i. Langerhans’ cells in epidermis present antigens to lymphocytes
ii. Dermal macrophages (2nd line of defense) – attack bacteria and viruses that have penetrated the epidermis
iii. DNA structure – the electrons in DNA absorb UV radiation and converts it to heat
2. Body Temperature Regulation
a. Production of copious amounts of sweat to dissipate heat
b. Constriction of dermal blood vessels to retain heat
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2. 3. Cutaneous Sensation – cutaneous sensory recptors (nervous system)
a. Meissner’s corpuscle and Merkel cells – detect changes in pressure
b. Pacinian receptors – detect deep pressure contacts
c. Hair follicle receptors – movement across the surface of the skin
d. Nerve endings – detect painful stimuli
4. Metabolic Functions
a. Synthesis of Vitamin D – increases calcium absorption in the body
b. Chemical conversion of many substances
5. Blood Reservoir – vasoconstriction and vasodilation
6. Excretion – elimination of nitrogen-containing wastes, salt, and water
Characteristics of Skin (or the integument)
1. Covers the entire body
2. Accounts for about 7% of total body weight
3. Pliable, yet durable
4. Thickness: 1.5 to 4.0 mm
5. Composed of the epidermis and dermis
a. Epidermis
i. Composed of epithelial tissue (keratinized stratified squamous)
ii. Cell population:
1. Keratinocytes (majority) – produce keratin
a. Keratin – fibrous protein; waterproofing
b. Keratinocytes arise from the stratum basale
c. Dead cells in the upper portions of the epidermis
2. Melanocytes – synthesize melanin
a. Found in the deepest layer of the epidermis
b. Melanin pigments are taken up by keratinocytes and accumulated on the superficial side of their
nuclei; protects the cells’ nuclei from UV radiation.
3. Langerhans’ cells (aka epidermal dendritic cells) – macrophages
a. Arise from the bone marrow
b. Most abundant in the stratum spinosum
4. Merkel cells – sensory reception
a. Located at the epidermal-dermal junction
iii. Outermost portion of the skin
iv. Subdivided into four or five distinct layers
1. Stratum basale (aka, stratum germinativum) – deepest layer
a. Attached to the dermis
b. Single row of rapidly dividing keratinocytes
c. Melanocytes and occasionally Merkel cells are found in this layer
2. Stratum spinosum
a. Several layers thick
b. Appear spiny in shape
c. Cells contain pre-keratin filaments
d. Melanin granules and Langerhans’ cells are present in this layer
3. Stratum granulosum
a. Three to five layers thick
b. Keratinocytes appear flattened, organelles and nuclei disintegrate; granulated cytoplasm
remains; cell membranes thicken
c. Distance from the dermal capillaries is too great – cells begin to die
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3. 4. Stratum lucidum (thick skin only)
a. Found only in the palms, fingertips, and soles of the feet
b. Appears translucent under the microscope
c. Few rows of clear, flat, dead keratinocytes
5. Stratum corneum – outermost layer
a. 20 to 30 cell layers thick
b. Protect deeper cells from waterloss, the effects of air, chemical, physical, and biological assault
c. Avascular region
b. Dermis
i. Composed of fibrous connective tissue
ii. Cell populations
1. Fibroblasts producing a semi-fluid matrix
2. Macrophages
3. Mast cells and white blood cells
iii. The bulk of the integument
iv. Subdivided into two layers
1. Papillary layer – thin layer
a. Composed of areolar connective tissue
b. Highly vascularized
2. Reticular layer
a. Composed of collagen fibers
v. Highly vascularized and innervated
vi. Major portions of the hair follicles and oil and sweat glands are found in this layer
6. Skin color
a.Three pigments contribute to skin color:
i. Melanin – brownish-black pigment produced by melanocytes in the skin
1. Freckles and pigmented moles result from an accumulation of melanin
ii. Carotene – yellow-orange pigment found in certain plants, such as carrots
1. Is usually deposited in the stratum corneum and the fatty tissue of the hypodermis
iii. Hemoglobin – pigment found in red blood cells
7. Appendages of the Skin are derived from the epidermis
a. Nails
i. The nail matrix contains rapidly dividing cells that eventually become dead and keratinized
ii. Hardened nails protect the delicate tissues of the fingers and toes
b. Hair follicles and hair
i. Hair produced the hair follicles in the dermal layer of the skin
1. Hair is composed mainly of dead, keratinized cells
2. A strand of hair is composed of three layers:
a. Medulla – the innermost layer
b. Cortex – surrounds the medulla
c. Cuticle – provides strength and maintains the structure of the inner layers
3. Hair color is determined by the pigment melanin produced by melanocytes at the base of the hair follicle
c. Sweat glands
i. Eccrine sweat glands
1. Found on the palms, soles, and forehead
2. Secretes sweat
a. Sweat is composed of mainly water and salts
b. Sweat is acidic and slows microbial growth on the skin
ii. Apocrine sweat glands
1. Found in the anogenital and axillary (armpit) regions
2. Secretion contains the same components of true sweat plus fatty substances and proteins
a. Produces “body odor”
iii. Ceruminous glands – produce wax
1. Wax deters insects and blocks the entry of foreign material into the ear canal
iv. Mammary gland – specialized sweat glands that secrete milk
d. Sebaceous (oil) glands
i. Found all over the body except on the palms and soles
ii. Produce oil (sebum)
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4. 1. Sebum softens and lubricates the hair and skin; waterproofs the hair and skin
2. Sebum is also important in inhibiting microbial growth on the surface of the skin
Clinical Disorders or Diseases of the Skin and its Appendages
• Acne – inflammation of the sebaceous glands
o Whitehead – blockage of the sebaceous gland by accumulating sebum
 Appears on the skin surface
o Blackhead – blockage of the sebaceous gland by accumulating sebum
 The material blocking the gland is oxidized and becomes darkened
• Burns – tissue damaged inflicted by intense heat, electricity, radiation, or certain chemicals
o Types of burns:
 First-degree – only the epidermis is damaged
• Symptoms: redness, swelling, and pain
• Example: sunburn
 Second-degree – the epidermis and upper dermis is damaged
• Symptoms: redness, swelling, pain, and blister formation
• Patients are susceptible to infection and subsequent scarring, if untreated
 Third-degree – the entire surface of the skin is damaged
• Fluid loss and infection are potentially fatal, if left untreated; No pain in these regions, because nerve
endings have been destroyed
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