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Integumentary System
• Cutaneous membrane (skin) – our largest organ
• Accounts for 7% of body weight• Divided into two distinct layers
•Epidermis•Dermis•Accessory structures
• Subcutaneous layer (hypodermis)
Functions Of The Integument
• Cushions and insulates deeper organs
• Protects body from abrasion, trauma, chemicals, pathogens, temperature extremes and UV rays
• Excretion and secretion
• Contains sensory receptors associated with nerve endings
• Synthesis and storage of nutrients (vitamin D3)
Integumentary Structures
• Components of the Integumentary System
Figure 5-1
Skin Structures
The Epidermis- Four Main Cell Types • Melanocytes - found in basal
layer, manufacture and secrete pigment
• Merkel cells - basal layer, attached to sensory nerve endings
• Keratinocytes – Arise from deepest layer of epidermis to stratum spinosum• Produce keratin – a tough
fibrous protein• Produce antibodies and
enzymes• Keratinocytes are dead at skin's
surface• Langerhans cells - stratum
spinosum, part of immune system macrophage-like
The Epidermis• Stratified squamous epithelium
• Several distinct cell layers• Thick skin—five layers on palms and soles• Thin skin—four layers on rest of body
Layers of The Epidermis
• Stratum corneum• Most superficial layer• Dead, flattened
(squamous) cells• Abundant keratin -
Keratinized (cornified) tough, water-resistant protein
• Protects skin against abrasion and penetration
• Stratum lucidum (clear layer)• Occurs only in thick
skin – palms and soles• Composed of a few
rows of flat, dead keratinocytes
Layers of The Epidermis• Stratum granulosum (grainy
layer)• Consists of keratinocytes
• Tonofilaments• Keratohyaline granules
– help form keratin• Lamellated granules –
contain a waterproofing glycolipid
• Stratum spinosum (spiny layer)• “Spiny” appearance caused
by artifacts of histological preparation
• Contains thick bundles of intermediate filaments (tonofilaments)
• Resist tension• Contain protein
prekeratin • Contains star-shaped
Langerhans cells
Layers of the Epidermis
• Stratum basale• Deepest layer of
epidermis• Attached to underlying
dermis• Stem cells actively divide• Merkel cells – associated
with sensory nerve ending• Melanocytes – secrete
the pigment melanin
Epidermal Cells and Layers of the Epidermis
Figure 5.3
Sources of Skin Color
• Melanocytes• Make melanin from tyrosine• Melanin provides UV
protection• Gives reddish-brown to
brown-black color
• Carotene• Contributes orange-yellow
color• Provided from diet (carrots
and tomatoes)
• Hemoglobin - blood pigment• Caucasian skin contains
little melanin• Allows crimson color of
blood to show through
Dermis• Second major layer of the skin• Provides mechanical strength, flexibility, and
protection for underlying tissues• Highly vascular and contains a variety of sensory
receptors that provide information about the external environment
• Two layers• Papillary layer – includes dermal papillae• Reticular layer - deeper layer – 80% of thickness of dermis
• Flexure lines - creases on palms
Layers of the Dermis• Papillary layer
• Underlies epidermis• Named for dermal papillae• Aerolar connective tissue• Supports, nourishes epidermis• Provides sensory nerves,
lymphatics, and capillaries
• Reticular layer• Tough, dense, fibrous layer• Dense irregular connective tissue• Collagen fibers - limit stretch• Elastic fibers - provide flexibility• Blends into papillary layer (above)• Blends into subcutaneous layer
(below)
Dermal Components• Epidermal accessory
organs
• Cells of connective tissues proper
• Communication with other organ systems• Cardiovascular• Lymphatic• Nervous
• Sensation• Control of blood flow
and secretion
Subcutaneous Layer - Hypodermis• Composed of loose connective tissue - areolar and adipose
• Stabilizes skin position• Loosely attached to dermis• Loosely attached to muscle
• Contains many fat cells• Provides thermal insulation• Cushions underlying organs
• Safely receives hypodermic needles
Hair
• Filamentous strands of dead keratinized cells produced by hair follicles
• Contains hard keratin which is tougher and more durable than soft keratin of the skin
• Chief parts of a hair• Root – imbedded in the
skin• Shaft – projects above
skin's surface
Hair
• Hair Shaft organized into three concentric layers• Medulla – central core • Cortex – surrounds medulla• Cuticle – outermost layer
• Pigmented by melanocytes at the base of the hair
Cross Section of a Hair
Figure 5.7a, b
Hair Follicle• Root sheath extending from
the epidermal surface into the dermis
• Deep end is expanded forming a hair bulb
• Papilla - nipple-shaped indentation with blood vessels and nerves
• Matrix - germinal layer of cells (actively dividing cells) right above the papilla
• A knot of sensory nerve endings (a root hair plexus) wraps around each hair bulb
• Bending a hair stimulates these endings, hence our hairs act as sensitive touch receptors
• Arrector pili muscle - bundle of smooth muscle contracts to make hair stand erect
Longitudinal Section of Follicle
Figure 5.7c, d
Hair Follicles
Hair Function and Distribution• Functions of hair include:
• Helping to maintain warmth
• Alerting the body to presence of insects on the skin
• Guarding the scalp against physical trauma, heat loss, and sunlight
• Hair is distributed over the entire skin surface except• Palms, soles, and lips
• Nipples and portions of the external genitalia
Sebaceous Glands (oil glands)• Occur over entire body - Except palms and soles• Simple alveolar glands
• Holocrine secretion – entire cell breaks up to form secretion• Secretes an oily substance called sebum• Most are associated with a hair follicle
• Functions of sebum• Softens and lubricates hair and skin• Skin waterproofing • Collects dirt
Sweat (Sudoriferous) Glands
• Two types:• Eccrine (Merocrine)
• Most abundant sweat gland• “True sweat”
• 99% water with some salts• Contains traces of
metabolic wastes ~ 2% urea
• Role in thermoregulation• Widely present in skin (up to
500/cm2)
• Apocrine• Odorous secretion • Absent before puberty• Present in axillary, areolar,
anal and genital areas
Eccrine (Merocrine) Gland
Figure 5.10b
Nails• Scalelike modification of epidermis made of hard keratin• Parts of the nail
• Free edge• Body - dense mass of keratinized cells• Root• Nail folds• Eponychium – cuticle
Skin Injury and Repair
Four Stages in Skin Healing• Inflammation
• Blood flow increases• Phagocytes attracted
• Scab formation• Cell division and
migration• Scar formation
Bleeding occurs at the site of injury immediately after the injury, and mast cells in the region trigger an inflammatory response.
Epidermis
Dermis
After several hours, a scab has formed and cells of the stratum germinativum are migrating along the edges of the wound. Phagocytic cells are removing debris, and more of these cells are arriving with the enhanced circulationin the area. Clotting around the edgesof the affected area partially isolatesthe region.
Sweat gland
Scab
Macrophagesand
fibroblasts
Migratoryepithelialcells
Granulationtissue
Skin Injury and Repair
One week after the injury, the scab has been undermined by epidermal cells migrating over the meshwork produced by fibroblast activity. Phagocytic activity around the site has almost ended, and the fibrin clot is disintegrating.
Fibroblasts
After several weeks, the scab has been shed, and the epidermis is complete. A shallow depression marks the injury site, but fibroblasts in the dermis continue to create scar tissue that will gradually elevate the overlying epidermis.
Scartissue
Skin Injury and Repair
Skin Injury and Repair
Table 5-1
Aging of the Skin
• Major Age-Related Changes• Injury and infection increase• Immune cells decrease•Sun protection diminishes•Skin becomes dry, scaly•Hair thins, grays•Sagging, wrinkles occur•Heat loss decreases•Repair slows
Effects of UV Radiation• Beneficial effect - activates synthesis of
vitamin D3
• Harmful effects• Sun burn• Wrinkles, premature aging• Malignant melanoma• Basal cell carcinoma
Types and Growth of Hair
Vellus hairs•Body hairs of women and children
Terminal hairs•Hair of scalp•Axillary and pubic area (at puberty)
Hair thinning and baldness•Due to aging•Male pattern baldness
Burns
Classified by severity•First-degree burn – only upper epidermis
is damaged•Second-degree burn – upper part of
dermis is also damaged• Blisters appear• Skin heals with little scarring
•Third-degree burn• Consume thickness of skin• Burned area appears white, red, or
blackened
Estimating Burns Using the Rule of Nines
Figure 5.11a
Skin Cancer
Basal cell carcinoma•Least malignant and most common
Squamous cell carcinoma•Arises from keratinocytes of stratum
spinosum
Melanoma•A cancer of melanocytes •The most dangerous type of skin cancer
Skin Cancer
Squamous cell carcinoma
Figure 5.12Melanoma
Squamous cell carcinoma
Basal cell carcinoma
The Skin Throughout Life
Epidermis•Develops from embryonic ectoderm
Dermis and hypodermis•Develop from mesoderm
Melanocytes•Develop from neural crest cells
The Skin Throughout Life
Fetal skin•Well formed after the fourth month•At 5-6 months
• The fetus is covered with lanugo (downy hairs)
•Fetal sebaceous glands produce vernix caseosa
The Skin Throughout Life
Middle to old age•Skin thins and becomes less elastic•Shows harmful effects of environmental
damage•Skin inflammations become more common