Perspiration Insensible perspiration: –interstitial fluid lost by evaporation through the stratum corneum Sensible perspiration: –water excreted by sweat glands

Water Loss Through Skin Dehydration results: –from damage to stratum corneum, e.g., burns and blisters (insensible perspiration) –from immersion in hypertonic solution, e.g., seawater (osmosis)

Water Gain Through Skin Hydration: –results from immersion in hypotonic solution, e.g., freshwater (osmosis) –causes stretching and wrinkling skin

Skin Color Skin color depends on: –the pigments carotene and melanin –blood circulation (red cells)

Melanocytes Skin color depends on melanin production, not number of melanocytes

Capillaries and Skin Color Oxygenated red blood contributes to skin color: –blood vessels dilate from heat, skin reddens –blood flow decreases, skin pales

Characteristics of Dermis Strong, due to collagen fibers Elastic, due to elastic fibers Flexible (skin turgor)

Skin Damage Sagging and wrinkles (reduced skin elasticity) are caused by: –dehydration –age –hormonal changes –UV exposure

Stretch Marks Thickened tissue resulting from: –excessive stretching of skin due to: pregnancy weight gain

Lines of Cleavage Collagen and elastic fibers in the dermis: –are arranged in parallel bundles –resist force in a specific direction

Clinical Importance Lines of cleavage establish important patterns: –a parallel cut remains shut, heals well –a cut across (right angle) pulls open and scars

Lines of Cleavage Figure 5–7

Nerves Nerve fibers in skin control: –blood flow –gland secretions –sensory receptors Tactile disks called Merkel cells

The Hypodermis The subcutaneous layer or hypodermis: –lies below the integument –stabilizes the skin –allows separate movement –not a skin layer

Structure of the Hypodermis The subcutaneous layer is: –made of elastic areolar and adipose tissues –connected to the reticular layer of integument by connective tissue fibers

Clinical Importance Subcutaneous layer: –has few capillaries and no vital organs –is the site of subcutaneous injections using hypodermic needles

Adipose Tissue Deposits of subcutaneous fat: –have distribution pattern determined by hormones –are reduced by cosmetic liposuction

Location of Hair The human body is covered with hair, except: –palms –soles –lips –portions of external genitalia

Functions of Hair Protects and insulates Guards openings against particles and insects Is sensitive to very light touch

The Hair Follicle Is located deep in dermis Produces nonliving hairs Is wrapped in a dense connective- tissue sheath Base is surrounded by sensory nerves (root hair plexus)

Layers in a Hair Medulla: –the central core Cortex: –the middle layer Cuticle –the surface layer

Types of Hairs Vellus hairs: –soft, fine –cover body surface Terminal hairs: –heavy, pigmented –head and eyebrows –other parts of body after puberty

Structure of Hair

Hair Color Produced by melanocytes at the hair papilla Determined by genes

Structure of Fingernail

Repair of Localized Injuries to the Skin: Step 1 Bleeding occurs Mast cells trigger inflammatory response Figure 5–13 (Step 1)

Repair of Localized Injuries to the Skin: Step 2 A scab stabilizes and protects the area Figure 5–13 (Step 2)

The Inflammatory Response Germinative cells migrate around the wound Macrophages clean the area Fibroblasts and endothelial cells move in, producing granulation tissue

Repair of Localized Injuries to the Skin: Step 3 Fibroblasts produce scar tissue Inflammation decreases, clot disintegrates Figure 5–13 (Step 3)

Repair of Localized Injuries to the Skin: Step 4 Fibroblasts strengthen scar tissue A raised keloid forms Figure 5–13 (Step 4)

Effects of Aging Epidermal thinning Decreased numbers of Langerhans cells Decreased vitamin D 3 production Decreased melanocyte activity Decreased glandular activity (sweat and oil glands)

Effects of Aging Reduced blood supply Decreased function of hair follicles Reduction of elastic fibers Decreased hormone levels Slower repair rate

Importance of the Integumentary System Protects and interacts with all organ systems Changes in skin appearance are used to diagnose disorders in other systems