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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)
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
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
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 D3 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