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Chapter 6: Skin and the Integumentary System. Skin: Largest organ Otherwise known as cutaneous membrane Forms barrier between our internal environment and the external world Vital in maintaining homeostasis Regulates body temperature Prevents water loss Houses sensory receptors - PowerPoint PPT Presentation
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Chapter 6: Skin and the
Integumentary System
Introduction Skin:
Largest organ Otherwise known as cutaneous membrane Forms barrier between our internal environment
and the external world Vital in maintaining homeostasis
Regulates body temperature Prevents water loss Houses sensory receptors Synthesize biochemicals Excretes wastes (very small amount)
Makes up integumentary system Includes skin and accessory organs
LAYERS OF SKIN
Layers Two layers:
1) Epidermis: Outer layer Composed of stratified squamous epithelial
tissue 2) Dermis
Inner layer Contains:
Connective tissues (collagenous fibers, elastic fibers, blood) Epithelial tissue Smooth muscle tissue Nervous tissue
Layers Other layers:
1) Basement: Anchors dermis to epidermis
2) Hypodermis or Subcutaneous: Beneath skin Contains masses of loose connective and adipose
tissue Binds skin to underlying organs
Epidermis Characteristics:
Lacks blood vessels Composed of stratified squamous epithelium
tissue Divides and grow
Pushes older cells away from dermis and towards surface
Become less and less nourished and eventually die Keratinization: older cells harden and die (cytoplasm
fills with keratin protein) Healthy skin: balances cell division with cell death Areas of continual wear: causes fast cell division and
thickened layers called calluses (hands, soles of feet) and corns (toes)
Epidermis Layers of epidermis:
Stratum corneum: Hardened outer layer (mostly
dead, keratinized cells) Stratum lucidum:
Only present in palms and soles of feet
Hardened, thickened layer Stratum granulosum:
Very thin layer Stratum spinosum:
More spacious, numerous Stratum basale:
Nourished by blood vessels in dermis, newest cells, most nourished, next to basement membrane
Epidermis Characteristics, cont.:
Important protective functions Shields moist underlying tissues against:
Excessive water loss Mechanical injury Effects of chemicals, mutagens, pollutants Pathogens
Contains melanocytes (cells which produces melanin – dark pigment that provides skin color to protect against UV)
Albinism: inability to produce melanin
Epidermis: Skin Color Largely due to amount of melanin All people have the same average number
of melanocytes Differences in color: come from the AMOUNT of
melanin the melanocytes produce Most genetically determined Environmental effects: UV (sun and artificial), X-
rays Physiological effects: blood in dermal layer
Red: well-oxygenated; Blue (very dark red)-deoxygenated
Called cyanosis Yellow (diet) – yellow vegetables containing B-carotene
Dermis Characteristics:
Contain dermal papillae (projections of the dermis which extend into epidermal spaces)
Fingerprints are as a result of these projections (determined by genes)
Binds epidermis to underlying tissues Composed of dense connective tissue (includes
collagenous and elastic fibers) Contains blood vessels (supply nutrients to all
skin cells, regulate body temperature) Nerve cells scattered throughout Contain hair follicles, sebaceous glands, sweat
glands
Subcutaneous Layer Characteristics:
Otherwise known as hypodermis Contains loose connective and adipose tissues Composed of collagenous and elastic fibers
(continuous with those of dermis) No sharp boundary between this layer and
dermis Adipose:
Insulates Regulates body temp (conserving body heat, not
allowing heat to enter) Contains blood vessels
ACCESSORY GLANDS OF SKIN
Nails Characteristics:
Protective coverings Consists of nail plate (overlies surface of the
skin called the nail bed) White, base of nail (lunula) – covers the most
actively growing portion of epidermis As cells divide here, they keratinize Then these keratinized cells become scales that
become part of nail plate Thumb: slowest Middle: fastest
Hair Follicles Characteristics:
Present everywhere BUT palms, soles, nipples
Hair develops from group of epidermal cells at the base of hair follicle
Follicle extends from surface into dermis Cells nourished via dermal blood vessels As cells grow and divide, pushed upward As push upward, keratinize and die
Hair Follicles Characteristics:
Remains become structure of hair (shaft extends outward)
Color: determined by genes (direct color and amount of pigment)
Arrector pili muscle – smooth muscle, attach to each hair follicle
These muscles can be stimulated to contract (when heat is needed) – produces gooseflesh (goosebumps)
Sebaceous glands Characteristics:
Otherwise known as oil glands Closely associated with hair follicles Holocrine glands (secrete oily mixture of
fatty and sebum – cellular wastes) Secrete mixture through small ducts Sebum – helps keep hair and skin soft, pliable
and waterproof
Sweat glands Characteristics:
Otherwise known as sudoriferous glands Exocrine gland Widespread Consists of:
Tiny coiled tube laying in subcutaneous layer or deep dermal layer
Most numerous type: eccrine (respond to body temperature changes)
Common forehead, neck and back (produce profuse sweat)
Sweat glands Characteristics:
Sweat (fluid) carried away via duct which leads to pore (on surface)
Sweat is mostly water Contains small amount of salt, wastes (urea, uric acid)
Apocrine glands: Become active at puberty Secrete via same mechanism as eccrine glands Secrete when person is emotionally upset, frightened
or in pain Most numerous in groin and axillary region
Mammary glands: Modified sweat glands, secrete milk
OTHER FUNCTIONS OF SKIN
Regulate body temperature Humans: Internal temp = 98.6oF (37oC) Mammals must balance heat gained with
heat lost Skin plays vital role in maintaining this
homeostatic mechanism As body temp drops, nerve impulses
stimulate structures in skin to conserve heat Blood vessels contract, decreasing flow (reduces
heat loss) Sweat glands are inactive Muscle contract – producing heat
Regulate body temperature As body temp rises, nerve impulses
stimulate structures in skin to release heat Blood dilation (more blood enter, heat
carries/escapes) Warm blood reaches hypothalamus (which
controls body temperature set point) Eccrine sweat glands release sweat (as sweat
evaporates, heat is carried away from surface) Hot vs. Cold
Healing Wounds Inflammatory response:
Normal response to injury or stress Red, painful, warm, swollen
Becomes red when blood vessels dilate and become more permeable (forces fluids to leave vessels and enter tissue)
Advantage: Provides tissue with more nutrients and oxygen (aid in healing process)
Healing Wounds Shallow cut
Epithelium will divide rapidly, filling in gap Deep cut
Blood vessels break, clot forms Clot and tissues form scab (protect
underlying tissues) Fibroblasts migrate to injury and begin
forming new collagenous fibers (bind edges of wound together)
Scar: forms when connective tissue appears on surface
Disorder Name DescriptionAcne Disease of sebaceous/oil glands
Alopecia Hair loss
Birthmark Congenital blemish, visible at birth
Boil Bacterial infection hair follicle
Dermatitis Inflammation of skin
Eczema Noncontagious skin rash, itching, blistering, scaling
Herpes Caused by herpes simplex virus, recurring formations of small sores
Keloid Elevated, enlarged scar tissue
Mole Fleshy skin tumor, usually pigmented
Psoriasis Chronic skin condition, red patches
Wart Flesh-color, raised area, viral infection
Skin Disorders
Boil
Dermatitis
Herpes
KeloidAlopeci
a
Mole
Wart
Psoriasis
Eczema