06 Integumentary System

INTEGUMENTARY SYSTEM SKIN

• BODY’S LARGEST ORGAN • APPROXIMATELY 7% ADULT BODY WEIGHT

Main Concepts • Functions – Holds it all together – Protection – Water Resistant – Temperature Reg. – BP Regulation – Excretion – Sensory Perception – Metabolic Function

• Anatomy – Epidermis • 4 cell types

– Dermis • 2 layers

– Hypodermis • (not part of integument)

FUNCTIONS OF SKIN • KEEP’S EVERYTHING IN!!! • PROTECTION – AGAINST INFECTION • RESISTANT TO INVASION • LOW pH OF SKIN SECRETIONS (‘ACID MANTLE’) KEEPS BACTERIA FROM MULTIPLYING • NATURAL ANTIBIOTIC SECRETION • CONTAINS MACROPHAGES AND LANGERHANS CELLS FOR CASES OF A BREAK IN THE SKIN

– PHYSICAL HARM • CONTINUITY OF SKIN • HARDNESS OF KERATINIZED CELLS

• WATER RESISTANT (NOT WATERPROOF) – GLYCOLIPIDS OF SKIN FORMS BARRIER TO WATER – LOSE APPX. 500 ml OF WATER/ DAY ON AVERAGE (WITHOUT VIGOROUS EXERCISE)

FUNCTIONS OF SKIN • TEMPERATURE REGULATION – SWEATING (EVAPORATION) – VASODILATION/ VASOCONSTRICTION (8x INCREASE IN HEAT CONDUCTANCE THROUGH SKIN WHEN VASODILATED) – INSULATION, ESPECIALLY SUBCUTANEOUS FAT – GOOSEBUMPS (WELL, NOT REALLY, BUT GOOD TRY!)

FUNCTION • BLOOD PRESSURE REGULATION – VASOCONSTRICTION/ VASODILATION

• EXCRETION OF WASTES – UREA, AMMONIA, URIC ACID, SALT

• SENSORY – – – – –

PAIN RECEPTORS TOUCH RECEPTORS TEMPERATURE RECEPTORS PRESSURE RECEPTORS VIBRATION RECEPTORS

• METABOLIC FUNCTION – ABLE TO PRODUCE VITAMIN D FROM CHOLESTEROL IN BLOOD VESSELS WHEN EXPOSED TO SUNLIGHT

SKIN ANATOMY • EPIDERMIS – STRATIFIED SQUAMOUS EPITHELIAL CELLS – NONVASCULAR

• DERMIS – TOUGH, FIBROUS CONNECTIVE TISSUE – VASCULAR

• HYPODERMIS : NOT PART OF THE INTEGUMENT (SUBCUTANEOUS) – SUPERFICIAL FASCIA – MOSTLY ADIPOSE – ANCHORS SKIN LOOSELY TO UNDERLYING STRUCTURES

EPIDERMIS: 4-5 LAYERS •

TOP 5: STRATUM CORNEUM: – KERATIN FILLED DEAD CELLS – GLYCOLIPIDS B/T CELLS – DURABLE OVERCOAT

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4: (STRATUM LUCIDUM) – ONLY IN THICK SKIN – NUCLEI DISINTEGRATE, CELLS DIE

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3: STRATUM GRANULOSUM – FLATTENED CELLS – ACCUMULATION OF GRANULES

• •

2: STRATUM SPINOSUM 1: STRATUM BASALE – – – –

SINGLE ROW YOUNG CELLS (KERATINOCYTES) RAPID DIVISION MELANOCYTES

BOTTOM

EPIDERMIS: CELL TYPES • Keratinocytes: – majority of epidermal cells – produce keratin (tough fibrous protein)

Melanocytes: – in stratum basale (10-25% of basal cells) – produce melanin (pigment) which is then taken in by keratinocyes (uv protection)

EPIDERMIS: CELL TYPES • Langerhans cells: – macrophages (protection from invasion)

• Merkel cells: – epidermal/ dermal junction – assists with sensory nerve ending

DERMIS (YOUR ‘HIDE’) • Strong and flexible (collagen, elastin, reticular fibers) • Contains nerves, bv’s, lymph • Houses glands and hair follicles (but does not create these) • 2 layers – papillary – reticular

DERMIS: PAPILLARY LAYER • Loose Areolar CT • Ridges in contact with epidermis – epidermal ridges form fingerprints • friction

• Contains: – capillary plexes – free nerve endings (pain sensation) – meissner’s corpuscles (soft touch)

DERMIS: RETICULAR LAYER • 80% of dermis • Dense Irregular CT – Collagen: • stregnth • binds h2o

– Elastin: • flexibility

BLISTERS AND CALLOUSES • Blister: – friction, burn, or pathology – separation between epidermis and dermis filled with fluid

• Callous: – overgrowth of epidermis – over time – protection

More Concepts • Pigments – melanin – carotene – hemoglobin

• Appendages – nails – hair – hair follicles – sweat glands – oil glands

SKIN COLOR • Due to 3 pigments – melanin – carotene – hemoglobin

• Range of colors – reds, yellows, browns

MELANIN • Two types – brown/ black – yellow to reddish brown

• All humans have same # of melanocytes – secrete different amounts, types, and sizes of granules to create different skin colors – freckles are uneven accumulations of melanin

• Stimulation of melanocytes by sunlight – protects keratinocytes from uv radiation – absorbs light and dissipates energy as heat.

SKIN COLOR: HEMOGLOBIN AND CAROTENE • Carotene: – yellow/orange pigment – accumulates in stratum corneum and fatty tissue – especially notable in palms and soles (when eating many carotene rich foods) • Hemoglobin: – pinkish – hemoglobin in RBC's circulating through capillaries – transparency of epidermis in caucasians allows this color to show through

‘ABNORMAL’ SKIN COLORS • Redness: – blushing; fever; hypertension; inflammation; allergy

• Pallor: – fear; anger; stress; anemia

• Jaundice: – liver disorder causes bile pigments to accumulate in tissues… including whites of the eyes

‘ABNORMAL’ SKIN COLORS • BRONZING: – ADDISON’S DISEASE

• BRUISING: – BLOOD BLEEDING UNDER INTACT SKIN, LEADS TO CLOTTING (HEMATOMA)

• CYANOSIS: – POORLY OXYGENATED HEMOGLOBIN, SKIN APPEARS BLUE

Moles

Skin Tags • Usually caused by friction • Over growth of epidermal cells • Have blood supply • Mostly benign

SKIN APPENDAGES • • • • •

Nails Hair Hair follicles Sweat glands Sebaceous glands

HAIR

• Functions: – insulation • trap heat (though not as much in humans) – protection • nose hairs trap foreign substances • eyelashes, eyebrows, and head hair protects from sunlight – sensation • (ie. whiskers) – social/ communication • Hair accessories – erector pili muscles – sebaceous glands (oil)

HAIR • • • •

Composed of keratin Hair shaft (above skin) Hair root (inside the skin) Hair follicle – in dermis, but made from epidermal pocket – surrounding follicle is knot of sensory nerve endings – expanded bulb is dermal papilla • capillary plexus w/ nutrients and growth signals

HAIR SHAPE AND COLOR • Shape of follicle: – oval: curly hair – c shape: wavy hair – round: straight hair

• Hair color: – melanocytes produce the melanin which is then picked up by the cortical cells – gray/ white hair: decreased melanin production

HAIR GROWTH • Cycles of growth lasting 6-10 yrs in scalp (3-4 months in eyebrows) • 2-5 mm per week (varies) • We lose appx. 50-100 hairs per day • Stimulated by testosterone – though testosterone is also what leads to male pattern baldness

INTERESTING HAIR FACTS: HAIR GROWS FASTER IN THE SUMMER THAN IN WINTER: CUTTING HAIR HAS NO EFFECT ON GROWTH: HAIR GROWS FASTEST BETWEEN 16-24 YEARS OF AGE

HAIR GROWTH

NAILS • Function – help in grasping and manipulation of small objects – protection for ends of digits • Scale-like modification of epidermis • Made of hard keratin

GLANDS • Derived from epithelial tissue; reside in dermis • Sweat glands: – everywhere except nipples and external genitalia – two types: • Eccrine • Apocrine • Sebaceous (oil) glands

SWEAT GLANDS • Eccrine – Most of our sweat glands – Temperature regulation – Ducts empty into pores • Apocrine – Axillary and anogenital regions only – Odorless until decomposed by bacteria on skin – Ducts empty into hair follicles – Sweat, fat and protein

Sweat • • • •

99% water Dermicidin Lactic acid Acidic (pH 4-6)

• • • •

NaCl Vit C Metabolic wastes Antibodies

SEBACEOUS GLANDS • Everywhere except palms/ soles • Produce sebum (lipid) – softens and lubricates skin and hair – slows water loss – bactericidal – secreted into hair follicles

• Pimples and acne

‘PIMPLES’ • WHITEHEAD: – PLUGGED SEBACEOUS GLAND

• BLACKHEAD (COMEDONE): – PLUGGED SEBACEOUS GLAND WHERE SEBUM UNDERGOES OXIDATION

CUTANEOUS RECEPTORS • Exteroreceptors – Two types (sensitive to stimuli arising outside the body) – encapsulated nerve endings • Vibration • Deep Pressure • Light touch – free nerve endings • Pain • Temperature • Pressure • Stretch • Touch

ENCAPSULATED NERVE ENDINGS

• End of the nerve is wrapped in a thin layer of connective tissue • Mechanoreceptors – Meissner’s corpuscles • just beneath epidermis • light touch

– Pacinian corpuscles • deep in dermis • Vibration, pressure

– Ruffini corpuscles • dermis and sub-q • Skin stretch, finger position

FREE NERVE ENDINGS • Naked nerve endings of sensory neurons • Found everywhere in the body (many in connective and epithelial tissue) • Nociceptors – Pain • Thermoreceptors – (cold/ heat) • Mechanoreceptors – merkel discs • deep in epidermis • light touch receptor – hair follicle receptors • wrap around hair follicles • detect bending of hair

TWO POINT DISCRIMINATION • Receptor fields • Receptor density