Integumentary System

Body Membranes Body membranes cover surfaces, line body cavities, and form protective sheets over organs Two major groups: Epithelial membranes – cutaneous (skin), mucous, and serous membranes Connective tissue membranes – synovial membranes

Epithelial Membranes Epithelial membranes – covering and lining membranes Contain an epithelial sheet, but it is always combined with a connective tissue layer 2 tissues = These membranes are actually simple organs

Cutaneous Membrane = Skin Its superficial epidermis is composed of keratinizing stratified squamous epithelium. Underlying dermis is mostly dense (fibrous) connective tissue. Exposed to air = dry membrane

Mucous Membrane = Mucosa Composed of epithelium resting on loose connective tissue called lamina propria. Lines all body cavities that open to exterior Wet membranes bathed in secretions or urine Adapted for absorption or secretion Varied types Stratified squamous epithelium in mouth, esophagus Simple columnar epithelium in digestive tract

Serous membrane = serosa Simple squamous epithelium resting on areolar connective tissue Line body cavities that are closed to exterior Occur in pairs: Parietal layer lines the wall of the ventral cavity Visceral layer covers the outside of those organs Layers separated by serous fluid, which allows organs to slide without friction (heart, stomach)

Serosa Serosa lining the abdominal cavity and covering its organs = peritoneum Membrane surrounding lungs = pleura Membrane around the heart = pericardium

Synovial Membranes Composed of soft areolar connective tissue and contain no epithelial cells. Line the fibrous capsules surrounding joints and tendon sheaths Secrete lubricating fluid to cushion organs during muscle activity

Tattoos Tattoos are made by using a needle to deposit pigment in the dermis. Risk of Hepatitis C is about 15x higher in people who have tattoos…

Cutaneous Membrane = Skin Skin and its glands (sweat, oil), along with hair and nails, make up the integumentary system Integument (covering): keeps water and other molecules in the body Insulates and cushions body organs Protects body from mechanical (bumps), chemical (acids and bases), thermal (heat and cold), UV (solar radiation), and bacteria damage. Uppermost layer of skin is full of keratin and is cornified (hardened) to help prevent H2O loss.

Capillary Network in Skin Capillary network and sweat glands regulate heat loss Urea, salts, and water are lost as sweat Manufactures proteins important to immunity and synthesizes Vitamin D (sunlight converts cholesterol in skin into vitamin D). Cutaneous sensory receptors are located in skin – sense pain, pressure, temperature, touch

Skin Structure Tissues in skin: Epidermis – stratified squamous epithelium, keratinizing (can become hard) Dermis – dense connective tissue Subcutaneous layer (hypodermis) – below dermis, adipose tissue, anchors skin to organs.

Skin Structure Subcutaneous layer – shock absorber and insulation from extreme T changes Thicker in women than in men (adipose tissue)

Epidermis Five layers / strata: Stratum Corneum Stratum Lucidum Stratum Granulosum Stratum Spinosum Stratum Basale Epidermis is avascular (no blood supply) Ex: shaving is cutting off cells w/ no blood (usually)

Stratum Basale Most cells of epidermis are keratinocytes (keratin cells) which produce keratin Keratin –protein that makes epidermis tough Deepest layer of epidermis / closest to dermis Daughter cells pushed upward into superficial layers

Epidermis Stratum basale constantly undergoing mitosis, a.k.a. stratum geminativum New cells become increasingly flatter and full of keratin Stratum Spinosum – cuboidal cells Stratum granulosum – cells granular

Epidermis As new cells die they form the stratum lucidum This layer is only present where skin is hairless and thick (palms of hands, soles of feet) Stratum corneum – ¾ of epidermal thickness Cornified or horny (cornu = horny) cells, completely keratinized

Melanin Melanin is a pigment that ranges from yellow to brown to black Produced by melanocytes, found in stratum basale. Everyone has same number of melanocytes Complexion determined by quantity of melanin produced Heredity – genes specific for melanin production; mutant genes can cause lack of melanin

Albinism Albinism results when genetic changes result in a lack of pigment (melanin) production Can have eye problems (light scattering, optic nerve problems)

Dermis = your hide Two major regions Papillary – upper dermal region Dermal papillae (papill=nipple) – house pain receptors, send nutrients to epidermis, form fingerprints Reticular – deepest skin layer Contains blood vessels, sweat and oil glands, and pressure receptors (Pacinian corpuscles) Collagen (toughness) and elastic (stretch when growing) fibers found in dermis Many receptors for nervous system

Skin Appendages Cutaneous glands – exocrine. Release secretions to skin surface via ducts. Sebaceous (oil) glands – often open into hair follicles. Everywhere but palms and soles. Secrete sebum – oil that keeps skin soft and kills bacteria. Increased amount in adolescence

Acne = infection of sebaceous gland When sebaceous gland’s duct is blocked by sebum, a whitehead appears on skin surface If the material accumulates and dries it darkens to form a blackhead.

Sweat Glands Sweat (Sudoriferous) Glands – more than 2.5 million per person. Two types: Eccrine glands – most numerous, all over body. Produce sweat (water plus salts and vitamins) Sweat is acidic (pH 4-6) so inhibits growth of bacteria Apocrine glands – confined to armpits and genital areas of the body. Secrete fatty acids and proteins Function unclear but activated during stress, pain, sex

Hair Millions of hairs Minor protection: Head bumps Eyelashes Nose hairs Early humans – provided insulation from cold weather

Hair Produced by hair follicle Flexible epithelial structure Root in follicle Shaft projects from skin Matrix (growth zone) of hair bulb at end of follicle Pigment made by melanocytes

Nails Scale-like modification of epidermis Free edge Body (visible portion) Mostly nonliving keratinized cells