Skin & Body Membranes Chapter 4

Classification of Body Membranes Two major categories (classified by tissue makeup): Epithelial Tissue – covering and lining membranes; always combined with underlying layer of CT (simple organs!) Cutaneous membranes Mucous membranes Serous membranes Connective Tissue (contain no epithelial cells) Synovial membranes

Cutaneous Membrane The skin Epidermis (superficial): Keratinized stratified squamous epithelium Dermis: dense fibrous connective tissue

Mucous Membrane (Mucosae) Line cavities that open to exterior (i.e. GI tract) Epithelium (type varies by site) & connective tissue layer called lamina propria Secretes mucous; continuously bathed in secretions Epithelium adapted for absorption or secretion

Serous Membrane Also known as serosa Layer of simple squamous epithelium resting on a thin layer of areolar connective tissue Lines body cavity not open to exterior (pleura, pericardium, peritoneum)- parietal and visceral Secrete serous fluid (separates membranes)

Connective Tissue Membranes Synovial Membranes Soft areolar connective tissue and no epithelial cells Line fibrous capsules surrounding joints Provide smooth surface and secrete lubricating fluid Line small sacs of CT called bursae and tendon sheaths – cushion organs moving against each other during muscle activity

Synovial Membrane Line joint cavities Do not contain epithelium Secrete synovial fluid

Integumentary System Cutaneous membrane Largest organ 16% body weight 2 square meters area The Skin

Functions of Integument Insulates and cushions Protects from mechanical damage, chemical damage, thermal damage, ultraviolet radiation, bacteria Keratin – prevents water loss from body surface Capillary network and sweat glands regulate heat loss Mini-excretory system: urea, salts, water lost when sweat Manufactures proteins important to immunity and synthesizes vitamin D Sensory receptors part of nervous system located here – touch, pressure, temperature, pain – provide info about external environment

sensations protection absorption blood reservoir thermoregulation FUNCTIONS OF SKIN THERMOREGULATION, THE HOMEOSTATIC CONTROL OF BODY TEMPERATURE, IS DUE TO THE SKIN LIBERATING SWEAT AT ITS SURFACE AND BY ADJUSTING THE FLOW OF BLOOD IN THE DERMIS. BECAUSE THE SHIN HAS AN EXTENSIVE NETWORK OF BLOOD VESSELS, IT FUNCTIONS AS A BLOOD RESERVOIR. THE SKIN PROVIDES PROTECTION THROUGH PHYSICAL, CHEMICAL AND BIOLOGICAL BARRIERS. CUTANEOUS SENSATIONS, INCLUDING TOUCH, PRESSURE, VIBRATION, TICKLE, HEAT, COLD, AND PAIN ARISE IN THE SKIN. THE SKIN PLAYS MINOR ROLES IN EXCRETION, THE ELIMINATION OF WASTES FROM THE BODY, AND ABSORPTION, THE PASSAGE OF MATERIAL FROM THE EXTERNAL ENVIRONMENT INTO BODY CELLS. SYNTHESIS OF VITAMIN D REQUIRES ACTIVATION OF A PRECURSOR MOLECULE IN THE SKIN BY UV LIGHT, WITH ENZYMES IN THE LIVER AND KIDNEYS MODIFYING THE ACTIVATED MOLECULE TO PRODUCE CALCITRIOL, THE MOST ACTIVE FORM OF VITAMIN D. TRANSDERMAL DRUG ADMINISTRATION IS A METHOD OF DRUG PASSAGE ACROSS THE EPIDERMIS AND INTO THE BLOOD VESSELS OF THE DERMIS (CLINICAL APPLICATION). blood reservoir thermoregulation

Stratified Squamous Epithelium (keratinized) Dense CT hypodermis

4 types of cells Keratinocytes: 90% Langerhans cells Merkel cells produce keratin and lamellar granules Langerhans cells mount immune response Scattered throughout epidermis Merkel cells contact sensory neurons (epidermal/dermal junction) Melanocytes: 8% produce pigments to absorb UV radiation (stratum basale)

Stratum basale (stratum germinativum): produce new keratinocytes/ tonofilaments for attachment *melanocytes found here

Stratum spinosum: tonofilaments for strength and stability

Stratum granulosum: flattened dying cells- release keratin and lamellar granules

Stratum lucidum: only in thick layers (i.e. palms of hands & soles of feet) flattened dead cells

Stratum corneum: flattened, dead, continually shed ¾ of epidermal thickness Durable, protects deeper cells from environment and water loss; resists biological, chemical, physical damage Lamellar granules make water repellant Callus forms here

Skin Graft

Psoriasis

Dermis Binds the body together Mostly Dense fibrous connective tissue, has two major regions: Papillary: upper dermal region; has dermal papillae that extend into the epidermis (areolar connective tissue containing fine elastic fibers) Contain capillary loops to furnish nutrients to the epidermis House pain receptors (free nerve endings) and touch receptors Give “fingerprints” (genetically determined) – enhance gripping ability and increase friction Reticular: deepest skin layer (dense, irregular CT) Contains irregularly arranged CT fibers and blood vessels, sweat, and oil glands Contains deep pressure receptors called lamellar corpuscles Phagocytes prevent bacteria to penetrate deeper into body Varies in thickness Collagen & elastic fibers found throughout (toughness & elasticity) – change with age! Dermis capillaries help maintain body temperature homeostasis

Dermis

Striae: Tears in Dermis (stretch marks)

Epidermal Ridges

Tanning Skin colors Freckles Melanin Moles

Vitiligo Albinism

McCune Albright Syndrome Link

Tattooing Currently there are two men who are nearly tied for the Most Tattoo Man record. One is a retired military man who lives in Scotland named Tom Leppard, who just happens to have 99.9% of his body covered in leopard spots. He has no other tattoo designs other than this all-covering pattern which is only absent from the insides of his ears and between his toes.

Elaine Davidson of Edinburgh, Scotland, has acquired a record 462 body piercings since January 1997, 192 of which are on her head.

Appendages of the Skin Cutaneous glands: Exocrine glands Formed by cells of stratum basale but reside almost entirely in the dermis Sebaceous glands: found all over the skin except on palms of hands and soles of feet; ducts typically empty into a hair follicle but some open directly to skin surface Product is SEBUM (mixture of oily substances and fragmented cells Lubricant: keeps skin soft, moist, prevents hair from becoming brittle; antibacterial Sweat glands: sudoriferous glands (more than 2.5 million per person) Eccrine glands: all over body, produce sweat Apocrine glands: axillary & genital regions of body Hair & hair follicles: guard against bumps, shielding eyes, keep foreign particles out of respiratory tract Nails: modification of epidermis; free edge, body, root Each arise from epidermis and help maintain homeostasis

Sebaceous gland- secretes oil to coat hair and skin Sudoriferous glands- secrete sweat Eccrine- throughout skin- regulate temp/ eliminate some Waste Apocrine- armpits, groin, breast, face- stimulated with stress

Ceruminous Gland (earwax)

Hair anatomy Shaft extends from the surface of the scalp/skin Produces hair; root is enclosed in follicle Bulk of hair shaft is dead material and almost entirely protein (cortex most heavily keratinized) Growth zone Blood supply

lanugo vellus terminal hair

Nails Tightly packed, hard, dead, keratinized epidermal cells NAILS NAILS ARE HARD, KERTAINIZED EPIDERMAL CELLS OVER THE DORSAL SURFACES OF THE TERMINAL PORTIONS OF THE FINGERS AND TOES. THE PRINCIPAL PARTS OF A NAIL ARE THE BODY, FREE EDGE, ROOT, LUNULA, EPONYCHIUM, AND MATRIX (FIGURE 5.7). CELL DIVISION OF THE MATRIX CELLS PRODUCES NEW NAILS. FUNCTIONALLY, NAILS HELP IN GRASPING AND MANIPULATING SMALL OBJECTS IN VARIOUS WAYS AND PROVIDE PROTECTION AGAINST TRAUMA TO THE ENDS OF THE DIGITS. CERTAIN NAIL CONDITIONS MAY INDICATE DISEASE (FIGURE 5.8) Tightly packed, hard, dead, keratinized epidermal cells

EPIDERMAL WOUND HEALING IN AN EPIDERMAL WOUND (E.G., AN ABRASION OR A FIRST-DEGREE OR SECOND-DEGREE BURN), THE CENTRAL PORTION OF THE WOUND USUALLY EXTENDS DEEP DOWN TO THE DERMIS, WHEREAS THE WOUND EDGES USUALLY INVOLVE ONLY SUPERFICIAL DAMAGE TO THE EPIDERMAL CELLS. EPIDERMAL WOUNDS ARE REPAIRED BY ENLARGEMENT AND MIGRATION OF BASAL CELLS (FIGURE 5.9A), CONTACT INHIBITION, AND DIVISION OF MIGRATING AND STATIONARY BASAL CELLS. EPIDERMAL GROWTH FACTOR STIMULATES BASAL CELLS TO DIVIDE AND REPLACE THE ONES THAT HAVE MOVED INTO THE WOUND (FIGURE 5.9B). Figure 1. Acute wound healing in porcine skin at 3 days (upper left panel), 5 days (upper right panel),7 days (lower left panel) and 10 days (lower right panel). An organized fibrin clot is observed at 3 days, but there is no evidence of new dermal tissue healing. In contrast, at 5 days connective tissue cells (fibroblasts) and blood vessels have filled the defect. Reorgan- zation of the tissue has occurred over the next week (days 7 and 10).

PHASES OF DEEP WOUND HEALING DURING THE INFLAMMATORY PHASE, A BLOOD CLOT UNITES THE WOUND EDGES, EPITHELIAL CELLS MIGRATE ACROSS THE WOUND, VASODILATATION AND INCREASED PERMEABILITY OF BLOOD VESSELS DELIVER PHAGOCYTES, AND FIBROBLASTS FORM (FIGURE 5.9C). DURING THE MIGRATORY PHASE, EPITHELIAL CELLS BENEATH THE SCAB BRIDGE THE WOUND, FIBROBLASTS BEGIN SCAR TISSUE, AND DAMAGED BLOOD VESSELS BEGIN TO GROW. DURING THIS PHASE, TISSUE FILLING THE WOUND IS CALLED GRANULATION TISSUE. DURING THE PROLIFERATIVE PHASE, THE EVENTS OF THE MIGRATORY PHASE INTENSIFY. DURING THE MATURATION PHASE, THE SCAB SLOUGHS OFF, THE EPIDERMIS IS RESTORED TO NORMAL THICKNESS, COLLAGEN FIBERS BECOME MORE ORGANIZED, FIBROBLASTS BEGIN TO DISAPPEAR, AND BLOOD VESSELS ARE RESTORED TO NORMAL (FIGURE 5.9). SCAR TISSUE FORMATION (FIBROSIS) CAN OCCUR IN DEEP WOUND HEALING. Figure 1. Acute wound healing in porcine skin at 3 days (upper left panel), 5 days (upper right panel),7 days (lower left panel) and 10 days (lower right panel). An organized fibrin clot is observed at 3 days, but there is no evidence of new dermal tissue healing. In contrast, at 5 days connective tissue cells (fibroblasts) and blood vessels have filled the defect. Reorgan- zation of the tissue has occurred over the next week (days 7 and 10).

(epidermis) Ectoderm Mesoderm (dermis) DEVELOPMENT OF THE INTEGUMENTARY SYSTEM THE EPIDERMIS IS DERIVED FROM ECTODERM. HAIR, NAILS, AND SKIN GLANDS ARE EPIDERMAL DERIVATIVES (FIGURE 5.10A). THE DERMIS IS DERIVED FROM WANDERING MESENCHYMAL CELLS. THE CONNECTIVE TISSUE AND BLOOD VESSELS ASSOCIATED WITH THE GLAND DEVELOP FROM MESODERM. Mesoderm (dermis)

Aging Mostly dermis- loss of collagen, elasticity of AGING AND THE INTEGUMENTARY SYSTEM MOST EFFECTS OF AGING OF THE SKIN DO NOT OCCUR UNTIL AN INDIVIDUAL REACHES THE LATE FORTIES. MOST OF THE CHANGES OCCUR IN THE DERMIS AMONG THE EFFECTS OF AGING ON THE INTEGUMENT ARE WRINKLING, SLOWER GROWTH OF HAIR AND NAILS, DRYNESS AND CRACKING DUE TO SEBACEOUS GLAND ATROPHY, DECREASE IN NUMBER OF MELANOCYTES (GRAY HAIR, BLOTCHING) AND LANGERHANS CELLS (DECREASED IMMUNE RESPONSIVENESS), AND LOSS OF SUBCUTANEOUS FAT (THINNER SKIN). CERTAIN ANTI-AGING TREATMENTS DIMINISH THE EFFECTS OF AGING. AMONG THEM ARE: MICRODERMABRASION, CHEMICAL PEEL, LASER RESURFACING, DERMAL FILLERS, BOTULIISM TOXIN INJECTION, AND NON SURGICAL FACE LIFTS. CHRONIC ULTRAVIOLET EXPOSURE CAUSES PHOTODAMAGE OF THE SKIN. THE USE OF SUN SCREENS AND SUN BLOCKS HELP TO MINIMIZE DAMAGE FROM THE SUN. Mostly dermis- loss of collagen, elasticity of fibers decreases, decreased immune response, less oil and sweat, less melanocytes, skin thins