• Epidermis (superficial region)
• Dermis (middle region)
• Hypodermis (superfical fascia - deepest region, subcutaneous layer deep to skin, not technically part of skin, mosty adipose tissue

• Keratinocytes - produce fibrous protein keratin (protects and waterproofs skin)
• Melanocytes - produce pigment melanin
• Epidermal dendritic (Langerhans) cells - macrophages that help activate immune system
• Tactile (Merkel) cells - touch receptors

• Stratum basale - mitotic layer
• Stratum spinosum - keratinocytes joined by desmosomes
• Stratum granulosum - keratinization begins
• Stratum lucidum - clear layer only in thick skin
• Stratum corneum - 20-30 layers layers of dead cells, sacs filled with keratin, protects from abrasion

• Strong, flexible connective tissue
• Cells include fibroblasts, macrophages, and occasionally mast cells and white blood cells
• Two layers: papillary, reticular

• Areolar connective tissue with collage and elastic fibers and blood vessels
• Dermal papillae contain:
  -capillary loops
  -Meissner's corpuscles (touch receptors)
  -free nerve endings (pain receptors) 

• ~80% of the thickness of dermis
• Collagen fibers provide strength and resiliency
• Elastic fibers provide stretch-recoil properties

• Melanin
  -responsible for dark skin colors
  -produced in melanocytes; migrates to keratinocytes where it forms "pigment shields" for nuclei
  -Freckles, pigmented moles: local accumulations of melanin
• Carotene - yellow to orange, most obvious in the palms and soles
• Hemoglobin - responsible for the pinkish hue of skin 

• Sweat glands
• Oil glands
• Hairs and hair follicles
• Nails
• (appendages of the skin are derivatives of the epidermis)

• Eccrine
• Apocrine

• Abundant on palms, soles, and foreheads
• Sweat: 99% water, NaCl, vitamin C, antibodies, dermcidin, metabolic wasters
• Ducts connect to pores
• Function in thermoregulation
• Most numerous

• Confined to axillary and anogenital areas
• Function not well known
• Sweat + fatty substances and proteins
• Ducts connect to hair follicles
• Functional from puberty onward (sexual scent glands?)

• Ceruminous glands - in external ear canal; secrete cerumen (ear wax)
• Mammary glands - milk

• Widely distributed
• Most develop from hair follicles
• Become active at puberty
• Sebum
  -Oily holocrine secretion
  -Bactericidal
  -Softens hair and skin 

• Alerting the body to the presence of insects on the skin
• Guarding the scalp against physical trauma, heat loss, and sunlight

• Distribution - entire surface except palms, soles, lips, nipples, and portions of external genitalia
• Consists of dead keratinized cells
• Hair pigments: melanins (yellow, rust brown, black)
• Gray/white hair: decreased melanin production, increased air bubbles in shaft

1 = Follicle Wall

2 = Cuticle

3 = Cortex

4 = Medulla

• Extends from the epidermal surface into dermis
• Two-layered wall: outer connective tissue root sheath, inner epithelial root sheath
• Hair bulb: expanded deep end

• sensory nerve endings around each hair bulb
• stimulated by bending a hair

• Smooth muscle attached to follicle
• Responsible for "goose bumps"

Alopecia - hair thinning

Hirsutism - excessive hairiness

• Chemical protection
• Physical/mechanical barriers
• Biological barriers
• Body temperature regulation
• Cutaneous sensations
• Metabolic functions
• Blood reservoir
• Excretion

• keratin and glycolipids block most water and water-soluble substances
• limited penetration of skin by lipid-soluble substances

• ~500 ml/day of routine insensible perspiration (at normal body temperature
• At elevated temperature, dilation of dermal vessels and increased sweat gland activity (sensible perspirations) cool the body

• Most skin tumors are benign (do not metastasize)
• Risk factors - overexposure to UV radiation, frequent irritation of the skin

• Basal cell carcinoma (least malignant, most common - 80% of skin cancers)
• Squamous cell carcinoma (second most common)
• Melanoma (most dangerous)

• Stratum basale cells proliferate and slowly invade dermis and hypodermis
• Cured by surgical excision in 99% of cases
• Sun exposed areas of skin
• Looks like shiny dome shaped nodule
• Slow growing

• Involves keratinocytes of stratum spinosum
• Most common on scalp, ears, lower lip, and hands
• Good prognosis if treated by radiation therapy or removed surgical
• scaly & reddened papule (small, rounded elevation)
• will grow fast and metastasize if not removed

• Only 2 - 3% of all skin cancers
• involves melanocytes
• highly metastatic and resistant to chemotherapy
• treated by wide surgical excision accompanied by immunotherapy
• can appear wherever there is pigment
• most appear spontaneously
• approx. 1/3 derive from existing mole
• early detection is important

A: Asymmetry; the two sides of the pigmented area do not match

B: Border exhibits indentations

C: Color is black, brown, tan, and sometimes red or blue

D: Diameter is larger than 6 mm (size of a pencil)

E: Elevation

• Can be caused by heat, electricity, radiation, certain chemical
• Can cause tissue damage, denatured protein, cell death
• Immediate threat: dehydration and electrolyte imbalance (loss of fluids), leading to renal shutdown and circulatory shock

• Used to estimate the volume of fluid loss from burns
• Divides body in 11 areas, each accounting for 9% of total body area

• Epidermal damage only
• Localized redness, edema (swelling), and pain

• Epidermal and upper dermal damage
• Blisters appear

• Entire thickness of skin damaged
• Gray-white, cherry red, or black
• No initial edema or pain (nerve endings destroyed)
• Skin grafting usually necessary

• >25% of the body has second-degree burns
• >10% of the body has third-degree burns
• Face, hands, or feet bear third-degree burns

• Contain no blood vessels or nerves
• Dense connective tissue girdle of perichondrium contains blood vessles for nutrient delivery to cartilage

• Hyaline cartilages (provide support, flexibility, and resilience - most abundant type)
• Elastic cartilages (similar to hyaline cartilages, but contain elastic fibers)
• Fibrocartilages (collagen fibers - have great tensile strength)

• Hyaline - articular cartilages, costal cartilages, respiratory cartilages, nasal cartilages
• Elastic - external ear and epiglottis
• Fibrocartilages - menisci of knee, discs between vertebrae, pubic symphysis

• Appositional - cells secrete matrix against the external face of existing cartilage
• Interstitial - Chondrocytes divide and secrete new matrix, expanding cartilage from within
• Calcification of cartilage occurs during normal bone growth, old age

• Axial - forms the long axis of the body; skull, vertebral column, rib cage
• Appendicular - bones of upper and lower limbs and the girdles (shoulder and hip bones) that attach the limbs to axial skeleton

• Long bones - longer than they are wide (humerus, femur, radius, ulna, tibia, fibula, etc.)
• Short bones - cube-shaped bones (wrist & ankles), sesamoid bones (within tendons, eg. patella)
• Flat bones - thin, flat, slightly curved (sternum)
• Irregular bones - complicated shapes (vertebra)

• Support (for the body and soft organs)
• Protection (for brain, spinal cord, vital organs)
• Movement (levers for muscle action)
• Storage (minerals-calcium & phosphorus-and growth factors)
• Blood cell formation (hematopoiesis in marrow cavities)
• Triglyceride (energy - storage in bone cavities)

• Compact bone (dense outer layer)
• Spongy - trabecular - bone (honeycomb of trabeculae)

• Diaphysis (shaft)
  -compact bone collar surrounds medullary (marrow) cavity
  -medullary cavity in adults contains fat (yellow marrow) 
• Epiphyses (ends)
  -expanded ends
  -spongy bone interior
  -epiphyseal line (remnant of growth plate)
  -articular (hyaline) cartilage on joint surfaces 

• Periosteum
• Endosteum

• Outer fibrous layer
• Inner osteogenic layer (osteoblasts, osteoclasts, osteogenic cells)
• Nerve fibers, nutrient blood vessels, and lymphatic vessels enter the bone via nutrient foramina
• Secured to underlying bone by Sharpey's fibers

• Delicate membrane on internal surfaces of bone
• Also contains osteogenic cells

• Periosteum-covered compact bone on the outside
• Endosteum-covered spongy bone within
• Spongy bone called diploë in flat bones
• Bone marrow between the trabeculae
• (looks like sandwich)

• Red marrow cavities of adults
  -trabecular cavities of the heads of the femur and humerus
  -trabecular cavities of the diploë of flat bones (sternum)
• Red marrow of newborn infants
  -medullary cavities and all spaces in spongy bone 

• Osteogenic (osteoprogenitor) cells - stem cells in periosteum and endosteum that give rise to osteoblast
• Osteoblasts - bone-forming cells, matrix-synthesizing cell responsible for bone growth
• Osteocytes - mature bone cells, maintain the matrix
• Osteoclasts - cells that break down (resorb) bone matrix

• Haversian system, or osteon - structural unit
• Lamella (pl. lamellae): weight-bearing, column-like matrix tubes, collagen fibers run in different directions
• Central (Haversian) canal - contains blood vessels and nerves

• Perforating (Volkmann's) canals - at right angles to the central canal, connects blood vessels and nerves of the periosteum and central canal
• Lacunae - small cavities that contain osteocytes
• Canaliculi - hairlike canals that connect lacunae to each other and the central canal

• Align along lines of stress
• No osteons
• Contain irregularly arranged lamellae, osteocytes, and canaliculi
• Capillaries in endosteum supply nutrients

• Osteogenic cells, osteoblasts, osteocytes, osteoclasts
• Osteoid - organic bone matrix secreted by osteoblasts
• Ground substance (proteoglycans, glycoproteins)
• Collagen fibers (provide tensile strength and flexibility)

• Hydroxyapatites (mineral salts)
• 65% of bone mass
• Mainly calcium phosphate crystals
• Responsible for hardness and resistance to compression

• Osteogenesis (ossification) - bone tissue formation
• Stages
  -(bone formation - begins in 2nd month of development)
  -Postnatal bone growth - until early adulthood
  -Bone remodeling and repair - lifelong

• Interstitial growth (increases length of long bones, epiphyseal plate)
• Appositional growth (increases thickness and remodelling of all bones by osteoblasts and osteoclasts on bone surfaces)

• Growth hormone stimulates epiphyseal plate activity (in infancy & childhood)
• Thyroid hormone modulates activity of growth hormone
• Testosterone and estrogen (sex hormones at puberty) promote adolescent growth spurts, end growth by inducing epiphyseal plate closure
• Too little - dwarfism
• Too much - gigantism

• Occurs where bone is injured or added strength is needed
• Osteocytes deposit new matrix
• Requires a diet rich in protein; vitamins C, D, and A; calcium; phosphorus; magnesium; and manganese

• Osteoclasts - move along surface creating grooves by secreting lysosomal enzymes and HCL
• Convert calcium salts into soluble calcium
• Dissolved matrix (including soluble calcium) enters interstitial fluid and then blood

• Hormonal mechanisms that maintain calcium homeostasis in the blood
• Mechanical and gravitational forces

• Transmission of nerve impulses
• Muscle contraction
• Blood coagulation
• Secretion by glands and nerve cells
• Cell division

• Primarily controlled by parathyroid hormone
• low levels of blood Ca²⁺ levels detected
• parathyroid glands release parathyroid hormone
• PTH stimulates osteoclasts to degrade bone matrix and release Ca²⁺
• Increase in Blood Ca²⁺levels
• May be affected to a lesser extent by calcitonin (lowers Blood Ca²⁺levels)

• Position of bone ends after fracture:
  - Nondisplaced-ends retain normal position
  - Displaced-ends out of normal alignment
• Completeness of the break:
  - Complete-broken all the way through
  - Incomplete-not broken all the way through
• Orientation vs long axis of the bone: 
  - Linear-parallel to long axis of the bone
  - Transverse-perpendicular to long axis of the bone
• Skin penetration:
  - Compound (open)-bone ends penetrate the skin
  - Simple (closed)-bone ends do not penetrate the skin

• Hematoma forms (bone cells deprived of nutrition die, tissue at site becomes swollen, painful, and inflamed)
• Fibrocartilaginous callus forms (within a few days - capillaries grow into hematoma, phagocytes clean up debris)
• Bony callus formation (within a week - new bone trabeculae converts fibrocartilaginous callus to spongy bone)
• Bone remodelling (2 months and longer - bony callus remodelled)

• Osteomalacia & rickets
• Osteoporosis
• Paget's Disease

• Osteomalacia - adults
• Rickets - children
• Calcium salts not deposited
• Rickets (childhood disease) causes bowed legs and other bone deformities (pelvis, skull, ribcage)
• Cause: vitamin D deficiency or insufficient dietary calcium

• loss of bone mass - bone resorption outpaces deposit
• Spongy bone of spine and neck of femur become most susceptible to fracture
• Risk factors: post-menopausal women; lack of estrogen, calcium or vitamin D; petite body form; immobility; low levels of TSH; diabetes mellitus

• Calcium, vitamin D, and fluoride supplements
• Increase weight-bearing exercise throughout life
• Hormone (estrogen) replacement therapy (HRT) slows bone loss
• Some drugs increase bone mineral density

• Excessive and haphazard bone formation and breakdown, usually in spine, pelvis, femur or skull
• Unknown cause (possibly viral)
• Treatment includes calcitonin and biphosphates

• Give skeleton mobility
• Hold skeleton together

Based on amount of movement allowed by the joint

• synarthrose = immovable joints
• amphiarthose = slightly movable joints
• diathrose = freely moveable joints

Based on material binding bones together and whether or not a joint cavity is present

• Fibrous
• Cartilagenous
• Synovial

• Bones joints by fibrous tissue
• Lack joint cavity
• Most immovable
• 3 types: Sutures, Syndemoses, Gomphoses

• Joint held together with very short, interconnecting fibers, and bone edges interlock
• Found only in the skull

• joint held together by a ligament
• fibrous tissue can vary in length, but is longer in the sutures
• fibula/tibia, radius/ulna

• "peg in socket" fibrous joint
• peridontal ligament holds tooth in socket

• Bone joints by cartilage
  
• Lack joint cavity
• Not highly movable
• Synchondroses
• Symphyses

• Bones united by hyaline cartilage
• Epiphyseal plate
• Joint between first rib and sternum

• Bones united by fibrocartilage
• Pubic symphysis
• Intervertebral discs

• All are diartrotic (freely movable)
• Include all limb joints, most joints of the body

• Articular cartilage
• Joint cavity
• Synovial fluid
• Articular joint capsule
• Reinforcing ligaments
• Rich nerve and blood vessel supply

• viscous slippery filtrate of plasma + hyaluronic acid (contains phagocytes, hyaluronic acid increases viscosity)
• lubricates and nourishes articular cartilage

• outer fibrous capsule of dense irregular connective tissue
• inner synovial membrane of loose connective tissue

• capsular (intrinsic) - part of the fibrous capsule
• extracapsular - outside the capsule
• intracapsular - deep to capsule; covered by synovial membrane

• nerve fibers detect pain, monitor joint position and stretch
• capillary beds produce filtrate for synovial fluid

• Bursae
• Tendon sheath

• Flattened, fibrous sacs lined with synovial membranes
• Contain synovial fluid
• Commonly act as "ball bearings" where ligaments, msucles, skin, tendons, or bones rub together

• Shapes of articular surfaces (minor roles)
• Ligament number and location (limited roles)
• Muscle tone, which keeps tendons that cross the joint taut - extremely important in reinforcing shoulder and knee joints and arches of the foot