Chapter 5: The Integumentary System
The Skin (Integument): composed of 2 regions:
- Epidermis: outermost layer composed of epithelial cells
- Dermis: underlying layer composed of fibrous connective tissue; vascularized
Epidermis: keratinized stratified squamous epithelium
-
Layers of Epidermis:
o Stratum Basale: basal layer; deepest epidermal layer firmly attached to dermis
• single layer of cells; cell division produces new keratinocytes for all layers
• dead cells hardened by keratin (keratinized)
• protects skin with keratin & thick plasma membranes; glycolipids prevent water loss
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Cell types in epidermis:
o keratinocytes: produce the fibrous protein keratin
• tightly connected by desmosomes
• outermost cells dead & keratinized; lifespan of 25-45 days
• thick skin has accelerated cell division & keratinization
o Langerhans' cells (epidermal dendritic cells): macrophages; part of immune system - kill microbes
• produced in bone marrow; migrate to epidermis & form network around keratinocytes
o melanocytes: spider-shaped cells that produce the pigment melanin
• located in deepest layer of epidermis; transfer melanin to keratinocytes
• melanin granules protect the cell nucleus from UV radiation
Skin Color: dictated by 3 pigments: melanin, carotene, & hemoglobin
- melanin: passed from melanocytes to basal keratinocytes
o melanin color ranges from yellow to reddish-brown to black
o freckles & pigmented moles are due to local melanin accumulations
- carotene: yellow-orange pigment found in plants (carrots...)
o accumulates in stratum corneum & dermis; gives skin yellowish color
- hemoglobin: oxygenated hemoglobin in dermal capillaries gives fair skin a pinkish color
Dermis: contains both loose & fibrous connective tissue
- collagen fibers: flexible but resist stretching (prevent skin from being torn)
- elastic fibers: stretch to allow movement of underlying muscles & joints
- dermal papillae: projections that indent into & anchor epidermis
- dermal ridges on palms of hand & soles of feet form epidermal ridges
o increase friction for better grip
o genetically determined pattern of ridges; leaves fingerprint
- rich supply of blood vessels nourishing skin
o increased blood flow: blushing; reduced blood flow: cyanosis
o restricted blood flow (in bedridden) can lead to decubitus ulcers (bedsores)
- accessory structures: hair follicles, nails, oil & sweat (sudoriferous) glands
- sensory nerve fibers: take nerve impulses to & from accessory structures
Subcutaneous Layer (Hypodermis): layer just deep to the dermis
- mostly adipose (fat) tissue with some other loose connective tissue
- adipose tissue serves as reserve energy store
- insulates, absorbs shocks, & anchors skin loosely to muscles
Accessory Structures of Skin:
Hair & hair follicles:
- hair is flexible strands of mostly dead, keratinized cells
- hair is found on all body parts except the palms, soles, lips, nipples & portions of external reproductive organs
o puberty stimulates new hair growth (axillary & pelvic regions in both sexes, & in several other body regions in males)
- hair follicle: extends from epidermal surface to dermis
o cells at base of follicle continually divide, pushing older cells toward surface & away from blood vessels (nourishment) - cells become keratinized & eventually die toward top of follicle
- hair has root within follicle & shaft extending beyond skin
- melanin from melanocytes at base of follicle produce color
- alopecia: hair loss brought on by aging & hormones
- each follicle has one or more sebaceous (oil) glands that empty into follicle
- arrector pili muscle: smooth muscle bundle that contracts to raise hair
Nails: scalelike epidermal modifications at dorsal surface of distal region of fingers & toes
- nail root cells produce new growth - cells become keratinized as they grow out over nail bed
- nail body: visible portion of nail
- cuticle: fold of skin over nail root
- blood in dermal blood vessels beneath nail give pink color to nails
- lunula: whitish half moon shaped base resulting from thicker skin in the area
Sweat (sudoriferous) glands: eccrine & apocrine
- eccrine sweat glands: far more numerous - most abundant on palms of hands, soles of feet & forehead
o ducts
opens into pore at skin surface
o secrete sweat: 99% water with salts, vitamin C, antibodies, metabolic wastes (form of excretion)
o sweat prevents overheating; regulated by sympathetic division of autonomic nervous system
- apocrine sweat glands: mostly confined to axillary & anogenital regions
o ducts
empty into hair follicles
o in addition to components of sweat, secretion contains lipid & proteins
- ceruminous glands: modified apocrine glands in the external ear canal
o secrete cerumen (earwax); deters insects & blocks foreign material
Sebaceous (oil) glands: located all over body except palms of hand & soles of feet
- secrete sebum (rich in oils) into hair follicle (or pore)... bacteriocidal; lubricates hair & skin
- inflammation/infection can lead to acne; overactivity leads to seborrhea
Mammary glands: modified sweat glands in breasts
- lobules within breast lobes contain numerous alveoli
- after childbirth, alveoli secrete milk, which enters a duct leading to nipple
Functions of Skin:
Protection: the skin forms a protective covering over body, guarding it from physical trauma
Synthesis of Vitamin D: UV light (sunlight) assists skin cells in producing vitamin D
Sensory Reception & Communication: specialized nerve endings in dermis are sensory receptors for touch, pressure. Pain, hot & cold
Body Temperature Regulation: some energy from breaking down ATP in chemical reactions is released as heat
- hypothalamus in brain has homeostatic mechanism for regulation of body temperature (36.2-37.7°C)
- skin regulates body temperature:
o blood vessels in dermis can constrict to receive less blood or dilate to receive more blood
o sweat glands can secrete sweat to cool body
- hyperthermia: body temperature above normal (regulatory mechanisms overcome)
o heat exhaustion: individual becomes tired; may be accompanied by headaches, vomiting
o heat stroke: elevated temperature (up to 43°C or 110°F); dizziness, confusion & delusions may occur
• important to cool body immediately: person is immersed in cool water, & fluids given to restore water & salt balance
o fever: elevated body temperature brought on by illness
• bacteria release pyrogens that reset the thermostat at higher temperature (accompanied by chills)
• thermostat reset when infection is cleared & fever breaks
-
hypothermia: body
temperature below normal (regulatory mechanisms overcome)
o body
temperature 90-95°C: uncontrollable shivering, incoherent speech &
lack of coordination
o body
temperature 80-90°C: pulse rate slows, hallucinations occur, person loses
consciousness
Disorders of skin:
- athlete's foot: caused by fungal infection, usually in skin of toes, sole of foot
- eczema & psoriasis: rapid cell division in skin cells, resulting in scaling, itching
o eczema: caused by sensitivity to chemicals (detergents), fabrics, heat
o psoriasis: chronic autoimmune disorder, may be hereditary (inherited); results in reddish (scaly) patches
o melanoma: malignant skin cancer; starts in melanocytes
• characterized by unusual moles that are linked to sun exposure
• may metastasize or spread to nearby organs or tissues
o basal cell carcinoma: most common skin cancer; UV exposure causes basal cells of epidermis to overgrow, forming tumor
o squamous cell carcinoma: tumors form in cells of lower layers of epidermis
• more likely to metastasize than basal cell carcinoma
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Burns
o first-degree: only epidermis is destroyed
o second-degree: entire epidermis & part of dermis is destroyed
o third-degree: full thickness (epidermis & dermis) is destroyed
o fourth degree: tissue down to bone is destroyed
Wound Healing:
-
if blood vessel is torn,
blood clots at vessel tear &
forms scab
-
basal layer of epidermis
produces new cells at rapid rate to replace damaged cells
-
if wound is deep, scar
tissue may form (many collagen
fibers add strength, but few cells present)
Effects of Aging: epidermis maintains thickness, but there is
decreased turnover of skin cells; epidermis becomes less firmly attached to
dermis; adipose tissue declines
-
decline in numbers of:
blood vessels, sweat glands, hair follicles, sebaceous glands & melanocytes
-
UV radiation can cause
rough skin, unusual pigmentation, wrinkles
Chapter 6: The Skeletal System
Classification of bone:
Human Skeleton: 206 named bones
- Axial skeleton: 80 bones... bones of skull, vertebral column & rib cage
- Appendicular skeleton: 126 bones... bones of upper & lower limbs, pectoral & pelvic girdles
Functions of bones:
- supports body & its organs against pull of gravity
- protects soft body parts
- blood cell formation (hematopoiesis): in some red bone marrow
- mineral storage: calcium salts (calcium phosphate)
- bones (particularly those of arms & legs) provide sites for muscle attachment & permit flexible movement
Bone structure:
Gross anatomy of long bones:
- compact bone: dense outer layer of bone
- spongy bone (cancellous bone): trabeculae - needle-like or flat pieces internal to compact bone; spaces between trabeculae filled with red or yellow bone marrow
- diaphysis (shaft): forms long axis of bone; thick collar of compact bone surrounding medullary (marrow) cavity
o In adults, marrow cavity contains fat - yellow bone marrow cavity
- epiphyses: ends of bone; often more expanded than diaphysis; outer compact & internal spongy bone
o Joint surfaces covered by articular cartilage
o Epiphyseal line: between diaphysis & each epiphysis - remnant of epiphyseal plate (site of bone growth during childhood)
- Periosteum: membrane that covers entire surface of bone except joint surfaces
o continuous with tendons & ligaments that anchor bones
o contains blood vessels that enter bones & deliver nutrients to bone cells
- Endosteum: inner membrane covers trabeculae of spongy bone & canals of compact bone; contains osteoblasts & osteoclasts
Hematopoietic tissue in bones:
- Hematopoiesis occurs in red marrow (in cavities of spongy bone of long bones & diploe of flat bones)
- In infants, medullary cavity & all spongy bone have red bone marrow
- In adults, red bone marrow in the head of the femur & humerus, & diploe of flat bones & some irregular bones (hip bone)
- During anemia (blood cell deficiency), yellow marrow can revert to red marrow
Microscopic structure of bone:
Compact bone (lamellar bone): units called osteons or Haversian systems
- within each cylnder (osteon) is tubes (concentric circles) of bone matrix (lamellae)
- central (Haversian) canal: runs through center of osteon; carries blood vessels & nerve fibers
- osteocytes: bone cells in small cavities called lacunae
- canaliculi: connect lacunae to each other & central canal
- lacunae separated by bone matrix containing collagen fibers & mineral deposits (calcium phosphate)
Spongy bone: trabeculae... a few cell layers of irregularly arranged lamellae & osteocytes connected by canaliculi
- no osteons; nutrients delivered by capillaries in endosteum
Bone development:
- osteogenesis (ossification)... in infants & adolescents for skeleton formation & growth; in adults for bone remodeling
- most of skeleton is cartilage model (cartilage shaped like future bones) during prenatal development
- cartilage models converted to bone when calcium salts deposited in bone matrix, first by cartilage cells & later by osteoblasts (bone-forming cells)
- endochondral ossification: bone forms by replacing hyaline cartilage
- intramembranous ossification: membrane bone forms from fibrous membrane
-
endochondral ossification:
o primary ossification center in middle of bone
o bone collar forms around diaphysis of cartilage
o central cartilage calcifies & cavitates
o diaphysis elongates & medullary cavity forms
o ossification of epiphyses at secondary ossification centers
o epiphyseal (growth) plates form at junction of diaphysis & epiphysis
Bone Remodeling: for bone growth, or to replace injured bone
- osteoclasts (giant multinucleate cells from same stem cells that differentiate into macrophages) secrete lysosomal enzymes to digest organic matrix & acids to release calcium into solution
- osteoclast damage repaired by osteoblasts
- osteoblasts take calcium from blood for new bone matrix
- some osteoblasts within new matrix become osteocytes (bone cells)
- requires calcium & phosphate & enzyme alkaline phosphatase
Repair of fractures:
Fracture types:
- displaced (ends out of alignment) & nondisplaced fractures
- complete (bone broken through) & incomplete fractures
- linear (along axis) & transverse (perpendicular to axis) fractures
- open (compound, breaks skin) & closed (simple) fractures
Reduction: realignment of broken bone ends
- closed reduction: bones coaxed into position by physician (or someone)
- open reduction: bone ends are secured together by pins or wires
- hematoma (mass of clotted blood) forms in space between broken bone as blood escapes from injured blood vessels
- fibrocartilage callus forms to fill space between broken ends of bone (collagen fibers tie bone ends together)
- bony callus forms from fibrocartilage callus as osteoblasts produce spongy bone to join bone ends together
-
bone remodeling: osteoblasts build new compact bone at
periphery & form medullary cavity from spongy bone
- consists of bones arranged along (longitudinal) axis of body
- includes: skull bones, auditory ossicles (ear bones), hyoid bone, ribs, sternum (breastbone) & vertebral column (backbone)
- cranial bones: 8 bones which enclose & protect the brain
o frontal bone: forms forehead & part of nose & orbits
o parietal bones (2): posterior to frontal bone; form roof & sides of cranium
o temporal bones (2): inferior to parietal bones; help form base of cranium
• external auditory meatus: canal to middle ear
• mandibular fossa: articulates with mandible
• mastoid process: point of attachment for neck muscle (sternocleidomastoid)
• styloid process: point of attachment for muscles of tongue & larynx
• zygomatic process: helps form cheekbone
o occipital bone: forms dorsal part of skull & base of cranium
• foramen magnum: large opening where spinal cord joins brain
• occipital condyles: articulate with 1st cervical vertebra
o sphenoid
bone: forms sides & base of cranium
& part of orbits
• articulates
with all other cranial bones
• sella turcica: depression that houses pituitary gland of brain
o ethmoid bone: forms part or orbits & nasal cavity
• perpendicular plate: upper nasal septum
• cribriform plate: contains opening for olfactory (smell) nerve fibers
• crista galli: ridge at base of cranial cavity for meninges attachment
• superior & middle nasal conchae: projections in mucous membranes of nasal cavity for filtering & warming air
-
Facial Bones: 14 bones
o nasal bones (2): form bridge of nose (most of outer nose is cartilage)
o maxillae (2): form upper jaw
• palatine process: forms anterior portion of hard palate (roof of mouth)
o zygomatic bones (2): form sides of orbits & cheekbones
• temporal process: joins zygomatic process of temporal bone
o lacrimal bones (2): at medial walls of orbits (eye sockets)
• lacrimal fossa: has opening for tears
o palatine bones (2): form posterior portion of hard palate
o inferior nasal conchae (2): projections in mucous membranes of nasal cavity for filtering & warming air (like nasal conchae of ethmoid bone)
o vomer: forms lower part of nasal septum (joins with perpendicular plate of ethmoid bone)
o mandible: lower jaw
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