chapter 7: skeletal system

skeletal system

includes bones, cartilage, ligaments, and other CT that stabilize or connect

bones

primary organs of skeletal systems

bones

form rigid framework of body

compact bone

rigid CT that appears white, smooth, and solid

compact bone

makes up 80% of of total bone mass

spongy bone

located internal to compact bone and appears porous

spongy bone

makes up 20% of bone mass

compact bone

also called dense or cortical bone

spongy bone

also called trabecular or cancellous bone

cartilage

semirigid CT that is more flexible than bone

mature cartilage

what cartilage is avascular (lack blood supply)

hyaline cartilage

provides model during development for formation of fetal skeleton

costal, articular, epiphyseal

types of hyaline cartilage

costal cartilage

attaches rib to sternum

articular cartilage

covers ends of some bones

epiphyseal

thin layer located within growth plate

fibrocartilage

weight-bearing that withstands compression

fibrocartilage

forms intervertebral discs, pubic symphysis, and pads of knee joint (menisci)

ligaments

dense regular CT that anchors bone to bone

tendons

dense regular CT that connects muscle to bone

support and protection, levers for movement, hematopoiesis, and storage of mineral and energy reserves

what are the functions of bone

hematopoiesis

red blood cell protection and occurs in red bone marrow CT

calcium and phosphate

what minerals are mainly stored and released from bone

calcium

essential mineral for muscle contraction, blood clotting, and release of neurotransmitter from nerve cells

phosphate

structural component of ATP, nucleotides, phospholipids, and important component of plasma membrane

some bone CT is broken down

how is calcium and phosphate released from bone when needed

long bones

most common, greater in length than width, and have elongated cylindrical shaft (disphysis)

short bones

length nearly equal to width

sesamoid

small, sesame seed-shaped bone along tendons of some muscles

flat bones

thin surfaces that may be slightly curved

flat bones

provide surface area for muscle attachment and protect underlying tissue

irregular bones

elaborate and sometimes complex bones

diaphysis

(shaft);elongated and usually cylindrical; provides for leverage and major weight support

diaphysis

composed of compact bone and spongy extends internally in form of spicules

medullary (marrow) cavity

hollow, cylindrical space within diaphysis

red bone marrow

what type of bone marrow does a child have

yellow bone marrow

what type of bone marrow does an adult have

epiphysis

expanded, knobby region at each end of long bone

proximal epiphysis

end of bone closest to trunk

distal epiphysis

end farthest from trunk

articular cartilage

covers joint surface to reduce friction and absorb shock

metaphysis

region where bone widens and transfers weight from disphysis to epiphysis

epiphyseal plate

growth plate found within metaphysis in growing bone

epiphyseal line

area of compact bone and is remnant of epiphyseal plate in adults

periosteum

tough sheath covering outer surface of bone except areas od articular surface

periosteum- outer fibrous layer of dense irregular CT

protects bone from surrounding structures, anchors blood vessels and nerves to bone surface, and attachment site for ligaments and tendons

periosteum- inner cellular layer

includes osteoprogenitor cells, osteoblasts, and osteoclasts

periosteum

responsible for growth in bone width and anchored to bone by perforating fibers

endosteum

thin layer of CT that covers internal surfaces of bone within medullary cavity and responsible for same things as periosteum

osteoprogenitor cells

stem cells derived from mesenchyme and matures to become osteoblasts

osteoblasts

synthesize and secrete osteoid (initial semisolid organic form of bone matrix) and then become osteocytes

osteocytes

mature bone cells that maintain bone matrix and detect mechanical stress on a bone to signal osteoblasts

osteoclasts

large, lultinuclear, phagocytic cells; break down bone in process called bone resorption

nutrient foramen

small opening or hole in bone where one nutrient artery enters and vein exits in order to intervate through periosteum, endostieum ,and marrow cavity

red bone marrow

main function is to form blood cells of the body and contains reticular CT, developing blood cells, and adipocytes

spongy bone of most bones and medullary cavity

where is red bone marrow mainly located in children

skull, vertebrae, ribs, sternum, ossa coxae, and proximal epiphysis of humerus and femur

where is red bone marrow located in adults

yellow bone marrow

product of red bone marrow degeneration as children mature with a decrease in developing blood cells adn increase in adipocytes

severe anemia

what causes yellow bone marrow to convert back to red bone marrow to facilitate production of additional erythrocytes

organic components

what gives bone tensile strength by resisting stretching and twisting to contribute to overall flexibility

osteoid

what is the organic component of the bone matrix

osteoid

composed of collagen and semisolid ground substance of proteoglycans and glycoproteins that suspend and support collagen fibers

salt crystals; primarily calcium phosphate

what are the inorganic components of the bone matrix

long axis of collagen fibers

where do crystals deposit in extracellular matrix

harden and account for rigidity that provides compressional strength

what do crystals do for matrix

when osteoblasts excrete osteoid

when does bone formation begin

calcification

what occurs to osteoid when hydroxyapatite crystals deposit in bone matrix

Vitamin D, Vitamin C, and calcium and phosphate for calcification

what substances are required for bone formation

bone resorption

process where bone matric is destroyed by substances released from osteoclasts into extracellular space adjacent to the bone

bone resorption

occurs when blood calcium levels are low

proteolytic enzymes

what is released from lysosomes within osteoclasts during bone resorption to digest organic components

hydrochloric acid

what dissolves the mineral parts of bone matrix during bone resorption

osteon

basic functional and structural unit of mature compact bone and oriented parallel to diaphysis of long bone

central (haversian) canal

cylindrical channel at center of osteon with blood vessels and nerves

concentric lamallae

rings of bone CT that surround central canal

concentric lamallae

contains collagen fibers that run at 90 angle from previous lamallae: which give bone strength and resilience

osteocytes

mature bone cells found in small spaces between adjacent concentric lamellae and maintain bone matrix

lacunae

small spaces that each house an osteocyte

canaliculi

interconnecting channels within bone CT that extend from lacunae, through lamellae, and connect to other lacuna and central canal

perforating (Volkmann) canal

run perpendicular to central canals and connect them with different osteons, forming channel for vascular and innervation connection among multiple osteons

external circumferential lamellae

rings of bone immediately internal to periosteum

internal circumferential lamellae

immediately external to the endosteum

interstitial lamellae

components of compact bone between osteons or leftover parts of osteons that have been partially resorbed

trabeculae of spongy bone

open lattice of narrow rods and plates of bone

parallel lamellae in spongy bone

bone matrix with osteocytes resting between adjacent lamellae with canaliculi radiating from lacunae

hyaline cartilage

population of cells scattered throughout glass-appearing matrix of protein fibers (collagen)

hyaline cartilage

has a high percentage of water (60-70% by weight) that allows it to be a good shock absorber

chondroblasts

derived from mesenchymal cells and produce cartilage matrix

chondrocytes

chondroblasts become encased within matrix they have produced and secreted; occupy lacunae

perichondrium

dense irregular CT that covers hyaline cartilage, except articular, and helps maintain shape

bone growth

occurs during enbryologic development and on

interstitial growth

growth in length and dependent on cartilage growth in epiphyseal plate

resting cartilage, proliferating cartilage, hypertrophic cartilage, calcified cartilage, ossification

what are the five microscopic zones nearest to epiphysis down to diaphysis

proliferating cartilage and hypertrophic cartilage

what zones are responsible for where bone length occurs

oppositional growth

occurs within periosteum throughout lifetime is bone matrix deposited within layers parallel to surface

oppositional growth

process where osteoblasts produce external circumferential lamellae and osteoclasts resorb bone matrix along medullary cavity

bone remodeling

ongoing process that occurs at periosteal and endosteal surfaces influenced by mechanical stress and hormones

mechanical stress

occurs in weight-bearing movement and exercise because as muscles grow, it applies stress to bone attachment where bone projections will grow

hormones

molecules released from one cell into blood and transported throughout body to affect other cells and some alter rates of chondrocte, osteoblast, and osteoclast activity

growth hormone (somatotropin)

produced by anterior pituitary gland and stimulates liver to release hormone insulin-like growth hormone (IGF) to stimulate growth of cartilage in epiphyseal plate