A & P Ch 6

Perichondrium

Dense irregular connective tissue membrane covering cartilage The perichondrium acts as a reinforcement to resist outward expansion when the cartilage is compressed. The perichondrium also contains blood vessels that nourish the cartilage cells. The thickness of cartilage is limited by the distance nutrients can diffuse through the matrix to reach the cells.

tuberosity

Large rounded projection; may be roughened

spongy bone

Layer of bone tissue that has many small spaces and is found just inside the layer of compact bone composed of small needlelike pieces of bone and lots of open space (trabeculae), open space contains red and yellow bone marrow

osteoblast

bone-forming cell; a cell that secretes the matrix for bone formation (unmineralized bone matrix they secrete includes collagen (90% of bone protein) and calcium-binding proteins that make up the initial unmineralized bone, or osteoid); secrete collagen, calcium-binding proteins; cube-shaped, responsible for bone remodeling

greenstick fracture

bending and incomplete break of a bone; most often seen in children

osteoclast

bone cell that absorbs and removes unwanted bony tissue; responsible for bone remodeling; giant and multinucleate cells actively resorbing (breaking down) bone, the osteoclasts lie in a shallow depression they have carved out. They have a distinctive ruffled border that directly contacts the bone. The deep plasma membrane infoldings of the ruffled border tremendously increase the surface area for enzymatically degrading the bones and seal off that area from the surrounding matrix

displaced fractures

bone ends are out of normal alignment

non displaced fractures

bone ends retain their normal position

Wolff's Laws

bone grows or remodels in response to the demands placed on it

complete fracture

bone is broken all the way through

incomplete fracture

bone is not broken all the way through

osteoprogenitor cells

bone stem cells; squamous; found in membranous periosteum and endosteum

endochondral bone (endochondral ossification)

bone that begins as hyaline cartilage that is subsequently replaced by bone tissue; all bones below base of skull (excepting clavicle)

bone markings

bones display projections, depressions, and openings that serve as sites of muscle, ligament, and tendon attachment, as joint surfaces, or as conduits for blood vessels

irregular bones

bones of the vertebrae, facial, and hip bones

short bones

bones of the wrist and ankles, cube-shaped

head

bony expansion carried on a narrow neck

closed (simple) fracture

break that does not penetrate the skin

open fracture (compound)

broken bone penetrates through the skin

depressed fracture

broken bone portion is pressed inward

interstitial lamallae

fill in the spaces between the osteons in compact bone They either fill the gaps between forming osteons or are remnants of osteons that have been cut through by bone remodeling

bone lining cells

flat cells found on bone surfaces where bone remodeling is not going on

comminuted fracture

fracture in which the bone is splintered or crushed

groove

furrow

other hormones

glucocorticoids (hormones from the adrenal cortex) and vitamin D indirectly stimulate osteoclast activity Sex hormones, on the other hand, have the opposite effect

canaliculi

hairlike canals that connect lacunae to each other and the central canal the canaliculi tie all the osteocytes in a mature osteon together, allowing them to communicate and permitting nutrients and wastes to be relayed from one osteocyte to the next throughout the osteon

First step of healing bone fracture

hematoma formation - The hemorrhaged blood clots, forming a hematoma (he˝mah-to´mah) at the fracture site. Soon, bone cells deprived of nutrition die, and the tissue at the site becomes swollen, painful, and inflamed.

sinus

hollow space in a bone; filled with air and lined with mucous membrane

calcitonin

thyroid gland that lowers blood calcium levels when administrated at high doses

osteoid

unmineralized bone matrix composed of ground substance and collagen; secreted by osteoblasts

fissure

an opening; a groove; a split

process

any bony prominence

appendicular skeleton

Bones of the limbs and limb girdles that are attached to the axial skeleton

First step of ossification (for endochrondral bone formation)

A bone collar forms around the diaphysis of the hyaline cartilage model. Like all cartilage, the cartilage model is initially surrounded by perichondrium. Ossification begins when the underlying mesenchymal cells (cells of the embryonic connective tissue, p. 129) in the deep layer of the perichondrium specialize into osteoblasts. As a result, the perichondrium becomes periosteum. Osteoblasts of the newly converted periosteum secrete osteoid against the hyaline cartilage diaphysis, encasing it in a collar of bone. As the bone collar forms, chondrocytes within the shaft hypertrophy

osteoporosis

A condition in which the body's bones become weak and break easily.

periosteum

A dense fibrous membrane covering the surface of bones (except at their extremities) and serving as an attachment for tendons and muscles; outer layer is dense irregular connective tissue; inner layer has osteoprogenitor cells and osteoclasts; rich blood vessels found here, secured to bone by fibers

parathyroid hormone

A hormone of the parathyroid gland that regulates the metabolism of calcium and phosphorus in the body; stimulates osteoclasts to resorb bone, increase calcium levels in blood As blood concentrations of calcium rise, the stimulus for PTH release ends. The decline of PTH reverses its effects and causes blood Ca2+ levels to fall.

osteon

A structural unit of compact bone consisting of a central canal surrounded by concentric cylindrical lamellae of matrix; group of hollow tubes in matrix

cartilage growth

Appositional growth: increase size by adding to outer surface; cartilage-forming cells in the surrounding perichondrium secrete new matrix against the external face of the existing cartilage tissue Interstitial growth: expands from within; the lacunae-bound chondrocytes divide and secrete new matrix, expanding the cartilage from within; ends in adolescence

Proliferation Zone

Area of cartilage on diaphysis side of epiphyseal plate that is rapidly dividing New cells formed move upward, pushing epiphysis away from diaphysis, causing lengthening

Hypertrophic zone

Area with older chondrocytes closer to diaphysis Cartilage lacunae enlarge and erode, forming interconnecting spaces

Nutrient artery and vein

Blood vessels that supply the diaphysis form by invading the cartilage model as endochondral ossification begins

Fourth step of healing bone fracture

Bone remodeling occurs - the bony callus is remodeled. The excess material on the diaphysis exterior and within the medullary cavity is removed. Compact bone is laid down to reconstruct the shaft walls. The repaired area resembles the original unbroken bony region because it responds to the same set of mechanical stressors.

Third step of healing bone fracture

Bony callus forms. Within this mass of repair tissue, osteoblasts begin forming spongy bone. Within a week, osteoblasts begin to lay down trabeculae of new bone around and within the fibrocartilaginous callus. These trabeculae span the width of the callus and unite the two fragments of broken bone. Gradually the fibrocartilaginous callus is replaced by immature bone, converting it to a bony (hard) callus. Bony callus formation continues until a firm union forms about two months later.

Second Step of Ossification

Cartilage calcifies in the center of the diaphysis and then develops cavities. The hypertrophied chondrocytes calcify the surrounding cartilage matrix. Then, because calcified cartilage matrix is impermeable to diffusing nutrients, the chondrocytes die and the matrix begins to deteriorate. This deterioration opens up cavities, but the bone collar stabilizes the hyaline cartilage model. Elsewhere, the cartilage remains healthy and continues to grow briskly, causing the cartilage model to elongate.

cartilage vs bone

Cartilage contains no nerves or blood vessels. It is surrounded by a layer of dense irregular connective tissue, the perichondrium

ossification zone

Chondrocyte deterioration leaves long spicules of calcified cartilage at epiphysis-diaphysis junction Spicules eroded by osteoclasts Covered with new bone by osteoblasts Ultimately replaced with spongy bone

Second step of healing bone fracture

Fibrocartilaginous callus forms. Within a few days, new blood vessels grow into the clot. Fibroblasts and chondroblasts invade the fracture site from the nearby periosteum and endosteum. The fibroblasts produce collagen fibers that span the break and connect the broken bone ends. The chondroblasts secrete a cartilaginous matrix that bulges externally and later calcifies, forming a fibrocartilaginous callus that spans the break and connects the broken bone ends

epiphyseal plate

Growth plate, made of cartilage, gradually ossifies; hyaline cartilaginous area at the ends of long bones where lengthwise growth takes place in the immature skeleton; houses line or metaphysis where diaphysis and epiphysis meet

compact bone

Hard, dense bone tissue that is beneath the outer membrane of a bone

hyaline cartilage

Most common type of cartilage; it is found on the ends of long bones, ribs, and nose includes: articular, costal, respiratory, nasal

line in bone

Narrow ridge of bone; less prominent than a crest

crest

Narrow ridge of bone; usually prominent

axial skeleton

Portion of the skeletal system that consists of the skull, rib cage, and vertebral column

epicondyle

Raised area on or above a condyle

foramen

Round or oval opening through a bone

fossa

Shallow, basinlike depression in a bone, often serving as an articular surface

tubercle

Small rounded projection or process

bone remodeling

The continuous turnover of bone matrix and mineral that involves first, an increase in resorption and osteoclast activity, and later, reactive bone formation by osteoblast activity.

Fourth Step of Ossification

The diaphysis elongates and a medullary cavity forms. As the primary ossification center enlarges, osteoclasts break down the newly formed spongy bone and open up a medullary cavity in the center of the diaphysis. Throughout the fetal period (week 9 until birth), the rapidly growing epiphyses consist only of cartilage, and the hyaline cartilage models continue to elongate by division of viable cartilage cells at the epiphyses. Ossification "chases" cartilage formation along the length of the shaft as cartilage calcifies, erodes, and then is replaced by little bony spikes on the epiphyseal surfaces facing the medullary cavity. At birth, most of our long bones have a bony diaphysis surrounding remnants of spongy bone, a widening medullary cavity, and two cartilaginous epiphyses. Shortly before or after birth, secondary ossification centers develop in one or both epiphyses. Typically, the large long bones form secondary centers in both epiphyses, whereas the small long bones form only one secondary ossification center. (In short bones, only the primary ossification center is formed. Most irregular bones develop from several distinct ossification centers.)

Fifth Step of Ossification

The epiphyses ossify. Secondary ossification reproduces almost exactly the events of primary ossification, except that the spongy bone in the interior is retained and no medullary cavity forms in the epiphyses.

Third Step of Bone Ossification

The periosteal bud invades the internal cavities and spongy bone forms. In month 3, the forming cavities are invaded by a collection of elements called the periosteal bud, which contains a nutrient artery and vein, nerve fibers, red marrow elements, osteoprogenitor cells, and osteoclasts. The entering osteoclasts partially erode the calcified cartilage matrix. The osteoprogenitor cells become osteoblasts that secrete osteoid around the remaining calcified fragments of hyaline cartilage. In this way, bone-covered cartilage trabeculae, the earliest version of spongy bone, is formed.

calcification of osteoid

The proteins of the newly deposited osteoid bind calcium ions (Ca2+), raising the local concentration of Ca2+ This in turn triggers osteoblasts to release matrix vesicles studded with the enzyme alkaline phosphatase The result is that calcium salts are deposited throughout the osteoid, creating calcified bone matrix.

trochanter

Very large, blunt, irregularly shaped process

osteocyte

a bone cell, formed when an osteoblast becomes embedded in the matrix it has secreted; occupy lacunae, spidery-shaped; monitor and maintain matrix, stress sensors that respond to stimuli, can help trigger bone remodeling; helps maintain calcium homeostasis by communicating with osteoblasts and osteoclasts

membranous bone

a bone develops from a fibrous membrane

Paget's disease

a bone disease of unknown cause characterized by the excessive breakdown of bone tissue, followed by abnormal bone formation

fractures

a crack or break in a bone

meatus

canal-like passageway

fibrocartilage

cartilage that contains fibrous bundles of collagen, such as that of the intervertebral disks in the spinal cord.

elastic cartilage

cartilage with abundant elastic fibers; more flexible than hyaline cartilage

medullary cavity

cavity within the shaft of the long bones filled with bone marrow; no bone tissue just yellow marrow (fat)

short, irregular, and flat bone structure

consist of thin plates of spongy bone (diploë) covered by compact bone. The compact bone is covered outside and inside by connective tissue membranes, respectively the periosteum and endosteum; no marrow cavity

central canal of bone

contains blood vessels and nerves, Haversian canal, serve osteon cells

osteomalacia

disease marked by softening of the bone caused by calcium and vitamin D deficiency

epiphyseal fracture

epiphysis separates from the diaphysis along the epiphyseal plate

notch

indentation at the edge of a structure

mineral salts

largely calcium phosphates present as tiny, tightly packed, needle-like crystals in and around collagen fibers in the extracellular matrix

circumferential lamallae

located just deep to the periosteum and just superficial to the endosteum, extend around the entire circumference of the diaphysis

long bones

longer than they are wide; shaft + 2 ends; all limb bones except patella, wrist, and ankle

skeletal cartilage

made of highly resilient, molded cartilage tissue that consists primarily of water Contains no blood vessels or nerves

Calcification zone

matrix calcifies; cartilage cells die; matrix begins deteriorating; blood vessels invade cavity

endosteum

membrane lining the medullary cavity of a bone; has osteoprogenitor cells and osteoclasts; covers the trabeculae of spongy bone and lines the canals that pass through the compact bone

compression fracture

occurs when the bone is pressed together (compressed) on itself, crushed bone

rickets

osteomalacia in children; causes bone deformity

intramembranous ossification

process by which bone forms directly from mesenchymal tissue; forms cranial and clavicle bones - mostly flat bones

epiphyseal arteries and veins

provide the blood supply to the epiphyses of the bone

spiral fracture

ragged break occurs when excessive twisting forces are applied to a bone

epiphyseal line

remnant of the epiphyseal plate, seen in adult bones; where diaphysis and epiphysis meet

sesamoid bones

round bones found near joints (e.g., the patella); reduce friction, alter tendon direction pull

condyle

rounded articular projection, often articulates with a corresponding fossa

mechanical stress

second set of controls regulating bone remodeling, bone's response to mechanical stress (muscle pull and gravity), keeps the bones strong where stressors are acting.

diaphysis

shaft of long bone, composed of compact bone, surrounds medullary cavity (is spongy bone layer in between)

spine

sharp, slender, often pointed projection

lacunae

small cavities in bone that contain osteocytes at lamellae junctions

nutrient foramen

small opening in the middle of the external surface of the diaphysis, through which an artery enters the bone to provide nourishment

facet

smooth, nearly flat articular surface

bone functions

support, protection, anchorage, mineral storage (calcium and phosphate), blood cell formation (Hematopoiesis), fat storage (yellow bone marrow), hormone production

Epiphysis

the end part of a long bone, initially growing separately from the shaft; the exterior is compact bone, the interior is spongy bone; hyaline cartilage covers joint surface

bone resorption

the removal of minerals and collagen fibers from bone by osteoclasts

flat bones

these bones are thin, flat, and curved.; they form the ribs, breastbone, and skull.

red marrow

thick, bloodlike material found in flat bones and the ends of long bones; location of blood cell formation in infants is in medullary cavity in diaphysis and spongy bone in adults red marrow is replaced with yellow marrow which extends into epiphysis; red marrow found in between trabeculae of spongy bone in flat and long bones

lamella

weight-bearing, column-like matrix tubes composed mainly of collagen - make up osteon; the collagen fibers in adjacent lamellae always run in different directions. This alternating pattern beautifully withstands torsional stresses