Chapter 6: Skeletal System: Bones and Bone Tissue

five major functions of skeletal system

1. support - strong bone sutied for bearing weight. cartilage provides firm yet flexible support. ligaments are strong bands of fibrous connective tissue that attach to bone

2. protection - protects organs

3. movement - muscles attach to bones via tendons

4. storage - mineral in blood are taken into bone and stored. if blood levels of these minerals decrease, minerals released from bone

5. blood cell production - bones contain cavities filled w/ red bone marrow which gives rise to blood cells and platelets

three types of cartilage

hyaline - precursor of most bones in the body

fibrocartilage

elastic cartilage

chondroblasts

cells that produce cartilage matrix

chondrocyte

when cartilage surrounds a chondroblast, it becomes a _______, a rounded cell that occupies a space called a lacunae within the matrix

perichondrium

Dense irregular connective tissue membrane covering cartilage. blood vessels penetrate outer layer, but do not enter the cartilage matrix

articular cartilage

cartilage covering the ends of bones where they come together to form joints. has no perichondrium

appositiional growth

type of cartilage growth. chondroblasts in the perichondrium add new cartilage to the outside of the existing cartilage. chondroblasts lay down new matrix and add new chondrocytes to the outside of the tissue

interstitial growth

type of cartilage growth where chondrocytes within the tissue divide and add more matrix between the existing cells.

bone matrix

composed of 35% organic and 65% inorganic material

hydroxyapatite

the inorganic calcium phosphate in bone

function of collagen fibers in bone

gives bone flexible strength (like steel bars)

function of mineral matrix in bone

gives bone weight-bearing strength

osteoblasts

bone-forming cells; produce collagen and proteoglycans

ossification

formation of bone by osteoblasts

osteocyte

term for an osteoblast once it becomes surrounded by bone matrix

lacunae

small cavities in the bone or cartilage that hold individual bones or cartilage cells

canaliculi

spaces occupied by the osteocyte cell processes

osteoclasts

responsible for the reabsorption or breakdown of bone. large cells that contain several nuclei.

ruffled border

areas where the plasma membrane of osteoclasts contacts the bone matrix

osteochondral progenitor cells

stems cells that can become osteoblasts or chondroblasts - located in inner layer of perichondrium and inner layers of connective tissue that covers bone (periosteium/endosteum)

woven bone

immature bone present during fetal development or in the early stages of bone repair (after a fracture); collagen fibers are randomly distributed and have crisscross pattern

bone remodling

process of removing old bone and adding new bone

lamellar bone

mature bone that is organized into thin sheets or layers approximately 3-7 micrometers thick called lamellae. collagen fibers lie parallel to one another but at an angle to the collagen fibers in adjacent lamellae

spongy bone

consists of interconnecting rods or plates of bone called trabeculae; the spaces are filled with bone marrow and blood vessels

trabeculae

supporting bundles of bony fibers in cancellous (spongy) bone; oriented along the lines of stress within the bone

compact bone

dense and thick bone matrix; lamellae are oriented around blood vessels that enter the bone

central canal

The hollow center of an osteon, also known as a Haversian canal. The central canal contains blood vessels, lymphatic vessels, and nerves. Bone is laid down around the central canal in concentric rings called lamellae.

osteon

The unit of combact bone, also called a Haversian system. Osteons are essentially long cylinders of bone; the hollow center is called the central canal, and is where blood vessels, nervs, and lymphatic vessels are found. Compact bone is laid down around the central canal in rings (lamellae). cut in cross section it resembles a bullseye

haversian system

A unit of compact bone consisting of a tube (haversian canal) with the laminae of bone that surrounds it

three types of lamellae

concentric - circular layers of bone matrix that surround a common central canal

circumferential - thin plates that extend around the bone (outer surfaces of central canal)

interstitial - between osteaons; remnants of concentric or circumferential lamellae that were partially removed during bone remodling

volkmann's canals aka perforating canals

channels lying at right angles to the central canal, connecting blood and nerve supply of the periosteum to that of the Haversian canal

four basic bone shapes

1. long bone - longer than they are wide (upper and lower limbs)

2. short bone - round or nearly cubed-shaped (wrist bone and ankle bone)

3. flat bone - relatively thin, flattened shape and usually curved (skull bones, ribs, sternum, shoulder blades)

4. irregular bone - does not fit readily into the other 3 categories (vertebrae and facial bones)

diaphysis

the shaft of a long bone

epiphysis

the end of a long bone (knobby ends); develops from a center of ossification distinct from the diaphysis

epiphyseal plate

cartilaginous area at the ends of long bones where lengthwise growth takes place in the immature skeleton; separates the epiphysis from the diaphysis

medullary cavity

cavity within the shaft of the long bones; filled with bone marrow

red marrow vs. yellow marrow

red - site of blood cell formation

yellow - mostly adipose tissue

periosteum

a dense fibrous membrane covering the surface of bones (except at their extremities) and serving as an attachment for tendons and muscles;

endosteum

vascular membrane that lines the inner surface of long bones

sinuses

air filled spaces inside flat and irregular bones that are lined with mucous membranes

intramembranous ossification

takes place in connective tissue membranes; begins when mesenchymal cells in the membrane become osteochondral progenitor cells

center of ossification

A location in a developing bone where osteoblasts produce and secrete bone matrix

fontanels

a soft, membrane-covered space between the bones at the front and the back of a newborn's skull

endochondral ossification

the most common bone formation process, which involves the replacement of hyaline cartilage (developed by mesenchyme) with bone,

occurs in postcranial skeleton (except clavicle) and in bones of cranial base

1. mesenchyme condenses to form hyaline cartilage precursor

2. A bone collar forms around the circumference of cartilage model--this is periosteal bone

3. At primary center of ossification (forms first): cartilage matrix becomes calcified, erodes and forms spicules; then, bone forms on spicules

4. Ossification repeats in secondary centers of ossification in epiphyses

bone collar

the osteoblasts produce compact bone on the surface of the cartilage model.

calcified cartilage

Cartilage tissue in which inorganic calcium salts are deposited in the matrix, which occurs prior to replacement by osseous tissue, and sometimes in aging cartilage.

bone growth

only occurs via appositional growth; new bone on the surface of older bone or cartilage

zone of resting cartilage

anchors growth plate to bone

zone of proliferation

2nd region of epiphyseal plate; made of a column of flattened cells. Region of rapid proliferation of chondroblasts from isogenous group. Actively makes cartilage via intersititial growth

zone of hypertrophy

chondrocytes mature and enlarge

zone of calcification

is very thin and contains hypertrophied chondrocytes and calcified cartilage matrix. The hypertrophied chondrocytes die, and blood vessels from the diaphysis grow into the area.

growth at articular cartilage

Increases size of bones with no epiphyses: e.g., short bones; chondrocytes near the surface of the articular cartilage similar to those in zone of resting cartilage

factors affecting bone growth

1. nutrition - vitamin d is necessary for the normal absorption of calcium from the intestines; vitamin c is necessary for collagen synthesis by osteoblasts

2. hormones - growth hormone stimulates cartilage growth and appositional bone growth, thyroid hormone necessary for growth of all tissues including cartilage; estrogen and testosterone stimulate bone growth.

bone remodling

converts old woven bone to new lamellar bone. is involved in bone growth, changes in bone shape, adjustment of bone to stress, bone repair, and calcium ion regulation in the body. causes the diameter of the medullary cavity to increase as the bone increases in length and width

interstitial lamellae

the areas between osteons that are fragments of older osteons that have been partially destroyed during bone rebuilding or growth

hematoma

localized mass of blood released from blood vessels, but confined in an organ or space; usually forms a clot that stops the bleeding; adjacent tissue to the bone fracture site dies

callus formation

osteoclasts digest into the hematoma as bone stem cells differentiate into osteoblasts and chondrocytes

callus ossification

during bone repair callus replaced by woven, cancellous bone through endochondral ossification

calcium homeostasis

minerals are deposited in the skeleton and withdrawn when they are needed for other purposes; depends on a balance btwn dietary intake, urinary and fecal loses, and exchanges btwn osseous tissue