BIO 168 Chapter 6: Skeletal System Bones and Bone Tissue

bones such as the capals that have the same length and width are classified as ____ bones.

SHORT

the perichondrium is

a double layer outer layer of dense irregular connective tissue containing fibroblasts. blood vessels and nerves penetrate the outer layer of the perichondrium but do not enter the cartilage matrix so nutrients must diffuse through the cartilage matrix to reach the chondrocytes.

spongy bone

appears porous, has less bone matrix and more space than compact bone. consists of interconnecting rods or plates of bone called trabeculae. between the trabeculae are spaces, which in life are filled with bone marrow and blood vessels.

long bones increase in width and other bones increase in size or thickness because of ____ growth beneath the periosteum

appositional

there are two types of cartilage growth:

appositional growth and interstitial growth.

bone growth, increasing size or thickness of a bone due to growth beneath the periosteum is called ____ growth.

appostitional

concentric lamellae

are circular layers of bone matrix that surround the central canal.

The ends of long bones are typically covered by ____.

articular cartilage

epiphyses increase in size because of growth at the:

atricular cartilage

what is the function of red bone marrow?

blood cell production

functions of the skeleton system

body support organ protection body movement mineral storage blood cell production

hyaline cartilage is most intimately associated with:

bone

bones of the cranium

(flat bones) frontal, parietal, occipital, temporal, sphenoid, ethmoid

Types of bone fractures

- Closed (simple) fracture: break that does not penetrate the skin - Open (compound) fracture: broken bone penetrates through the skin

bone growth in width

1. osteoblasts beneath the periosteum lay down bone (dark brown) to form ridges separated by grooves. blood vessels of the periosteum lie in the grooves 2. the groove is transformed into a tunnel when the bone built on adjacent ridges meets. the periosteum of the groove becomes the endosteum of the tunnel. 3. appositional growth by osteoblasts from the endosteum results in the formation of a new concentric lamella. 4. the production of additional concentric lamellae fills in the tunnel and completes the formation of the osteon.

mature bone matrix is normally about: (by weight)

35% organic and 65% inorganic material the organic material consists mostly of collagen and proteoglycans the inorganic material consists mostly of a calcium phosphate crystal called HYDROXYAPATITE Ca10(PO4)6(OH)2

What is the expanded end of a long bone to which tendons and ligaments attached called?

Epiphysis

Bones are classifies as one of four types based on their shape. The bones of the cranium are examples of ____ bones.

FLAT

articular cartilage

which is hyaline cartilage that covers the ends of bones where they come together to for joints, has no perichondrium, blood vessels, or nerves.

fatty bone marrow that no longer produces blood cells and is mostly adipose tissue is called ____ bone marrow.

yellow

the epiphyseal plate is organized into four zones

zone of resting cartilage zone of proliferation zone of hypertrophy zone of calcification

place the zones of the epiphyseal plate in order beginning with the zone nearest the epiphysis and ending at the diaphysis

zone of resting cartilage zone of proliferation zone of hypertrophy zone of calcification zone of ossified bone

osteoclasts are

bone destroying cells. these cells perform reabsorption, or breakdown, of bone that mobilizes crucial Ca2+ and phosphate ions for use in many metabolic processes. as bone is broken down Ca2+ goes "back" into the blood. these cells are massive multinucleated cells whose differentiation follows a complex pathway. they are derived from red bone marrow cells that also differentiate into monocytes (called macrophages in the tissues). these precursors attach to the bone matrix where direct contact with osteoblasts is required to allow eventual maturation into functional osteoclasts.

intramembranous ossification and endochondral ossification

bone forms in two patterns (intramembranous and endochondral) during fetal development intramembranous ossification bone forms in preexisting connective tissue membranes endochondral ossification bone forms from a preexisting cartilage model. both methods produce woven bone which is then remodeled into lamellar bone. after remodeling, bone formed by intramembranous ossification cannot be distinguished from bone formed by endochondral ossification

Identify the four components of the skeletal system

bone, cartilage, tendons, ligaments

four components of the skeletal system

bones cartilage tendons ligaments

endochondral ossification

formation of cartilage begins at approx. the end of the fourth week of embryonic development bones of the base of the skull, part of the mandible, the epiphyses of the clavicles, and most of the remaining skeletal system develop through endochondral ossification steps are as follows: 1. Endochondral ossification begins as embryonic mesenchymal cells aggregate in regions of future bone formation. The mesenchymal cells differentiate into osteochondral progenitor cells that become chondroblasts. The chondroblasts produce a hyaline cartilage model having the approximate shape of the bone that will later be formed. As the chondroblasts are surrounded by cartilage matrix, they become chondrocytes. The cartilage model is surrounded by perichondrium, except where a joint will form connecting one bone to another bone. The perichondrium is continuous with tissue that will become the joint capsule later in development (see chapter 8). 2. When blood vessels invade the perichondrium surrounding the cartilage model (figure 6.13, step 2), osteochondral progenitor cells within the perichondrium become osteoblasts. Once the osteoblasts begin to produce bone, the perichondrium becomes the periosteum. The osteoblasts produce compact bone on the surface of the cartilage model, forming a bone collar. Two other events occur at the same time that the bone collar is forming. First, the cartilage model increases in size as a result of interstitial and appositional cartilage growth. Second, the chondrocytes in the center of the cartilage model absorb some of the cartilage matrix and hypertrophy (hī-per′trō-fē), or enlarge. The chondrocytes also release matrix vesicles, which initiate the formation of hydroxyapatite crystals in the cartilage matrix. At this point, the cartilage is called calcified cartilage. The chondrocytes in this calcified area eventually die, leaving enlarged lacunae with thin walls of calcified matrix. 3. Blood vessels grow into the enlarged lacunae of the calcified cartilage (figure 6.13, step 3). Osteoblasts and osteoclasts migrate into the calcified cartilage area from the periosteum by way of the connective tissue surrounding the outside of the blood vessels. The osteoblasts produce bone on the surface of the calcified cartilage, forming bone trabeculae, which transforms the calcified cartilage of the diaphysis into spongy bone. This area of bone formation is called the primary ossification center. 4. As bone development proceeds, the cartilage model continues to grow, more perichondrium becomes periosteum, and the bone collar thickens and extends farther along the diaphysis. Additional cartilage within both the diaphysis and the epiphysis is calcified (figure 6.13, step 4). Remodeling converts woven bone to lamellar bone and contributes to the final shape of the bone. Osteoclasts remove bone from the center of the diaphysis to form the medullary cavity, and cells within the medullary cavity specialize to form red bone marrow. 5. In long bones, the diaphysis is the primary ossification center, and additional sites of ossification, called secondary ossification centers, are created in the epiphyses by osteoblasts that migrate into the epiphysis (figure 6.13, step 5). The events occurring at the secondary ossification centers are the same as those at the primary ossification centers, except that the spaces in the epiphyses do not enlarge to form a medullary cavity as in the diaphysis. Primary ossification centers appear during early fetal development, whereas secondary ossification centers appear in the proximal epiphysis of the femur, humerus, and tibia about 1 month before birth. A baby is considered full-term if one of these three ossification centers can be seen on radiographs at the time of birth. At about 18-20 years of age, the last secondary ossification center appears in the medial epiphysis of the clavicle. 6. Replacement of cartilage by bone continues in the cartilage model until all the cartilage, except that in the epiphyseal plate and on articular surfaces, has been replaced by bone (figure 6.13, step 6). The epiphyseal plate, which exists during the time a person's bones are actively growing, and the articular cartilage, which is a permanent structure, are derived from the original embryonic cartilage model. After a person's bones have stopped growing, the epiphyseal plate regresses into a "scar," called the epiphyseal line

compact bone

has more matrix and is denser with fewer pores than spongy bone. blood vessels enter the substance of the bone itself and the lamellae of compact bone are primarily oriented around those blood vessels.

bleeding at the site of a bone fracture results in the formation of a fracture ____, a blood clot

hematoma

three types of cartilage

hyaline cartilage fibrocartilage elastic cartilage

what effects can be attributed to increased pressure on a bone?

increased osteoblast activity electrical charge changes

unlike cartilage bones cannot grow by:

interstitial growth. Bones can increase in size only by appositional growth.

lamellar bone

is mature bone that is organized into thin, concentric sheets or layers approx. 3-1 micrometers thick called lamellae. in general, collagen fibers of one lamella lie parallel to one another, but at an angle to the collagen fibers in the adjacent lamellae. osteocytes within their lacunae are arranged in layers sandwiched between lamellae.

calcitonin

is secreted from the thyroid gland when blood Ca2+ levels are too high, inhibits osteoclast activity by binding receptors on the osteoclasts.

Ossification (osteogenesis)

is the formation of new bone by osteoblasts. it occurs by appositional growth on the surface of previously existing material (bone or cartilage) example: osteoblasts beneath the periosteum cover the surface of preexisting bone. elongated cell extensions from osteoblasts connect to the cell extensions of other osteoblasts through gab junctions. bone matrix produced by the osteoblasts covers the older bone surface and surrounds the osteoblast cell bodies and extensions. the result is a new layer of bone.

a rounded cell that occupies a space called a ____ within the matrix

lacuna

Fontanels (soft spots)

large membrane-covered spaces between developing skull bones; unossified these bones eventually grow together and all the fontanels have usually closed by the age of 2

bones are attached to other bones by

ligaments

bones that are longer than they are wide

long bones

individual bones are classified according to shape

long, flat, short, or irregular. long- most bones of the upper and lower limbs are long bones. flat- relatively thin, flat shape and usually curved like some skull bones, rubs, breastbone, shoulder-blades (scapulae) short- round or nearly cube shaped. like bones of the wrist (carpal bones) and ankle (tarsal bones) irregular- like vertebrae and facial bones, have shapes that do not readily fit into the other three categories.

what is the hollow space within the diaphysis of a long bone called?

medullary cavity

connective tissue develops embryologically from

mesenchymal cells. some mesenchymal cells become stem cells, some of which replicate and become more specialized cell types. osteochondral progenitor cells are stem cells that can become osteoblasts or chondroblasts. they are located in the inner layer of the perichondrium and in layers of connective tissue that cover bone.

which of the following describes the zone of calcification in an epiphyseal plate?

minerals are deposited between the columns of lacunae

Hyaline cartilage

most bones in the body start out as a hyaline cartilage model. growth in bone length and bone repair often involve making hyaline cartilage first, then replacing it with bone.

osteocytes

once an osteoblast has secreted enough bone matrix to become surrounded by it the cell is then referred to as an osteocyte they retain their connections to neighboring osteocytes through their cell extensions. osteocytes retain their connections to neighboring osteocytes become relatively inactive, compared with most osteoblasts, but it is possible for them to produce the components needed to maintain the bone matrix

bone remodeling

ongoing replacement of old bone tissue by new bone tissue involved a basic multicellular unit (BMU)

instead of diffusing through the mineralized matrix nutrients and gases can pass through the small amount of fluid surrounding the cells in the canaliculi and lacunae

or pass from cell to cell through the gap junctions connecting the cell extensions.

immature bone cells that produce the organic bone matrix are called:

osteoblasts

three types of bone cells

osteoblasts osteocytes osteoclasts

the bone cells responsible for the breakdown of bone tissue are called

osteoclasts

the removal of bone matrix is the function of the bone cells called ____.

osteoclasts

mature bone cells found within lacunae of compact bone are called

osteocytes

what are mature bone cells found within lacunae of compact bone called?

osteocytes

three bone cells

osteocytes osteoblasts osteoclasts

what eliminate waste products through the canal system within compact bone?

osteocytes receive nutrients and eliminate waste products through the canal system within compact bone.

two terms which describe the entire process of bone formation are ___ and ____.

osteogenesis and ossification

the structure of compact bone that consists of a central canal and all the concentric lamellae that surround it is called a haversian system or a(n) ____.

osteon

calcium homeostasis is maintained by three hormones

parathyroid hormone, vitamin d from a precursor in the skin or from the diet, and calcitonin from C-cells in the thyroid gland. PTH is the major regulator of blood Ca2+ it is secreted from the parathyroid glands. when blood Ca2+ levels are too low, stimulates an increase in the number of osteoclasts, which break down bone elevate blood Ca2+ levels. in addition, PTH stimulates osteoblasts to release enzymes that break down the layer of unmineralized organic bone matrix covering bone, thereby making the mineralized bone matrix available to osteoclasts.

what is the term for the connective tissue sheath around the external surface of a bone?

periosteum

Hyaline cartilage chondroblasts

produce a matrix surrounding themselves.

most cartilage is covered by a

protective connective tissue sheath called the perichondrium

bone matrix can be compared to

reinforced concrete. like reinforcing steel bars, the collagen fibers lend flexible strength to the matrix; like concrete, the mineral components give the matrix weight-bearing strength.

the amount of stress applied to a bone can modify the bones strength through:

remodeling (the formation of additional bone, alteration in trabecular alignment to reinforce the scaffolding, or other changes). pressure in bone causes an electrical change that increases the activity of osteoblasts; therefore, applying weight (pressure) to a broken bone can speed up the healing process. Weak pulses of electric current are sometimes applied to a broken bone to speed healing.

the zone of the epiphyseal plate that is nearest the epiphysis and contains randomly arranged chondrocytes is the zone of ____.

resting cartilage

perforating canals (Volkmann's canals)

run perpendicular to the length of the bone. blood vessels from the peristeum or medullary cavity enter the bone through perforating canals. nutrients in the blood vessels enter the central canals, pass into the canaliculi, and move through the cytoplasm of the osteocytes that occupy the canaliculi and lacunae to the most peripheral cells at the edge of each osteon. waste products are removed in the reverse direction

the lacunae of the bone can be described at the ____.

spaces between lamellae that contain osteocyte

functions of the skeletal system

storage of minerals protections of internal organs production of blood cells and platelets movement

trabeculae

supporting bundles of bony fibers in cancellous (spongy) bone the surfaces of trabeculae are covered with a single layer of cells consisting mostly of osteoblasts with a few osteoclasts trabeculae are oriented along the lines of mechanical stress within a bone. if the force on a bone is changes slightly, the trabecular pattern realigns with the new lines of stress

the periosteum covers the bone ridges and extends down into:

the bottom of the grooves, and one or more blood vessels of the periosteum lie within each groove.

What are responsible for the major functional characteristics of bone?

the collagen and mineral components are responsible for the major functional characteristics of a bone.

woven bone

the collagen fibers are randomly oriented in many directions

what is the perichondrium

the connective tissue covering cartilage

long bone

the diaphysis (shaft) is composed primarily of compact bone but can also contain some spongy bone. the end of the long bone is mostly spongy body with an outer layer of compact bone. within joints, end of a long bone is covered with hyaline cartilage called articular cartilage.

intramembranous ossification of the membrane begins at approximately

the eighth week of embryonic development and its completed by approximately two years of age.

osteon

the functional unit of a long bone is an osteon it is composed of concentric rings of the matrix which surround a central tunnel and contain osteocytes vessels that run parallel to the long axis of the bone are contained within the central canals. central canals are lined with endosteum and contain blood vessels, nerves, and loos connective tissue. osteocytes are located in the lacunae between the lamellar rings, and canaliculi radiate between lacunae across the lamellae, looking like minute cracks across the rings of a target.

osteoclast numbers are regulated by:

the interactions of osteoblasts and red bone marrow stem cells of the monocyte/macrophage lineage.

centers of ossification

the locations in the membrane where ossification begins

circumferential lamellae

the outer surfaces of compact bone are formed by the circumferential lamellae thin plates that extend around the bone. in some bones, like on the face, the layer of compact bone can be so thin that no osteons exist and the compact bone is composed of only circumferential lamellae. between osteons are interstitial lamellae, which are remnants of concentric or circumferential lamellae that were partially removed during bone remodeling

bone remodeling

the process of removing old bone and adding new bone is called bone remodeling

canaliculi

the spaces occupied by the osteocyte cell extensions are called canaliculi

lacunae

the spaces without matrix but occupied by the osteocyte cell bodies.

osteoblasts are bone forming cells

they have extensive endoplasmic reticulum and numerous ribosomes produce collagen and proteoglycans they release matrix vesicles which contain high concentrations of Ca2+ and PO43- (when the concentration reaches a critical level, needlelike hydroxyapatite crystals form.)

long bones increase in width (diameter) and other bones increase in size or:

thickness because of appositional bone growth beneath the periosteum

true or false: once closed or ossified, growth in length no longer occurs at an epiphyseal plate.

true

this vitamin is necessary for collagen synthesis by osteoblasts

vitamin c

passageways or canals that extend from the periosteum to the medullary canal are called ____. (two answers)

volkmann canals perforating canals

In adults, what is the remnant of the growth plate called?

epiphyseal line

the structure found between the epiphysis and diaphysis in a child and is the site of bone growth is the ____ ____.

epiphyseal plate

the channel extending through the center of an osteon is called a ____ canal.

central

Describe the diaphysis

central shaft of a long bone

match the cell to its description

chondroblast - immature cells that produce cartilage matrix chondrocyte - mature cells surrounded by cartilage matrix osteoblast - immature bone cell osteocyte - mature bone cell

in appositional growth

chondroblasts in the perichondrium add new cartilage to the outside edge of the existing cartilage.

by the time the matrix has surrounded a chondroblast the cell has differentiated into a

chondrocyte

in interstitial growth

chondrocytes in the center of the tissue divide and add more matrix in between the existing cells.

which of the following describes the zone of cell hypertrophy in an epiphyseal plate

chondrocytes in this zone are no longer dividing, but enlarging; there is a thinning of lacunae walls

if all the mineral is removed from a long bone...

collagen becomes the primary constituent and the bone is overly flexible. On the other hand, if the collagen is removed from the bone, the mineral component becomes the primary constituent and the bone is very brittle.

descrice perforating (sharpey) fibers.

collagen fibers from tendons and ligaments that penetrate the periosteum and firmly adhere the structures to the bone.

what is the role of vitamin c in skeletal development?

collagen synthesis by osteoblasts requires vitamin c

the matrix contains

collagen, which provides strength proteoglycans, which make cartilage resilient by trapping water

bone tissue is comprised of osteons (haversian systems) is called ____ bone.

compact

the name of the periosteum in the tunnel changes to

endosteum because the membrane now lines an internal bone surface.

immature cell names often end with the suffix

-blast *which means seed or bud

once the immature cell has grown and differentiated into its mature forms, the suffix is

-cyte

steps of endochondral ossification

1. Most bones develop from a carilage model 2. The cartilage matrix is calcified and chondrocytes die 3. Osteoprogenirator cells move in and start to differentiate. 4. Blood vessles enter developing bone bringing nutrients 5. Osteoblast build an outer surface of compact bone 6. Primary ossification centers form marrow cavity 7. Cartilage starts to ossify to form skeletal bones.

the steps of bone repair

1. hematoma formation - blood released from damaged blood vessels forms a hematoma 2. callus formation - the internal callus forms between the ends of the bones and the external callus forms a collar around the break 3. callus ossification - woven spongy bone replaces the internal and external calluses 4. bone remodeling - compact bone replaces woven bone, and part of the internal callus is removed, restoring the medullary cavity

steps of intramembranous ossification

1. intramembranous ossification begins when some of the embryonic mesenchymal cells in the membrane differentiate into osteochonral progenitor cells which then specialize to become osteoblasts. the osteoblasts produce bone matrix that surrounds the collagen fibers of the connective tissue membrane and the osteoclasts become osteocytes. as a result of this process, many tiny traneculae of woven bone develop. Additional osteoblasts gather on the surfaces of the trabeculae and produce more bone, thereby causing the trabeculae to become larger and longer (figure 6.11, step 2. Spongy bone forms as the trabeculae join together, resulting in an interconnected network of trabeculae separated by spaces. 3. Cells within the spaces of the spongy bone specialize to form red bone marrow, and cells surrounding the developing bone specialize to form the periosteum. Osteoblasts from the periosteum lay down bone matrix to form an outer surface of compact bone *************************************** 1. development of ossification center 2. calcification 3. formation of trabeculae 4. development of periosteum

What is articular cartilage?

Hyaline cartilage that covers the ends of long bones.

Bones that have elaborate shapes are classified as ____ bones.

IRREGULAR

a layer of reticular connective tissue lining internal surfaces of a bone is called the

endosteum

calcium homeostasis

bones play an important role in regulating blood Ca2+ levels (which must be maintained within narrow limits for functions such as muscle contraction and membrane potentials to occur normally. bone is the major storage for calcium in the body. calcium ions move into bone as osteoblasts build new bone, and they move out of bone as osteoclasts break down bone. when blood Ca2+ levels are too low, osteoclast activity increases. osteoclasts release more Ca2+ from bone into blood than osteoblasts remove from the blood to make new bone. consequently, a net movement of Ca2+ occurs from bone into blood, and blood Ca2+ levels increase. Conversely, if blood Ca2+ levels are too high, osteoclast activity decreases. Osteoclasts release fewer Ca2+ from bone into the blood than osteoblasts remove from the blood to produce new bone. As a result, a net movement of Ca2+ occurs from the blood to bone, and blood to Ca2+ levels decrease.

the hormone ____ inhibits osteoclasts to help lower blood calcium levels

calcitonin

parathyroid hormone (pth) is the principle hormone in regulating blood levels of _____.

calcium

when the epiphyses reach their full size the growth of the cartilage and its replacement by bone _____.

cease.

long bones grow by

creating new cartilage in the epiphyseal plate. new cartilage form through interstitial cartilage growth followed by appositional bone growth on the surface of existing cartilage.

Gross anatomy of a long bone

diaphysis - shaft of the bone epiphysis - part of the bone that develops from a center of ossification distinct from the diaphysis periosteum - double layers connective tissue membrane covering the outer surface of bone except where articular cartilage is present endosteum - thin connective tissue membrane lining the inner cavities of a bone articular cartilage - thin layer of hyaline cartilage covering a bone where it forms a joint epiphyseal plate - area of hyaline cartilage between the diaphysis and the epiphysis spongy bone - bone having many small spaces found mainly in the epiphysis compact bone - dense bone with few internal spaces organized into osteons; forms the diaphysis and covers the spongy bone of the epiphyses medullary cavity - large cavity within the diaphysis red marrow - connective tissue in the spaces of spongy bone or in the medullary cavity; site of blood cell production yellow marrow - fat (adipose tissue) stored within the medullary cavity or in the spaces of spongy bone