BUILDING MATERIAL

Functions of the skeletal system__________________ (support for body,

attachment for soft tissues)Storage of _______________ (calcium and

phosphate) Calcium most abundant mineral in body

(~2–4 lb)98% stored in bones

Blood ____________ production (all formed elements of blood)

Protection (delicate tissues and organs surrounded by bone)

____________________ (act as levers with skeletal muscles to move body)

QUICK REVIEW Six categories based on shape

1. ____________ bones Thin, roughly parallel surfaces Examples: cranial bones, sternum

2. Sutural bones (Wormian bones) Irregular bones formed between cranial

bones Number, size, and shape vary

3. ___________ bones Relatively long and slender Examples: various bones of the limbs

Six categories based on shape (continued)4. Irregular bones

Complex shapes Examples: vertebrae, bones of pelvis, facial

bones5. _______________ bones

Small, flat, and somewhat shaped like sesame seed

Develop in tendons of knee, hands, and feet Individual variation in location and

number6. Short bones

Small and boxy Examples: bones of the wrist (carpals) and

ankles (tarsals)

FUNCTIONS OF BONE Bones are important mineral reservoirs

Mostly _____________________________ but other ions as well

Calcium Most abundant mineral in body1–2 kg (2–4 lb)~__________% deposited in skeletonVariety of physiological functions

Concentration variation greater than 30–35% affects neuron and muscle function

Normal daily fluctuations are <10%

Levels controlled by activities of: Intestines

Absorb calcium and phosphate under hormonal control Bones

Remodeling by osteoblasts and osteoclasts Kidneys

Calcium and phosphate loss in urine under hormonal control

As a calcium reserve, skeleton has primary role in calcium _________________________

Has direct effect on shape and length of bonesRelease of calcium into blood weakens bonesDeposit of calcium salts strengthens bones

Factors that increase blood calcium levels____________________ hormone Responses

Bones: stimulates osteoclasts to release calcium

Intestines: enhances calcitriol effects and increases calcium absorption

Kidneys: increase release of hormone calcitriol, which causes calcium reabsorption in kidneys

Factors that decrease blood calcium levels___________________

ResponsesBone: decrease osteoclast activity Intestines: decreased absorption with

decreasing PTH and calcitriolKidneys: inhibits calcitriol release and calcium

reabsorption

Long bone features______________________ (expanded ends)

Consist largely of _________________ bone (trabecular bone)Network of struts and platesResists forces from various directions and

directs body weight to diaphysis and joints Outer covering of ______________________ bone

Strong, organized bone Articular _________________________

Covers portions of epiphysis that form articulations

Avascular and receives resources from synovial fluid

Long bone features (continued)_____________________________ (connects

epiphysis to shaft)______________________ (shaft)

Contains medullary cavity (marrow cavity)Filled with marrow

Red bone marrow (red blood cell production) Yellow bone marrow (adipose storage)

FIGURE 6.2 1 - 2

Coronal sections through a right femur, showing the boundaries of a long bone’s majorregions, plus the bone’s internal organization and how it distributes the forces appliedto the bone

The epiphysis(e-PIF-i-sis) is anexpanded areafound at each endof the bone.

The metaphysis(me-TAF-i-sis; meta,between) is a narrowzone that connectsthe epiphysis to theshaft of the bone.

The diaphysis(shaft) is long andtubular.

The epiphysis consistslargely of spongy bone,also called trabecularbone. Spongy boneconsists of an open networkof struts and plates thatresembles latticework witha thin covering, or cortex, ofcompact bone.

The medullary cavity(medulla, innermost part), ormarrow cavity, is a spacewithin the hollow shaft. Inlife, it is filled with bonemarrow, a highly vasculartissue. Red bone marrowis highly vascular andinvolved in the productionof blood cells. Yellowbone marrow is adiposetissue important in thestorage of energy reserves.

Compressionon medial

side of shaft

Tensionon lateral

side ofshaft

Body weight(applied force)

The wall of the diaphysisconsists of a layer ofcompact bone.

Metaphysis

Epiphysis

FIGURE 6.2 3

A longitudinal section of the humerus, showing the extensive|network of blood vessels in long bones

Epiphyseal arteryand vein

Metaphysis

An articular cartilage covers portions ofthe epiphysis that articulate with other bones. The cartilage is avascular, and itrelies primarily on diffusion from thesynovial fluid to obtain oxygen andnutrients and eliminate wastes.

The metaphyseal artery (red) andmetaphyseal vein (blue) carry blood toand from the area of the metaphysis and tothe epiphysis through epiphyseal arteriesand veins.

Periosteum

Compactbone

Medullarycavity

Metaphysis

Metaphysealartery and vein

Most bones have only onenutrient artery (shown inred) and one nutrient vein(shown in blue), but a fewbones, including the femur,have more than one of each.

A nutrient foramen is a tunnel that penetrates thediaphysis and providesaccess for the nutrient arteryand/or vein. Branches ofthese large vessels supplythe osteons of thesurrounding compact bonebefore entering andsupplying the tissues of themedullary cavity.

Bone vasculatureGrowth and maintenance requires extensive

_______________________ supplyVascular features

Nutrient artery/vein (commonly one each/bone)Nutrient __________________(tunnel providing

access to marrow cavity)Also supplies osteons of compact bone with

blood Metaphyseal artery/vein

Carry blood to/from metaphysisConnects to epiphyseal arteries/veins

_____________________ featuresSmaller blood vessels (supply superficial

osteons)Lymphatic vessels (collect lymph from bone

and osteons)____________________ nerves (innervate

diaphysis, medullary cavity, and epiphyses)

BONE CELLS Four bone cell types

1. __________________________ (osteo-, bone + cyte, cell)

Mature bone cells that cannot divide Most numerous bone cell type Maintain protein and mineral content of

adjacent matrix Dissolve matrix to release minerals Rebuild matrix to deposit mineral

crystals Occupy ____________________(pocket)

Separated by layers of matrix (lamellae)

Connected with canaliculi

2. ______________________ (blast, precursor) Produce new bony matrix (osteogenesis or

ossification) Begins with release of proteins and other

organic components to produce unmineralized matrix (= osteoid)

Then assists in depositing calcium salts to convert osteoid to bone

Become osteocytes once surrounded by bony matrix

FIGURE 6.3 1 - 2

The layers of matrixare called lamellae(lah-MEL-lē; singular,lamella, a thin plate).

The structures of osteocytes and osteoblasts within along bone

Osteocytes account for mostof the cell population in bone.Each osteocyte occupies alacuna, a pocket sandwichedbetween layers of matrix.Osteocytes cannot divide,and a lacuna never containsmore than one osteocyte.

Narrow passagewayscalled canaliculipenetrate the lamellae,radiating through thematrix and connectinglacunae to one anotherand to various bloodvessels that supplynutrients.

Osteoblast

Osteoid

3. _________________________ cells (progenitor, ancestor)

Mesenchymal (stem) cells that produce cells that differentiate into osteoblasts

Important in fracture repair Locations

Inner lining of periosteum Lining endosteum in medullary cavity Lining passageways containing blood

vessels

4. ______________________ (clast, to break) Remove and remodel bone matrix Giant cells with ______________+ nuclei

Derived from same stem cells as macrophages

Release acids and proteolytic enzymes to dissolve matrix and release stored minerals = Osteolysis (lysis, loosening)

FIGURE 6.3 3 - 4

Endosteum

Osteoprogenitor cell

Osteoclast

The structures of osteocytes and osteoblastswithin a long bone

BUILDING A BONE Bone _________________

Collagen fibers account for ~1/3 bone weight Provide _________________

Calcium phosphate (Ca3(PO4)2) accounts for ~2/3 bone weight Interacts with calcium hydroxide (Ca(OH)2) to

form crystals of hydroxyapatite (Ca10(PO4)6(OH)2) salts Incorporates other salts (calcium carbonate,

CaCO3) and ions (Na, Mg2, F)Provides _______________________

_________________ boneFunctional unit is _________________

Organized concentric lamellae around a central canalOsteocytes (in lacunae) lie between lamellaeCentral canal contains small blood vessels

Canaliculi connect lacunae with each other and central canal

Strong along its length

FIGURE 6.4 1 - 2

The structure of compact bone, as shown inthe shaft of a long bone

Capillary and venule

Central canal

Concentric lamellae

Canaliculi radiatingthrough the lamellaeinterconnect the lacunaeof the osteons with oneanother and with thecentral canal.

Endosteum

Periosteum

Central canal

Vein

Artery

Osteon

Compact bone LM x 375

The osteocytes occupy lacunae that liebetween the lamellae. In preparing thismicrograph, a small piece of bone wasground down until it was thin enough totransmit light. In this process, the lacunaeand canaliculi are filled with bone dust, andthus appear black.

Circumferentiallamellae

Interstitiallamellae

Central canal

Perforating canal

Typical long bone organization Periosteum (outermost layer) Compact bone (outer bone tissue layer)

___________________________ lamellae (circum-, around + ferre, to bear)Outer and inner surfaces of compact bone

layer Interstitial lamellae

Fill spaces between osteons _______________________________

Contain central canals (parallel to bone surface)

Connected by perforating canals (perpendicular)

Spongy bone (innermost layer)

_______________________ boneLocated where bones not heavily stressed

or in many directionsLamellae form struts and plates

(trabeculae) creating an open network _______________________ weight of skeleton No blood vessels in matrix

Nutrients reach osteons through ___________________________________ open to trabeculae surfaces

FIGURE 6.4 3 – 4

Trabeculae ofspongy bone

Canaliculiopening on

surface

Endosteum Lamellae

The structure of spongy bone, as shown in the head of the femur

_____________________ bone growth Increases bone diameter of existing bones

Does not form original bonesOsteoprogenitor cells differentiate into

osteoblasts that ____________ bone matrix under periosteum Adds successive _____________________ of

circumferential lamellae Trapped _____________________ become osteocytes

Deeper lamellae recycled and replaced by osteons

Osteoclasts remove matrix at inner surface to enlarge medullary cavity

FIGURE 6.5 1

Increase in bone diameter resulting from appositional growth

Additional circumferentiallamellae are deposited, andthe bone continues toincrease in diameter.

Periosteum

FIGURE 6.5 2

Enlargement of the medullary cavity with increased bone diameterresulting from appositional growth

Bone matrix is removedby osteoclasts

Bone deposited bysuperficial osteoblastsInfant Child Young adult Adult

_________________Two layers

1. _________________________ outer layer2. _____________________________ inner layer

Functions1. ________________ bone from surrounding

tissues2. Route for blood and nervous supply3. Actively participate in bone growth and

_____________________

____________________ fibers Created by osteoblasts in periosteum

cellular layer Strongly connect tendons, ligaments, and

joint capsules to bone through periosteum

FIGURE 6.5 3

Structure of the periosteum

Circumferentiallamellae

Fibrous layerof periosteum

Cellular layerof periosteum

Canaliculi

Osteocytein lacuna

Perforatingfibers

__________________ Incomplete cellular layer lining medullary

cavity Covers spongy bone and lines central

canals Consists of simple layer of

osteoprogenitor cells Where incomplete, osteoclasts and

osteoblasts remodel matrix

FIGURE 6.5 4

Structure of the endosteum

Endosteum

Osteoclast

Circumferential lamella

Osteocyte

Osteoprogenitorcell

Osteoid

Osteoblast

FETAL BONE DEVELOPEMENT Initial bone formation in embryo

begins with ______________________ Replaced by bone through

endochondral (endo-, inside + chondros, cartilage) _______________________________ Uses cartilage as small model Bone grows in diameter and length

Diameter growth involves appositional bone deposition

Steps of endochondral ossification1. In shaft, _______________________ enlarge

and matrix ossifies Chrondrocytes die, leaving cavities within

cartilage

2. ___________________ vessels grow around cartilage edge and osteoblasts form to create a superficial layer of bone

3. Blood vessels penetrate central region Allow entering fibroblasts to change into

osteoblasts Spongy bone produced

(_______________________________ ossification center) and spreads toward bone ends

4. _____________________ cavity created as cartilage replaced by osseous tissue Bone grows in length and diameter

5. __________________ ossification centers form as capillaries and osteoblasts migrate into epiphyses

6. Epiphyses fill with __________________ bone Only articular cartilage (on epiphyses) and

epiphyseal cartilage (in metaphysis) remain

FIGURE 6.6 1 – 6

The process of endochondral ossification

Enlargingchondrocytes within

calcifying matrix

Hyaline cartilage

Epiphysis

Diaphysis

Boneformation

Bloodvessel

Medullarycavity

Primaryossificationcenter

Superficialbone

Spongybone

Medullarycavity

Metaphysis

Enlargement ofchondrocytes

Formation of superficiallayer of bone

Production of spongy bone ata primary ossification center

Further growth in lengthand diameter

Hyaline cartilage

Epiphysis

Metaphysis

Periosteum

Compactbone

Secondaryossification

center

Formation of secondaryossification centers

Formation of an epiphysealcartilage between epiphysis

and diaphysis

Articular cartilage

Spongybone

Epiphysealcartilage

Diaphysis

7. Bone grows in _________________ at epiphyseal cartilage Chondrocytes actively produce more

cartilage on epiphysis side Osteoblasts _____________________ replace

cartilage with bone on shaft side As long as both processes are equally active,

bone lengthening continues At puberty, hormones increase bone

growth and epiphyseal cartilage is replaced

Leaves _____________________________________________________in adults

INTRAMENBRANOUS OSSIFICATION Steps of intramembranous ossification

_____________________________ cells secrete osteoid matrix

Differentiate into osteoblasts Osteoid matrix becomes mineralized

Forms _________________________________ Bone grows out in small struts

(____________________________) Osteoblasts become trapped and

mature into osteocytes Mesenchymal cells produce more osteoblasts

Blood vessels enter and become trapped in developing bone

Further membranous bone development __________________ bone formed initially Remodeling around blood vessels forms

osteons of compact bone Periosteum forms, lined with osteoblasts Begins at approximately ____________ week

of embryonic development Examples:

Roofing bones of skull Lower jaw Collarbone Sesamoid bones such as patella

FIGURE 6.7 4

Futurehip bone

Primaryossification

centers of thelong bones of

the lower limb

Intramembranousossification centers

that produce theroofing bones of

the skull

Long bonesof the limbs

10 weeks of development Flat bonesof the skull

16 weeks of development

The extent of intramembranous andendochondrial ossification occurring between10 and 16 weeks of development

ABNORMAL BONE GROWTH Endocrine and metabolic problems can

affect the skeletal system

FIGURE 6.8 1

Reduction in _______________ hormone leads to reduced epiphyseal cartilage activity and short bones

FIGURE 6.8 2

Epiphyseal cartilage grows unusually slowly

FIGURE 6.8 3

_______________ syndromeExcessive

cartilage formation at epiphyseal cartilage

FIGURE 6.8 4

_______________Overproduct

ion of growth hormone before puberty

FIGURE 6.8 5

Gene mutation that causes bone deposition around skeletal muscles

FIGURE 6.8 6

Growth hormone levels rise after epiphyseal plates close

Bones get thickerEspecially those in

face, jaw, and hands

FOR WEDNESDAY Joint

Cht 8 Movement

8.3-8.4 Labs

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