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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

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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
Quick Review
  • Six categories based on shape
    • ____________ bones
      • Thin, roughly parallel surfaces
      • Examples: cranial bones, sternum
    • Sutural bones (Wormian bones)
      • Irregular bones formed between cranial bones
      • Number, size, and shape vary
    • ___________ bones
      • Relatively long and slender
      • Examples: various bones of the limbs

Six categories based on shape (continued)

    • Irregular bones
      • Complex shapes
      • Examples: vertebrae, bones of pelvis, facial bones
    • _______________ bones
      • Small, flat, and somewhat shaped like sesame seed
      • Develop in tendons of knee, hands, and feet
        • Individual variation in location and number
    • Short bones
      • Small and boxy
      • Examples: bones of the wrist (carpals) and ankles (tarsals)
functions of bone
Functions of Bone
  • Bones are important mineral reservoirs
    • Mostly _____________________________ but other ions as well
  • Calcium
    • Most abundant mineral in body
    • 1–2 kg (2–4 lb)
    • ~__________% deposited in skeleton
    • Variety 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 bones
    • Release of calcium into blood weakens bones
    • Deposit 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

    • ___________________
      • Responses
        • Bone: decrease osteoclast activity
        • Intestines: decreased absorption with decreasing PTH and calcitriol
        • Kidneys: inhibits calcitriol release and calcium reabsorption

Long bone features

    • ______________________ (expanded ends)
      • Consist largely of _________________ bone (trabecular bone)
        • Network of struts and plates
        • Resists 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
Figure 6.2 1 - 2

Coronal sections through a right femur, showing the boundaries of a long bone’s major

regions, plus the bone’s internal organization and how it distributes the forces applied

to the bone

The epiphysis consists

largely of spongy bone,

also called trabecular

bone. Spongy bone

consists of an open network

of struts and plates that

resembles latticework with

a thin covering, or cortex, of

compact bone.

Body weight

(applied force)

The epiphysis

(e-PIF-i-sis) is an

expanded area

found at each end

of the bone.

The metaphysis

(me-TAF-i-sis; meta,

between) is a narrow

zone that connects

the epiphysis to the

shaft of the bone.

The wall of the diaphysis

consists of a layer of

compact bone.


on lateral

side of


The medullary cavity

(medulla, innermost part), or

marrow cavity, is a space

within the hollow shaft. In

life, it is filled with bone

marrow, a highly vascular

tissue. Red bone marrow

is highly vascular and

involved in the production

of blood cells. Yellow

bone marrow is adipose

tissue important in the

storage of energy reserves.

The diaphysis

(shaft) is long and



on medial

side of shaft



figure 6 2 3
Figure 6.2 3

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

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.

Epiphyseal arteryand vein

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


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.

Metaphysealartery and vein



Bone vasculature

    • Growth and maintenance requires extensive _______________________ supply
    • Vascular 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 metaphysis
        • Connects to epiphyseal arteries/veins

_____________________ features

    • Smaller blood vessels (supply superficial osteons)
    • Lymphatic vessels (collect lymph from bone and osteons)
    • ____________________ nerves (innervate diaphysis, medullary cavity, and epiphyses)
bone cells
Bone cells
  • Four bone cell types
    • __________________________ (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

______________________ (blast, precursor)

    • Produce new bony matrix (osteogenesisor 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
Figure 6.3 1 - 2

The structures of osteocytes and osteoblasts within a

long bone

The layers of matrix

are called lamellae

(lah-MEL-lē; singular,

lamella, a thin plate).

Narrow passageways

called canaliculi

penetrate the lamellae,

radiating through the

matrix and connecting

lacunae to one another

and to various blood

vessels that supply


Osteocytes account for most

of the cell population in bone.

Each osteocyte occupies a

lacuna, a pocket sandwiched

between layers of matrix.

Osteocytes cannot divide,

and a lacuna never containsmore than one osteocyte.




_________________________ 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

______________________ (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
Figure 6.3 3 - 4

The structures of osteocytes and osteoblasts

within a long bone


Osteoprogenitor cell


building a 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 _______________________

_________________ bone

    • Functional unit is _________________
      • Organized concentric lamellae around a central canal
        • Osteocytes (in lacunae) lie between lamellae
        • Central canal contains small blood vessels
      • Canaliculi connect lacunae with each other and central canal
      • Strong along its length
figure 6 4 1 2
Figure 6.4 1 - 2

The structure of compact bone, as shown in

the shaft of a long bone

Capillary and venule

Central canal

Concentric lamellae

Canaliculi radiating

through the lamellae

interconnect the lacunae

of the osteons with one

another and with the

central canal.


Central canal









Compact bone

LM x 375

The osteocytes occupy lacunae that lie

between the lamellae. In preparing this

micrograph, a small piece of bone was

ground down until it was thin enough to

transmit light. In this process, the lacunae

and canaliculi are filled with bone dust, and

thus appear black.

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)

_______________________ bone

    • Located where bones not heavily stressed or in many directions
    • Lamellae 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
Figure 6.4 3 – 4

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

Trabeculae of

spongy bone


opening on





_____________________ bone growth

    • Increases bone diameter of existing bones
      • Does not form original bones
    • Osteoprogenitor 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
Figure 6.5 1

Increase in bone diameter resulting from appositional growth

Additional circumferential

lamellae are deposited, and

the bone continues to

increase in diameter.


figure 6 5 2
Figure 6.5 2

Enlargement of the medullary cavity with increased bone diameter

resulting from appositional growth

Bone matrix is removed

by osteoclasts

Bone deposited by

superficial osteoblasts




Young adult



    • Two layers
      • _________________________ outer layer
      • _____________________________ inner layer
    • Functions
      • ________________ bone from surrounding tissues
      • Route for blood and nervous supply
      • 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
Figure 6.5 3

Structure of the periosteum



Fibrous layer

of periosteum

Cellular layer

of periosteum



in lacuna





    • 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
Figure 6.5 4

Structure of the endosteum



Circumferential lamella






fetal bone developement
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 ossification

    • In shaft, _______________________ enlarge and matrix ossifies
      • Chrondrocytes die, leaving cavities within cartilage
    • ___________________ vessels grow around cartilage edge and osteoblasts form to create a superficial layer of bone
    • Blood vessels penetrate central region
      • Allow entering fibroblasts to change into osteoblasts
        • Spongy bone produced (_______________________________ ossification center) and spreads toward bone ends

_____________________ cavity created as cartilage replaced by osseous tissue

    • Bone grows in length and diameter
  • __________________ ossification centers form as capillaries and osteoblasts migrate into epiphyses
  • Epiphyses fill with __________________ bone
    • Only articular cartilage (on epiphyses) and epiphyseal cartilage (in metaphysis) remain
figure 6 6 1 6
Figure 6.6 1 – 6

The process of endochondral ossification

Hyaline cartilage

Articular cartilage





chondrocytes within

calcifying matrix























Formation of an epiphyseal

cartilage between epiphysis

and diaphysis







Hyaline cartilage

Further growth in length

and diameter

Enlargement of


Formation of superficial

layer of bone

Production of spongy bone at

a primary ossification center

Formation of secondary

ossification centers


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
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
Figure 6.7 4

16 weeks of development

10 weeks of development

Flat bones

of the skull


ossification centers

that produce the

roofing bones of

the skull



centers of the

long bones of

the lower limb


hip bone

Long bones

of the limbs

The extent of intramembranous and

endochondrial ossification occurring between

10 and 16 weeks of development

abnormal bone growth
Abnormal Bone Growth
  • Endocrine and metabolic problems can affect the skeletal system
figure 6 8 1
Figure 6.8 1
  • Reduction in _______________ hormone leads to reduced epiphyseal cartilage activity and short bones
figure 6 8 2
Figure 6.8 2
  • Epiphyseal cartilage grows unusually slowly
figure 6 8 3
Figure 6.8 3
  • _______________ syndrome
    • Excessive cartilage formation at epiphyseal cartilage
figure 6 8 4
Figure 6.8 4
  • _______________
    • Overproduction of growth hormone before puberty
figure 6 8 5
Figure 6.8 5
  • Gene mutation that causes bone deposition around skeletal muscles
figure 6 8 6
Figure 6.8 6
  • Growth hormone levels rise after epiphyseal plates close
  • Bones get thicker
    • Especially those in face, jaw, and hands
for wednesday
For Wednesday
  • Joint
    • Cht 8
  • Movement
    • 8.3-8.4
  • Labs
    • Pages 19-27