© 2011 Pearson Education, Inc. Module 7.8: Fontanelles Fontanelles Large fibrous areas between cranial bones of infants and small children Ease passage

© 2011 Pearson Education, Inc.

Module 7.8: Fontanelles

• Fontanelles

• Large fibrous areas between cranial bones of infants and small children

• Ease passage of head through birth canal

• Allow for cranial growth to keep pace with brain growth and later fetal stages

• Over time, fontanelles are replaced with sutures

• Occipital, sphenoidal, and mastoid fontanelles disappear a month or two after birth

• All fontanelles replaced before age 5 when brain stops growing

© 2011 Pearson Education, Inc.Figure 7.8 3

A lateral view of the skull of an infant

Parietalbone

Frontalbone

Temporalbone

Coronalsuture

Sphenoid

Nasal bone

Maxilla

Mandible

Occipital bone

Lambdoid suture

Sphenoidal fontanelle

Mastoid fontanelle

Squamous suture


Module 7.8: Fontanelles

• Fontanelles

• Anterior

• Largest fontanelle

• At intersection of frontal, sagittal, and coronal sutures

• Sphenoidal

• Junction of squamous and coronal sutures

• Mastoid

• Junction of squamous and lambdoid sutures

• Occipital

• Junction of lambdoid and sagittal sutures


The anterior fontanelle (“soft spot”) and associated sutures in theskull of an infant

Rightparietal

bone

Leftparietal

bone

Sagittal suture

Anterior fontanelle

Coronal suture

Frontal suture

Frontal bone

Frontal suture


Sagittal suture

Rightparietal

bone

Leftparietal

bone

Lambdoid suture

Occipital fontanelle

Occipital bone

The occipital fontanelle and associated suturesin a posterior view of the skull of an infant


Frontal suture

A superior view of the skull of an infant

Frontalbone

Parietalbone

Frontalbone Parietal

boneCoronal suture

Anterior fontanelleSagittal suture Occipital fontanelle

Occipital bone

Lambdoid suture

What purposes do fontanelles serve


Section 1: An Introduction to Bones

• Learning Outcomes

• 6.1 Classify bones according to their shapes, identify the major types of bone

markings, and explain the functional significance of surface features.

• 6.2 Identify the parts of a typical long bone, and describe its internal

structures.


• Skeletal system components

• Bones (206 total)

• Divisions

1. Axial skeleton (126 bones)

• Bones of skull, thorax, and vertebral column

• Form longitudinal axis of body

2. Appendicular skeleton (80 bones)

• Bones of the limbs and girdles that attach them to the axial skeleton

• Cartilages

• Ligaments and other connective tissues


© 2011 Pearson Education, Inc.Figure 6 Section 1 1

Axial Skeleton(126 Bones)

The axial skeletonconsists of thebones of the skull,thorax, and vertebralcolumn. Theseelements form thelongitudinal axis ofthe body.

The adult skeletalsystem, which can bedivided into the axialskeleton and theappendicular skeleton

The appendicularskeleton includesthe bones of thelimbs and thepectoral and pelvicgirdles that attachthe limbs to theaxial skeleton.

AppendicularSkeleton (80 Bones)


• Functions of the skeletal system

• Support (support for body, attachment for soft tissues)

• Storage of minerals (calcium and phosphate)

• Calcium most abundant mineral in body (~2–4 lb)

• 98% stored in bones

• Blood cell production (all formed elements of blood)

• Protection (delicate tissues and organs surrounded by bone)

• Leverage (act as levers with skeletal muscles to move body)



Module 6.1: Bone classification

• Six categories based on shape

1. Flat 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. Long 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 bones

5. Sesamoid bones

• Small, flat, and somewhat shaped like sesame seed

• Develop in tendons of knee, hands, and feet

• Individual variation in location and number

6. Short bones

• Small and boxy

• Examples: bones of the wrist (carpals) and ankles (tarsals)



• Bone surface features

• Also known as bone markings

• External and internal features related to functions!!!!

• Elevations/projections for tendon and ligament attachment

• Depressions/grooves/tunnels for blood vessels or nerves to lie alongside or penetrate



• Skull surface features

• Canal or meatus (large passageway)

• Process (projection or bump)

• Sinus (chamber within bone, usually filled with air)

• Foramen (small rounded passageway)

• Fissure (elongated cleft or gap)



• Humerus surface features

• Head (expanded proximal end that forms part of joint)

• Tubercle (small, rounded projection)

• Sulcus (deep, narrow groove)

• Tuberosity (small, rough projection; may occupy broad area)

• Diaphysis (shaft; elongated body)

• Trochlea (smooth, grooved articular process)

• Condyle (smooth, rounded articular process)



• Femur surface features

• Trochanter (large, rough projection)

• Head

• Neck (narrow connection between head and diaphysis)

• Diaphysis

• Facet (small, flat articular surface)

• Condyle



• Pelvis surface features

• Crest (prominent ridge)

• Fossa (shallow depression or recess)

• Line (low ridge; more delicate than crest)

• Spine (pointed or narrow process)

• Ramus (extension that makes angle with rest of structure)



Module 6.2: Typical long bone structure

• Long bone features

• Epiphysis (expanded ends)

• Consist largely of spongy bone (trabecular bone)• Network of struts and plates

• Resists forces from various directions and directs body weight to diaphysis and joints

• Outer covering of compact bone• Strong, organized bone

• Articular cartilage• Covers portions of epiphysis that form articulations

• Avascular and receives resources from synovial fluid


• Long bone features Metaphysis (connects epiphysis to shaft)

• Diaphysis (shaft)

• Contains medullary cavity (marrow cavity)

• Filled with marrow

• Red bone marrow (red blood cell production)

• Yellow bone marrow (adipose storage)

Bone vasculatureGrowth and maintenance requires extensive blood supplyVascular features

Nutrient artery/vein (commonly one each/bone)Nutrient foramen (tunnel providing access to marrow cavity)Also supplies osteons of compact bone with blood

© 2011 Pearson Education, Inc.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


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 Layers: Periosteum, Compact Bone, Medullary Cavity

• Periosteum features

• Smaller blood vessels (supply superficial osteons)

• Lymphatic vessels (collect lymph from bone and osteons)

• Sensory nerves (innervate diaphysis, medullary cavity, and epiphyses)

Module 6.2: Typical long bone structure


Module 6.2 Review

a. List the major parts of a long bone.

b. Describe the function of the medullary cavity.

c. If articular cartilage is avascular, how is it nourished?


• Four bone cell types

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

• Mature bone cells that cannot divide

• Most numerous bone cell type

• Maintain protein and mineral content of adjacent matrix

• Occupy lacunae (pocket)• Separated by layers of matrix (lamellae)

• Connected with canaliculi

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

ossification)Become osteocytes once surrounded by bony matrix


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. Osteoprogenitor 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

4. Osteoclasts (clast, to break)Remove and remodel bone matrixGiant cells with 50+ nuclei

Derived from same stem cells as macrophagesRelease acids and proteolytic enzymes to dissolve matrix

and release stored minerals = Osteolysis (lysis, loosening)


Endosteum

Osteoprogenitor cell

Osteoclast

The structures of osteocytes and osteoblastswithin a long bone


Module 6.3: Bone tissue

• Bone matrix

• Collagen fibers account for ~1/3 bone weight

• Provide flexibility

• 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 strength



Module 6.3 Review

a. Define osteocyte, osteoblast, osteoprogenitor cell, and osteoclast.

b. How would the compressive strength of a bone be affected if the ratio of collagen to hydroxyapatite increased?

c. If osteoclast activity exceeds osteoblast activity in a bone, what would be the effect on the bone?


Module 6.4: Compact and spongy bone

• Compact bone

• Functional unit is osteon

• 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


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)

• Circumferential lamellae (circum-, around + ferre, to bear)

• Outer and inner surfaces of compact bone layer

• Interstitial lamellae

• Fill spaces between osteons

• Osteons

• Contain central canals (parallel to bone surface)

• Connected by perforating canals (perpendicular)

• Spongy bone (innermost layer)


• Spongy bone

• Located where bones not heavily stressed or in many directions

• Lamellae form struts and plates (trabeculae) creating an open network

• Reduces weight of skeleton

• No blood vessels in matrix• Nutrients reach osteons through canaliculi open to

trabeculae surfaces


© 2011 Pearson Education, Inc.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


Increase in bone diameter resulting from appositional growth

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

Periosteum


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


Structure of the endosteum

Endosteum

Osteoclast

Circumferential lamella

Osteocyte

Osteoprogenitorcell

Osteoid

Osteoblast


Module 6.6: Endochondral ossification

• Initial bone formation in embryo begins with cartilage

• Replaced by bone through endochondral (endo-, inside + chondros, cartilage) ossification

• Uses cartilage as small model

• Bone grows in diameter and length

• Diameter growth involves appositional bone deposition

Animation: Early Endochondral Ossification


• Steps of endochondral ossification

1. In shaft, chondrocytes enlarge and matrix ossifies

• Chrondrocytes die, leaving cavities within cartilage

2. Blood 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 (primary ossification center)

and spreads toward bone ends



• Steps of endochondral ossification (continued)

4. Medullary cavity created as cartilage replaced by osseous tissue

• Bone grows in length and diameter

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

6. Epiphyses fill with spongy bone

• Only articular cartilage (on epiphyses) and epiphyseal cartilage (in metaphysis) remain



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


• Steps of endochondral ossification (continued)

7. Bone grows in length at epiphyseal cartilage

• Chondrocytes actively produce more cartilage on epiphysis side

• Osteoblasts actively 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 epiphyseal line in adults



Formation of an epiphysealcartilage between epiphysis

and diaphysis

Articular cartilage

Spongybone

Epiphysealcartilage

Diaphysis

Medullarycavity

Osteoblasts Osteoid

Epiphysealcartilage matrix

Cartilage cells undergoingdivision and secreting

additional cartilage matrix

The ossifying surface of anepiphyseal cartilage

LM x 250


Module 6.6 Review

a. Define endochondral ossification.

b. In endochondral ossification, what is the original source of osteoblasts?

c. How could x-rays of the femur be used to determine whether a person has reached full height?


Module 6.7: Intramembranous ossification

• Begins as mesenchymal (stem) cells differentiate into osteoblasts within embryonic or fibrous connective tissue

• Normally occurs in deeper layers of dermis

• = Dermal bones (or membrane bones)

• Examples:

• Roofing bones of skull

• Lower jaw

• Collarbone

• Sesamoid bones such as patella


• Steps of intramembranous ossification

• Mesenchymal cells secrete osteoid matrix• Differentiate into osteoblasts

• Osteoid matrix becomes mineralized• Forms ossification center

• Bone grows out in small struts (spicules)

• Osteoblasts become trapped and mature into osteocytes• Mesenchymal cells produce more osteoblasts

• Blood vessels enter and become trapped in developing bone



Osteocyte in lacunaBone matrix

Osteoblast

Osteoid

Embryonic connective tissue

Mesenchymal cell

The process of intramembranous ossification

Bloodvessel

Osteocytesin lacunae

Osteoblastlayer

Blood vessel Osteoblasts Spicules Blood vessels

LM x 32 LM x 32

The growth of developing bone outward from the ossificationcenter in small struts called spicules

The growth and entrapment ofblood vessels within developingbone

Spongy bone, the initial form ofintramembranous bone


• Further membranous bone development

• Spongy bone formed initially

• Remodeling around blood vessels forms osteons of compact bone

• Periosteum forms, lined with osteoblasts

• Begins at approximately 8th week of embryonic development



Futurehip bone

Primaryossification

centers of thelong bones ofthe 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


Section 2: Bone Physiology

• Learning Outcomes

• 6.9 Discuss the effects of hormones on bone development, and explain the

homeostatic mechanisms involved.

• 6.10 CLINICAL MODULE Describe the types of fractures, and explain how

fractures heal.


• Bones are important mineral reservoirs

• Mostly calcium but other ions as well

• Calcium

• Most abundant mineral in body

• 1–2 kg (2–4 lb)

• ~99% deposited in skeleton

• Variety of physiological functions

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

• Normal daily fluctuations are <10%


© 2011 Pearson Education, Inc.Figure 6 Section 2 1

Composition of Bone Bone Contains …

99% of the body’s calcium

4% of the body’s potassium

35% of the body’s sodium

50% of the body’s magnesium

80% of the body’s carbonate

99% of the body’s phosphate

Calcium 39%

Potassium 0.2%

Sodium 0.7%

Magnesium 0.5%

Carbonate 9.8%

Phosphate 17%

67%Total inorganiccomponents

Organiccompounds

(mostly collagen)33%

The importance of bones as mineral reservoirs


• Calcium (continued)

• Levels controlled by activities of:

• Intestines

• Absorb calcium and phosphate. Under hormonal control

• Bones

• Release Calcium in blood stream or Lay down calcium to make new bone. (Remodeling by osteoblasts and osteoclasts)

• Kidneys

• Calcium and phosphate loss in urine. Under hormonal control



Module 6.9: Hormonal control of calcium

• Factors that increase blood calcium levels

• Parathyroid hormone (from parathyroid glands)

• Responses

• Bones: Stimulates bone cells (osteoclasts) to release calcium

• Intestines: Increases calcium absorption

• Kidneys: Causes calcium reabsorption in kidneys


• Factors that decrease blood calcium levels

• Calcitonin from thyroid gland C cells

• Responses

• Bone: decrease osteoclast activity (Bone cells keep calcium in bone therefore blood calcium levels are low)

• Intestines: decreased absorption

• Kidneys: inhibits calcium reabsorption



• As a calcium reserve, skeleton has primary role in calcium homeostasis

• Has direct effect on shape and length of bones

• Release of calcium into blood weakens bones

• Deposit of calcium salts strengthens bones



Module 6.9 Review

a. Identify the hormones involved in stimulating and inhibiting the release of calcium ions from bone matrix.

b. What effect would increased PTH secretion have on blood calcium levels?

c. How does calcitonin lower the calcium ion concentration of blood?


Module 6.10 CLINICAL MODULE: Fractures

• Fracture

• Crack or break due to extreme mechanical stress

• Most heal as long as blood supply and cellular parts of periosteum and endosteum survive


• Steps of fracture repair

1. Large blood clot (fracture hematoma) develops

2. Calluses form

• Internal callus (network of spongy bone uniting inner edges)

• External callus (cartilage and bone stabilizes outer edges)




Animation: Steps in the Repair of a Fracture

• Steps of fracture repair (continued)

3. Calluses replaced and dead bone removed

• Spongy bone unites broken ends

• Cartilage of external callus replaced by bone

4. Remodeling of healed bone


The events in the repair of a bone fracture

Spongy boneof internal

callus

Cartilageof external

callus

Fracturehematoma

Deadbone

Bonefragments

Spongy bone ofexternal callus

Periosteum

Internalcallus

Externalcallus

Externalcallus

Formation of a fracturehematoma

Formation of an internalcallus and an externalcallus

Replacement of thecartilage of the externalcallus with bone

Remodeling overtime andcompletion ofrepair


Transversefractures, such asthis fracture of theulna, break a boneshaft across its longaxis.

Types of Fractures

Spiral fractures,such as thisfracture of thetibia, are producedby twistingstresses thatspread along thelength of the bone.

Displaced fracturesproduce new andabnormal bone ar-rangements;nondisplacedfractures retain thenormal alignment ofthe bones orfragments.

Compression fracturesoccur in vertebraesubjected to extremestresses, such as thoseproduced by the forces thatarise when you land on yourseat in a fall.

In a greenstickfracture, such as thisfracture of the radius,only one side of theshaft is broken, andthe other is bent. Thistype of fracturegenerally occurs inchildren, whose longbones have yet toossify fully.

Comminutedfractures, such asthis fracture of thefemur, shatter theaffected area into amultitude of bonyfragments.

Epiphyseal fractures, such as thisfracture of the femur, tend to occur wherethen bone matrix is undergoing calcificationand chondrocytes are dying. A cleantransverse fracture along this line generallyheals well. Unless carefully treated, fracturesbetween the epiphysis and the epiphysealcartilage can permanently stop growth atthis site.

A Pottfracture occursat the ankle andaffects bothbones of the leg.

A Colles fracture, abreak in the distalportion of the radius,is typically the resultof reaching out tocushion a fall.

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© 2011 Pearson Education, Inc. Module 7.8: Fontanelles Fontanelles Large fibrous areas between cranial bones of infants and small children Ease passage