Skeletal System:Bones and Bone Tissue

Four major components: BONES

CARTILAGE

TENDONS

LIGAMENTS

1. Support - provides hard framework for soft tissueStrong bones to bear weight

2. Protection of underlying organsSkull – BrainRib cage - heart & lungs

3. Movement - skeletal muscles use bones as leversTendons hold muscles to bones Joints – two bones come togetherLigaments –provide limited movement

4. StorageCalcium and PhosphorousFat stored in marrow cavities

5. Blood cell production (Hematopoiesis) Red bone marrow blood cells and

platelets

Hyaline cartilageMost bones develop from this type of

cartilage

Fibrocartilage

Elastic cartilage

Hyaline – specialized cells that produce matrix surrounding cells

Chondroblasts – produce new cartilage matrix

Chondrocyte – cells that maintain the cartilage

Lacunae – space within the matrix

Matrix – contains collagen, provides strength

Perichondrium – double layered connective tissue sheathCovers most cartilage

Blood vessels and nerves penetrate outer layer of perichondrium

Does not enter cartilage matrix

Nutrients diffuse through cartilage matrix to reach chondrocytes

Articular cartilage Cartilage that covers end of bones where they form joints

Has no perichondrium, blood or nerves

Bone connective tissue

Bone matrixSteel bars is collagen fibers, weight bearing

strength or cement is mineral components

Organic components (35%)Primarily collagen

Inorganic mineral salts (65%) Primarily calcium phosphate

Hydroxyapatite Gives bone its hardness; resists compression

(b) If minerals are removed, bone is too bendable (collagen is present)

(c) If collagen removed, bone is too brittle (minerals are present)

OsteoblastsActive in bone formation = ossificationForm collagen and hydroxyapatite crystals

OsteocytesEssentially osteoblasts that are surrounded by bone matrix

Relatively inactive

Found in compact and spongy bone

OsteoclastsCells used to breakdown bone (bone resorption)

Stimulated by need for calcium & phosphate in the body

Breaks down mineral salts (demineralization or decalcification)

Resorption starts to exceed formation as people age

Bone classified based on collagen fibers within bone matrix:1. Woven bone – collagen randomly

oriented in many directions

Formed during fetal development or repair of fracture

Remodeling forms lamellar bone

2. Lamellar bone – mature bone organized into thin sheets or layers (lamallae)

Collagen fibers of one lamallae lie parallel to one another

Bone classified by amount of matrix relative to amount of space in bone

Cancellous – less bone matrix, more space

Compact – more bone matrix less space; denser

Trabeculae: interconnecting rods or plates of boneBetween the trabeculae - filled with bone

marrow and blood vessels

Porous appearance

No blood vessels, osteocytes obtain nutrients through canaliculi

Covered with single layers of cells of osteoblasts and few osteoclasts

Denser

Has fewer spaces than cancellous bone

Blood vessels enter the substance of the bone itself

Figure 6.6

Osteon or Haversian SystemBasic unit of compact bone

Consists of a central canalrun parallel to surface of bone

Contains blood vesselsConcentric lamellae - cylinders of

bone

Circumferential lamellae – outer surfaces of compact bone

Interstitial lamellae – in between osteons Perforating or Volkmann’s canal –

Osteocytes receive nutrients and eliminate waste products through canal system

Contain blood vessels that then branch to enter central canal

Figure 6.6

Long – longer than wide

Ex. Upper and lower limbs

Short – as broad as wide

Ex. Carpals (wrist) and tarsals (ankle)

Flat – thin, flattened shape, curved

Ex. Ribs, sternum, skull, scapulae

Irregular – doesn’t fit in other category

Ex. Vertebrae, facial

DiaphysisShaft of boneMostly compact bone, can contain cancellous

EpiphysisEnd of the bone - Cancellous boneCovered with articular cartilageDevelops from center of ossificationBones with one or more epiphyses:

Long bone of arm Forearm Thigh bone Lower leg

Epiphyseal plate - responsible for growth in length of bone

Composed of hyaline cartilage

Present until growth stops

Then becomes epiphyseal line

Medullary cavity - central, hollow cavityFilled with marrow

At birth, there’s more red marrow

Conversion from red to yellow as you age

Yellow marrow completely replaces red in long bones of limbs, except in proximal part of arm and thigh bones

Periosteum – connective tissue membrane covers outside of boneFibers of tendon that bind muscle to

bone become continuous with fibers of periosteum.

Sharpey’s fibers - fibers that penetrate into the bone matrixStrengthen attachment of tendon

to bone

EndosteumSimilar to inner layer of periosteum

Lines all internal spaces including spaces in cancellous bone

Figure 6.3a-c

1. What are the 4 different types of bones?

2. Identify the following:The end of a bone is called – The shaft of the bone is called –

3. What is found in the medullary cavity?

4. What is the difference between red and yellow marrow?

5. What is the name of cells that make new cartilage?

6. What is the name of cells that maintain cartilage?

7. What makes up the bone matrix?

8. What is the difference between cancellous and compact bone?

1. What are the 4 different types of bones?Long, short, flat and irregular

2. Identify the following:The end of a bone is called – EpiphysisThe shaft of the bone is called – Diaphysis

3. What is found in the medullary cavity? - Bone marrow

4. What is the difference between red and yellow marrow? Red – blood formation Yellow – adipose tissue

5. What is the name of cells that make new cartilage? Chondroblasts

6. What is the name of cells that maintain cartilage? Chondrocytes

7. What makes up the bone matrix? Collagen (35%)Calcium phosphate (65%) – aka hydroxy

apatite

8. What is the difference between cancellous and compact bone?Cancellous – less bone matrix, more space

betweenCompact – More bone matrix, less space,

denser

Flat BonesNo diaphyses or epiphyses

A sandwich of cancellous (spongy) bone between compact

Short and Irregular bonesSimilar composition to epiphyses of

long bones

Compact bone surfaces that surround cancellous bone center with small spaces filled with marrow

Short and Irregular bonesNot elongated and have no diaphyses

Certain regions of these bones have epiphyseal growth plates and small epiphyses

Bone formation occurs in 2 different ways Intramembranous ossification

Occurs in connective tissue membrane

Endochondral ossification Occurs in cartilage

Both produce woven bone that is then remodeled to lamellar

Internally, osteoblasts form cancellous bone

Externally, osteoblasts form compact bone

Forms many flat skull bones, part of mandible, diaphyses of clavicles

When remodeled, indistinguishable from endochondral bone

ALL bones except some bones of the skull and clavicles

Bones are modeled in hyaline cartilage

Begins forming late in 2nd month of human development

Continues forming until early adulthood

Blood vessel invade cartilage, matrix becomes calcified and chondrocytes die

Perichondrium becomes periosteum

Figure 6.10

1. How are short, flat and irregular bones different from long bones?

2. What is “remodeling”?

3. How is intramembranous ossification different from endochondral ossification?

1. How are short, flat and irregular bones different from long bones?Short bones have no diaphysis or epiphysis;

cancellous bone sandwiched between compact

2. What is “remodeling”?Bone metabolismLife long process where mature bone tissue

is removed from the skeleton and new tissue is formed

3. How is intramembranous ossification different from endochondral ossification? Intramembranous

Forms the skull, shoulder blades, jaw Occurs in the connective tissue membrane Occurs in fetal development Cartilage is NOT present

Endochondral ALL other bones Cartilage (hyaline) is present Continues forming until early adulthood

Bone formation happens on surface of older bone or cartilage

Long bones increase in length because of growth at epiphyseal plate

Involves formation of new cartilage from inside of preexisting cartilage and bone growth of surface of cartilage

Interstitial growth – new cells formed from within tissue (cyte cells)

Appositional growth – new cells added to surface of tissue by blast cells

Composed of 4 zones:

1. Zone of resting cartilage – nearest epiphysis and contains random chondrocytes that don’t divide rapidly

2. Zone of proliferation – produce new cartilage through interstitial cartilage growth; chondrocytes form stacks

3. Zone of hypertrophy – chondrocytes produced mature and enlarge

cells nearer epiphysis: younger and actively proliferate

cells nearer diaphysis:older and maturing

4. Zone of calcification – thin and contains hypertrophied chondrocytes and calcified cartilage matrixHypertrophied chondrocytes die

Blood vessels from diaphysis grow into area

Connective tissue surround blood vessels contains osteoblasts

Osteoblasts make new bone matrix

In epiphyseal plates of growing bones...Length of diaphysis increases

Cells push the epiphysis away from the diaphysis

Once bones reach adult size, epiphyseal plate ossifies and becomes epiphyseal line

Occurs between 12-25 yrs of age (depends on bone and individual)

Long bones increase in width; other bones increase in size or thickness

Rapid growth – young bones or puberty

Size and shape of a bone determined genetically but can be modified

Influenced by Nutrition Hormones

NutritionLack of calcium, protein and other nutrients

during growth and development can cause bones to be small; illness and malnutrition

Nutrition con’tVitamin D

Necessary for absorption of calcium from intestines

Can be eaten or manufactured in the body

Rickets: lack of vitamin D during childhood

Osteomalacia: lack of vitamin D during adulthood leading to softening of bones

Nutrition con’tVitamin C

Necessary for collagen synthesisCan cause growth retardationScurvy: due to deficiency of vitamin C

Ulceration & hemorrhage in any area of body

Lack of vitamin C also causes wounds not to heal, teeth to fall out

HormonesGrowth hormone stimulates

interstitial cartilage growth appositional bone growth

Thyroid hormone required for growth of all tissues

HormonesSex hormones : estrogen and

testosterone

Cause growth at puberty, but also cause closure of the epiphyseal plates

Females stop growing earlier than males because estrogen causes quicker closure of epiphyseal plate

Bone deposit and removal Occurs at periosteal and endosteal surfaces

Bone deposition – accomplished by osteoblasts

Bone reabsorption – accomplished by osteoclasts

Converts woven bone into lamellar bone

Involves bone growth, change in bone shape, adjustment of bone stress, and bone repair

Completed through osteoclasts and osteoblasts

Travel through bone, removing old bone matrix and replacing it with new bone matrix

These specific cells renew the entire skeleton every 10 years

1. Hematoma formation - blood clot formation

Hematoma – localized mass of blood released from blood vessels but confined within a space

Injury followed by inflammation and swelling

2. Callus formation - mass of tissue that forms at a fracture site and connects the broken ends of the bone

Internal and external callus

Cartilage is formed

Osteoblasts invade = New bone is formed

Bone/cartilage (woven bone) stabilizes broken bone

3. Callus ossification Callus replaced by woven, cancellous bone

Stronger external callus

4. Bone remodeling Replacement of cancellous bone and damaged

material by compact bone

Remodeling takes sometimes more than a year; repaired zone thicker than adjacent bone

Open (compound) – bone break with open wound. Bone may be sticking out of wound.

Closed (simple) – Skin not perforated.

Complicated – soft tissue around closed fracture is damaged

Incomplete - doesn’t extend across the bone. (2+ fragments)

Complete – does extend across the bone

Greenstick – incomplete fracture that occurs on the convex side of the curve of a bone

Hairline: incomplete where two sections of bone do not separateCommon in skull fractures

RicketsSoft bonesVitamin D/Calcium/Phosphate deficiency in

CHILDREN If the blood levels of these mineral become

too low, hormones cause Ca and P to be released from bones

OsteomalaciaSoftening of bonesVitamin D deficiency in ADULTSLeads to improper calcium absorption

OsteomalaciaNormal bone density

Not enough Vitamin D in the diet Note enough exposure to sunlight Lactose intolerant

Bone fractures happen with very little injury

Widespread bone pain

Complete healing with treatment takes place in 6 months

Osteomyelitis Bacterial infections (or fungal) of bones

Infections spread via the blood from wounds, boils, TB

Infection can start after bone surgeryEspecially when rods or plates are used

Leads to destruction of bone

A condition of abnormally increased height

Results from excessive cartilage and bone formation at epiphyseal plates of long bones.

What causes What causes Giantism?Giantism?

Pituitary giantism – excess secretion of pituitary growth hormone.

Robert Wadlow's height of 8' 11.1" qualifies him as the tallest person in history.

Acromegaly – excess pituitary growth hormone secretion

Involves growth of connective tissue, including bones, after epiphyseal plates ossified

Mainly involves increased diameter of all bones

Growth hormone deficiency involves abnormally short stature with normal body proportions.

AchondroplasticMost common type long bones stop growing

in childhood normal torso, short limbs

Parents are normal height

Pituitary dwarfism lack of growth hormonenormal proportions with

short stature

Bone matrix decreases More brittle due to lack of collagenAlso less hydroxyapetite (calcium

phosphate)

Bone mass decreasesHighest around 30 yrs of ageMale bone mass denser due to

testosterone and greater weightRate of bone loss increases 10 fold after

menopause

Increased bone fractures

Bone loss causes deformity, loss of height, pain, stiffness Stooped posture Loss of teeth

Decrease in bone densityDepletion of calcium and phosorphous

Porous bone

Occurs when rate of bone resorption exceeds rate of bone formation

Bone is deformed and prone to fracture

Occurs mostly in older people

Occurrence increases in ageStrong genetic component 60% genetic; 40% environmental or lifestyle

(diet & exercise)

Loss of bone mass

Curvature of spine

Muscle weakness

Pain sensations

Impaired respiration

Postmenopausal women (> 50) at greatest riskDecrease of estrogen – maintains bone

mass Estrogen maintains density in both

sexes (inhibits resorption) Males, reduction of testosterone levels

Testosterone levels don’t decrease significantly until age 65

TreatmentsHRT – uses estrogen to decrease osteoclast

numbers Reduces bone loss

SERMS – class of drugs bind to estrogen receptors Inhibit osteoclasts, stimulate osteoblasts,

increase bone mass

Prevention -- exercise and calcium intake (1000 mg/day) between ages 25 and 40

What you need to know… The 5 functions of the skeletal system Components of the bone matrix Types of cartilage found in the body Chondroblasts vs chondrocytes vs condroclasts Osteoblasts vs osteocytes vs osteoclasts Compact vs cancellous bones Bone types & examples Compare & contrast the 4 bone types Types of marrow Factors affecting bone growth Labeling diagram of compact bone (ex – osteons)