chapter 5 the skeletal system: osseous tissue and skeletal...

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Chapter 5

The Skeletal System:

Osseous Tissue and

Skeletal Structure


Introduction

• The skeletal system is made of:

• Skeletal bones

• Cartilage

• Ligaments

• Connective tissue to stabilize the skeleton

• Bones are dynamic organs, which consist

of several tissue types and interacts with all

organ systems

• Continually rebuilds and remodels itself


Introduction

• Functions of the skeletal system

• Support • Provides the framework for the attachment of other

organs

• Storage of minerals • Calcium ions: 98% of the body’s calcium ions are

in the bones

• Phosphate ions

• Blood cell production • Bone marrow produces erythrocytes, leukocytes,

and platelets


Introduction

• Functions of the skeletal system (continued)

• Leverage

• Muscles pull on the bones to produce movement

• Protection

• Ribs protect heart and lungs

• Skull protects the brain

• Vertebrae protect the spinal cord

• Pelvic bones protect the reproductive organs


• 3 types:

• Hyaline=most

abundant; flexible

and resilient

• Elastic=highly

bendable

• Fibro=resists

compression and

tension

Cartilages:


Cartilages:

• 3 Major functions of Cartilages

• Supporting soft tissues

• Providing a gliding surface at articulations

(joints), where two bones meet

• Providing a model for the formation of most of

the bones in the body


Structure of Bone

• Bones (osseous

tissue)

• Supporting connective

tissue

• Specialized cells

• Solid matrix


The Histological Organization of Bone

• The matrix

• Calcium phosphate eventually converts to hydroxyapatite crystals

• Make up 2/3 of the bone weight

• Hydroxyapatite crystals resist compression

• Collagen fibers

• Contribute to the tensile strength of bones

• Collagen and hydroxyapatite make bone tissue extremely strong

• Bone cells

• Contribute only 2% of the bone mass


The Cells of Mature Bone

• Osteocytes

• Mature bone cells, reside in spaces called lacunae

(interconnected by canaliculi)

• Maintain the protein and mineral content of the matrix

• Osteoblasts

• Immature bone cells

• Found on the inner and outer surfaces of bones

• Produce osteoid, which is involved in making the

matrix

• Osteoblasts are involved in making new bone. This is

a process called osteogenesis

• Osteoblasts can convert to osteocytes


The Cells of Mature Bone

• Osteoprogenitor cells

• Found on the inner and outer surfaces of bones

• Differentiate to form new osteoblasts

• Heavily involved in the repair of bones after a

break

• Osteoclasts

• Secrete acids, which dissolve the bones thereby

causing the release of stored calcium ions and

phosphate ions into the blood

• This process is called osteolysis


Figure 5.1a Histological Structure of a Typical Bone

Osteocyte: Mature bone cell

that maintains the bone matrix

Osteoblast

Matrix

Matrix

Canaliculi Osteocyte

Osteoid

Osteoblast: Immature bone

cell that secretes organic

components of matrix The cells of bone

Endosteum Osteoprogenitor cell

Medullary

cavity

Osteoprogenitor cell:

Stem cell whose divisions produce

osteoblasts

Matrix Osteoclast

Medullary

cavity

Osteoclast: Multinucleate cell

that secretes acids and enzymes

to dissolve bone matrix


Two types of osseous tissue

• Compact bone (dense bone) • Compact bones are

dense and solid

• Forms the walls of bone outlining the medullary cavity

• Medullary cavity consists of bone marrow

• Spongy bone (trabecular bone) • Open network of plates


Compact vs. Spongy bone

• Structural Differences

• Compact bone • Consists of osteons

• Makes up the dense, solid portion of bone

• Central canal contains blood vessles and nerves

• Volkmann’s canals carry blood to central canal

• Spongy bone • Trabeculae are arranged in thick branching plates

• Creates the lightweight nature of bones

• No central canal

• Blood enters from bone marrow into tracecular spaces


Figure 5.2a-c The Internal Organization in Representative Bones

Spongy bone

Blood vessels

Compact bone

Medullary cavity

Endosteum

Periosteum

Gross anatomy

of the humerus

Compact

bone

Spongy

bone

Medullary

cavity

Concentric

lamellae

Interstitial

lamellae

Capillary

Small vein

Circumferential

lamellae

Osteons

Periosteum

Collagen fiber

orientation

Concentric

lamellae

Central

canal

Endosteum

The organization of collagen

fibers within concentric lamellae

Trabeculae of

spongy bone

Central

canal

Diagrammatic view of the histological

organization of compact and spongy bone

Perforating

canal

Artery Vein


Microscopic view of the compact bone

• The Osteon

• It is the basic unit of

compact bones

• Consists of:

• Central canal

• Canaliculi

• Osteocytes

• Lacunae

• Lamellae (layers of

calcified matrix)


Figure 5.1d Histological Structure of a Typical Bone

A single osteon at higher

magnification

Osteon LM 343

Canaliculi

Concentric

lamellae

Osteon

Lacunae

Central canal


Figure 5.2d The Internal Organization in Representative Bones

Canaliculi

opening

on surface

Location and structure of spongy bone. The photo

shows a sectional view of the proximal end of the femur.

Trabeculae of

spongy bone

Lamellae

Endosteum


Compact vs. Spongy bone

• Functional Differences

• Compact bone

• Conducts stress from one area of the body to

another area of the body

• Generates tremendous strength from end to end

• Weak strength when stress is applied to the side

• Spongy bone

• Trabeculae create strength to deal with stress from

the side


Structure of Bone

• Organization of Compact

and Spongy Bone

• Epiphysis (spongy)

• Each end of the long

bones

• Diaphysis (walls filled

with compact)

• Shaft of the long bones

• Metaphysis

• Narrow growth zone

between the epiphysis and

the diaphysis


The Periosteum and Endosteum • Periosteum

• Outer surface of the bone

• Isolates and protects the bone from surrounding tissue

• Provides a route and a place for attachment for circulatory and nervous supply

• Actively participates in bone growth and repair

• Attaches the bone to the connective tissue network of the deep fascia

• Endosteum

• Inner surface of bone

• Lines the medullary cavity

• Consists of osteoprogenitor cells

• Actively involved in repair and growth


Figure 5.4ab Anatomy and Histology of the Periosteum and Endosteum

The endosteum is an incomplete

cellular layer containing osteoblasts,

osteoprogenitor cells, and osteoclasts.

Joint capsule

Osteoblasts

Osteoid

Osteocyte

Osteoprogenitor

cell

Endosteum

Giant

multinucleate

osteoclast

Bone

matrix

Compact bone

Fibrous layer

of periosteum

Cellular layer

of periosteum

Endosteum

The periosteum contains outer

(fibrous) and inner (cellular) layers.

Collagen fibers of the periosteum are

continuous with those of the bone,

adjacent joint capsules, and attached

tendons and ligaments.

Circumferential

lamellae

Cellular layer

of periosteum

Fibrous layer

of periosteum

Canaliculi

Lacuna

Osteocyte

Perforating

fibers


Bone Development and Growth

• Before six weeks of development, the

skeleton is cartilage

• Cartilage cells will be replaced by bone cells

• This is called ossification

• Osteogenesis

• Bone formation

• Calcification

• The deposition of calcium ions into the bone

tissue



• There are two types of ossification

• Intramembranous ossification

• Bone develops from a fibrous membrane

• Involved in the development of clavicle, mandible,

skull, and face

• Endochondral ossification

• Bone forms by replacing hyaline cartilage

• Involved in the development of limbs, vertebrae,

and hips



• Intramembranous ossification

• Mesenchymal cells differentiate to form

osteoblasts

• Osteoblasts begin secreting a matrix

• Osteoblasts become trapped in the matrix

• Osteoblasts differentiate and form osteocytes

• More osteoblasts are produced, thus move

outward

• Eventually, spongy bone and compact bone is

formed



• Endochondral ossification • The developing bone begins as cartilage cells

• Requires breakdown of hyaline cartilage prior to ossification

• Invasion of hyaline cartilage by the osteoblasts, they begin to develop spongy bone in the diaphysis (primary center of ossification)

• Formation of the medullary cavity (secondary center of ossification) in epiphysis

• Ossification of the epiphysis, with hyaline cartilage remaining only in the epiphyseal plates

(New cartilage is added at the epiphyseal side, where osseous tissues replaces older cartilage at the diaphyseal side)



• Epiphyseal plate

• Endochondral ossification

of a long bone occurs in

progressive stages.

• Bone growth is complete

when each epiphyseal

plate has ossified and the

epiphyseal line has formed.

• Epiphyseal plate

ossification occurs between

the ages of 10 and 25.

• The width of this zone gets

narrower as we age


Long Bone Growth and Remodeling

• Growth in length – cartilage continually grows and is replaced by bone (increases length at the epiphyseal cartilage)

• Appositional bone growth (enlarging the diameter of bone)

• Osteoblasts begin to produce matrix, thus creating concentric rings

• As osteoblasts are laying down more bone material, osteoclasts are dissolving the inner bone, thus creating the marrow cavity


Figure 5.9b Appositional Bone Growth

Bone resorbed

by osteoclasts

Bone deposited

by osteoblasts Child Infant

Young adult Adult A bone grows in diameter as new bone is added to the outer surface. At the same

time, osteoclasts resorb bone on the inside, enlarging the medullary cavity.


Bone remodeling

When adult bone size has been reached, the bone continues to reshape itself

throughout a person’s lifetime in a constant process of bone resorption and deposition.


• Nutrition • Calcium ions, Phosphate ions, Magnesium ions,

Citrate, Carbonate ions, Sodium ions

• Vitamins A, C, D (calcitriol)

• Hormones • Parathyroid hormone

• Thyroid hormone

• Growth hormone

• Sex hormones (estrogen & testosterone)

Factors Regulating Bone Growth


• Hormones: Parathyroid gland

• Releases parathyroid hormone

• Stimulates osteoclasts & osteoblasts

• Increases calcium ion absorption from the small

intestine to the blood

• Hormones: Thyroid gland

• Releases calcitonin

• Inhibits osteoclasts

• Removes calcium ions from blood and adds it to bone




• Hormones: Thyroid gland

• Releases thyroxine (T4)

• Increases osteoblasts activity

• Maintains normal activity of the epiphyseal cartilage

• Hormones: Pituitary gland

• Releases growth hormone (somatotropin)


• Maintains normal activity of the epiphyseal cartilage

• Hormones: Reproductive organs



Bone Maintenance, Remodeling, and Repair

• Aging and the Skeletal System

• When we are young, osteoblast activity

balances with osteoclast activity

• When we get older, osteoblast activity slows

faster than osteoclast activity

• When osteoclast activity is faster than

osteoblast activity, bones become porous

• Estrogen keeps osteoclast activity under

control



• Aging and the Skeletal System

• As women age, estrogen levels drop

• Osteoclast control is lost

• Osteoclasts are overactive

• Bones become porous

• This is osteoporosis



• Injury and Repair

• When a bone is

broken, bleeding

occurs

• A network of spongy

bone forms

• Osteoblasts are overly

activated, thus

resulting in enlarged

callused area

• This area is now

stronger and thicker

than normal bone


Anatomy of Skeletal Elements

• There are seven broad categories of bones according to their shapes

• Sutural bones

• Irregular bones

• Short bones

• Pneumatized bones

• Flat bones

• Long bones

• Sesamoid bones


Figure 5.11 Shapes of Bones

Irregular Bones

Sutural

bone

Sutures

Pneumatized Bones Sutural Bones

Air cells Ethmoid

Vertebra

Carpal

bones

Humerus

External table Parietal bone

Internal

table

Diploë

(spongy bone)

Patella

Short Bones

Flat Bones

Long Bones

Sesamoid Bones


Anatomy of Skeletal Elements


Figure 5.12a Examples of Bone Markings (Surface Features)

Trochanter

Head

Neck

Femur

Facet

Tubercle

Condyle


Figure 5.12b Examples of Bone Markings (Surface Features)

Fissure

Ramus

Process

Foramen

Skull, anterior view


Figure 5.12c Examples of Bone Markings (Surface Features)

Canal

Sinuses

Meatus

Skull, sagittal section


Figure 5.12d Examples of Bone Markings (Surface Features)

Humerus

Condyle

Trochlea

Fossa

Tuberosity

Neck

Sulcus

Head Tubercle


Figure 5.12e Examples of Bone Markings (Surface Features)

Crest

Pelvis

Spine

Line

Foramen

Fossa

Ramus


Table 5.1 Common Bone Marking Terminology

chapter 5 the skeletal system: osseous tissue and skeletal...

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