Chapter 6: The Skeletal System

http://www.accessexcellence.org/RC/VL/xrays/

FYE: Your Bones…

Bones aren’t just pieces of your skeleton They are a connective tissue impregnated with minerals! Bones aren’t dead!

They have cells, bloody supply & nerves (feelings!) Bones are strong!

Standing still the force on hip = 3x bodyweight (muscle pull) & a running man exerts a dead wt force of ~590 lbs!

The Skeletal System

Parts of the skeletal system

Some Vocab…• BONE = Osseous Tissue• Osteology = Study of bones• Arthrology = Study of joints• Kinesiology = Study of movement

Bones Cartilage

Ligaments (connect bone to bone) Tendons (connect muscle to bone)

Functions of the Skeletal System

Support For wt of entire body Framework for attachment

Leverage for muscle action Protection of internal organs

Storage Calcium & Phosphate Fat cells (in yellow marrow!)

Blood cell production = Hemopoiesis Red marrow makes cells Found in: pelvis, ribs, clavicle, vertebra, skull, ends of long bones

Bone Shapes

Figure 6-1

Femur, Phalanges & metacarpals Tarsals

Sternum, scapula, ribs

Clavicle, patella

The Structure of Bone

Figure 6-2

Features in a Long Bone Diaphysis (shaft)

Compact bone Marrow cavity

Epiphyses (ends) Spongy bone

Articular cartilage

Periosteum (covering)

Endosteum (lining)

The Structure of Bone

Bone (Osseous Tissue) Specialized cells

2% of bone wt Calcium Phosphate crystals

67% of bone wt

Collagen fibers

Two types: Compact & Spongy

Bone Tissue

Compact Bone Layers of compact cover all bone surfaces, except at joints

Found where stresses occur Osteon = basic functional unit of compact bone

Osteocytes surrounded by rings of matrix with a central canal

Bone Tissue

Spongy Bone Network of bony rods (trabeculae) Found in center & in epiphysis Lighter to decrease wt of skeleton Spaces filled with marrow

Microscopic Structure of Bone

Figure 6-3(a)

Microscopic Structure of Bone

Figure 6-3(b)

BONE CELLS

1. Osteocytes Mature bone cells in osteons & trabeculae

Most abundant cell Maintain normal structure by recycling Ca in matrix

2. Osteoblasts Cells that make new bone (osteogenesis)

3. Osteoclasts Bone eaters - secrete acid that dissolves matrix (osteolysis) to release stored minerals

Regulate Ca & Phosphate in blood

= Found in Endosteum & Periosteum

Bone Formation and Growth

• Begins ~6wks after fertilization - embryo is ~12mm long

• Continues until 18-25 yrs

• Ossification = process of replacing connective tissue & cartilage with bone

1. Intramembranous Ossification

• Stem cells in connective tissue (usually deep dermis) turn into osteoblasts & secrete matrix

• When matrix calcifies osteoblasts turn into osteocytes

• Ossification Center = where ossification 1st occurred, forms osteons of compact bone over time

• Flat bones of skull, lower jaw, clavicles form this way!

1. Endochondral Ossification

• Cartilage model replaced by bone

• Most bones form this way - especially long bones

Figure 6-52 of 6

Enlargingchondrocytes within

calcifying matrix

Chondrocytes at the center of the growing cartilage model enlarge and then die as the matrix calicifies.

Cartilagemodel

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Figure 6-53 of 6

Enlargingchondrocytes within

calcifying matrix

Chondrocytes at the center of the growing cartilage model enlarge and then die as the matrix calicifies.

Newly derived osteoblasts cover the shaft of the cartilage in a thin layer of bone.

Cartilagemodel

Boneformation

Epiphysis

Diaphysis

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Figure 6-54 of 6

Enlargingchondrocytes within

calcifying matrix

Chondrocytes at the center of the growing cartilage model enlarge and then die as the matrix calicifies.

Newly derived osteoblasts cover the shaft of the cartilage in a thin layer of bone.

Blood vessels penetrate the cartilage. New osteoblasts form a primary ossification center.

Cartilagemodel

Boneformation

Epiphysis

Diaphysis Marrowcavity

Primaryossificationcenter

Bloodvessel

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Figure 6-55 of 6

Enlargingchondrocytes within

calcifying matrix

Chondrocytes at the center of the growing cartilage model enlarge and then die as the matrix calicifies.

Newly derived osteoblasts cover the shaft of the cartilage in a thin layer of bone.

Blood vessels penetrate the cartilage. New osteoblasts form a primary ossification center.

The bone of the shaft thickens, and the cartilage near each epiphysis is replaced by shafts of bone.

Cartilagemodel

Boneformation

Epiphysis

Diaphysis Marrowcavity

Primaryossificationcenter

Bloodvessel

Marrowcavity

Bloodvessel

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Enlargingchondrocytes within

calcifying matrix

Chondrocytes at the center of the growing cartilage model enlarge and then die as the matrix calicifies.

Newly derived osteoblasts cover the shaft of the cartilage in a thin layer of bone.

Blood vessels penetrate the cartilage. New osteoblasts form a primary ossification center.

The bone of the shaft thickens, and the cartilage near each epiphysis is replaced by shafts of bone.

Blood vessels invade the epiphyses and osteo-blasts form secondary centers of ossification.

Cartilagemodel

Boneformation

Epiphysis

Diaphysis Marrowcavity

Primaryossificationcenter

Bloodvessel

Marrowcavity

Bloodvessel

Secondaryossificationcenter

Epiphysealcartilage

Articularcartilage

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

http://commons.bcit.ca/biology/ossification/files/ossification2.html

Appositional Bone Growth

Figure 6-6

Requirements For Normal Bone Growth

Hormones Growth Hormone Sex hormones, thyroid hormone, others

MineralsCalcium, phosphate

VitaminsVitamin D3

Vitamin CVitamin A

Bone Remodeling/Homeostasis

• Remodeling - Continuous breakdown and reforming of bone tissue - 18% turned over/year

enables skeleton to adapt to new stresses

inactivity = degenerationFYE: Cast on leg for 6 wks - leg loses 1/3 bone mass!

FYE: your oldest bones are ~7 yrs!

needed for Ca regulation - bones store 2-4 lbs hormones control release into blood & storage

Disorders in Bone Growth & Remodeling

• Osteoporosis = bone mass reduced, can happen at any age

inactivity low Ca age (males - lose 3%/decade starting in 30’s, females lose 8%)

Disorders in Bone Growth & Remodeling

• Osteomalacia (Rickets) = Soft Bones from lack of Vit.D causes low Ca

Disorders in Bone Growth & Remodeling

• Osteogenesis Imperfecta = Genetic disorder affecting collagen fiber formation (1 in 20,000)

Disorders in Bone Growth & Remodeling

• Achondroplasia (Dwarfism) = Genetic disorder affecting cartilage formation mainly at epiphyses

Disorders in Bone Growth & Remodeling

• Acromegaly (Giantism) = Excess growth hormone - most often after epiphyseal plates closed

Disorders in Bone Growth & Remodeling

• Marfan’s Syndrome = Defective CT - excess cartilage at epiphyseal plates

An Overview of the Skeleton

Figure 6-8(a)

An Overview of the Skeleton

Figure 6-8(b)

An Overview of the Skeleton

Figure 6-9

The Axial Division: The Skull

Figure 6-10

The Axial Division: The Skull

Figure 6-11(a)

The Axial Division: The Skull

Figure 6-11(b)