Chapter 6: The Skeletal System

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 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 of 6 Enlarging chondrocytes within calcifying matrix Chondrocytes at the center of the growing cartilage model enlarge and then die as the matrix calicifies. Cartilage model Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Figure of 6 Enlarging chondrocytes 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. Cartilage model Bone formation Epiphysis Diaphysis Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Figure of 6 Enlarging chondrocytes 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. Cartilage model Bone formation Epiphysis Diaphysis Marrow cavity Primary ossification center Blood vessel Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Figure of 6 Enlarging chondrocytes 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. Cartilage model Bone formation Epiphysis Diaphysis Marrow cavity Primary ossification center Blood vessel Marrow cavity Blood vessel Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Enlarging chondrocytes 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. Cartilage model Bone formation Epiphysis Diaphysis Marrow cavity Primary ossification center Blood vessel Marrow cavity Blood vessel Secondary ossification center Epiphyseal cartilage Articular cartilage Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Appositional Bone Growth Figure 6-6

Requirements For Normal Bone Growth  Hormones  Growth Hormone  Sex hormones, thyroid hormone, others  Minerals  Calcium, phosphate  Vitamins  Vitamin D 3  Vitamin C  Vitamin A

Bone Remodeling/Homeostasis Remodeling - Continuous breakdown and reforming of bone tissue - 18% turned over/year  enables skeleton to adapt to new stresses  inactivity = degeneration FYE: 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)