Chapter 5 The Skeletal System: Osseous Tissue and Skeletal

Chapter 5 The Skeletal System: Osseous Tissue and Skeletal Structure

© 2012 Pearson Education, Inc.

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 © 2012 Pearson Education, Inc.

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


Cartilages: • 3 types: • Hyaline=most abundant; flexible and resilient • Elastic=highly bendable • Fibro=resists compression and tension


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 © 2012 Pearson Education, Inc.

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

Canaliculi

Osteocyte

Matrix

Endosteum

Osteoprogenitor cell

Medullary cavity Osteocyte: Mature bone cell that maintains the bone matrix

Osteoblast

Osteoid

Osteoprogenitor cell: Stem cell whose divisions produce osteoblasts

Osteoclast

Matrix

Matrix

Medullary cavity

Osteoblast: Immature bone cell that secretes organic components of matrix


The cells of bone

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 Concentric lamellae

Spongy bone Blood vessels Collagen fiber orientation

Compact bone Medullary cavity

Central canal

Endosteum

Endosteum

The organization of collagen fibers within concentric lamellae Periosteum

Compact Spongy Medullary cavity bone bone

Capillary Small vein

Gross anatomy of the humerus

Circumferential lamellae

Concentric lamellae

Osteons Periosteum

Interstitial lamellae

ArteryVein

Trabeculae of spongy bone Perforating canal

Central canal

Diagrammatic view of the histological organization of compact and spongy bone


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

Canaliculi

Concentric lamellae Central canal

Osteon Lacunae

Osteon

LM  343

A single osteon at higher magnification © 2012 Pearson Education, Inc.

Figure 5.2d The Internal Organization in Representative Bones

Trabeculae of spongy bone

Canaliculi opening on surface

Endosteum Lamellae

Location and structure of spongy bone. The photo shows a sectional view of the proximal end of the femur. © 2012 Pearson Education, Inc.

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 © 2012 Pearson Education, Inc.

Figure 5.4ab Anatomy and Histology of the Periosteum and Endosteum

Joint capsule Cellular layer of periosteum Fibrous layer of periosteum Endosteum

Compact bone

Circumferential lamellae Cellular layer of periosteum Fibrous layer of periosteum Canaliculi Lacuna Osteocyte Perforating fibers

Bone matrix Giant multinucleate osteoclast Endosteum Osteoprogenitor cell Osteocyte

Osteoid Osteoblasts

The endosteum is an incomplete cellular layer containing osteoblasts, osteoprogenitor cells, and osteoclasts.


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.

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 © 2012 Pearson Education, Inc.


• 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 © 2012 Pearson Education, Inc.


Bone Development and Growth • 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)



Bone Development and Growth • 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

Infant

Child

Bone deposited by osteoblasts Young 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.


Adult

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. © 2012 Pearson Education, Inc.

Factors Regulating Bone Growth • 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


Factors Regulating Bone Growth • Hormones: Thyroid gland • Releases thyroxine (T4) • Increases osteoblasts activity • Maintains normal activity of the epiphyseal cartilage

• Hormones: Pituitary gland • Releases growth hormone (somatotropin) • Increases osteoblasts activity • Maintains normal activity of the epiphyseal cartilage

• Hormones: Reproductive organs • Increases osteoblasts activity


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


Bone Maintenance, Remodeling, and Repair

• Aging and the Skeletal System • As women age, estrogen levels drop • Osteoclast control is lost • Osteoclasts are overactive • Bones become porous • This is osteoporosis


Bone Maintenance, Remodeling, and Repair • 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 © 2012 Pearson Education, Inc.

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 Sutural Bones

Flat Bones

Pneumatized Bones

External table

Parietal bone

Sutures

Sutural bone

Ethmoid

Diploë Internal table (spongy bone)

Air cells

Long Bones

Irregular Bones

Vertebra Humerus

Short Bones

Carpal bones


Sesamoid Bones

Patella

Anatomy of Skeletal Elements




Figure 5.12a Examples of Bone Markings (Surface Features)

Trochanter Head Neck

Facet Tubercle

Condyle

Femur © 2012 Pearson Education, Inc.

Figure 5.12b Examples of Bone Markings (Surface Features)

Fissure Process

Foramen

Ramus

Skull, anterior view © 2012 Pearson Education, Inc.

Figure 5.12c Examples of Bone Markings (Surface Features)

Canal

Sinuses

Meatus

Skull, sagittal section


Figure 5.12d Examples of Bone Markings (Surface Features)

Tubercle

Head Sulcus Neck

Tuberosity

Fossa Trochlea

Condyle

Humerus


Figure 5.12e Examples of Bone Markings (Surface Features)

Crest

Spine

Fossa

Line

Foramen Ramus

Pelvis


Table 5.1 Common Bone Marking Terminology


Chapter 5 The Skeletal System: Osseous Tissue and Skeletal

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