HAN 200 - Chapter 7 (Bone Tissue)

Functions of bones

• Support - for body and soft organs

• Protection - for brain, spinal cord, vital organs

• Movement - levers for muscle action

• Storage - minerals (calcium and phosphorus) and growth factors

• Blood cell formation (hematopoiesis) in marrow cavities

• Triglyceride (energy storage) in bone cavities

Long Bones

Longer than they are wide (legs, arms, phalanges)

Short Bones

• Cube-shaped bones (wrist, ankle)

• Sesamoid bones (patella)

Flat Bones

Thin, flat, slightly curved (skull, scapula, sternum)

Irregular bones

Complicated shapes (vertebrae, pelvis)

Bone Markings

• Bulges, depressions, holes

Serve as:

• Site of attachment for muscles, tendons, and ligaments

• Joint surfaces

• Conduits for blood vessels and nerves

• Helps understand function of bones

Sites of muscle and ligament attachment

• Tuberosity

• Crest

• Trochanter

• Line

• Tubercle

• Epicondyle

• Spine

• Process

Tuberosity

Rounded projection

Crest

Narrow, prominent ridge

Trochanter

Large, blunt, irregular surface

Line

Narrow ridge of bone

Tubercle

Small, rounded projection

Epicondyle

Raised area above a condyle

Spine

Sharp, slender projection

Process

Any bony prominence

Projections that help form joints

• Head

• Facet

• Condyle

• Ramus

Head

Bony expansion carried on a narrow neck

Facet

Smooth, nearly flat articular surface

Condyle

Rounded articular projection

Ramus

Armlike bar

Depressions and openings

• Meatus

• Sinus

• Fossa

• Groove

• Fissure

• Foramen

Meatus

Canal-like passageway

Sinus

Cavity within a bone

Fossa

Shallow, basinlike depression

Groove (bicipital)

Furrow

Fissure

Narrow, slitlike opening

Foramen

Round or oval opening through a bone

Compact bone

10 years, dense outer layer

Spongy (cancellous) bone

3-4 years, honeycomb made of trabeculae, porous like sponge

Periosteum

• Outer fibrous layer

• Inner osteogenic layer

  • Osteoblasts (bone-forming cells)

  • Osteoclasts (bone-destroying cells)

  • Osteogenic cells (stem cells)

Endosteum

• Delicate membrane on internal surface of bone

• Also contains osteoblasts and osteoclasts

Osteoblasts

Bone forming cells, secrete bone matrix

Osteoclasts

Cells that break down (resorb) bone matrix

Osteogenic (Osteoprogenitor) cells

Stem cells in periosteum and endosteum that give rise to osteoblasts

Osteocytes

Mature bone cells, monitor/maintain matrix

Location of hematopoietic tissue (red marrow)

- Trabecular cavities of the heads of the femur and humerus

- Trabecular cavities of the dipole of flat bones

Haversian system or osteon

Structural unit of compact bone.

• Lamellae

• Central (haversian) canal

Lamellae

• Concentric rings

• Weight-bearing

• Column-like matrix tubes

• Contains collagen

Central (Haversian) canal

Contains blood vessels and nerves

Perforating (Volkmann’s) canals

• At right angles of central canal

• Connects blood vessels and nerves of the periosteum and central canal

Lacunae

Small cavities that contain osteocytes

Canaliculi

Hairlike canals that connect lacunae to each other and the central canal

Trabeculae

Found in spongy bone

• Align along lines of stress

• No osteons

• Contain irregularly arranged lamellae, osteocytes, and canaliculi

• Capillaries in endosteum supply nutrients

Chemical composition of bone: Organic

Osteogenic cells, osteoblasts, osteocytes, osteoclasts, osteoid

Osteoid

Organic bone matrix secreted by osteoblasts.

• Ground substance (proteoglycans, glycoproteins)

• Collagen fibers (provide tensile strength and flexibility)

Hydroxyapatites

• 65% of bone by mass

• Mainly calcium phosphate crystals

• Responsible for hardness and resistance to compression

Osteogenesis (ossification)

Bone tissue formation.

Types of ossification:

• Intramembranous ossification

• Endochondral ossification

Stages of osteogenesis

1. Initial formation in embryo and fetus

2. Growth from infancy through adolescence

3. Remodeling of bone throughout life

4. Repair of fractures

Intramembranous ossification

• Membrane bone develops from fibrous membrane

• Forms flat bones, e.g. clavicles and cranial bones

Endochondral ossification

• Cartilage (endochondral) bone forms by replacing hyaline cartilage

• Uses hyaline cartilage models

• Requires breakdown of hyaline cartilage prior to ossification

• Forms all bones below skull except clavicles

Intramembranous ossification

1. Development of the ossification center

2. Bone matrix (osteoid) secreted and calcifies

3. Trabeculae of woven bone and periosteum form

4. Bone collar of compact bone forms and red marrow appears

Interstitial growth

Increase length of long bones

Appositional growth

• Increase thickness and remodeling of all bones by osteoblasts and osteoclasts on bone surfaces

• Bone matrix secreted under periosteum

Growth hormone

Stimulates epiphyseal plate activity (from pituitary gland)

Thyroid hormone

Modulates activity of growth hormone

Testosterone and estrogen (at puberty)

• Promote adolescent growth spurts

• End growth by inducing epiphyseal plate closure (18 yo females, 21 yo males)

Hormonal control of blood Ca 2+

1. Primarily controlled by parathyroid hormone (PTH)

2. Decrease Ca²+ levels

3. Parathyroid glands release PTH

4. PTH stimulates osteoclasts to degrade bone matrix and release Ca²+

5. Increase blood Ca²+ levels

Control of remodeling bones

1. Hormonal mechanisms that maintain calcium homeostasis in the blood

2. Mechanical and gravitational forces (Wolff’s law)

Wolff's law

A bone grows or remodels in response to forces or demands placed upon it

Observations supporting Wolff's law

• Handedness, bone of one upper limb to be stronger

• Curved bones are thickest where they are most likely to buckle

• Trabeculae form along lines of stress

• Large, bony projections occur where heavy, active muscles attach

• Increased stress or decreased stress (i.e. astronauts)

Fracture classification

- Displaced or nondisplaced

- Open or closed

- Comminuted - bone fragments

- Spiral - excessive twisting force

- Compression - common in osteoporosis

- Depressed

- Greenstick

Stages in the healing of a bone fracture

1. Hematoma

2. Fibrocartilaginous callus

3. Bony callus formation

4. Bone remodeling

Osteoporosis (osteopenia)

• Loss of bone mass, bone resorption outpaces deposit

• Spongy bone of spine and neck of femur become most susceptible to fracture

Risk factors:

• Lack of estrogen, calcium, vitamin D, petite body, immobility, low TSH, diabetes mellitus

• At risk: petite white post menopausal female who is a nonexercising smoker

Osteoporosis prevention

• Calcium, vitamin d, fluoride supplements

• Increased weight-bearing exercise throughout life

• Hormone (estrogen) replacement therapy (HRT) slows bone loss

• Some drugs increase bone mineral density (Fosamax, SERMs, statins)

Membranes of bone

Periosteum and endosteum

Chemical composition of bone: Inorganic

Hydroxyapatites (mineral salts)

Hormonal regulation of bone growth

• Growth hormone

• Thyroid hormone

• Testosterone and estrogen

Hematoma

Mass of clotted blood forms, site becomes swollen, painful, and inflamed

Fibrocartilaginous callus

• Fibroblasts secrete collagen to connect bone ends

• Osteoblasts begin forming spongy bone in 1 week

Bony callus formation

Firm union in 8 weeks

Bone remodeling

In response to mechanical stress