Bone Tissue

Cartilage Review

• Hyaline Cartilage:

  • Location: Ends of long and short bones, joints (hip, leg), nose tip.
  • Function: Provides smooth surfaces for joint movement, support for nose.

• Elastic Cartilage:

  • Location: Outer ear, epiglottis (top of trachea).
  • Function: Provides elasticity and support; epiglottis prevents fluid entry into lungs.

• Fibrocartilage:

  • Location: Between knee bones (femur and tibia), pubic symphysis, intervertebral discs.
  • Function: Acts as a shim for bones, provides cushioning and stability between vertebrae.

Axial vs. Appendicular Skeleton

• Axial Skeleton (dark brown):

  • Components: Skull, vertebrae, ribs.
  • Function: Forms the central axis of the body, protects internal organs.

• Appendicular Skeleton (tan):

  • Components: Arms, legs, hip bones, shoulder blade.
  • Function: Facilitates movement and connects limbs to the axial skeleton.

Bone Classification by Shape

• Long Bones:

  • Characteristics: Longer than wide.
  • Example: Humerus (upper arm bone).

• Irregular Bones:

  • Characteristics: Complex, irregular shapes.
  • Example: Vertebra.

• Flat Bones:

  • Characteristics: Relatively flat.
  • Example: Sternum (breastbone).

• Short Bones:

  • Characteristics: Roughly cube-shaped.
  • Example: Talus (ankle bone).

Functions of Bone

• Protection:

  • Hard bone protects internal organs (brain, spinal cord, heart, lungs).
  • Example: Skull protects the brain.
  • Real-world Relevance: Nail gun accident illustrates relative protection; skull protected the brain even with a nail through it, minimizing damage.

• Support:

  • Bones provide shape and support to the body.
  • Example: Fish skeleton demonstrates how bones give shape to the body.

• Leverage:

  • Bones act as levers for muscles to pull on, enabling movement.
  • Muscles contract, pulling on bones to create movement around joints (e.g., elbow).

• Mineral Storage:

  • Bones store minerals like calcium and phosphorus.
  • These minerals are essential for various bodily functions.

• Blood Formation:

  • Hematopoiesis: Blood cells are formed in the bone marrow.
  • Erythrocytes (red blood cells) and leukocytes (white blood cells) are produced in the bone marrow.

• Triglyceride Storage:

  • Fat is stored in the bone marrow cavity.
  • Serves as an energy reserve for blood cell production and general energy needs.

Bone Structure

• Types of Bone Tissue:

  • Spongy Bone:
    • Location: Insides of long bones, ends of long bones.
    • Function: Helps resist forces of compression because of its porous nature.
  • Compact Bone:
    • Location: Outside of all bones.
    • Function: Provides strength and smoothness to the outer portion of the bone.

• Flat Bone Structure:

  • Compact bone on the outside and inside, spongy bone in the middle without a marrow cavity.
  • Spongy bone absorbs pressure to protect the brain.
  • Trabeculae: Bone marrow is stuffed in between the trabeculae or bone spicules.

Long Bone Structure

• Marrow Cavity:

  • Location: Hollow area inside the diaphysis.
  • Function: Contains bone marrow for blood production and fat storage.

• Compact Bone:

  • Location: Outer surface of bone.
  • Function: Provides strength and smoothness.

• Epiphysis:

  • Location: Head of the bone.
  • Types: Proximal (closer to the trunk) and distal (further from the trunk).

• Diaphysis:

  • Location: Shaft of the bone.

• Metaphysis:

  • Location: Where the epiphysis and diaphysis meet.

• Endosteum:

  • Location: Lining of the marrow cavity.
  • Function: Protects blood cells forming inside the marrow cavity.

• Periosteum:

  • Location: Outer surface of the bone.
  • Function: Connective tissue covering for bone protection and muscle attachment.

• Articular Cartilage:

  • Location: Hyaline cartilage at the ends of long bones in joints (articulations).

Periosteum and Endosteum Details

• Periosteum:

  • Structure:
    • Outer Fibrous Layer: Dense irregular connective tissue with collagen fibers merging with tendons.
    • Inner Osteogenic Layer: Contains osteogenic cells, osteoblasts, and osteoclasts for bone growth and repair.
  • Function:
    • Periosteum actually grows into the bone.

• Endosteum:

  • Structure:
    • Made of a single layer of reticular connective tissue.
  • Function:
    • Lines the marrow cavity and contains bone cells.
    • Protects delicate blood cells.

Bone Cells

• Osteogenic Cells:

  • Function: Original bone cells that divide to become osteoblasts.

• Osteoblasts:

  • Function: Bone-building cells that produce collagen and gel (osteoid).

• Osteocytes:

  • Function: Mature bone cells that maintain calcium balance in bone.
  • Involved in sending and receiving calcium to and from the blood.

• Osteoclasts:

  • Function: Large cells that dissolve bone tissue by releasing acids and enzymes.
  • Important for bone remodeling and repair.
  • The osteocytes are instrumental in moving the bloodstream back into the bone.

Microscopic Anatomy of Compact Bone

• Osteons:

  • Structure: Circular structures extending vertically through the bone.

• Central Canal:

  • Structure: Central area within the osteon that houses blood vessels.

• Lamellae:

  • Structure: Concentric rings that make up the osteon.

• Osteocytes and Canaliculi:

  • Osteocytes reside within the lamellae.
  • Canaliculi are small canals extending from osteocytes, facilitating nutrient and waste exchange.

Microscopic Anatomy of Spongy Bone

• Nutrient Supply:
  • Osteocytes are close to the blood supply within the marrow.
  • No need for compact bone structure or canaliculi.

Components of Bone (Analogy to Concrete and Rebar)

• Calcium Phosphate:

  • Function: Provides hardness and strength to bone.

• Collagen:

  • Function: Provides flexibility and prevents shattering.

• Osteoid Formation:

  • Osteoblasts secrete collagen fibers and gel (osteoid).
  • Calcium ions and phosphate attach to collagen for bone hardening.

Long Bone Formation (Endochondral Ossification)

• Process:

  • Begins with hyaline cartilage connective tissue in the shape of a long bone.
  • Chondroblasts multiply under the influence of thyroid and growth hormones.

• Key Structures:

  • Diaphysis: Shaft of the bone.
  • Epiphysis: Knob-like ends of the bones.
  • Metaphysis (Growth Plate): Area between the epiphysis and diaphysis made of cartilage.
    • Important because bone growth actually happens here.

• Process Steps:

  • Cartilage does not turn into bone; cartilage is killed and replaced with bone.
  • Bone length actually occurs because of cartilage growth
  • Growth plate destruction at puberty due to high hormone levels:
    • Estrogen in females
    • Testosterone
    • Epiphyseal Line forms

Epiphyseal Plate Zones

• Zone of Resting Cartilage:

  • Function: Anchors the epiphysis.

• Proliferation Zone:

  • Description: Chondrocytes multiply and stack.

• Hypertrophic Zone:

  • Description: Older cells enlarge and start to die.

• Calcification Zone:

  • Description: Oldest cartilage cells die, and calcium is deposited.

• Ossification Zone:

  • Description: New bone formation by osteoblasts.

Flat Bones

• They are formed by a process called intramembranous ossification
  • intra=within.
  • membrane= a flat membrane.
  • Ossification= the of bone.

Bone Growth

Bone shape depends upon the forces placed upon it, and bone responds to use.

Blood Calcium Homeostasis:

• When the blood calcium levels are LOW:
  • Parathyroid glands sense low blood calcium, releasing parathyroid hormone (PTH) into the blood.
  • PTH travels to the bone and binds to osteoclasts, which become activated, and help release calcium back into the blood.

Bone Fractures

*Nondisplaced Fracture
*Displaced Fracture

• Complete Fracture
• Incomplete Fracture
• Linear Fracture
  *Transverse Fracture
  *Compound (Open) Fracture
• Simple Fracture

Types of Fractures more likely with older ages:

• Comminuted Fracture
• Compression Fracture

Types of Fractures more likely with younger ages:

• Spiral Fracture
• Greenstick Fracture
• Epiphyseal Fracture

Bone Homeostatic Imbalances

• Rickets and Osteomalacia
  * Vitamin D deficiencies in children can lead to bowing of the bones
• Osteoporosis-* means porous bone
  -lack of estrogen in the bone
  -immobility can also cause this
  - the ovaries are the organs that produce estrogen in the body