Skeletal System Notes

How many bones do the adult human consists of?

206 bones (cartilage, ligaments, and joints included)

What are the 5 Functions of the Skeletal Systems

1. Support

2. Protection

3. Storage

4. Blood Cell Production

5. Movement

Functions of the Skeletal System: Support

The skeleton provides a rigid framework that supports the body and bears its weight

Functions of the Skeletal System: Protection

Bones protect vital organs; for example, the skull protects the brain, the rib cage protects the heart and lungs, and the vertebrae protect the spinal cord.

Functions of the Skeletal System: Storage

Bones store essential minerals such as calcium and phosphate, which can be released into the bloodstream as needed. Fat is also stored in yellow bone marrow.

Functions of the Skeletal System: Blood Cell Production

Red bone marrow produces red blood cells, white blood cells, and platelets through a process called hematopoiesis.

Functions of the Skeletal System: Movement

Bones act as levers, and joints allow movement when skeletal muscles contract

Bones Composition

• Solid matrix of living cells and collagen fibers

• Bones are classified by their shape:

  • Long Bones

  • Short bones: roughly cubed shape

  • Flat bones: thin and flattened

  • Irregular bones: complex shapes

  • Sesamoid bones: Small bones embedded in tendons

Anatomy of a Long Bone

• Diaphysis: The shaft of the bone

• Epiphyses: The expanded ends of the bone

• Epiphyseal plate (growth plate): A layer of hyaline cartilage between the diaphysis and epiphysis that allows for bone growth during childhood and adolescence

• Articular cartilage: Covers the epiphyses, reducing friction and absorbing shock at joints

The Diaphysis

• Contains a medullary cavity

  • Holds red bone marrow in children (stays in hematopoiesis)

  • Replaced by yellow bone marrow (stores fat)

Compact Bone

• Dense and Strong, found beneath the periosteum

• Forming the outer layer of bones

• Cylindrical units called osteons

  • Consists of lamellae (concentric circles)

  • Lamellae surround the Haversian canal (containing blood vessels and nerves)

  • Haversian canals are connected by Volkmann’s canals

Spongy Bone

• Found at ends of long bones and inside flat bones

• Consists of a lattice of trabeculae (little beams)

  • Found along lines of stress for perfect resistance to compression

• Between the trabeculae, space contains marrow and blood vessels

Periosteum

Tough connective tissue membrane covering the outer surface of bones. It is essential for bone growth, repair, and muscle attachm

Osteocytes

• Mature bone cells make up the majority of the bone structure

• Canaliculi connects all bone cells (receive nutrients and remove wastes)

Osteoblasts

Bone-forming cells that produce new bone matrix

Osteoclasts

Bone-resorbing cells that break down bone tissue

Bone Formation

• Embryo’s skeleton is made of cartilage

• Osteoblasts start at third month (ossification)

  • Cartilage is replaced by bone (secretes mineral)

• Osteoblasts mature into osetocytes

Ossificiation

Calcium and minerals is incorporated into cartilage to become bone

Two hormones control

• Bone remodeling is a continuous process regulated by calcium levels in blood

• Parathyroid Hormone (PTH): Increases blood calcium by stimulating bone resorption

• Calcitnonin: Lowers blood calcium by promoting bone formation

Bone Composition: Organic

• 35% Osteoid (made of ground substance & collagen)

• Provides the flexibility & tensile strength required to keep bones from constantly breaking.

• Lack of collagen causes “Brittle Bone Disease”

Bone Composition: Inorganic

• 65% mineral salts

• Crystalline salts made of hydroxyapatites

  • Ca₁₀(PO₄)(OH)₂

• Provides bone strength & hardness

• Lack of hydroxyapatite causes “Rickets”

Four Stages of Bone Repair

1. Hematoma formation: Blood vessels break, forming a clot and initiating inflammation.

2. Fibrocartilaginous callus formation: New blood vessels and cartilage stabilize the fracture.

3. Bony callus formation: Spongy bone replaces cartilage.

4. Bone remodeling: Compact bone replaces spongy bone, restoring the medullary cavity.

What are the 2 major sections of the skeleton?

Axial Skeleton and Appendicular Skeleton

Axial Skeleton

• 80 bones

• Central axis of the body

• Skull, ribs, sternum, and vertebrae

Appendicular Skeleton

• 126 bones

• Pectoral and Pelvic girdles

• Bones of the arms, legs, pelvis, and shoulders

The Skull

• 22 bones

  • Cranial Bones and Facial Bones

• Protect the brain, support the facial structure

• House the special sense organs

• Most skull bones are joined together by immovable joints called sutures

Cranial bones

The cranium encloses and protects the brain. It is composed of eight cranial bones

Facial Bones

The facial skeleton consists of 14 bones that form the framework of the face, support the teeth, and shape the nasal and oral cavities.

Sutures

• Fibrous joints that tightly connect the bones of the skull

• coronal, sagittal, lambdoid, and squamous structures

Fontanels

• In infants, sutures are separated by flexible connective tissues

• Allow skull growth and deformation during childbirth

• Fontanels gradually ossify as skull develops

Paranasal Sinuses

• Skull bones containing air-filled spaces

• Frontal, maxillary, sphenoid, and ethmoid bones

• Reduce weight of skull, help warm and humidify inhaled air

• Contribute to voice resonance

Vertebral Column

• Vertebral column extends from skull to pelvis

• Protects spinal cord

• consists of 33 vertebrae at birth

33 Vertebrae’s

• Cervical (7)

• Thoracic (12)

• Lumbar (5)

• Sacral (5 fused)

• Coccygeal (4 fused)

Fibrous Joints

• Immovable or slightly movable

• Held together by fibrous connective tissue

Cartilaginous Joints

• Immovable or slightly movable

• Held together by cartilage

Synovial Joints

• Highly movable

• Contain synovial fluid for frictionless movement

What is the structure of synovial joints?

• Joint capsule filled with synovial fluid surrounds the end of the bones

• A synovial membrane and articular cartilage line the joint cavity

• Ligaments attach the bones of the joint

Ligaments

connect bone to bone

What are the types of Synovial Joints?

• Pivot Join (between C1 and C2 vertebrae)

• Hinge Joint (elbow)

• Ball & Socket Joint (hip)

• Saddle Joint (between trapezium carpal bone & first metacarpal bone)

• Condylar joint (between radius and carpal bone of wrist)

• Gliding joint or plane joint (between tarsal bones)

Bone Fractures

Disruption in the continuity of bone tissue that occurs when a bone is subjected to forces greater than it can withstand. May result from acute trauma, repetitive stress, or underlying disease processes that weaken bone structure