Skeletal System

• Support

• Protecction

• Movement

• Blood Cell Formation

• Storage

FUNCTIONS OF THE SKELETAL SYSTEM (5)

Support

Forms internal framework that supports the body and cradles its organs

Protection

Bones protect soft body organs

Movement

Skeletal muscles attached to bones by tendons, use bones as levers to move body and its

parts

Blood Cell Formation

Process by which body produces blood cells which occur in red bone marrow, the spongy tissue found inside bones (cavities of spongy bone)

• Stem Cells

• Differentiation

• Maturation and Release

Process of Blood Cell Formation

Stem Cells

Starts with hematopoietic stem cells (hemocytoblasts) in the bone marrow ("father cell", potential to become any type of blood cell).

Differentiation

also called Progenitor cells

RBC (Erythrocytes)

Oxygen from lungs to rest of body. Regulated by hormone erythropoietin (EPO).

WBC (Leukocytes)

Fights infections. If WBC high, infection is present; regulated by cytokines

Platelets (Thrombocytes)

Help with blood clotting, stops wound from bleeding; regulated by thrombopoietin.

Maturation and Release

Cells matured and released into bloodstream. Hematopoiesis adjusts to meet the body's needs.

35% organic and 65% inorganic material

Mature bone matrix is normally about ________ and __________

Osteoprogenitor Cells

Stem cells that undergo mitosis to develop into osteoblasts.

Osteoblasts

Maker of new bone tissue, produce bone matrix (osteoid: collagen &

proteoglycans). Responsible for Ossification (Osteogenesis).

Osteocytes

Mature osteoblasts (account for 90–95% of bone cells, life span up to 25

years). Housed within bone matrix in spaces called lacunae. Cell

extensions are housed in narrow, long spaces called canaliculi (nutrients

and gases pass through fluid surrounding cells). Monitor and maintain

bone structure.

Osteoclasts

Bone-destroying cells; break down damaged bones / old bone in a

process called bone resorption. Massive, multinucleated cells derived from red bone marrow cells (white blood cell lineage). Develop a ruffled

border in a sealed compartment; secrete acid and protein-digesting

enzymes that digest bone matrix, releasing Ca²⁺ into the bloodstream.

Compact Bone

Heavy, tough, compact in nature; solid outer layer surrounding each bone

Spongy Bone

Found in long bones, surrounded by compact bone. Consists of interconnecting rods or plates of bone called trabeculae. Spaces between trabeculae are filled with red or yellow bone marrow and blood vessels.

• Long Bones

• Short Bones

• Flat Bones

• Irregular Bones

4 Shapes of Bones

Long Bones

Longer than they are wide; enhance function in movement of appendages. Femur (longest bone), tibia, fibula, humerus, radius, ulna, metacarpals, metatarsals, phalanges.

Short Bones

Short, cubelike; approximately as wide as

they are long. No cavity, mostly spongy inside with thin layer

of compact outside. Transfer force between long bones.

Carpals (wrist) and tarsals (ankle).

Flat Bones

Flat, platelike, thin. No cavity; sandwich of

compact bone with spongy bone inside. Cranial skull bones,

ribs, sternum, scapula, pelvis.

Irregular Bones

Weird shaped, complex; no cavity, spongy inside enclosed with compact bone. Specialized

functions (protection/bending). Vertebrae, facial bones, jaw (mandible).

Sesamoid Bones

Small bones embedded in tendons (e.g.,Patella / kneecap)

• Diaphysis

• Epiphysis

• Metaphysis

Structure of a Typical Long Bone

Diaphysis

Shaft / center portion of the long bone; composed primarily of compact bone surrounding the hollow center.

Epiphyses

Expanded ends of a long bone attached with other bones; mostly spongy bone with an outer

layer of compact bone.

Metaphysis

Flared region where growth line is located; between growth plate and shaft

Epiphyseal Plate

Plate of hyaline cartilage found in children and adolescents located between epiphysis and

diaphysis; where bone grows in length

Epiphyseal Line

Bony scar/line formed when bone stops growing in length and the epiphyseal plate becomes ossified (closure between 12 and 25 years old).

Medullary Canal

Central hollow space in diaphysis where red bone marrow (in youth) / yellow bone marrow

(fats, in adults) is stored.

Periosteum

Double-layered connective tissue membrane covering outer surface of bone (except joints/articular cartilage). Outer

layer contains blood vessels and nerves; inner layer contains osteoblasts and osteoclasts. Helps in bone elongation, modeling,

and growth development. Attached by perforating (Sharpey's) fibers

Endosteum

Single cell layer membrane that lines internal surfaces of all cavities within bones (surface of medullary cavity,

trabeculae of spongy bone). Includes osteoblasts and osteoclasts.

Articular Cartilage

Thin layer of hyaline cartilage covering ends of long bones within joints; provides smooth lubricated surface

for articulation and reduces friction

Osteoblasts and Osteoclasts

the osteocytes that make up bone tissue

• Intramembranous Ossification

• Endochondral Ossification

Types of Ossification (Osteogenesis)

Intramembranous Ossification

Formed in sheet-like layers that resemble membranes (starts within embryonic

connective tissue membranes).

membrane-like

Endochondral Ossification

Starts with hyaline cartilage model to mostly long bones (compact & spongy bone).

• Hematoma formation

• Fibrocartilaginous Callus

• Bony Callus Formation

• Bone Remodeling

Stages of Healing in Bone Fracture (4)

• Synarthrosis

• Amphiarthrosis

• Diarthrosis

Functional Classification (Movement of Joints) (3)

Synarthrosis

Immovable joint. Mostly fibrous joints (e.g., sutures of skull)

Amphiarthrosis

Slightly movable joint. Mostly cartilaginous joints (e.g., intervertebral discs, pubic

symphysis).

Diarthrosis

Freely movable joint. Includes all synovial joints (shoulder, elbow, wrist, knee).

• Fibrous Joints

• Cartilaginous Joints

• Synovial Joints

Structural Classification of Joints

Fibrous Joints

Immovable / joined by dense regular connective tissue, rich in collagen, no joint cavity)

Sutures

Syndesmosis

Gomphosis

Fibrous Joints (3)

Sutures

Immovable joints between skull bones; interlocking edges bound by dense fibrous tissue

Syndesmosis

Fibrous joint between two parallel articulating bones separated by some distance (e.g., fibrous interosseous

membrane connecting distal radius-ulna and tibia-fibula).

Gomphosis

Peg-and-socket joint between teeth and alveolar process of mandible/maxilla held by periodontal ligaments.

Cartilaginous Joints

Joined by cartilage, allow some / slight movement, no joint cavity

Acetabulofemoral joint

Hip Joint

Acetabulum of coxal bone + Head of femur.

Glenohumeral joint

Shoulder Joint

Glenoid cavity of scapula + Head of humerus.

Tibiofemoral joint

Patellofemoral joint

Knee Joint Articulations (2)

Tibiofemoral joint

Femur + Tibia

Patellofemoral joint

Femur + Patella

Humeroulnar joint

Humeroradial joint

Proximal radioulnar joint

Elbow Joint Articulations (3)

Humeroulnar joint

Humerus (trochlea) + Ulna (trochlear notch)

Humeroradial joint

Humerus (capitulum) + Radius (head).

Proximal radioulnar joint

Proximal articulation of Radius + Ulna.