Skeletal System

Technically organs; contain more than one type of tissue

Average number of bones

206 total bones on average

Bone tissue composition

Mostly osseous (bone) tissue; also cartilage, muscle, nervous, and epithelial tissue

Bone tissue activity

Active connective tissue constantly breaking down, regenerating, and repairing itself

Skeleton renewal

You need a new skeleton every 7–10 years

Support and scaffolding

Function of the skeletal system

Movement

Ability to move around

Mineral storage

Stores calcium, phosphorus, and other minerals

Neuron and muscle function

Needed to keep neurons going and muscles contracting

Homeostasis

Maintain homeostasis

Blood calcium regulation

Regulating blood calcium levels

Osteocalcin

Hormone produced by bones

Osteocalcin function

Regulates bone formation; protects against glucose intolerance and diabetes

Hematopoiesis

Blood cell production

Axial bones

80 bones divided into the skull, vertebral column, and thoracic cage

Axial skeleton function

Carry other body parts; provide skeleton support; organ protection

Appendicular bones

Everything else

Appendicular skeleton function

Bones that help us move around

Long bones

Example: Fibula, Tibia

Short bones

Bone shape type

Flat bones

Bone shape type

Irregular bones

Bone shape type

Compact bone

Dense smooth external layer of bone

Cortical bone

Another name for compact bone

Spongy bone

Porous area of bone

Trabeculae

Tiny cross-hatching supports in spongy bone

Trabeculae function

Help the bone resist stress

Bone marrow location

Found in spongy bone

Red bone marrow

Produces blood cells

Yellow bone marrow

Stores energy as fat

Epiphyses

Tips of long bones where spongy bone and red marrow are concentrated

Diaphysis

Long bone’s shaft

Medullary cavity

Hollow cavity in the diaphysis filled with yellow marrow

Osteons

Cylindrical, weight-bearing structures that run parallel to the bone’s axis

Osteon structure

Tubes inside of tubes

Lamellae

Concentric (circular) tubes of osteons

Collagen fibers

Fill lamellae and run in the same direction

Alternating lamellae pattern

Neighboring lamellae run in different directions

Torsion resistance

Helps resist torsion stress

Central canals

Hold nerves and blood vessels

Lacunae

Tiny spaces between layers of lamellae

Osteocytes

Mature bone cells housed in lacunae

Osteocyte function

Monitor and maintain the bone matrix

Osteoblasts

Bone makers

Cartilage origin

Bone tissue starts off as cartilage

Osteoblast secretion

Collagen and enzymes that absorb calcium, phosphate, and other minerals

Calcium phosphate

Minerals that crystallize to form bone matrix

Bone matrix composition

1/3 mineral, 2/3 protein

Osteoclasts

Bone breakers

Bone remodeling

Process maintained by osteoblasts and osteoclasts

Fracture detection

Osteocytes detect tiny fractures

Chemical signaling

Osteocytes release chemical signals to direct osteoclasts

Resorption

Osteoclasts dissolve calcium phosphate and release components into the blood

Rebuilding

Osteoblasts rebuild bone

Apoptosis

Osteoclasts self-destruct

Exercise effect

Stimulates bone remodeling and bone strength

Low gravity effect

Osteoclast resorption increases; osteoblast formation decreases

Joints (articulations)

Meeting places between two or more bones

Structural classification

What joints are made of / material binding bones

Fibrous joints

Bones connected by dense fibrous connective tissue; don’t move

Cartilaginous joints

Bones united by cartilage; don’t move very much

Synchondroses

Type of cartilaginous joint

Symphyses

Type of cartilaginous joint

Synovial joints

Freely moveable joints

Articular cartilage

Covers opposing bone surfaces

Ligaments

Bandlike structures in synovial joints

Joint cavity

Space within synovial joint

Synovial fluid

Lubricant

Fibrous joint capsule

Encloses synovial joint

Sensory nerves and blood vessels

Found in synovial joints

Plane joints

Gliding movement

Gliding movement

Flat bone surface glides over another

Hinge joints

Uniaxial movement

Flexion

Bending that decreases joint angle

Extension

Bending that increases joint angle

Hyperextension

Dangerous overextension

Condylar joints

Biaxial movement

Abduction

Movement away from the body

Adduction

Movement toward the body

Circumduction

Circular movement

Ball-and-socket joints

Multiaxial movement

Rotation

Bone turns around its axis

Saddle joints

Opposition movement

Pivot joints

Supination and pronation

Supination

Rotation forward or anteriorly

Pronation

Rotation backward or posteriorly

Function classification

What joints do and how much they move

Synarthroses

Non-moving joints

Amphiarthroses

Partly-moving joints

Diarthroses

Fully moveable joints

Diarthroses location

Mostly found in limbs

Exoskeleton

Outside skeleton

Endoskeleton

Inside skeleton

Skeletal support

Supports and framework for movement

Organ protection

Protects vital organs

Storage function

Storage of calcium and hematopoiesis

5 primary skeletal functions

Support; storage of minerals and lipids; blood cell production; protection; leverage

Bone classification

Shape; internal tissue organization; bone markings

Flat bones

Shape of bones

Long bones

Shape of bones

Short bones

Shape of bones

Irregular bones

Shape of bones

Structure of a long bone

Diaphysis and epiphysis

Diaphysis

Shaft with compact bone and medullary cavity

Epiphysis

Wide ends; articulation with other bones; mostly spongy bone; covered with compact bone