Unit 2 Concepts 1

12th Grade

Skeletal system

Made of 206 bones, cartilage, ligaments, and joints

Bone

A rigid but living organ made of all 4 types of tissue

Connective tissue in bone

Mostly osseous tissue, with cartilage and dense connective tissue covering the outside

Nervous tissue in bone

Found in nerves

Epithelial tissue in bone

Found in blood vessels that provide nourishment

Muscle tissue in bone

Skeletal muscle tissue

Skeletal system body weight

About 1/5 of a healthy person's body weight

Babies' bones

Babies have about 270 bones that fuse as they grow

Skeleton regeneration

The skeleton is constantly rebuilding itself, with a whole new skeleton approximately every 7–10 years

Main functions of skeletal system

Support, protection, movement, storage, blood cell formation, hormone production

Support

The skeleton provides a framework that holds up the entire body

Protection

The skeleton protects vital organs, such as the skull protecting the brain and rib cage protecting the heart

Movement

Skeletal muscles attach to bones through tendons and use bones as levers at joints to create movement

Storage

Bones store minerals such as calcium and phosphate and can release them into the blood when needed

Yellow bone marrow

Stores energy in the form of fat

Blood cell formation

Hematopoiesis

Hematopoiesis location

Occurs in red bone marrow of certain bones

Hormone production

Bones help maintain homeostasis

Osteocalcin

A hormone produced by bone that helps regulate insulin secretion, glucose regulation, and energy usage

Bone classification

Bones are classified by location and shape

Axial vs appendicular skeleton

Bones can be classified by whether they belong to the axial or appendicular skeleton

Bone shape and function

A bone's shape dictates its function

4 main bone types

Long, short, flat, and irregular bones

Long bones

Longer than they are wide

Long bone structure

Usually have a long shaft with wider ends

Long bone location

Mostly found in the limbs

Long bone function

Act as levers to aid movement

Long bone examples

Humerus, radius, ulna, metacarpals, phalanges, femur, tibia, fibula, metatarsals

Short bones

More cube-shaped and tend to be as wide as they are long

Short bone function

Provide support and stability with little movement

Short bone examples

Carpals in wrists and tarsals in ankles

Sesamoid bones

A special type of short bone embedded within tendons

Sesamoid bone example

Patella

Flat bones

Thin and flat, often with some curvature

Flat bone function

Provide a large surface area for muscle attachment

Flat bone examples

Sternum, scapulae, ribs, and most cranial bones

Irregular bones

Bones that do not fit into the other categories

Irregular bone structure

Have highly specialized shapes and structures

Irregular bone examples

Hip bones and vertebrae

Compact bone

Dense and smooth bone tissue on the outside of a bone

Spongy bone

More porous bone tissue found inside bones

Bone structure

Most bones have an outer layer of compact bone surrounding inner spongy bone

Water in bone

About 22% of bone is water

Bone strength

Bone is strong like steel but lightweight like aluminum and somewhat flexible

Osteon

The basic structural unit of compact bone

Osteons

Long cylinders that act as tiny weight-bearing pillars

Lamellae

Hollow tubes arranged in layers around the central canal of an osteon

Lamellae function

Contain salts and collagen fibers that help bone resist torsion stress

Haversian canal

The central canal running through the middle of an osteon

Haversian canal contents

Contains small blood vessels for nourishment and nerve fibers for signaling

Lacunae

Small gaps between the lamellae that contain osteocytes

Spongy bone organization

Less organized than compact bone

Spongy bone osteons

Spongy bone does not contain osteons

Trabeculae

Tiny bone struts in spongy bone that help resist stress

Bone marrow in spongy bone

Bone marrow is found among the trabeculae

Red bone marrow

Produces blood cells

Yellow bone marrow

Stores energy as fat

Bone markings

Distinct features on the external surface of bones related to muscles and ligaments

3 types of bone markings

Projections, surfaces, and depressions/openings

Bone marking projections

Places where muscles and ligaments attach

Bone marking surfaces

Surfaces that form joints

Bone marking depressions/openings

Openings that allow blood vessels and nerves to pass through

Osteocytes

Maintain healthy bone structure

Osteocyte location

Housed in lacunae between the lamellae

Osteoblasts

Build and construct bone by calcifying bone as it forms

Osteoclasts

Break down and absorb bone tissue during bone remodeling

Osteoprogenitor cells

Active stem cells in the periosteum and endosteum that can differentiate into osteoblasts

Bone lining cells

Found on bone surfaces where remodeling is not occurring and help osteocytes maintain the bone matrix

Osteoblast transformation

Some osteoblasts become osteocytes

Ossification

The process of bone tissue formation

Ossification importance

Forms the skeleton during embryonic development, supports bone growth, and later helps with remodeling and repair

Intramembranous ossification

Bone develops from a fibrous membrane

Intramembranous examples

Clavicle and skull bones

Endochondral ossification

Bone develops by replacing cartilage

Endochondral examples

All other bones

Articular cartilage

Cartilage that remains on the ends of bones

Epiphyseal plates

Areas where bone growth occurs as bones elongate

Bone remodeling

The constant process of breaking down and rebuilding bone

Why bone remodeling is important

Prevents calcium in bones from crystallizing and making bones brittle

Bone remodeling step 1

Osteocytes release chemical signals telling osteoclasts to go to damaged areas

Bone remodeling step 2

Osteoclasts release enzymes that digest calcium phosphate and return calcium and phosphate to the blood

Resorption

The process of osteoclasts breaking down bone tissue and releasing calcium and phosphate into the blood

Bone remodeling step 3

Macrophages promote bone tissue remodeling

Bone remodeling step 4

Osteoblasts build new bone and then undergo apoptosis

Skeleton replaced each year

About 5–10% of the skeleton is replaced each year

Exercise and bone remodeling

Exercise stimulates bone remodeling because stress on bones signals osteocytes to activate osteoclasts

Fracture

A break in a bone

Fracture treatment

Reduction and immobilization

Reduction

Realignment of broken bone ends

Immobilization

Keeping the broken bone stable so it can heal

Bone fracture repair step 1

A hematoma forms from hemorrhaged blood clots after blood vessels are torn

Bone fracture repair step 2

A fibrocartilaginous callus forms across the break and connects the broken ends

Bone fracture repair step 3

Osteoblasts form spongy bone and replace the cartilaginous callus

Bone fracture repair step 4

Bone remodeling occurs