Unit 4 - Skeletal System

Functions of the Skeletal System

• Supports body though changes from mechanical stress

• Protects small organs

• Attatched skeletal muscles allow movement.

• Stores calcium, phospherous, and fat

• Hematopoiesis (Blood Formation)

Long Bones

Longer than wide, shaft with enlarged ends, contains mostly compact bones and spongy ends, most bones of limbs

Short Bones

Cube shaped, contains mostly spongy bone with outer compact layer, Carpals and Tarpals.

Sesamoid bones

Type of short bone that form within tendons like the patella

Flat Bones

Thin, flattened, usually curved, two thin layers of compact bone sandwich a layer of spongy, most bones of skull

Irregular Bones

Irregular shape, like vertebrae and hip bones

Diaphysis

Makes up long bone length and composed of compact bone

Periosteum

Outside covering of the Diaphysis, fibrous connective tissue membrane, perforating fibers secure it to the underlying bone

Epiphysis

Ends of long bone composed of mostly spongy tissue enclosed by a thin layer of compact bone

Articular Cartilage

Covers external surface of epiphysis, made up of hyaline cartilage to decrease friction at joint surfaces

Articular

Forming Joints

Epiphyseal Plate

Flat plate of hyaline cartilage in young bones, cause lengthwise growth of long bones

Epiphiseal Line

Remnant of epiphyseal plate, seen in adult bone

Endosteum

Lines inner surface of the diaphysis and made of connective tissue

Medullary Cavity

Cavity inside the diaphysis, contains yellow marrow in adults and red marrow for blood cell formation in infants

Yellow marrow

Adipose tissue

Anatomy of spongy bone

Composed of trabeculae and open spaces filled with marrow, blood vessels, and nerves.

Trabeculae

Needlelike pieces of bone

Osteocytes

Mature bone cells in bone matrix of long bones, maintain and regulates osteons

Lacunae

Cavities in bone matrix that houses osteocytes

Lamellae

Concentric circles of lacunae situated around central canal

Central Canal

Opening in center of osteon, runs lengthwise and carries blood vessels and nerves

Osteons

Unit of bone containing central canal and matrix rings, structural and functional unit

Canaliculi

Tiny canals in osteons, radiate from central canal to lacunae, form transport system connecting all bone cells to nutrient supply.

Perforating Canal

Perpendicular to central canal and carries blood vessels and nerves

Bone Functions

Lightweight and resists tension and other forces and made of organic parts (Collagen fibers) of the bone make it flexible and have great tensile strength, calcium salts make it hard to resist compression.

Osteoblasts

Builds new bone tissue

Osteoclasts

Reabsorbs bone to free calcium

Osteogenic Cells

stem cells capable of differentiation into bone cells

Ossification

Bone formation

Bone formation

Occurs on or within hyaline cartilage models endochondral or fibrous membrane

Endochondral Ossification

1. Osteoblasts cover hyaline cartilage modal with bone matrix

2. In a fetus, enclosed cartilage is digested away by chondraclasts

Appositional Growth

Bones grow in width/density, osteoblasts in the periosteum add bone matrix to outside of diaphysis, and osteoclasts in the endosteum remove bone from the inner surface of the diaphysis

Bone remodeling causes

1. Calcium ion levels in the blood determines when bone matrix is to be broken down or formed

2. Pull of gravity and muscles on the skeleton determines where bone matrix is to be broken down or formed

Parathyroid Hormone

Released when calcium ion levels in blood are low and activates osteoclasts to break down ones and release calcium ions into blood

Hypercalcemia 

High blood calcium levels prompts calcium storage to bones by osteoblasts via calcitonin

Steroid Hormones

Sex hormones that stimulate osteoblasts and conversion of epiphyseal plate to line

Human Growth Hormone

Stimulates osteoblasts released after mechanical stress on bones

Remodeling - Exercise

Mechanical stress stimulates osteoblasts, exercising people can have 20% more bone density than non-exercisers, and resistance training can provide a stronger stimulus than endurance exercise

Remodeling - Nutrition

Calcium obtained via diets, vitamin D required to absorb calcium in small intestines

Sources of Calcium

Milk, dairy, green leafy vegetables, brassicas, cruciferous vegetables, nuts, beans, seeds, and shellfish

Sources of Vitamin D

Juices, dairy, cereals/grains, most is produced by integumentary system with given exposure to sunlight. 

Fracture

Break in bone

Closed fracture 

Break that doesn’t break skin

Opened fractures

Break that does break skin

Closed reduction

Bones manually coaxed into position via physicians hands

Open reduction

bones secured with pins or wires during surgery

Fracture Healing Step One

Hematoma (blood-filled swelling or bruise) forms

Fracture Healing Step Two

Fibrocartilage callus forms, cartilage matrix, bony matrix, and collagen fibers splint the bone

Fracture healing Step Three

Bony Callus replaces fibrocartilage callus where osteoclasts move in

Fracture Healing Step Four

Bone remodeling occurs in response to mechanical stress

Joints

Articulations where two bones meet and holds them together which allow for mobility

Synarthroses 

Immovable Joints

Amphiarthroses

Slightly movable joints

Diarthroses

Freely movable joints

Fibrous joints

Synarthroses joints united by fibrous tissue like sutures and syndesmobes

Sutures

Immovable joints found in cranium

Syndesmoses

Allow more movement that sutures but still immobile, found on distal ends of fibula and tibia

Cartilaginous Joints

Amphiarthroses joints connected by fibrocartilage like synchondrosis and symphysis 

Synchondrosis

Immobile joints found in epiphyseal plates

Symphysis

Slightly movable joints found in the pubic symphysis and intervertebral joints

Pubic Symphysis

Between two halves of pelvis

Synovial Joints

Diarthroses Joints with articulating bones separated by joint cavity filled with synovial fluid

Distinguishing features of Synovial Joints

1. Articular Cartilage

2. Articular Capsule

3. Joint Cavity

4. Reinforcing Ligaments

Bursae

Flattened fibrous sacs lined with synovial membranes and filled with synovial fluid that cushion the bone or tendon at the joint

Tendon Sheath

Elongated bursa that wraps around tendon