HKIN 473 BONES

Kim Bryce Lisa Maralyn D’Alice Jae Callan Derick Dan Wendy

BONES -Functions of Bones

1) Support:- framework, without bones our bodies would be in a lump or a blob

figure-support for soft tissue-provides structures for muscle origins and insertions to attach to

2) Protection:-keeps internal organs safe

examples: skull protects brain ribs protect the heart and lungs vertebrae protect the spinal cord

-protects from fractures being worse, from continuous large forces exerted by muscles3) Assisting in Movement:

-muscle origins and insertions attach to bones-when muscles contract they move the bones, thus creating

movement

4) Storage of Minerals:-97% of the body’s calcium is stored in bones-also is main storage for phosphorus-releases needed minerals into the blood and distributes them-this maintains a crucial homeostasis

5) Production of Blood Cells:-in certain bones (ex. Pelvis, sternum, ribs, vertebrae, condyles of humerus and femur) connective tissue called red bone marrow exists

--usually exist in spongy bone-red bone marrow goes through a process called hemopoiesis (hemo- =blood, poiesis = making)-red bone marrow produces red blood cells (erythrocytes)white blood cells (leukocytes)platelets6) Storage of Chemical Energy:

-as we age most of our marrow changes from red to yellow-yellow bone marrow mainly contains adipose cells which contain

triglycerides(fat cells for energy)-yellow bone marrow is usually found in the medullary cavity

Types of Bones Long Bones Clavicle, humerus, radius, ulna, femur. Shaft - the diaphysis, a thick layer of compact bone surrounding bone marrow cavity. Ends- metaphysis and epiphysis-compact bone covering spongy inner bone. Periosteum covers the outside of

bone. Body support and provide interconnected set of levers and linkages allowing movement. Strongest when

force is on the long axis. Beam shaped to handle the bending loads. Short Bones Carpals of the hand, tarsals of the foot. Consists of spongy bone with compact covering. Role in shock absorption and force transmission Flat Bones Ribs, ileum, sternum, scapula. Two layers of compact bone w spongy and marrow. Protect internal structures and offer broad surface for muscular attachment Irregular Bones Skull, pelvis, vertebrae. Spongy bone with thin compact bone exterior Support weight, dissipate loads, protect spinal cord, aid mvmt, site for muscle attachment Sesamoid Bones Patella, bones in thumb, at base of 1st metatarsal Short bone embedded in tendon or joint capsule Alter angle of insertion of the muscle.

Strength and Stiffness

There are 2 types of bone tissue: Compact bone tissue Soft bone tissue

Compact Bone

Contains very few spaces Forms external layer of all

bones Most of the diaphyses of

long bones are long bones Resist stresses produced by

weight and movement Osteons are aligned in the

same direction along lines of stress

Compact Bone Continued

In the shaft, osteons are parallel to the long axis of the bone

As a result, the shaft resists bending or fracturing when considerable for is applied from either end

Compact bone is thickest where stresses are applied in relatively few directions

The lines of stress in a bone are not static They change in response to repeated strenuous

physical activity

Osteon

Spongy Bone

Does not contain osteons Instead, it consists of trabeculae

An irregular latticework of thin columns of bone Tend to be located where bones are not heavily stressed, or

stressed from many directions Makes up most of the bone tissue of short, flat and irregular

shaped bones The trabeculae are precisely orientated along lines of stress

This helps bone resist stresses and transfer force without breaking

Spongy Bone

Load

The skeletal system is subject to a variety of forces as bone is loaded in different directions

Loads: produced by weight bearing, gravity, muscular forces and external forces

Forces applied to bone dictate the deposition pattern of bone

Types of Load

Compression Tension Shear Bending Torsion

Compression

Presses ends of bone together

Produced by muscles, weight bearing, gravity or external loading

Bone absorbs maximal stress on a plane perpendicular to the compressive load, therefore shortening and widening the bone

Tension

Applied to bony surface, pulls and stretches bone apart

Bone lengthens and narrows

Source is usually muscle tendon (pulling)

Collagen in the bone rearranges and aligns in line with the tensile force

Shear Forces

Applied parallel to the surface of an object Creates internal angular deformation Can occur with compressive forces, tension

forces or both Most destructive force because bone is

anisotropic

Bending Forces

Applied to an area having no support offered by the structure

Causes the bone to bend…..(obviously)

Torsional

Twisting force creates a shear stress over the entire bone

Magnitude of the stress increases with distance from the axis of rotation

Bone Response

As described by Wolff’s law different bones and different sections of a bone will respond to tension and compression forces differently.

StressStress is a force and is categorized based on it’s direction with respect to the cross-section of an object.

2 types of stress

1. Normal Stress

2. Shear Stress

Normal Stress

- acts perpendicular to the cross-section of the loaded object

Shear Stress- acts parallel to the cross-section of the

loaded object

Stress vs. Strain

Strain is a direct result of stress Normal stress produces normal strain Shear stress produces shear strain

Normal Vs. Shear Strain

Normal Strain produces a change in length

Normal Vs. Shear Strain

Shear Stain produces a change in angle

Bone Remodeling

There are three major ways in which bone structure may be changed.

1. Osteogenesis 2. Modeling 3. Remodeling

Physical Activity vs Bone Remodeling

Bones continually undergoes remodeling to adapt to the stresses generated by physical activity by replacing old bone with new bone.

Ordinary activity causes microscopic cracks in the bone, and these are dissolved and replaced with new bone.

Remodeling allows bone to respond to changes in mechanical forces (Wolff's law). Exercise can increase the diameter and strength of bone; inactivity can decrease them.

For example

Dominant arm of professional tennis player have thickness that are 35% greater than the other arm.

Osteocytes

Two main types of cells are responsible for bone renewal:

osteoblasts involved in bone formation

osteoclasts involved in bone resorption.

Osteocytes

Bone remodeling appears to be governed by a feedback system in which the bone cells sense the state of strain in the bone matrix around them and either add or remove bone as needed to maintain the strain within normal limits. The process or processes by which the cells are able to sense the strain and the important aspects of the strain field are presently unknown.

Bone formation and resorption are influenced by many other factors like:

Hypergravity, Stress, Temperature, Pressure, Parathyroid Hormone, Vitamin D, etc.