Bone has at least sex functions in the body
1.Support
2. Locomotion
3. Protection
4. Storage of chemicals
5. Nourishment
6. Sound transmission (in the middle of ear)
• The body s muscles attached to the bone through tendons and ligaments (the system of bones plus muscles support the body)
• Bone joints permit movement of one bone with respect to another.
• The skull protect the brain and several of the most important sensory organs (eye and ears), the ribs form protective cage for heart and lungs
• Bones acts as chemical bank for storing element for future use.
Ex. Minimum calcium is needed in the blood if the level falls too law calcium causes parathyroid glands to release more parathormone into blood and this causes bones to release the needed Ca.
. The teeth are specialized bones can cut food and serve nourishment.
Three smallest bones of the body are oscillate in middle air to provide matching system for converting sound vibration in air to sound vibration in fluid in cochlea. They are the only bones that attain full adult size before birth.
Bone consist of two different materials plus water, collagen (organic fraction 40% of the bone weight, 60% of its volume and bone mineral (inorganic 60% of its weight ,40% its volume).
There are large percentage of Ca in the body, it has much heavier nucleus than most elements of the body, it absorbs x-ray much better than surrounding soft tissue.
This the reason x-ray show bones so well, using x-ray scattering indicates that bone mineral crystals are rod shaped of diameter 20-70A? and length 50-100A?
• How strong are your bones?
Let us look at how bones have developed to meet our needs, the approximately 200 bones sort into various piles according to their shapes, so there are five piles:
- Pile of flat, plate-like bones (shoulder blade, some of skull bones
- Long hollow bones (arms, legs, fingers)
- Cylindrical bones from the spine (vertebrae)
- Irregular bones the wrist and ankle
- Ribs that don t belong to the above piles
Trabecular bone is weaker than compact due to the reduced amount of bone in a given volume.
• bone is a living tissue and has a blood supply as well as nerves . It undergoes change destroying old bone and building new one .this continuous process is called bone remodeling. Is performed by specialized bone cells. Osteoclasts destroy bone, osteoblasts build it . Compare to many body process, bone remodeling is slow work , we have equivalent of new skeleton every seven years. Each day osteoclast destroy bone containing of 0.5 g of Ca and osteoblast build the same amount , while the body is young and growing , osteoblast do more than osteoclast , but after 35-40 years old the activity of osteoclast is greater than osteoblast resulting in gradual decrease in bone mass that continuous until death. This decrease is faster in women than in men and lead to weak bones in older women this called osteoporosis result in spontaneous fractures especially in the spine and hips.
• All materials change in length when placed under tension or compression.
• In running, the forces on the hip bone when the heel strikes the ground may be four times the body s weight. In normal walking the force on the hip are twice the body s weight. Exceeding maximum compressive strength of bone is not as dangerous as the same force applied over a longer period of time this property called viscoelasticity.
• The local electrical fields may play a role when bone is bent it generates an electrical charge on its surface called (piezoelectricity) may be physical stimulus for bone growth and repair. Experiments with animal bone fracture have shown that bone heals faster if an electrical potential is applied across the break bone.
• The synovial membrane encase the joint and retains the lubricating fluid . The surface of joints are articular cartilage, a smooth, some what rubbery materials that is attached to the bone
• The lubricating properties depend on fluid viscosity so it decreases under large shear stress in the joint.
• Measurement of bone mineral
• A few years ago, osteoporosis was difficult to detect until a patient appeared with broken hip or crushed vertebra. At that time it was too late to use preventive therapy. The strength of bone depends on the mass of bone mineral present. The physical techniques for studying bones are:
• 1. x-ray image: to measure the bone mineral , its an old one. There are some problems of using x-ray, these are : x-ray beam has different energies and the absorption of x-ray by Ca varies rapidly with energy, scattered radiation when it reaches the film, the film is a poor detector for making quantitative measurements
• The three problems are eliminated by using
• Monoenergetic x-ray or gamma ray source, a narrow beam to minimize scatter, a scintillation detector that detects all photons
• 2. photon absorptiometry technique: the determination of bone mineral mass by using
• MB=K Log (I?/I)
MB: bone mineral:
I?: initial intensity
I : final intensity
k: constant
3. Activation technique:
take the fact that nearly all of calcium in the body is in the bones. The whole body is irradiated with energetic neutrons that convert a small amount of calcium and some other elements into radioactive forms that given off gamma rays, and the emitted gamma rays then detected and counted,the gamma rays from radioactive calcium can be identified by their unique energy.