1. As we know bone is a hard tissue so in comparison to other tissues the vascularization and how it gets nutrients in general is unique and different from any other part of human body. A bone is blood supplied by three different systems, these are: Nutrient artery, Periosteal vessel, and epiphyseal vessels. The first layer covering any bone tissue is periosteum. Periosteum is a thin membrane, covering the outer surfaces of all bones. It contains an extensive network of blood vessels, and it’s small branches penetrate into the bone through minute channels, these branches supply the outer ⅓ of cortex. Endosteum also plays the same role with this difference that it is the lining for medullary cavity and haversian canal.
We should remember that long bones have a compact and an spongy section. Compact section, as you can see in the picture, is basically made of osteon which is the fundamental functional unit.
Osteon has the lamellae around itself and in the center of osteon central canal is located which contains vascularities and nerve branches. We know that between each layer of lamellae there are small spaces which are called lacunae, and therefore the tiny canals that project outward and in all directions from it are called canaliculi. Canaliculi contain osteocyte processes which supply oxygen and nutrients to osteocytes. And the spongy section of the bone. It is consist of trabecula which is an irregular latticework of thin bone plates, and between these plate lacunae lie exactly where the osteocytes are nourished by circulation of blood in bone marrow.
2. What is joint? Joint is connection of 2 or more bones. According to this definition we can assume that the joints might be movable, partially movable, and immovable. Synarthrosis is the type of joint that you can see in skull structure, this type of joint allows little or no movements.
Partially movable or amphiarthroses which allow slight movements. For example intervertebral disks which consist of cartilage pad, a fibrous capsule which holds vertebrae and cartilage together and in one place, in such joints the cartilage has a shock absorber role either.
And finally the movable joints or so called diarthroses, which can move freely but the movement still depends on articulating surface and the elastic ligaments which hold them together. These joints are unique because of their structure, in these joints we can see articular cartilage, articular capsule, capsular ligaments, synovial fluid and the synovial membrane plus the blood vessels and sensory nerves which create a unique structure which we can not see in other joints.
The hip joint is stronger due to the fact that is designed to bear weight and retain stability and strength, but on the other side shoulder is designed for movements that are beyond the hip joint movements and also it is not as strengthened as the hip joint.
3. Cytoplasm in muscle cells is called sarcoplasm and but unlike other cells it has it’s own unique structure, it houses large amounts of glycosomes, myoglobin and an oxygen binding protein
4. Basically many pathological factor may cause such an inhibition but in general we can classify them in three main groups.
Any problem with innervation of a muscle, no message no movement.
Lack of calcium. we know that an adequate amount of calcium in sarcoplasmic reticulum is essential. Not enough calcium no contraction.
Any ion imbalance in or out of the cell may terminate sodium channel activity and may cause abnormal opening or closing which finally terminates the action potential. No action potential, no contraction.
5. Osteoporosis is the situation when the density of the bone tissue is reduced due to factors such as age or malnutrition, in this situation the bone is weaker and fracture is much common, but in osteoarthritis, the problem is in the joint not the bone itself. It is characterized with loss of cartilage in a joint and subsequent overgrowth and remodeling of the adjacent bone. Remember that osteoporosis is a result of general metabolic condition but osteoarthritis is local non-inflammatory process in one or a group of specific joints.
References
Hearne, C., & Gale, J. (2013, October 8). What Is the Diaphysis?. WiseGeek. Retrieved October 25, 2013, from http://www.wisegeek.com/what-is-the-diaphysis.htm
Vascular supply and circulation. (n.d.). Encyclopedia Britannica Online. Retrieved October 25, 2013, from http://www.britannica.com/EBchecked/topic/72869/bone/41885/Vascular-supply-and-circulation
periosteum (anatomy). (n.d.).Encyclopedia Britannica Online. Retrieved October 25, 2013, from http://www.britannica.com/EBchecked/topic/451978/periosteum
Joints. (n.d.). mccc.edu. Retrieved October 26, 2013, from http://www.mccc.edu/~behrensb/documents/Joints2bjb_000.pdf
Human Physiology - Muscle. (n.d.). Human Physiology - Muscle. Retrieved October 25, 2013, from http://people.eku.edu/ritchisong/301notes3.htm
