Bone blog

Something that you should know about bones, is that they have no blood vessels or nerves. That doesn't mean that they won't hurt if you break one though. You're bones are surrounded by the perichondrium that resists outward expansion. There are 3 different types of skeletal cartilage, Hyline, Elastic, and Fibrocartilage. The Hyline Cartilage is the mot abundant skeletal cartilage, and provides support, flexibility, and resilience to your bones. It is present in Articular (covers the ends of long bones), Costal (connects the ribs to the sternum), respiratory (Makes up larynx and reinforces air passages) and nasal (supports the nose) cartilage. The Elastic Cartilage is similar to the Hyaline cartilage but contains elastic fibers and is found in the external ear and the epiglottis. Fibrocartilage is a cartilage that is highly compressed and has great tensile strength. it contains collagen fibers and is found in the menisci of the knee, and in intervertebral discs.

You may no have known, but your cartilage actually grows. it can grow Appositional and/or Interstitial. Appositional is where cells of the perichondrium secrete matrix against the external face of existing cartilage. If it were to grow interstitial, then the lacunae-bound chondrocytes inside the cartilage would divide and secrete new matrix, expanding the cartilage from within. There is something interesting that happens with the bones during a certain time, called calcification. It occurs during normal bone growth, and during old age. Calcification is the process in which calcium salts build up in soft tissue, making it harden into bone.

There are a couple of ways to classify bones in the human body, Axial, and Appendicular. The Axial bones consist of the skull, vertebral column, and rib cage. Whereas the Appendicular bones consists of the upper and lower limbs, shoulders, and hips.  You could also classify bones by their shape, such as the long bone, which is any bone that is longer than it is wide, such as your humerus (bone under bicep).  Then there is the opposite of that, which is the short bone, which has to be cube-shaped (wrists and ankles), or be a bone that has formed inside of a tendon (patella). There is also the flat bone, which are bones that are thin, flat and a bit curved (sternum, most skulls). There are also the Irregular bones, which are bones that have a complicated shape (hip bones and vertebrae).

Bones help people in many different ways. they help to support the body by providing a framework that supports the whole body, and cradles the softer organs. It helps to protect the brain, spinal cord, and other vital organs, which simultaneously providing levers for muscles creating an easier way to move for humans. Bones also store minerals, especially calcium and phosphorus, but they also help with blood cell formations. Seeing as how hematopoiesis occur within the marrow cavities of the bones. So, bones are a vital part of our body, without bones, we could look more like jello...There are some bones that have "markings," such as bulges, depressions, and holes that serve as areas where muscles, ligaments, and tendons can attach themselves. They also might have joint surfaces, and Conduits for blood vessels and nerves. We have named some of the areas where muscles and ligaments attach themselves. These would be Tuberosity, Crest, Trochanter, and Line. The Tuberosity is a rounded projections, and the crest is a narrow, prominent ridge of the bone. Whereas the line is just the narrow ridge of the bone. The trochanter is a large, blunt, irregular surface in the bone. There is also the Tubercle, Epicondyle, Spine, and Process. The Tubercle is a small rounded projection, and the Epicondyle is a raised area above the condyle. The Spine is with sharp, slender projections, and the process is and bones prominence. That brings us to the Head, Facet, Condyle, and Ramus. The head is a bony expansion carried on a narrow neck, and the facet is a smooth, nearly flat articular surface. The Condyle (below the Epicondyle) is rounded auricular projections, and the Ramus is the armlike bar of the bone.  There are approximately six depressions and openings in the body. There is the Meatus (canal-like passageway), the Sinus (cavity within a bone), the Fossa (shallow, basin like depression), a Groove (furrow), a fissure (narrow, slit-like opening), and the legendary Foramen (A round or oval opening through a bone). Out of all these holes and stuff in the body, you tend to wonder what exactly the texture of it is. Well, there is the compact bone, which is the dense outer layer, which is smooth. Then there is the Spongy bone, which is like a honeycomb of Trabeculae filled with yellow bone marrow. The long bones consist of diaphysis and an epiphysis. The diaphysis is a Tubular shaft that forms the axis of long bones, composed of compact bones that surround the medullary cavity. There is some below bone marrow (fat) that is contained in the medullary cavity. The Epiphysis is the expanded ends of long bones, and its exterior is compact bone, whereas the interior is spongey bone. Its join surface is covered with articular (hyaline) cartilage. The Epiphyseal line separates the diaphysis from the epiphysis.

Included with the bones, is the bone membranes, which have the Periosteum and the endosteum. The Perosteum is a double-layered protective membrane, which is an outer fibrous layer which is a dense regular connective tissue. Its inner osteogenic layer is composed of osteoblasts and osteoclasts. As well as being supplied with nerve fibers, blood, and lymphatic vessels, which enter the one via nutrient foramina. The perosteum is secured to underlying bone to Sharpey's fibers. Endosteum is a delicate membrane curing internal surfaces of bone. The Structure of irregular and flat bones include the thin plates of periosteum is covered by compact bone on the outside with endosteum, which is covered by spongy bone on the inside. It has no diaphysis or epiphysis, although it does contain bone marrow between the trabeculae.
Hematopoietic tissue (red marrow) an be found in all people of all ages. In infants it is found in the medullary cavity, and in all areas of spongy bone. In adults it is found in the diplo of flat bones, and the head of the femur and humerus. In the structure of bone, the compact bone has the Haversian system, or the osteon, which is the structural unit of compact bone. There is also the Lamella (weight-bearing, column-like matrix tubes composed mainly of collagen), the Haversian or central canal (central channel containing blood vessels and nerves), and Volkmann's canal (channels lying at right canals to the central canal, connecting blood and nerve supply of the periosteum to that of the haversian canal. There are also Osteocytes (mature bone cells), the Lacunae (small cavities in bone that contain osteocytes), and Canaliculi (hairlike canals that connect lacunae to each other and the central canal). The organic chemical composition of bones include the Osteoblasts (bone-forming cells), Osteocytes (mature bone cells), Osteoclasts (large cells that resorb or break down bone matrix), and Osteoid (unmineralized bone matrix composed of proteoglycans, glycoprotiens, and collagen).  As for the inorganic compostiion of bone, there are Hydroxyapatites,  or mineral salts. They make up sixty-five percent of bone by mass and are made of primarily calcium phosphates. It is also responsible for bone hardness and resistance to compression. The process of bone tissue formation is known as Osteogeness and ossification. They lead to the formation of the bony skeletons in embryos, along with bone thickness, remodeling of the bones, and bone repairs. They help the bones grow until early childhood. The Formation of the boney skeleton, begins at week 8 of embryo development. it includes Intramembranous ossification (bone develops from a fibrous membrane) and Endochondral ossification (bone forms by replacing hyaline carilage). Intramembranous Ossification is the formation of most of the flat bones of the skull and the clavicles. It also has fibrous connective tissue membranes are formed by mesenchymal cells, and has an ossification center appears in the fibrous connective tissue membrane. Bone matrices are sevreted within the fibrous membrane, and is where woven bone and perosteum form. The bone collar of compact bone forms, and red marrow appears. There are some stages of intramembranous ossification, it starts out with an ossification center appearing in the fibrous connective tissue membrane. Bone matrix is then secreted within the fibrous membrane, and woven bone and the periosteum forms. The Bone collar of compact bone forms, and red marrow appears. Now, its time for Endochondral Ossification.

Endochondral ossification begins in the second month of development, and it uses hyaline cartilage "bones" as models for bone construction. It even requires breakdown of hyaline cartilage prior to ossification. The ossification involves the formation of bone collar, cavitation of the hyaline cartilage, and invasion of internal cavities by the periosteal bud and spongy formation. It also includes the formation of the medullary cavity (appearance of secondary ossification centers in the epiphyses), and the ossification of the epiphyses, with hyaline cartilage remaining only in the epiphyseal plates.

In postnatal bone growth, long bones grow in length and cartilage on the side of the epiphyseal plate closest to the epiphysis is relatively inactive. Cartilage abetting the shaft of the bone organizes into a pattern that allows fast, efficient growth and cells of the epiphyseal plate proximal to the resting cartilage form three functionally different zones: growth, transformation, and osteogenic. The functional zones of the long bones include the growth zone (catilage cells undergo mitosis, pushing the epiphysis away from the diaphysis), transformation zone (older cells enlarge, the matrix becomes calcified, cartilage cells die, and the matrix begins to deteriorate), and the osteogenic zone (new bone formation). The long bone grown in length because the cartilage continually grows and is replaced by bone as shown, and is remodeled when bone is resorbed and aded by appositional growth as shown. As for the hormone regulation of bone growth during a persons youth, it is mainly during infancy and childhood, the epiphyseal plate activity is stimulated by growth hormones. During puberty, there is a lot of testosterone and estrogen that is released, which is initially promoting adolescent growth spurts. They cause masculinization, and feminization of specific parts of the skeleton. They also later induce epiphyseal plate closure, ending the longitudinal bone growth. As for remodeling the units of the bone, includes the adjacent osteoblasts and osteoclasts deposit and resorb bone at periosteal and endsteal surfaces. Which brings us to bone deposition, which occurs where the bone is injured or added strength is needed and requires a diet rich in protein, vitamins C, D, and A, calcium, phosphorus, magnesium, and manganese. Many alkaline phosphate is essential for mineralization of bone, and the location of new matrix depositions are shown by the osteoid seam (unmineralized band of bone matrix) and calcification fronts (abrupt transition zone between osteoid seam and the older mineralized bone).

Sometimes the bones do interesting things, such as Resorption (process where the osteoclasts break down bone to release minerals resulting in the transfer of calcium from bone fluid to the blood). This process of resorption is done by osteoclasts. They use these things called resorption bays (grooves formed by osteoclasts as they brea down bone matrix), and involve the secretion of Lysosomal enzymes that digest organic matrix and acids that convert calcium salts into soluble form, both of which come from the osteoclasts. The dissolved matrix is transcytosed across the osteoclasts cell where it is secreted into the interstitial fluid and then into the blood, such is the process of resorption. Which then leads us to why exactly calcium is so important in our bodies. Well, for starters, it helps the transmission of nerve impulses, controls muscle contractions, helps the blood coagulation, secretes by glands and nerve cells, and helps when it comes to cell division. When it comes to the remodeling of the bones, it is up to two control loops regulating the bones remodeling process. The hormonal mechanism maintains calcium homeostasis in the blood, while mechanical and gravitational forces acting on the skeleton help to remodel the bones. The hormonal mechanism consists of rising blood Ca2+ levels trigger the thyroid to release calcitonin. Calcitonin stimulates calcium salt deposit in bone, where falling blood Ca2+ levels signal the parathyroid glands to release PTH. PTH signals osteoclasts to degrade bone matrix and release Ca2+ into the blood. According to Wolff's law, a bone grows or remodels in response to the forces or demands placed upon it. The observations supporting Wolff's law include long bones are thickest midway along the shaft, where bending stress is greatest. Also, curved bones are thickest where they are most likely to buckle. The trabeculae form along lines of stress, large. bony projections occur where heavy, active muscles are attached.

Bone fractures and breaks are pretty common among the human race for some...odd reason? They are classified by the position of the bone ends after fracture, the completeness of the break, the orientation of the bone to the long axis, and whether or not the bones end penetrates the skin. There are a few different types of bone fractures, which are; non-displaced, displaced, complete, incomplete, linear, transverse, compound, simple, comminuted, spiral, depressed, compression, epiphyseal, and Greenstick. Non-displaced fractures consist of bone ends retaining their normal position. Displaced fractures have the bone ends out of their normal alignment, whereas a complete fracture is broken all the way through. An incomplete fracture is not broken all the way through, and Linear fractures are parallel to the long axis of the bone. Transverse is when the fracture is perpendicular to the long axis of the bone, and the compound (open) is when the bone ends penetrate the skin. Simple (closed) is when the bone ends don't penetrate the skin. A comminuted fracture is when the bone is fragmented into three or more pieces; common injury of the elderly. A spiral fracture is a raged break where the bone is excessively twisted; common sports injury. When the bon is broken into portions thats are pressed inward its a Depressed fracture, which is also a typical skull fracture.  Compression breaks are when the bone is crushed; common is porous bones. The epiphyseal fracture is where the epiphysis separates from diaphysis along epiphyseal line, occurs where cartilage cells are dying, and Greenstick is an incomplete fracture where one side of the bone breaks and the other side bends; common in children. By now, you are probably wondering how exactly a bone is healed after it breaks or fractures.

Well, when a bone heals, it started with the bony callus formation, where new bone trabeclae appear in fibrocartilaginous callus. That fibrocartilaginous callus converse into a bone (hard) callus, then it begins a 3-4 week journey after injury, and continues until firm union is form 2-3 months later. Bone remodeling is then done, where excess material on the bone shaft exterior and in the medullary canal is removed, and compact bone is laid down to reconstruct shaft walls. A homeostatic imbalance occurs and the osteomalacia goes to work. Bones are inadequately mineralized causing soft, weakened bones. The main symptom is pain when weight is put on the affected bone. Osteomalacia is caused by insufficient calcium in the diet, or by vitamin D deficiency. Next come the Rickets, where bones of children are inadequately mineralized casing soft weak bones. Bowed legs and deformities of the pelvis, skull, and rib cage common. They are all caused by insufficient calcium in the diet, or by vitamin D deficiency.  Osteoporosis, is a pretty well-known disease where the bone reabsorption outpaces bone deposit. The spongy bone of the spine is most vulnerable, although it does occur most often in post menopausal women. Bones become so fragile that sneezing or stepping off a curb can cause fractures. The treatment for osteoporosis consists of calcium and vitamin D supplements, increased weight-bearing exercised, hormone (strogen) replacement therapy (HRT) to slow bone loss, natural progesterone cream prompts new bone growth, and statins increase bone mineral density. Pagets disease is characterized by excessive bone formation and breakdown. Pagetic bone with an excessively high ratio of woven to compact bone is formed, and a reduction of mineralization causes spotty weakening of the bone. Osteoclast activity wanes, but osteoblast activity continues to work. Pagets disease is usually localized in the spine, pelvis, femur, and skill. There is no known causes for Pagets disease and the treatment includes the drugs didronate and fosamax.

In the developmental aspects of bones, the mesoderm gives rise to embryonic mesenchymal cells, which produce membranes and cartilages that form the embryonic skeleton. The embryonic skeleton ossifies in a predictable timetable that allows fetal age to be easily determined from sonograms. At birth, most long bones are well ossifies (except for their epiphyses). By age 25, nearly all bones are completely ossifies, and in old age, bone resorption predominates. A single gene that codes for vitamin d docking determines both the tendency to accumulate bone mass early in life, and the risk for osteoporosis later in life.

As we all know, your bones are not super strength, and as such break a lot. The video to the left shows many people breaking bones simply by trying to catch themselves with their hands.