So you are wondering all about your bones and "HOW TO MAKE OUR BONES GROW" huh?? Well there are 206 bones in the human body. Although adults have 206 bones, that number actually decreases as we age. Certain bones fuse, joining individual bones into a fused single segment. Bones serve a number of important functions for normal living. They provide support for the body, giving it shape, form, and the ability to move. They guard vital organs and serve as levers to make movement possible. Bones are storage reservoirs for minerals and vitamins. Bone marrow is responsible for the production of new blood cells. Bones are living, changing structures that require adequate calcium and weight-bearing exercise to build and maintain their density and strength. Living bone tissue is a combination of hard organic salts (minerals) and organic compounds (collagen). Mineral storage in the bones not only ensures the structural strength and health of the bone, but also provides a reservoir of minerals, which are readily available to the body whenever needed. Microscopically, bone is a strong matrix (framework) of fibers cris-crossed in intricate patterns, embedded with mineral salts. The most prominent mineral salt in the body is collagen (95%) a very strong and durable material. About 20% of the weight of bone is water.

Bones are classified according to their physical appearance and structural make-up. Long bones have an elongated shaft with a central medullary cavity. They always have articulations (joints) on both ends. All long bones have three major parts: a shaft (diaphysis), an expanded portion of the shaft (metaphysis), and the bone ends (epiphysis). Short bones have the same structural appearance as long bones, but are proportionally smaller.

Flat bones are made up of two opposed layers of cortical bone (smooth, dense bone) separated by a thin medullary cavity (soft, spongy bone). Examples of flat bones include the skull, scapula and pelvis.

Irregular bones come in a variety of specialized shapes and sizes that do not fit into either the long or flat bone category. Carpals and tarsals are examples.

In addition to being classified by physical appearance, bones are also classified by the make-up of their internal structure. Compact bone is very dense and smooth. It is always found on the exterior surface of a bone. Its purpose is to surround (provide an outer shell for) softer, spongy bone. Within compact bone are a network of vascular channels through which arteries and veins pass.

Spongy bone (also known as cancellous or trabecular bone) is very porus and soft. In appearance, it looks something like a honeycomb. The structural framework is made of trabeculae (rigid bony fibers) with bone marrow filling in the spaces.

At birth, all bone marrow is red. As we age, most of it is transformed into yellow marrow by the addition of fat cells. Red marrow produces red blood cells, platelets, and certain white blood cells. It fills the cavities of many bones, especially long bones. By adolescence, most of our marrow is yellow. In an adult, red marrow is only found on the proximal epiphysis of long bones, in vertebral bodies, sternum, ribs, and bones of the cranium. If necessary, yellow marrow can be stimulated to produce new red blood cells. Red blood cells only live about 120 days, after which they are replaced and recycled. Every day, the liver destroys about the same number of red blood cells as bone marrow creates to maintain a balance.

Components of Blood

1. Red blood cells (RBC), called erythrocytes, carry 99% of the body's oxygen. Red blood cells are the most abundant cells in the body (45%). Their main function is to carry oxygen to tissues and to remove carbon dioxide waste. They are made of water and hemoglobin (a protein containing iron). Hemoglobin gives blood its deep red color. Each RBC is only about .008 centimeter (3/1000 of an inch) in diameter. About two and a half million red blood cells are created and destroyed every second. When RBC?s are destroyed, they are broken down into their constituent parts, some of which can be used again to manufacture new cells. Normal red blood cell production depends upon the body having an adequate supply of iron and two main vitamins, B12 and folic acid.
2. White blood cells, called leukocytes, are outnumbered by red blood cells 600 to 1. They are spherical in shape and slightly larger than red blood cells. There are five types of leukocytes. Their main function is to provide a defense against "foreign" material (infectious agents, foreign bodies, abnormal proteins). Red bone marrow continually produces white blood cells, except lymphocytes and monocytes, and keeps a reserve ready.
3. Platelets are specialized cells activated whenever blood clotting or repair to a vessel is necessary. They are called cells, but are really fragments of other cells. Made in bone marrow, they are much smaller than red blood cells. A single drop of blood contains 15 million platelets. When a blood vessel is cut, platelets respond by swelling into irregular shapes, growing sticky to form a plug. If the cut is too large for platelets, they send out signals to initiate clotting through a release of the hormone serotonin, which stimulates blood vessels to contract. Blood flow is reduced throughout the body. Clotting is really a change of soluble plasma protein fibrinogen into insoluble, thread-like protein (fibrin). Fibrin forms a mesh around blood cells and adds serum (a clear yellowish fluid that forms a solid clot). The process of clotting also creates a framework on which to build new tissue.

Bone Development

Prior to birth and for several months after birth, the skeleton has very little bone. Many bones start out as cartilage. As the child grows, cartilage transforms into true bone (endochondral ossification). Ossification rates appear at set time in healthy children and can be evaluated by radiographic imaging.

Bones are a storehouse of minerals. They hold 99% of the bodies calcium, 86% of its phosphate, and 54% of our magnesium. Calcium is an essential element in keeping bones healthy and strong. But calcium plays an important role in other essential functions as well: - Calcium keeps membranes permeable
- Muscles can not contract without calcium
- Blood can not clot without calcium
- Certain enzymes can not function without calcium
To keep bones healthy and in good repair, other nutrients are needed. Vitamin D stimulates the body to absorb calcium and phosphorus. It plays a key role in making it possible for calcium and phosphorus to cross through the intestinal wall. Lack of vitamin D causes the condition known as Rickets.
Vitamins A and C are essential for bone remodeling and growth. Insufficient supply of vitamin A results in a serious condition of decreased osteoblast activity, commonly known as Scurvy.



Bone Formation

Step 1: Bone resorption and remodeling begins when hormones are sent out into the bloodstream, triggering osteoclasts to respond to the site where new bone needs to be produced.

Step 2: Osteoclasts dissolve away existing bone (resorption ... remodeling), creating an indentation or cavity.

Step 3: Once the osteoclasts have prepared the site, osteoblasts move in and begin to secrete collagen fibers, which will provide a framework for new bone formation.

Step 4: Hormones cause minerals to be pulled out of bones throughout the body and into the bloodstream. They are attracted to the site where new bone is being formed and bind to the new collagen framework. New bone tissue is created.

To keep bones healthy and in good repair, there is a mechanism in place to repair damaged tissue and to revitalize old, weakened bone with new, strong material. Specialized cells called osteoblasts accomplish this. Blast means make or form. Osteoblasts converge at the site where bone repair will take place. They secrete collagen fibers, which bind to minerals absorbed from the bloodstream, and new bone is created. Forming new bone requires adequate Calcium and Phosphorous. Certain hormones can activate a release of these minerals into the bloodstream so they are readily available when needed.

About 5% - 10% of our existing bone is replaced each year throughout our lives. The process gradually slows as we get older, resulting in brittle bones. Bone cells responsible for the resorption and remodeling of bone are osteoclasts. Clast means to remove or dissolve. When fractures occur or as bone ages, new bone must be laid down. Osteoclasts prepare the site by dissolving old injured or weakened bone, leaving a crater for osteoblasts to assemble into as they begin forming new bone. Without osteoclasts preparing the site, osteoblasts would be inefficient.

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