Long bones take their name from their elongated shape. The bones have a uniform medullary cavity that contains the bone marrow. They are found exclusively in the extremities.
What is a long bone?
The long bones can be divided into “long tubular bones” and “short tubular bones”. Long tubular bones include the humerus (upper arm bone) and ulna (ulna) and radius (radius), as well as bones of the extremities of the legs such as the femur (thigh bone), tibia (shin bone), and fibula (calf bone). In contrast, there are the “short tubular bones”. These include metacarpal and metatarsal bones (metacarpalia and metatarsalia, respectively) and finger and toe bones (ossa digitorum manus and pedis, respectively). In addition to tubular bones, osteology distinguishes between flat bones (skull, ribs), short bones (carpal bones), sesamoid bones (patella), air-filled bones (frontal bone) and irregular bones such as the spine. Bones are living organs, well supplied with blood, made of different tissues. They are part of the musculoskeletal system and at the same time protect the internal organs. The mechanical properties and strength of bones against pressure, traction, bending and torsion are based on the incorporation of inorganic components into the organic intercellular substance. The tissue of the bones is constantly regenerating. According to the type of arrangement of collagen fibrils, a further distinction is made between lamellar bones and braided bones. However, the braided bones are found only during the leading phase of bone development as well as at the beginning of fracture healing.
Anatomy and structure
Bone tissue is largely composed of inorganic components, and here again, hydroxyapatite. Only 25% makes up the organic portion, primarily collagen, and 10% is water. The bone tissue also forms the storage organ for calcium and phosphate. The long bones consist of two bone ends, called epiphyses, and a bone shaft, the diaphysis. The short transitional section between the epiphysis and diaphysis is called the metaphysis. Finally, the entire long bone is surrounded by the periosteum, the so-called periosteum. Morphologically, two bone architectures can be distinguished in the long bones. The inner, spongy structure with the bone tubercles (trabeculae) is called the subtantia spongiosa, or “spongiosa” for short. In addition, there is the outer substantia compacta, or “compacta”. It is made up of compact bone. The spongiosa, provides a weight reduction and protected in it lies the bone marrow. The Copacta forms the actual support function of the bone. It consists of lamellar bone organized in the form of osteons. At the epiphyses there is the cartilaginous articular surfaces, which protect the bone from wear.
Function and tasks
The tubular bones serve mainly to support the body. Although bones are also the site of hematopoiesis, the flat bones are mainly responsible for this. The red bone marrow contained within them is involved in the formation of red blood cells, white blood cells, as well as platelets. Bone formation is in dynamic equilibrium with boil dissolution. Osteoblasts are responsible for building the basic bone substance. They secrete calcium phosphates and calcium carbonates. These salts crystallize along the collagen fibers and brick the osteoblasts, forming osteocytes. This tissue hardens and forms bone structure. The counterpart to osteoblasts are osteoclasts. They can dissolve bone again. For example, if the bone is not loaded, e.g. if the bone is in a plaster cast for a long period of time, there is significant bone resorption and thus calcium loss from the skeleton. The longitudinal growth of the bones originates from the epiphyseal joint, or growth plate. It consists of a hyaline cartilage and is located between the epiphyses and the bone shaft. With age, this causes the diaphysis and epiphysis to become longer and stronger. After growth is complete, around age 20, the growth plate ossifies. The blood supply is guaranteed by an artery that enters the bone through the diaphysis. The opening where the blood vessel enters the bone is called the foramen nutricium. The artery supplying the blood is the arteria nutricia. The epiphyses usually have their own artery that supplies them with blood – The Arteriae epiphyseales.Thus, they are independent of the nutric artery of the diaphysis.
Diseases
The most common ailments that can occur in connection with the long bones are fractures. Almost every person suffers a bone fracture at some point in his or her life. It is the result of excessive mechanical stress on the bone. It often occurs during sports, such as skiing or mountain biking. The bone can no longer withstand a sudden, violent impact. Fractures can be single or multiple, and open or closed. A multiple fracture is when the bone is severed more than once. In an open fracture, the soft tissues overlying the bone are also severed, so the bone is often visible to the naked eye. The affected person suffers severe pain and the injured section can no longer be moved voluntarily. In addition, enormous deformities or abnormal degrees of movement of the bone often become apparent. A disease that is associated with an increased tendency to fracture is osteoporosis. It usually occurs with increasing age, and there is a reduction in bone quality and a decrease in bone mass. Bone mass naturally starts to decrease somewhat from the age of 35 to 40. Therefore, people with congenital low bone mass have increased risk of developing osteoporosis. Women are also affected more often than men because of this. Prevention and treatment of osteoporosis are very similar. Those affected are provided with more calcium and vitamin D by means of dietary changes or medication.
Typical and common bone diseases
- Osteoporosis
- Bone pain
- Bone fracture
- Paget’s disease
