Bone density, or bone mineral density, is the amount of bone mineral in bone tissue. The concept is of mass of mineral per volume of bone, although clinically it is measured by proxy according to optical density per square centimetre of bone surface upon imaging. Bone density measurement is used in clinical medicine as an indirect indicator of osteoporosis and fracture risk, it is measured by a procedure called densitometry performed in the radiology or nuclear medicine departments of hospitals or clinics. The measurement involves low radiation exposure. Measurements are most made over the lumbar spine and over the upper part of the hip; the forearm may be scanned if the lumbar spine are not accessible. There is higher probability of fracture. Fractures of the legs and pelvis due to falls are a significant public health problem in elderly women, leading to much medical cost, inability to live independently and risk of death. Bone density measurements are used to screen people for osteoporosis risk and to identify those who might benefit from measures to improve bone strength.
Bone density tests are not necessary for people without risk factors for weak bones. Unnecessary testing is more to result in superfluous treatment rather than discovery of a true problem; the following are risk factors for low bone density and primary considerations for the need for a bone density test. Females age 65 or older males age 70 or older people over age 50 with any of the following: previous bone fracture from minor trauma rheumatoid arthritis low body weight a parent with a hip fracture Individuals with vertebral abnormalities. Individuals receiving, or planning to receive, long-term glucocorticoid therapy. Individuals with primary hyperparathyroidism. Individuals being monitored to assess the response or efficacy of an approved osteoporosis drug therapy. Individuals with a history of eating disordersOther considerations that are related to risk of low bone density and the need for a test include smoking habits, drinking habits, the long-term use of corticosteroid drugs, a vitamin D deficiency.
For those people who do have bone density tests, two conditions which may be detected are osteoporosis and osteopenia. The usual response to either of these indications is consultation with a physician. Results are reported in 3 terms: Measured areal density in g cm−2 Z-score, the number of standard deviations above or below the mean for the patient's age and ethnicity T-score, the number of standard deviations above or below the mean for a healthy 30-year-old adult of the same sex and ethnicity as the patient While there are many different types of BMD tests, all are non-invasive. Most tests differ according to; these tests include: Dual-energy X-ray absorptiometry Dual X-ray Absorptiometry and Laser Quantitative computed tomography Quantitative ultrasound Single photon absorptiometry Dual photon absorptiometry Digital X-ray radiogrammetry Single energy X-ray absorptiometry DXA is the most used, but quantitative ultrasound has been described as a more cost-effective approach to measure bone density.
The DXA test works by measuring a specific bone or bones the spine and wrist. The density of these bones is compared with an average index based on age and size; the resulting comparison is used to determine risk for fractures and the stage of osteoporosis in an individual. Average bone mineral density = BMC / W BMC = bone mineral content = g/cm W = width at the scanned line Results are scored by two measures, the T-score and the Z-score. Scores indicate. Negative scores indicate lower bone density, positive scores indicate higher; the T-score is the relevant measure. It is the bone mineral density at the site, it is a comparison of a patient's BMD to that of a healthy 30-year-old. The US standard is to use data for a 30-year-old of the same sex and ethnicity, but the WHO recommends using data for a 30-year-old white female for everyone. Values for 30-year-olds are used in post-menopausal women and men over age 50 because they better predict risk of future fracture; the criteria of the World Health Organization are: Normal is a T-score of −1.0 or higher Osteopenia is defined as between −1.0 and −2.5 Osteoporosis is defined as −2.5 or lower, meaning a bone density, two and a half standard deviations below the mean of a 30-year-old man/woman.
The Z-score is the comparison to the age-matched normal and is used in cases of severe osteoporosis. This is the number of standard deviations a patient's BMD differs from the average BMD of their age and ethnicity; this value is used in premenopausal women, men under the age of 50, in children. It is most useful. In this setting, it is helpful to scrutinize for coexisting illnesses or treatments that may contribute to osteoporosis such as glucocorticoid therapy, hyperparathyroidism, or alcoholism. Use of BMD has several limitations. Measurement can be affected by the size of the patient, the thickness of tissue overlying the bone, other factors extraneous to the bones. Bone density is a proxy measurement for bone strength, the resistance to fracture and the significant characteristic. Although the two are related, there are some circumstances in which bone density is a poorer indicator of bone strength. Reference standard
Necrosis is a form of cell injury which results in the premature death of cells in living tissue by autolysis. Necrosis is caused by factors external to the cell or tissue, such as infection, toxins, or trauma which result in the unregulated digestion of cell components. In contrast, apoptosis is a occurring programmed and targeted cause of cellular death. While apoptosis provides beneficial effects to the organism, necrosis is always detrimental and can be fatal. Cellular death due to necrosis does not follow the apoptotic signal transduction pathway, but rather various receptors are activated, result in the loss of cell membrane integrity and an uncontrolled release of products of cell death into the extracellular space; this initiates in the surrounding tissue an inflammatory response which attracts leukocytes and nearby phagocytes which eliminate the dead cells by phagocytosis. However, microbial damaging substances released by leukocytes would create collateral damage to surrounding tissues.
This excess collateral damage inhibits the healing process. Thus, untreated necrosis results in a build-up of decomposing dead tissue and cell debris at or near the site of the cell death. A classic example is gangrene. For this reason, it is necessary to remove necrotic tissue surgically, a procedure known as debridement. Structural signs that indicate irreversible cell injury and the progression of necrosis include dense clumping and progressive disruption of genetic material, disruption to membranes of cells and organelles. There are six distinctive morphological patterns of necrosis: Coagulative necrosis is characterized by the formation of a gelatinous substance in dead tissues in which the architecture of the tissue is maintained, can be observed by light microscopy. Coagulation occurs as a result of protein denaturation, causing albumin to transform into a firm and opaque state; this pattern of necrosis is seen in hypoxic environments, such as infarction. Coagulative necrosis occurs in tissues such as the kidney and adrenal glands.
Severe ischemia most causes necrosis of this form. Liquefactive necrosis, in contrast to coagulative necrosis, is characterized by the digestion of dead cells to form a viscous liquid mass; this is typical of bacterial, or sometimes fungal, infections because of their ability to stimulate an inflammatory response. The necrotic liquid mass is creamy yellow due to the presence of dead leukocytes and is known as pus. Hypoxic infarcts in the brain presents as this type of necrosis, because the brain contains little connective tissue but high amounts of digestive enzymes and lipids, cells therefore can be digested by their own enzymes. Gangrenous necrosis can be considered a type of coagulative necrosis that resembles mummified tissue, it is characteristic of ischemia of the gastrointestinal tracts. If superimposed infection of dead tissues occurs liquefactive necrosis ensues Caseous necrosis can be considered a combination of coagulative and liquefactive necrosis caused by mycobacteria and some foreign substances.
The necrotic tissue appears as friable, like clumped cheese. Dead cells disintegrate but are not digested, leaving granular particles. Microscopic examination shows amorphous granular debris enclosed within a distinctive inflammatory border. Granuloma has this characteristic. Fat necrosis is specialized necrosis of fat tissue, resulting from the action of activated lipases on fatty tissues such as the pancreas. In the pancreas it leads to acute pancreatitis, a condition where the pancreatic enzymes leak out into the peritoneal cavity, liquefy the membrane by splitting the triglyceride esters into fatty acids through fat saponification. Calcium, magnesium or sodium may bind to these lesions to produce a chalky-white substance; the calcium deposits are microscopically distinctive and may be large enough to be visible on radiographic examinations. To the naked eye, calcium deposits appear as gritty white flecks. Fibrinoid necrosis is a special form of necrosis caused by immune-mediated vascular damage.
It is marked by complexes of antigen and antibodies, sometimes referred to as "immune complexes" deposited within arterial walls together with fibrin. There are very specific forms of necrosis such as gangrene, gummatous necrosis and hemorrhagic necrosis; some spider bites may lead to necrosis. In the United States, only spider bites from the brown recluse spider reliably progress to necrosis. In other countries, spiders of the same genus, such as the Chilean recluse in South America, are known to cause necrosis. Claims that yellow sac spiders and hobo spiders possess necrotic venom have not been substantiated. In blind mole rats, the process of necrosis replaces the role of the systematic apoptosis used in many organisms. Low oxygen conditions, such as those common in blind mole rats' burrows cause cells to undergo apoptosis. In adaptation to higher tendency of cell death, blind mole rats evolved a mutation in the tumor suppressor protein p53 to prevent cells from undergoing apoptosis. Human cancer patients have similar mutations, blind mole rats were thought to be more susceptible to cancer because their cells cannot undergo apoptosis.
However, after a specific amount of time (within 3 days according to a study conducted at the University of
The medullary cavity is the central cavity of bone shafts where red bone marrow and/or yellow bone marrow is stored. Located in the main shaft of a long bone, the medullary cavity has walls composed of spongy bone and is lined with a thin, vascular membrane. However, the medullary cavity is the area inside any bone; this area is involved in the formation of red blood cells and white blood cells, the calcium supply for bird eggshells. The area has been detected in fossil bones despite the fossilization process. Intramedullary is a medical term meaning the inside of a bone. Examples include intramedullary rods used to treat bone fractures in orthopedic surgery and intramedullary tumors occurring in some forms of cancer or benign tumors such as an enchondroma. "Medullary cavity" at Dorland's Medical Dictionary
Haversian canals are a series of microscopic tubes in the outermost region of bone called cortical bone that allow blood vessels and nerves to travel through them. Each haversian canal contains one or two capillaries and nerve fibres; the channels are formed by concentric layers called lamellae. The haversian canals surround blood vessels and nerve cells throughout bones and communicate with bone cells through connections called canaliculi; this unique arrangement is conducive to mineral salt deposits and storage which gives bone tissue its strength. In mature compact bone most of the individual lamellae form concentric rings around larger longitudinal canals within the bone tissue; these canals are called haversian canals. Haversian canals are contained within osteons, which are arranged along the long axis of the bone in parallel to the surface; the canals and the surrounding lamellae form the functional unit, called a haversian system or osteon. Http://www.lab.anhb.uwa.edu.au/mb140/ "Bone Anatomy - Haversian canals within bone".
November 4, 2006 – via YouTube. Video of haversian canal system within cortical bone
The periosteum is a membrane that covers the outer surface of all bones, except at the joints of long bones. Endosteum lines the inner surface of the medullary cavity of all long bones; the periosteum consists of dense irregular connective tissue. It is divided into an outer "fibrous layer" and inner "cambium layer"; the fibrous layer contains fibroblasts, while the cambium layer contains progenitor cells that develop into osteoblasts. These osteoblasts are responsible for increasing the width of a long bone and the overall size of the other bone types. After a bone fracture the progenitor cells develop into osteoblasts and chondroblasts, which are essential to the healing process; as opposed to osseous tissue, the periosteum has nociceptive nerve endings, making it sensitive to manipulation. It provides nourishment by providing the blood supply to the body from the marrow; the periosteum is attached to the bone by strong collagenous fibers called Sharpey's fibres, which extend to the outer circumferential and interstitial lamellae.
It provides an attachment for muscles and tendons. The periosteum that covers the outer surface of the bones of the skull is known as the "pericranium", except when in reference to the layers of the scalp; the word periosteum is derived from the Greek Peri-, meaning "surrounding", -osteon, meaning "bone". The Peri refers to the fact that the Periosteum is the outermost layer of long bones, surrounding other inner layers. Periostitis Endochondral ossification Intramembranous ossification Brighton, Carl T.. "Early histologic and ultrastructural changes in microvessels of periosteal callus". Journal of Orthopaedic Trauma. 11: 244–253. PMID 9258821. Periosteum - InnerBody