Flashcards
Bone
Flashcards do conjunto (22)
- 1Bone marrow exists as two types: red bone marrow, in which blood cells are forming, and yellow bone marrow, composed mostly of fat.Primary bone is immature in that it is the first bone to form during fetal development and during bone repair.
It has abundant osteocytes and irregular bundles of collagen, which are later replaced and organized as secondary bone except in certain areas (e.g., at sutures of the calvaria, insertion sites of tendons, and bony alveoli surrounding the teeth).
The mineral content of primary bone is also much less than that of secondary bone. - 2Bone is a reservoir for several minerals of the body; for example, it stores about 99% of the body's calcium.periosteum, consists of an outer layer of dense fibrous connective tissue and an inner cellular layer containing osteoprogenitor (osteogenic) cells.
Bone is covered on its external surface, except at synovial articulations.
The central cavity of a bone is lined with endosteum, a specialized thin, connective tissue composed of a monolayer of osteoprogenitor cells and osteoblasts - 3Bone is composed of cells lying in an extracellular matrix that has become calcified. The calcified matrix is composed of fibers and ground substance.The fibers constituting bone are primarily type I collagen.
The ground substance is rich in proteoglycans with chondroitin sulfate and keratan sulfate side chains. In addition, glycoproteins such as osteonectin, osteocalcin, osteopontin, and bone sialoprotein - 4Secondary bone is mature bone composed of parallel or concentric bony lamellae 3- to 7-μm thick. Osteocytes in their lacunae are dispersed at regular intervals between, or occasionally within, lamellae. Canaliculi, housing osteocytic processes, connect neighboring lacunae with one another, forming a network of intercommunicating channels that facilitate the flow of nutrients, hormones, ions, and waste products to and from osteocytes. Because the matrix of secondary bone is more calcified, it is stronger than primary bone.The outer circumferential lamellae are just deep to the periosteum, forming the outermost region of the diaphysis, and contain Sharpey's fibers anchoring the periosteum to the bone.
- 5The organic component of bone matrix, constituting approximately 35% of the dry weight of bone, includes fibers that are almost exclusively type I collagenThe fact that bone matrix stains with PAS reagent and displays slight metachromasia indicates the presence of sulfated glycosaminoglycans, namely chondroitin sulfate and keratan sulfate.
The abundance of collagen, however, causes the matrix to be acidophilic. - 6The inner circumferential lamellae, analogous to but not as extensive as outer circumferential lamellae, completely encircle the marrow cavity. Trabeculae of spongy bone extend from the inner circumferential lamellae into the marrow cavity, interrupting the endosteal lining of the inner circumferential lamellaeThe bulk of compact bone is composed of an abundance of haversian canal systems (osteons); each system is composed of cylinders of lamellae, concentrically arranged around a vascular space known as the haversian canal
- 7Osteoprogenitor cells are located in the inner cellular layer of the periosteum, lining haversian canals, and in the endosteum . under certain conditions of low oxygen tension, these cells may differentiate into chondrogenic cells.These cells are most active during the period of intense bone growth.
- 8Each haversian canal, lined by a layer of osteoblasts and osteoprogenitor cells, houses a neurovascular bundle with its associated connective tissue. Haversian canals of adjacent osteons are connected to each other by Volkmann's canals. These vascular spaces are oriented oblique to or perpendicular to haversian canals.As additional lamellae are added to the system, the diameter of the haversian canal is reduced, and the thickness of the osteon wall increases.
Remnants of osteons remain as irregular arcs of lamellar fragments, known as interstitial lamellae, surrounded by osteons. Like osteons, interstitial lamellae are also surrounded by cementing lines.
Each osteon is bounded by a thin cementing line, composed mostly of calcified ground substance with a scant amount of collagen fibers - 9The difference between Primary and secondary ossifacation center , is that in secondary there is no collar formsBone growth in width takes place by oppitional growth
- 10Osteoblasts synthesize the organic matrix of bone and possess receptors for parathyroid hormone. Osteoblasts are derived from osteoprogenitor cells and develop under the influence of the bone morphogenic protein (BMP) family and transforming growth factor-β.they produce RANKL (receptor for activation of nuclear factor kappa B): a key factor for osteoclast differentiation and activation ,
2) osteocalcin (for bone mineralization), 3) osteopontin (for formation of sealing zone between osteoclasts and the subosteoclastic compartment), 4) osteonectin (related to bone mineralization), bone sialoprotein (binding osteoblasts to extracellular matrix), - 11osteoblasts as well as osteocytes are always separated from the calcified substance by a thin, noncalcified layer known as the osteoidThe interval between the osteocyte plasmalemma and the walls of the lacunae and canaliculi, known as the periosteocytic space, is occupied by extracellular fluid.
- 12One theory, called heterogeneous nucleation, is that collagen fibers in the matrix are nucleation sites for the metastable calcium and phosphate solution and that the solution begins to crystallize into the gap region of the collagen. Once this region has "nucleated," calcification proceeds.Bone repair involves both intramembranous and endochondral bone formation.
- 13Individuals suffering from Osteopetrosis may exhibit anemia resulting from decreased marrow space, as well as blindness, deafness, and cranial nerve involvement because of impingement of the nerves due to narrowing of the foraminaThe bone-resorbing activity of osteoclasts is regulated by two hormones, parathyroid hormone and calcitonin, produced by the parathyroid and thyroid gland, respectively
- 14Whenever the bone's haversian systems are without a blood supply, osteocytes become pyknotic and undergo lysis, leaving empty lacunaeThe blood clot filling the site of the fracture is invaded by small capillaries and fibroblasts from the surrounding connective tissue, forming granulation tissue
- 15The very dense bone on the outside surface is compact bone, whereas the porous portion lining the marrow cavity is cancellous or spongy bone. There are no haversian systems in spongy bone, but there are irregular arrangements of lamellae.Trabeculae and spicules
- 16the clot is soon invaded by osteoprogenitor cells of the endosteum and multipotential cells of the bone marrow, forming an internal callus of bony trabeculaeThe deepest layer of proliferating osteoprogenitor cells of the periosteum (those closest to the bone), which are in the vicinity of capillaries, differentiate into osteoblasts and begin elaborating a collar of bone, cementing it to the dead bone about the injury site.
- 17Although the capillaries are growing, their rate of proliferation is much slower than that of the osteoprogenitor cells; thus the osteoprogenitor cells in the middle of the proliferating mass are now without a profuse capillary bed. This results in lowered oxygen tension, and these cells become chondrogenic cells, giving rise to chondroblasts that form cartilage in the outer parts of the collar.The calcium ions retrieved from bone to maintain blood calcium levels come from new and young osteons, where mineralization is incomplete. Because bone remodeling is constant, new osteons are always forming where labile calcium ions are available
- 18Bone marrow exists as two types: red bone marrow, in which blood cells are forming, and yellow bone marrow, composed mostly of fat.Primary bone is immature in that it is the first bone to form during fetal development and during bone repair.
It has abundant osteocytes and irregular bundles of collagen, which are later replaced and organized as secondary bone except in certain areas (e.g., at sutures of the calvaria, insertion sites of tendons, and bony alveoli surrounding the teeth).
The mineral content of primary bone is also much less than that of secondary bone. - 19Osteoporosis often affects women older than 40 years of age, especially postmenopausal women. Osteoporosis is related to decreasing bone mass, which becomes more serious after menopause, when estrogen secretion drops appreciably.Binding of estrogen to specific receptors on osteoblasts activates the cells to manufacture and secrete bone matrix. With diminished secretion of estrogen, osteoclastic activity is greater than bone deposition,
- 20Rickets is a disease in infants and children who are deficient in vitamin D. Without vitamin D, the intestinal mucosa cannot absorb calcium even though there may be adequate dietary intake. This results in disturbances in ossification of the epiphyseal cartilages and disorientation of the cells at the metaphysis, giving rise to poorly calcified bone matrix. Children with rickets display deformed bones, particularly in the legs, simply because the bones cannot bear their weight.Osteomalacia, or adult rickets, results from prolonged deficiency of vitamin D. When this occurs, the newly formed bone in the process of remodeling does not calcify properly. This condition may become severe during pregnancy because the fetus requires calcium, which must be supplied by the mother.
- 21with only a minimum of movement between them are called synarthroses; joints in which the bones are free to articulate over a fairly wide range of motion are classified as diarthroses.synarthrosis joints
1 Synostosis. There is little if any movement, and joint-uniting tissue is bone (e.g., skull bones in adults).
2 Synchondrosis. There is little movement, and joint-uniting tissue is hyaline cartilage (e.g., joint of first rib and sternum).
3 Syndesmosis. There is little movement, and bones are joined by dense connective tissue (e.g., pubic symphysis). - 22The capsule is composed of an outer fibrous layer of dense connective tissue, which is continuous with the periosteum of the bones, and an inner cellular synovial layer, which covers all nonarticular surfaces. Some prefer to call this a synovial membrane.Type A cells are macrophages displaying a well-developed Golgi apparatus and many lysosomes but only a small amount of RER. These phagocytic cells are responsible for removing debris from the joint space.
2 Type B cells resemble fibroblasts, exhibiting a well-developed RER; these cells are thought to secrete the synovial fluid.
Synovial fluid contains a high concentration of hyaluronic acid and the glycoprotein lubricin combined with filtrate of plasma. In addition to supplying nutrients and oxygen to the chondrocytes of the articular cartilage, this fluid has a high content of hyaluronic acid and lubricin that permits it to function as a lubricant for the joint. Moreover, macrophages in the synovial fluid act to phagocytose debris in the joint space.
Informações
- Descrição
- FlashCards sobre Bone, criado por ehab mahajna em 13-05-2015.
- Criado por
- ehab mahajna
- Visualizações
- 1
- Avaliação