Bone phisiology

Editor's Notes

• #5: -Bone is highly vascular, living, constantly changing, mineralized connective tissue.-Sesamoid bone are the bones embedded within tendon. Found in hand, knee and foot. Eg patella.-They act to protect the tendon and increase its mechanical effect.
• #6: -Supports soft tissues and provide attachment for tendons of most skeletal muscles.-Bone protects many internal organs from injury eg. Skull protect brain.-Red bone marrow (medulla ossiumrubra) consist mainly of hematopoietic tissue. Found mainly in flat bones.-Yellow bone marrow (medulla ossiumflava) : consist mainly of adipose cells which stores triglycerides, which body use as a last reservior in cases of extreme starvation.
• #8: Flat bones- skull, sternum, pelvis and ribs.Long bones- bones of limbs.Irregular bones- face bone and vertebral column.Short bones- bones of hands and feets such as phalanges, metacarpals and metatarsals.Accessory or supernumerary bone- extra bone that develop in additional ossification centers failed to fuse with main parts during development. These bones may be mistaken for bone chips or fractures.
• #10: epiphysis – its is the region between the growth or growth plate scar and the expanded end of bone, covered by articular cartilage. It is present at both the ends of bone except clavical, ribs, phalanges proximal end, proximal first and distal second through fifth meta carpals and pfads through fifth metatarsals.Carpal, tarsal bones and patella are also called epiphysioid bones and are developmentally equivalent to epiphysis of long bones.Metaphysis – this region is a comman site for many primary bone tumors and similar lesions.Diaphysis – located in the region between metaphyses.Physis – seperates epiphysis from metaphysis. It is zone of endochodral ossification.
• #11: -Endosteum is made up of loose irregular connective tissue, with osteoblast and osteoclast. It is highly vascular condensation of areolar tissue lining various medullary spaces.Long b ones include- femora, tibiae and fibulae of the legs; humeri, radii and ulnae of the arms; metacarpals and metatarsals of hands and feet;phalanges of fingers and toes and the clavicals or the collar bone, mandible.
• #14: Forms cortex or outer shell of most bones.Present between osteogenic layer of periosteum and spongy bone.Chifly consist of calcium phosphate and type 1 collagen.. These are arranged in concentric circles around central haversian canal.
• #16: It is primary anatomical and functional unit of cortical bone.Osteon- consist of concentric layers of lamellae of compact bone tissue that surrounds a central canal, Haversian canal, which contains blood and nerve supply to bone.The boundry of the osteon is CEMENT LINE.Osteons are connected to each other and the periosteum bye oblique channels called volkman’s canals or perforating canals.
• #17: Also known as cancellous boas compared to compact bone it has higher surface area, is less dense, softer, weaker and less stiff.Found in ends of long bones, proximal to joints and within the interior of vertebrae.
• #18: - The alveolar process contains a region of compact bone adjacent to the periodontal ligament called lamina dura- It is stated that in the posterior maxilla; the trabeculae are typically thin, and numerous, forming a fine, granular, dense pattern, and the marrow spaces are consequently slightly larger than the anterior region of the maxilla and relatively numerous. In the posterior mandible, the periradiculartrabeculae are somewhat thicker than in the maxilla resulting in a coarser pattern and they are relatively larger than the trabeculae in the anterior region of the mandible. The trabecular plates in the mandible are also fewer than in the maxilla and marrow spaces are correspondingly larger
• #20: It is also an pathologic tissue in adults, except in few places such as near the suture of the flat bones of skull, tooth sockets.
• #29: In diagram - One small and 1 large plasma cell in top left frame. 2 osteoblasts in top right frame, 1 osteoblast in lower frame.cuboidal and columnar in shape with a central nucleus.found on the bone surface. osteoblasts come from the poorly differentiated mesenchymal cell of the internal osteogenic layer of periosteum and the bone marrowThey have receptors for hormones such as vitamin D, estrogen, and parathyroid hormone.  secrete factors that activate osteoclasts (RANK-ligand) secrete PHEX, a protein that helps to regulate the amount of phosphate excreted by the kidney. Procollagen molecules are produced bythe ribosomes and extruded into extracellular space , proteolysis and polymerization within the extracellular space results in formation of collagen fibrils. - Combination of thes extracellular and intracellular events leads to production of osteoid seam.
• #30: osteocyte, mature bone cells, a star shaped cellOsteocytes have an average half life of 25 years, they do not divide, and they are derived from osteoprogenitors, some of which differentiate into active osteoblastsCells contain a nucleus and a thin ring piece of cytoplasm. space that an osteocyte occupies is called a lacuna Osteocytes are networked to each other via long cytoplasmic extensions that occupy tiny canals called canaliculi, which are used for exchange of nutrients and waste through gap junctions-These have also been show to act as mechanosensoryreceptars regulating the bones response to stress and mechanical load.
• #31: Precursors (blood monocytes) circulate in the blood and bone marrow. formed from fusion of the precursors. happens when RANK receptors on the osteoclast precursors are activated by the RANK-ligand which was secreted by osteoblasts. Osteoprotegerin (OPG) is a factor in the marrow which also binds RANK-ligand, so it can help to regulate the osteoclast activation. After they finish resorbing bone, they undergo apoptosis (programmed cell death, sometimes called 'cell suicide'). This process is regulated by proteins from other cells.
• #33: Nerve supply: Hilton’s law: according to this law nerve supplying a muscle will aslo supply the underlying bone.Most of the nerves coming to bone are sympathetic(activate fight or flight response) and vasomotor(causing or regulating dilation or constriction of blood vessels) in function.Some nerves are sensory and are distributed to the articular ends and the periosteum
• #43: At periphery of cartilage mesenchymal cells continue to proliferate and differentiate. Called as appositiona growth.In interstitial growth cell proliferation and synthesis of new matrix between chondrocytes occur.
• #46: Begin to form at epiphyseal ends.By similar process , as in development of primary ossification center , trabecular bone and marrow space are formed at these ends..
• #51: Zone of resting cartilage- cells separated by abundant extracellular matrix and have less tendancy to proliferate.Zone of proliferating cartilage- chondroblast divide actively forms groups and actively synthesize the matrixUpperZone of hypertrophic cartilage- increased vacuolation of cells. Matrix synthesis increased 3 fold compared to proliferative zone.
• #56: bone in a healthy person or animal will adapt to the loads under which it is placed.If loading on a particular bone increases, the bone will remodel itself over time to become stronger to resist that sort of loading. The internal architecture of the trabeculae undergoes adaptive changes, followed by secondary changes to the external cortical portion of the bone,perhaps becoming thicker as a result. The inverse is true as well: if the loading on a bone decreases, the bone will become weaker due to turnover, it is less metabolically costly to maintain and there is no stimulus for continued remodeling that is required to maintain bone mass.
• #60: It is refinement of wolfs law.Mechanostat is model describing bone growth and bone loss.
• #62: Bennighof studied the natural line of stress in skull by piercing small holes into fresh skulls.When skull were dried he observed holes assumed a linear form in the direction of bony trabeculae these were called benninghoff’s line or trajectories.It indicates direction of functional stresses
• #63: Canine lines run superiorly by the sides of piriform aperture and crest of nasal bone to frontal boneZygomatic lines runs inferiorly along the orbit,superiorly along the lateral wall of orbit,runs along the zygomatic arch.In mandible it radiates from beneath the teeth in the alveolar process & join common stress pillar that terminates in condyle.Lower border and mylohyoid ridges are other prominent buttresses of mandible.
• #69: Insulin-like growth factors (IGFs): These growth factors are produced by osteoblastic cells in response to several bone active hormones, such as parathyroid hormone and estrogens, or BMPs. Growth factorsBone morphogenetic proteins (BMPs): BMPs are produced in the bone or bone marrow. They bind to BMP receptors that are on mesenchymal stem cells within the bone marrow. This causes the cells to produce Cbfa 1, which is a factor that activates the DNA so proteins can be made -- a process known as gene transcription. When Cbfa 1 activates the genes, the cells differentiate into mature osteoblasts. Without Cbfa 1, the cells would turn into fat cells instead!IGFs accumulate in the bone matrix and are released during the process of bone remodeling by osteoclastsCytokinesInterleukin-1 (IL-1), interleukin-6 (IL-6), and tumor necrosis factor (TNF) family of cytokines: These factors are produced by osteoblastic cells in response to systemic hormones or other cytokines. IL-6 can cause: * Bone marrow stem cells to differentiate into pre-osteoclasts * Changes in proliferation and differentiation of osteoblasts * Inhibition of apoptosis of osteoblastsRANKL (RANK-ligand) is a cytokine that stays on the surface of osteoblast-related cells.
• #72: Parfit states that a fully developed BMU consists of a team of osteoclasts forming the cutting cone or hemicone, a team of osteoblast forming the closing cone, some boold vessels and associated connective tissue
• #75: The cutting head is stimulated by inflammatory cytokines produced by osteocytes in damagedbone (left). Preosteoclasts have RANK receptors that are bound and activated by RANKL, probably produced ormediated by T cells (lymphocytes) near the resorption front. Growth factors from resorbed bone (bottom)stimulate production of preosteoblasts, which then produce OPG to block the RANK receptors on osteoclasts;the latter then withdraw from the scalloped surface and degenerate. Relatively flat mononuclear cells (bottomcenter) form cementing substance to form a resorption arrest line. Osteoblasts (bottom right) produce newlamellar bone to fill the resorption cavity.
• #76: Regional accelerIt is an important reaction of bone Any regional noxious stimulus can evoke RAPMost of the active vital processes are accelerated like perfusion,growth of bone cartilage ,BMU turnover of woven & lamellar bone ,turnover of connective tissueWhen RAP fails to develop ,healing is delayed & infection progressesDuration of RAP is in the range of months to years