Bone (osseous tissue)
Bone is specialized c.t. composed of intercellular calcified material.Matrix composed:
organic compound: protein- polysaccharides containing condroitin sulfate
Inorganic component: calcium, phosphate and calcium carbonate with small amount of mangnesium, fluoride, sulfate. The organic matter in bone matrix is type I collagen and ground substance
Cells of bone:
Osteoblasts: are responsible for synthesis of the organic components of bone matrix (type I collagen) .
Osteocytes: which derive from osteoblasts lie in the lacunae situated between matrix, cylindrical matrix canaliculi house cytoplasmic processes of osteocytes.these cells use activetly involved in the maintenance of the bony matrix. Their death is followed by resorption of this matrix.
osteoclasts: are very large branched motile cells. Contain from 5 to 50 nuclei. Osteoclasts are devrived from the fusion of bone marrow- derived monoucleated cells. Osteoclasts lie within enzymatically atched depressions in the matrix known as howships lacunae .
periosteum and endosteum
enternal and external surfaces of bone are covered by layers of bone- forming cells and c.t.sharpeys fibers : bundles of periosteal collagen fibers penetrate the bone matrix, binding the periosteum to bone
osteoprogenitor cell : cells located in the inner layers of periosteum it is like fibroblast with the potential to divide by mitosis and differentiate into osteoblasts.
Types of bone:
compact bone
cancellons ( spongy) bone microscopic examination of bone shows two varieties primary bone is the first bone tissue to appear in embryonic development and in fracture repair it is characterized by random disposition of fine collagen fibers. This tissue is usually temporary except in few places in body, primary bone are lower mineral content and a higher proportion of osteocytes than in secondary bone t.
HYPERLINK "http://en.wikipedia.org/wiki/File:Gingival_sulcus.PNG" \o "Enlarge" INCLUDEPICTURE "http://bits.wikimedia.org/skins-1.17/common/images/magnify-clip.png" \* MERGEFORMATINET
Sharpey's fibres (bone fibres, or perforating fibres) are a HYPERLINK "http://en.wikipedia.org/wiki/Matrix_(biology)" \o "Matrix (biology)" matrix of HYPERLINK "http://en.wikipedia.org/wiki/Connective_tissue" connective tissue consisting of bundles of strong HYPERLINK "http://en.wikipedia.org/wiki/Collagen" \o "Collagen" collagenous HYPERLINK "http://en.wikipedia.org/wiki/Fiber" \o "Fiber" fibres connecting HYPERLINK "http://en.wikipedia.org/wiki/Periosteum" periosteum to HYPERLINK "http://en.wikipedia.org/wiki/Bone" bone. They are part of the outer fibrous layer of periosteum, entering into the outer circumferential and interstitial HYPERLINK "http://en.wikipedia.org/wiki/Lamellae_(zoology)" \o "Lamellae (zoology)" lamellae of bone tissue.
INCLUDEPICTURE "http://neuromedia.neurobio.ucla.edu/campbell/bone/wp_images/142%20sharpeys%20fibers%20longt.jpg" \* MERGEFORMATINET
Histogenesis
interamembranous ossification
some of the embryonic c.t. (mesenchyme) transforms into a highly vascular sheet
cells enlarge and differentiate into osteogenic cells then to osteoblasts
mesenchyme condenses into a network of soft trabeculae
osteoblast deposit an organic matrix (osteoid tissue ) lack of ca++ salts
calcium phosphate is deposited in the matrix
Endochondral ossification
Take place with a piece of hyaline cartilage whose shape resmbles model
The bone tissue appears as a hallow bone cylinder that surrounds the mid portion of the cartilage model [bone collar]
the local cartilage undergoes a degenerative process this processes begins at the central portion of the cartilage diaphysis where B.V. penetrate through the bone collar
proliferation
hypertrophy
calcified zone
chondrocyte die
ossification zone epiphyseal plate : connect the two epiphyses and diephysis and responsible for the growth in length of the bone
oseopetrosis : a disease caused by a defect in osteoclast function that results in overgrowth , thickening , and hardening of bones.
Obesity imposes significant strain on the articular cartilage , accelerating its degeneration , joint problems are far more frequent in obesity individuals.
Chondroplastic dwarfism : results from the chondrocytes in multiplication and hypertrophy zones fail to multiply, the long bone grow slowly and stop growing early
Bone Fracture
There are three processes involved in the healing of fractures - inflammatory, reparative and remodelling phases or 6 stages - the hematoma stage, inflammatory stage, formation of granulation tissue, soft and 'hard' callus formation, and remodelling. Their duration depends on age, health and nutritional status.Hematoma Stage: Hemorrhage, clot formation - within hours to days.
Inflammatory Stage: Begins within 48 hours, inflammatory cells appear. Organization and resorption of
Granulation Tissue: From 2 days. Presence of - 12 mesenchymal cells, fibroblasts, new capillaries.
Soft Callus: One week to several months. Callus grows and bridges the fracture site; cartilage and trabelcular bone laid down.
Hard Callus: One week to several months. When callus has sealed the bone ends. Trabecular bone.
Remodelling: Continues for several months. Reorganization of bon.
Bone marrow
There are two types of bone marrow: red marrow (consisting mainly of HYPERLINK "http://en.wikipedia.org/wiki/Hematopoiesis" \o "Hematopoiesis" hematopoietic tissue) and yellow marrow (consisting mainly of HYPERLINK "http://en.wikipedia.org/wiki/Fat_cells" \o "Fat cells" fat cells). HYPERLINK "http://en.wikipedia.org/wiki/Red_blood_cell" \o "Red blood cell" Red blood cells, HYPERLINK "http://en.wikipedia.org/wiki/Platelet" \o "Platelet" platelets and most HYPERLINK "http://en.wikipedia.org/wiki/White_blood_cell" \o "White blood cell" white blood cells arise in red marrow. Both types of bone marrow contain numerous blood vessels and capillaries.
At birth, all bone marrow is red. With age, more and more of it is converted to the yellow type. About half of adult bone marrow is red. Red marrow is found mainly in the HYPERLINK "http://en.wikipedia.org/wiki/Flat_bone" \o "Flat bone" flat bones, such as the HYPERLINK "http://en.wikipedia.org/wiki/Pelvis" \o "Pelvis" hip bone, HYPERLINK "http://en.wikipedia.org/wiki/Human_sternum" \o "Human sternum" breast bone, HYPERLINK "http://en.wikipedia.org/wiki/Human_skull" \o "Human skull" skull, HYPERLINK "http://en.wikipedia.org/wiki/Rib" \o "Rib" ribs, HYPERLINK "http://en.wikipedia.org/wiki/Vertebra" \o "Vertebra" vertebrae and HYPERLINK "http://en.wikipedia.org/wiki/Shoulder_blade" \o "Shoulder blade" shoulder blades, and in the HYPERLINK "http://en.wikipedia.org/wiki/Cancellous" \o "Cancellous" cancellous ("spongy") material at the HYPERLINK "http://en.wikipedia.org/wiki/Epiphysis" \o "Epiphysis" epiphyseal ends of the HYPERLINK "http://en.wikipedia.org/wiki/Long_bone" \o "Long bone" long bones such as the HYPERLINK "http://en.wikipedia.org/wiki/Femur" femur and HYPERLINK "http://en.wikipedia.org/wiki/Humerus" humerus. Yellow marrow is found in the hollow interior of the middle portion of long bones.
In cases of severe blood loss, the body can convert yellow marrow back to red marrow to increase blood cell production.
INCLUDEPICTURE "http://www.gla.ac.uk/ibls/US/fab/images/generic/bofractu.gif" \* MERGEFORMATINET