A Practical Approach, Second Edition=Ronald D. Ho.pdf

996 DEVELOPMENTAL REPRODUCTIVE TOXICOLOGY: A PRACTICAL APPROACH, SECOND EDITIONPeri-articular arcadeLevel ofgrowth plateEpiphysealvesselsMetaphyseal vesselsAscending branchesNutrient arteryPeriosteal boneDescending branchesLevel ofgrowth plateCortical networkMetaphysealvesselsEpiphysealvesselsFigure 6a (2)A summary of the main arterial supply to a developing long bone.Postnatally, nutrient arteries supply the diaphysis and central portion of the metaphysis withblood while the epiphyseal arteries supply only the epiphyses. The metaphyseal arteries supply theperipheral regions of the metaphysis (103).In addition, during early postnatal development in the epiphyseal region, cartilage canalspersisting from the fetal period are a source of nutrition for the epiphyses. Cartilage canals mayalso play a role in the appearance of the secondary center of ossification (55, 103).7.1.1 Diaphyseal ArteriesDiaphyseal arteries gain entry to the diaphysis of long bones through nutrient foramens that leadinto nutrient canals (2). Once inside of the medullary cavity, the diaphyseal arteries branch proximallyand distally (2, 104). The ascending and descending branches of the vessel travel throughoutthe marrow cavity and end in helical loops near the metaphysis. In the metaphyseal region thesevessels connect with both the metaphyseal and periosteal arteries (104).The main nutrient artery is surrounded by several venules that merge into 1 or 2 large nutrientveins. In fact, in bone, many openings or foramina give exit to veins alone so that the number ofnutrient veins draining a bone usually exceeds the number of the nutrient arteries supplying it (103).Long bones are sometimes supplied by more than one nutrient diaphyseal artery (103). Forexample, the rabbit tibia has 2 diaphyseal arteries and the artery of the trochanteric fossa in the ratfemur can develop into a second afferent vessel to the diaphysis. On occasion, the diaphysis of thehuman humerus may have 3 nutrient arteries and the diaphysis of the human femur may have upto 2 nutrient arteries (103).In the scientific literature conflicting views exist regarding the direction and source of arterialblood flow in the cortex of the diaphysis. Historically, scientists believed that the compact bone ofthe diaphyseal cortex was fed by periosteal vessels, and the inner portion of the shaft received itsblood supply from the nutrient artery (102, 2). However, modern research has demonstrated thatin young bones (< 35 years old), the diaphyseal cortex primarily receives its blood supply fromthe nutrient artery of the diaphysis, but as bones age, periosteal arteries may begin to supply bloodto the cortex (2).© 2006 by Taylor & Francis Group, LLC