Flashcards in Bone Biology Deck (33):
T/F: All axial bones form by ossification of a cartilaginous model, endochondral ossification, whereas membranous bones like the skull form from a fibrous precursor
T/F: Endochondral ossification, responsible for long
bone longitudinal growth, occurs as chondrocytes arranged in columns parallel to the long axis of the bones differentiate and form histologically distinct zones.
Adjacent to the zone of resting cartilage, in the zone of __________, cell division occurs in a plane perpendicular to the long axis of the bone and thereby increases the length of the cell column.
T/F: Chondrocytes mature, become encased in extracellular matrix, and assume a round morphology in the pre-hypertrophic zone just prior to the hypertrophic zone, where chondrocytes cease dividing, increase in size, and hypertrophy
Hypertrophic chondrocytes are replaced by mineralized bone and bone marrow via vascular invasion, cartilaginous matrix resorption, and recruitment of osteoblasts that deposit bone matrix in the zone of ___________.
T/F: Cortical bone is more metabolically active and responsive to metabolic homeostasis changes than cancellous bone.
False; Trabecular (aka cancellous or spongey) bone is more metabolically active and responsive to metabolic homeostasis changes than cortical bone.
cortical and trabecular bone are composed of osteons. Cortical osteons are called __________ ________ (they have a cylindrical shape and form a branching network within cortical bone) and trabecular osteons are called _______ (they are also composed of concentric lamellae, but they are semilunar in shape).
Haversian systems; packets
What is the difference between primary and secondary osteons?
Primary osteons form during appositional bone growth (growth resulting in increased bone thickness). Secondary osteons are created throughout life when osteoblasts deposit bone at the end of bone tunnels (cutting cones) created by osteoclasts during the process of bone remodeling.
The ______ _______ layer of periosteum is composed of fibroblasts, collagen and elastin fibers, and a nerve and microvascular network.
The ______ ________ layer, which directly contacts the bone surface, contains adult mesenchymal progenitor cells, differentiated osteogenic progenitor cells, osteoblasts, fibroblasts, microvessels, and sympathetic nerves.
Which layer of the periosteum provides cells for fracture healing and appositional bone growth.
The inner cambium layer
What are Sharpey's fibers?
thick collagenous fibers that attach the periosteum to the outer cortical surface of a bone.
T/F: Bones widen through periosteal apposition when osteoblasts add mineralized tissue on the periosteal bone surface.
the endosteum is a membranous structure covering the inner surface of cortical bone, trabecular bone, and the blood vessel canals (_______ ______) that contains blood vessels, osteoblasts, and osteoclasts.
The endosteum is a membranous structure covering the inner surface of cortical bone, trabecular bone, and the blood vessel canals (_______ ______) that contains blood vessels, osteoblasts, and osteoclasts.
T/F: The direction of blood flow in the efferent (venous) system is primarily away from the cortex toward the medulla (centripedal) and volume is about six- to eightfold greater than the afferent (arterial) system.
True; in mature animals, about 70% of the afferent blood flow within the diaphysis of mature bone is toward the cortex away from the medulla (centrifugal) and 30% toward the medulla (centripedal).
T/F: In mature animals, about 70% of the afferent blood flow within the diaphysis of mature bone is toward the cortex away from the medulla (centrifugal) and 30% toward the medulla (centripedal).
True; the primary blood supply and direction of blood flow in the afferent vascular system changes during long bone growth, and in the young animal, the periosteal contribution is much greater than at skeletal maturity.
From what structures does cortical bone receive its blood supply?
The endosteal circulation supplies the medullary areas and the inner two thirds of cortical bone, whereas the periosteal arterioles supply the outer third.
Inorganic, organic, and water components of bone are approximately 40%, 30%, and 25% by volume, respectively. The inorganic component is mostly __________ ___________ and 90% of the organic matrix is composed of ____ _ _________.
crystalline hydroxyapatite: [ca3(Po4)2]3ca(oH)2 ;
type I collagen
T/F: In normal bone, the mineral provides stiffness and strength, and collagen conveys ductility (the ability to plastically deform without fracture) and toughness (the ability to absorb energy).
The __________ matrix provides structural strength to tissues to maintain the complex architecture and the shape of organs. It is a scaffold for the cells and a reservoir for ____________ and _________, and it modulates cell activation and turnover.
extracellular; growth factors and cytokines
When embedded in matrix, the osteoblasts become _________, which have extensive __________, actin-based morphological structures at the periphery of cells, within canaliculi in mineralized bone.
At the completion of bone formation, 50% to 70% of osteoblasts undergo apoptosis, and the remainder become osteocytes or bone-lining cells.
__________ are proteins that maintain gap junctions between cells to allow direct communication through intercellular channels.
the __________________ regulate mineral ion influx and efflux into and out of bone extracellular fluid, and they retain the ability to redifferentiate into osteoblasts.
T/F: Activated osteoblasts are derived from mononuclear precursor cells of the monocyte-macrophage lineage originating in bone marrow.
False; Activated osteoclasts are derived from mononuclear precursor cells of the monocyte-macrophage lineage originating in bone marrow. Osteoblasts are derived from self-renewing, multipotent stem cells through a multistep differentiation pathway. The multipotent cells give rise to osteoprogenitor cells, which differentiate into preosteoblasts and then mature into ostoeblasts.
____________________ is part of the tumor necrosis factor family and is required for osteoclast formation, whereas _______________________ is necessary for differentiation of osteoclast precursors, osteoclast survival, and cytoskeletal changes for bone resorption.
receptor activator of nuclear factor κB ligand (RANKL); macrophage colony-stimulating factor (M-CSF),
_______________ is a membrane-bound and -secreted protein that binds RANKL to inhibit its action at the RANK receptor.
T/F: Activated osteoclasts secrete hydrogen ions via H+-ATP proton pumps and chloride channels in their cell membranes to lower the pH and mobilize bone mineral.
Bone is strongest in ___________, weaker in ______, and weakest in _________.
compression; shear; tension
T/F: For three-point bending, three forces produce two equal moments. Each moment is the product of one of the two peripheral forces and its perpendicular distance from the middle force.
True; Failure typically begins on the tensile surface of the bone and propagates along the maximum tension plane toward the compressed surface until the maximum shear force at about 45 degrees from the neutral axis is reached and exceeds the tensile forces and the fracture continues along them. the typical fracture contains a butterfly fragment on the compressive side.
T/F: Four-point bending describes two force couples producing two equal moments. the bending moment is the same in the areas between the force couples.
True; Four-point bending rarely results in a fracture clinically, but it is often used for bone testing. Because the bending moment is uniform between the two central force couples, bone fractures at the weakest point between the two.
_______ fracture healing involves direct regeneration of the Haversian system between abutted fracture fragments to restore mechanical integrity. Healing occurs by direct growth of secondary ________ from one fragment to another and by intramembranous bone formation. Vascular endothelial cells and perivascular mesenchymal cells provide _____________ cells that differentiate into osteoblasts.
Direct; osteons; osteoprogenitor