ORTHOPEDICS HYPERGUIDE MCQ 601-650

601. (734) Q2-995:

Which of the following collagens stabilizes the collagen network by linking the type II collagen fibrils:

1) Type I

3) Type IX

2) Type III

5) Type XII

4) Type X

The strength of articular cartilage comes in part from the relative insolubility of cartilage collagens. This insolubility is secondary to the extensive cross-linking. There are a number of factors for this cross-linking:

Covalent cross links in type II collagen Links between types II and type IX Links between chains of type XI

Type IX collagen stabilizes the collagen network by linking the type II collagen fibers.

Correct Answer: Type IX

602. (735) Q2-996:

Which of the following is the most prevalent glycosaminoglycan in articular cartilage:

1) Keratan sulfate

3) Hyaluronate

2) Chondroitin sulfate

5) Fibromodulin

4) Dermatan sulfate

The three major types of glycosaminoglycans in articular cartilage are chondroitin sulfate, keratan sulfate, and dermatan sulfate. Chondroitin sulfate is the most common glycosaminoglycan in articular cartilage. Chondroitin 4-sulfate and chondroitin 6-sulfate isomers account for 55% to 90% of the total amount.

The glycosaminoglycan chains contain repeating carboxyl and sulfate groups that become ionized in solution. These free-floating ions account for the Donnan osmotiCpressure and the large charge-to-charge repulsive forces of the glycosaminoglycan chains.

Most of the glycosaminoglycans are in the form of large aggregates called aggrecan. Link protein binds to both the G1 domain of aggrecan and the hyaluron to form the aggrecan-hyaluronate-link protein complexes, which are called proteoglycan aggregates.

Correct Answer: Chondroitin sulfate

603. (736) Q2-997:

Which of the following binds to both the G1 domain of large aggregating type of proteoglycans (aggrecan molecule) and hyaluron:

1) Keratan sulfate

3) Fibromodulin

2) Chondroitin sulfate

5) Link protein

4) Dermatan sulfate

The three major types of glycosaminoglycans in articular cartilage are chondroitin sulfate, keratan sulfate, and dermatan sulfate. Chondroitin sulfate is the most common glycosaminoglycan in articular cartilage. Chondroitin 4-sulfate and chondroitin 6-sulfate isomers account for 55% to 90% of the total amount.

The glycosaminoglycan chains contain repeating carboxyl and sulfate groups that become ionized in solution. These free-floating ions account for the Donnan osmotiCpressure and the large charge-to-charge repulsive forces of the glycosaminoglycan chains.

Most of the glycosaminoglycans are in the form of large aggregates called aggrecan. Link protein binds to both the G1 domain of aggrecan and the hyaluron chain to form the aggrecan-hyaluronate-link protein complexes, which are called proteoglycan aggregates.

Correct Answer: Link protein

604. (737) Q2-998:

Which of the following proteoglycans is involved with collagen fibrillogenesis and fibril diameter:

1) Chondroitin sulfate

3) Fibromodulin

2) Keratan sulfate

5) Biglycan

4) Decorin

Biglycan and decorin are two small proteoglycans (biglycan has two dermatan sulfate chains and decorin contains one dominant sulfate chain). Decorin is located on the surface of collagen fibrils and is believed to be involved with fibrillogenesis and fibril diameter.

Correct Answer: Decorin

605. (738) Q2-999:

To which of the following long and unbranched molecules does link protein form a bond with G1 domain of aggrecan:

1) Chondroitin 4-sulfate

3) Keratan sulfate

2) Chondroitin 6-sulfate

5) Dermatan sulfate

4) Hyaluronate

Link protein binds to both the G1 domain of aggrecan and the hyaluronate chain forming the aggregan-hyaluronate-link protein complexes referred to as proteoglycan aggregates.

Correct Answer: Hyaluronate

606. (739) Q2-1000:

Adult articular cartilage receives its nutrition through which of the following mechanisms:

1) Fine capillary network from the synovial tissues

3) Fine capillary network from the perichondral ring

2) Fine capillary network through the subchondral bone

5) Diffusion from the synovial fluid through small pores

4) Diffusion from the synovial fluid through large pores

Articular cartilage receives its nutrition through small pores (approximately 50 angstroms) from the synovial fluid. Adult articular cartilage has no blood supply. Diffusion rates vary between 10 seconds to 1 hour. Degradation products are able to leave the cartilage rapidly.

Correct Answer: Diffusion from the synovial fluid through small pores

607. (740) Q2-1001:

In which of the following sites are the glycosaminoglycan chains added to the protein cores:

1) Nucleus

3) Secretory vesicles

2) Golgi apparatus

5) Extracellular matrix

4) Pericellular matrix

The proteins for glycosaminoglycan synthesis are synthesized in the ribosomes. The glycosaminoglycan chains are added in the Golgi apparatus. Protoeglycan aggregates are formed in the extracellular matrix where link protein, hyaluronate, and aggrecan come together. Many factors may influence the quantity and makeup of the proteoglycans.

Glycosaminoglycan chains are formed intracellularly, whereas large proteoglycan aggregates are formed outside the cell in the extracellular matrix.

Correct Answer: Golgi apparatus

608. (741) Q2-1002:

In which of the following sites does aggrecan, link protein, and hyaluronate come together to form the proteoglycan aggregate:

1) Secretory vesicles

3) Extracellular matrix

2) Pericellular matrix

5) Golgi apparatus

4) Nucleus

The proteins for glycosaminoglycan synthesis are synthesized in the ribosomes (hence, intracellular). The glycosaminoglycan chains are added in the Golgi apparatus. Protoeglycan aggregates are formed in the extracellular matrix where link protein, hyaluronate, and aggrecan come together. Many factors may influence the quantity and makeup of the proteoglycans.

Correct Answer: Extracellular matrix

609. (742) Q2-1003:

Which of the following statements is true concerning the changes seen in human articular cartilage as a person ages (normal cartilage):

1) Progressive increase in chondroitin 4-sulfate

3) Progressive decrease in collagen concentration

2) Progressive decrease in chondroitin 6-sulfate

5) Progressive increase in keratan sulfate concentration

4) Progressive increase in collagen concentration

There are several important points concerning aging and articular cartilage. The collagen content increases quickly after birth, attaining adult levels, and then it does not materially change. The water level is high in immature individuals but remains constant in the adult. In contrast to the stable levels of collagen and water, the proteoglycan composition changes:

Chondroitin 4-sulfate levels progressively decrease. Chondroitin 6-sulfate levels progressively increase.

Keratan sulfate levels progressively increase in the human. At age 30, the level increases to 25% to 50% of proteoglycan content.

Aggregation decreases with advancing age.

Correct Answer: Progressive increase in keratan sulfate concentration

610. (743) Q2-1004:

Which of the following two components account for the biphasiCbehavior of cartilage:

1) Chondroitin 4-sulfate and chondroitin 6-sulfate

3) Collagen and proteoglycans

2) Chondroitin 6-sulfate and keratan sulfate

5) Collagen and fibronectin

4) Water and the solid matrix of cartilage (collagen and proteoglycans)

Cartilage is a biphasiCmaterial. Water and the solid matrix (collagen and the proteoglycans) account for this behavior. Articular cartilage is viscoelastiCand will exhibit time-dependent behavior. There are two mechanisms for the viscoelasticity. One mechanism is flow independent. The flow independent behavior derives from the collagen-proteoglycan matrix. The flow dependent mechanism depends on the interstitial fluid flow and pressurization.

Cartilage must be compressed for 2.5 to 6 hours before the interstitial fluid flow ends and the load is fully borne by the collagen proteoglycan matrix (this virtually never happens in humans). The ratio of load supported by the fluid pressure to that supported by solid matrix is greater than 20:1.

In osteoarthritis cartilage, there is increased water content and decreased proteoglycan content. These changes increase cartilage permeability and lower the ability to carry load.

Correct Answer: Water and the solid matrix of cartilage (collagen and proteoglycans)

611. (744) Q2-1005:

Which of the following changes occurs in the articular cartilage following immobilization of a joint:

1) Increase in proteoglycan concentration

3) Increase in type II collagen

2) Decrease in proteoglycan concentration

5) Increase in type IX collagen

4) Decrease in type II collagen

Reduced joint motion and loading results in decreased proteoglycan concentration. Collagen concentration does not change. Normal tensile properties are maintained which reflect the relatively constant collagen concentration. Nutrition of the joint decreases because of reduced loading.

Correct Answer: Decrease in proteoglycan concentration

612. (745) Q2-1006:

Which of the following collagens forms part of the matrix immediately surrounding the chondrocytes and may help attach the chondrocyte to the matrix macromolecular framework:

1) Type II

3) Type XI

2) Type IX

5) Type X

4) Type VI

Type II, IX, and XI collagen forms a fibrillar network that gives cartilage its form and tensile stiffness and strength. Type VI collagen forms part of the matrix immediately surrounding chondrocytes and may help attach the cells attach to the matrix macromolecular framework.

Correct Answer: Type VI

613. (746) Q2-1007:

A genetiCmutation accounts for the manifestations of achondroplasia. Which of the following proteins has a genetiCmutation that has been linked to achondroplasia:

1) Fibroblast growth factor (FGF) receptor 3

3) Fibrillin

2) Type I collagen

5) Cartilage oligomeriCmatrix protein (COMP)

4) Type II collagen

The genetiCdefect in achondroplasia involves fibroblast growth factor (FGF) receptor 3.

The other answers refer to:

Osteogenesis imperfecta Type I collagen

Marfan syndrome Fibrillin

Spondyloepiphyseal

dysplasia Type II collagen

Pseudoachondroplasia Cartilage oligomeriCmatrix protein (COMP) Correct Answer: Fibroblast growth factor (FGF) receptor 3

614. (747) Q2-1008:

A genetiCmutation accounts for the manifestations of osteogenesis imperfecta. Which of the following factors has a genetiCmutation that has been linked to osteogenesis imperfecta:

1) Fibroblast growth factor (FGF) receptor 3

3) Cartilage oligomeriCmatrix protein (COMP)

2) Type I collagen

5) Type II collagen

4) Fibrillin

Osteogenesis imperfecta has been linked to defect in type I collagen.

The other answers refer to:

Achondroplasia Fibroblast growth factor (FGF) receptor 3

Marfan syndrome Fibrillin

Spondyloepiphyseal

dysplasia Type II collagen

Pseudoachondroplasia Cartilage oligomeriCmatrix protein (COMP) Correct Answer: Type I collagen

615. (748) Q2-1009:

A genetiCmutation accounts for the manifestations of pseudoachondroplasia. Which of the following factors has a genetiCmutation that has been linked to pseudoachondroplsia:

1) Fibroblast growth factor (FGF) receptor 3

3) Cartilage oligomeriCmatrix protein (COMP)

2) Type I collagen

5) Type II collagen

4) Fibrillin

The genetiCdefect in pseudoachondroplasia involves cartilage oligomeriCmatrix protein (COMP). The other answers refer to:

Achondroplasia Fibroblast growth factor (FGF) receptor 3

Marfan syndrome Fibrillin

Spondyloepiphyseal

dysplasia Type II collagen

Osteogenesis imperfecta Type I collagen

Correct Answer: Cartilage oligomeriCmatrix protein (COMP)

616. (749) Q2-1010:

A genetiCmutation accounts for the manifestations of Marfan syndrome. Which of the following factors has a genetiCmutation that has been linked to Marfan syndrome:

1) Fibroblast growth factor (FGF) receptor 3

3) Cartilage oligomeriCmatrix protein (COMP)

2) Type I collagen

5) Type II collagen

4) Fibrillin

The molecular defect in Marfan syndrome involves fibrillin. The other answers refer to:

Achondroplasia Fibroblast growth factor (FGF) receptor 3

Pseudoachondroplasia Cartilage oligomeriCmatrix protein (COMP) Spondyloepiphyseal

dysplasia Type II collagen

Osteogenesis imperfecta Type I collagen

Correct Answer: Fibrillin

617. (750) Q2-1011:

A genetiCmutation accounts for the manifestations of spondyloepiphyseal dysplasia. Which of the following factors has a genetiCmutation that has been linked to spondyloepiphyseal dysplasia:

1) Fibroblast growth factor (FGF) receptor 3

3) Cartilage oligomeriCmatrix protein (COMP)

2) Type I collagen

5) Type II collagen

4) Fibrillin

The genetiCdefect in spondyloepiphyseal dysplasia involves type II collagen.

The other answers refer to:

Achondroplasia Fibroblast growth factor (FGF) receptor 3

Pseudoachondroplasia Cartilage oligomeriCmatrix protein (COMP) Marfan syndrome Fibrillin

Osteogenesis

imperfecta Type I collagen

Correct Answer: Type II collagen

618. (751) Q2-1012:

A genetiCmutation accounts for the manifestations of Duchenne muscular dystrophy. Which of the following factors has a genetiCmutation that has been linked to Duchenne muscular dystrophy:

1) Dystrophin

3) CarboniCanhydrase type II proton pump

2) PEX (a cellular endopeptidase)

5) EXT1, EXT2 genes

4) Gs alpha (receptor-coupled signaling protein)

In Duchenne muscular dystrophy, the genetiCdefect involves dystrophin. The other answers refer to:

X-linked hypophosphatemic

rickets PEX (a cellular endopeptidase)

Osteopetrosis CarboniCanhydrase type II proton pump

Fibrous dysplasia Gs alpha (receptor-coupled signaling protein)

Multiple hereditary exostoses EXT1, EXT2 genes

Correct Answer: Dystrophin

619. (752) Q2-1013:

A genetiCmutation accounts for the manifestations of X-linked hypophosphatemiCrickets. Which of the following factors has a genetiCmutation that has been linked to X-linked hypophosphatemiCrickets:

1) Dystrophin

3) CarboniCanhydrase type II proton pump

2) PEX (a cellular endopeptidase)

5) EXT1, EXT2 genes

4) Gs alpha (receptor-coupled signaling protein)

The genetiCdefect in X-linked hypophosphatemiCrickets involves PEX (a cellular endopeptidase).

The other answers refer to:

Duchenne muscular dystrophy

Â

Dystrophin

Osteopetrosis CarboniCanhydrase type II proton pump

Fibrous dysplasia Gs alpha (receptor-coupled signaling protein)

Multiple hereditary exostoses EXT1, EXT2 genes

Correct Answer: PEX (a cellular endopeptidase)

620. (753) Q2-1014:

A genetiCmutation accounts for the manifestations of osteopetrosis. Which of the following factors has a genetiCmutation that has been linked to osteopetrosis:

1) Dystrophin

3) CarboniCanhydrase type II proton pump

2) PEX (a cellular endopeptidase)

5) EXT1, EXT2 genes

4) Gs alpha (receptor-coupled signaling protein)

The genetiCdefect in osteopetrosis involves the carboniCanhydrase type II proton pump.

The other answers refer to:

Duchenne muscular dystrophy

 Dystrophin

X-linked hypophosphatemic

rickets PEX (a cellular endopeptidase)

Fibrous dysplasia Gs alpha (receptor-coupled signaling protein)

Multiple hereditary exostoses EXT1, EXT2 genes

Correct Answer: CarboniCanhydrase type II proton pump

621. (754) Q2-1015:

A genetiCmutation accounts for the manifestations of fibrous dysplasia. Which of the following factors has a genetiCmutation that has been linked to fibrous dysplasia:

1) Dystrophin

3) CarboniCanhydrase type II proton pump

2) PEX (a cellular endopeptidase)

5) EXT1, EXT2 genes

4) Gs alpha (receptor-coupled signaling protein)

The genetiCdefect in fibrous dysplasia involves an activity mutation of Gs alpha (a receptor coupled signaling protein).

The other answers refer to:

Duchenne muscular dystrophy

 Dystrophin

X-linked hypophosphatemic

rickets PEX (a cellular endopeptidase)

Osteopetrosis CarboniCanhydrase type II proton pump

Multiple hereditary exostoses EXT1, EXT2 genes

Correct Answer: Gs alpha (receptor-coupled signaling protein)

622. (755) Q2-1016:

A genetiCmutation accounts for the manifestations of multiple hereditary exostoses. Which of the following factors has a genetiCmutation that has been linked to hereditary exostoses:

1) Dystrophin

3) CarboniCanhydrase type II proton pump

2) PEX (a cellular endopeptidase)

5) EXT1, EXT2 genes

4) Gs alpha (receptor-coupled signaling protein)

The genetiCdefect in multiple hereditary exostoses involves EXT1 and EXT2 genes. The other answers refer to:

Duchenne muscular dystrophy Dystrophin

X-linked hypophosphatemic

rickets PEX (a cellular endopeptidase)

Osteopetrosis CarboniCanhydrase type II proton pump

Fibrous dysplasia Gs alpha (receptor-coupled signaling protein) Correct Answer: EXT1, EXT2 genes

623. (756) Q2-1017:

Which of the following types of bone behaves in an isotropiCmanner when loaded in different directions:

1) Lamellar bone

3) Cortical bone

2) Woven bone

5) Plexiform bone

4) Cancellous bone

Woven bone is immature bone that is found in newborns, fracture callus, and the metaphyses of growing bone. In woven bone, the collagen fibers are oriented in a completely random fashion. When woven bone is loaded, it performs in an isotropiCmanner. The other types of bone (lamellar, cortical, cancellous, and plexiform) contain collagen that is oriented along the long axis of the bone and cause the bone to perform anisotropically.

Correct Answer: Woven bone

624. (757) Q2-1018:

Haversian bone is composed of vascular channels surrounded circumferentially by lamellar bone. Which of the following terms is used to describe the unit of bone composed of a neurovascular channel surrounded by a cell-permeated layer of bone matrix:

1) Bone remodeling unit

3) Osteon

2) Plexiform bone

5) Canaliculi

4) Volkman unit

The osteon is a unique arrangement of bone cells and matrix surrounding a blood vessel. The osteon is an irregular branching, anastomosing cylinder composed of a centrally placed neurovascular canal surrounded by cell-permeated layers of bone matrix.

The bone remodeling unit refers to the cutting cone of leading osteoclasts and following osteoblasts.

Plexiform bone is a structural type of bone found in large animals where rapid bone growth occurs. There are alternating layers of lamellar and woven bone.

Volkman canals are the channels connecting different osteons or Haversian units.

Canaliculi are small channels through which the cell processes of the osteocytes connect to each other. Correct Answer: Osteon

625. (758) Q2-1019:

The normal porosity of cortical bone is:

1) 5%

3) 20%

2) 10%

5) 30%

4) 25%

The normal porosity of cortical bone is 10% compared to trabecular bone, which is 50% to 90%. Cortical bone porosity occurs because of the Haversian and Volkman canals and, to a lesser extent, from the osteocyte lacunae and canaliculi.

Trabecular bone is arranged as a series of interconnecting small plates and rods. The porosity may vary between 50% to 90%. This porosity is secondary to the spaces between the trabecular pieces of bone rather than voids in the actual pieces of trabecular bone.

Correct Answer: 10%

626. (759) Q2-1020:

The normal porosity of trabecular bone is:

1) 10%

3) 30%

2) 20%

5) 50% to 90%

4) 40%

Trabecular bone is arranged as a series of interconnecting small plates and rods. The porosity may vary between 50% to 90%. This porosity is secondary to the spaces between the trabecular pieces of bone rather than voids in the actual pieces of trabecular bone.

The normal porosity of cortical bone is 10%. Cortical bone porosity occurs because of the Haversian and Volkman canals and, to a lesser extent, from the ostocyte lacunae and canaliculi.

Correct Answer: 50% to 90%

627. (760) Q2-1021:

Which of the following cells produce osteocalcin and bone sialoprotein:

1) Osteocytes

3) Mast cells

2) Osteoblasts

5) Fibroblasts

4) Osteoclasts

Osteoblasts are metabolically active cells that line the bone surface. Osteoblasts produce type I collagen and many

noncollagenous proteins such as osteocalcin, bone sialoprotein, and extracellular matrix proteins. Osteoblasts have large amounts of rough endoplasmiCreticulum because they prepare large amounts of protein for export out of the cell. The Golgi apparatus exports the protein.

Correct Answer: Osteoblasts

628. (761) Q2-1022:

Osteoblasts predominantly form which of the following types of collagen:

1) Type VI

3) Type X

2) Type IX

5) Type II

4) Type I

Osteoblasts produce type I collagen. This is the major type of collagen found in bone. Type I collagen is the only collagen capable of mineralization.

Correct Answer: Type I

629. (762) Q2-1023:

Osteocytes differ from osteoblasts because osteocytes:

1) Have a higher nucleus to cytoplasm ratio

3) Line the bone surfaces

2) Have a larger number of organelles

5) Have alkaline phosphatase that is distributed over the outer surface of the cell

4) Are isolated individually from other bone cells

Osteoblasts that become imbedded into the bone matrix become osteocytes. Osteocytes are less metabolically active because they do not produce large amounts of protein for export. Thus, osteocytes have a higher nucleus to cytoplasm ratio than osteoblasts. Osteocytes have fewer organelles as they do not need extensive intracellular machinery to export protein products.

Osteocytes have extensive connections with other osteocytes through the cell processes that travel through the canaliculi. Strain generated signals such as cell deformation, streaming potentials, or shear stress by fluid flow could be perceived by the osteocytes and passed on to other cells.

Osteocytes do not line the bone surface as osteoblasts do. In addition, osteoblasts have alkaline phosphatase covering the cell membranes.

Correct Answer: Have a higher nucleus to cytoplasm ratio

630. (763) Q2-1024:

Which of the following is characteristiCof an active osteoclast:

1) A large amount of rough endoplasmiCreticulum

3) Ruffled border adjacent to the bone surface

2) Paucity of intracellular smooth vesicles

5) Low acid phosphatase activity

4) Few mitochondria

Active osteoclasts resorb the mineral and organiCmatrix of bone. Active osteoclasts also attach the cell to exposed bone matrix. When osteoclasts are studied with an electron microscope, there are two prominent findings â a ruffled border and a clear zone. In the clear zone, the osteoclast seals off the area of bone to be resorbed and attaches to the bone surface through a receptor- mediated process with the assistance of proteins called integrins. The ruffled border is an area found in the infoldings of the cell membrane. At the area of the ruffled border, the osteoclasts lower the pH with hydrogen ions through the carboniCanhydrase system. This lowered pH increases the solubility of the apatite crystals and the mineral can be removed. The organiCcomponents of the bone are then hydrolyzed through acidiCproteolytiCdigestion.

Correct Answer: Ruffled border adjacent to the bone surface

631. (764) Q2-1025:

Osteoclasts bind to the bone surface through which of the following proteins:

1) Osteocalcin (bone Gla protein)

3) Osteopontin (bone sialoprotein 1)

2) Integrins

5) Bone sialoprotein 2

4) Fibromodulin

Active osteoclasts resorb the mineral and organiCmatrix of bone. Active osteoclasts also attach the cell to exposed bone matrix. When osteoclasts are studied with an electron microscope, there are two prominent findings â a ruffled border and a clear zone. In the clear zone, the osteoclast seals off the area of bone to be resorbed and attaches to the bone surface through a receptor- mediated process with the assistance of proteins called integrins. The ruffled border is an area found in the infoldings of the cell membrane. At the area of the ruffled border, the osteoclasts lower the pH with hydrogen ions through the carboniCanhydrase system. This lowered pH increases the solubility of the apatite crystals and the mineral can be removed. The organiCcomponents of the bone are then hydrolyzed through acidiCproteolytiCdigestion.

Correct Answer: Integrins

632. (765) Q2-1026:

Which of the following cells receive the majority of systemiCendocrine-based signals for control of bone metabolism:

1) Osteocytes

3) Osteoclasts

2) Osteoblasts

5) Platelets

4) Mast cells

Osteoblasts have receptors for parathyroid hormone, vitamin D, testosterone, thyroid hormone, and glucocorticoids. Osteoblasts receive the majority of systemiCendocrine-based signals. The osteoblasts, which are in physical contact with the osteocytes through osteocytiCcell processes, transmit the signals to the osteoclasts.

In contrast, strain generated signals, such as cell deformation, streaming potentials, or shear stress caused by fluid flow, are received by the osteocyte and transmitted to other cells.

Correct Answer: Osteoblasts

633. (766) Q2-1027:

Resting bone-lining cells have which of the following functions:

1) Produce acid phosphatase

3) Lower the pericellular pH through the carboniCanhydrase system

2) Produce enzyme regulatory proteins (e.g., collagenase and plasminogen activator)

5) Produce large amounts of type I collagen

4) Receive strain generated signals such as cell deformation

Osteoblasts can be active metabolically or in a resting phase. Active osteoblasts are plump in shape with a low nucleus to cytoplasm ratio and they produce and excrete both type I collagen and noncollagenous proteins that make up the bone matrix.

In contrast, resting bone-lining cells are not metabolically active compared to the active osteoblasts. The resting bone-lining cells are elongated and flat. These cells secrete enzyme-regulating proteins such as collagenase, collagenase inhibitor, and plasminogen activator. These enzymes help to control bone degradation. The osteoblasts respond to parathyroid hormone, 1,25 dihydroxyvitamin D3, and prostaglandins of the E series. The osteoblasts withdraw from the bone surface, begin degradation with their enzymes, and then the osteoclasts move in and resorb the inorganiCand organiCmatrix of bone.

Correct Answer: Produce enzyme regulatory proteins (e.g., collagenase and plasminogen activator)

634. (767) Q2-1028:

Which of the following cells have receptors for the hormone estrogen:

1) Osteoclasts

3) Lymphocytes

2) Osteocytes

5) Mast cells

4) Osteoblasts

Osteoblasts have receptors for parathyroid hormone, prostaglandins, 1,25 dihydroxyvitamin D3, glucocorticoids, and estrogen. Although the osteoblasts have receptors for estrogen, their exact role is unknown.

Correct Answer: Osteoblasts

635. (768) Q2-1029:

Osteoclasts are activated following disruption of the osteoid layer that covers the bone surface. Which of the following cells is responsible for this disruption:

1) Osteoclasts

3) Active osteoblasts

2) Resting bone-lining cells

5) Mast cells

4) Macrophages

The resting bone-lining cells (flat, elongated osteoblasts) begin the bone resorption process by secreting collagenases that degrade the osteoid layer covering bone. These cells may also contract to expose the bone surface and allow access for the osteoclasts.

Parathyroid hormone (PTH) mediates bone resorption by stimulation of PTH receptors on the osteoblasts. Osteoclasts do not have receptors for PTH.

Correct Answer: Resting bone-lining cells

636. (769) Q2-1030:

Which of the following areas of the osteoclast is responsible for attachment to the bone surface prior to the bone resorption process:

1) Golgi apparatus

3) Clear zone

2) Ribosome

5) Secretory vesicles

4) Ruffled border

Active osteoclasts resorb the mineral and organiCmatrix of bone and attach to the exposed bone matrix. When osteoclasts are studied with an electron microscope, there are two prominent findings â a ruffled border and a clear zone. In the clear zone, the osteoclast seals off the area of bone to be resorbed by attaching to the bone surface. The osteoclast attaches to the bone surface through a receptor-mediated process with the assistance of proteins called integrins. The ruffled border is an area found in the infoldings of the cell membrane. At the area of the ruffled border, the osteoclasts lower the pH with hydrogen ions through the carboniCanhydrase system. This lowered pH increases the solubility of the apatite crystals and the mineral can be removed. The organiCcomponents of the bone are then hydrolyzed through acidiCproteolytiCdigestion.

Correct Answer: Clear zone

637. (770) Q2-1031:

Which of the following cells have receptors for parathyroid hormone:

1) Osteoclasts

3) Lymphocytes

2) Osteoblasts

5) Fibroblasts

4) Mast cells

Parathyroid hormone (PTH) mediates bone resorption by stimulation of PTH receptors on the osteoblasts. Osteoclasts do not have receptors for PTH.

Correct Answer: Osteoblasts

638. (771) Q2-1032:

Water comprises what percentage of bone composition:

1) 5% to 8%

3) 30%

2) 20%

5) 50%

4) 40%

Bone has the following composition:

Mineral or inorganiCphase 70% Water 5% to 8% OrganiCmatrix 22% to 25% Collagen type I 90% Noncollagenous proteins 5% to 8%

Correct Answer: 5% to 8%

639. (772) Q2-1033:

With regard to the organiCphase of bone, which of the following accounts for 90% of the organiCmatrix:

1) Type I collagen

3) Osteonectin

2) Type II collagen

5) Matrix Gla protein

4) Osteocalcin (bone Gla protein)

Bone has the following composition:

Mineral or inorganiCphase 70% Water 5% to 8% OrganiCmatrix 22% to 25% Collagen type I 90% Noncollagenous proteins 5% to 8%

Correct Answer: Type I collagen

640. (773) Q2-1034:

Which of the following proteins helps in the initiation of mineral nucleation in the initial stages of mineralization:

1) Bone sialoprotein (bone sialoprotein 2)

3) Type II collagen

2) Osteocalcin (bone Gla protein)

5) Decorin

4) Aggrecan

Bone sialoproteins are important in the initiation of mineralization of collagen. They promote apatite nucleation and growth of the crystals. Osteocalcin (bone Gla protein) is important for mineral proliferation and maturation.

Note the role of promoters and inhibitors: Apatite nucleation and growth Promoters

Type I collagen Bone sialoprotein Matrix vesicles Phosphoproteins Proteolipids Biglycan

Inhibitors

Large proteoglycans Pyrophosphate Adenosine triphosphate Citrate

Mineral proliferation

Regulators

Osteocalcin Phosphoproteins Proteoglycans

Correct Answer: Bone sialoprotein (bone sialoprotein 2)

641. (774) Q2-1035:

Which of the following noncollagenous proteins aid in regulating the maturation of bone mineral crystals:

1) Aggrecan

3) Bone sialoprotein (bone sialoprotein 2)

2) Vitronectin

5) Osetocalcin (bone Gla protein)

4) Osteopontin (bone sialoprotein 1)

Bone sialoproteins are important in the initiation of mineralization of collagen. They promote apatite nucleation and growth of the crystals. Osteocalcin (bone Gla protein) is important for mineral proliferation and maturation.

Note the role of promoters and inhibitors: Apatite nucleation and growth Promoters

Type I collagen Bone sialoprotein Matrix vesicles Phosphoproteins Proteolipids Biglycan

Inhibitors

Large proteoglycans Pyrophosphate Adenosine triphosphate Citrate

Mineral proliferation

Regulators

Osteocalcin Phosphoproteins Proteoglycans

Correct Answer: Osetocalcin (bone Gla protein)

642. (775) Q2-1036:

Which of the connective tissue collagens may facilitate calcification in the holes and pores of bone collagen fibrils:

1) Type I

3) Type I, II, VI, and XI

2) Type I and II

5) Type X

4) Type IX and X

Only type I collagen is capable of supporting mineralization. Correct Answer: Type I

643. (776) Q2-1037:

Which of the following promotes physiologiCcalcification at the level of apatite nucleation and growth:

1) Phosphoproteins

3) Pyrophosphates

2) Large proteoglycans

5) Citrate

4) Adenosine triphosphate (ATP)

Bone sialoproteins (phosphoproteins) are important in the initiation of mineralization of collagen. They promote apatite nucleation and growth of the crystals. Large proteoglycans, pyrophosphates, adenosine triphosphate, and citrate are all inhibitors.

Note the role of promoters and inhibitors: Apatite nucleation and growth Promoters

Type I collagen Bone sialoprotein Matrix vesicles Phosphoproteins Proteolipids Biglycan

Inhibitors

Large proteoglycans Pyrophosphate Adenosine triphosphate Citrate

Mineral proliferation

Regulators

Osteocalcin Phosphoproteins Proteoglycans

Correct Answer: Phosphoproteins

644. (777) Q2-1038:

Which of the following promotes physiologiCcalcification at the level of apatite nucleation and growth:

1) Bone sialoprotein

3) Pyrophosphates

2) Large proteoglycans

5) Citrate

4) Adenosine triphosphate

Bone sialoproteins are important in the initiation of mineralization of collagen. They promote apatite nucleation and growth of the crystals. Large proteoglycans, pyrophosphates, adenosine triphosphate, and citrate are all inhibitors.

Note the role of promoters and inhibitors: Apatite nucleation and growth Promoters

Type I collagen Bone sialoprotein Matrix vesicles Phosphoproteins Proteolipids Biglycan

Inhibitors

Large proteoglycans Pyrophosphate Adenosine triphosphate Citrate

Mineral proliferation

Regulators

Osteocalcin Phosphoproteins Proteoglycans

Correct Answer: Bone sialoprotein

645. (778) Q2-1039:

Which of the following promotes physiologiCcalcification at the level of apatite nucleation and growth:

1) Matrix vesicles

3) Pyrophosphates

2) Large proteoglycans

5) Citrate

4) Adenosine triphosphate

Matrix vesicles are important in the initiation of mineralization of collagen. They promote apatite nucleation and growth of the crystals. Large proteoglycans, pyrophosphates, adenosine triphosphate, and citrate are all inhibitors.

Note the role of promoters and inhibitors: Apatite nucleation and growth Promoters

Type I collagen Bone sialoprotein Matrix vesicles Phosphoproteins Proteolipids Biglycan

Inhibitors

Large proteoglycans Pyrophosphate Adenosine triphosphate Citrate

Mineral proliferation

Regulators

Osteocalcin Phosphoproteins Proteoglycans

Correct Answer: Matrix vesicles

646. (779) Q2-1040:

Which of the following can be an inhibitor of physiologiCcalcification in bone:

1) Type I collagen

3) Matrix vesicles

2) Large proteoglycans

5) Bone sialoprotein

4) Phosphoproteins

Large proteoglycans, pyrophosphate, adenosine triphosphate, and citrate all act as inhibitors of physiologiCcalcification of bone. Note the role of promoters and inhibitors:

Apatite nucleation and growth

Promoters

Type I collagen Bone sialoprotein Matrix vesicles Phosphoproteins Proteolipids Biglycan

Inhibitors

Large proteoglycans Pyrophosphate Adenosine triphosphate Citrate

Mineral proliferation

Regulators

Osteocalcin Phosphoproteins Proteoglycans

Correct Answer: Large proteoglycans

647. (780) Q2-1041:

Cortical bone remodeling in a healthy older adult is typically:

1) 20%

3) 50%

2) 30%

5) 10%

4) 2% to 5%

Cortical bone remodeling can be as high as 50% in the femoral diaphysis during the first 2 years of life. In older adults, the cortical remodeling rate is only 2% to 5% per year. Trabecular bone remodels at a rate 5 to 10 times higher than cortical bone.

Correct Answer: 2% to 5%

648. (781) Q2-1042:

The periosteal vessels supply what portion of the cortical bone blood circulation:

1) 5% to 10% of the inner endosteal surface

3) 1% to 5% of the outer periosteal surface

2) 10% to 20% of the inner endosteal surface

5) 30% to 50% of the outer periosteal surface

4) 15% to 20% of the outer periosteal surface

The periosteal vessels supply 15% to 20% of the outer periosteal surface. There are three defined blood supplies:

Nutrient vessel entering in the diaphysis

Metaphyseal vessels from the periarticular vessels (geniculate vessels) Periosteal vessels supply the outer 15% to 20% of the cortex

Correct Answer: 15% to 20% of the outer periosteal surface

649. (782) Q2-1043:

Human calcium absorption occurs in the

1) Stomach

3) Large intestine

2) Small intestine

5) Parathyroid glands

4) Liver

Dietary calcium is absorbed in the small intestine. This absorption is stimulated by 1,25 dihydroxyvitamin D3. Correct Answer: Small intestine

650. (783) Q2-1044:

Approximately how many hours of sunlight are necessary to produce the daily requirement of 400 units of vitamin D in white people:

1) 1 hour

3) 4 hour

2) 2 hour

5) 81 hour

4) 6 hour

One hour of sunlight per day is necessary in white people to convert 7-dehydrocholesterol to vitamin D3 (cholecalciferol). A longer exposure is necessary in dark-skinned people.

Correct Answer: 1 hour