SKELETAL SYSTEM _____________________ Developed by Will Kleinelp Associate Professor Department of Biology ©2006_____________________ Developed by Will Kleinelp Associate Professor Department of Biology ©2006

Functions 1.Support A.Body Framework 2.Movement A.Muscle attachment to skeleton B.Movable Joints 3.Protection A.Vital Organs 4.Mineral Reservoir A.Storage of Calcium, Phosphorus, Sodium, Potassium 5.Hemopoiesis A.Bone Marrow produces blood cells 5.Triglyceride storage A.yellow bone marrow 1.Support A.Body Framework 2.Movement A.Muscle attachment to skeleton B.Movable Joints 3.Protection A.Vital Organs 4.Mineral Reservoir A.Storage of Calcium, Phosphorus, Sodium, Potassium 5.Hemopoiesis A.Bone Marrow produces blood cells 5.Triglyceride storage A.yellow bone marrow

Classifications Axial Skeleton Appendicular Skeleton

Classes of Bones Long Short Flat Irregular Sesamoid

G ro s s St ru ct ur e G ro s s St ru ct ur e articular cartilage epiphyseal plate red bone marrow cancellous bone endosteum compact bone periosteum medullary canal nutrient artery & foramen articular cartilage proximal epiphysis metaphysis diaphysis metaphysis distal epiphysis

Structure Microscopic Structure blood vessel lamellae concentric lamellae interstitial lamellae circumferential lamellae central Haversian canal osteocyte canaliculi lacnuae Volkman’s canal osteon compact bone spongy bone trabeculae

Bone Cells osteogenic cell osteoblast osteocyte osteoclast

Blood Supply - Long Bones articular cartilage epiphyseal artery & vein epiphyseal line metaphyseal artery & vein periosteum periosteal artery & vein medullary cavity nutrient foramen nutrient artery & vein epiphysis metaphysis diaphysis

OsteogenesisOsteogenesis There are two major forms of ossification A.Intramembranous Ossification originating tissue is fibrous membranous connective tissue involves the bones of skull, mandible and clavicle first process to begin roughly 4-6 weeks in utero A.Intramembranous Ossification originating tissue is fibrous membranous connective tissue involves the bones of skull, mandible and clavicle first process to begin roughly 4-6 weeks in utero B.Intramembranous Ossification originating tissue is hyaline cartilage involves all bones other than skull, mandible and clavicle B.Intramembranous Ossification originating tissue is hyaline cartilage involves all bones other than skull, mandible and clavicle Fetus is comprised of loose mesenchymal cells shaped like little bones and provide a template for the overall process of ossification. Ossification begins at about six weeks and continues until final closure at years. Fetus is comprised of loose mesenchymal cells shaped like little bones and provide a template for the overall process of ossification. Ossification begins at about six weeks and continues until final closure at years.

Intramembranous Ossification ★ Ossification Center Development ★ Calcification ★ Trabecular Formation ★ Periosteum Formation ★ Ossification Center Development ★ Calcification ★ Trabecular Formation ★ Periosteum Formation Four Process Involved:

Ossification Center Development ✴ the bone model consists of fibrous membranous connective tissue ✴ under specific chemical messengers fetal mesenchymal cells condense and begin to differentiate ✴ some differentiate into blood vessels while other differentiate into osteoblasts - committed bone forming cells ✴ the osteoblasts secrete collagen-proteoglycan tendriles that are able to bind to calcium salts ✴ through this binding, the PREBONE or OSTEOID matrix becomes calcified ✴ the bone model consists of fibrous membranous connective tissue ✴ under specific chemical messengers fetal mesenchymal cells condense and begin to differentiate ✴ some differentiate into blood vessels while other differentiate into osteoblasts - committed bone forming cells ✴ the osteoblasts secrete collagen-proteoglycan tendriles that are able to bind to calcium salts ✴ through this binding, the PREBONE or OSTEOID matrix becomes calcified CalcificationCalcification ✴ the secretion of the extracellular matrix stops and the osteoblasts are separated from the calcified matrix by a layers of the osteoid matrix they secrete ✴ the osteoblasts become trapped in the calcified matrix and become osteocytes - or bone cells ✴ as calcification proceeds, bony spicules radiate out from the region where ossification began ✴ the secretion of the extracellular matrix stops and the osteoblasts are separated from the calcified matrix by a layers of the osteoid matrix they secrete ✴ the osteoblasts become trapped in the calcified matrix and become osteocytes - or bone cells ✴ as calcification proceeds, bony spicules radiate out from the region where ossification began Trabecular Formation ✴ as the calcified spicules form, they fuse and develops large spacial areas called trabeculae ✴ Trabeculae fuse with one another and form the spongy bone where blood vessels fill the trabecular spaces ✴ connective tissue associated with the blood vessels in the trabeculae differentiates into red one marrow ✴ as the calcified spicules form, they fuse and develops large spacial areas called trabeculae ✴ Trabeculae fuse with one another and form the spongy bone where blood vessels fill the trabecular spaces ✴ connective tissue associated with the blood vessels in the trabeculae differentiates into red one marrow Periosteum Formation ✴ the entire region of calcified spicules become surrounded by compact mesenchymal cells that form the periosteum ✴ the cells on the surface become osteoblasts and deposit an osteoid matrix to that of the pre-exiting spicules forming the layers of compact bone on the outside ✴ the entire region of calcified spicules become surrounded by compact mesenchymal cells that form the periosteum ✴ the cells on the surface become osteoblasts and deposit an osteoid matrix to that of the pre-exiting spicules forming the layers of compact bone on the outside

Endochondral Ossification CARTILAGE MODEL DEVELOPMENT The original model is mesenchymal connective tissue Specific chemical messengers cause the mesenchymal cells to crowd together in the shape of the future bone The mesenchymal cells differentiate into chrondroblasts - cartilage forming cells The chondroblasts secrete and extracellular matrix producing a cartilage model consisting of hyaline cartilage A membrane called the perichondium forms around the perimeter of the model CARTILAGE MODEL GROWTH The chondroblasts become embedded in the cartilage extracellular matrix Interstitial growth - or growth in length - occurs by continuous cell division of the chondrocytes and additional matrix secretion. Appositional growth - or growth in diameter - is accomplished by adding more extracelllar matrix to the perimeter of the cartilage model and on the surface. As the cartilage template grows chondrocytes in the mid-region increase in size (hypertrophy) and the surrounding extracellular matrix begins to calcify Chondrocytes now lying within the calcified matrix die and their empty spaces now form lacunae. The lacunae merge together and form small cavities within the bone. CARTILAGE MODEL DEVELOPMENT The original model is mesenchymal connective tissue Specific chemical messengers cause the mesenchymal cells to crowd together in the shape of the future bone The mesenchymal cells differentiate into chrondroblasts - cartilage forming cells The chondroblasts secrete and extracellular matrix producing a cartilage model consisting of hyaline cartilage A membrane called the perichondium forms around the perimeter of the model CARTILAGE MODEL GROWTH The chondroblasts become embedded in the cartilage extracellular matrix Interstitial growth - or growth in length - occurs by continuous cell division of the chondrocytes and additional matrix secretion. Appositional growth - or growth in diameter - is accomplished by adding more extracelllar matrix to the perimeter of the cartilage model and on the surface. As the cartilage template grows chondrocytes in the mid-region increase in size (hypertrophy) and the surrounding extracellular matrix begins to calcify Chondrocytes now lying within the calcified matrix die and their empty spaces now form lacunae. The lacunae merge together and form small cavities within the bone.

PRIMARY OSSIFICATION CENTER Nutrient arteries now penetrate the perichondrium and the calcifying cartilage model through a nutrient foramen in the mid-region of the model this stimulates the osteogenic cells in the perichondrium to differentiate into osteoblasts Once the periosteum starts to from bone it becomes the periosteum In the midsection, periosteal capillaries grow into the disintegrating calcified cartilage and form the primary ossification center It is at this center that bone tissue will replace most of the cartilage The osteoblasts begin to deposit bone extracellular matrix over the remaining calcified cartilage forming the spongy trabeculae PRIMARY OSSIFICATION CENTER Nutrient arteries now penetrate the perichondrium and the calcifying cartilage model through a nutrient foramen in the mid-region of the model this stimulates the osteogenic cells in the perichondrium to differentiate into osteoblasts Once the periosteum starts to from bone it becomes the periosteum In the midsection, periosteal capillaries grow into the disintegrating calcified cartilage and form the primary ossification center It is at this center that bone tissue will replace most of the cartilage The osteoblasts begin to deposit bone extracellular matrix over the remaining calcified cartilage forming the spongy trabeculae Endochondral Ossification

Medullary Canal Formation osteoclasts start to break down some of the newly formed spongy bone in the mid section this destruction results in a cavity in the middle of the bone called the medullary cavity in the diaphysis of the forming bone the walls of the diaphysis will be replaced by compact bone Medullary Canal Formation osteoclasts start to break down some of the newly formed spongy bone in the mid section this destruction results in a cavity in the middle of the bone called the medullary cavity in the diaphysis of the forming bone the walls of the diaphysis will be replaced by compact bone Secondary Ossification Center Formation Epiphyseal arteries enter the epiphyses of the bone and cause the development of secondary ossification centers at the proximal and distal epiphyses Secondary ossification begins shortly after birth Development occurs in the same mode as the primary ossification center BUT the spongy bone remains in the interior of the epiphyses Secondary ossification proceeds outward towards the outer surface of the bone. Secondary Ossification Center Formation Epiphyseal arteries enter the epiphyses of the bone and cause the development of secondary ossification centers at the proximal and distal epiphyses Secondary ossification begins shortly after birth Development occurs in the same mode as the primary ossification center BUT the spongy bone remains in the interior of the epiphyses Secondary ossification proceeds outward towards the outer surface of the bone.

Endochondral Ossification Articular Cartilage Formation The hyaline cartilage that coves the ends of the bone forms the articular cartilage Hyaline cartilage also remains between the diaphysis and the epiphyseal ends forming the epiphyseal plate, and will remain until adulthood Articular Cartilage Formation The hyaline cartilage that coves the ends of the bone forms the articular cartilage Hyaline cartilage also remains between the diaphysis and the epiphyseal ends forming the epiphyseal plate, and will remain until adulthood

Bone Growth Articular Cartilage Formation During childhood bone grows in thickness by appositional growth The long bones increase in length by the addition of bone material of the diaphyseal side of the epiphyseal plate by interstitial growth Articular Cartilage Formation During childhood bone grows in thickness by appositional growth The long bones increase in length by the addition of bone material of the diaphyseal side of the epiphyseal plate by interstitial growth epiphyseal end dipahyseal end zone of resting cartilage zone of proliferating cartilage zone of hypertrophic cartilage zone of calcified cartilage diaphysis this zone is nearest the epiphysis contains scatted chondrocytes cells are non-functional function to anchor epiphyseal plate to epiphysis this zone is nearest the epiphysis contains scatted chondrocytes cells are non-functional function to anchor epiphyseal plate to epiphysis contains chondrocytes arranged like coin stacks function to replace dying chondrocytes at the diaphyseal end of the epiphyseal plate contains chondrocytes arranged like coin stacks function to replace dying chondrocytes at the diaphyseal end of the epiphyseal plate consists of large maturing chondrocytes structured in columns only a few cells in thickness of dean chondrocytes extracellular matrix surrounding chondrocytes is calcified osteoclasts dissolve calcified cartilage replacing with osteoblasts and bone osteoblasts lay down new bone forming a new diaphysis only a few cells in thickness of dean chondrocytes extracellular matrix surrounding chondrocytes is calcified osteoclasts dissolve calcified cartilage replacing with osteoblasts and bone osteoblasts lay down new bone forming a new diaphysis

Factors Affecting Bone Growth Minerals Calcium Phosphorous Fluoride magnesium iron manganese Vitamins C K B-12 Hormones IGF thyrocalcitonin thyroxin parathyroid hormone testosterone estrogen Minerals Calcium Phosphorous Fluoride magnesium iron manganese Vitamins C K B-12 Hormones IGF thyrocalcitonin thyroxin parathyroid hormone testosterone estrogen

FracturesFractures