Test Two-Chapter Six

Hyaline Cartilage Growth (Appositional vs. Interstitial)

Appositional growth: the addition of new cartilage matrix on the surface of cartilage. Chondroblasts in the inner layer of the perichondrium lay down new matrix on the surface of the cartilage. Once chondroblasts are surrounded by matrix they become chondrocytes in the new layer of cartilage Interstitial Growth:The addition of new cartilage matrix within cartilage (chondrocytes within the tissue divide and add more matrix between the cells increasing the thickness of cartilage

Woven bone

Collagen fibers randomly oriented in many different directions -formed during fetal development or the repair of a fracture -Remodeled (osteoclasts break down woven bone and osteoblasts build new matrix) to form lamellar bone

Growth for Width

1. Appositional bone growth beneath the periosteum increases the diameter of long bones and the size of other bones 2. Osteoblasts from the periosteum form ridges with grooves between them 3. Ridges grow together, converting the grooves into tunnels filled with concentric lamellae to form osteons 4. Osteoblasts from the periosteum lay down concentric lamellae, which can be remodeled.

Process for Blood Calcium

1. Osteoclasts break bone down and release calcium int the blood. Osteoblasts remove calcium to make bone. 2. In the kidneys, PTH increases calcium abosorbption from urine 3. In the kidneys, PTH promotes the formation of active vitamin D, which increases calcium reabsorbtion from the small intestine

Growth process for length

1. Zone of Resting Cartilage -Attaches to epiphysis -Contains chondrocytes that do not divide rapidly 2. Zone of Proliferation: -New cartilage is produced through interstitial cartilage growth -Chondrocytes divide and form columns of cells 3. Zone of hypertropy: -Chondrocytes mature and enlarge 4. Zone of calcification: -Matrix is calcified and hypertrophied chondrocytes die 5. Ossified bone: calcified cartilage on the diaphyseal side of the plate is replaced by bone

Bone Growth: Length

Bone length increases occur at the epiphyseal plate -Epiphyseal plate growth involves 1. Interstitial (within matrix) formation of new cartilage 2. Appositional (on surface) bone growth on the cartilage -Epiphyseal plate growth results in an increase in the length of the diaphysis and bony processes -Growth in length ceases when the epiphyseal plate becomes ossified and forms epiphyseal line

Circulation in Compact Bone

Canals transfer nutrients, gasses, and waste -Perforating volkmann's canals carry blood vessels to central canals (run perpendicular to long axis of bone) -Canaliculi: help carry nutrients through the canal system

Components of Hyaline Cartilage

Chondroblasts: Specialized cells that produce cartilage matrix. When the matrix surrounds a chondroblast it develops into a chondrocyte. Chondrocytes:Located in lacunae within the matrix. Maintains mature cartilage

Short and Irregular Bones

Composition similar to ends of long bones -compact bone surfaces surround a cancellous center -bone center has small spaces filled with marrow -not elongated, no ephiphyses -certain regions have epiphyseal growth plates

Compact Bone

Consists of organized lamellae STRUCTURES: Circumferential Lamellae: Form the outer surface of compact bones Concentric Lamellae: Surround central canals forming osteons (haversian system) Interstitial Lamellae: Remnants of lamellae left after bone remodeling

Flat Bone Structure

Contain an interior framework of cancellous bone sandwiched between two layers of compact bone

Hyaline Cartilage Matrix

Contains collagen fibers (for strength) and proteoglycans that trap water (for resilience)

Bone Remodeling

Converts woven bone to lamellar bone (allows bones to change shape, adjust to stress, repair themselves, and regulate blood calcium levels) Basic Multicellular units (BMUs)- assemblies of osteoclast & osteoblasts that travel through or across the surface of bone removing old matrix and replacing with new matrix -Osteoclasts break down bone matrix, making tunnels in bone -Osteoblasts move in and lay down a new layer of bone on the tunnel wall, forming concentric lamellae -Interstitial lamellae are remnants of bone not removed by BMUs BMU ACTIVITY RENEWS THE ENTIRE SKELETON EVERY 10 YEARS Epiphysis enlarges, diaphysis increases in length as new cartilage is formed by bone and then remodeled. Diameter increases as bone grows on outside of the bone, and the size of medullary cavity increases due to bone resorption.

Long Bone Structure

Diaphysis: tubular shaft that forms the axis of long bones. Composed of compact bone that surrounds the medullary cavity (contains yellow and red bone marrow) Epiphyses: Expanded ends of long bones. Exterior is compact bone/interior is cancellous bone. Joint surfaces are covered with articular (hyaline cartilage). Epiphyseal plate is the site of bone growth in length. Becomes the epiphyseal line (separates diaphysis from epiphyses) when cartilage is replaced with bone. Bone Marrow: Red bone marrow: site of blood cell formation. Converted to yellow bone marrow just before birth and this process continues into adulthood. In mature bone, yellow marrow replaces red marrow in the limbs except for some red marrow in the proximal arm and thigh

Intramembraneous Ossification

Formation of bone within a connective tissue membrane (some skull bones, part of mandible, and diaphyses of clavicles) 1. Osteochondral progenitor cells become osteoblasts 2. Osteoblasts lay down bone matrix on collagen fibers of connective tissue membrane forming trabeculae 3.Trabeculae enlarge as more osteoblasts lay down cell matrix 4. Cancellous bone forms as trabeculae join together 5. Red bone marrow develops in spaces within matrix and surrounding cells specialize to form periosteum 6. Beneath periosteum, osteoblasts lay down bone matrix to form outer surface of compact bone CENTERS OF OSSIFICATION: where ossification begins FONTANELS: areas of membrane where developing skull bones have not been ossified

Endochondral Ossification

Formation of bone within cartilage (bones of the base of skull, part of mandible, epiphyses of clavicles, and most of the remaining skeletal system) 1. Chondroblasts produce cartilage model that is surrounded by perichondrium, except where joints are formed. 2. Perichondrium of diaphyses becomes periosteum and a bone collar is produced. Chondrocytes hypertrophy and calcified cartilage forms. 3. Primary ossification center forms as blood vessels and osteoblasts invade calcified cartilage. Osteoblasts lay down bone matrix, forming spongy bone 4. Process continues. Calcified cartilage begins to form in epiphyses. A medullary cavity begins to form in the center of the diaphysis. 5. Secondary ossification centers form the epiphyses 6. Original cartilage model almost completely ossified. Unossified cartilage becomes epiphyseal plate of articular cartilage. 7. In a mature bone, the epiphyseal plate has become epiphyseal line and all the cartilage in the epiphyses, except the articular cartilage, has become bone.

What are the three types of cartilage in skeletal system?

Hyaline- Where bones rub against each other. Most bones in the body develop from hyaline cartilage (aids in bone growth and bone repair) Fibrocartilage and Elastic Cartilage: More specialized and fibrocartilage exists where there are more areas of compression/stress

Bone Growth

Increase in size by appositional growth only (unlike cartilage) -Addition of new bone on the surface of older bone (trabeculae grow in size by the deposition of new bone matrix by osteoblasts on the trabecular surface)

Cancellous (spongy) Bone

Less bone matrix and more space than compact bone (internal layer is a honey comb of trabeculae filled with red or yellow bone marrow. -Consists of thin rods or plates of interconnecting bone called trabeculae (oriented along lines of stress and provide structural strength) -Bone marrow and blood vessels fill spaces between trabeculae -Covered with endosteum

Bone Shapes

Long Bones: Longer than are wide, most bones of upper and long limbs (femur) Short Bones: Wide as are long, bones of wrist (carpals) and ankle (tarsals) Flat Bones:Thin flattened shape, usually curved, bones of skull, ribs, sternum, scapulae Irregular: Do not fit into other three categories, bones of vertebrae, pelvic girdle, and facial bones

Aging

Matrix: more brittle due to lack of collagen and less hydroxyapatite Bone Mass: Can be slowed by adequate nutrition and weight bearing activtiy Cancellous Bone Loss: Thinning and loss of trabeculae Compact Bone Loss: Less osteon formation

Lamellar Bone

Mature bone -arranged in thin sheets or layers called lamellae -has collagen fibers oriented parallel but at an angle to collagen fibers in other lamellae

Origin of bone cells

Mesenchymal cells can develop into stem cells that give rise to more specialized cell types Osteochondral progenitor cells (OPCs): Stem cells that become osteoblasts or chondroblasts. Located in the inner layer of the periochondrium, periosteum, and endosteum Osteocytes: Derived from osteoblasts Osteoclasts: Derived from red bone marrow and white blood cells (monocytes)

Bone Matrix

Mostly inorganic material but also organic material Organic: Collagen provides flexible strength to the matrix with proteoglycans Inorganic: Hydroxapatite (calcium phosphate crystal) provides compression (weight bearing) strength to the matrix

Factors that affect bone growth

Nutrition: Lack of calcium, protein, and vitamin D can cause bones to be small. Vitamin D is needed to absorb calcium -Rickets: disease from reduced mineralization of bone matrix. Osteomalacia is adult form of rickets. Hormones: Can increase bone growth and close epiphyseal plates. Growth hormone increases bone growth by stimulating interstitial cartilage growth and appositional bone growth. Giantism: abnormally increased height from abnormal cartilage and bone formation of the epiphyseal plates. -Thyroid regulate growth -Estrogen/testosterone stimulate bone growth (burst) and stimulate closure (ossification) of epiphyseal plates

Haversian System in Compact Bone

Osteon: modular unit of compact bone Central Canal: canal in the center of an osteon that contains blood vessels Lacuna: space within an osteon where osteocytes are located Concentric Lamellae: Surround central canals Canaliculi: Connect central canal to osteocytesC

Bone Membranes

Periosteum: Double layer of protective membrane coving the outer surface of the bone -Outer fibrous layer: dense reticular connective tissue, which contains blood vessels and nerves -Inner osteogenic layer: osteoblasts, osteoclasts, and osteochondral and progenitor cells

What are the five functions of bones?

Support: Form the framework that supports the body and cradles soft organs. (Bone is the main supporting tissue of the body, cartilage is the firm yet flexible support) Protection: Hard structure provides a protective case for the organs, brain, and spinal cord Movement: Provides levers for skeletal muscle. Storage: Some minerals from the blood are stored within the bone (calcium, phosphorus, fats). Blood cell production: Hematopoeisis occurs within the marrow cavities of bones

What happens if matrix composition changes?

Without mineral the bone would be too flexible and without collagen the bone would shatter

What are the four components of the skeletal system?

-Bone -Cartilage (Hyaline, Fibro, Elastic) -Tendon -Ligaments

Trabeculae of Canecellous Bone

-Consist of several lamellae -Osteocytes located between lacunae (each osteocytes associated with other osteocytes through -Each osteocyte is associated with other osteocytes through canaliculi (osteocytes obtain nutrients through caniliculi) -Trabecular surface covered with a single layer of cells (mostly osteoblasts with a few osteoclasts)

Growth for Articular Cartilage

-Interstitial cartilage growth followed by appositional bone growth -results in larger epiphyses and an increase in the size of bones that do not have epiphyseal plates (short) -Growth of articular cartilage ceases, when bone reach mature size -Articular cartilage lasts throughout life and does not become ossified

Calcium Homeostasis

Bone: Major storage site for calcium. Blood calcium levels depend on movement of calcium into and out of bone Osteoblast activity: Increases bone density, increases calcium Osteoclast activity: decreases bone density, decreases calcium in the bone TWO HORMONES REGULATE CALCIUM LEVELS IN THE BLOOD -Parathyroid Hormone: The major regulator of blood calcium (crucial for normal muscle and nervous tissue formation). Falling calcium levels signal the parathryroid glands to release PTH. PTH stimulates: osteoclasts to degrade bone matrix and release calcium into the blood. Calcium absorption from the small intestines. Reabsorption of calcium from the urine. -Calcitonin: Rising blood calcium levels triggers the thyroid to release calcitonin. Calcitonin stimulates: Calcium salt deposition in bone by decreasing osteoclast activity.

Bone Fractures

Open/Closed: Whether or not the bone ends penetrate the skin Incomplete/Complete: Complete is broken into two pieces, incomplete is not Comminuated: Bone breaks into more than two pieces Impacted: one fragment is driven into the cancellous portion of the other fragment Transverse: occurs at a right angle to the long axis Spiral: Helical course around the bone Oblique: Run obliquely to the direction of the long axis

What is the ossification of the bone?

Osteoblasts rest on a pre-existing surface, such as cartilage or bone. The cell processes of different osteoblasts join together. Osteoblasts surround themselves with bone matrix and the osteoblasts are now osteocytes.

What are the cells of a bone?

Osteoblasts: produces new bone matrix. Have extesnive ER, ribosomes, and golgi apparatus. Produce collagen proteoglycans that are packaged into vesicles by the golgi apparatus and released from the cell by exocytosis. Produce matrix vesicles. Osteocytes: Mature bone cells that maintain bone matrix. Located in lacunae. Osteocyte cell processes are connected to one another via canaliculi (nutrients and gasses pass through fluid surrounding cels in canaliculi or lacunae or pass from cell to cell via gap junctions) Osteoclasts: Responsible for resorption (breakdown) of bone. Large multinucleated cells. Release hydrogen to decalcify the bone matrix. Release enzymes that digest the protein of matrix. Use endocytosis to take products of resorption into osteoclast

Perichondrium of Hyaline Cartilage

Perichondrium: A double layered connective tissue sheath that surrounds most cartilage Outerlayer: Dense irregular connective tissue containing fibroblasts Inner layer: more delicate (fewer fibers) and contains condroblasts The outer layer contains blood vessels but they do not enter the cartilage matrix (nutrients must diffuse through the cartilage matrix to reach the chondrocytes ARTICULAR CARTILAGE (covers the ends of bones) does not contain perichondrium, blood vessels, or nerves

Bone Repair Process

1. Hematoma formation: Torn blood vessels hemorrhage. A mass of clotted blood (hematoma) forms at the fracture site. Site becomes swollen, painful, and inflamed. 2. Callus Formation: Granulation tissue (soft tissue) forms a few days after the fracture. Capillaries grow into the tissue and phagocytic cells begin cleaning debris. Internal callus forms between the ends of bones. External callus forms a collar around fracture. External Callus: Osteoblasts and fibroblasts migrate to the fracture and begin reconstructing a bone. Fibroblasts secrete collagen fibers that connect broken bone ends. Osteoblasts begin forming woven bone. Osteoblasts furthest from capillaries secrete an externally bulging cartilaginous matrix that later calcifies. 3. Callus Ossification: The fibers and cartilage of the internal and external calluses are ossified to produce woven, cancellous bone. Cancellous bone formation in the callus is complete 4-6 weeks after the injury 4. Bone remodeling: Excess material on the bone shaft exterior and in the medullary canal is removed. Compact bone is laid down to reconstruct shaft walls. Remodeling may take more than a year to complete.