Anatomy Chapter 6: Cartilage & Bones

Greenstick:

Partial fracture in which the convex side of the bone breaks, which the other side bends.

How are fractures repaired? Why is it rare to break a bone in the same place twice?

...

Describe the process of endochondral bone formation. What is the role of the bone collar in starting this process?

1. Hyaline cartilage is formed into the skeletal structure. 2. Chondroblasts within lacunae enlarge and resorb surrounding cartilage matrix, leaving large holes in the matrix. 3. Remaining matrix begins to calcify, cutting of nutrient sources for chondroblasts, which die. 4. During this process, blood vessels grow toward the cartilage and penetrate the perichondrium around the bone shaft. 5. Stem cells within the perichondrium divide to form osteoblasts, and the tissue becomes highly vascularlized. 6. The perichondrium becomes periosteum. 7. Osteoblasts w/in periosteum secrete osteoid around the calcified cartilage shaft. 8. The osteoid hardens and forms a bone collar around the shaft. 9. Periosteal bud (osteoblasts & capillaries) extends from the periosteum into the core of the calcified cartilage shaft. 10. Osteoblasts begin to produce osteiod onto remains of calcified cartilage, creating the primary ossification center. 11. Bone development extends in both directions toward the epiphyses, replacing calcified cartilage. 12. Process repeated in the epiphyses. 13. Bone has replaced cartilage everywhere except articular cartilage and epiphyseal plates. The bone collar supports the growing bone and helps it retain its shape. It also cuts off nutrient diffusion to the internal cartilage, killing off the chondrocytes.

Describe the composition of the bone matrix and consider what each of the components adds in terms of the physical properties of the bone.

1/3 is made up of organic compounds: cells (bone matrix construction and maintenance), collagen fibers (plasticity), and ground substance (matrix that supports the collagen fibers). 2/3 is composed of inorganic minerals, mostly calcium phosphate. Calcium phosphate interacts with calcium hydroxide to form crystals of hydroxyapatite which deposits around the collagen fibers (hardening and strength). In addition, calcium carbonate, and ions such as sodium, magnesium, sulfate, and fluoride are incorporated.

What is the role of the peri(chondrium) in appositional growth? Which of the two cartilage growth processes is most important in healing from injury?

Appositional growth occurs in the periosteum. Osteoblasts in the inner cellular layer lay down bone matrix parallel to the bone surface. ??

Describe the distribution of the blood vessels and nerves in the bone.

Bone is highly vascularized, but with limited entry points from the periosteum. The nutrient vein and artery enter through the forumen, after which they branch and extend along the length of the shaft. Metaphyseal vessels supply the diaphyseal side of the epiphyseal plate (new bone ossification). Epiphyseal vessels supply the epiphyses. In childhood the plate separates these vessels from the rest, but as the plate ossifies, the vessels and the metaphyseal vessels interconnect. Periosteal vessels supply the external circumferential lamellae and superficial osteons. These vessels and accompanying nerves penetrate the diaphysis and enter the perforating canals at many locations. Nerves that supply bones accompany vessels through the nutrient foramen and innervate the bone as well as its periosteum, endosteum, and marrow cavity.

Comminuted:

Bone is splintered into several small pieces between the main parts.

List the functions served by bone. Why do we refer to bones as an organ rather than a tissue?

Bones are composed of several tissue types, making them organs: cartilage, dense irregular connective tissue, osseous connective tissue, etc. Bone perform functions of support & protection, movement, hemopoesis, and storage of mineral & energy reserves.

Compound:

Broken ends of the bone protrude through the skin.

Distinguish between the kinds of functions where bone is employed versus those where cartilage is found.

Cartilage: used where toughness and flexibility is important (ears, nose, trachea, intervertebral discs), where a smooth gliding surface is needed (joints) where bones meet, and as a model for future bone formation. Bone: used where rigidity is important, and flexibility isn't.

Distinguish between compact and spongy bone. Are these terms macro-or microscopic in designation? What advantages do each of these two different forms of bone serve?

Compact bone vs spongy bone is a macroscopic designation. Compact bone is solid and dense, and forms the solid external walls of the bone. Spongy bone appears porous, like a sponge, and forms an open lattice of narrow plates of bone, called trabeculae, located internal to the compact bone. Compact bone is heavier than spongy and would make skeletons too inefficient to move. Spongy bone is less strong and would make bones too weak to provide sufficient support and leverage, but is strong enough while cutting weight.

Oblique:

Diagonal fracture at an angle between linear and transverse

Whey are bones a good example of modular construction? Be able to describe the characteristics of some of the modules.

Each bone develops independently of the others, yet functions as a unit. Also, some parts of a bone are created independently. For example, the diaphysis develops separately from the epiphysis, which develops from different tissue than the perichondrium.

Distinguish between the formation of bone in the flat bones of the skull versus most of the rest of the skeleton. What is the role of hyaline cartilage in the latter process?

Flat bones of the skull are formed through intramembranous ossification, while the rest of the skeleton is formed through endrochondral ossification. Hyaline cartilage forms the initial structure of the skeleton, providing a surface for the perichondrium to form around. The perichondrium then provides the osteoprogenitor cells that will fill in the spaces left by the disintegrated chondrocytes.

Transverse:

Fracture at right angles to the long axis of the bone.

Pott:

Fracture at the distal end of the fibula and malleolus of the tibia.

Colles:

Fracture of the distal end of the radius

Spiral:

Fracture spirals around the axis of long bone, results from twisting stress

Distinguish between the hormones responsible for normal bone growth and development, for calcium metabolism, and for gender specific bone density differences.

Growth hormones growth hormones (stimulate liver to produce somatomedin, causing cartilage proliferation at epiphyseal plates) thyroid (stimulates metabolic rate of osteoblasts) Calcium metabolism calcitonin promotes calcium deposition and inhibits osteoclasts parathyroid increases blood calcium levels by promoting osteoclast activity Gender-specific action estrogen and testosterone stimulate osteoblasts and promote epiphyseal plate growth and closure

Based on the structure of the three different types of cartilage, describe how each is able to meet unique functional demands. (eg resisting compression versus friction)

Hyaline Cartilage: glassy and smooth. Useful as a smooth surface at articulations. Supports soft tissues and provides a model for bone growth. Fibrocartilage: parallel collagen fibers make this useful for resisting compression and absorbing shock in vertebral joints. Elastic Cartilage: loose elastic fibers make this type more useful for areas that need to flex: ears, epiglottis. Elasticity allows it to bounce back after compression, rather than resist it.

When can interstitial growth occur during development? When does this growth process become limited?

Interstitial growth occurs through maturity and ends at different times in development depending on the bone and the individual. It becomes limited by cartilage production.

Do you find osteons in spongy bone? If not, how is the microscopic structure of these organized?

No, the trabeculae of spongy bone are composed of parallel lamellae. Between adjacent lamellae are osteocytes resting in lacunae

Distinguish between the four different types of bone cells in terms of their functions and location in the bone. Where do these cells originate from (i.e. from within the bone, the periosteum, or beyond?)

Osteoprogenitor Cell: Stem cells derived from mesenchyme. When they divide, they produce one stem cell and one committed cell that matures into an osteoblast. Osteoblast: are often cuboidal. They secrete the initial semi-solid bone matrix called osteoid, thus producing new bone. Osteocyte: An osteoblast that has become encased in the osteoid it produced. Its shape changes to fit within the space within the matrix called the lacunae. They maintain the bone matrix and detect mechanical stress to the bone. This information is communicated to the osteoblast, which may result in deposition of new bone matrix at the surface. Osteoclast: large, multinuclear phagocytic cells. They appear to be derived from fused bone marrow cells. They have a ruffled border where they contact bone. They are often located in "resorption lacunae"-pits on the bone surface. They are involved in bone resorption through the release of hydrochloric acid (dissolves minerals out) and lysosomal action (dissolves the organic part of the matrix). All four types of cell appear to originate from both the periosteum and the endosteum.

Draw a typical bone (femur), and label its parts.

Parts to be included are: Diaphysis (shaft of bone) Epiphysis (ends of bone) Metaphysis (growth area between the Diaphysis and epiphysis) tubercle Periosteum (hyaline cartilage surrounding bone) Endosteum (hyaline cartilage lining compact bone internally) Epiphyseal line (divides epiphysis from metaphysis) Nutrient artery (enters diaphysis) spongy bone (contains red bone marrow in epiphysis) Medullary cavity (contains yellow bone marrow along length of center of diaphysis) Articular cartilage (outside ends of bone at joints)

What is the reason why bone is constantly being remodeled? How does this process occur?

Remodeling helps maintain calcium and phosphate levels in body fluids, and can be stimulated by stress on the bone to strengthen or lay down stronger bone tissue.

Describe the role of the epiphyseal growth plate once the bone has formed. How does this group of cartilage cells accomplish this function? Consider the 5 zones.

The epiphyseal plates promote bone growth in length, once the overall structure has been converted from hyaline cartilage to bone. Within the Epiphyseal plate, there are 5 zones, beginning with cartilage and ending with new bone growth at the end of the diaphysis. Zone 1 is resting cartilage attaching the epiphysis to the plate. Zone 2 is where chondrocytes divide rapidly, enlarge and align into columns of flattened lacunae. In zone 3, chondrocytes cease dividing, enlarge greatly, and resorb matrix. Walls of the lacunae become thin and more closely packed. In zone 4, minerals are deposited in the matrix between columns of lacunae. This calcification kills the chondrocytes. In zone 5, the walls of the empty lacunae break down forming longitudinal channels. These spaces are invaded by capillaries and osteoprogenitor cells from the medullary cavity. New bone matrix is deposited on the remaining calcified cartilage matrix.

How is the periosteum different from the endosteum?

The periosteum surrounds each bone, except for the area covered by articular cartilage. It is made of dense irregular tissue and consists of an outer fibrous layer and an inner cellular layer. The inner layer contains osteoprogenitor cells, osteoblasts, and anchoring collagen fibers (perforating fibers) The endosteum is an incomplete layer of cells that lines all internal surfaces of the medullary cavity. It contains osteoprogenitor cells, osteoblasts, and osteoclasts. It is active during bone growth, repair and remodeling.

Distinguish between lamellar and woven bone. Micro or macro level?

Woven bone is the primary/immature bone formed in intramembranous ossification. It is not well organized. Eventually, it is replaced by lamellar bone. Lamellar bone is secondary/mature bone and has a more regular structure, consisting of alternately laid layers of collagen (concentric lamellae) within each osteon. micro

During growth of a long bone would you observe appositional growth?

Yes, new bone would be laid down from the periosteum.

What is osteoporosis and how can it be prevented?

bone matrix and calcium are lost, particularly in spongy bone. It can't be cured, but there are prevention options. It can be slowed by promoting greater bone growth and density earlier in life, through increased physical activity and good nutrition, including bone producing vitamins & calcium.