Ch. 6

Describe the structure of hyaline cartilage. Name the two types of cartilage cells. What is lacuna?

consists of specialized cells called chrondroblasts that produce a matrix surrounding themselves chondroblasts & chondocytes A space within the matrix

What are the four steps of bone repair?

1. Hematoma formation 2. Callus formation 3. callus ossification 4. bone remodeling.

Name and describe the events occurring in the four zones of the epiphyseal plate. Explain how the epiphyseal plate remains the same thickness while the bone increases in lenth.

1. Zone of resting: cartilage attaches to the epiphysis. 2. Zone of proliferation: new cartilage is produced on the epiphyseal side of the plate as the chondrocytes divide and form stacks of cells. 3. Zone of hypertrophy: Chondrocytes mature and enlarge. 4. Zone of calcification: matrix is calcified and chondrocytes die. The thickness of the epiphyseal plate does not increase because the rate of cartilage growth on the epiphyseal side of the plate is equal to the rate of cartilage replacement by bone on the diaphyseal side of the plate.

Why is it important for bone remodeling to occur?

Bone remodeling converts woven bone into lamellar bone and is involved in several important functions, including bone growth, changes in bone shape, adjustment of the bone to stress, bone repair, and calcium ion regulation in the body.

Why is remodeling of the ossified callus necessary?

Bone remodeling fills the gap between bone fragments with an internal callus of woven bone is not the end of the repair process because woven beone is ot as structurally strong as the original lamellar bone. Repair is only complete when the woven bone of the internal callus and the dead bone adjacent to the fracture site have been replaced by compact bone.

Hydroxyapatite

Calcium Phosphate Crystals Inorganic material

How is calcium moved into and out of bone? What happens in bone when blood calcium levels decrease? When blood calcium levels increase?

Calcium ions move into bone as osteoblasts build new bone, and they move out of bone as osteoclasts break down bone. Osteoclast activity increases. Osteoclast activity decreases.

Describe the structure of compact bone. What is an osteon? Name three types of lamellae found in compact bone.

Compact bone is denser and has fewer spaces than spongy bone. Osteon consists of a single central canal, its contents, and associated concentric lamellae and osteocytes. Concentric lamellae, circumferential lamellae, & interstitial lamellae.

Describe the formation of spongy and compact bone during intramembranous ossification. What are centers of ossification? What are fontanels?

Embryonice mesenchyme forms a collagen membrane containing osteochondral progenitor cells. Embryonic mesenchyme forms the periosteum, which contains osteoblasts. Osteochondral progenitor cells become osteoblasts at centers of ossification; internally, the osteoblasts form spongy bone; externally, the periosteal osteoblasts form compact bone. Centers of ossification are the locations in the membrane where ossification begin. Fontanels or soft spots are the large, membrane-covered spaces between the developing skull bones that have not yet been ossified.

How does estrogen and testosterone affect bone growth? How do these effects account for the average height difference observed in men and women?

Estrogen and testosterone initially stimulate bone growth, which accounts for the burst of growth at puberty, when production of these hormones increases. However, both hormones also stimulate ossification of epiphyseal plates and thus the cessation of growth. Females usually stop growing earlier than males because estrogens cause quicker closure of the epiphyseal plate than testosterone does. Because the whole process is shorter, females usually do not reach the same height as males.

Explain the process of growth at the articular cartilage. What happens to th epiphyeal plate and the articular cartilage when bone growth ceases?

Growth at the articular cartilage increases the size of bones that do not have an epiphysis, such as short bones. The process of growth in articular cartilage is similar to that occurring in the epiphyseal plate. When the epiphyses reach their full size, the growht of cartilage and its replacement by bone cease. The articular cartilage, however persists throughout life and does not become ossified as the epiphyseal plate does.

What are the three types of cartilage? Which type is more closely associated with bone?

Hyaline cartilage, fibrocartilage, and elastic cartilage Hyaline cartilage

Describe the formation of new bone by appositional growth. Name the spaces that are occupied by osteocyte cell bodies and cell processes.

In appositional growth, chondroblasts in the perichondrium add new cartilage to the outside edge of the existing cartilage. The chondroblasts lay down new matrix and add new chondrocytes to the outside of the tissue. Lacunae are the spaces that are occupied osteocyte cell bodies and canaliculi are the spaces that are occupied by osteocyte cell processes.

Explain how illness or malnutrition can affect bone growth. How do vitamins D and C affect bone growth.

Illness and malnutrition during the time of bone growth can cause a person to be shorter than he or she would have been otherwise. Vitamin D is necessary for the normal absorption of calcium from the intestines. Vitamin C is necessary for collagen synthesis by osteoblasts.

How is the organization of collagen fibers different in woven and lamellar bone? What process produces woven bone?

In woven bone: collagen fibers are randomly oriented in many directions and in Lamellar bone: the collagen fibers lie parallel to one another, but at an angle to the collagen fibers in the adjacent lamellae. A mature bone Bone remodeling

What bones or parts of bones are formed from each type of ossification?

Intramembranous ossification: many skull bones, part of the mandible, and the diaphyses of the clavicles. Endochondral ossification: Bones of the skull base, part of the mandible, the epiphyses of the clavicles, and most of the remaining skeletal system.

differentiate among the characteristics and functions of osteoblasts, osteocytes, and osteoclasts.

Osteoblasts are bone-forming cells, have an extensive endoplasmic reticulum and numerous ribosomes. Ossification is the formation of bone by osteoblasts. Osteocytes become surrounded by bone matrix and are relatively inactive, but do have the capability to produce components needed to maintain the bone matrix if needed. Osteoclasts are responsible for the reabsorption or breakdown of bone. They are large cells with several nuclei.

Describe how PTH controls the number of osteoclasts. What are the effects of PTH on the formation of vitamin D, ca2+ uptake in the small intestine, and reabsorption of ca2+ from urine?

PTH stimulates osteoblasts to release enzymes that break down the layer of unmineralized organic bone matrix covering bone, thereby making the mineralized bone matrix available to osteoclasts. Increased PTH promotes the activation of vitamin D in the kidneys, and vitamin D increases the absorption of CA2+ from the small intestines. PTH also increases the reabsorption of Ca2+ from urine in the kidneys, which reduces the amount of Ca2+ lost in the urine.

Name the hormone that is the major regulator of Ca2+ levels in the body. What stimulates the secretion of this hormone?

Parathyroid hormone Parathyroid gland is stimulated when blood calcium levels are too low, which increase the number of osteoclasts.

Where are the periosteum and endosteum located and what types of cells are found in each? What is the function of perforating fibers?

Periosteum covers the outer surface of a bone and it contains osteoblasts, osteoclasts, and osteochondral progenitor cells. Endosteum lines the internal surfaces of all cavities within bones and contains osteoblasts, osteoclasts, and osteochondral progenitor cells. Strengthen the attachment of the tendons or ligaments to the bone.

When do primary and secondary ossification centers appear during endochondral ossification?

Primary ossification centers appear during early fetal development, whereas secondary ossification centers appear in the proximal epiphysis of the femur, humerus, and tibia about 1 month before birth.

What are red and yellow bone marrows? Where are they located in a child and in an adult?

Red bone marrow is the site of blood cell formation and Yellow marrow is mostly adipose tissued. There is a good mixture of yellow and red bone marrow in various places throughout the body. For example, an a childs long bone, the medullary cavity contains red bone marrow. An adult long bone's medullary cavitiy contains yellow bone marrow, which replaced the red bone marrow.

Describe the structure of spongy bone. What are trabeculae, and what is their function? How do osteocytes within trabeculae obtain nutrients?

Spongy bone appears porous, has less bone matrix and more space than compact bone. Trabeculae are interconnecting rods or plates in spongy bone, which bear weight and help bones resist bending and twisting. Through their canaliculi.

Describe how new osteons are produced as a bone increases in width.

When a bone grows in width slowly, the surface of the bone becomes smooth as osteoblasts from the periosteum lay down even layers of bone to form circumferential lamellae. The circumferential lamellae break down during remodeling to form osteons.

How does breaking a bone result in hematoma formation?

When a bone is fractured, the blood vessels in the bone and surrounding periosteum are damage, and a hematoma forms. Hematoma is a localized mass of blood relaeased from blood vessels but confined within an organ or a space.

What effect does aging have on the quality and quantity of bone matrix?

With aging, the amount of matrix also decreases because the rate of matrix formation by osteoblasts becomes slower than the rate of matrix breakdown by osteoclasts.

For the process of Endochondral ossification, describe the formation of the structures included in the process.

Cartilage model - produced by the chondroblasts, is surrounded by perichondrium, except where a joint will form connecting one bone to another bone. Bone Collar - is formed by osteoblasts that produce compact bone on the surface of the cartilage model. Calcified cartilage - where chondrocytes also release matrix vesicles, which initiate the formation of hydroxyapatite crystals in the cartilage matrix. Primary ossification center - the osteoblasts produce bone on the surface od the calcified cartilage, forming bone trabeculae, which cahnges the calcified cartilage of the diaphysis into spongy bone. Medullary Cavity - osteoclasts remove bone from the center of the diaphysis to form this structure. Secondary ossification center - are additional sites of ossification that appear in the epiphyses. Epiphyseal plate - exists during the time a person's bones are actively growing and are drived from the origial embryonic cartilage model. Epiphyseal line - was the epiphyseal plate and is spongy and compact bone that is fully developed. Articular cartilage - In mature bone, it is the only cartilage present and is located at the ends of the bone.

Compare the structure of a long bone with flat, short, and irregular bones. Explain where compact and spongy bones are found in each type.

Flat bones contain an interior framework of spongy bone sandwiched between two layers of compact bone. Short and irregular bones have a composition similar to the epiphyses of long bones - compact bone surfaces surrounding a spongy bone center with small spaces that are usually filled with marrow.

What cells give rise to osteochondral progenitor cells? What kinds of cells are derived from osteochondral progenitor cells? What types of cells give rise to osteoclasts?

Stem cells Osteoblasts Stem cells from red bone marrow