Anatomy Chapter 6

e.

Interstitial lamella: groups of incomplete lamellae lying between the osteons; remains of old osteons that have been cut through by bone remodeling

g.

Medullary cavity: very center of the daphysis; contains tno bone tissue at all, filled with yellow bone marrow

c.Mesenchyme

Mesenchyme: what membranous bones form from directly without first being modeled in cartilage first;

36.

Describe the two mechanisms of bone remodeling: deposition and reabsorption.

32.

Identify the function and zones of the epiphyseal plate.

b.Epiphysis

Epiphysis: the ends of a long bone

a.Appositional growth

Appositional growth "growth from outside": cartilage -forming cells, chondroblasts, in the surrounding perichondrium produce the new cartilage tissue by actively secreting matrix

m.Articular cartilage

Articular cartilage: hyaline cartilage that coats bones where they come into contact with each other

d.Articulations

Articulations: where bones connect

d.

Volkmann's (perforating) canal: lie at right angels to the central canals and connect the blood and nerve supply of the periosteum to that of the central canals and the marrow cavity

b.Woven bone

Woven bone: bone tissue that has formed between embryonic blood vessels, which are woven in a random network; woven bone tissue has trabeculae arranged in networks; trabeculae just deep to the periosteum thicken and are later preplaced with mature lamellar bone, forming compact bone plates of flat bone, while spongy bone (diploe), consisting of distinct trabeculae, persists internally

1. Identify the functions of the skeletal system.

a. Support b. Provides surface area for attachments (of ligaments, muscles, tendons) c. Permits movement d. Protection of organs—cranial, ribs, vertebrae e. Storage of minerals—calcium and phosphate f. Blood cell formation (hematopoiesis in red bone marrow) and energy storage (in yellow bone marrow) g. Energy metabolism—osteoblasts secrete a hormone that influences blood sugar regulation and energy metabolism: osteocalcin, ehich stimulates pancreatic secretions that reduce blood sugar levels (insulin) and influences fat cells, causing them to store less fat and to secrete a hormone that increases the insulin sensitivity of cells

44.

Describe changes that occur in the skeleton throughout the lifespan.

43.

Describe the following bone disorders: osteoporosis, osteomalacia, rickets, Paget's disease, and osteosarcoma.

41.

Describe the following types of fractures (Table 6.2): comminuted, compression, spiral, epiphyseal, depressed, and greenstick.

33.

Describe the formation of the epiphyseal line.

35.

Describe the process of appositional bone growth.

a.Diaphysis

Diaphysis: shaft that forms the long axis of the long bone

d.Diploe

Diploe: the internal spongy bone of flat bones; does contain bone marrow

b.

Elastic: similar to hyaline cartilage, but is matrix contains many elastic fibers along with the delicate collagen fibrils. This cartilage is more elastic than hyaline cartilage and better able to tolerate repeated bending. The epiglottis, which bends down to cover the glottis of the larynx each time we swallow, is made of elastic cartilage, as is the highly bendable cartilage in the outer ear.

j.

Endosteum: thin connective tissue membrane that covers the internal bone surfaces, especially the trabeculae of spongy bone, canals of osteons; osteogenic, containing both osteoblasts and osteoclasts

d.

Epiphyseal line: remnant of the epiphyseal plate; in adult long bone

c.

Epiphyseal plate: between the diaphysis and each epiphysis of young long bone; disc of hyaline cartilage that grows during childhood to lengthen the bone

b.

Female: 18 yrs

h.

Lacuna: hollow spaces osteocytes occupy in the bone

b.Lamella

Lamella: concentric plates or tubes, layers of bone matrix in which the collagen fibers and mineral crystals align and run in a single direction (but adjacent lamella fibers always run in roughly opposite directions

c.

Ligaments: connect bone to bone

a.Long bone

Long bone: longer than wide; shaft plus two distinct ends; most in limbs. Elongated shape, not overall size: bones of fingers are long bones even though they are small.

a.

Males: 21 yrs

a.

Hematoma formation. The fracture is usually accompanied by hemorrhaging. Blood vessels break in the periosteum and inside the bone, releasing blood that clots to form a hematoma. The stages of inflammation are evident in and around the clot.

a.Hyaline

Hyaline: looks like frosted glass when viewed by the unaided eye; the most abundant kind of cartilage. Its chondrocytes appear spherical. Only fiber is a collagen unit fibril, which forms networks that are too thin to be seen with a light microscope. Contains large amounts of water and thus resists compression well. Provides support through flexibility and resilience. Makes up the articular cartilage that covers the ends of adjoining bones in movable joints. It also forms the cartilaginous attachments of the ribs to the sternum, accounts for most of the cartilage found in the respiratory structures, and forms the embryonic skeleton.

Describe the inorganic components of bone.

Hydroapatites, or mineral salts, primarily calcium phosphate; present as tiny crystals that lie in and around the collagen fibrils in the extracellular matrix, packing tightly to provide bone with hardness; resists compression

iii.

Hypertrophic zone: older chondrocytes deeper in the stack, enlarge and signal the surrounding matrix to calcify

39.

Define the following: fracture, reduction, and immobilization.

31.

Define the following terms: bone collar, periosteal bud, and primary and secondary ossification centers.

a.Bones

Bones: provide support and shape to the body, attachment sites for muscle, and storage depot for essential minerals

a.

As adolescence draws to an end, the chondroblasts in the epiphyseal plates divide less often, and the plates become thinner. Eventually, they exhaust their supply of mitotically active cartilage cells, so the cartilage stops growing and is replaced by bone tissue. Long bones stop lengthening when the bone of the epiphyses and diaphysis fuses. This process, called closure of the epiphyseal plates, occurs between the ages of 15 and 23.

a.Define hematopoiesis

Blood cell formation in red bone marrow

a.Identify the stages of endochondral ossification.

Bone collar forms around the diaphysis. In the late embryo (week 8), the endochondral bone begins as a piece of cartilage called a cartilage model. Like all cartilages, it is surrounded by a perichondrium. Then, at the end of week 8 of development, the perichondrium surrounding the diaphysis is invaded by blood vessels and becomes a bone-forming periosteum. Osteoblasts in this new periosteum lay down a collar of bone tissue around the diaphysis. Cartilage calcifies in the center of the diaphysis. At the same time the bone collar forms, the chondrocytes in the center of the diaphysis enlarge (hypertrophy) and signal the surrounding cartilage matrix to calcify. The matrix of calcified cartilage is impermeable to diffusing nutrients. Cut off from all nutrients, the chondrocytes die and disintegrate, leaving cavities in the cartilage. No longer maintained by chondrocytes, the cartilage matrix starts to deteriorate. This doesn't seriously weaken the diaphysis, which is well stabilized by the bone collar around it. These changes affect only the center of the diaphysis. Elsewhere, the cartilage remains healthy and continues to grow, causing the entire endochondral bone to elongate. The periosteal but invades the diaphysis, and the first bone trabeculae form. In the third month of development, the cavities within the diaphysis are invaded by a collections of elements called the periosteal bud. This bud consists of a nutrient artery and vein, along with the cells that will form the bone marrow. Most important, the bud contains bone-forming and bone-destroying cells (osteogenic stem cells and osteoclasts). The entering osteoclasts partly erode the matrix of calcified cartilage, and the osteogenic cells differentiate into osteoblasts, which secrete osteoid around the remaining fragments of this matrix, forming bone-covered trabeculae. In ths way, the earliest version of spongy bone appears within the diaphysis. By the 3rd month of development, bone tissue continues to form around the diaphysis from the periosteum and has begun to appear in the center of the diaphysis. This bone tissue of the diaphysis makes up the primary ossification center. Diaphysis elongates, and the medullary cavity forms. Throughout the rest of the fetal period, the cartilage of the epiphysis continues to grow rapidly, with the part nearest the diaphysis continually calcifying and being replaced by the bone trabeculae, thus elongating the diaphysis. Osteoclasts in turn break down the ends of these bone trabeculae to form a central, boneless medullary cavity. Shortly before or after birth, the epiphyses begin to ossify: First, the cartilage in the center of each epiphysis calcifies and degenerates. Then a bud containing the epiphyseal vessels invades each epiphysis. Bone trabeculae appear, just as they appeared earlier in the primary ossification center. The areas of bone formation in the epiphyses are called secondary ossification centers. The larger long bones of the body can have several ossification centers in each epiphysis. Epiphyses ossify, and cartilaginous epiphyseal plates separate diaphysis and epiphyses. After the secondary ossification centers have appeared and epiphyses have largely ossified, hyaline cartilage remains at only two places: (1) on the epiphyseal surfaces, where it forms the articular cartilages; and (2) between the diaphysis and the epiphysis, where it forms the epiphyseal plates. The epiphyseal plates, also called growth plates, are responsible for lengthening the bones during the 2 decades following birth.

a.

Bone collar: what forms around the cartilaginous model of bone in the embryo around week 8; laid down by osteoblasts of the recently formed periosteum (from the perichondrium) around the diaphysis

a.

Bone deposition: accomplished by osteoblasts which lay down organic osteoid on bone surfaces, and calcium salts crystallize within this osteoid. This process takes about a week. Once the osteoblasts are surrounded by bone matrix, they turn into osteocytes

Define osteoid

Bone matrix secreted by osteoblasts consisting of the ground substance and collagen fibers (organic)

d.

Bone remodeling. Over a period of many months, the bony callus is remodeled. The excess bony material is removed from both the exterior of the bone shaft and the interior of the medullary cavity. Compact bone is laid down to reconstruct the shaft walls. The repaired area resembles the original unbroken bone region, because it responds to the same set of mechanical stresses.

b.

Bone resorption: accomplished by osteoclasts, which each have many nuclei. Osteoclasts crawl along bone surfaces, essentially digging pits as they break down the bone tissue. The part of their plasma membrane that touches the bone surface is highly folded, or ruffled. This expanded membrane forms tight seal against the bone and secretes concentrated hydrochloric acid, which dissolves the mineral part of the matrix. The liberated calcium ions (CA^2+) and phosphate ions enter the tissue fluid and the bloodstream. Lysosomal enzymes are also released across the ruffled membrane and digest the organic part of the bone matrix. Finally, osteoclasts apparently take up collagen and dead osteocytes by phagocytosis.

Define ossification (osteogenesis).

Bone tissue formation; begins in the embryo, proceeds through childhood and adolescence as the skeleton grows, and then occurs at a slower rate in the adult as part of a continual remodeling of the skeleton; for skeleton production, remodeling, and repair

c.

Bony callus formation. Within a week, trabeculae of new bone begin to form in the callus, mostly by endrochondral ossification. These trabeculae span the width of the callus and unite the two fragments of the broken bone. The callus is now called a bony callus, or hard callus, and its trabeculae grow thicker and stronger and become firm about 2 months after the injury.

iv.

Calcification zone: cartilage matrix bcomes calcified, and the chondrocytes die, leaving long spicules (trabeculae) of calcified cartilage on the diaphysis side of the epiphysis-diaphysis junction.

g.

Canaliculi: thin tubes extending from bone lacunae that osteocytes occupy; connects neighboring lacunae to one another and to the nearest capillaries. The extensions of neighboring osteocytes touch each other and form gap junctions through which nutrients can pass through, allowing access to the entire osteon

a.

Cartilage grows quickly during youth and then stops growing during early adulthood. In older adults, cartilage contains fewer chondrocytes and shows some degradation and calcification of its matrix, resulting in thinning of articular cartilage. Bones can be said to be on a timetable from the time they form until death. The mesoderm germ layer and neural crest (in the skull) give rise to embryonic mesenchyme cells, which in turn produce the membranes and cartilages that form most of the embryonic skeleton. These structures then ossify according to a predictable schedule. Although each bone of the skeleton has its own developmental schedule, most long bones start ossifying by week 8 and have obvious primary ossification centers by week 12. So precise is the ossification timetable that the age of a fetus in the womb can be determined from X-ray images or sonograms of the fetal skeleton. At birth, all bones are relatively smooth and featureless. As the child increasingly uses its muscles, the bones develop projections and other markings. Children's bones are not particularly weak, but the cartilage of their epiphyseal plates is not as strong as bone. Thus, childhood injuries often split the epiphyses off from the diaphysis. To treat such injuries, the bone parts are manipulated back into place, then stabilized with metal pins. As mentioned earlier, the skeleton keeps growing until the age of 118-20 years. In children and adolescents, the rate of bone formation exceeds the rate of bone resorption. In young adults, these two processes are in balance. In old age, resorption predominates. Beginning at about age40, the mass of both compact and spongy bone begins to decline. Among young adults, skeletal mass is generally greater in men than in women. Age-related bone loss is greater in women than in men. As bone mass declines with age, other changes occur. An increasing number of osteons remain incompletely formed, and mineralization is less complete. The amount of nonliving compact bone increases, reflecting a diminished blood supply to the bones in old age.

b.

Cartilage: component of many joints, aids in support and movement as it cushions abutting bone surfaces; composition of pre-bones

Identify the following as organic components of bone: cells, fibers, ground substance.

Cells: produce, maintain, or remodel bone tissue Osteogenic cells: stem cells that produce osteoblasts Osteoblasts immature, produce organic portion of extracellular matrix (osteoid); branched; secrete ground substance and collagen fibers Osteocytes: mature bone cells that are trapped in and maintain matrix; located in lacuna Osteoclasts: remove extracellular matrix by secreting lysosomal enzymes and hydrochloric acid Fibers: abundant collagen fibers—strong; secreted by osteoblasts; orientation determines structure; contributes to flexibility and tensile strength Ground substance: body of extracellular matrix; secreted by osteoblasts

f.

Circumferential lamella: occur in the external and internal surfaces of the layer of compact bone; extend around the entire circumberence of the diaphysis; function like osteons but on a much larger scale; resist twisting of the entire long bone

6.Classify bones as long, short, irregular or flat bones.

Classify bones as long, short, irregular or flat bones.

a.Identify the two types of bone tissue: compact and spongy bone tissue.

Compact: dense outer layer of bone tissue that looks smooth and solid Spongy: also called trabecular bone, a honeycomb of small needle-like or flat pieces called trabeculae, that form spaces filled with red or yellow bone marrow

Identify the locations in bones of both compact and spongy bone tissues.

Compact: superficial surface of all bones Spongy: in epiphysis and outer edge of diaphysis of long bones; inside short, irregular, and flat bones; called diploe in flat bones

b.

Compound: fracture in which the bone ends protrude through the skin

40.

Contrast simple and compound fractures.

38.

Contrast the responses both osteoblasts and osteoclasts to stress placed on bone.

c.

Fibrocartilage: unusual tissue that resists both strong compression and strong tension (pulling) forces. It occurs in certain ligaments and certain cartilages that experience both of these forces. It is a perfect structural intermediate between hyaline cartilage and dense regular connective tissue. It consists of thick collagen fibers (as in dense regular connective tissue) surrounding the chondrocytes within the lacunae. Two specific locations of the fibrocartilage are in the annulus fibrosus portion of the discs between the vertebrae and in the articular discs of some joints, for example the menisci of the knee. Chondrocytes in rows of lacunae.

b.

Fibrocartilaginous callus formation. Within a few days, new blood vessels grow into the clot. The periosteum and endosteum near the fracture site show a proliferation of bone-forming cells, which then invade the clot, filling it with repair tissue called soft callus. Initially, the soft callus is a fibrous granulation tissue. As more fibers are produced, the soft callus becomes a dense connective tissue containing fibrocartilage and hyaline cartilage. At this point, the soft callus is also called a fibrocartilaginous callus.

c.

Flat bones: thin, flattened, and usually somewhat curved; most cranial bones, ribs, sternum, and scapula

a.

Fracture: breaks of/in the bone

a.

Function: keeps bone elongating as medullary cavity lengthens; keeps separation between epiphyses and diaphysis

c.

Haversian (central) canal: lined with osteogenic endosteum; contains blood vessels, which supply nutrients to the bone cells of the osteon, and its own nerve fibers

a.Haversian system

Haversian system (osteon): long, cylindrical structures oriented parallel to the long axis of the bone and to the main compression stress; miniature weight-bearing pillars; a group of concentric tubes resembling the rings of a tree trunk in cross section

d.

Irregular bones: various shapes that don't fit into the previous categories. Examples are the vertebrae; hip bones

5.Identify 206 as the number of bones in a typical human skeleton.

Identify 206 as the number of bones in a typical human skeleton.

42.

Identify and describe the stages of fracture healing.

18.Identify bone as possessing 35% organic components and 65% inorganic components.

Identify bone as possessing 35% organic components and 65% inorganic components.

34.

Identify the approximate age at which long bones cease growing in males and females.

12.

Identify the location and function of the following structures associated with compact bone tissue: Haversian system (osteon), lamella, Haversian (central) canal, Volkmann's (perforating) canal, interstitial lamella, circumferential lamella, canaliculi, lacuna, and osteocyte.

37.

Identify the roles of both osteoblasts and osteoclasts in bone remodeling. ^^

c.

Immobilization: the stabilizing of a broken bone within a cast or traction to allow the healing process to begin

b.Inorganic

Inorganic: from outside the body: inorganic hydroapatites, or mineral salts, primarily calcium phosphate; present as tiny crystals that lie in and around the collagen fibrils in the extracellular matrix, packing tightly to provide bone with hardness

b.Interstitial growth

Interstitial growth "growth from within": the chondrocytes within the cartilage divide and secrete new matrix

Contrast intramembranous ossification and endochondral ossification.

Intramembranous ossification: membranous bones form directly from mesenchyme without first being modeled in cartilage. Endochondral ossification: first modeled in hyaline cartilage, which then is gradually replaced by bone tissue.

Define membrane and endochondral bones and identify the skeletal location of each.

Membrane bones: bones that form directly from mesenchyme without first being modeled in cartilage; most skull bones (except the base ones) and the clavicles Endochondral bones: bones first modeled in hyaline cartilage, then gradually ossified; all other bones of the body besides skull and clavicles Identify the stages of intramembranous ossification.

Identify the stages of intramembranous ossification.

Mesenchymal cells cluster within the connective tissue membrane and become bone-forming osteoblasts These cells begin secreting the organic part of bone matrix, called osteoid, which then becomes mineralized Once surrounded by their own matrix, the osteoblasts are called osteocytes. The new bone tissue forms between embryonic blood vessels, which are woven in a random network The result is woven bone tissue, with trabeculae arranged in networks. This embryonic tissue lacks the lamellae that occur in mature spongy bone. During this same stage, more mesenchyme condenses just external to the developing membrane bone and becomes the periosteum. The trabeculae at the periphery grow thicker until plates of compact bone are present on both surfaces. In the center of the membranous bone, the trabeculae remain distinct, and spongy bone results. The final pattern is that of the flat bone.

e.

Nutrient artery: main artery serving the diaphysis

f.

Nutrient foramen: hole in the wall of the diaphysis through which the nutrient artery and nutrient vein flow

a.Organic

Organic: made by body: cells, fibers, ground substance; provide elasticity of bone

a.Ossification center

Ossification center: the place where bone formation (ossification) takes place:

v.

Ossification zone: trabeulae spicules are partly eroded by osteoclasts, then covered with bone tissue by osteoblasts, forming spicules of bone; which are destroyed from within the diaphysis by the action of osteoclasts at the same rate that they are formed at the epiphysis; thus they stay a constant length and the marrow cavity grows longer as the long bone lengthens.

a.

Osteoblasts in the osteogenic layer of the periosteum add bone tissue in circumferential lamellae to the external face of the diaphysis as osteoclasts in the endosteum remove bone from the internal surface of the diaphysis wall. Thse two processes occur at about the same rate, so that the circumference of the long bone expands and the bone widens.

a.

Osteoblasts lay down more bone tissue where there is more stress (remodeling osteons of compact bone tissue and creating trabeculi that are aligned with new compressive and tensile stresses)

b.

Osteoclasts remove bone tissue when there is an absence of stresses on the bone

i.Osteocyte

Osteocyte: mature bone cell that maintains the extracellular matrix; located in lacunae between lamellae; posses canaliculi

b.Osteocytes

Osteocytes: live in trabeculae and maintain them

Identify the functions of each of the following bone-related cells: osteogenic cells, osteoblasts, osteocytes, and osteoclasts.

Osteogenic cells: stem cells that produce osteoblasts Osteoblasts: immature, produce organic portion of extracellular matrix (osteoid); branched; secrete ground substance and collagen fibers Osteocytes: mature bone cells that are trapped in and maintain matrix; located in lacuna Osteoclasts: remove extracellular matrix by secreting lysosomal enzymes and hydrochloric acid

b.

Osteomalacia: a number of disorders in adults in which the bones are inadequately mineralized. Even though osteoid matrix is produced, calcification does not occur, and the bones soften and weaken. The main symptom is pain when weight is but on the affected bone.

a.

Osteoporosis: characterized by low bone mass and a deterioration of the microscopic architecture of the bony skeleton. Although the chemical composition of the bone matrix remains normal, bone resorption outpaces bone deposition, in association with elevated numbers of osteoclasts. Osteoporotic bones become porous and light. The compact bone becomes thinner and less dense than normal, and the spongy bone has fewer trabeculae. The loss of bone mass often leads to fractures. Even though osteoporosis affects the whole skeleton, the vertebral column is most vulnerable, and compression fractures of the vertebrae are frequent. The femur (thigh bone), especially its neck near the hip joint, is also very susceptible to fracture. A break there, called a broken hip, is a common problem in ppl with osteoporosis. Osteoporosis occurs most often in the aged, particularly in women who have one through menopause. Although men develop it to a lesser degree, 30% of American women between ages 60 and 70 have osteoporosis; 70% have it by age 80. Estrogen deficiency is strongly implicated in osteoporosis in older women because the secretion of estrogens, which helps maintain bone density, wanes after menopause. Insufficient exercise, a poor diet in calcium and protein, and inadequate levels of vitamin contribute to this condition also.

b.

Reduction: the realignment of broken bone ends to help bone heal; two types: closed reduction, when the bones are coaxed back into position by the physician's hands; and open reduction, when the bones are joined surgically with pins or wires

e.

Osteosarcoma: bone cancer primarily affecting young people between 10 and 25 years of age. It usually originates in a long bone of the upper or lower limb, with 50% of cases arising near the knee. The cancer cells derive from osteoblast-like cells of mesenchymal origin in the parts of the diaphysis nearest the epiphyses. Secreting osteoid and growing quickly, the tumor alters the affected bone by eroding the medullary cavity internally and the compact bone externally. The tumor metastasizes, and most deaths result from secondary tumors in the lungs. Most osteosarcomas are recognized by the pain and the visible swelling they produce in the affected bone, and the diagnosis is confirmed by X-ray studies or other medical imaging techniques. Treatment begins by removing the cancerous region of the bone and replacing it with bone grafts or prostheses (although limb amputation is necessary in severe cases). This is followed by chemotherapy and surgical removal of any metastases in the lung. Survival rate of 60-70% if detected early.

d.

Paget's Disease is characterized by excessive rates of bone deposition and bone resorption. The newly formed bone has an abnormally high ratio of immature woven bone to mature compact bone. This, along with reduced mineralization, makes most of the bones soft and weak. Late in the course of the disease, the activity of osteoblasts outpaces that of osteoclasts. Therefore, the bones can thicken, but in an irregular manner, and the medullary cavities may fill with bone. Paget's disease may affect many parts of the skeleton but is usually a localized and intermittent condition. It rarely occurs before age 40 and affects about 3% of all older people in North America. It progresses slowly, often produces no symptoms, and is seldom life-threatening. Its cause is unknown. Treatment involves inhibiting osteoclasts with bisphosphonate drugs or calcitonin.

b.

Periosteal bud: invades the diaphysis, brining osteogenic stem cells and osteoclasts to erode matrix of calcified cartilage and build new bone in the form of trabeculae around fragments

h.

Periosteum: a connective tissue membrane that covers the entire outer surface of each bone except on the endso fo the epiphyses

c.

Primary ossification center: location of bone trabeculae formation in the diaphysis

i.Primary

Primary: bone tissue of the diaphysis

ii.

Proliferation zone: cartilage cells at "top" of column, divide quickly, pushing the epiphysis away from the diaphysis, thereby causing the entire long bone to lengthen

l.

Red bone marrow: contained in the epiphyses and ends of diaphysis; manufactures blood cells

c.Red bone marrow

Red bone marrow: within the spaces formed by trabeculae; manufacture blood cells (hematopoiesis)

i.

Resting zone: nearest epiphysis; cells are relatively small and inactive

c.

Rickets: more severe than osteomalacia, though similar symptoms. Along with weakened and bowed leg bones, malformations of the child's head and rib case are common. Because the epiphyseal plates cannot be replaced with calcified bone, they grow atypically thick, and the epiphyses of the long bones become abnormally long. Caused by inadequate amounts of vitamin D or calcium phosphate in the diet. They are cured by drinking vitamin D fortified milk and exposing the skin to sunlight. In 1800s, est of 90% of children in the industrialized cities of North America dn Europe suffered from rickets. Vitamin D added to milk in 1930. Rickets is now increasing in prevalence in children aes 6-24 months. Several factors have contributed to this increase; breast-feedin without vitamin D supplementation, spending more time indoors, and increased use of sunscreen. A short period (10-15 minutes) of sun exposure three times per week is adequate for vitamin D synthesis.

d.

Secondary ossification center: location of bone trabeculae formation in the epiphyses

ii.Secondary

Secondary: areas of bone formation in the epiphyses

a.Sesamoid bones

Sesamoid bones are a special type of short bone that forms within a tendon; the kneecap, for example. Sesamoid bones vary in size and number in different people. Some sesamoid bones clearly act to alter the direction of pull of a tendon. Others reduce friction and modify pressure in tendons, thus reducing abrasion or tearing.

i.

Sharpey's fibers (perforating collagen fiber bundles): thick bundles of collagen that run from the periosteum into the bone matrix to secure the periosteum to the underlying bone

b.Short bone

Short bone: cube-shaped; occur in wrist and the ankle. A special type, sesamoid bones, form within a tendon. Ex: kneecap. Some act clearly to alter the direction of pull of a tendon, while others reduce friction and modify pressure in tendons, thus reducing abrasion or tearing.

a.

Simple: fracture in which the bone breaks cleanly but does not penetrate through the skin

16.Describe the two layers of the periosteum.

Superficial layer: dense irregular connective tissue which resists tension placed on a bone during bending Deep layer: abuts the compact bone; osteogenic, containing osteoblasts and osteoclasts—remodel bone surfaces

Describe the composition of the embryonic skeleton prior to week 8.

The skeleton of the human embryo consists only of hyaline cartilage and some membranes of mesenchyme, an embryonic connective tissue.

a.Describe the characteristics of bone

They are organs because they contain several different tissues. Although bone tissue predominates, bones also contain nervous tissue in nerves, blood tissue in blood vessels, cartilage in articular cartilages, adipose tissue in yellow bone marrow, and epithelial tissue lining the blood vessels. Highly vascular; many collagen fibers reduce tension forces; hard mineralized extracellular matrix

a.Trabeculae

Trabeculae: irregular bony plates that are in line with stress put on bone; small needle-like or flat pieces that form honeycomb structure of spongy bone

k.

Yellow bone marrow: contained in the medullary cavity; stores energy as fat

a.Contrast the functions and locations of yellow and red bone marrow.

Yellow: energy storage—fat Red: hematopoiesis—blood manufacture

b.

Zones:

1. Define the following bone marking terms (Table 6.1): tuberosity, crest, trochanter, line tubercle, epicondyle, spine, process, head, facet, condyle, foramen, groove, fissure, notch, fossa, meatus, and sinus.

a. Tuberosity: large rounded projection; may be roughened b. Crest: narrow ridge of bone; usually prominent c. Trochanter: very large, blunt, irregularly shaped process (the only examples are on the femur) d. Line: narrow ridge of bone; less prominent than a crest e. Tubercle: small rounded projection or process f. Epicondyle: raised area on or above a condyle g. Spine: sharp, slender, often pointed projection h. Process: any bony prominence i. Head: bony expansion carried on a narrow neck j. Facet smooth, nearly flat articular surface k. Condyle: rounded articular projection, often articulates with a corresponding fossa l. Foramen: round or oval opening through a bone m. Groove: furrow n. Fissure: narrow, slitlike opening o. Notch: indentation at the edge of a structure p. Fossa: shallow basinlike depression in a bone, often serving as an articular surface q. Meatus: canal-like passageway Sinus: cavity within a bone, filled with air and lined with mucous membrane