Bone tissue (141)

Groove-like impressions or holes

indicate locations where nerves and blood vessels pass through the bones.

Ch. 7

Axial skeleton

The distal portion of the femur is replaced

Every 4 months.

cranial bones

Forms cranial cavity Encloses and protects the brain. The eight cranial bones are the frontal bone, two parietal bones, two temporal bones, the occipital bone, the sphenoid bone, and the ethmoid bone.

Colles

Fracture of the distal end of the lateral forearm bone (radius) in which the distal fragment is displaced posteriorly.

Pott

Fracture of the distal end of the lateral leg bone (fibula), with serious injury of the distal tibial articulation.

bone abnormalities

Indicated by Darker or lighter areas bone abnormalities.

Bone resorption

Involved in remodeling of bone. removal of minerals and collagen fibers from bone by osteoclasts results in the breakdown of bone extracellular matrix, and bone deposition results in its formation. About 5-10 percent of the total bone mass in the body is remodeled each year.

Fissure

Narrow slit between adjacent parts of bones through which blood vessels or nerves pass Superior orbital fissure of the sphenoid bone (Figure 7.6f and 7.10b)

Nutrient artery

Near the center of the diaphysis, a large artery. enters the compact bone at an oblique angle through a hole called the nutrient foramen (Figure 6.5). The path of the artery through the bone is always away from the dominant growth end of the bone. (This is true of all the long bones of the limbs.

Growth of the cartilage model

Once chondroblasts become deeply buried in the cartilage extracellular matrix, they are called chondrocytes. The cartilage model grows in length by continual cell division of chondrocytes, accompanied by further secretion of the cartilage extracellular matrix. This type of cartilaginous growth, called interstitial (endogenous) growth (growth from within), results in an increase in length. In contrast, growth of the cartilage in thickness is due mainly to the deposition of extracellular matrix material on the cartilage surface of the model by new chondroblasts that develop from the perichondrium in a process called appositional (exogenous) growth (a-pō-ZISH-i-nal), meaning growth of the outer surface (described shortly). As the cartilage model continues to grow, chondrocytes in its midregion hypertrophy (increase in size), and the surrounding cartilage extracellular matrix begins to calcify. Other chondrocytes within the calcifying cartilage die because nutrients can no longer diffuse quickly enough through the extracellular matrix. As these chondrocytes die, the spaces left behind by the dead chondrocytes merge into small cavities called lacunae.

Bones

Organ made up of several diff. tissues working together. bone (osseous) tissue, cartilage, dense connective tissue, epithelium, adipose tissue, and nervous tissue.

orthopedics

The branch of medical science concerned with the prevention or correction of disorders of the musculoskeletal system

Open (Compound)

The broken ends of the bone protrude through the skin. Conversely, a closed (simple) fracture does not break the skin.

entering the medullary cavity

These branches supply both the inner part of compact bone tissue of the diaphysis and the spongy bone tissue and red bone marrow as far as the epiphyseal plates (or lines). nutrient artery divides into proximal and distal branches that course toward each end of the bone

Musculoskeletoal system

Together, the bones, muscles, and joints form an integrated system

bone mineral density (BMD) test

Undergo Osteoporosis is diagnosed by taking a family history Measuring bone density.

Development of the secondary ossification centers.

When branches of the epiphyseal artery enter the epiphyses, secondary ossification centers develop, usually around the time of birth. Bone formation is similar to what occurs in primary ossification centers. However, in the secondary ossification centers spongy bone remains in the interior of the epiphyses (no medullary cavities are formed here). In contrast to primary ossification, secondary ossification proceeds outward from the center of the epiphysis toward the outer surface of the bone.

bone scan

is a diagnostic procedure that takes advantage of the fact that bone is living tissue. A small amount of a radioactive tracer compound that is readily absorbed by bone is injected intravenously.

metaphyseal arteries

enter the metaphyses of a long bone and, together with the nutrient artery, supply the red bone marrow and bone tissue of the metaphyses.

osteoclasts

secrete enzymes and acids that break down the extracellular matrix of bone.

Osteoarthritis

(osˊ-tē-ō-ar-THRĪ -tis; arthr=joint) The degeneration of articular cartilage so that the bony ends touch; the resulting friction of bone against bone worsens the condition. Usually occurs in older individuals.

Osteosarcoma

(osˊ-tē-ō-sar-KŌ-ma; sarcoma=connective tissue tumor) Bone cancer that primarily affects osteoblasts and occurs most often in teenagers during their growth spurt; the most common sites are the metaphyses of the thighbone (femur), shinbone (tibia), and arm bone (humerus). Metastases occur most often in lungs; treatment consists of multidrug chemotherapy and removal of the malignant growth, or amputation of the limb.

There are two principal effects of aging on bone tissue

1. Demineralization: Loss of bone mass. the loss of calcium and other minerals from bone extracellular matrix. This loss usually begins after age 30 in females, accelerates greatly around age 45 as levels of estrogens decrease, and continues until as much as 30 percent of the calcium in bones is lost by age 70. Once bone loss begins in females, about 8 percent of bone mass is lost every 10 years. In males, calcium loss typically does not begin until after age 60, and about 3 percent of bone mass is lost every 10 years. The loss of calcium from bones is one of the contributing factors in osteoporosis. 2. aging on the skeletal system, brittleness: results from a decreased rate of protein synthesis. Recall that the organic part of bone matrix, mainly collagen fibers, gives bone its tensile strength. The loss of tensile strength causes the bones to become very brittle and susceptible to fractures. In some elderly people, collagen fiber synthesis slows, in part, due to diminished production of human growth hormone. In addition to increasing the susceptibility to fractures, loss of bone mass also leads to deformity, pain, loss of height, and loss of teeth.

Blood and Nerve Supply of Bone

1. Long bones are supplied by periosteal, nutrient, metaphyseal, and epiphyseal arteries; veins accompany the arteries. 2.Nerves accompany blood vessels in bone; the periosteum is rich in sensory neurons.

Repair of bone fractures

1. Reactive phase: Blood vessels crossing the fracture line are broken. As blood leaks from the torn ends of the vessels, it forms a mass of blood (usually clotted) around the site of the fracture. This clot, called a fracture hematoma (hē-ma-TŌ-ma; hemat-=blood; -oma=tumor), usually forms 6 to 8 hours after the injury. Because the circulation of blood stops at the site where the fracture hematoma forms, nearby bone cells die. Swelling and inflammation occur in response to dead bone cells, producing additional cellular debris. Phagocytes (neutrophils and macrophages) and osteoclasts begin to remove the dead or damaged tissue in and around the fracture hematoma. This stage may last up to several weeks. 2. Reparative phase: formation of a fibrocartilaginous callus and a bony callus. Blood vessels grow into the fracture hematoma and phagocytes begin to clean up dead bone cells. Fibroblasts from the periosteum invade the fracture site and produce collagen fibers. In addition, cells from the periosteum develop into chondroblasts and begin to produce fibrocartilage in this region. These events lead to the development of a fibrocartilaginous (soft) callus (fi-brō-kar-ti-LAJ-i-nus), a mass of repair tissue consisting of collagen fibers and cartilage that bridges the broken ends of the bone. Formation of the fibrocartilaginous callus takes about three weeks. In areas closer to well-vascularized healthy bone tissue, osteoprogenitor cells develop into osteoblasts, which begin to produce spongy bone trabeculae. The trabeculae join living and dead portions of the original bone fragments. In time, the fibrocartilage is converted to spongy bone, and the callus is then referred to as a bony (hard) callus. The bony callus lasts about three to four months. 3. Bone remodeling phase: The final phase of fracture repair is bone remodeling of the callus. Dead portions of the original fragments of broken bone are gradually resorbed by osteoclasts. Compact bone replaces spongy bone around the periphery of the fracture. Sometimes, the repair process is so thorough that the fracture line is undetectable, even in a radiograph (x-ray). However, a thickened area on the surface of the bone remains as evidence of a healed fracture.

Facial bone

14 bones. two nasal bones, two maxillae (or maxillas), two zygomatic bones, the mandible, two lacrimal bones, two palatine bones, two inferior nasal conchae, and the vomer.

Osteomyelitis

An infection of bone characterized by high fever, sweating, chills, pain, and nausea; pus formation, edema, and warmth over the affected bone; and rigid overlying muscles. It is often caused by bacteria, usually Staphylococcus aureus. The bacteria may reach the bone from outside the body (through open fractures, penetrating wounds, or orthopedic surgical procedures); from other sites of infection in the body (abscessed teeth, burn infections, urinary tract infections, or upper respiratory infections) via the blood; and from adjacent soft tissue infections (as occurs in diabetes mellitus).

Histology of Bone Tissue

Bone tissue consists of widely separated cells surrounded by large amounts of extracellular matrix. 2.The four principal types of cells in bone tissue are osteoprogenitor cells (bone stem cells), osteoblasts (bone-building cells), osteocytes (maintain daily activity of bone), and osteoclasts (bone-destroying cells). 3.The extracellular matrix of bone contains abundant mineral salts (mostly hydroxyapatite) and collagen fibers. 4.Compact bone tissue consists of osteons (haversian systems) with little space between them. 5.Compact bone tissue lies over spongy bone tissue in the epiphyses and makes up most of the bone tissue of the diaphysis. Functionally, compact bone tissue protects, supports, and resists stress. 6.Spongy bone tissue does not contain osteons. It consists of trabeculae surrounding spaces filled with red bone marrow. 7.Spongy bone tissue forms most of the structure of short, flat, and irregular bones, and the epiphyses of long bones. Functionally, spongy bone tissue trabeculae offer resistance along lines of stress; support and protect red bone marrow; and make bones lighter for easier movement.

Osteopenia

Reduced bone mass due to a decrease in the rate of bone synthesis to a level insufficient to compensate for normal bone resorption; any decrease in bone mass below normal. Osteoporosis is an example of severe osteopenia.

Treatment for fractures

Reduction: Setting a fracture. bones to unite properly, the fractured ends must be brought into alignment. a fractured bone may be kept immobilized by a cast, sling, splint, elastic bandage, external fixation device, or a combination of these devices. Closed reduction: fractured ends of a bone are brought into alignment by manual manipulation, and the skin remains intact. Open reduction: fractured ends of a bone are brought into alignment by a surgical procedure using internal fixation devices such as screws, plates, pins, rods, and wires.

ligaments

Usually bone to bone.

skull (168, 7.2)

bony framework of the head and contains 22 bones, not counting the bones of the middle ears.

stress fracture

fracture without visibly breaking series of microscopic fissures in bone that forms without any evidence of injury to other tissues.

Remodeling

building of new bone tissue and breaking down of old bone tissue.

The two methods of bone formation, which both involve the replacement of a preexisting connective tissue with bone

-Don't lead to diff. in structures of mature ones. -Soley diff. methods of bone development

Spongy bone features

precisely oriented along lines of stress, a characteristic that helps bones resist stresses and transfer force without breaking. tends to be located where bones are not heavily stressed or where stresses are applied from many directions. The trabeculae do not achieve their final arrangement until locomotion is completely learned. In fact, the arrangement can even be altered as lines of stress change due to a poorly healed fracture or a deformity.

Veins that carry blood away from long bones are evident in three places:

(1) One or two nutrient veins accompany the nutrient artery and exit through the diaphysis; (2) numerous epiphyseal veins and metaphyseal veins accompany their respective arteries and exit through the epiphyses (3) many small periosteal veins accompany their respective arteries and exit through the periosteum; surrounding the bone has numerous lymphatic capillaries and lymph vessels, but there is no evidence of any lymphatic vessels within the bone tissue.

The growth in length of a long bone involves

(1) interstitial growth of cartilage on the epiphyseal side of the epiphyseal plate and (2) replacement of cartilage with bone by endochondral ossification on the diaphyseal side of the epiphyseal plate.

endochondral ossification steps

-Best observed in long bones. 1. Development of the cartilage model. At the site where the bone is going to form, specific chemical messages cause the cells in mesenchyme to crowd together in the general shape of the future bone, and then develop into chondroblasts. The chondroblasts secrete cartilage extracellular matrix, producing a cartilage model (future diaphysis) consisting of hyaline cartilage. A mesenchymal covering called the perichondrium (per-i-KON-drē-um) develops around the cartilage model. 2. Growth of the cartilage model.Once chondroblasts become deeply buried in the cartilage extracellular matrix, they are called chondrocytes. The cartilage model grows in length by continual cell division of chondrocytes, accompanied by further secretion of the cartilage extracellular matrix. This type of cartilaginous growth, called interstitial (endogenous) growth (growth from within), results in an increase in length. Contrast, growth of the cartilage in thickness is due mainly to the deposition of extracellular matrix material on the cartilage surface of the model by new chondroblasts that develop from the perichondrium in a process called appositional (exogenous) growth (a-pō-ZISH-i-nal), meaning growth of the outer surface 3. Devel. of primary ossification center. 4. Devel. of medullary (marrow) cavity 5. Development of the secondary ossification centers 6. Formation of articular cartilage and the epiphyseal (growth) plate.

Renewal rate for bone tissue

-Compact bone: ~ 4% per year. -Spongy bone: ~20% per year. also removes injured bone, replacing it with new bone tissue. Remodeling may be triggered by factors such as exercise, lifestyle modifications, and changes in diet.

hip bones, ribs, sternum (breastbone), vertebrae, and the proximal ends of the humerus and femur

-Spongy bone; only site where red bone marrow is stored and, thus, the site where hemopoiesis (blood cell production) occurs in adults.

Foramen (fō-RĀ-men=hole; plural is foramina)

Opening through which blood vessels, nerves, or ligaments pass Optic foramen (canal) of the sphenoid bone *Same IMG as fissure.

2 major types of surface markings

1. Depressins & openings: which form joints or allow the passage of soft tissues (such as blood vessels and nerves) 2. Processes: projections or outgrowths that either (a) help form joints or (b) serve as attachment points for connective tissue (such as ligaments and tendons).

Intramembranous Ossification process

1. Development of the ossification center. At the site where the bone will develop, specific chemical messages cause the mesenchymal cells to cluster together and differentiate, first into osteoprogenitor cells and then into osteoblasts. The site of such a cluster is called an ossification center. Osteoblasts secrete the organic extracellular matrix of bone until they are surrounded by it. 2. Calcification. Next, the secretion of extracellular matrix stops and the cells, now called osteocytes, lie in lacunae and extend their narrow cytoplasmic processes into canaliculi that radiate in all directions. Within a few days, calcium and other mineral salts are deposited and the extracellular matrix hardens or calcifies (calcification). 3. Formation of trabeculae. -As the bone extracellular matrix forms, it develops into trabeculae that fuse with one another to form spongy bone around the network of blood vessels in the tissue. CT associated with the blood vessels in the trabeculae differentiates into red bone marrow. 4. Development of the periosteum. In conjunction with the formation of trabeculae, the mesenchyme at the periphery of the bone condenses and develops into the periosteum. Eventually, a thin layer of compact bone replaces the surface layers of the spongy bone, but spongy bone remains in the center. Much of the newly formed bone is remodeled (destroyed and reformed) as the bone is transformed into its adult size and shape.

Functions of bones

1.Supports soft tissue and provides attachment for skeletal muscles. 2.Protects internal organs. 3.Assists in movement along with skeletal muscles. 4.Stores and releases minerals. 5.Contains red bone marrow, which produces blood cells. 6.Contains yellow bone marrow, which stores triglycerides (fats), a potential chemical energy reserve.

Greenstick

A partial fracture in which one side of the bone is broken and the other side bends; similar to the way a green twig breaks on one side while the other side stays whole, but bends; occurs only in children, whose bones are not fully ossified and contain more organic material than inorganic material.

Sutural bones (wormian bones)

Additional bone shape dependent on location NOT SHAPE.

Development of the medullary (marrow) cavity.

As the primary ossification center grows toward the ends of the bone, osteoclasts break down some of the newly formed spongy bone trabeculae. This activity leaves a cavity, the medullary (marrow) cavity, in the diaphysis (shaft). Eventually, most of the wall of the diaphysis is replaced by compact bone.

Development of the cartilage model

At the site where the bone is going to form, specific chemical messages cause the cells in mesenchyme to crowd together in the general shape of the future bone, and then develop into chondroblasts. The chondroblasts secrete cartilage extracellular matrix, producing a cartilage model (future diaphysis) consisting of hyaline cartilage. A mesenchymal covering called the perichondrium (per-i-KON-drē-um) develops around the cartilage model.

lacunae (la-KOO-nē=little lakes; singular is lacuna)

Between the concentric lamellae are small spaces contain osteocytes

blood supply of a long bone using the mature tibia (shin bone)

Bone is richly supplied with blood. Blood vessels, which are especially abundant in portions of bone containing red bone marrow, pass into bones from the periosteum.

Orthodontics

Branch of dentistry concerned w prevention & correction of poorly aligned teeth. The movement of teeth by braces places a stress on the bone that forms the sockets that anchor the teeth. In response to this artificial stress, osteoclasts and osteoblasts remodel the sockets so that the teeth align properly.

Processes that form attachment points for connective tissue:

CrestProminent ridge or elongated projectionIliac crest of the hip bone (Figure 8.9b)Epicondyle (epi-=above)Typically roughened projection above a condyleMedial epicondyle of the femur (Figure 8.11a)LineLong, narrow ridge or border (less prominent than a crest)Linea aspera of the femur (Figure 8.11b)Spinous processSharp, slender projectionSpinous process of a vertebra (Figure 7.16a)Trochanter (trō-KAN-ter)Very large projectionGreater trochanter of the femur (Figure 8.11a)Tubercle (TOO-ber-kul; tuber=knob)Variable sized rounded projectionGreater tubercle of the humerus (Figure 8.4a)TuberosityVariable sized projection that has a rough, bumpy surfaceIschial tuberosity of the hip bone (Figure 8.9b)

Long bones

Diaphysis: bone's shaft, or body—the long, cylindrical, main portion of the bone. epiphyses (e-PIF-i-sēz=growing own; singular is epiphysis) or extremities are the proximal and distal ends of the bone. 3.The metaphyses (me-TAF-i-sēz; meta-=between; singular is metaphysis) are the regions between the diaphysis and the epiphyses. In a growing bone, each metaphysis contains an epiphyseal (growth) plate (ep-i-FIZ-ē-al), a layer of hyaline cartilage that allows the diaphysis of the bone to grow in length (a process described later in this chapter). When bone growth in length stops somewhere between the ages of 14 and 24, the cartilage in the epiphyseal plate is replaced by bone and the resulting bony structure is known as the epiphyseal line. 4.The articular cartilage is a thin layer of hyaline cartilage covering the part of the epiphysis where the bone forms an articulation (joint) with another bone. Articular cartilage reduces friction and absorbs shock at freely movable joints. Because articular cartilage lacks a perichondrium and lacks blood vessels, repair of damage is limited. 5.The periosteum (per-ē-OS-tē-um; peri-=around) is a tough connective tissue sheath and its associated blood supply that surrounds the bone surface wherever it is not covered by articular cartilage. It is composed of an outer fibrous layer of dense irregular connective tissue and an inner osteogenic layer that consists of cells. Some of the cells enable bone to grow in thickness, but not in length. The periosteum also protects the bone, assists in fracture repair, helps nourish bone tissue, and serves as an attachment point for ligaments and tendons. The periosteum is attached to the underlying bone by perforating (Sharpey's) fibers, thick bundles of collagen that extend from the periosteum into the bone extracellular matrix. 6.The medullary cavity (MED-ū-lar-ē; medulla-=marrow, pith), or marrow cavity, is a hollow, cylindrical space within the diaphysis that contains fatty yellow bone marrow and numerous blood vessels in adults. This cavity minimizes the weight of the bone by reducing the dense bony material where it is least needed. The long bones' tubular design provides maximum strength with minimum weight. 7.The endosteum (end-OS-tē-um; endo-=within) is a thin membrane that lines the medullary cavity. It contains a single layer of bone-forming cells and a small amount of connective tissue. *The spongy bone tissue of the epiphysis and metaphysis contains red bone marrow, and the medullary cavity of the adult diaphysis contains yellow bone marrow.

Bone Growth During Infancy, Childhood, and Adolescence

During infancy, childhood, and adolescence, bones throughout the body grow in thickness by appositional growth, and long bones lengthen by interstitial growth.

osteonic (haversian or central) canal

Each osteon consists of concentric lamellae arranged around osteons

Epiphyseal arteries

Enter epiphyses of long bone Supply the red bone marrow and bone tissue of the epophyses.

Sectional view of several osteons (havarian systems) of femur (thigh) and details of one osteon

Histology of compact and spongy bone: (a) Sections through the diaphysis of a long bone, from the surrounding periosteum on the right, to compact bone in the middle, to spongy bone and the medullary cavity on the left. The inset at the upper right shows an osteocyte in a lacuna. (b and c) Details of spongy bone. (d) for a photomicrograph of compact bone tissue and the Clinical Connection on osteoporosis in Section 6.7 for a scanning electron micrograph of spongy bone tissue.

Impacted

One end of the fractured bone is forcefully driven into the interior of the other.

Growth in thickness

Like cartilage, bone can grow in thickness (diameter) only by appositional growth 1. At the bone surface, periosteal cells differentiate into osteoblasts, which secrete the collagen fibers and other organic molecules that form bone extracellular matrix. The osteoblasts become surrounded by extracellular matrix and develop into osteocytes. This process forms bone ridges on either side of a periosteal blood vessel. The ridges slowly enlarge and create a groove for the periosteal blood vessel. 2Eventually, the ridges fold together and fuse, and the groove becomes a tunnel that encloses the blood vessel. The former periosteum now becomes the endosteum that lines the tunnel. 3Osteoblasts in the endosteum deposit bone extracellular matrix, forming new concentric lamellae. The formation of additional concentric lamellae proceeds inward toward the periosteal blood vessel. In this way, the tunnel fills in, and a new osteon is created. 4As an osteon is forming, osteoblasts under the periosteum deposit new circumferential lamellae, further increasing the thickness of the bone. As additional periosteal blood vessels become enclosed as in step 1, the growth process continues.

Four types of cells are present in bone tissue

Osteoprogenitor cells (os-tē-ō-prō-JEN-i-tor; -genic=producing) are unspecialized bone stem cells derived from mesenchyme, the tissue from which almost all connective tissues are formed. They are the only bone cells to undergo cell division; the resulting cells develop into osteoblasts. Osteoprogenitor cells are found along the inner portion of the periosteum, in the endosteum, and in the canals within bone that contain blood vessels. 2.Osteoblasts (OS-tē-ō-blasts; -blasts=buds or sprouts) are bone-building cells. They synthesize and secrete collagen fibers and other organic components needed to build the extracellular matrix of bone tissue, and they initiate calcification. As osteoblasts surround themselves with extracellular matrix, they become trapped in their secretions and become osteocytes. (Note: Cells with the suffix blast in bone or any other connective tissue secrete extracellular matrix.) 3.Osteocytes (OS-tē-ō-sīts; -cytes=cells), mature bone cells, are the main cells in bone tissue and maintain its daily metabolism, such as the exchange of nutrients and wastes with the blood. Like osteoblasts, osteocytes do not undergo cell division. (Note: Cells with the suffix cyte in bone or any other tissue maintain and monitor the tissue.) 4.Osteoclasts (OS-tē-ō-klasts; -clast=break), huge cells derived from the fusion of as many as 50 monocytes (a type of white blood cell), are concentrated in the endosteum. The plasma membrane of an osteoclast is deeply folded into a ruffled border on the side of the cell that faces the bone surface. Here the cell releases powerful lysosomal enzymes and acids that digest the protein and mineral components of the underlying extracellular matrix of bone. This breakdown of the extracellular matrix of bone, termed bone resorption (re-SORP-shun), is part of the normal development, growth, maintenance, and repair of bone. (Note: Cells with the suffix clast in bone break down extracellular matrix.) As you will see later, osteoclasts help regulate blood calcium level in response to certain hormones. They are also the target cells for drug therapy used to treat osteoporosis.

Development of the primary ossification center

Primary ossification proceeds inward from the external surface of the bone. A nutrient artery penetrates the perichondrium and the calcifying cartilage model through a nutrient foramen in the midregion of the cartilage model, stimulating osteoprogenitor cells in the perichondrium to differentiate into osteoblasts. Once the perichondrium starts to form bone, it is known as the periosteum. Near the middle of the model, periosteal capillaries grow into the disintegrating calcified cartilage, inducing growth of a primary ossification center, a region where bone tissue will replace most of the cartilage. Osteoblasts then begin to deposit bone extracellular matrix over the remnants of calcified cartilage, forming spongy bone trabeculae. Primary ossification spreads from this central location toward both ends of the cartilage model.

Ossification (osteogenesis)

Process of bone formation (1) the initial formation of bones in an embryo and fetus (2) Growth of bones during infancy, childhood, and adolescence until their adult sizes are reached (3) the remodeling of bone (replacement of old bone by new bone tissue throughout life) (4) the repair of fractures (breaks in bones) throughout life. We will discuss the first three situations in this section

PROCESSES

Projections or outgrowths on bone that form joints or attachment points for connective tissue, such as ligaments and tendons Condyle (KON-dīl; condylus=knuckle)Large, round protuberance with a smooth articular surface at the end of a boneLateral condyle of the femur (Figure 8.11a)Facet (FAS-et or fa-SET)Smooth, flat, slightly concave or convex articular surfaceSuperior articular facet of a vertebra (Figure 7.16a)HeadUsually rounded articular projection supported on the neck (constricted portion) of a boneHead of the femur (Figure 8.11a)

canaliculi

Radiating in all directions from the lacunae are these small channels which are filled with extracellular fluid. -Inside canaliculi: slender fingerlike processes of osteocytes Neighboring osteocytes communicate via gap junctions The canaliculi connect lacunae with one another and with the central canals, forming an intricate, miniature system of interconnected canals throughout the bone. This system provides many routes for nutrients and oxygen to reach the osteocytes and for the removal of wastes.

concentric lamellae

Resembling the growth rings of a tree are circular plates of mineralized extracellular matrix of increasing diameter, surrounding a small network of blood vessels and nerves located in the central canal These tube-like units of bone generally form a series of parallel cylinders that, in long bones, tend to run parallel to the long axis of the bone.

Fossa (FOS-a=trench; plural is fossae, FOS-ē)

Shallow depression (fossa=trench)Coronoid fossa of the humerus *(a) anterior view (b) posterior view

DEPRESSIONS AND OPENINGS

Sites allowing the passage of soft tissue (nerves, blood vessels, ligaments, tendons) or formation of joints Fissure (FISH-ur)Narrow slit between adjacent parts of bones through which blood vessels or nerves passSuperior orbital fissure of the sphenoid bone (Figure 7.6f and 7.10b)Foramen (fō-RĀ-men=hole; plural is foramina)Opening through which blood vessels, nerves, or ligaments passOptic foramen (canal) of the sphenoid bone (Figure 7.6f and 7.10b)Fossa (FOS-a=trench; plural is fossae, FOS-ē)Shallow depression (fossa=trench)Coronoid fossa of the humerus (Figure 8.4a)Sulcus (SUL-kus=groove; plural is sulci, SUL-sī)Furrow along a bone surface that accommodates a blood vessel, nerve, or tendonIntertubercular sulcus (groove) of the humerus (Figure 8.4a)Meatus (mē-Ā-tus=passageway; plural is meati, me-Ā-tī)Tubelike openingExternal and internal auditory meati of the temporal bone (Figure 7.3c and 7.4a)

Formation of articular cartilage and the epiphyseal (growth) plate

The hyaline cartilage that covers the epiphyses becomes the articular cartilage. Prior to adulthood, hyaline cartilage remains between the diaphysis and epiphysis as the epiphyseal (growth) plate, the region responsible for the lengthwise growth of long bones that you will learn about next.

Functions of skeletal bones

Support. The skeleton serves as the structural framework for the body by supporting soft tissues and providing attachment points for the tendons of most skeletal muscles. 2.Protection. The skeleton protects the most important internal organs from injury. For example, cranial bones protect the brain, vertebrae (backbones) protect the spinal cord, and the rib cage protects the heart and lungs. 3.Assistance in movement. Most skeletal muscles attach to bones; when they contract, they pull on bone to produce movement. 4.Mineral storage and release. Bone tissue makes up about 18 percent of the weight of the human body and stores several minerals, especially calcium and phosphorus, which contribute to the strength of bone. Bone tissue stores about 99 percent of total body calcium. On demand, bone releases minerals into the blood to maintain critical mineral balances and to distribute the minerals to other parts of the body. 5.Blood cell production. Within certain bones, a connective tissue called red bone marrow produces red blood cells, white blood cells, and platelets in a process called hemopoiesis (hēm-ō-poy-Ē-sis; hemo-=blood; poiesis-=making) or hematopoiesis (hē-ma-tō-poy-Ē-sis). Red bone marrow consists of developing blood cells, adipocytes, fibroblasts, and macrophages within a network of reticular fibers. It is present in developing bones of the fetus and in some adult bones, such as the hip bones (pelvic bones), ribs, sternum (breastbone), vertebrae (backbones), skull, and ends of the humerus (arm bone) and femur (thigh bone). In a newborn, all bone marrow is red and is involved in hemopoiesis. With increasing age, much of the bone marrow changes from red to yellow. 6.Triglyceride storage. Yellow bone marrow consists mainly of adipose cells, which store triglycerides. The stored triglycerides are a potential chemical energy reserve..

Comminuted (KOM-i-noo-ted; com-=together; -minuted=crumbled)

The bone is splintered, crushed, or broken into pieces at the site of impact, and smaller bone fragments lie between the two main fragments.

skeletal system

The entire framework of bones and their cartilages constitute

epiphyseal line

The epiphyseal plate fades, leaving a bony structure. adolescence comes to an end (~ 18 in females and age 21 in males), the epiphyseal plates close; that is, the epiphyseal cartilage cells stop dividing and bone replaces all remaining cartilage.

calcium phosphate [Ca3(PO4)2]

The most abundant mineral salt It combines with another mineral salt, calcium hydroxide [Ca(OH)2], to form crystals of hydroxyapatite [Ca10(PO4)6(OH)2]

Tendons

Various bumps, ridges, or rough areas indicate where soft tissues typically attach skeletal muscle to bone; ligaments typically attach one bone to another bone.)

The epiphyseal (growth) plate

a layer of hyaline cartilage in the metaphysis of a growing bone. The epiphyseal plate appears as a dark band between whiter calcified areas in the radiograph (x-ray) shown in part (a).

Paget's disease

an excessive proliferation of osteoclasts so that bone resorption occurs faster than bone deposition. In response, osteoblasts attempt to compensate, but the new bone is weaker because it has a higher proportion of spongy to compact bone, mineralization is decreased, and the newly synthesized extracellular matrix contains abnormal proteins. The newly formed bone, especially that of the pelvis, limbs, lower vertebrae, and skull, becomes enlarged, hard, and brittle and fractures easily.

Osteons in compact bone tissue

are aligned in the same direction and are parallel to the length of the diaphysis. As a result, the shaft of a long bone resists bending or fracturing even when considerable force is applied from either end tends to be thickest in those parts of a bone where stresses are applied in relatively few directions. The lines of stress in a bone are not static. They change as a person learns to walk and in response to repeated strenuous physical activity, such as weight training. The lines of stress in a bone also can change because of fractures or physical deformity. Thus, the organization of osteons is not static but changes over time in response to the physical demands placed on the skeleton.

The ends of long bones

are supplied by the metaphyseal and epiphyseal arteries, which arise from arteries that supply the associated joint.

Sesamoid bones in lower limbs

are two constant sesamoid bones in addition to the patellae; these occur on the plantar surface of each foot in the tendons of the flexor hallucis brevis muscle at the metatarsophalangeal joint of the great (big) toe (see Figure 8.12b).

Rickets and osteomalacia (os-tē-ō-ma-LĀ-shē-a; malacia=softness)

are two forms of the same disease that result from inadequate calcification of the extracellular bone matrix, usually caused by a vitamin D deficiency.

cartilage model continues to grow

chondrocytes in its midregion hypertrophy (increase in size), and the surrounding cartilage extracellular matrix begins to calcify. Other chondrocytes within the calcifying cartilage die because nutrients can no longer diffuse quickly enough through the extracellular matrix. As these chondrocytes die, the spaces left behind by the dead chondrocytes merge into small cavities called lacunae.

Like other connective tissues, bone, or osseous tissue

contains an abundant extracellular matrix that surrounds widely separated cells.

Bone hardening

depends on the crystallized inorganic mineral salts, a bone's flexibility depends on its collagen fibers. Like reinforcing metal rods in concrete, collagen fibers and other organic molecules provide tensile strength, resistance to being stretched or torn apart.

Sesamoid bone

develop in certain tendons where there is considerable friction, compression, and physical stress. They are not always completely ossified and measure only a few millimeters to centimeters in diameter except for the two patellae (kneecaps), the largest of the sesamoid bones. Sesamoid bones vary in number from person to person except for the patellae, which are located in the quadriceps femoris tendon (see Figure 11.24a, b) and are normally present in all individuals. Functionally, sesamoid bones protect tendons from excessive wear and tear, and they can alter the direction of pull of a tendon, which improves the mechanical advantage at a joint.

spongy bone tissue (trabecular or cancellous bone tissue)

does not contain osteons (Figure 6.4b, c) always located in the interior of a bone, protected by a covering of compact bone. It consists of lamellae that are arranged in an irregular pattern of thin columns called trabeculae (tra-BEK-ū-lē=little beams; singular is trabecula). Between the trabeculae are spaces that are visible to the unaided eye. These macroscopic spaces are filled with red bone marrow in bones that produce blood cells, and yellow bone marrow (adipose tissue) in other bones. Both types of bone marrow contain numerous small blood vessels that provide nourishment to the osteocytes. Each trabecula consists of concentric lamellae, osteocytes that lie in lacunae, and canaliculi that radiate outward from the lacunae.

2nd type of ossification bone forms within hyaline cartilage that develops from mesenchyme. The remaining bones form by endochondral ossification, which will be described later in this section. Also, the "soft spots" that help the fetal skull pass through the birth canal later harden as they undergo intramembranous ossification, which occurs as follows

endochondral ossification

Smooth surfaces

indicate areas of movement between neighboring bones. In general, a smooth-surfaced depression on one bone accommodates a smooth-surfaced projection from another bone to form the joint surfaces so that bones can fit together. In response to tension on a bone surface where tendons, ligaments, aponeuroses, and fasciae pull on the periosteum of bone, new bone is deposited, resulting in raised or roughened areas.

Flat bones

generally thin and composed of two nearly parallel plates of compact bone enclosing a layer of spongy bone. The layers of compact bone are called external and internal tables. In cranial bones, the spongy bone is referred to as diploë (DIP-lō-ē) (see Figure 6.6). Flat bones afford considerable protection and provide extensive areas for muscle attachment. They include the cranial (skull) bones, which protect the brain; the sternum (breastbone) and ribs, which protect organs in the thorax; and the scapulae (shoulder blades).

Closure of the epiphyseal plate

gradual process and the degree to which it occurs is useful in determining bone age, to predict adult height, and to establish age at death from skeletal remains, especially in infants, children, and adolescents. For example, an open epiphyseal plate indicates a younger person, while a partially closed epiphyseal plate or a completely closed one indicates an older person. It should also be kept in mind that closure of the epiphyseal plate, on average, takes place 1-2 years earlier in females.

Long bones

greater length than width and consist of a diaphysis (shaft) and a variable number of epiphyses or extremities (ends) Slightly curved for strength A curved bone absorbs the stress of the body's weight at several different points so that it is evenly distributed. If such bones were straight, the weight of the body would be unevenly distributed and the bone would fracture easily. Long bones consist mostly of compact bone tissue, which is dense and has smaller spaces, but they also contain considerable amounts of spongy bone tissue, which has larger spaces (see Figure 6.4). Long bones include the humerus (arm bone), ulna and radius (forearm bones), femur (thigh bone), tibia and fibula (leg bones), metacarpals (hand bones), metatarsals (foot bones), and phalanges (finger and toe bones).

long bones of the limbs 6.2

growth in length does not occur equally at both ends of the bones; one end is always the dominant growing end. The dominant growing end is always directed away from the orientation angle of the nutrient foramen in the diaphysis. Therefore, the ends of the femur, tibia, and fibula toward the knee are the dominant growing epiphyseal plates and the ends of the humerus, ulna, and radius at the ends opposite the elbow are the dominant growing epiphyseal plates

Irregular bone

have complex shapes and cannot be grouped into any of the three categories just described. They also vary in the amounts of spongy and compact bone they contain. Such bones include the vertebrae (backbones), certain facial bones, and the calcaneus (heel bone).

calcification

initiated by bone-building cells called osteoblasts, and will be described shortly. Mineral salts begin to crystallize in the microscopic spaces between collagen fibers. After the spaces are filled, mineral crystals accumulate around the collagen fibers. The combination of crystallized salts and collagen fibers is responsible for the characteristics of bone.

The areas between neighboring osteons contain lamellae, which also have lacunae with osteocytes and canaliculi. are fragments of older osteons that have been partially destroyed during bone rebuilding or growth.

interstitial lamellae

1st and simplest type of ossification bone forms directly within condensed mesenchyme, which is arranged in sheetlike layers that resemble membranes. Formation of: flat bones of the skull, most of the facial bones, mandible (lower jawbone), and the medial part of the clavicle (collar bone)

intramembranous ossification

Rickets

is a disease of children in which the growing bones become "soft" or rubbery and are easily deformed. Because new bone formed at the epiphyseal (growth) plates fails to ossify, bowed legs and deformities of the skull, rib cage, and pelvis are common.

The epiphyseal (growth) plate 6.8b

is a layer of hyaline cartilage in the metaphysis of a growing bone that consists of four zones: 1. Resting cartilage: nearest the epiphysis and consists of small, scattered chondrocytes. The term resting is used because the cells do not function in bone growth. Rather, they anchor the epiphyseal plate to the epiphysis of the bone. 2. Proliferating cartilage: Slightly larger chondrocytes (only in this zone will divide and replace those dead @ diaphyseal side of the epiphyseal plate) arranged like stacks of coins undergo interstitial growth as they divide and secrete extracellular matrix. 3. Hypertrophic cartilage: consists of large, maturing chondrocytes arranged in columns. 4. Calcified cartilage: The final zone of the epiphyseal plate is only a few cells thick and consists mostly of chondrocytes that are dead because the extracellular matrix around them has calcified. Osteoclasts dissolve the calcified cartilage, and osteoblasts and capillaries from the diaphysis invade the area. The osteoblasts lay down bone extracellular matrix, replacing the calcified cartilage by the process of endochondral ossification. As a result, the zone of calcified cartilage becomes "new diaphysis" that is firmly cemented to the rest of the diaphysis of the bone.

Osteomalacia

is the adult counterpart of rickets, sometimes called adult rickets. New bone formed during remodeling fails to calcify, and the person experiences varying degrees of pain and tenderness in bones, especially the hips and legs. Bone fractures also result from minor trauma. Prevention of and treatment for rickets and osteomalacia consists of the administration of adequate vitamin D and exposure to moderate amounts of sunlight. •

Sponge in respect to compact

light, which reduces the overall weight of a bone. This reduction in weight allows the bone to move more readily when pulled by a skeletal muscle. Second, the trabeculae of spongy bone tissue support and protect the red bone marrow.

Spongy bone examples

makes up most of the interior bone tissue of short, flat, sesamoid, and irregularly shaped bones. In long bones it forms the core of the epiphyses beneath the paper-thin layer of compact bone, and forms a variable narrow rim bordering the medullary cavity of the diaphysis. Spongy bone is always covered by a layer of compact bone for protection.

A scanning device (gamma camera)

measures the radiation emitted from the bones, and the information is translated into a photograph that can be read like an x-ray on a monitor. Normal bone tissue is identified by a consistent gray color throughout because of its uniform uptake of the radioactive tracer.

Bone remodeling

ongoing replacement of old bone tissues by new bone tissue.

Compact bone tissue is composed of repeating structural units

osteons, or haversian systems

osteoporosis

primarily affects middle-aged and elderly people, 80 percent of them women. (1) Women's bones are less massive than men's bones, and (2) production of estrogens in women declines dramatically at menopause, whereas production of the main androgen, testosterone, in older men wanes gradually and only slightly. Estrogens and testosterone stimulate osteoblast activity and synthesis of bone matrix. Besides gender, risk factors for developing osteoporosis include a family history of the disease, European or Asian ancestry, thin or small body build, an inactive lifestyle, cigarette smoking, a diet low in calcium and vitamin D, more than two alcoholic drinks a day, and the use of certain medications.

a bone fracture damages the epiphyseal plate

the fractured bone may be shorter than normal once adult stature is reached. because damage to cartilage, which is avascular, accelerates closure of the epiphyseal plate due to the cessation of cartilage cell division, thus inhibiting lengthwise growth of the bone.

Periosteal arteries

small arteries accompanied by nerves, enter the diaphysis through numerous interosteonic canals and supply the periosteum and outer part of the compact bone

Short bone

somewhat cube-shaped and nearly equal in length, width, and depth. They consist of spongy bone except at the surface, where there is a thin layer of compact bone. Examples of short bones are most carpal (wrist) bones and most tarsal (ankle) bones.

surface markings or osseous landmarks

structural features adapted for specific functions. Most are not present at birth but develop later in response to certain forces; they are most prominent during adult life

Compact bone (cortical or dense bone)

surface of a bone, but it also can extend deeper into the bone tissue. It makes up the bulk of the diaphyses of long bones under a microscope: -compact bone is quite porous, with an abundance of microscopic spaces and canals provides protection and support and resists the stresses produced by weight and movement.

Bone deposition

the addition of minerals and collagen fibers to bone by osteoblasts.

spurs

too much mineral material is deposited in the bone, the surplus may form thick bumps, on the bone that interfere with movement at joints Leads: 1. osteoporosis: Excessive loss of calcium or tissue weakens the bones, and they may break 2. rickets and osteomalacia Becomes too flexible.

Sesamoid bones in upper limbs

usually occur only in the joints of the palmar surface of the hands. Two frequently encountered sesamoid bones are in the tendons of the adductor pollicis and flexor pollicis brevis muscles at the metacarpophalangeal joint of the thumb (see Figure 8.6a)