Anatomy Chapter 6: Bone Tissue

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; and (3) many small periosteal veins accompany their respective arteries and exit through the periosteum. 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.

Growth of the cartilage model (Endochondral Ossification)

.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, meaning growth of the outer surface

Development of the primary ossification center (Endochondral Ossification)

.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.

summary function of bone tissue

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.

How many bones are there in an adult skeleton?

206

Why does osteoporosis affect more women than men?

80 percent of them women. Older women suffer from osteoporosis more often than men for two reasons: (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.

Foramen (depressions and openings)

Opening through which blood vessels, nerves, or ligaments pass example: Optic foramen (canal) of the sphenoid bone

circumferential lamellae

Arranged around the entire outer and inner circumference of the shaft of a long bone. They develop during initial bone formation.

Formation of trabeculae (Intramembranous Ossification)

As the bone extracellular matrix forms, it develops into trabeculae that fuse with one another to form spongy bone around the network of blood ve

Development of the medullary (marrow) cavity (Endochondral Ossification)

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 (Endochondral Ossification)

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 develops around the cartilage model.

Development of the ossification center (Intramembranous Ossification)

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.

lacunae

Between the concentric lamellae are small spaces called lacunae - which contain osteocytes

transverse interosteonic (volkmann or perforating) canals

Blood vessels and nerves from the periosteum penetrate the compact bone through: The vessels and nerves of the interosteonic canals connect with those of the medullary cavity, periosteum, and central canals.

ossification or osteogenesis

Bone formation occurs in four principal situations: (1) the initial formation of bones in an embryo and fetus, (2) the 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), and (4) the repair of fractures (breaks in bones) throughout life.

Mineral storage and release (bone function)

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.

Suclus (depressions and openings)

Furrow along a bone surface that accommodates a blood vessel, nerve, or tendon Example: intertubercular sulcus (groove) of the humerus

Development of the periosteum (Intramembranous Ossification)

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.

Condyle (processes that form joints)

Large, round protuberance with a smooth articular surface at the end of a bone example: Lateral condyle of the femur

Line (Processes formed where tendons or ligaments attach)

Long, narrow ridge or border (less prominent than a crest) example: Linea aspera of the femur

Assistance in movement (bone function)

Most skeletal muscles attach to bones; when they contract, they pull on bone to produce movement.

fissure (depressions and openings)

Narrow slit between adjacent parts of bones through which blood vessels or nerves pass example: Superior orbital fissure of the sphenoid bone

nutrient artery

Near the center of the diaphysis, a large nutrient artery enters the compact bone at an oblique angle through a hole called the nutrient foramen

Calcification (Intramembranous Ossification)

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).

Crest (Processes formed where tendons or ligaments attach)

Prominent ridge or elongated projection example Iliac crest of the hip bone

canaliculi

Radiating in all directions from the lacunae are canaliculi which are filled with extracellular fluid. Inside the canaliculi are slender fingerlike processes of osteocytes

fossa (depressions and openings)

Shallow depression (fossa=trench) example: Coronoid fossa of the humerus

spinous process

Sharp, slender projectionSpinous process of a vertebra

Zone of proliferating cartilage

Slightly larger chondrocytes arranged like stacks of coins undergo interstitial growth as they divide and secrete extracellular matrix. The chondrocytes in this zone divide to replace those that die at the diaphyseal side of the epiphyseal plate.

Facet (processes that form joints)

Smooth, flat, slightly concave or convex articular surface example: Superior articular facet of a vertebra

Trochanter (Processes formed where tendons or ligaments attach)

Very large projectionGreater trochanter of the femur

skeletal system

The entire framework of bones and their cartilages constitute the:

Zone of 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.

Formation of articular cartilage and the epiphyseal (growth) plate (Endochondral Ossification)

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

Protection (bone function)

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.

Support (bone function)

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.

Osteology

The study of bone structure and the treatment of bone disorders

surface markings or osseous landmarks

The surface of a bone is marked by a variety of bumps, grooves, indentations, projections, and holes. These characteristic features of bones

Zone of hypertrophic cartilage

This layer consists of large, maturing chondrocytes arranged in columns.

Zone of resting cartilage

This layer is 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.

meatus (depressions and openings)

Tubelike opening example: External and internal auditory meati of the temporal bone

Epicondyle (Processes to which tendons, ligaments and other connective tissues attach)

Typically roughened projection above a condyle example: Medial epicondyle of the femur

head (processes that

Usually rounded articular projection supported on the neck (constricted portion) of a bone example: Head of the femur

Tuberosity (Processes formed where tendons or ligaments attach)

Variable sized projection that has a rough, bumpy surface example: Ischial tuberosity of the hip bone

Tubercle (Processes formed where tendons or ligaments attach)

Variable sized rounded projection example: Greater tubercle of the humerus

epiphyseal line

When adolescence comes to an end (at about age 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. The epiphyseal plate fades, leaving a bony structure called the epiphyseal line.

Development of the secondary ossification centers (Endochondral Ossification)

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.

Blood cell production (bone function)

Within certain bones, a connective tissue called red bone marrow produces red blood cells, white blood cells, and platelets in a process called hemopoiesis or hematopoiesis. 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.

Triglyceride storage (bone function)

Yellow bone marrow consists mainly of adipose cells, which store triglycerides. The stored triglycerides are a potential chemical energy reserve.

epiphyseal (growth) plate

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.

Compact bone

also referred to as cortical or dense bone, is the type of bone tissue observed at the 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. It provides protection and support and resists the stresses produced by weight and movement.

spongey bone tissue

also referred to as trabecular or cancellous bone tissue, does not contain osteons. Spongy bone tissue is 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

Osteoblasts

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.)

concentric lamellae

are circular plates of mineralized extracellular matrix of increasing diameter, surrounding a small network of blood vessels and nerves located in the central canal 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.

flat bones

are 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. 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).

sutural bones or wormian bones are

are small bones located within the sutures (joints) of certain cranial bones. The number of sutural bones varies greatly from person to person.

short bones

are 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.

metaphyses

are the regions between the diaphysis and the epiphyses. In a growing bone, each metaphysis contains an epiphyseal (growth) plate

Osteoprogenitor cells

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.

interstitial lamellae

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

Bone growth in thickness

bone can grow in thickness (diameter) only by appositional growth

Bone and blood

bone is richly supplied with blood

During infancy, childhood, and adolescence, growth

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

bone, or osseous tissue

contains an abundant extracellular matrix that surrounds widely separated cells. The extracellular matrix is about 15 percent water, 30 percent collagen fibers, and 55 percent crystallized mineral salts

Sesamoid bones

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 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.

Rickets

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

epiphyseal arteries

enter the epiphyses of a long bone and supply the red bone marrow and bone tissue of the epiphyses.

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

intramembranous ossification

first type of ossification: bone forms directly within condensed mesenchyme, which is arranged in sheetlike layers that resemble membranes

Irregular bones

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).

long bones

have greater length than width and consist of a diaphysis (shaft) and a variable number of epiphyses or extremities (ends). They are 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).

Osteoclasts

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.) osteoclasts help regulate blood calcium level in response to certain hormones. They are also the target cells for drug therapy used to treat osteoporosis.

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. The degree of uptake of the tracer is related to the amount of blood flow to the bone.

medullary cavity 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.

epiphyseal (growth) plate

is a layer of hyaline cartilage in the metaphysis of a growing bone that consists of four zones

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.

endosteum

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.

periosteum

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,

bone

is an organ made up of several different tissues working together: bone (osseous) tissue, cartilage, dense connective tissue, epithelium, adipose tissue, and nervous tissue

embryonic "skeleton"

is at first composed of mesenchyme in the general shape of bones. These become the sites where subsequent cartilage formation and then ossification occurs. (Recall that mesenchyme is a connective tissue found mostly in an embryo and is the tissue from which most other connective tissues develop.) This begins during the sixth week of embryonic development and follows one of two patterns.

diaphysis

is the bone's shaft, or body—the long, cylindrical, main portion of the bone.

orthodontics

is the branch of dentistry concerned with the prevention and 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.

bone remodeling

is the ongoing replacement of old bone tissue by new bone tissue

Intramembranous ossification

is the simpler of the two methods of bone formation. The flat bones of the skull, most of the facial bones, mandible (lower jawbone), and the medial part of the clavicle (collar bone) are formed in this way.

Osteoporosis

literally a condition of porous bones, affects 10 million people a year in the United States. In addition, 18 million people have low bone mass (osteopenia), which puts them at risk for osteoporosis. The basic problem is that bone resorption (breakdown) outpaces bone deposition (formation). In large part this is due to depletion of calcium from the body—more calcium is lost in urine, feces, and sweat than is absorbed from the diet. Bone mass becomes so depleted that bones fracture, often spontaneously,

Osteocytes

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.)

epiphyses

or extremities are the proximal and distal ends of the bone

hint

osteoBlasts Build bone, while osteoClasts Carve out bone.

endochondral ossification

second type of ossification, bone forms within hyaline cartilage that develops from mesenchyme.

antireabsorptive drugs (osteoporosis treatment)

slow down the progression of bone loss,

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

processes, projections or outgrowths (surface markings)

that either (a) help form joints or (b) serve as attachment points for connective tissue (such as ligaments and tendons).

endochondral ossification

the "soft spots" that help the fetal skull pass through the birth canal later harden as they undergo intramembranous ossification,

bone deposition

the addition of minerals and collagen fibers to bone by osteoblasts. results in its formation.

osteomalacia

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

Remodeling

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

bone resorption

the removal of minerals and collagen fibers from bone by osteoclasts, results in the breakdown of bone extracellular matrix,

Paget's disease

there is 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.

perforating (Sharpey's) fibers

thick bundles of collagen that extend from the periosteum into the bone extracellular matrix.

depressions and openings (surface markings)

which form joints or allow the passage of soft tissues (such as blood vessels and nerves)