Chapter Seven: Bone Tissue

hydroxyapatite

- 85% of the inorganic matter in the matrix of osseous tissue - a crystallized calcium phosphate salt [Ca10(PO4)6(OH)2]; 10% calcium carbonate (CaCO3); and lesser amounts of magnesium, sodium, potassium, fluoride, sulfate, carbonate, and hydroxide ions - the calcium-phosphate salt that mineralizes bone tissue

articular cartilage

A thin layer of hyaline cartilage covering the articular surface of a bone at a synovial joint, serving to reduce friction and ease joint movement. - covers ends of bones within a joint

endosteum

A thin layer of reticular connective tissue that lines the internal marrow cavity, covers all the honeycombed surfaces of spongy bone, and lines the canal system - lines internal surfaces of bones

Osteoblasts

Bone-forming cell that arises from an osteogenic cell, deposits bone matrix, and eventually becomes an osteocyte. - produce organic bone matrix - deposits osteoid tissue - make new bone - located in the osteogenic layer of the periosteum - bone building cells - involved with bone deposition - calcitonin causes these cells to become more active - parathyroid hormone inhibits these cells from synthesizing collagen - thee cells should become more active when blood calcium levels are high - ove activity of these cells could contribute to hypocalcemia

solubility product

Hydroxyapatite crystals form only when the product of calcium and phosphate concentration in the tissue fluids, represented [Ca2+] • [PO43−], reaches a critical value called the solubility product.

Osteoclasts

Macrophage of the bone surface that dissolves the matrix and returns minerals to the extracellular fluid. - The side of the osteoclast facing the bone surface has a ruffled border with many deep infoldings of the plasma membrane. These increase the cell surface area and thus enhance the efficiency of bone resorption. - located in resorption bays - as spongy bone is produced by intramembrous ossification, osteoclasts reabsorb and remodel the forming bone - cell type that is resposible or most of the reabsorbing of minerals from bone matrix - bone resorbing cells - parathyroid hormone causes these cells to become more active - massive, multinucleate cells

Zone of reserve cartilage

This region, farthest from the marrow cavity, consists of typical hyaline cartilage that as yet shows no sign of transforming into bone. - zone of the metaphysis that is located the farthest from the marrow space - elongation of bones through endochondral ossification requires the zone of reserve cartilage when normal hyaline cartilage persists in the metaphysis

Osteoclast inhibition

Within 15 minutes after it is secreted, calcitonin reduces osteoclast activity by as much as 70%, so osteoclasts liberate less calcium from the skeleton.

Osteoblast stimulation

Within an hour, calcitonin increases the number and activity of osteoblasts, which deposit calcium into the skeleton.

Zone of bone deposition

Within each column, the walls between the lacunae break down and the chondrocytes die. This converts each column into a longitudinal channel (white spaces in the figure), which is immediately invaded by blood vessels and marrow from the marrow cavity. Osteoblasts line up along the walls of these channels and begin depositing concentric lamellae of matrix, while osteoclasts dissolve the temporarily calcified cartilage - the are where the chondrocytes die and are replaced by blood vessels and osteoblasts, which then for the final trabeculae and osteoclasts that refine the distal contours of the medullary chamber

ectopic ossification

abnormal calcification of tissues - formation of osseous tissues in areas outside of bone

irregular bones

bones that do not fit into the short and long bone categories are considered irregular bones—the vertebrae and the sphenoid and ethmoid bones of the skull, for example.

skeletal system

composed of bones, cartilages, and ligaments joined tightly to form a strong, flexible framework for the body The skeleton plays at least six roles: Support. Bones of the lower limbs, pelvis, and vertebral column hold up the body; nearly all bones provide support for the muscles; the mandible and maxilla support the teeth. Protection. Bones enclose and protect the brain, spinal cord, heart, lungs, pelvic viscera, and bone marrow. Movement. Limb movements, breathing, and other movements are produced by the action of muscles on the bones. Electrolyte balance. The skeleton stores calcium and phosphate ions and releases them into the tissue fluid and blood according to the body's physiological needs. Acid-base balance. Bone tissue buffers the blood against excessive pH changes by absorbing or releasing alkaline phosphate and carbonate salts. Blood formation. Red bone marrow is the major producer of blood cells, including cells of the immune system.

osseous (bone) tissue

connective tissue in which the matrix is hardened by the deposition of calcium phosphate and other minerals

osteitis deformans (Paget disease)

developmental abnormalities/ disorder

Open reduction

involves the surgical exposure of the bone and the use of plates, screws, or pins to realign the fragments

compact (dense or lamellar) bone

outer shell of dense white osseous tissue in the long bone. - made up of parallel osteons that are tightly packed and covers the SURFACE of most bones ad forms most of the diaphysis - made up of osteons - also called coritcal bone - found in greater proportion in the bone diaphyses - visible, obvious central canals - found lining the superficial regions of all bones

resorption bays (Howship lacunae)

pits that contain ostepclasts

tendons

structurally similar to ligaments but attach muscle to bone

nondisplaced fracture

the bone pieces remain in proper anatomical alignment

perichondrium

the dense connective tissue (hyaline cartilage) found covering and surrounding the surface of the cartilage model

appositional growth

the deposition of new tissue at the surface - occurs within a mature bone and results in the bone becoming thicker

cartilage

the forerunner of most bones in embryonic and childhood development, covers many joint surfaces in the mature skeleton

calcification (mineralization)

the hardening of a tissue due to the deposition of calcium salts.

hemopoiesis

the process of blood cell formation that occurs in the bone marow

metaphysis

the region of transition from cartilage to bone at each end of the primary marrow cavity - The transitional zone, facing the marrow cavity

vitamin D synthesis and its effects

(1) sunlight contacting the epidermis converts 7-dehydrocholesterol to vitamin D3, otherwise known as cholecalciferol. (2) transported via the blood to the liver, cholecalciferol is converted to calcidiol (3) calcidiol returns to the blood oe again where transport to the kidneys then allows the final conversion to calcitrol. (4) now in th most active form, clcitrol acts to increase blood calcium by acting on three target organs: 1) small intestines 2) skeleton, and 3) kidneys

osteon (haversian system)

- A central canal and its lamellae - the basic structural unit of compact bone - a cylinder of tissue surrounding a central canal

Osteogenic (osteoprogenitor) cells

- stem cells that develop from embryonic mesenchymal cells and then give rise to most other bone cell types (osteoblasts) - found in the endosteum, the inner layer of the periosteum, and in the central canals - they multiply continually, and some go on to become the osteoblasts - stem cells - cacitrol causes these cells to differentiate into osteoblasts

fracture hematoma

A bone fracture severs blood vessels of the bone and periosteum, causing bleeding and the formation of a blood clot

long bones

A bone such as the femur or humerus that is markedly longer than wide and that generally serves as a lever.

calculus

A calcified mass in an otherwise soft organ such as the lungs is called a calculus.

periosteum

A layer of fibrous connective tissue covering the surface of a bone.

granulation tissue

All of this capillary and cellular invasion converts the blood clot to a soft fibrous mass called granulation tissue.

nutrient foramina

Blood vessels penetrate into the bone through minute holes

interstitial growth

Cartilage growth from within, by the multiplication of chondrocytes and deposition of new matrix in the interior, is called interstitial growth.

circumferential lamellae

The inner and outer boundaries of dense bone are arranged in circumferential lamellae that run parallel to the bone surface. - the surface layers of bone

secondary marrow cavity

The secondary ossification center becomes hollowed out by the same process as the diaphysis, generating a secondary marrow cavity in the epiphysis. This cavity expands outward from the center, in all directions.

diaphysis

The shaft of a long bone. - provides leverage - the primary ossification center during endochondral ossification in a long bone

pituitary dwarfism

a deficiency of growth hormone stunts the growth of all of the bones, and a person has short stature but normal proportions throughout the skeletal system

hyaline cartilage

a form of cartilage with a relatively clear matrix and fine collage fibers but no conspicuous elastic fibers or coarse collagen bones - locate at articular catilage

Calcitriol

a form of vitamin D produced by the sequential action of the skin, liver, and kidneys - Although calcitriol promotes bone resorption, it is also necessary for bone deposition. Without it, calcium and phosphate levels in the blood are too low for normal deposition. The result is a softness of the bones called rickets in children and osteomalacia34 in adults.

Bone marrow

a general term for soft tissue that occupies the marrow cavity of a long bone, the spaces amid the trabeculae of spongy bone, and the larger central canals. There are two kinds of marrow—red and yellow

closed reduction

a procedure in which the bone fragments are manipulated into their normal positions without surgery

Calcium homeostasis

depends on a balance between dietary intake, urinary and fecal losses, and exchanges with the osseous tissue. It is regulated by three hormones: calcitriol, calcitonin, and parathyroid hormone.

osteogenesis imperfecta (brittle bone disease)

developmental abnormalities/ disorder

osteoporosis

developmental abnormalities/ disorder

epiphyseal line

used twice (64) -marks where the epiphyseal plate used to be - the junctional region where they meet is filled with spongy bone, and the site of the original epiphyseal plate is marked with a line of slightly denser spongy bone called the epiphyseal line - Often a delicate ridge on the bone surface marks the location of this line.

chodrocyte

- former chondroblast - has become enclosed in a lucana in the cartilage matrix

increases blood calcium

- osteoclastic activity - calcitrol - parathyrod hormone - increased calcium absorption by the digestive system - inhibition of ostoblasts - increased calcium reabsorption from the kidneys - increased bone resorption - increased urinary excretion of phosphate

Trousseau sign

- sign of hypocalcemia is strong spasmodic flexion of the wrist and thumb and extension of the other fingers - often induced by the inflation of a blood pressure cuff putting pressure on the brachial nerve

tetany

- the inability of the muscle to relax - begins to occur as the plasma Ca2+ concentration falls to 6 mg/dL.

epiphysis

1. The head of a long bone. 2. The pineal gland (epiphysis cerebri). - enlarged to strengthen the joint and provide added surface area for the attachment of tendons and ligaments

short bones

The wrists and ankles have a total of 30 short bones (carpal and tarsal bones), which are approximately equal in length and width and which produce relatively limited gliding movements. The patella is also a short bone. - have the same length and width

C cells (clear cells)

clear cells of the thyroid gland

hypercalcemia

- a blood calcium excess - excessive amounts of calcium bind to the cell surface, increasing the charge difference across the membrane and making sodium channels less responsive

composite

- a combination of two basic structural materials, in this case a ceramic and a polymer - a composite can combine the optimal mechanical properties of each component.

Achondroplastic dwarfism

- a condition in which the long bones of the limbs stop growing in childhood, while the growth of other bones is unaffected. - a person has a short stature but a normal-size head and trunk

laryngospasm

- at 4 mg/dL, muscles of the larynx contract tightly, a condition - can shut off airflow and cause suffocation

organic bone matrix

- collagen - proteoglycans - glycosaminoglycans - glycoproteins - provides flexibility - resists tensile (pulling) forces

central (haversian or osteonic) canal

- connect concentric lamellae to canaliculi - extends trough the center of an osteon - at the center of osteons for blood vessels, nerves and lymphatic vessels

acid phosphatase

- enzyme secreted by an osteoclast - digests the collagen of the bone matrix - enzyme is named for its ability to function in a highly acidic environment

trabeculae (thin plates)

- found in spongy bone - form lattice with spicule - structure of spongy none that line up along the bone's lines of stress

spicules (rods or spines)

- found in spongy bone - form lattice with trabeculae - slivers of bone

inorganic bone matrix

- hydroxyapatite - calcium carbonate - fluoride - CaCO3 - clcium phosphate - magnesium - sulfate - Ca10(PO4)6(OH)12 - provides hardness - resists compressive forces (pushing)

red bone marrow (myeloid tissue)

- in a child, the marrow cavity of nearly every bone is filled with this tissue - composed of multiple tissues in a delicate but intricate arrangement, and is properly considered an organ unto itself - limited to the skull, vertebrae, ribs, sternum, part of the pelvic (hip) girdle, and the proximal heads of the humerus and femur

yellow bone marrow

- in adults, most of the red marrow turns to FATTY yellow bone marrow - no longer produces blood, although in the event of severe or chronic anemia, it can transform back into red marrow

decreases blood calcium

- osteoblastic activity - increased used of sunblock - living at a northern latitude - calcitonin

Parathyroid hormone (PTH)

- secreted by the parathyroid glands, which adhere to the posterior surface of the thyroid gland - released when blood calcium is low. A mere 1% drop in the blood calcium level doubles the secretion of PTH. - the hormone that reduces kidney excretion of calcium - when levels of blood calcium decrease the hormone is released from the four nodular parathyroid glands located on the posterior thyroid - causes an increase in the number of osteoclasts and greater rates of bone resorption - at the level of the kidney, parathyroid hormone will decrease the amount of calcium excreted by increasing reabsorption from the kidney tubules. - inhibition of osteoblasts by parathyroid hormone occurs as a result of a decreases production of organic matrix - as a result of direct actions on the target cells of the bone and kidneys along with an indirect action on the small intestine (calcitriol), parathyroid hormone works to increase blood calcium levels

Mineral resorption

- the process of dissolving bone - releases minerals into the blood and makes them available for other uses

lacunae

- tiny cavities that tore osteocytes - interconnected by slender channels called canaliculi

secretion of calcitonin

- when levels of blood calcium increase in children, calcitonin is released from the c cells of the thyroid gland - this circluating calcitonin inhibits osteoclasts and stimulate osteoblasts within minutes - the effects on osteoclasts cause a decrease in bone reabsorption and a concurrent increase in bone deposition due to the activity of osteoblasts. - the decline in bone breakdown and increased minearlization causes blood calcium to decrease back to normal levels

Healing of Fractures

1. Formation of hematoma and granulation tissue. A bone fracture severs blood vessels of the bone and periosteum, causing bleeding and the formation of a blood clot (fracture hematoma). Blood capillaries soon grow into the clot, while fibroblasts, macrophages, osteoclasts, and osteogenic cells invade the tissue from both the periosteal and medullary sides of the fracture. Osteogenic cells become very abundant within 48 hours of the injury. All of this capillary and cellular invasion converts the blood clot to a soft fibrous mass called granulation tissue. 2. Formation of a soft callus.36 Fibroblasts deposit collagen in the granulation tissue, while some osteogenic cells become chondroblasts and produce patches of fibrocartilage called the soft callus. 3. Conversion to hard callus. Other osteogenic cells differentiate into osteoblasts, which produce a bony collar called the hard callus around the fracture. The hard callus is cemented to dead bone around the injury site and acts as a temporary splint to join the broken ends or bone fragments together. It takes about 4 to 6 weeks for a hard callus to form. During this period, it is important that a broken bone be immobilized by traction or a cast to prevent reinjury. 4. Remodeling. The hard callus persists for 3 to 4 months. Meanwhile, osteoclasts dissolve small fragments of broken bone, and osteoblasts deposit spongy bone to bridge the gap between the broken ends. This spongy bone gradually fills in to become compact bone, in a manner similar to intramembranous ossification. Usually the fracture leaves a slight thickening of the bone visible by X-ray, but in some cases, healing is so complete that no trace of the fracture can be found.

hypocalcemia

A deficiency of calcium ions in the blood. - characterized by excessive excitability of the nervous system and muscular systems, due to abnormal blood calcium levels

osteoporosis

A degenerative bone disease characterized by a loss of bone mass, increasing susceptibility to spontaneous fractures, and sometimes deformity of the vertebral column; causes include aging, estrogen hyposecretion, and insufficient resistance exercise.

Zone of cell proliferation

A little closer to the marrow cavity, chondrocytes multiply and arrange themselves into longitudinal columns of flattened lacunae. - nearer to the medullary cavity, the zone of cell proliferation is marked by an expansive production of chondrocytes that align in rows in order to replenish those undergoing calcification

Osteocyte

A mature bone cell formed when an osteoblast becomes surrounded by its own matrix and entrapped in a lacuna. -bone cells encased in matrix

primary marrow cavity

As the center of the model is hollowed out and filled with blood and stem cells, it becomes the primary marrow cavity.

spongy (cancellous) bone

At the ends of the bone, the central space is occupied by a more loosely organized form of osseous tissue called spongy (cancellous) bone - found DEEP to compact bone (interior of flat bones and epipheses) - mainly consists of trabeculae - spicules are common - arranged along the lines of forces that are encountered - found in greater proportions in flat bones - gaps between ossified material are filled with arrow - convey strength with light weight - displays a higher rate of bone turnover - found in greater proportions in bone epiphysis

interstitial lamellae

Between osteons, we can find irregular regions called interstitial lamellae, the remains of old osteons that broke down as the bone grew and remodeled itself.

ossification (osteogenesis)

Bone formation.

Zone of calcification

Minerals are deposited in the matrix between the columns of lacunae and calcify the cartilage. These are not the permanent mineral deposits of bone, but only a temporary support for the cartilage that would otherwise soon be weakened by the breakdown of the enlarged lacunae - enlarged condrocytes die and the cartilage matrix is calcified - mineralization of the cartilaginous walls between lacunae provides a temporary framework in the zone of calcification by which the final stages of ossification will take place

flat bones

Most of the cranial bones are in the form of thin curved plates called flat bones, such as the paired parietal bones that form the dome of the top of the head. The sternum (breastbone), scapula (shoulder blade), ribs, and hip bones are also flat bones.

Zone of cell hypertrophy

Next, the chondrocytes cease to divide and begin to hypertrophy (enlarge), much like they do in the primary ossification center of the fetus. The walls of matrix between lacunae become very thin. - the layer after the zone of cell proliferation is the zone of hypertrophy is, columnar chondrocytes enlarge and thus force the separations between lacunae to become very thin.

stress fracture

a break caused by abnormal trauma to a bone, such as fractures incurred in falls, athletics, and military combat

pathological fracture

a break in a bone weakened by some other disease, such as bone cancer or osteoporosis, usually caused by a stress that would not normally fracture a bone

Mineral deposition (mineralization)

a crystallization process in which calcium, phosphate, and other ions are taken from the blood plasma and deposited in bone tissue, mainly as needlelike crystals of hydroxyapatite. Deposition begins in fetal ossification and continues throughout life.

mesenchyme

a gelatinous embryonic connective tissue derived from the mesoderm, which differentiates into all permanent connective tissues and most muscle

Endochondral ossification

a process in which the bone is preceded by a hyaline cartilage "model" (location) that becomes replaced by osseous tissue. It begins around the sixth week of fetal development and continues into a person's 20s.

secondary ossification center

chondrocyte enlargement and death occur in the epiphysis of the model as well, creating a secondary ossification center.

perforating (Sharpey) fibers.

collagen fibers of the outer layer that penetrate into the bone matrix

bone collar

during endochondral ossificaion, as cartilage at the primary ossification center beaks down, osteoblasts begin to form a bone collar around the cartilage model. this helps provide support a well as initiating bone formation at the surface.

ligaments

hold bones together at the joints

medullary cavity (marrow cavity)

is the central cavity of bone shafts where red bone marrow and/or yellow bone marrow (adipose tissue) is stored (which is why medullary cavity is also known as marrow cavity). - hollow cavity within the diaphysis of a long bone - found deep in the diaphysis of long bones and are filled with yellow marrow in the adult

comminuted fracture

one in which a bone is broken into three or more pieces

displaced fracture

one in which at least one piece is shifted out of alignment with the other

greenstick fracture

one in which the bone is incompletely broken on one side but merely bent on the opposite side (the way a green twig breaks only partially and not into separate pieces)

concentric lamellae

onionlike layers of matrix concentrically arranged around a central canal

epiphyseal plate

plate of hyaline cartilage separates the marrow spaces of the epiphysis and diaphysis - a zone where the bones grow in length - In adults, the epiphyseal plate is depleted and the bones can grow no longer, but an epiphyseal line marks where the plate used to be. - a thin wall of cartilage separating the primary and secondary marrow cavities at one or both ends of the bone. The epiphyseal plate persists through childhood and adolescence and serves as a growth zone for bone elongation

intramembranous ossification

produces the flat bones of the skull and most of the clavicle (collarbone). Such bones develop within a fibrous sheet similar to the dermis of the skin, so they are sometimes called dermal bones

primary ossification center

region of chondrocyte enlargement

Calcitonin

secreted by C cells (clear cells) of the thyroid gland, a large endocrine gland in the neck . It is secreted when the blood calcium concentration rises TOO HIGH, and it lowers the concentration by two principal mechanisms - inhibits osteoclasts and simulates osteoblasts

canaliculi

slender channels interconnected with the lacunae - connect adjacent osteocytes

osteoid tissue

soft collagenous tissue similar to bone except for a lack of minerals

diploe

spongy layer in the cranium - absorbs impacts and leave the inner layer of compact bone unharmed

Wolff's law of bone

states that the architecture of a bone is determined by the mechanical stresses placed upon it, and the bone thereby adapts to withstand those stresses

orthopedics

the study of bone disorder - treatment of skeletal deformities in children - deals with the prevention and correction of injuries and disorders of the bones, joints, and muscles. It includes the design of artificial joints and limbs and the treatment of athletic injuries.

hemopoietic tissue

tissue that produces blood cells SAME A RED BONE MARROW

perforating (Volkmann) canals

transverse or diagonal passages that join central canals - contain blood vessels and nerves