AP Chapter 7

Complete union

(all visible aspects of the epiphysis are united to the rest of the bone)

ligaments

(dense regular connective tissue that anchors bone to bone)

tendons

(dense regular connective tissue that connects muscle to bone)

Red bone marrow

(myeloid tissue) is hemopoietic (blood cell forming) and contains reticular connective tissue, immature blood cells, and fat.

Open

(no bony fusion or union between the epiphysis and the other bone end)

Partial union

(some fusion between the epiphysis and the rest of the bone, but a distinct line of separation may be seen)

Hyaline cartilage—except the articular cartilage—is covered by a dense irregular connective tissue sheet called the ______. Avascular

perichondrium

calcitonin

primarily inhibits osteoclast activity. In addition, calcitonin stimulates the kidneys to increase the loss of calcium in the urine. The result is a reduction in blood calcium levels.

Intramembranous ossification

produces the flat bones of the skull, some of the facial bones (zygomatic bone, maxilla), the mandible (lower jaw), and the central part of the clavicle (collarbone)

Ossification, or osteogenesis

refers to the formation and development of bone connective tissue.

Perforating (Volkmann) canals

resemble central canals in that they also contain blood vessels and nerves. However, perforating canals run perpendicular to the central canals and help connect multiple central canals within different osteons, thus forming a vascular and innervation connection among the multiple osteons.

Osteitis deformans (Paget disease of bone)

results from a disruption in the balance between osteoclast and osteoblast function. It is characterized by excessive bone resorption (excessive osteoclast activity) followed by excessive bone deposition (excessive osteoblast activity). excessive bone

Parathyroid Hormone (PTH)

secreted and released by the parathyroid glands in response to reduced blood calcium levels

trabeculae

structure is an open lattice of narrow rods and plates of bone

Bones perform several basic functions:

support and protection, movement, hemopoiesis (blood production), and storage of mineral and energy reserves.

simple fracture,

the broken bone does not penetrate the skin

Bones of the skeleton are

the primary organs of the skeletal system.

Lacunae are

the small spaces that each house an osteocyte.

Canaliculi are

tiny, interconnecting channels within the bone connective tissue that extend from each lacuna, travel through the lamellae, and connect to other lacunae and the central canal.

pathologic fracture

usually occurs in bone that has been weakened by disease.

Bone is highly _______ (meaning it is supplied by many blood vessels)

vascularized

inter ossification

Ossification centers form within thickened regions of mesenchyme beginning at the eighth week of development. Osteoid undergoes calcification. Woven bone (primary) to lamellar bone (secondary) and its surrounding periosteum form. Lamellar bone replaces woven bone, as compact bone and spongy bone form.

Bone connective tissue of the skeleton.

PTH and calcitriol act synergistically (their combined effect is greater than the sum of their individual effects) to increase the release of calcium from the bone into the blood, by increasing osteoclast activity.

Kidneys.

PTH and calcitriol act synergistically to stimulate the kidney to excrete less calcium in the urine (and thus retain more calcium in the blood). This occurs by increasing calcium reabsorption in the tubules in the kidney

Calcitonin

Promotes calcium deposition in bone and inhibits osteoclast activity. increases blood calcium levels in children.

Sex hormones (estrogen and testosterone)

Stimulate osteoblasts; promote epiphyseal plate growth and closure

Thyroid hormone

Stimulates bone growth by stimulating metabolic rate of osteoblasts

Growth hormone

Stimulates liver to produce the hormone IGF, which causes cartilage proliferation at epiphyseal plate and resulting bone elongation

Bone fracture Repair

A fracture hematoma forms (tears blood vessels) A fibrocartilaginous (soft) callus forms A hard (bony) callus forms The bone is remodeled

endochondrial bone growth

A hyaline cartilage model of bone forms. Bone first replaces hyaline cartilage in the diaphysis. Next, bone replaces hyaline cartilage in the epiphyses. Eventually, bone replaces hyaline cartilage everywhere, except the epiphyseal plates and articular cartilage. By a person's late 20s, all epiphyseal plates typically have ossified, and lengthwise bone growth is complete.

Parafollicular

Calcitonin is produced by these cells in the thyroid gland

interstitial growth

Chondrocytes housed within lacunae are stimulated to undergo mitotic cell division. Following cell division, two cells occupy a single lacuna; they are now called chondroblasts. As chondroblasts begin to synthesize and secrete new cartilage matrix, they are pushed apart. These cells now reside in their own lacuna and are called chondrocytes. The cartilage continues to grow in the internal regions as chondrocytes continue to produce more matrix.

osteopenia

Decreased calcification or density of bone

Vitamin D to Calcitriol

Ultraviolet light converts keratinocytes to vitamin D3(cholecalciferol) that's released into the blood. Vitamin D3 converted to calcidiol by addition of -OH group Calcidiol converted to calcitriol (active form of vitamin D) by addition of another -OH The presence of parathyroid hormone increases level of calcitriol

two types of cartilage:

Hyaline cartilage attaches ribs to the sternum (costal cartilage), covers the ends of some bones (articular cartilage), and is the cartilage within growth plates (epiphyseal plates). Hyaline cartilage also provides a model for the formation of most of the bones in the body. Fibrocartilage is a weight-bearing cartilage that withstands compression. It forms the intervertebral discs, the pubic symphysis (cartilage between bones of the pelvis), and cartilage pads of the knee joints (menisci).

Glucocorticoids

Increase bone loss and, in children, impair bone growth when there are chronically high levels of glucocorticoids. Released from the adrenal cortex

Parathyroid hormone

Increases blood calcium levels by encouraging bone resorption by osteoclasts

Serotonin

Inhibits osteoprogenitor cells from differentiating into osteoblasts when there are chronically high levels of serotonin

Appositional growth

Undifferentiated stem cells at the internal edge of the perichondrium begin to divide. (Note the perichondrium contains mesenchymal cells as well as these stem cells.) New undifferentiated stem cells and committed cells that differentiate into chondroblasts are formed. These chondroblasts are located at the periphery of the old cartilage, where they begin to produce and secrete new cartilage matrix. The chondroblasts, as a result of matrix formation, push apart and become chondrocytes, with each occupying its own lacuna. The cartilage continues to grow at the periphery as chondrocytes continue to produce more matrix.

Interstitial Growth

Zone of resting cartilage- farthest from the medullary cavity of the diaphysis and nearest the epiphysis. Zone of proliferating cartilage- (divide)aligned like a stack of coins. Zone of hypertrophic cartilage- (stop dividing) Enlarge in size, hypertrophy. Zone of calcified cartilage- 2-3 layers. destroys chondrocytes (opaque). Zone of ossification- bone

Achondroplasia is characterized by

abnormal conversion of hyaline cartilage to bone. The most common form is achondroplastic dwarfism, in which the long bones of the limbs stop growing in childhood, whereas the other bones usually continue to grow normally.

where can red bone marrow be found in adults, kids?

adults have red bone marrow only in selected portions of the axial skeleton, such as the flat bones of the skull, the vertebrae, the ribs, the sternum, and the ossa coxae (hip bone). Adults also have red bone marrow in the proximal epiphyses of each humerus and femur. Children is everywhere

Chondroblasts

are derived from mesenchymal cells and they produce the cartilage matrix.

Interstitial lamellae (interstitial systems)

are either the components of compact bone that are between osteons or are the leftover parts of osteons that have been partially resorbed—thus they often look like a "bite" has been taken out of them. The interstitial lamellae are incomplete and typically have no central canal.

Osteoblasts

are formed from osteoprogenitor stem cells. perform the important function of synthesizing and secreting the initial semisolid organic form of bone matrix called osteoid. Osteoid later calcifies as a result of salt crystal deposition. As a consequence of this mineral deposition on osteoid, osteoblasts become entrapped within the matrix they produce and secrete, and thereafter they differentiate into osteocytes.

Long bones

are greater in length than width. These bones have an elongated, cylindrical shaft (diaphysis). This is the most common bone shape. Long bones are found in the upper limbs (namely, the arm, forearm, palm, and fingers) and lower limbs (thigh, leg, sole of the foot, and toes).MOST COMMON

Osteoclasts

are large, multinuclear, phagocytic cells. An osteoclast is often located within or adjacent to a depression or pit on the bone surface called a resorption lacuna (Howship's lacuna). Osteoclasts are involved in breaking down bone in an important process called bone resorption (described shortly).

Osteocytes

are mature bone cells derived from osteoblasts that have lost their bone-forming ability when enveloped by calcified osteoid. (maintain bone matrix and stress)

Concentric lamellae

are rings of bone connective tissue that surround the central canal and form the bulk of the osteon.

Circumferential lamellae

are rings of bone immediately internal to the periosteum of the bone (external circumferential lamellae) or internal to the endosteum (internal circumferential lamellae). Both external and internal circumferential lamellae run the entire circumference of the bone itself (hence, their name).

Flat bones

are so named because they have flat, thin surfaces that may be slightly curved. They provide extensive surfaces for muscle attachment and protect underlying soft tissues. Flat bones form the roof of the skull, the scapulae (shoulder blades), the sternum (breastbone), and the ribs.

Osteoprogenitor cells

are stem cells derived from mesenchyme. When they divide through the process of cellular division, another stem cell is produced along with a "committed cell" that matures to become an osteoblast. (periosteum and endosteum)

Bone formation

begins when osteoblasts secrete the initial semisolid organic form of bone matrix called osteoid.

This constant, dynamic process of continual addition of new bone tissue (bone deposition) and removal of old bone tissue (bone resorption) is a process called _____ ______.

bone remodeling

The inorganic portion of the bone matrix is made up of salt crystals that are primarily ______ ______

calcium phosphate, Ca3(PO4)2

Once chondroblasts become encased within the matrix they have produced and secreted, the cells are called _______ and occupy small spaces called lacunae.

chondrocytes

In a flat bone of the skull, the spongy bone is also called _____

diploë

Short bones

have a length nearly equal to their width. Examples of short bones include the carpals (wrist bones) and tarsals (bones in the foot). Sesamoid bones, which are small, sesame seed-shaped bones along the tendons of some muscles, are also classified as short bones. The patella (kneecap) is the largest sesamoid bone.

Irregular bones

have elaborate, sometimes complex shapes and do not fit into any of the preceding categories. The vertebrae; ossa coxae (hip bones); and several bones in the skull, such as the ethmoid, sphenoid, and sutural bones, are examples of irregular bones.

Calcium phosphate and calcium hydroxide interact to form crystals of _______

hydroxyapatite

High levels of cortisol ______ bone lose

increase

Appositional Growth

increased diameter and medullary cavity

The central (Haversian) canal

is a cylindrical channel that lies in the center of the osteon and runs parallel to it. Extending through the central canal are the blood vessels and nerves that supply the bone.

Rickets

is a disease caused by a vitamin D deficiency in childhood and characterized by overproduction and deficient calcification of osteoid tissue. (bowlegged)

Bone resorption

is a process whereby bone matrix is destroyed by substances released from osteoclasts into the extracellular space adjacent to the bone.

Compact bone (also called dense or cortical bone)

is a relatively dense connective bone tissue that appears white, smooth, and solid. It makes up approximately 80% of the total bone mass

Cartilage

is a semirigid connective tissue that is more flexible than bone.

stress fracture

is a thin break caused by increased physical activity in which the bone experiences repetitive loads

The periosteum

lines the external surface of the bone shaft.

The endosteum

lines the internal surface of the bone along the edge of the medullary cavity.

Spongy bone (also called cancellous or trabecular bone) is

located internal to compact bone, appears porous, and makes up approximately 20% of the total bone mass.

The four classes of bone as determined by shape are

long bones, short bones, flat bones, and irregular bones

Osteocytes are .

mature bone cells found in small spaces (see next) between adjacent concentric lamellae. These cells maintain the bone matrix

yellow bone marrow

mature fatty substance

Osteoporosis,

meaning porous bones, is a disease that results in decreased bone mass and leads to weakened bones that are prone to fracture

Mechanical stress .

occurs in the form of weight-bearing movement and exercise, and it is required for normal bone remodeling

compound fracture,

one or both ends of the broken bone pierce the overlying skin

Calcification in the bone matrix.

or mineralization, subsequently occurs to the osteoid when hydroxyapatite crystals deposit

The primary component of bone is bone connective tissue, also called_____ connective tissue

osseous

The organic component is _______, which is produced by osteoblasts. These organic components give bone tensile strength by resisting stretching and twisting, and contribute to its overall flexibility.

osteoid

Unlike compact bone, spongy bone contains no _____

osteons

Four types of cells are found in bone connective tissue:

osteoprogenitor cells, osteoblasts, osteocytes, and osteoclasts