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Flashcards in Bones, Ch 6 Deck (59):

4 classes of bones?

Irregular, long, short, flat, sesamoid


This type of bone appears white, smooth, and solid. It comprises 80% of bone mass.

Compact bone


Also called cancellous or trabecular bone. Located internal to compact bone and appears porous. 20% of bone mass.

Spongy bone


Bones that are greater in length than width. Most common bone shape, found in the upper and lower limbs. Vary in size. Has medullary cavity.

Long bones


Bones with a length that is nearly equal to the width. Carpal bones, sesamoids, bones along the tendons of muscles.

Short bones


Bones with flat, thin surfaces, that may be slightly curved. Provide surfaces for muscle attachment and protect underlying soft tissues. Roof of skull, scapulae, sternum, ribs.

Flat bones

Spongy bone in these is called the diploë


Bones that have elaborate shapes. Vertebra, ossa coxae (hips), ethmoid, sphenoid, etc.

Irregular bones


Elongated, usually cylindrical shaft of bone. Provides leverage and major weight support.



Hollow, cylindrical space within the diaphysis. Contain red bone marrow in children, yellow marrow (fat) in adults

Medullary cavity


Knobby region at the ends of a long bone. Joint surface covered by thin layer of hyaline cartilage (articular cartilage)

Proximal and distal


Region of mature bone between the diaphysis and the epiphysis. Contains the epiphyseal plate.



In metaphysis. Thin layer of hyaline cartilage that provides for continued lengthwise bone growth. Remnant in adults termed the epiphyseal line.

Epiphyseal plate


Tough, outer sheath covering the surface of a bone. Composed of dense irregular connective tissue. Protects bone from surrounding structures, attachment site for ligaments and tendons. Inner cellular layer contains osteoprogenitors, osteoblasts, and osteoclasts

Attached to bone by numerous collagen perforating fibers.


Covers all internal surfaces of bone within the medullary cavity, like the bony struts if spongy bone. Incomplete layer of cells. Contains osteoprogenitors, osteoblasts, and osteoclasts.



Blood supply of the bone?

Bone is highly vascularized, especially spongy bone. Vessels enter from the periosteum. Most bones have only one nutrient artery and one nutrient vein. A few bones, like the femur, have more than one of each.


A tunnel that penetrates the diaphysis and provides access for the nutrient artery and/or vein. Branches of these large vessels supply the osteons of the compact bone before entering and supplying the medullary cavity.

Nutrient foramen


Hemopoietic (blood cell forming). Contains reticular (loose) connective tissue, immature blood cells, and fat. Myeloid tissue

Red bone marrow


Product of red bone marrow degeneration, blood vessels and adipocytes. May convert back to red bone marrow during severe anemia to facilitate the production of additional erythrocytes

Yellow bone marrow


Stem cells derived from mesenchyme that produce cells that mature to become osteoblasts. Located in the periosteum and endosteum.

Osteroprogenitor cells.


Cell that are often positioned side by side on bone surfaces. Synthesize and secrete osteoid through bone deposition. Initial semisolid form of bone matrix, later calcifies. Become entrapped in the matrix they produce. Differentiate into osteocytes.



Mature bone cells derived from osteoblasts. Mostly retired but secrete chemicals to maintain the bone matrix and detect mechanical stress on the bone. If stress is detected, they may deposit new bone matrix by recruiting osteoblasts.



Large, multinuclear, phagocytic cells. Derived from fused bone marrow cells. Ruffled border to increase surface area exposed to bone. Often located within or adjacent to a depression or pit on the bone surface, termed resorption lacuna. Break down bones, bone reabsorption.



The unmineralized organic bone matrix produced by osteoblasts. Its organic components give bone tensile strength by resisting stretching and contribute to bone flexibility.



To grow, bones need what?

Vitamin D enhances calcium absorption from the gastrointestinal tract. Vitamin C helps collagen formation. Calcium and phosphate for calcification.


Small cylindrical structures that are the basic functional and structural unit of mature compact bone. Oriented parallel to cone diaphysis.

Osteons, Haversian system


Lies at the center of the osteon and runs parallel to it. Blood vessels and nerves traveling here.

Central canal


Rings of bone connective tissue that surround the central canal. Contains collagen fibers that give bone part of its strength and reliance.

Concentric lamellae


Tiny interconnecting channels within bone connective tissue that extend from each lacunae and travel through the lamellae. Connect to others and central canal. House osteocyte projections

Allows travel of nutrients, minerals, gases, and wastes between blood vessels and osteocytes.


Run perpendicular to the central canals. They carry blood vessels, nerves from the periosteum that merge with the vessels in the central canals

Perforating (Volkmann) canals


Runs the entire circumference of bone. Just inside the bone periosteum and outside the spongy bone. Adds strength to the bone as a whole.

Circumferential lamella


Lamellae that are remnants of resorbed osteons

Interstitial lamellae


Growth in length.
Growth from inside. Depends on the cartilage growth on the epiphyseal plate.

Interstitial cartilage growth


Growth in width, growth from outside in
Thickness and remodeling of all bones by osteoblasts and osteoclasts on bone surfaces.

Appositional cartilage growth


Bone develops from a thin layer of mesenchymal cells referred to as a membrane. Centrally located mesenchymal cells cluster and differentiate into osteoblasts, forming an ossification center. Osteoid is secreted within the membrane and calcifies. Woven bone and periosteum form, which turns into lamellar bone and red marrow.

Intramembraneous ossification.
Produces flat bones of the skull, some of the facial bones, mandible, and central part of the clavicle.


Begins with a hyaline cartilage model, and requires breakdown of hyaline cartilage prior to ossification. Cartilage in the center of the diaphysis calcifies, with the periosteal bud and spongy bone/medullary beginning to form in cavities. Then the epiphysis ossify at the end.

Endochondral ossifcation
Produces most bones of the skeleton, including bones of the limbs, pelvis, vertebrae, and ends of the clavicle.
At the end, hyaline cartilage remains only in the epiphyseal plates and articular cartilages.


First zone nearest the epiphysis, composed of small chondrocytes distributed throughout the matrix. Resembles mature hyaline cartilage and secures epiphysis to the plate.

Zone of resting cartilage (reserve cartilage)


Second zone, chondrocytes undergo rapid mitotic divison, and become aligned into longitudinal columns of flattened lacunae. Columns parallel to diaphysis.

Zone of proliferating cartilage


Third zone, chondrocytes cease to divide and begin to hypertrophy. Walls of the lacuna become thin.

Zone of hypertrophic cartilage


Fourth zone, composed of 2-3 layers of chondrocytes. Minerals deposited between columns of lacunae. Destroys chondrocytes.

Zone of calcified cartilage


Fifth zone. The walls break down between lacunae in columns and spaces invaded by capillaries and osteoprogenitor cells. New bone matrix deposited on the calcified cartilage matrix.

Zone of ossification


Occurs in weight-bearing movement and exercise, required for normal bone remodeling. Detected by osteocytes and communicated to osteoblasts to increase synthesis of osteoid.

Mechanical stress

Causes increase in bone strength and results from skeletal contraction and gravitational forces


Calcium is required for?

Initiation of muscle contraction. Exocytosis of molecules from cells, including neurons. Stimulation of the heart by pacemaker cells. Blood clotting.


Hormones that regulate blood calcium levels?

Calcitriol (vit D) stimulates Ca++ absorption from the small intestine into the blood.
Parathyroid hormone (parathyroid glands)
Calcitonin (thyroid gland)


Disease caused by Vit D deficiency in childhood. Characterized by deficient calcification of osteoid tissue. Acquires bowlegged appearance. Disturbances growth, hypocalcemia, and tetany from low blood calcium.


Continues to occur in developing nations and increasing in urban US children


Characterized by abnormal conversion of hyaline cartilage to bone. Long bones of limbs stop growing during childhood while others continue to grow normally.

Achondroplasia (dwarfism, most commonly)
Results from a failure of the chondrocytes in plate to grow and enlarge causing too little endochondral ossification .


Red bone marrow transplant may be required if it's destroyed or abnormally functioning. Harvested cells injected into bloodstream of patient, migrate to normal locations.

Bone marrow transplant


Reduced bone mass sufficient to compromise normal function. Occurs in a significant percentage of older women, less men. Weakened bones due to fracture, especially at wrist, hip, vertebrae. Smoking, white people.

Reduced hormones with age like growth hormone, estrogen, and testosterone contributes to reduction in bone mass.
Best treatment is prevention with diet and physical activity in young adults.


Thin break in a bone caused by increased physical activity.

Stress fracture


Break in a bone that occurs because of weakening by disease

Pathologic fracture


Broken bone not penetrating the skin

One of both ends piercing overlying skin

Simple fracture

Compound fracture


Bone fragments into three more pieces. Particularly common in the aged, whose bones are more brittle.

Comminuted fracture


Bone is crushed, common in porous bones (osteoporosis) subjected to extreme trauma, like a fall

Compression fracture


Ragged break occurs when excessive twisting forces are applied to a bone. Common sports fracture.

Spiral fracture


Epiphysis separates from the diaphysis along the plate. Tends to occur where cartilage cells are dying and calcification of the matrix is occurring.

Epiphyseal fracture


Broken bone is depressed inward, typical of skull fracture
Bone breaks incompletely, only side of the shaft breaks. Common in children with more organic matrix.

Depressed fracture

Greenstick fracture


Four steps in fracture repair? Simple fracture about 2-3 months, compound is longer. Slower with age.

A hematoma forms. A fibrocartilaginous callus forms. A hardy, bony callus forms. The bone is remodeled.


Functions of the skeletal system?

Protection, mineral storage and acid-base homeostasis, blood cell formation, fat storage, movement, support


Specialized bones located within tendons. Generally small, relatively flat, and oval-shaped. Give tendon a mechanical advantage, providing better leverage for muscles, and also reduce wear and tear on the tendon. Patella.

Sesamoid bones


Explain the extracellular matrix of bone.

65% of the total weight of bone is inorganic matrix, which is composed of minerals.
35% is organic matrix, which contains the usual ECM stuff.