Bones and Skeletal Tissues

Flashcards about bones and skeletal tissues.

Skeletal cartilage

Made of highly resilient, molded cartilage tissue that consists primarily of water and contains no blood vessels or nerves.

Perichondrium

Layer of dense connective tissue surrounding cartilage; helps cartilage resist outward expansion and contains blood vessels for nutrient delivery to cartilage.

Hyaline cartilage

Provides support, flexibility, and resilience; most abundant type of cartilage; contains collagen fibers only.

Elastic cartilage

Similar to hyaline cartilage, but contains elastic fibers; found in the external ear and epiglottis.

Fibrocartilage

Contains thick collagen fibers and has great tensile strength; found in the menisci of the knee and vertebral discs.

Appositional growth

Cartilage-forming cells in perichondrium secrete matrix against external face of existing cartilage; new matrix laid down on surface of cartilage.

Interstitial growth

Chondrocytes within lacunae divide and secrete new matrix, expanding cartilage from within; new matrix made within cartilage.

Calcification of cartilage

Process that occurs during normal bone growth in youth but can also occur in old age; hardened cartilage is not the same as bone.

Functions of Bones

Support, protection, movement, mineral and growth factor storage, blood cell formation, triglyceride storage, hormone production

Axial skeleton

Long axis of body; includes the skull, vertebral column, and rib cage.

Appendicular skeleton

Bones of the upper and lower limbs and girdles attaching limbs to the axial skeleton.

Long bones

Longer than they are wide; limb bones.

Short bones

Cube-shaped bones in the wrist and ankle; sesamoid bones form within tendons (example: patella).

Flat bones

Thin, flat, slightly curved bones; sternum, scapulae, ribs, most skull bones.

Irregular bones

Bones with complicated shapes; vertebrae and hip bones.

Compact bone

Dense outer layer on every bone that appears smooth and solid.

Spongy bone

Made up of a honeycomb of small, needle-like or flat pieces of bone called trabeculae.

Diaphysis

Tubular shaft that forms long axis of bone; consists of compact bone surrounding central medullary cavity filled with yellow marrow in adults.

Epiphyses

Ends of long bones that consist of compact bone externally and spongy bone internally; articular cartilage covers articular (joint) surfaces.

Epiphyseal line

Remnant of childhood epiphyseal plate where bone growth occurs.

Periosteum

White, double-layered membrane that covers external surfaces except joints; contains fibrous and osteogenic layers.

Fibrous layer

Outer layer of the periosteum consisting of dense irregular connective tissue consisting of Sharpey’s fibers that secure to bone matrix.

Osteogenic layer

Inner layer of the periosteum abutting bone and contains primitive osteogenic stem cells that gives rise to most all bone cells

Endosteum

Delicate connective tissue membrane covering internal bone surface; covers trabeculae of spongy bone and lines canals that pass through compact bone.

Hematopoietic tissue in bones

Red marrow is found within trabecular cavities of spongy bone and diploë of flat bones; yellow marrow can convert to red if person becomes anemic.

Projection

Outward bulge of bone; may be due to increased stress from muscle pull or is a modification for joints.

Depression

Bowl- or groove-like cut-out that can serve as passageways for vessels and nerves, or plays a role in joints.

Opening

Hole or canal in bone that serves as passageways for blood vessels and nerves.

Osteogenic cells

Mitotically active stem cells in periosteum and endosteum; differentiate into osteoblasts or bone-lining cells.

Osteoblasts

Bone-forming cells that secrete unmineralized bone matrix called osteoid.

Osteocytes

Mature bone cells in lacunae that no longer divide; maintain bone matrix and act as stress or strain sensors.

Bone-lining cells

Flat cells on bone surfaces believed to also help maintain matrix (along with osteocytes); called periosteal cells or endosteal cells depending on location.

Osteoclasts

Derived from hematopoietic stem cells; giant, multinucleate cells that function in bone resorption (breakdown of bone).

Compact bone

Also called lamellar bone; consists of osteons, canals, canaliculi, interstitial and circumferential lamellae.

Osteon (Haversian system)

Structural unit of compact bone; elongated cylinder that runs parallel to long axis of bone; consists of rings of bone matrix called lamellae.

Central (Haversian) canal

Central canal runs through core of osteon; contains blood vessels and nerve fibers.

Perforating (Volkmann’s) canals

Canals lined with endosteum that occur at right angles to central canal; connect blood vessels and nerves of periosteum, medullary cavity, and central canal.

Lacunae

Small cavities that contain osteocytes.

Canaliculi

Hairlike canals that connect lacunae to each other and to central canal; allow communication between osteocytes.

Interstitial lamellae

Lamellae that are not part of osteon; some fill gaps between forming osteons; others are remnants of osteons cut by bone remodeling.

Circumferential lamellae

Layers of lamellae extend around entire surface of diaphysis; help long bone to resist twisting.

Spongy bone

Appears poorly organized but is actually organized along lines of stress to help bone resist any stress; trabeculae confer strength.

Organic components of bone

Includes osteogenic cells, osteoblasts, osteocytes, bone-lining cells, osteoclasts, and osteoid; osteoid makes up one-third of organic bone matrix and is secreted by osteoblasts.

Resilience of bone

Sacrificial bonds in or between collagen molecules that stretch and break to dissipate energy and prevent fractures; bonds re-form if no additional trauma.

Inorganic components of bone

Hydroxyapatites (mineral salts); make up 65% of bone by mass; consist mainly of tiny calcium phosphate crystals in and around collagen fibers.

Ossification (osteogenesis)

The process of bone tissue formation.

Endochondral ossification

Bone forms by replacing hyaline cartilage; bones are called cartilage (endochondral) bones; forms most of skeleton.

Intramembranous ossification

Bone develops from fibrous membrane; bones are called membrane bones.

Resting (quiescent) zone

Area of cartilage on epiphyseal side of epiphyseal plate that is relatively inactive.

Proliferation (growth) zone

Area of cartilage on diaphysis side of epiphyseal plate that is rapidly dividing; new cells formed move upward, pushing epiphysis away from diaphysis, causing lengthening.

Hypertrophic zone

Area with older chondrocytes closer to diaphysis; cartilage lacunae enlarge and erode, forming interconnecting spaces.

Calcification zone

Surrounding cartilage matrix calcifies; chondrocytes die and deteriorate.

Ossification (osteogenic) zone

Chondrocyte deterioration leaves long spicules of calcified cartilage at epiphysis-diaphysis junction; spicules are then eroded by osteoclasts and are covered with new bone by osteoblasts.

Growth hormone

Most important hormone in stimulating epiphyseal plate activity in infancy and childhood.

Thyroid hormone

Modulates activity of growth hormone, ensuring proper proportions.

Testosterone and Estrogens

Promote adolescent growth spurts and end growth by inducing epiphyseal plate closure.

Bone remodeling

Consists of both bone deposit and bone resorption; occurs at surfaces of both periosteum and endosteum.

Bone Resorption

Dig depressions or grooves as they break down matrix; secrete lysosomal enzymes and protons (H+) that digest matrix; acidity converts calcium salts to soluble forms.

Osteoid seam

Band of unmineralized bone matrix that marks area of new matrix.

Calcification front

Abrupt transition zone between osteoid seam and older mineralized bone.

Hormonal controls

Negative feedback loop that controls blood Ca2+ levels.

Parathyroid hormone (PTH)

Stimulates osteoclasts to resorb bone; calcium is released into blood, raising levels; PTH secretion stops when homeostatic calcium levels are reached.

Calcitonin

Effects are negligible, but at high pharmacological doses it can lower blood calcium levels temporarily

Leptin

Hormone released by adipose tissue that may play role in bone density regulation by inhibiting osteoblasts.

Serotonin

Neurotransmitter that regulates mood and sleep; also interferes with osteoblast activity.

Wolf’s law

States that bones grow or remodel in response to demands placed on them; stress is usually off center, so bones tend to bend.

Fractures

Breaks in bone; during youth, most fractures result from trauma; in old age, most result from weakness of bone due to bone thinning.

Fracture Treatment

Involves reduction, the realignment of broken bone ends; closed reduction involves physician manipulation; open reduction involves surgical pins or wires.

Hematoma formation

Torn blood vessels hemorrhage, forming mass of clotted blood called a hematoma; site is swollen, painful, and inflamed.

Fibrocartilaginous callus formation

Capillaries grow into hematoma; phagocytic cells clear debris; fibroblasts secrete collagen fibers to span break and connect broken ends; fibrocartilaginous callus forms.

Bony callus formation

New trabeculae appear in fibrocartilaginous callus; callus is converted to bony (hard) callus of spongy bone.

Bone remodeling

Excess material on diaphysis exterior and within medullary cavity is removed; compact bone is laid down to reconstruct shaft walls.

Osteomalacia

Bones are poorly mineralized; osteoid is produced, but calcium salts not adequately deposited; results in soft, weak bones; pain upon bearing weight.

Rickets

Osteomalacia of children; results in bowed legs and other bone deformities because bones ends are enlarged and abnormally long; cause: vitamin D deficiency or insufficient dietary calcium.

Osteoporosis

Group of diseases in which bone resorption exceeds deposit; matrix remains normal, but bone mass declines; spongy bone of spine and neck of femur most susceptible; vertebral and hip fractures common.

Paget’s Disease

Excessive and haphazard bone deposit and resorption cause bone to grow fast and develop poorly; called Pagetic bone; very high ratio of spongy to compact bone and reduced mineralization.