Lecture 5: Bone Tissue

bone (osseous) tissue

Calcified connective tissue; matrix hardened by calcium phosphate and other minerals

mineralization (calcification)

The hardening process of bone

flat bones

Thin, curved plates of bone that protect soft organs; includes parietal bones of skull, sternum, scapula, ribs, hip bones

long bones

Bones that are longer than they are wide; rigid levers acted upon by muscles that are crucial for movement; includes the humerus, radius, ulna, femur, tibia, fibula, metacarpals, metatarsals, phalanges

short bones

Bones that are approximately equal in length and width; includes bones of wrist/ankle

irregular bones

Elaborately shaped bones; includes vertebrae and some skull bones

diaphysis

The shaft of a long bone; provides leverage

epiphysis

The enlarged end of a long bone; strengthens joint surface and anchors tendons/ligaments

epiphyseal line

The remnant of the epiphyseal plate (childhood growth)

articular cartilage

Hyaline cartilage covering joint surfaces; reduces friction and allows joints to move more freely

periosteum

External sheath covering most of the bone; comprised of an outer fibrous layer (collagen) and inner osteogenic layer (bone-forming cells)

endosteum

Thin layer of reticular connective tissue lining medullary (marrow) cavity and all internal bone surfaces

compact (dense/cortical) bone

Dense outer shell enclosing the marrow (medullary) cavity; organized into osteons (Haversian systems)

spongy (cancellous) bone

Loosely organized bone tissue; lattice of trabeculae; spaces filled with red or yellow bone marrow

nutrient foramina

Small holes in bone surface for blood vessel entry

osteogenic cells

Stem cells in periosteum (inner layer) and endosteum that arise from mesenchyme and give rise to osteoblasts

osteoblasts

Bone-forming cells which perform osteogenesis (synthesize organic matter of matrix and promote mineralization)

osteocytes

Former osteoblasts trapped in lacunae (cavities); maintain matrix and detect mechanical strain via canaliculi

canaliculi

Tiny channels connecting lacunae that allow osteocytes to exchange nutrients and communicate

osteoclasts

Bone-dissolving cells on bone surface which perform osteolysis (secretion of acid/proteolytic enzymes to break down bone as a part of remodeling)

rickets/osteomalacia

Inadequate mineral deposition as a result of Vitamin D (calcitriol) deficiency which causes soft, deformable bones

Wolff’s Law

Bone architecture adapts to the mechanical stresses placed upon it; increased stress causes bone to thicken and strengthen, and disuse causes a decrease in bone density

ectopic ossification

Abnormal calcification in soft tissues (tendons, arteries, brain, lung, eye) from excess mineral deposition

calculus

A calcified mass in an otherwise soft organ

osteopenia

A measurable decline in bone density which may advance to osteoporosis

osteoporosis

Severe loss of bone density; bones easily fracture

mineral deposition (mineralization)

Crystallization process in which calcium, phosphate, and other ions are taken from blood and deposited in bone

calcitriol (vit. D)

Produced in kidneys from sun-activated precursor; increases intestinal Ca2+ and phosphate absorption; inadequate amounts results in rickets/osteomalacia

calcitonin

Produced by thyroid C cells and secreted when blood Ca2+ is high; inhibits osteoclasts and stimulates osteoblasts; more active in children due to faster remodeling

parathyroid hormone (PTH)

Secreted when blood Ca2+ is low; stimulates osteoclasts, promotes renal Ca2+ reabsorption, activates calcitriol synthesis

negative feedback of calcium homeostasis

PTH and calcitonin act antagonistically to maintain serum Ca2+ in narrow range (8.5-10.5 mg/dL)

concentric lamellae

Layers of matrix in compact bone surrounding a central (Haversian) canal running longitudinally

osteon (Haversian system)

Central canal (connected by transverse perforating canals) and lamellae

cement line

Separates osteons and prevents spread of microfractures

circumferential lamellae

Encircles inner outer region of dense bone

interstitial lamellae

Fills irregular regions between osteons

bone marrow

Soft tissue occupying marrow cavities of long bones and small spaces of spongy bone

red bone marrow (myeloid tissue)

Contains multiple tissues, including hematopoietic tissue (produces blood cells)

yellow bone marrow

Fatty bone marrow that does not produce blood; can transform back to red marrow in the event of chronic anemia

ossification (osteogenesis)

Formation of bone

achondroplastic dwarfism

Long bones stop growing in childhood, resulting in a normal torso and short limbs; spontaneous mutation produces mutant dominant allele which causes failure of cartilage growth in metaphysis

pituitary dwarfism

Lack of growth hormone, resulting in normal proportions with a short stature

orthopedics

Branch of medicine for prevention/correction of disorders of bones, joints, and muscles

stress fracture

A break caused by abnormal trauma to a bone

pathological fracture

A break in a bone weakened by disease, usually caused by a stress that would not break a healthy bone

closed reduction

The manipulation of bone fragments into their normal positions without surgery

open reduction and internal fixation (ORIF)

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

electrical stimulation

For fractures taking 2+ months to heal; suppresses effects of parathyroid hormone