Lectures 1-4

Osteocytes

Inactive and entrapped osteoblasts within bone matrix. Can revert back when surrounding matrix is dissolved.

Osteoprogenitor

A germ cell that turns into other cells in bone.

Osteoclasts

Large, multinucleated cells at bone surface and actively resorb bone.

Primary Ossification

Formation of 1-cell thick layer covering surfaces undergoing remodeling.

Osteoblasts

Mononuclear cells that form new bone (ossification) and originate from mesenchymal cells in bone marrow.

Endosteum

A membrane lining inner surface of bony wall and bone marrow. Layer on the inside.

Periosteum

A dense outer layer of bone that contains vascular connective tissue enveloping bones, except at surfaces of joints. Layer on the outside, covering.

Compact/cortical bone

The hard, dense outer layer of all bones throughout the body. Dense bone where bony matrix is solidly filled with organic ground substance and inorganic salts.

Trabecular/cancellous/spongy bone

A hierarchical, spongy, and porous material composed of hard and soft tissue components. Found in epiphysis and metaphysis of long bones and in vertebral bodies. Can also be in medullary space. Forms matrix for bone marrow.

Medullary space

The hallow part of bone that contains bone marrow.

Epiphyseal/Growth Plate

A hyaline cartilage plate in metaphysis at each end of a long bone.

Metaphysis

The region where epiphysis joins diaphysis.

Diaphysis

The shaft or central part of a long bone, contains mostly compact bone.

Epiphysis

The end part of a long bone, initially growing separately from shaft.

Glycoproteins

Proteins with covalently bound carbohydrates in various patterns. Necessary for mineral regulation.

Proteoglycans

Small leucine-rich______ (SLRPs) necessary for cell proliferation, mineral deposition, and remodeling.

Ground substance

A substance rich in a mineralized calcium phosphate compound known as hydroxyapatite.

Osteon

Cylindrical structures composed of concentric layers of bone tissue called lamellae that surround a central canal.

Haversian/Central canals

Any of the minute tubes which form a network in bone and contain blood vessels that run PARALLEL to length of bone.

Volkmann/Perforating canals

Channels that contain smaller blood vessels that run PERPENDICULAR to length of bone. Connect Haversian canals to periosteum and medullary cavity.

Lacunae

Small areas of holes in bone matrix where osteocytes reside.

Canaliculi

Tunnels that form a labyrinth of connections between neighboring osteocytes. Where cytoplasmic projections go. Communication.

Trabeculae

Thin columns and plates of bone that create spongy structure along stress lines. Provides flexibility and improves resistance to fracturing.

Red bone marrow

Contains hematopoietic tissue that creates blood cells. Located throughout most flat and long bones in young animals and will recede from long bones with maturity in trabecular spaces. In adults, found in flat bones of vertebrae, sternum, ribs, and pelvis, along with proximal ends of humerus and femur.

Yellow bone marrow

Contains mostly adipose tissue (fat tissue). Majority of marrow, but has potential to convert back to red marrow under severe necessity. Located primarily in long bones.

Ca2+ and phosphorous

Most abundant minerals in bones.

Mg2+, Na+, K+, Cl-, and F-

Other bone minerals

Type I collagen

Main form found in bone (90%). Synthesized mostly by osteoblasts. Hydroxylation with Vitamin C is required.

Tropocollagen

Braided collagen fibrils that have improved strength and rigidity. 5 join together to form microfibril.

Collagen matrix

Microfibrils laid end-to-end in staggered formation in same direction in single bone metabolic unit. Small spaces in between allow initial nucleation of mineral crystals on matrix.

Hydroxyproline

A neutral heterocyclic protein amino acid that’s commonly found in bone and gelatin. Digestion of bone collagen causes concentrations to rise in blood, which is used as a diagnostic indication of bone destruction.

Hydroxylysine

Amino acid unique to collagen-like peptides. Has covalent cross-link norlecine across adjacent collagen fibrils, which stabilizes fibrils. Creates banding pattern on collagen fibrils

Osteocalcin

A protein that is found in extracellular matrix of bone and in serum of circulating blood. Produced solely by osteoblasts - Vitamin K is often present. Inhibits haphazard formation of hydroxyapatite precipitates and mineralization. Hemoattractant of leukocytes (attracts osteoclasts to areas in need of resorption and remodeling) JOB: keeping regulation of bone composition.

Intramembranous ossification (IO)

Bone formation within primitive connective tissue

Endochondral Ossification (EO)

Pre-existing cartilage is turned into bone

Ectopic bone formation

pathologic process in which connective tissues that aren’t usually turned into bone are ossified. Abnormal

Mesenchyme

Tissue characterized by primordial cell types surrounded by large amount of extracellular matrix (loose connective tissue).

Woven bone

Early bone where collagen fibrils remain randomly interwoven. Quick construction but weak, more flexible, higher rate of turnover

Osteoid

The unmineralized, organic portion of the bone matrix that forms PRIOR to the maturation of bone tissue. Can be found in woven and lamellar bone

embryo development

Where does intramembranous ossification begin?

Hyaline cartilage

A translucent bluish-white type of cartilage present in the joints, the respiratory tract, and the immature skeleton

Endochondral Ossification (EO)

Starts as hyaline cartilage. Long bones specifically. Includes: bones in extremities, base of skull, vertebral column, and pelvis. Mesenchyme differentiates into chondrocytes.

Chondrocytes

Lay out in shape of bone being formed. (EO)

Centers of ossification

Within hyaline cartilage and are distinguished by enlargement of chondrocytes in particular areas of cartilaginous bone

Apoptosis

Calcification causes hypertrophies chondrocytes to do _______

Zone of proliferation

formed by chondrocytes that are further from diaphysis

Zone of maturation

formed by chondrocytes that have stopped dividing and have become enlarged

Zone of hypertrophy

formed by hypertrophy and vacuolation of chondrocytes

Zone of provisional calcification

formed by cartilaginous matrix surrounding cells beginning to calcify. Begin mineralization to thicken cartilage.

Somatotropin

Hormone that controls bone growth. From the pituitary gland. Causes local production of insulin-like growth factor 1 (somatomedin), which encourages zone of proliferation chondrocytes to divide

Hyena disease

condition where growth plates in hindlimbs closes prematurely compared to front limbs, happens in heifers secondary to vitamin A toxicosis as calves

Bone remodeling units (BRU)

small units of bone that undergo remodeling at any given time

Activation, Resorption, Reversal, Formation

The steps of bone remodeling (cycles)

Activation

Converts resting/inactive bone surface into that to be remodeled. Either from a random event (trauma) or selective remodeling directed by a signal from bone.

Resorption

Osteoclasts release acids and proteolytic enzymes from ruffled border, which dissolves bone matrix. Makers = quiet, Breakers = busy.

Howship’s lacuna

hole created by osteoclasts during resorption

Reversal

Needs insulin-like growth factor 2 and transforming growth factor (TGF) - beta. Released during collagen matric breakdown, activate cells lining surface to revert to osteoblasts.

Formation

Deposition of osteoid by osteoblasts. Consists mostly of type 1 collagen, proteoglycans, and smaller proteins found in mature bone. Lays osteoid down in lamellae with fibrils parallel to each other. Trabecular bone deposited in curved sheets following hollow shape. Mineralization occurs after time delay but happens quick when activated

Complete fracture

Through entire bone

Transverse fracture

Straight line through entire bone

Oblique fracture

Line at an angle through entire bone

Spiral fracture

Corkscrew line through entire bone

Comminuted fracture

More than 2 parts to a fracture through entire bone

Incomplete fracture

Not entirely through bone

Bowing fracture

Bone is bent

Buckle fracture

Fracture on concave side

Greenstick fracture

fracture on convex side

Avulsion fracture

Bone fragment separates from the rest of the bone, often attached to ligament or tendon

Displacement fracture

ends of fracture not within same area, created a gap

Type 1 fracture

Through growth plate

Type 2 fracture

Through growth plate and metaphysis

Type 3 fracture

Through growth plate and epiphysis

Type 4

Through all three elements (growth plate, metaphysis, and epiphysis)

Type 5 fracture

Crush injury of growth plate

Osteocytic osteolysis

Process of Ca2+ resorption from bone

Vitamin D hormone

Indirectly affects bone Ca2+ concentration in osteocytic osteolysis

Calcitonin

Major Ca2+ regulating hormone. Acts on osteoblasts to inhibit bone resorption.