EXAM 2 PT.2 OSSEOUS TISSUES & THE AXIAL SKELETON

Osteogenic cells

Mitotic stem cells that can give rise to the osteoblasts, found in the periosteum and endosteum.

Osteoblasts

Cells that produce new bone matrix (osteoid), become trapped within calcified osteoid, and differentiate into osteocytes.

Osteocytes

Mature bone cells that cannot make new bone, reside within lacuna in the bone matrix, and maintain the bone matrix while detecting mechanical stress.

Osteoclasts

Large, multinuclear phagocytic cells derived from a hematopoietic progenitor, located within depressions on the bone surface called resorption lacuna, and break down the bone matrix during resorption.

Bone matrix composition - Organic

Includes osteoid (~1/3rd of the matrix), collagen fibers, and semi-solid ground substance (proteoglycans and glycoproteins), giving bone tensile strength.

Bone matrix composition - Inorganic

Consists of mineral salts (~2/3rd of the matrix), primarily Ca3(PO4)2, which combines with other salts to form hydroxyapatite crystals that harden the matrix.

Bone matrix formation

Osteoblasts secrete bone matrix (osteoid), which calcifies as a result of high plasma Ca2+ levels or when bone needs to respond to greater stress.

Bone matrix resorption

Osteoclasts destroy bone matrix, releasing Ca2+ into blood plasma.

Osteon

The structural unit of compact bone that runs parallel with the long axis and acts as weight-bearing pillars resisting torsion stress.

Central canals

Contain small blood vessels and nerve fibers that serve the osteon's cells and run parallel to the long axis of the bone.

Lamellae

Concentric layers of bone composed of collagen fibers running in alternating directions in each layer, providing strength and resilience.

Lacunae

Small spaces that contain osteocytes and are found at the junctions of the lamellae.

Caniculi

Tiny canals between lacunae that allow osteocytes to connect with one another to pass nutrients and waste.

Perforating (Volkmann) canals

Canals that connect and supply small blood vessels and nerves to the central canals and medullary cavity, lying at right angles to the long axis of the bone.

Circumferential lamellae

Rings of bone that run the entire circumference of the bone, protecting against torsion.

Hydroxyapatite

Crystals formed when Ca3(PO4)2 combines with other salts, which deposit along the long axis of collagen, hardening the bone matrix.

Osteoid

The unmineralized, organic component of the bone matrix, secreted by osteoblasts.

Mechanical stress detection

Function of osteocytes that allows them to maintain the bone matrix.

Resorption lacuna

Depressions on the bone surface where osteoclasts are located to break down the bone matrix.

Torsion stress

A type of mechanical stress that osteons are designed to resist.

Weight-bearing pillars

The function of osteons in compact bone to support body weight and resist stress.

Interstitial lamellae

Located between intact osteon, incomplete and have no central canal, remnants of resorbed osteons or fill-ins.

Spongy bone

Structure appears more haphazard than compact bone, has an open lattice.

Trabeculae

Narrow plates and rods of bone that align along lines of stress and distribute stress throughout.

Osteons

Not present in spongy bone.

Parallel lamellae

Possessed by spongy bone.

Canaliculi

Some open to surface to allow the diffusion of nutrients and waste.

Hyaline Cartilage

Resilient and flexible, covered by dense irregular connective tissue called perichondrium.

Extracellular matrix

Primarily collagen, ground substance is similar to that of bone but lacks the inorganic salts.

Water content in Hyaline Cartilage

Contains between 60-70% H2 O.

Chondroblasts

Cells derived from mesenchyma that produce matrix.

Chondrocytes

Mature cartilage cell found in lacunae that maintain matrix.

Avascular cartilage

Lacks nerves and nutrients are supplied to cells by diffusion.

Cartilaginous Growth (length)

Begins during embryonic development and gives rise to bone growth.

Interstitial growth

Occurs within internal regions of cartilage and involves four steps: chondrocytes undergo mitotic division, daughter cells are called chondroblasts, they secrete new matrix and become separated, and cartilage grows as chondrocytes produce more matrix.

Appositional growth

Occurs along cartilage's outer edge.

Five cartilaginous zones

Involved in interstitial bone growth: Zone of resting cartilage, Zone of Proliferating cartilage, Zone of hypertrophic cartilage, Zone of calcified cartilage, Zone of ossification.

Zone of resting cartilage

Furthest from medullary cavity of diaphysis, resembles healthy cartilage, secures epiphysis to epiphyseal plate.

Zone of Proliferating cartilage

Characterized by rapid mitotic division and cells aligned in columns.

Zone of hypertrophic cartilage

Cells are no longer dividing and become hypertrophic and resorb matrix.

Zone of calcified cartilage

Involves mineral deposition in the matrix and chondrocytes die.

Zone of ossification

Involves vascularization and bone deposition.

Bone formation

Also known as ossification or osteogenesis, begins in the embryo through childhood and adolescence.

Intramembranous ossification

Bone growth within a membrane, yields flat bones.

Endochondral ossification

Bone development that replaces cartilage used as a model for construction.

Perichondrium

A layer of connective tissue that surrounds cartilage.

Cartilage growth

Declines rapidly as cartilage becomes semi-rigid and can no longer expand.

Ossification

The process of bone formation, also known as osteogenesis.

Woven bone

Immature and unorganized bone formed during ossification.

Lamellar bone

Mature bone that replaces woven bone.

Primary ossification center

The first area of bone development in the diaphysis.

Fibrous connective tissue

The supportive structure on which ossification occurs in intramembranous ossification.

Mesenchyme

Connective tissue that condenses to form the periosteum.

Secondary ossification center

Forms in the epiphysis.

Articular cartilage

Remains on epiphyseal surfaces during endochondral ossification.

Epiphyseal plate

The junction between the diaphysis and the epiphysis where cartilage growth occurs.

Interstitial bone growth

Growth in length dependent upon cartilage growth within the epiphyseal plate.

Appositional bone growth

Growth in width where bone is added to the external surface and resorbed on the internal surface.

Bone mass recycling

Bone continues to renew and reshape, recycling approximately 5-7% of our bone mass every week.

Wolff's law

States that bones grow or remodel in response to the demands placed on them.

Growth Hormone (GH)

Produced in the anterior pituitary gland, stimulates liver to produce somatomedins which stimulate chondrocyte activity.

Thyroid Hormone (T3 and T4)

Produced in the thyroid gland, regulates metabolic rate of cells including bone cells.

Sex hormones

Produced in the gonads and adrenal gland, includes Estrogens and Androgens, secreted in large amounts at puberty.

Glucocorticoids

Produced in the adrenal gland, regulate blood glucose levels and high levels interfere with growth at the epiphyseal plate.

Calcitriol

Vitamin D produced in the skin on exposure to UV light, increases intestinal reabsorption of Ca2+ and PO43-.

Parathyroid hormone (PTH)

Secreted in response to low Ca2+ levels, increases osteoclast activity and enhances production of calcitriol.

Calcitonin

Produced in C cells of the thyroid gland, secreted in response to high Ca2+ levels, inhibits osteoclast activity.

Bone fractures

Break in the bone classified in several ways.

Repair of the simple fracture

Involves four steps including hematoma formation and bony callus formation.

Hematoma

Results from blood vessels in the bone being torn.

Fibrocartilagenous callus

Formed when fibrous tissue invades the site and begins depositing collagen to span the break.

Bony callus formation

New bone replaces the cartilaginous tissue during the repair of a fracture.

Bone remodeling

Excessive material is removed; final structure resembles previous bone but responds to the same set of mechanical stress.

Bone markings

Surface features that characterize each bone in the body.

Depressions

Clefts located when bone meets another structure; allow blood vessels and nerves to travel along the bone; allows two bones to articulate.

Openings

Holes in the bone; indicate where blood vessels or nerves travel through the bone.

Projections

Bony extensions; variety of shapes and sizes; points where muscles, tendons, and ligaments attach to the bone.

Axial skeleton

Forms the long axis of the body; includes skull, vertebral column, rib cage; bones involved with protecting, supporting, and carrying other body parts.

Appendicular skeleton

Bones of the upper and lower limbs and girdles; includes hip and shoulder; bones involved in locomotion.

The Skull

Most complex bony structure in the body; composed of 22 bones.

Cranial bones

8 bones that form the upper part of the skull.

Facial bones

14 bones that form the face.

Sutures

Interlocking joints with saw-toothed or serrated appearances that unite the bones of the skull.

Mandible

The only freely moving bone in the skull.

Cranial vault

Round portion that makes up the superior, lateral, and posterior portions of the skull.

Cranial base

Makes up the floor or interior portion of the skull.

Foramen magnus

Where the spinal cord exits the cranium.

Cranial fossae

Contoured depressions that make up the floor of the cranium.

Anterior cranial fossa

Supports the frontal lobe; formed by frontal bone, ethmoid bone, and sphenoid bone.

Middle cranial fossa

Supports the temporal lobe and the pituitary gland; formed by sphenoid bone and temporal bone.

Posterior cranial fossa

Supports the cerebellum and part of the brainstem; formed by temporal bone and occipital bone.

Coronal suture

Extends laterally across the superior surface along the coronal plane; articulation between frontal and parietal bones.

Lambdoid suture

Arc across the posterior surface of the skull; articulation between parietal and occipital bones.

Sagittal suture

Extends between coronal and lambdoid sutures along the midsagittal plane; articulates between the paired parietal bones.

Squamous suture

One on each side of the skull; articulates between the temporal and parietal bone.

Facial skeleton

Bones that form the framework for the face.

Single bones in the facial skeleton

Mandible and vomer.

Paired bones in the facial skeleton

Nasal bones, lacrimal bones, zygomatic bone, palatine bones, maxilla, and inferior nasal concha.

Cavities of the skull

Include cranial cavity, orbital cavities, nasal cavity, and oral cavity.

Nasal cavity

Contains passages for air and special sensory neurons for smell; considered the first part of the respiratory tract.