BIO 1314 UNIT 3 - Day 4 : Bone Tissue, Matrix, Bone Cells, Compact & Spongy Bone, Osteons + Microscopic Anatomy

Tissue classification of bone

Specialized connective tissue

Osseous tissue

Another term for bone tissue

Two major components of bone matrix

Organic components and inorganic components

Major organic component of bone matrix

Collagen fibers

Functional role of collagen fibers in bone

Provides tensile strength and flexibility

Functional role of inorganic mineral salts in bone

Provides hardness and resistance to compression

Hydroxyapatite

The major inorganic mineral crystal found in bone matrix

Primary mineral constituent of hydroxyapatite

Calcium phosphate

Bone component providing hardness

Inorganic mineral salts (hydroxyapatite)

Bone component providing resistance to stretching and twisting

Collagen fibers

Osteoid

The unmineralized organic portion of the bone matrix

Bone cell type that secretes osteoid

Osteoblasts

Mineralization process of osteoid

Deposition of mineral salts into osteoid, causing it to harden

Dual physical properties of bone tissue

Hardness (from minerals) combined with flexibility (from collagen)

Effect of removing collagen from bone matrix

Bone becomes hard but highly brittle

Effect of removing mineral salts from bone matrix

Bone becomes soft, flexible, and vulnerable to compression

Living status of bone matrix vs. cells

Matrix is nonliving, while the cells within it are living

Four major cell types in bone tissue

Osteogenic cells, osteoblasts, osteocytes, and osteoclasts

Features making bone a living tissue

Contains living cells, blood vessels, and nerves, and undergoes continuous remodeling

Dynamic nature of adult bone tissue

Bone is continuously remodeled rather than remaining static after adulthood

Osteogenic cells

Mitotic stem cells that divide and differentiate into osteoblasts

Osteoprogenitor cells

Another name for osteogenic cells

Mitotic capability of osteogenic cells

Able to undergo cell division (mitosis)

Cell type derived directly from an osteogenic cell

Osteoblast

Primary anatomical locations of osteogenic cells

Periosteum and endosteum

Role of osteogenic cells during fracture repair

Divide to produce new osteoblasts to build replacement bone

The stem cell of bone tissue

Osteogenic cell

Only bone cell type capable of division

Osteogenic cell

Starting cell in the osteogenic differentiation sequence

Osteogenic cell

Osteoblast

An immature bone-building cell that secretes matrix

Primary function of osteoblasts

To produce and deposit new organic bone matrix (osteoid)

Organic material secreted by osteoblasts

Osteoid

Physiological role of osteoblasts in matrix turnover

Bone formation/deposition

Microscopic location of active osteoblasts

Along bone surfaces where new bone matrix is actively being deposited

Cellular fate of an osteoblast trapped in matrix

Differentiates into a mature osteocyte

Immature bone-building cell

Osteoblast

Bone cell responsible for depositing collagen-rich matrix

Osteoblast

Bone cell type predominant during active bone deposition

Osteoblast

Osteocyte

A mature bone cell that maintains existing bone matrix

Precursor cell of an osteocyte

Osteoblast

Microscopic structural location of osteocytes

Lacunae

Primary function of osteocytes

Maintaining the existing surrounding bone matrix

Capacity of osteocytes for large-scale matrix production

Low/minimal (does not build large amounts of new matrix)

Canaliculi

Microscopic channels connecting adjacent lacunae and central canals

Functional necessity of canaliculi for osteocytes

Permits transport of nutrients, removal of wastes, and cellular signaling

Viability status of osteocytes

Living cells enclosed within mineralized matrix

Mechanism allowing osteocytes to survive in solid matrix

Intercellular contact and nutrient transport through the canalicular network

Mature cell residing within a lacuna

Osteocyte

Osteoclast

A large, multinucleated cell that breaks down and resorbs bone matrix

Bone resorption

The enzymatic breakdown and removal of mineralized bone matrix

Main functional activity of osteoclasts

Bone resorption

Size and nuclear structure of osteoclasts

Large size with multiple nuclei

Systemic outcome of osteoclast resorption on blood calcium

Releases stored calcium into the bloodstream

Bone cell elevated during periods of increased bone breakdown

Osteoclast

Functional antagonist to the osteoblast

Osteoclast

Physiological necessity of osteoclast activity

Essential for bone remodeling, repair, structural growth, and blood mineral homeostasis

The stem cell among bone cell types

Osteogenic cell

The bone-building cell

Osteoblast

The bone-maintaining cell

Osteocyte

The bone-destroying cell

Osteoclast

Developmental pathway sequence of bone cells

Osteogenic cell $\rightarrow$ osteoblast $\rightarrow$ osteocyte

Lineage origin of osteoclasts compared to osteoblasts

Osteoclasts derive from macrophage/monocyte lineage, not the osteogenic cell line

Compact bone

Dense, hard outer layer of bone tissue providing structural support

Cortical bone

Another term for compact bone

Structural unit of compact bone

Osteon

Haversian system

Another name for an osteon

Geometric shape of an osteon

Cylindrical

Orientation of osteons in long bones

Parallel to the long axis of the bone

Functional advantage of parallel osteon alignment

Allows long bones to resist heavy mechanical stress along their axis

Structure found at the center of an osteon

Central canal (Haversian canal)

Contents of a central canal

Blood vessels, lymphatic vessels, and nerves

Lamellae

Concentric or linear layers of mineralized bone matrix

Concentric lamellae

Circular layers of bone matrix arranged concentrically around a central canal

Microscopic definition of lacunae

Small cavities or spaces within bone matrix housing osteocytes

Position of lacunae within an osteon

Situated between adjacent concentric lamellae

Microscopic definition of canaliculi

Hairlike canals extending from lacunae to connect with other lacunae and central canals

Structure contained within canaliculi

Cytoplasmic processes of osteocytes

Primary physiological role of canaliculi

Facilitating nutrient and waste exchange via gap junctions between osteocytes and blood vessels

Reason direct blood vessel contact is absent for most osteocytes

Dense, calcified matrix isolates individual osteocytes from distant blood supply

Indirect connection between osteocytes and blood supply

Canalicular network radiating toward central canals

Physical nature of lamellae

Nonliving layers of matrix (not cells)

Physical nature of lacunae

Cavities or spaces within matrix (not cells)

Physical nature of canaliculi

Microscopic channels (not cells)

Structure enclosing an osteocyte

Lacuna

Microscopic structure connecting neighboring lacunae

Canaliculi

Structural rings immediately surrounding a central canal

Concentric lamellae

Feature located at the exact center of concentric lamellae

Central canal

Appearance of lacunae on histological slide sections

Small, dark oval spaces situated between matrix rings

Appearance of canaliculi on histological slide sections

Tiny, dark, radiating hairlike lines extending from lacunae

Perforating canals

Transverse channels connecting blood vessels and nerves of central canals, periosteum, and endosteum

Volkmann canals

Another name for perforating canals

Orientation of perforating canals relative to central canals

Perpendicular (transverse)

Difference in path between central canals and perforating canals

Central canals run longitudinally through osteon centers; perforating canals run horizontally across osteons

Primary function of perforating canals

To connect the vascular and nerve supplies of osteons with each other and the periosteum/medullary cavity

Interstitial lamellae

Incomplete matrix layers located in regions between intact osteons

Origin of interstitial lamellae

Remnants of older osteons partially resorbed during bone remodeling

Circumferential lamellae

Broad layers of bone matrix extending around the entire outer or inner circumference of bone tissue

Outer circumferential lamellae location

Directly deep to the periosteum on the outer surface of bone

Inner circumferential lamellae location

Deep to the endosteum surrounding the medullary cavity

Structural difference between concentric and interstitial lamellae

Concentric form complete circular rings around central canals; interstitial fill irregularly shaped spaces between osteons