Skeletal System: Bones and Bone Tissue - Seeley’s 13th Edition, Lesson #6

Vocabulary flashcards covering key terms from the lecture notes on bones and bone tissue.

Functions of the Skeletal System

Support, protection of organs, movement via muscles and tendons, mineral storage (calcium and phosphate), adipose storage in marrow, and hematopoiesis (blood cell production).

Cartilage

Flexible, avascular connective tissue; major types include hyaline cartilage (major type), fibrocartilage, and elastic cartilage; chondroblasts form matrix; chondrocytes in lacunae; matrix contains collagen and proteoglycans; surrounded by perichondrium.

Hyaline cartilage

Major type of cartilage with glassy matrix; rings in the trachea, nose, and articular surfaces; chondrocytes in lacunae; typically covered by perichondrium.

Fibrocartilage

Rugged cartilage that resists compression and provides support in intervertebral discs and knee menisci.

Elastic cartilage

Cartilage with high elastin content that allows resilience and shape recovery (e.g., external ear, epiglottis).

Chondroblasts

Cartilage-forming cells that produce the cartilage matrix and become chondrocytes when embedded in matrix.

Chondrocytes

Mature cartilage cells located in lacunae; maintain cartilage tissue.

Matrix components (cartilage)

Collagen fibers for strength and proteoglycans for resiliency in the cartilage matrix.

Perichondrium

Double-layer connective tissue sheath surrounding cartilage; inner layer contains chondroblasts; outer layer contains blood vessels and nerves; cartilage itself is avascular.

No blood vessels in cartilage

Cartilage tissue lacks its own blood supply; nutrients diffuse through the matrix from the perichondrium.

Articular cartilage

Hyaline cartilage that covers bones at joints; has no perichondrium at articulations.

Appositional growth

Growth of cartilage by adding new chondrocytes and matrix at the periphery.

Interstitial growth

Growth of cartilage by chondrocyte division within the tissue and matrix expansion between cells.

Osteoblasts

Bone-forming cells that synthesize osteoid matrix and become embedded as osteocytes; derived from osteochondral progenitor cells.

Osteocytes

Mature bone cells embedded in lacunae; maintain bone and participate in minimal matrix turnover.

Osteoclasts

Bone-resorbing multinucleated cells derived from monocytes; contribute to bone remodeling; possess a ruffled border and secrete acid and enzymes.

Ruffled border

Membrane area of an osteoclast facing bone where resorption occurs; rich in proton pumps and lysosomal enzymes.

Lacunae

Small cavities in bone matrix housing osteocytes.

Canaliculi

Small channels containing osteocyte processes that connect lacunae and enable nutrient/waste exchange via gap junctions.

Osteon (Haversian system)

Functional unit of compact bone consisting of concentric lamellae around a central (Haversian) canal with blood vessels.

Central canal (Haversian canal)

Longitudinal channel within an osteon containing blood vessels and nerves.

Lamellae

Concentric layers of bone matrix; include concentric, circumferential, and interstitial lamellae.

Perforating canal (Volkmann’s canal)

Canals that run perpendicular to the long axis, connecting adjacent osteons and carrying vessels.

Woven bone

Immature bone with randomly oriented collagen fibers; formed first during ossification and fracture repair; later remodeled into lamellar bone.

Lamellar bone

Mature bone with parallel collagen fibers arranged in lamellae; forms osteons in compact bone and trabeculae in spongy bone.

Spongy bone

Also called cancellous bone; lattice of trabeculae with spaces filled by marrow; lighter and weaker than compact bone.

Trabeculae

Interconnected rods/plates of bone in spongy bone; orient along stress lines.

Compact bone

Dense outer layer of bone comprised of osteons; highly organized lamellae around central canals.

Diaphysis

Shaft of a long bone; mainly compact bone surrounding the medullary cavity.

Epiphysis

Ends of a long bone; contains mostly spongy bone enclosed by a thin layer of compact bone; articular cartilage covers joint surfaces.

Medullary cavity

Central cavity of a long bone; in children red marrow; in adults typically yellow marrow in the diaphysis.

Red marrow

Hematopoietic tissue that produces blood cells; found in the ends of long bones and in children’s medullary cavities.

Yellow marrow

Fat-rich marrow that replaces red marrow in most medullary cavities of adults.

Periosteum

Dense CT membrane covering the outer surface of a bone; two layers (outer fibrous, inner osteogenic); Sharpey’s fibers anchor tendon/ligament; contains vessels and nerves.

Endosteum

Single cellular layer lining internal bone spaces (cavities and trabeculae); contains osteoblasts, osteoclasts, and osteochondral progenitor cells.

Sharpey’s fibers

Penetrating collagenous fibers that anchor tendons/ligaments into bone via the periosteum.

Epiphyseal plate (growth plate)

Hy­l­ine cartilage plate between diaphysis and epiphysis responsible for length growth in growing bones.

Epiphyseal line

Calcified remnant of the epiphyseal plate after growth stops; marks end of growth in length.

Intramembranous ossification

Bone development within a connective tissue membrane; forms flat bones of the skull, part of the mandible, and clavicle; involves osteoblast differentiation from mesenchyme and formation of woven bone with subsequent remodeling.

Endochondral ossification

Bone development from a cartilage model; most bones form this way; involves cartilage calcification, bone collar formation, primary/secondary ossification centers, and replacement of cartilage by bone.

What are the primary minerals stored within bone?

Bone stores calcium and phosphate, which are essential for various body functions.

Where does hematopoiesis occur in the skeletal system, and what is its primary function?

Hematopoiesis, the production of blood cells, occurs in the red bone marrow.

What is the main role of the perichondrium in cartilage tissue?

The perichondrium provides nutrients to the avascular cartilage tissue (through diffusion) and contains chondroblasts in its inner layer, contributing to cartilage growth and repair.

Name the main bones formed by intramembranous ossification.

Intramembranous ossification forms the flat bones of the skull, part of the mandible, and the clavicle.

Describe the structural organization of compact bone and its functional unit.

Compact bone is densely packed and organized into osteons (Haversian systems), which are its functional units. Osteons consist of concentric lamellae around a central canal containing blood vessels and nerves.

What is the primary function of canaliculi in bone tissue?

Canaliculi are small channels that connect lacunae, allowing osteocyte processes to enable nutrient and waste exchange via gap junctions.

How do osteoclasts contribute to bone remodeling?

Osteoclasts resorb bone tissue by secreting acid and enzymes from their ruffled border, which is essential for bone remodeling and calcium homeostasis.

Explain the difference between appositional and interstitial growth in cartilage.

Appositional growth adds new chondrocytes and matrix at the periphery of the cartilage, while interstitial growth occurs from within the tissue as chondrocytes divide and expand the matrix between them.

What are the major functions of the skeletal system?

The skeletal system provides support, protects internal organs, allows movement (in conjunction with muscles and tendons), stores minerals (calcium and phosphate) and adipose tissue in marrow, and is the site of hematopoiesis (blood cell production).

Differentiate between woven bone and lamellar bone.

Woven bone is immature bone characterized by randomly oriented collagen fibers, typically formed during initial ossification and fracture repair. Lamellar bone is mature bone with parallel collagen fibers organized into lamellae, forming the structured osteons in compact bone and trabeculae in spongy bone. Woven bone is later remodeled into lamellar bone.

Explain the difference between the epiphyseal plate and the epiphyseal line.

The epiphyseal plate (growth plate) is a hyaline cartilage plate in growing bones responsible for longitudinal bone growth. The epiphyseal line is the calcified remnant of the epiphyseal plate that forms after growth ceases, indicating the end of growth in length.

What are the functions of the periosteum and endosteum?

The periosteum is a dense connective tissue membrane covering the outer surface of bone, involved in growth, repair, and attachment for tendons/ligaments. The endosteum is a single cellular layer lining internal bone spaces, containing cells important for bone growth, remodeling, and repair (osteoblasts, osteoclasts, and osteochondral progenitor cells).

What are the key characteristics and components of cartilage?

Flexible, avascular connective tissue; major types include hyaline cartilage (major type), fibrocartilage, and elastic cartilage; chondroblasts form matrix; chondrocytes in lacunae; matrix contains collagen and proteoglycans; surrounded by perichondrium.

What is the primary function of osteoblasts in bone tissue?

Osteoblasts are bone-forming cells that synthesize osteoid matrix and become embedded as osteocytes; they are derived from osteochondral progenitor cells.

Describe the structure and key features of spongy bone.

Spongy bone, also known as cancellous bone, is a lattice of interconnected rods and plates called trabeculae, with spaces filled by marrow. It is lighter and weaker than compact bone, and its trabeculae orient along stress lines.

Briefly explain the process of endochondral ossification.

Endochondral ossification is the process where bone develops from a cartilage model. Most bones form this way, involving cartilage calcification, bone collar formation, primary and secondary ossification centers, and the replacement of cartilage by bone.

What is the 'ruffled border' in bone cells, and what is its role?

The 'ruffled border' is a specialized membrane area of an osteoclast that faces the bone surface where resorption occurs. It is rich in proton pumps and lysosomal enzymes, which are critical for secreting acid and enzymes to break down bone tissue.

What is the diaphysis?

Shaft of a long bone; mainly compact bone surrounding the medullary cavity.

What is the epiphysis?

Ends of a long bone; contains mostly spongy bone enclosed by a thin layer of compact bone; articular cartilage covers joint surfaces.

Central cavity of a long bone; in children red marrow; in adults typically yellow marrow in the diaphysis.

What is the medullary cavity?

Central cavity of a long bone; in children red marrow; in adults typically yellow marrow in the diaphysis.

What is articular cartilage and a key characteristic regarding its perichondrium?

Articular cartilage is hyaline cartilage that covers bones at joints; it importantly has no perichondrium at articulations.

What are the different types of lamellae found in bone matrix?

The different types of lamellae include concentric lamellae (forming osteons), circumferential lamellae (around the bone's outer and inner surfaces), and interstitial lamellae (between osteons).