Human Anatomy and Physiology: Chapter 06 - Bone and Skeletal Tissues

Comprehensive practice flashcards reviewing skeletal cartilages, gross anatomy, classification of bones, microscopic structures (osteons, bone cells), and chemical composition from Chapter 06 Lecture A.

What is skeletal cartilage composed of, and what vascular and neural structures are present within it?

Skeletal cartilage is made of highly resilient cartilage tissue consisting primarily of water, and it contains no blood vessels or nerves.

What is the perichondrium, and what are its two primary functions?

The perichondrium is a layer of dense connective tissue surrounding cartilage like a girdle. It helps cartilage resist outward expansion and contains blood vessels for nutrient delivery to the cartilage.

What are the structural characteristics and primary locations of hyaline cartilage?

Hyaline cartilage provides support, flexibility, and resilience, and is the most abundant type containing collagen fibers only. It is found in articular cartilage (joints), costal cartilage (ribs), respiratory cartilage (larynx), and nasal cartilage (nose tip).

What are the characteristics and locations of elastic cartilage and fibrocartilage?

Elastic cartilage resembles hyaline cartilage but contains elastic fibers; it is located in the external ear and epiglottis. Fibrocartilage possesses thick collagen fibers with great tensile strength; it is found in the menisci of the knee and vertebral discs.

How do appositional growth and interstitial growth differ in cartilage?

In appositional growth (outside to in), new matrix is laid down on the surface of cartilage. In interstitial growth (inside to out), chondrocytes within lacunae divide and secrete new matrix, expanding the cartilage from within.

Into which two major groups is the human skeleton divided, and how many named bones does it contain?

The human skeleton contains $206$ named bones divided into the axial skeleton (skull, vertebral column, and rib cage along the long axis) and the appendicular skeleton (bones of upper and lower limbs, and the girdles attaching limbs to the axial skeleton).

What are the four classifications of bones based on shape, along with examples for each?

Long bones (longer than wide; limb bones), Short bones (cube-shaped in wrist and ankle, including sesamoid bones like the patella), Flat bones (thin, flat, slightly curved; sternum, scapulae, ribs, most skull bones), and Irregular bones (complicated shapes; vertebrae and hip bones).

What are the seven major functions of bones?

Support, protection, movement (levers for muscles), mineral and growth factor storage (calcium, phosphorus, and growth factors), blood cell formation (hematopoiesis in red marrow), triglyceride (fat) storage, and hormone production (osteocalcin).

What is osteocalcin and what is its role in the body?

Osteocalcin is a hormone secreted by bones that helps regulate insulin secretion, glucose levels, and metabolism.

What is the structural difference between compact bone and spongy bone?

Compact bone is a dense outer layer that looks smooth and solid. Spongy bone consists of a honeycomb of small, needle-like or flat pieces called trabeculae, with open spaces filled with red or yellow bone marrow.

What is the general gross structure of short, irregular, and flat bones?

They consist of thin plates of spongy bone (diploë) covered by compact bone, sandwiched between connective tissue membranes: periosteum on the outside and endosteum on the inside, with bone marrow scattered throughout and no defined marrow cavity.

What are the primary structural regions and components of a typical long bone?

A long bone consists of a tubular shaft called the diaphysis (compact bone surrounding a central medullary cavity filled with yellow marrow in adults), bone ends called epiphyses (compact bone externally, spongy bone internally, covered by articular cartilage), and an epiphyseal line between them.

What is the epiphyseal line?

The epiphyseal line is a remnant located between the diaphysis and epiphysis of an adult long bone, marking the childhood epiphyseal plate where bone growth occurred.

What are the two layers of the periosteum and how is it secured to the bone matrix?

The periosteum has an outer fibrous layer of dense irregular connective tissue secured to bone matrix by Sharpey's fibers (perforating fibers), and an inner osteogenic layer containing primitive osteogenic stem cells.

What is the endosteum and what surfaces does it cover?

The endosteum is a delicate connective tissue membrane covering internal bone surfaces. It covers the trabeculae of spongy bone, lines canals passing through compact bone, and contains osteogenic cells.

Where is red bone marrow located in newborns compared to adults?

In newborns, red marrow fills medullary cavities and all spongy bone. In adults, red marrow is confined to the heads of the femur and humerus, with the most active hematopoiesis in flat bone diploë (such as the sternum) and irregular bones (such as hip bones).

What are the three main categories of bone markings?

Projections (outward bulges serving as sites of muscle, ligament, and tendon attachment, or joint modifications), Depressions (bowl- or groove-like cutouts for vessels, nerves, or joints), and Openings (holes or canals for blood vessels and nerves).

What is a trochanter, and on which bone is it exclusively found?

A trochanter is a very large, blunt, irregularly shaped process; the only examples are located on the femur.

What are the differences between a condyle, a head, and a facet?

A condyle is a rounded articular projection often articulating with a fossa; a head is a bony expansion carried on a narrow neck; a facet is a smooth, nearly flat articular (joint) surface.

What are the five major cell types found in bone tissue?

Osteogenic cells, osteoblasts, osteocytes, bone-lining cells, and osteoclasts.

What are osteogenic cells (osteoprogenitor cells) and what do they become when stimulated?

Osteogenic cells are mitotically active stem cells located in the periosteum and endosteum; when stimulated, they differentiate into osteoblasts or bone-lining cells, while some persist as stem cells.

What is the role of osteoblasts and what is osteoid made of?

Osteoblasts are actively mitotic, bone-forming cells that secrete unmineralized bone matrix called osteoid, which consists of collagen and calcium-binding proteins. Collagen makes up $90\%$ of bone protein.

What are osteocytes and what is their primary function in bone tissue?

Osteocytes are mature, non-dividing bone cells located in lacunae that maintain the bone matrix, act as stress or strain sensors, and communicate mechanical stimuli to osteoblasts and osteoclasts to drive bone remodeling.

What are bone-lining cells and what are their specific names based on location?

Bone-lining cells are flat cells on bone surfaces that help maintain the matrix alongside osteocytes; they are called periosteal cells on the external bone surface and endosteal cells on internal surfaces.

What are osteoclasts, from what lineage do they derive, and what structural specializations do they possess?

Osteoclasts are giant, multinucleate cells derived from the hematopoietic stem cell (macrophage) lineage that function in bone resorption. Active cells sit in resorption bays and feature ruffled borders to increase surface area for enzymatic degradation.

What is an osteon (Haversian system) and what constitutes its structural arrangement?

An osteon is the structural unit of compact bone, consisting of an elongated cylinder running parallel to the long axis as a weight-bearing pillar, made of concentric rings of bone matrix called lamellae.

How do collagen fibers in adjacent lamellae of an osteon contribute to bone strength?

Collagen fibers run in different directions in adjacent lamellar rings, which enables the osteon to withstand stress and resist twisting forces.

What is the difference between central (Haversian) canals and perforating (Volkmann's) canals?

A central canal runs lengthwise through the core of an osteon containing blood vessels and nerves. Perforating canals are lined with endosteum and run at right angles to central canals, connecting vessels and nerves of the periosteum, medullary cavity, and central canals.

What are canaliculi and how do they form?

Canaliculi are hairlike canals connecting lacunae to each other and to the central canal. They form when osteoblasts maintain contact via cell projections and gap junctions as the matrix hardens, allowing nutrient and waste transport among osteocytes.

What are interstitial lamellae and circumferential lamellae?

Interstitial lamellae fill gaps between forming osteons or represent remnants of remodeled osteons. Circumferential lamellae extend around the entire surface of the diaphysis just deep to the periosteum to help resist long bone twisting.

How is spongy bone structurally organized at the microscopic level?

Spongy bone lacks osteons; its trabeculae are organized along lines of stress and contain irregularly arranged lamellae and osteocytes interconnected by canaliculi, with nutrients supplied by capillaries in the endosteum.

What constitutes the organic components of bone, and how do sacrificial bonds prevent fractures?

Organic components include bone cells and osteoid (ground substance and collagen fibers, making up $\frac{1}{3}$ of organic matrix). Sacrificial bonds in or between collagen molecules stretch and break to dissipate energy upon impact, and can re-form if no further trauma occurs.

What are hydroxyapatites and what percentage of bone mass do they comprise?

Hydroxyapatites are mineral salts consisting mainly of tiny calcium phosphate crystals in and around collagen fibers. They make up $65\%$ of bone by mass and provide hardness and resistance to compression.

How does the mechanical strength of bone compare to steel in compression and tension?

Bone is half as strong as steel in resisting compression and as strong as steel in resisting tension.