Chapter 6: Skeletal System - Bones and Joints

Flashcards covering skeletal system structure, connective tissue extracellular matrix, bone cells, ossification processes, axial and appendicular bone anatomy, joint classifications, calcium homeostasis, and aging effects based on Seeley's Essentials of Anatomy & Physiology (10th Edition).

What are the four primary components of the skeletal system?

Bones, cartilages, tendons, and ligaments.

What are the five main functions performed by the skeletal system?

1. Support
2. Protect
3. Movement
4. Storage
5. Blood cell production

What are the structural components of cartilage extracellular matrix, and what properties do they provide?

The matrix contains collagen and proteoglycans. Collagen makes cartilage tough, while water-filled proteoglycans make it smooth, resilient, and an excellent shock absorber.

What gives bone extracellular matrix its flexible strength and weight-bearing strength?

Ropelike collagen fibers lend flexible strength to bone, while the mineral component (mostly calcium phosphate crystals called hydroxyapatite) gives bone compression or weight-bearing strength.

How are bones classified based on shape, and what are examples of each?

1. Long bones: longer than wide (e.g., upper and lower limb bones)
2. Short bones: as wide as long (e.g., wrist and ankle bones)
3. Flat bones: thin, flattened shape (e.g., skull bones, sternum)
4. Irregular bones: unique shapes (e.g., vertebrae, facial bones)

In long bone structure, what are the diaphysis, epiphysis, and epiphyseal plate?

The diaphysis is the shaft of compact bone. The epiphyses are the ends composed of spongy bone. The epiphyseal plate is the site of bone growth located between the diaphysis and epiphysis.

What is the difference between periosteum and endosteum?

The periosteum is the membrane around a bone's outer surface, whereas the endosteum is the membrane lining the interior medullary cavity.

Where is red bone marrow located in adults versus newborns?

In newborns, most bones contain red bone marrow. In adults, red marrow in the diaphysis is replaced by yellow bone marrow (fat), leaving red bone marrow primarily in flat bones and the long bones of the femur and humerus.

What is an osteon, and what structures are contained within it?

An osteon (Haversian system) is the structural unit of compact bone. It consists of concentric rings of bone matrix called lamellae, spaces called lacunae containing osteocytes, tiny nutrient-transporting canals called canaliculi, and a central canal containing blood vessels.

What structural characteristics define spongy (cancellous) bone tissue?

Spongy bone consists of interconnecting rods called trabeculae and spaces filled with marrow. It lacks osteons and is located at the epiphyses of long bones and the center of other bones.

What are the primary roles of osteoblasts, osteocytes, and osteoclasts?

Osteoblasts form new bone matrix and assist in repair and remodeling. Osteocytes maintain the existing bone matrix. Osteoclasts remove existing bone through bone reabsorption during repair and remodeling.

How do intramembranous ossification and endochondral ossification differ?

Intramembranous ossification forms bone within connective tissue membranes (primarily skull bones). Endochondral ossification forms bone inside a hyaline cartilage model (e.g., long bones).

How does a bone increase in width through appositional growth?

Osteoblasts deposit new bone matrix lamellae onto the outer surface of existing bone between the periosteum and current bone matrix, increasing its width or diameter.

What are the four major steps involved in bone repair after a fracture?

1. Hematoma formation: blood released from damaged blood vessels forms a blood clot.
2. Callus formation: internal and external calluses of fibers, cartilage, and woven bone form a bridge around the break.
3. Callus ossification: woven, spongy bone replaces internal and external calluses.
4. Bone remodeling: compact bone replaces woven bone and medullary cavity is restored.

How does parathyroid hormone (PTH) function when blood $\text{Ca}^{2+}$ levels decrease?

Decreased blood $\text{Ca}^{2+}$ stimulates PTH secretion from parathyroid glands. PTH stimulates osteoclasts to break down bone and release $\text{Ca}^{2+}$ into blood, increases $\text{Ca}^{2+}$ reabsorption in the kidneys, and stimulates active Vitamin D formation to promote intestinal $\text{Ca}^{2+}$ absorption.

How does calcitonin lower elevated blood $\text{Ca}^{2+}$ levels?

Increased blood $\text{Ca}^{2+}$ stimulates calcitonin secretion from the thyroid gland. Calcitonin inhibits osteoclasts, allowing osteoblasts to increase $\text{Ca}^{2+}$ uptake from the blood and deposit it into bone.

Define the anatomical bone features: foramen, fossa, process, condyle, meatus, and tubercle.

• Foramen: hole • Fossa: depression • Process: projection • Condyle: smooth, rounded end • Meatus: canal-like passageway • Tubercle: lump of bone

Which bone of the skull forms a freely movable joint with the rest of the skull?

The mandible (lower jawbone).

Which four bones contain paranasal sinuses?

Frontal, ethmoid, sphenoid, and maxillary bones.

Why is the hyoid bone unique in the human body?

It is an unpaired, U-shaped bone that does not articulate with any other bone in the body, serving as an attachment point for tongue muscles and neck muscles that elevate the larynx.

What are the five regions and four major curvatures of the adult vertebral column?

The 26 individual bones are grouped into cervical (7), thoracic (12), lumbar (5), sacrum (1), and coccyx (1). The four major curvatures are cervical (curved anteriorly), thoracic (curved posteriorly), lumbar (curved anteriorly), and sacrococcygeal (curved posteriorly).

What are the atlas and axis vertebrae, and what are their specific functions?

The atlas is the 1st cervical vertebra and holds the head. The axis is the 2nd cervical vertebra and allows rotation of the head.

How are the 12 pairs of ribs classified based on their attachment to the sternum?

• True ribs (1–7): attach directly to the sternum by costal cartilage. • False ribs (8–12): attach indirectly to the sternum by cartilage. • Floating ribs (11–12): false ribs that have no attachment to the sternum.

What bones constitute the pectoral girdle and pelvic girdle?

The pectoral girdle is composed of the scapula and clavicle. The pelvic girdle consists of the sacrum and hip bones (ilium, ischium, and pubis).

What are the functional categories of joints based on degree of movement?

• Synarthrosis: non-movable joint (e.g., skull sutures) • Amphiarthrosis: slightly movable joint (e.g., intervertebral joints) • Diarthrosis: freely movable joint (e.g., knee, elbow, wrist)

What are the structural features present in a synovial joint?

A synovial joint features articular cartilage covering bone ends, a fluid-filled joint cavity containing synovial fluid, a joint capsule (composed of an outer fibrous layer and inner synovial membrane), nerves, blood vessels, and associated bursae or tendon sheaths.

What three main effects does aging have on the skeletal system and joints?

1. Decreased collagen production
2. Loss of bone density
3. Degenerative changes