Skeletal System & Joints (Anatomy and Physiology I)

Flashcards covering skeletal system anatomy, bone tissue histology, bone development and growth, calcium homeostasis, fracture repair, joint classifications, synovial joint structure, joint movements, and specific clinical conditions.

What are the six primary functions of the skeletal system?

1. Protection of underlying organs and senses.
2. Mineral storage and acid/base homeostasis (calcium, phosphorus, and magnesium salts).
3. Blood cell formation (hematopoiesis in red bone marrow).
4. Fat storage (triglycerides in yellow bone marrow).
5. Movement (muscle attachment around joints).
6. Support (holding body weight and structure).

How many bones are in the adult body, and what are the five shape classifications of bones?

An adult body contains $206$ bones classified into five shape categories:

1. Long bones
2. Short bones
3. Flat bones
4. Irregular bones
5. Sesamoid bones

What defines a long bone versus a short bone?

Long bones are longer than they are wide (e.g., upper and lower limbs, hands, feet, fingers, toes). Short bones are as long as they are wide and tend to look like a cube (e.g., carpals and tarsals).

What are sesamoid bones?

Small, flat, oval-shaped bones located within tendons, such as the patella.

Describe the external gross anatomy of a long bone.

It consists of a middle shaft called the diaphysis and two rounded ends called epiphyses, which are covered in articular cartilage to reduce friction. The exterior is covered by a periosteum membrane anchored to the bone by perforating fibers.

What is the structural arrangement of short, flat, irregular, and sesamoid bones?

They feature a "sandwich" arrangement with an outer layer of compact bone surrounding an inner layer of spongy bone. In flat bones, the inner spongy bone is called diploë.

How do long bones receive blood and nerve supply?

They receive blood supply from vessels in the periosteum and two nutrient arteries that enter the diaphysis through small openings called nutrient foramina. They are also supplied with abundant sensory nerve fibers.

Compare red bone marrow and yellow bone marrow in terms of function and adult location.

Red bone marrow contains reticular fibers supporting hematopoietic cells (found in adults in the pelvis, proximal femur, humerus, vertebrae, ribs, sternum, clavicles, and scapulae). Yellow bone marrow stores triglycerides and consists of blood vessels and adipocytes.

What are the two major components of the extracellular matrix (ECM) of bone tissue?

1. Organic matrix ($35$%): composed of collagen fibers (osteoid), proteoglycans, glycosaminoglycans, glycoproteins, and osteocalcin.
2. Inorganic matrix ($65$%): composed of mineral deposits, predominantly hydroxyapatite crystals made of calcium and phosphorus salts.

What happens to bone tissue if either the organic matrix or the inorganic matrix is absent?

Without the organic matrix, the bone becomes brittle and splinters. Without the inorganic matrix, the bone becomes malleable and prone to bending under pressure.

What are the functions of osteoblasts, osteocytes, and osteoclasts?

• Osteoblasts: perform bone deposition by secreting organic matrix and aiding inorganic matrix formation.
• Osteocytes: trapped osteoblasts residing in lacunae that maintain the ECM and recruit osteoblasts under mechanical tension.
• Osteoclasts: large multinucleated cells that perform bone resorption.

How do osteoclasts accomplish bone resorption?

Osteoclasts secrete hydrogen ions and enzymes from their ruffled border. The hydrogen ions make the local environment acidic to dissolve the inorganic matrix, while enzymes break down the organic matrix.

What structural components comprise an osteon in compact bone?

An osteon (Haversian system) consists of concentric lamellae surrounding a central canal (Haversian canal) containing blood vessels and nerves. Osteocytes reside in lacunae between lamellae and extend through canaliculi connected via gap junctions.

How do spongy bone trabeculae differ structurally from compact bone osteons?

Trabeculae are branching projections covered with endosteum that contain concentric lamellae and lacunae, but they lack osteons, central canals, and perforating canals. They absorb nutrients directly from bone marrow vessels.

What are the four steps of intramembranous ossification?

1. Osteoblasts develop in the primary ossification center from mesenchymal cells.
2. Osteoblasts secrete organic matrix, which calcifies, trapping osteoblasts as osteocytes.
3. Osteoblasts lay down trabeculae of early spongy bone; surrounding mesenchyme differentiates into periosteum.
4. Osteoblasts in the periosteum lay down early compact bone.

What are the five steps of endochondral ossification?

1. Chondroblasts in the perichondrium differentiate into osteoblasts.
2. Osteoblasts build a bone collar on the external surface as bone ossifies from the outside.
3. Internal cartilage calcifies and chondrocytes die.
4. Osteoblasts replace calcified cartilage with early spongy bone in the primary ossification center; secondary ossification centers and medullary cavity develop.
5. Epiphyses finish ossifying and remaining cartilage is replaced by bone as the medullary cavity enlarges.

What are the five functional zones of cells in the epiphyseal plate during longitudinal growth, from epiphysis to diaphysis?

1. Zone of reserve cartilage
2. Zone of proliferation
3. Zone of hypertrophy and maturation
4. Zone of calcification
5. Zone of ossification

How does appositional growth increase the diameter of a bone?

Osteoblasts in the periosteum lay down new circumferential lamellae on the outer surface, while osteoclasts resorb inner circumferential lamellae along the medullary cavity to expand the cavity proportionally.

How do Growth Hormone, Testosterone, and Estrogen affect bone growth?

• Growth Hormone: increases chondrocyte mitosis in epiphyseal plates, stimulates osteogenic cells and zone of ossification, and promotes appositional growth.
• Testosterone: increases appositional growth, chondrocyte mitosis, and accelerates epiphyseal plate closure.
• Estrogen: increases longitudinal growth rate, inhibits osteoclasts, and accelerates epiphyseal plate closure faster than testosterone.

How does parathyroid hormone (PTH) regulate blood calcium ion homeostasis when blood calcium drops?

Parathyroid gland cells detect low blood calcium and increase PTH release. PTH stimulates osteoclasts to resorb bone, prompts kidneys to retain calcium, and causes intestines to absorb calcium into the blood.

What are the four steps of bone fracture repair?

1. A hematoma fills the gap between bone fragments.
2. Fibroblasts and chondroblasts infiltrate the hematoma, forming a soft callus.
3. Osteoblasts build a bone callus of primary bone.
4. The bone callus is remodeled, replacing primary bone with secondary bone.

Differentiate between a simple (closed) fracture and a compound (open) fracture.

A simple/closed fracture occurs with the surrounding skin and tissue remaining intact. A compound/open fracture causes damage beyond the bone, breaking through the skin.

What are the three functional classifications of joints?

1. Synarthrosis: allows no movement between articulating bones (highest stability).
2. Amphiarthrosis: allows small movement and provides high stability.
3. Diarthrosis: freely movable joint (least stability).

What are the three structural classifications of joints?

1. Fibrous joints: no joint space; joined by short collagen fibers.
2. Cartilaginous joints: no joint space; bones joined by cartilage.
3. Synovial joints: contains a fluid-filled joint cavity.

Describe the three types of fibrous joints.

1. Sutures: synarthrotic joints between skull bones that calcify into synostoses with age.
2. Gomphoses: synarthrotic peg-in-socket fibrous joints anchoring teeth in jaw sockets.
3. Syndesmoses: amphiarthrotic joints united by interosseous ligaments/membranes (e.g., radius/ulna or tibia/fibula).

Compare the two types of cartilaginous joints: synchondroses and symphyses.

Synchondroses are joined by hyaline cartilage and permit no motion (e.g., epiphyseal plates, first sternocostal joint). Symphyses are joined by a fibrocartilage pad allowing amphiarthrotic movement (e.g., intervertebral discs, pubic symphysis).

What are the functions of the two layers of the articular capsule in a synovial joint?

The outer layer keeps bones from pulling apart and isolates the joint cavity from surrounding blood vessels and tissue. The inner layer (synovial membrane) secretes synovial fluid and supplies oxygen and nutrients to the joint.

What are the three key functions of synovial fluid?

1. Lubrication: reduces friction during movement.
2. Metabolic functions: supplies nutrients and removes waste for avascular joint structures.
3. Shock absorption: evenly distributes mechanical forces across the joint.

What are bursae and tendon sheaths?

Bursae are synovial fluid-filled sacs lined by synovial membranes that minimize friction in high-stress areas. Tendon sheaths are elongated bursae that wrap around long tendons crossing high-stress joints.

Define osteoarthritis, rheumatoid arthritis, and gouty arthritis.

• Osteoarthritis: "wear and tear" arthritis causing breakdown of articular cartilage; common in individuals over $65$.
• Rheumatoid arthritis: autoimmune disease where the immune system attacks articular cartilage and joint tissue; common onset between $30$ and $50$ years of age.
• Gouty arthritis: joint inflammation caused by uric acid crystal deposits in joint tissue (commonly affecting the first metatarsophalangeal joint).

What are the four functional motion classes of synovial joints?

1. Nonaxial: allows motion in planes without moving around an axis.
2. Uniaxial: allows motion around one axis.
3. Biaxial: allows motion around two axes.
4. Multiaxial (Triaxial): allows motion around three axes.

Define flexion, extension, and hyperextension.

• Flexion: decreases the angle between articulating bones.
• Extension: increases the angle between articulating bones.
• Hyperextension: movement beyond the anatomical position of the joint.

Define abduction, adduction, and circumduction.

• Abduction: movement of a body part away from the midline.
• Adduction: movement of a body part toward the midline.
• Circumduction: cone-shaped movement where the distal bone moves while the proximal end remains stationary.

Differentiate between dorsiflexion/plantar flexion and inversion/eversion.

• Dorsiflexion: lifting foot upward so angle between foot and tibia decreases.
• Plantar flexion: pointing foot downward so angle between foot and tibia increases.
• Inversion: rotating sole of foot inward toward midline.
• Eversion: rotating sole of foot outward away from midline.

What articulations and extrinsic ligaments form the elbow joint?

Articulations: humeroulnar joint and humeroradial joint. Extrinsic ligaments: radial collateral ligament, ulnar collateral ligament, and anular ligament.

What internal and external structures stabilize the knee joint?

• Fibrocartilage pads: medial meniscus and lateral meniscus.
• Extrinsic collateral ligaments: tibial (medial) collateral ligament and fibular (lateral) collateral ligament.
• Intracapsular ligaments: anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL).

What constitutes the "unhappy triad" knee injury?

Concurrent damage to the tibial collateral ligament, medial meniscus, and anterior cruciate ligament (ACL).

What structures reinforce the glenohumeral (shoulder) joint capsule?

Biceps brachii muscle tendon, coracohumeral ligament, three glenohumeral ligaments, subacromial bursa, and subscapular bursa.

What ligaments support the coxal (hip) joint?

Iliofemoral ligament, ischiofemoral ligament, pubofemoral ligament, ligament of the head of the femur, and retinacular fibers.

What is the difference between total hip replacement surgery and partial hip replacement surgery?

Total hip replacement replaces both the head of the femur with a metal implant and reconstructs the acetabulum. Partial hip replacement replaces only the head of the femur with a prosthesis, leaving the acetabulum intact.