HESI A2 - Skeletal System - Key Terms and Concepts

Compact bone

Dense bone tissue that provides strength and protection for the skeletal system.

Spongy bone

Porous bone tissue that contains red bone marrow and helps reduce bone weight.

Osteon

Composed of concentric rings of bone tissue encircling a central channel, the basic building block of compact bone.

Haversian canal

A central channel within an osteon that contains blood vessels and nerves supplying the bone.

Volkmann’s canal

A channel that runs perpendicular to Haversian canals, connecting blood vessels and nerves between osteons.

Periosteum

A dense fibrous membrane covering the outer surface of bones, providing attachment for muscles and ligaments.

Endosteum

A thin membrane lining the inner surface of bones, involved in bone growth and remodeling.

Bone marrow

The soft tissue found within bones that stores fat and produces blood cells.

Trabeculae

A network of bony struts within spongy bone that provides support and houses marrow.

Lacuna

A small cavity within bone tissue that contains an osteocyte.

Osteoprogenitor cell

A stem cell that differentiates into osteoblasts during bone development and repair.

Bone remodeling

The ongoing process of bone production and resorption that preserves mineral balance and bone strength.

Epiphyseal plate

A cartilage layer located near the ends of long bones where bone growth takes place during developmental years.

Epiphyseal line

The remnant of the epiphyseal plate that signifies the completion of bone growth.

Intramembranous ossification

The process of bone development from connective tissue, primarily forming flat bones.

Endochondral ossification

The process in which bone forms by replacing cartilage, responsible for the development of long bones.

Wolff’s law

A principle stating that bone grows and remodels in response to mechanical stress.

Calcification

The deposition of calcium salts in bone tissue makes it hard and durable.

Resorption

The breakdown of bone tissue by osteoclasts, which releases minerals into the blood.

Mineralization

The incorporation of minerals like calcium and phosphate into bone tissue to enhance strength.

Long bone

A bone that is longer than it is wide and primarily functions in movement and support.

Short bone

A bone that is nearly equal in length and width, providing stability and absorbing shock.

Flat bone

A thin, broad bone that protects internal organs and provides surface area for muscle attachment.

Irregular bone

A bone with a complex shape that does not fit into other categories, providing support and protection.

Sesamoid bone

A small, rounded bone embedded in tendons that changes pressure distribution and reduces friction.

Diaphysis

The shaft of a long bone that provides leverage and structural support.

Epiphysis

The end portion of a long bone that contains spongy bone and articulates with other bones.

Metaphysis

The growth plate of developing bones is located in the space between the diaphysis and epiphysis.

Medullary cavity

The internal hollow space within the shaft of a long bone that stores bone marrow.

Articular cartilage

A slick, cushioning cartilage that covers the ends of bones at joints, minimizing friction and absorbing impact.

Joint capsule

A fibrous structure that encloses a synovial joint, providing stability and containing synovial fluid.

Synovial fluid

A lubricant within synovial joints that reduces friction between bones.

Ligament

A robust strip of connective tissue that stabilizes joints and joins bones.

Tendon

A fibrous tissue that attaches muscle to bone and facilitates movement.

Fibrous joint

A type of joint where bones are joined by tough connective tissue, offering little to no flexibility.

Cartilaginous joint

A joint where bones are connected by cartilage, providing slight flexibility.

Synovial joint

A type of joint surrounded by a fluid-filled capsule that allows for a wide range of motion.

Ball-and-socket joint

A highly mobile joint where a rounded bone end fits into a cup-like socket, enabling movement in several directions (e.g., shoulder or hip).

Hinge joint

A joint, like the knee and elbow, that permits movement in a single plane.

Pivot joint

A joint that allows rotational movement, such as the joint between the atlas and axis in the neck.

Axial skeleton

The central framework of the body, consisting of the skull, vertebral column, and rib cage.

Appendicular skeleton

Movement-enabling portion of the skeleton that contains the limbs and girdles.

Bone density

The measurement of mineral content in bone, indicating strength and risk of fracture.

Osteoporosis

A disorder that causes a reduction in bone density, which makes bones brittle and increases the chance of fractures.

Osteomalacia

A condition in which bones soften due to vitamin D deficiency and inadequate mineralization.

Rickets

A childhood disorder caused by vitamin D deficiency, resulting in soft and deformed bones.

Fracture

A break or crack in a bone brought on by trauma or underlying diseases that impair bone integrity.

Greenstick fracture

A type of incomplete fracture where one side of the bone bends while the other side breaks.

Comminuted fracture

An injury where the bone breaks into several pieces.

Callus formation

The process in which a temporary bony structure forms around a fracture site to aid healing.

Knee joint

It is known as the largest joint in the body and is reinforced by multiple ligaments for strength and stability.

Shoulder joint

It is a ball-and-socket joint that delivers the most pronounced range of motion in the body.

Hip joint

A ball-and-socket joint that connects the femur to the pelvis, allowing a wide range of movement while being stabilized by strong ligaments.

Elbow joint

A hinge joint that enables the humerus to connect with the ulna and radius, allowing the forearm to flex and extend.

Upper limbs

The functional upper extremity of the body, which consists of the humerus, ulna, radius, carpals, metacarpals, and phalanges.

Lower limbs

The lower extremities, including the femur, patella, tibia, fibula, and foot bones, support the body’s weight and enable movement.

True ribs

The first seven pairs of ribs, whose costal cartilages directly connect to the sternum, forming a rigid attachment to the thoracic cavity.

False ribs

The lower five pairs of ribs, whose costal cartilages do not directly attach to the sternum but connect through the cartilage of the seventh rib.

Number of vertebrae

The vertebral column consists of 7 cervical, 12 thoracic, 5 lumbar, 5 fused sacral, and 4 coccygeal vertebrae.

Number of skull bones

The skull consists of 14 facial bones, 8 cranial bones, and 6 paired bones of the ear (ossicles).

Hyoid bone

The only bone in the body that is not directly connected to any other bone, suspended by ligaments in the neck.

Calcitonin

A hormone that helps regulate calcium levels in the blood by inhibiting bone resorption and promoting calcium deposit in bones.

Parathyroid hormone

A hormone that plays a crucial role in maintaining calcium homeostasis by stimulating osteoclast activity to increase bone resorption when calcium levels are low.

Osteogenic stem cell

A type of stem cell that differentiates into osteoblasts, which are responsible for bone formation.

Types of specialized bone cells

1. Osteoclasts

2. Osteoblasts

3. Osteocytes

Osteoblasts

Cells that synthesize and secrete the extracellular matrix for bone formation and mineralization.

Osteoclasts

Large, multinucleated cells that break down bone tissue during the process of bone resorption.

Osteocytes

These are mature bone cells that reside within the mineralized matrix of bone tissue, playing a crucial role in regulating bone maintenance and the metabolism of minerals.

Femur

The longest bone in the human body, which supports the upper body's weight.