BIO 161 — Exam 3 Study Guide: Skeletal System and Joints

Comprehensive vocabulary flashcards covering skeletal anatomy, bone histology, bone formation and remodeling, calcium regulation, joint classifications, synovial joint architecture, and the anatomical structures of the shoulder, hip, and knee joints for BIO 161 Exam 3.

Long bone

A bone that is longer than it is wide (e.g., femur, tibia, humerus).

Short bone

A small, cube-like bone (e.g., carpals, tarsals).

Flat bone

A thin, flattened bone that often provides protective surfaces (e.g., sternum, skull, scapula).

Irregular bone

A bone with a complicated or odd shape (e.g., vertebrae).

Sesamoid bone

A small bone embedded within a tendon (e.g., patella).

Proximal epiphysis

The expanded end of a long bone located closer to the trunk of the body.

Diaphysis

The long, tubular middle shaft of a long bone.

Distal epiphysis

The expanded end of a long bone located farther from the trunk of the body.

Articular cartilage

Smooth layer covering the ends of bones at joints that reduces friction during movement.

Periosteum

Tough, fibrous membrane forming the outer covering of a bone.

Compact bone

Dense, hard bone tissue that forms the sturdy outer shell of bones and is organized into osteons.

Spongy bone

Porous, lightweight bone tissue containing open spaces between bony struts called trabeculae.

Trabeculae

Thin, branching bony struts that make up the latticework of spongy bone.

Medullary cavity

The hollow space within the diaphysis (shaft) of a long bone, lined by endosteum.

Yellow bone marrow

Fat-storing tissue found primarily within the medullary cavity of adult long bones.

Red bone marrow

Vascular tissue found within the spaces of spongy bone that produces blood cells.

Epiphyseal plate

A layer of hyaline cartilage located between the epiphysis and diaphysis where a long bone grows in length (growth plate).

Osteon

The fundamental cylindrical structural unit of compact bone, also known as a Haversian system.

Central canal

A longitudinal channel running through the center of an osteon that houses blood vessels and nerves.

Perforating canal

A transverse channel (Volkmann's canal) that carries blood vessels and nerves horizontally, connecting central canals to each other and to the periosteum.

Concentric lamellae

Concentric rings or circular layers of calcified bone matrix surrounding the central canal within an osteon.

Lacunae

Small spaces or cavities embedded within the lamellae of bone matrix that house mature osteocytes.

Canaliculi

Tiny, hair-like canals radiating from lacunae that connect them to each other and to the central canal for nutrient and waste exchange.

Osteogenic cell

An undifferentiated stem cell that divides and develops into an osteoblast ('origin cell').

Osteoblast

A bone-building cell that synthesizes and secretes new bone matrix ('blast = builds').

Osteocyte

A mature bone cell trapped within a lacuna that maintains existing bone tissue ('cyte = cell that maintains').

Osteoclast

A large multinucleated cell that resorbs and breaks down bone matrix ('clast = crushes').

Intramembranous ossification

The process of bone development directly from mesenchymal connective tissue, producing flat bones such as skull bones and clavicles.

Endochondral ossification

The process of bone development in which a pre-existing hyaline cartilage model is broken down and replaced by bone tissue, forming most bones including long bones.

Resting zone

The zone of the epiphyseal plate closest to the epiphysis where cartilage cells are relatively inactive.

Proliferation zone

The zone of the epiphyseal plate where chondrocytes (cartilage cells) rapidly divide and multiply.

Hypertrophic zone

The zone of the epiphyseal plate where older cartilage cells enlarge significantly.

Calcification/ossification zone

The zone of the epiphyseal plate where the cartilage matrix hardens, chondrocytes die, and osteoblasts replace the matrix with new bone.

Bone remodeling

The continuous cyclical process wherein old bone is resorbed by osteoclasts and new bone matrix is deposited by osteoblasts.

Hematoma formation

The initial stage of fracture healing during which broken blood vessels hemorrhage and blood clots around the fracture site.

Soft callus (fibrocartilaginous callus)

The second stage of fracture healing characterized by the formation of a temporary collagenous and cartilaginous bridge across the fracture gap.

Hard callus (bony callus)

The third stage of fracture healing where the soft fibrocartilaginous callus is replaced by trabecular/spongy bone.

Parathyroid hormone (PTH)

A hormone released by the parathyroid glands when blood $Ca^{2+}$ is low that raises blood calcium by stimulating osteoclasts, reducing urinary calcium excretion, and activating vitamin D.

Calcitonin

A hormone released by the thyroid gland when blood $Ca^{2+}$ is high that lowers blood calcium by inhibiting bone breakdown and promoting calcium excretion in urine.

Fibrous joint

A joint where adjacent bones are held together by dense connective tissue with no joint cavity (e.g., skull sutures).

Cartilaginous joint

A joint where articulating bones are united by cartilage with no joint cavity (e.g., pubic symphysis).

Synovial joint

A freely movable joint characterized by a fluid-filled joint cavity separating the articulating bones (e.g., knee, shoulder, hip).

Synarthrosis

A functional classification for an immovable joint that allows no movement (e.g., skull sutures).

Amphiarthrosis

A functional classification for a joint that allows slight movement (e.g., intervertebral joints between vertebrae).

Diarthrosis

A functional classification for a freely movable joint (e.g., knee or shoulder).

Synovial fluid

A viscous, lubricating fluid contained within the synovial cavity that reduces friction between joint surfaces.

Articular capsule

A double-layered sleeve-like structure surrounding and enclosing the synovial joint cavity, consisting of an outer fibrous capsule and an inner synovial membrane.

Synovial membrane

The inner vascular lining of the articular capsule that produces and secretes synovial fluid.

Fibrous capsule

The tough, dense outer layer of the articular capsule that strengthens the joint.

Bursae

Small, fluid-filled sacs lined by synovial membrane that cushion and alleviate friction between tendons, ligaments, and bones.

Ligament

A band of dense fibrous regular connective tissue that connects bone to bone.

Tendon

A band of dense fibrous regular connective tissue that connects muscle to bone.

Plane joint (gliding joint)

A synovial joint with flat articulating surfaces that allow bones to slide past each other (e.g., intercarpal joints).

Hinge joint

A uniaxial synovial joint that permits bending and straightening movements in a single plane (e.g., elbow, knee).

Pivot joint

A uniaxial synovial joint that permits rotational movement around a central axis (e.g., atlas-axis joint in the neck).

Condyloid joint

A biaxial synovial joint that allows movement in two directions without rotation (e.g., knuckles).

Saddle joint

A biaxial synovial joint where both articulating bones have complementary concave and convex surfaces, permitting movement in two directions with greater range (e.g., thumb joint).

Ball-and-socket joint

A multiaxial synovial joint where a spherical head fits into a rounded cup, permitting movement in many directions including rotation (e.g., shoulder, hip).

Glenoid cavity

A shallow socket on the lateral angle of the scapula that articulates with the head of the humerus.

Glenoid labrum

A fibrocartilaginous rim attached to the margin of the glenoid cavity that deepens the shoulder socket.

Acetabulum

The deep, cup-shaped socket on the lateral surface of the pelvis that articulates with the head of the femur.

Acetabular labrum

A fibrocartilaginous lip or rim that encircles and deepens the acetabulum of the hip joint.

Cruciate ligaments (ACL and PCL)

Intracapsular anterior and posterior ligaments that cross inside the knee joint to prevent anterior and posterior displacement of the tibia relative to the femur.

Collateral ligaments (MCL and LCL)

Medial and lateral extracapsular ligaments that stabilize the sides of the knee joint and prevent side-to-side displacement.

Menisci

Crescent-shaped fibrocartilaginous pads (medial and lateral) that cushion, absorb shock, and improve articulation between the femoral condyles and tibial plateau.