What are the five main functions of the skeletal system?	Support, protection of organs, movement (with muscles), mineral storage (calcium/phosphorus), and blood cell production (hematopoiesis).
What are the four bone classifications by shape?	Long (femur), short (carpals), flat (sternum), and irregular (vertebrae). Some sources add sesamoid (patella).
What is the difference between compact and spongy bone?	Compact bone is dense, forming the outer shell (cortex) for strength. Spongy (cancellous) bone has a trabecular lattice, found at bone ends, housing red marrow.
What is an osteon (Haversian system)?	The structural unit of compact bone: concentric lamellae of bone matrix surrounding a central (Haversian) canal containing blood vessels and nerves.
What are the roles of osteoblasts, osteocytes, and osteoclasts?	Osteoblasts build new bone matrix, osteocytes maintain bone tissue, and osteoclasts resorb (break down) bone.
What is the periosteum?	A tough connective tissue membrane covering the outer surface of bone. It anchors tendons and ligaments and supplies blood for bone repair and growth.
What is the endosteum?	A thin membrane lining the medullary cavity and trabecular surfaces of spongy bone. It contains osteoblasts and osteoclasts for remodeling.
Name the two divisions of the skeleton and their bone counts.	Axial skeleton (80 bones): skull, vertebral column, ribs, sternum. Appendicular skeleton (126 bones): limbs, pectoral girdle, pelvic girdle.
How many vertebrae are in each region of the spinal column?	Cervical 7, thoracic 12, lumbar 5, sacral 5 (fused), coccygeal 4 (fused). Total: 33 vertebrae, 26 individual bones.
What is the epiphyseal plate and why is it important?	A cartilage growth plate near the ends of long bones where longitudinal bone growth occurs. It ossifies into the epiphyseal line when growth is complete.
What are the three types of cartilage in the body?	Hyaline (joint surfaces, trachea), elastic (ear, epiglottis), and fibrocartilage (intervertebral discs, menisci).
What is articular cartilage?	A thin layer of hyaline cartilage covering the ends of bones at synovial joints. It reduces friction and absorbs shock during movement.
What are the three structural classifications of joints?	Fibrous (sutures, no movement), cartilaginous (symphyses, limited movement), and synovial (freely movable, with a joint cavity).
Name four types of synovial joints and give an example of each.	Hinge (elbow), ball-and-socket (hip), pivot (atlas-axis), and condyloid (wrist). Others include saddle (thumb) and gliding (intercarpal).
What is the function of synovial fluid?	Lubricates joint surfaces, reduces friction, nourishes articular cartilage, and absorbs shock within synovial joints.
What is bone remodeling?	A continuous process in which osteoclasts resorb old bone and osteoblasts deposit new bone, allowing the skeleton to adapt to stress and maintain calcium homeostasis.
How does Wolff's law relate to bone structure?	Wolff's law states that bone remodels in response to mechanical stress, becoming thicker and stronger along lines of force.
What hormones regulate bone growth and remodeling?	Parathyroid hormone (stimulates osteoclasts, raises blood Ca2+), calcitonin (inhibits osteoclasts, lowers blood Ca2+), and growth hormone/sex hormones during development.
What is the medullary cavity and what does it contain?	The hollow center of the diaphysis (shaft) of long bones. It contains yellow marrow (fat) in adults; red marrow fills it in children.
Where is red bone marrow found in adults?	In the spongy bone of flat bones (sternum, pelvis, skull) and the proximal epiphyses of the humerus and femur. It produces blood cells.
What is the difference between a ligament and a tendon?	Ligaments connect bone to bone, stabilizing joints. Tendons connect muscle to bone, transmitting force for movement.