All flashcards
Flashcard 1: What structure runs perpendicular to Haversian canals to connect osteons?
Answer: Volkmann canals (perforating canals). Volkmann canals facilitate nutrient and waste exchange by linking Haversian systems transversely.
Flashcard 2: What are canaliculi in compact bone?
Answer: Channels connecting lacunae for nutrient and signal exchange. Canaliculi enable osteocytes to communicate and exchange nutrients despite being encased in bone.
Flashcard 3: What is the key structural difference between compact and spongy bone?
Answer: Compact: osteons; spongy: trabeculae with marrow spaces. Compact bone's dense osteons provide strength, while spongy bone's trabeculae offer lightness and marrow space.
Flashcard 4: What is the primary inorganic mineral in bone matrix?
Answer: Hydroxyapatite (calcium phosphate). Hydroxyapatite crystals provide compressive strength and rigidity to the bone matrix.
Flashcard 5: What are the four major bone cell types and their primary roles?
Answer: Osteoblast build; osteoclast resorb; osteocyte maintain; progenitor form. These cells collaborate in bone formation, resorption, maintenance, and regeneration to ensure skeletal integrity and remodeling.
Flashcard 6: What are lacunae in bone tissue?
Answer: Small cavities that house osteocytes. Lacunae embed osteocytes within the mineralized matrix, allowing them to sense mechanical stress.
Flashcard 7: What is the primary organic component of bone matrix?
Answer: Type I collagen (osteoid). Type I collagen forms the flexible organic framework that is mineralized to create bone tissue.
Flashcard 8: What is an osteon (Haversian system) in compact bone?
Answer: Concentric lamellae around a central (Haversian) canal. Osteons form the structural units of compact bone, providing strength and housing vascular channels.
Flashcard 9: What is the functional significance of trabeculae in spongy bone?
Answer: Reduce weight and align along lines of stress. Trabeculae optimize bone's strength-to-weight ratio by aligning with mechanical forces per Wolff's law.
Flashcard 10: What is the periosteum and what is its key function?
Answer: Outer fibrous covering; anchors tendons/ligaments and supports growth/repair. The periosteum nourishes bone via blood vessels and houses progenitor cells for repair and growth.
Flashcard 11: What is the endosteum and where is it located?
Answer: Cellular lining of medullary cavity and trabecular surfaces. The endosteum contains osteoprogenitor cells essential for bone remodeling and repair.
Flashcard 12: What is the medullary cavity and what does it typically contain in adults?
Answer: Central cavity of long bone; usually yellow (fatty) marrow in adults. The medullary cavity stores adipose tissue, serving as an energy reserve in adult long bones.
Flashcard 13: What is the difference between red marrow and yellow marrow?
Answer: Red: hematopoiesis; yellow: fat storage (can revert to red if needed). Red marrow produces blood cells, while yellow marrow stores fat but can convert for increased hematopoiesis.
Flashcard 14: What are the main functions of the skeletal system tested on the MCAT?
Answer: Support, protection, movement, mineral storage, hematopoiesis. The skeletal system provides structural support, protects organs, enables mobility, stores minerals, and produces blood cells.
Flashcard 15: What is intramembranous ossification and which bones primarily use it?
Answer: Bone forms from mesenchyme; flat bones (skull, clavicle). Intramembranous ossification directly converts mesenchymal tissue to bone, typical for flat bones like the skull.
Flashcard 16: What is endochondral ossification and which bones primarily use it?
Answer: Bone replaces cartilage model; long bones. Endochondral ossification uses a cartilage template replaced by bone, enabling longitudinal growth in long bones.
Flashcard 17: What is the epiphyseal (growth) plate and what happens to it after puberty?
Answer: Hyaline cartilage growth zone; closes to epiphyseal line. The epiphyseal plate facilitates bone lengthening through chondrocyte proliferation until fusing post-puberty.
Flashcard 18: What are the two main hormones that directly regulate blood calcium homeostasis?
Answer: Parathyroid hormone (PTH) and calcitonin. PTH and calcitonin maintain calcium balance by opposing effects on bone, kidney, and intestine.
Flashcard 19: Which option best describes the net effect of PTH on serum Ca2+?
Answer: Increases serum Ca2+. PTH elevates blood calcium by promoting bone resorption, renal reabsorption, and vitamin D activation.
Flashcard 20: Which option best describes the net effect of calcitonin on serum Ca2+?
Answer: Decreases serum Ca2+. Calcitonin lowers blood calcium by inhibiting osteoclast activity and enhancing renal excretion.
Flashcard 21: What is the net renal effect of PTH on phosphate reabsorption?
Answer: Decreases phosphate reabsorption (increases phosphate excretion). PTH promotes phosphaturia to balance calcium mobilization and prevent precipitation in tissues.
Flashcard 22: What is the active form of vitamin D that increases intestinal calcium absorption?
Answer: Calcitriol (1,25-dihydroxyvitamin D). Calcitriol, activated in the kidney, enhances intestinal uptake of calcium and phosphate for homeostasis.
Flashcard 23: Identify the bone remodeling cell activated by RANKL signaling from osteoblast lineage cells.
Answer: Osteoclast (via RANK activation on osteoclast precursors). RANKL from osteoblasts binds RANK to differentiate precursors into mature osteoclasts for resorption.
Flashcard 24: Which option best describes the net effect of mechanical loading on bone mass?
Answer: Increases bone formation and bone density (Wolff law). Mechanical stress stimulates osteoblast activity, leading to bone adaptation and increased density per Wolff's law.
Flashcard 25: What is the primary mineral reservoir function of bone in homeostasis?
Answer: Storage and release of Ca2+ and phosphate as needed. Bone acts as a dynamic reservoir, mobilizing minerals via hormonal regulation to maintain blood levels.