Module 8: Bone Health and Remodeling

Comprehensive vocabulary flashcards covering bone remodeling, mineral metabolism, hormonal regulation, diagnostic metrics, and osteoporosis from Module 8: Bone Health.

Wolff’s Law

The physiological principle stating that bones develop a structure that is best able to resist the physical forces acting upon them, meaning exercise and strength training increase bone strength.

Bone Remodeling

The ongoing physiological process where bone tissue is systematically broken down and subsequently rebuilt at the exact same location, renewing approximately $10\%$ of adult bone tissue annually.

Osteoblasts

Specialized bone-building cells that synthesize and deposit new unmineralized osteoid tissue, including collagen fibers.

Osteoclasts

Large bone-degrading cells that break down bone tissue by secreting hydrogen ions to acidify the local environment and dissolve minerals in the bone matrix.

Osteocytes

Star-shaped cells that are the most abundant cell type in mature bone tissue, responsible for exchanging nutrients and signaling factors between bone, blood, and lymph.

Resorption

The initial stage of bone remodeling where osteoclasts attach to the bone surface, acidify the microenvironment using hydrogen ions, and dissolve the mineralized matrix.

Reversal

The remodeling phase where sugars and proteins accumulate along the eroded bone surface to form a cement line, and osteoblasts begin to form and increase in number.

Cement Line

A cohesive layer of sugars and proteins deposited during the reversal stage that creates a strong adhesive bond between pre-existing old bone and newly synthesized bone tissue.

Formation (Bone Remodeling)

The bone remodeling phase during which osteoblasts actively synthesize and lay down new osteoid tissue, such as unmineralized collagen.

Mineralization

The prolonged bone remodeling phase lasting several months during which calcium and phosphate salts crystallize into the osteoid matrix and pack densely.

Hydroxyapatite

The crystallized mineral salt compound composed of calcium and phosphorus that incorporates into bone osteoid to increase bone mineral density and compressive strength.

Tetany

A condition characterized by involuntary muscle stiffness and twitching that occurs when extracellular blood calcium levels fall abnormally low.

Parathyroid Hormone (PTH)

A hormone released by the parathyroid glands that increases blood calcium levels by stimulating calcium release from bones, decreasing kidney excretion, and activating calcidiol into calcitriol.

Calcitriol

The bioactive hormonal form of vitamin D that cooperates with parathyroid hormone ($\text{PTH}$) to increase intestinal calcium absorption and limit calcium excretion in the urine.

Calcitonin

A hormone released by the thyroid gland that lowers elevated blood calcium levels by inhibiting osteoclastic bone breakdown, promoting renal calcium excretion, and reducing absorption.

Calcium Bioavailability

The degree to which dietary calcium is absorbed into circulation; increased by stomach acid, estrogen, and vitamin D, and decreased by phytates, oxalates, high-fiber intake, and aging.

Calcium Absorption Threshold

The physiological capacity limit of the human gastrointestinal tract, which can effectively process approximately $500\,\text{mg}$ of elemental calcium in a single dose.

Rickets

A pediatric skeletal disorder caused by vitamin D deficiency that leads to poorly mineralized, soft, weak bones prone to bowing and fractures.

Osteomalacia

An adult skeletal disease resulting from a deficiency in vitamin D that causes defective bone mineralization and painful softening and weakening of the skeleton.

Peak Bone Mass

The maximum amount of bone density and mineral mass accumulated across a lifetime, typically achieved around age $30$ before age-related bone loss begins around age $40$.

Bone Mineral Density (BMD)

A clinical measure of bone strength and fracture risk that quantifies the total mass of calcified bone tissue in grams per square centimeter ($\text{g/cm}^2$).

Dual X-ray Absorptiometry (DEXA)

An imaging modality used to accurately evaluate bone mineral density and compute a standardized T-score to screen for osteopenia and osteoporosis.

T-score

A standardized clinical score derived from DEXA: $-1.0$ or above is normal, $-1.0$ to $-2.5$ represents osteopenia (low BMD), and $-2.5$ or below confirms osteoporosis.

Osteopenia

A condition characterized by moderately low bone mass (DEXA T-score between $-1.0$ and $-2.5$), often serving as an early clinical precursor to osteoporosis.

Osteoporosis

A progressive skeletal disorder characterized by excessive bone loss over time, deteriorated bone microarchitecture, and heightened susceptibility to fractures.

Type 1 Osteoporosis (Postmenopausal)

A subtype of osteoporosis occurring between ages $50$ and $70$ driven by postmenopausal estrogen decline, primarily causing trabecular bone loss in the wrist and spine.

Type 2 Osteoporosis (Senile)

Age-related osteoporosis occurring in adults older than $70$ years, being twice as common in females and primarily predisposing individuals to hip and spinal fractures.

Osteocalcin

A bone matrix protein modified by vitamin K that regulates bone mineral crystallization and participates in continuous bone remodeling.

Fluoride

A trace mineral that promotes bone and tooth development while preventing cavities by inhibiting bacterial acid formation, reducing demineralization, and stimulating enamel remineralization.

Glucocorticoids

A class of steroid medications identified as a non-modifiable risk factor for secondary osteoporosis due to their mechanism of stimulating bone resorption.

Primary Prevention (Osteoporosis)

Proactive interventions implemented prior to disease onset to build bone reserve, focusing on optimizing peak bone mass during puberty through nutrition, physical exercise, and fall prevention.

Secondary Prevention (Osteoporosis)

Clinical, pharmacological, and lifestyle strategies designed to halt or reverse progression in individuals with established low bone mass to prevent subsequent fractures.