Bone Tissue: Structure, Growth, Remodeling & Homeostasis

Vocabulary practice flashcards reviewing osseous tissue anatomy, cellular physiology, ossification, mineral regulation, bone remodeling, and skeletal pathologies.

Osteology

The scientific study of bone tissue and the skeletal system.

Osseous Tissue

A hard, dense connective tissue with a matrix hardened by calcium phosphate and other minerals that constitutes most of the adult skeleton.

Mineralization (Calcification)

The hardening process of bone matrix through the deposition of calcium phosphate, calcium carbonate, and other mineral salts.

Diaphysis

The elongated shaft of a long bone that provides leverage for movement.

Epiphysis

The expanded head located at each end of a long bone that strengthens the joint and offers attachment surface area for ligaments and tendons.

Epiphyseal Plate

A layer of hyaline cartilage located between the diaphysis and epiphysis of an immature long bone that functions as the growth zone for elongation.

Articular Cartilage

A layer of hyaline cartilage covering the joint surface of an epiphysis that lubricates movement and reduces friction where two bones articulate.

Periosteum

A tough external sheath of bone consisting of an outer fibrous layer of collagen and an inner osteogenic layer containing bone-forming cells.

Endosteum

A thin layer of reticular connective tissue lining the medullary cavity, covering trabeculae of spongy bone, and lining the central and perforating canals.

Diploë

The spongy bone layer sandwiched between the dense compact bone layers (inner and outer tables) of flat cranial bones.

Nutrient Foramina

Minute openings on the bone surface through which blood vessels penetrate to supply internal bone tissues.

Osteogenic Cells

Stem cells originating from embryonic mesenchyme, located in the endosteum and inner periosteum, that continually divide to give rise to osteoblasts.

Osteoblasts

Cuboidal, non-mitotic bone cells that synthesize osteoid, promote matrix calcification, and secrete the hormone osteocalcin.

Osteocytes

Mature bone cells residing inside lacunae that comprise $90\%$ to $95\%$ of all bone cells, connected through canaliculi, and acting as strain sensors (mechanosensors).

Osteoclasts

Large, multinucleated cells developed from hematopoietic stem cells that possess a ruffled border and dissolve bone matrix inside resorption bays.

Osteocalcin

A hormone produced by osteoblasts and osteocytes that stimulates pancreatic insulin release, enhances adipocyte insulin sensitivity, and moderates the body's stress response.

Hydroxyapatite

A crystallized calcium phosphate salt with the chemical formula $\text{Ca}_{10}(\text{PO}_4)_6(\text{OH})_2$, composing about $85\%$ of the inorganic matrix of osseous tissue.

Osteon (Haversian System)

The cylindrical, structural unit of compact bone composed of concentric lamellae of calcified matrix surrounding a central canal.

Concentric Lamellae

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

Canaliculi

Microscopic channels traversing bone matrix that connect lacunae to each other and to the central canal, permitting passage of nutrients and cellular signals.

Perforating (Volkmann's) Canals

Transverse or diagonal vascular channels that connect central Haversian canals to the periosteum and endosteum at right angles.

Trabeculae

A lattice-like network of thin plates and rods found in spongy (cancellous) bone aligned along lines of mechanical stress, devoid of osteons.

Red Bone Marrow (Myeloid Tissue)

Hematopoietic tissue filling spongy bone spaces and marrow cavities that produces red blood cells, white blood cells, and platelets.

Yellow Bone Marrow

Fat-storing adipose tissue that occupies the medullary cavity of adult long bones and can revert to red marrow during chronic anemia.

Intramembranous Ossification

The mode of bone formation where osseous tissue develops directly within embryonic mesenchyme without a prior cartilage stage, creating flat bones of the skull and clavicles.

Endochondral Ossification

The process of bone development in which an embryonic hyaline cartilage model is gradually broken down and replaced by osseous tissue.

Interstitial Growth

Cartilage growth from within via the multiplication of chondrocytes and secretion of internal matrix, responsible for bone elongation at the epiphyseal plate.

Appositional Growth

The growth process by which bone increases in diameter and wall thickness via deposition of osteoid by periosteal osteoblasts on the outer surface.

Wolff's Law of Bone

The architectural principle stating that the architecture and density of a bone adapt directly to withstand the mechanical loads and stresses imposed upon it.

Achondroplastic Dwarfism

A form of disproportionate dwarfism caused by a dominant mutation in the FGFR3 gene that causes failure of cartilage growth in the metaphysis of long bones.

Pituitary Dwarfism

A form of proportionate dwarfism characterized by reduced growth of all bone and cartilage tissue due to a deficiency in growth hormone from the anterior pituitary.

Ectopic Ossification

The abnormal formation and calcification of osseous tissue in soft tissues and organs such as the lungs, brain, eyes, muscles, or arteries.

Calculus

A calcified, mineralized deposit or stone that develops within an otherwise soft organ, such as the kidney.

Hypocalcemia

A deficiency of calcium in the blood below $9.2\,\text{mg/dL}$ that causes excessive nervous excitability, muscle spasms, tremors, and potentially fatal laryngeal tetany.

Hypercalcemia

An excessive concentration of calcium in the blood above $10.4\,\text{mg/dL}$ that depresses neural and muscular excitability, leading to muscle weakness, sluggish reflexes, and cardiac arrest.

Calcitriol

The most active form of vitamin D ($1,25\text{-dihydroxyvitamin D}$) produced by the skin, liver, and kidneys that acts hormonally to raise blood calcium and phosphate levels.

Parathyroid Hormone (PTH)

A peptide hormone secreted by the parathyroid glands in response to low blood calcium that stimulates osteoclast resorption, promotes renal calcium conservation, and activates calcitriol synthesis.

Calcitonin

A hormone secreted by parafollicular (C) cells of the thyroid gland during hypercalcemia that lowers blood calcium by inhibiting osteoclasts and stimulating osteoblasts.

Rickets

A childhood bone-softening disorder caused by vitamin D and calcium deficiency, characterized by defective matrix mineralization, bone pain, pelvic deformities, and bowed legs.

Osteomalacia

An adult form of vitamin D deficiency causing bone softening, lumbar aching, muscle weakness, spinal deformity, and an elevated risk of pathological fractures.

Osteoporosis

The most prevalent bone disease, characterized by severe loss of bone mass and density across both compact and trabecular bone, predisposing patients to pathological fractures and kyphosis.

Osteogenesis Imperfecta

A genetic disorder, also known as brittle bone disease, resulting from a defect in type I collagen synthesis that leads to fragile bones, multiple fractures, hearing loss, and blue sclera.

Stress Fracture

A bone fracture caused by abnormal trauma or excessive physical forces, such as those sustained during sports, falls, or automobile collisions.

Pathological Fracture

A break occurring in a bone that has been structurally compromised and weakened by an underlying condition, such as osteoporosis or cancer, under normal physiological loads.

Comminuted Fracture

A bone fracture in which the bone breaks or splinters into three or more distinct pieces.

Greenstick Fracture

A partial fracture common in children in which the bone breaks along one cortical side while merely bending on the opposite cortex.

Hard Callus

A temporary bony collar formed by osteoblasts around a healing bone fracture within $4\text{ to }6\,\text{weeks}$ to unite broken fragments before complete remodeling occurs.