Skeleton Parts, Identified - BIO 3202 Unit 4 Bones A

80 vocabulary flashcards covering skeletal system structure, classification of bones, microscopic osseous tissue components, cellular functions, ossification, bone growth, and hormonal regulation.

Axial Skeleton

The portion of the skeleton consisting of the skull, vertebral column, and rib cage that forms the longitudinal axis of the body.

Appendicular Skeleton

The division of the skeleton comprising the upper and lower limb bones and the pelvic and pectoral girdles that attach limbs to the axial skeleton.

Long Bones

Bones that are longer than they are wide, comprising all limb bones except the patella, wrist bones, and ankle bones.

Short Bones

Cube-shaped bones located in the wrist and ankle.

Flat Bones

Thin, flattened, and usually curved bones, including the sternum, scapulae, ribs, and most skull bones.

Irregular Bones

Bones with complex shapes that do not fit into other classification categories, such as vertebrae, hip bones, mandible, and facial bones.

Sesamoid Bones

Special short bones formed within tendons, such as the patella.

Hydroxyapatites

Inorganic mineral salts, primarily calcium phosphate and calcium carbonate, accounting for approximately $\sim 2/3$ of bone tissue mass that resist compression and make bone hard.

Osteoid

The organic bone matrix secreted by osteoblasts, accounting for approximately $\sim 1/3$ of bone mass, composed of collagen that resists tension and provides bone flexibility.

Osteogenesis Imperfecta

A clinical genetic disorder caused by a mutation that reduces the amount of collagen in bone tissue, leading to fragile bones.

Osteogenic Cells

Mitotically active stem cells located in the periosteum and endosteum that differentiate into osteoblasts.

Osteoblasts

Mitotic, bone-forming cells that synthesize and secrete osteoid matrix and osteocalcin before maturing into osteocytes.

Osteocalcin

A protein hormone secreted by osteoblasts that helps regulate glucose metabolism.

Osteocytes

Mature, non-mitotic bone cells that reside inside lacunae to monitor environmental changes, respond to mechanical stimuli, and regulate osteoblast and osteoclast activity.

Osteoclasts

Large, multinucleated bone-resorbing cells derived from hematopoietic stem cells that break down and degrade bone matrix.

Hydrochloric Acid ($\text{HCl}$)

An acidic secretion produced by osteoclasts to dissolve and degrade hydroxyapatites (inorganic mineral salts) in bone.

Cathepsin K

A lysosomal enzyme released by osteoclasts to degrade collagen fibers in the organic bone matrix.

Osteon

The structural unit of compact bone (also called the Haversian system), composed of concentric cylinders aligned along the long axis to act as weight-bearing pillars.

Central Canal

The central channel running through the core of each osteon that contains blood vessels and nerve fibers (also known as the Haversian canal).

Lamellae

Concentric rings of hard, calcified matrix surrounding the central canal of an osteon.

Lacunae

Small microscopic cavities within the bone matrix that house mature osteocytes.

Canaliculi

Microscopic hair-like canals connecting adjacent lacunae to one another and to the central canal, enabling nutrient and waste exchange between osteocytes.

Perforating Canal

Canals running at right angles to long-axis central canals (also known as Volkmann's canals) that deliver blood vessels and nerves from the periosteum to central canals and medullary cavities.

Interstitial Lamellae

Incomplete lamellae filling the gaps between active osteons, representing remnants of osteons partially destroyed during bone remodeling.

Circumferential Lamellae

Layers of bone matrix located immediately deep to the periosteum or superficial to the endosteum that extend around the entire perimeter of the shaft.

Trabeculae

A structural network of tiny supporting beams or struts comprising spongy bone, aligned along lines of stress.

Diploë

The internal layer of spongy bone found sandwiched between inner and outer compact bone plates in flat bones such as the skull.

Diaphysis

The elongated, tubular shaft forming the primary axis of a long bone, consisting of a collar of compact bone surrounding a medullary cavity.

Epiphyses

The expanded terminal ends of a long bone, covered externally by articular cartilage and filled internally with spongy bone tissue.

Metaphysis

The transitional region of a long bone situated between the diaphysis and epiphysis, containing the epiphyseal plate or line.

Epiphyseal Plate

A layer of active hyaline cartilage located at the metaphysis in growing children that enables lengthwise bone elongation (interstitial growth).

Epiphyseal Line

The bony remnant left behind in adult long bones after the epiphyseal plate cartilage completely ossifies and growth in length ceases.

Medullary Cavity

The central hollow space within the diaphysis of a long bone that houses bone marrow.

Articular Cartilage

A smooth layer of hyaline cartilage covering joint surface ends of epiphyses to cushion bones and reduce friction during movement.

Periosteum

A double-layered connective tissue membrane covering the exterior surface of bones, containing an outer fibrous layer and an inner osteogenic layer.

Fibrous Layer of Periosteum

The outer layer of the periosteum composed of dense irregular connective tissue where skeletal muscles and tendons attach.

Osteogenic Layer of Periosteum

The delicate inner layer of periosteum touching the bone surface, populated primarily by osteoblasts and osteoclasts.

Perforating Fibers

Thick collagen bundles (also called Sharpey's fibers) extending from the fibrous periosteum layer into the bone matrix to anchor the membrane firmly to bone.

Endosteum

A delicate internal connective tissue membrane covering trabeculae of spongy bone and lining canals running through compact bone.

Yellow Bone Marrow

Bone marrow filled mainly with adipose tissue (fat cells) that serves as an energy reserve in adult long bones.

Red Bone Marrow

Highly vascularized hematopoietic tissue that actively produces red blood cells, white blood cells, and platelets.

Hematopoiesis

The physiological process of blood cell formation occurring within red bone marrow cavities.

Hematopoietic Stem Cells

Multipotent precursor stem cells in red marrow that give rise to both lymphoid and myeloid blood cell lineages.

Iliac Crest

The superior margin of the ilium bone commonly chosen as a primary anatomical location for bone marrow aspiration biopsies.

Ossification

The developmental process of bone tissue formation (also known as osteogenesis).

Intramembranous Ossification

Bone development occurring directly within a condensation of mesenchymal fibrous connective tissue membranes, producing skull flat bones, parts of the mandible, and clavicles.

Endochondral Ossification

Bone development wherein a pre-existing hyaline cartilage model is broken down and replaced by bone tissue, forming most skeleton bones below the skull.

Primary Ossification Center

The region located in the middle of the hyaline cartilage diaphysis where bone formation begins during endochondral ossification.

Bone Collar

A superficial ring of compact periosteal bone formed around the diaphysis of a cartilage model in early endochondral ossification.

Periosteal Bud

A vascular collection containing blood vessels, nerve fibers, red marrow, osteogenic cells, and osteoclasts that invades calcified cartilage cavities during endochondral ossification.

Secondary Ossification Centers

Centers of bone formation that develop within the epiphyses of long bones around birth or early childhood during endochondral ossification.

Interstitial Growth

Lengthwise elongation of bones caused by growth and division of hyaline chondrocytes within the epiphyseal plate.

Appositional Growth

Diameter or thickness growth of bones caused by new bone matrix deposition beneath the periosteum.

Resting Zone

The region of epiphyseal plate cartilage closest to the epiphysis containing inactive, anchored chondrocytes.

Proliferation Zone

The region of the epiphyseal plate where chondrocytes rapidly divide by mitosis, stacking into columns and pushing the epiphysis away from the diaphysis.

Hypertrophic Zone

The region of the epiphyseal plate where older chondrocytes enlarge significantly, leading to thinning and erosion of matrix walls.

Calcification Zone

The region of the epiphyseal plate where surrounding matrix calcifies, cutting off nutrients and causing chondrocytes to die.

Ossification Zone

The region of the epiphyseal plate closest to the diaphysis where osteoblasts cover calcified cartilage spicules with new osteoid tissue to form early spongy bone.

Epiphyseal Plate Closure

The event near the end of adolescence ($\sim 18$ years old in females, $\sim 21$ years old in males) when epiphyseal cartilage mitosis ceases and epiphyses fuse with the diaphysis.

Growth Hormone (GH)

An anterior pituitary hormone that acts as the primary stimulator of postnatal skeletal growth in children by triggering chondrocyte division and osteoblast activity.

Thyroid Hormone

A metabolic hormone that modulates growth hormone activity to ensure proper proportioning of the skeleton during growth.

Gigantism

A clinical condition caused by hypersecretion of growth hormone during childhood (e.g., from pituitary gland hypertrophy), leading to excessive skeletal elongation.

Achondroplastic Dwarfism

A genetic skeletal disorder where chondrocytes in the proliferation and hypertrophic zones fail to grow, restricting long bone lengthening while head and trunk proportions remain typical.

Bone Remodeling

The lifelong, continuous process balancing bone resorption by osteoclasts and bone deposition by osteoblasts to reshape bone and maintain mineral balance.

Sealing Zone

An isolated extracellular environment formed between the osteoclast ruffled border and bone matrix via $\alpha_v\beta_3$ integrins, allowing localized acid breakdown of bone.

V-ATPase

A membrane-bound proton pump in osteoclasts that uses $\text{ATP}$ to pump $\text{H}^+$ into the resorption space, lowering local $\text{pH}$ to approximately $5$.

Carbonic Anhydrase II (CAII)

An osteoclast enzyme that catalyzes the synthesis of carbonic acid ($\text{H}_2\text{CO}_3$) from $\text{CO}_2$ and $\text{H}_2\text{O}$ to supply hydrogen ions for acid degradation.

ClC-7

A chloride channel in osteoclasts that transports $\text{Cl}^-$ ions into the sealing zone alongside $\text{H}^+$ to produce hydrochloric acid ($\text{HCl}$).

RANK / RANKL Pathway

A receptor-ligand signaling pathway on osteoclasts and osteoblasts that drives osteoclast differentiation, maturation, and bone degradation activity.

Calcitonin

A peptide hormone that binds to osteoclast receptors to suppress bone resorption when circulating blood calcium levels are high.

Mesenchyme

Embryonic connective tissue that condenses to form initial fibrous membranes or hyaline cartilage templates prior to ossification.

Calcium Phosphate

The primary inorganic mineral component ($\text{Ca}_3(\text{PO}_4)_2$) contained within hydroxyapatites that provides compressive strength to bone.

Calcium Carbonate

An inorganic mineral constituent ($\text{CaCO}_3$) of hydroxyapatite crystals embedded in the organic bone matrix.

Perichondrium

A dense irregular connective tissue layer enveloping hyaline cartilage models prior to vascularization and transformation into periosteum.

Nutrient Foramen

An opening in the compact bone wall through which nutrient blood vessels pass to enter the medullary cavity and supply bone tissues.

Myeloid Progenitor Cell

A lineage cell derived from multipotential stem cells in red marrow that gives rise to red blood cells, platelets, neutrophils, basophils, eosinophils, and monocytes.

Lymphoid Progenitor Cell

A progenitor cell derived from hematopoietic stem cells in red marrow that gives rise to T lymphocytes, B lymphocytes, and Natural Killer (NK) cells.

Stromal Stem Cell

A multipotent stem cell present in bone marrow capable of giving rise to osteoblasts, pre-osteoblasts, lining cells, osteocytes, adipocytes, and skeletal muscle stem cells.

Estrogen

A female sex hormone produced during puberty that induces rapid growth spurts and triggers epiphyseal plate closure around age $18$.

Testosterone

A male sex hormone produced in abundance at puberty that drives bone growth spurts and leads to epiphyseal plate closure around age $21$.