Bones, Skeletal Tissue, and the Skeletal System Chapter 6

Comprehensive vocabulary flashcards covering skeletal tissues, bone histology, development, homeostasis, and anatomy of the axial and appendicular skeleton.

Perichondrium

A dense irregular connective tissue girdle that surrounds skeletal cartilage, resists outward expansion when compressed, and contains blood vessels for nutrient delivery.

Hyaline cartilage

The most abundant type of skeletal cartilage; contains collagen fibers only and provides support, flexibility, and resilience in articular, costal, respiratory, and nasal cartilages.

Fibrocartilage

A skeletal cartilage containing thick collagen fibers that is highly compressible with great tensile strength, located in the menisci of the knee and intervertebral discs.

Appositional growth

Growth from the outside where cartilage- or bone-forming cells secrete new matrix against the external face of existing tissue, increasing thickness or diameter.

Interstitial growth

Growth from within where lacunar chondrocytes divide by mitosis and secrete new matrix, expanding cartilage and lengthening long bones.

Sesamoid bones

A special class of short bones that form within tendons, such as the patella, which vary in size and number among individuals.

Osteocalcin

A hormone produced by bones that regulates bone formation and protects against obesity, glucose intolerance, and diabetes mellitus.

Diaphysis

The tubular shaft forming the long axis of a long bone, composed of a thick collar of compact bone surrounding a central medullary cavity filled with fat (yellow marrow).

Epiphyses

The expanded ends of a long bone bordering the diaphysis, featuring an outer shell of compact bone, an interior of spongy bone, and articular cartilage on joint surfaces.

Epiphyseal plate

A disc of hyaline cartilage located at the junction of the diaphysis and epiphysis in growing bones that allows longitudinal bone lengthening during childhood and adolescence.

Periosteum

A white, double-layered membrane covering the entire external surface of bone (except joint surfaces), composed of an outer fibrous layer and an inner osteogenic layer containing stem cells.

Endosteum

A delicate connective tissue membrane covering internal bone surfaces, lining the canals of compact bone and trabeculae of spongy bone, and containing osteogenic cells.

Osteogenic cells

Mitotically active squamous stem cells located in the periosteum and endosteum that give rise to osteoblasts or bone lining cells.

Osteoblasts

Actively mitotic, bone-forming cells that synthesize and secrete the unmineralized bone matrix (osteoid), including collagen fibers and calcium-binding proteins.

Osteocytes

Mature bone cells occupying lacunae that monitor and maintain the mineralized bone matrix and act as stress or strain sensors to direct remodeling.

Osteoclasts

Giant, multinucleated cells derived from hematopoietic stem cells that break down bone matrix using a ruffled border, lysosomal enzymes, and secreted protons ($H^+$).

Osteon (Haversian system)

The structural unit of compact bone; an elongated cylinder running parallel to the long axis, made of concentric matrix tubes called lamellae surrounding a central canal.

Canaliculi

Hairlike canals that radiate through bone matrix connecting lacunae to each other and to the central canal, permitting osteocytes to communicate via gap junctions.

Osteoid

The unmineralized organic component of the bone matrix secreted by osteoblasts, comprising ground substance and collagen fibers that provide tensile strength and flexibility.

Hydroxyapatites

Inorganic mineral salts, predominantly tiny calcium phosphate crystals, that constitute about 65% of bone by mass and confer hardness and compression resistance.

Endochondral ossification

The developmental process by which bone tissue replaces a preexisting hyaline cartilage model, forming nearly all bones inferior to the base of the skull except the clavicles.

Intramembranous ossification

The process of bone formation in which bone develops directly within fibrous connective tissue membranes formed by mesenchymal cells, producing cranial flat bones and clavicles.

Wolff's law

The principle stating that bones grow or remodel in direct response to the mechanical demands and physical stresses placed upon them.

Parathyroid hormone (PTH)

A hormone produced by the parathyroid glands that stimulates osteoclasts to resorb bone matrix and release $Ca^{2+}$ into blood when blood calcium levels decline.

Calcitonin

A hormone produced by the parafollicular cells of the thyroid gland that lowers blood calcium levels temporarily when administered in pharmacological doses by encouraging $Ca^{2+}$ bone deposition.

Greenstick fracture

An incomplete bone fracture where one side of the shaft breaks while the other side bends, common in children whose bones have relatively more organic matrix.

Fibrocartilaginous callus

A mass of repair tissue composed of collagen fibers, cartilage matrix, and spongy bone trabeculae that bridges broken bone ends during the second stage of fracture repair.

Osteomalacia

A disorder characterized by inadequate bone mineralization due to insufficient calcium salts or vitamin D deficiency, resulting in soft, weak, painful bones (called rickets in children).

Osteoporosis

A group of skeletal diseases in which bone resorption outpaces bone deposit, causing bone mass to decline and making spongy bone of the spine and neck of the femur porous and fragile.

Paget's disease

A disorder marked by excessive and haphazard bone deposit and resorption, resulting in hastily made, poorly mineralized pagetic bone with a high ratio of spongy to compact bone.

Axial skeleton

The 80 bones that form the longitudinal axis of the human body, consisting of the skull, vertebral column, and thoracic cage.

Appendicular skeleton

The bones of the upper and lower limbs along with the pectoral and pelvic girdles that attach the limbs to the axial skeleton.

Coronal suture

The suture where the parietal bones articulate anteriorly with the frontal bone across the superior skull.

Sagittal suture

The midline cranial suture where the right and left parietal bones articulate superiorly along the midline of the skull.

Lambdoid suture

The posterior cranial suture where the parietal bones meet the occipital bone.

Squamous suture

The cranial suture on each lateral aspect of the skull where a parietal bone articulates with a temporal bone.

Sphenoid bone

The complex, bat-shaped keystone cranial bone that articulates with all other cranial bones and houses the hypophyseal fossa within the sella turcica.

Ethmoid bone

The deepest bone of the skull, forming the superior part of the nasal septum, the roof of the nasal cavity, and parts of the medial orbital walls, containing the crista galli.

Sutural bones

Tiny, irregularly shaped bones that can appear within the sutures of the cranial vault.

Mandible

The lower jawbone; the largest and strongest bone of the face, forming the temporomandibular joint, which is the only freely movable joint in the skull.

Maxillary bones

Medially fused facial keystone bones that form the upper jaw and central portion of the facial skeleton, articulating with all other facial bones except the mandible.

Vomer

A slender, plow-shaped facial bone situated in the nasal cavity that forms the inferior portion of the bony nasal septum.

Paranasal sinuses

Mucosa-lined, air-filled spaces situated within the frontal, sphenoid, ethmoid, and maxillary bones that warm and humidify air, lighten the skull, and enhance voice resonance.

Hyoid bone

A U-shaped bone in the anterior neck that does not articulate directly with any other bone; serves as a movable base for the tongue and attachment site for swallowing and speech muscles.

Scoliosis

An abnormal lateral curvature of the vertebral column, most frequently presenting in the thoracic region.

Kyphosis

An exaggerated posterior thoracic curvature of the spine, commonly referred to as hunchback.

Lordosis

An accentuated lumbar curvature of the spine, commonly referred to as swayback.

Nucleus pulposus

The inner gelatinous core of an intervertebral disc that provides elasticity and compressibility.

Anulus fibrosus

The strong outer ring of an intervertebral disc, composed of collagen fibers and fibrocartilage that limits expansion of the nucleus pulposus.

Atlas (C1)

The first cervical vertebra, which lacks a body and spinous process and has superior articular facets that articulate with the occipital condyles to enable nodding ('yes').

Axis (C2)

The second cervical vertebra characterized by a superior projection called the dens (odontoid process) that acts as a pivot for rotation of the atlas ('no').

True ribs

Rib pairs 1 through 7 (vertebrosternal ribs) that attach directly to the sternum by individual costal cartilages.

False ribs

Rib pairs 8 through 12, which either attach indirectly to the sternum via the cartilage of the rib above (pairs 8–10, vertebrochondral ribs) or have no sternal attachment (pairs 11–12, floating ribs).

Pectoral girdle

The shoulder girdle composed of the clavicle anteriorly and the scapula posteriorly, attaching the upper limbs to the axial skeleton.

Carpus

The wrist region comprising eight short bones arranged in two rows: scaphoid, lunate, triquetrum, and pisiform proximally; and trapezium, trapezoid, capitate, and hamate distally.

Pelvic girdle

The heavy bony basin formed by two coxal (hip) bones and the sacrum that attaches the lower limbs to the axial skeleton and supports visceral pelvic organs.

Acetabulum

The deep lateral socket on the coxal bone formed by the fusion of the ilium, ischium, and pubis that articulates with the head of the femur.

Fontanelles

Unossified fibrous membrane remnants in the fetal and infant skull (anterior, posterior, mastoid, and sphenoidal) that allow cranial compression during birth and rapid brain growth.