1: Skeletal System- Anatomy & Histology

Flashcards covering vocabulary related to the skeletal system, joint classifications, long bone anatomy, bone cells, bone histology, and cartilage types.

Osteo-

A Greek-derived prefix that refers to bone.

Chondr-

A Greek-derived prefix that refers to cartilage.

Arthr-

A Greek-derived prefix that refers to joints.

Musculoskeletal system

The integrated system formed by the interaction between the muscular system and the skeletal system (bones, cartilage, and joints).

Synarthrotic

A functional classification for joints that allow no movement.

Amphiarthrotic

A functional classification for joints that allow a little movement that is not easily observable or voluntarily controlled.

Diarthrotic

A functional classification for freely moveable joints; all are synovial joints.

Fibrous joints

A structural classification where bones are bound together by dense connective tissue with a high collagen content.

Cartilaginous joints

A structural classification where bones are bound together by hyaline or fibrocartilage.

Synovial joints

A structural classification where bones are bound by a joint capsule that creates a joint cavity filled with lubricating fluid.

Ligaments

Dense bands of dense regular connective tissue that connect adjoining bones to provide stability along specific lines of stress.

Diaphysis

The tubular shaft of a long bone that forms its long axis.

Medullary cavity

The central cavity within the diaphysis that contains bone marrow.

Epiphyses

The bone ends of a long bone.

Articular cartilage

A thin layer of hyaline cartilage covering the articulating surface of each epiphysis to provide cushioning and shock absorption.

Metaphysis

The flared portion of a long bone where the diaphysis and epiphysis meet.

Epiphyseal plate

Commonly called the growth plate, it is a layer of growing hyaline cartilage where bone lengthens during childhood.

Epiphyseal line

The remnant of the epiphyseal plate in adults once bone growth has ceased and the plate has closed.

Endosteum

A thin, delicate membrane lining the internal bone surfaces, such as the medullary cavity and canals.

Periosteum

A highly vascularized and innervated double-layered membrane covering the external surface of the bone (except joint surfaces).

Perforating (Sharpey's) fibers

Bundles of collagen fibers that secure the periosteum to the underlying bone.

Entheses

The specific sites where tendons, ligaments, and fascia attach to the bone via the periosteum.

Red marrow

Hemopoietic tissue responsible for producing red blood cells, white blood cells, and platelets.

Yellow marrow

Bone marrow that serves as a storehouse for adipose tissue; it can convert back to red marrow in life-threatening blood loss.

Nutrient foramen

A hole in the wall of the diaphysis through which nutrient arteries, veins, and nerves access the inner bone tissue.

Osteoprogenitor cells

Undifferentiated bone stem cells that develop into osteoblasts.

Osteoblasts

Bone-building cells that produce the organic bone matrix (osteoid) and control bone mineralization.

Osteocytes

Mature bone cells that reside in lacunae and account for > $90\%$ of all bone cells; they maintain the tissue using mechanosensation.

Osteoclasts

Bone-carving cells that develop from macrophages and function in bone resorption by breaking down the extracellular matrix.

Bone Lining cells

Flat surface cells located where remodeling is not occurring; they inhibit bone resorption by preventing osteoclast interaction with the matrix.

Osteoid

The organic part of the bone matrix, consisting of > $90\%$ collagen fibers, providing tensile strength and flexibility.

Hydroxyapatite

The inorganic bone matrix represented by crystallized calcium phosphate ($Ca_{3}(PO_{4})_{2}$), providing hardness and resistance to compression.

Compact bone

A dense layer of bone tissue making up $80\%$ of the skeleton; it is built to withstand longitudinal forces and appears smooth to the naked eye.

Spongy (trabecular) bone

Bone tissue consisting of a honeycomb-like network of trabeculae arranged along lines of stress.

Osteon

The structural unit of compact bone, consisting of concentric layers of mineralized matrix oriented parallel to the long axis.

Lamellae

The concentric circular layers of mineralized extracellular matrix that make up an osteon.

Lacunae

Small cavities or "pits" sandwiched between lamellae where osteocytes reside.

Canaliculi

Tiny canals radiating from lacunae that connect osteocytes to each other and to the blood supply.

Bone remodeling

The lifelong process where bone is resorbed by osteoclasts and replaced by new bone deposited by osteoblasts.

Mechanosensation

The process by which osteocytes detect mechanical loading/pressure and transform it into biological signals to direct bone remodeling.

Parathyroid hormone (PTH)

A hormone released when blood $Ca^{2+}$ levels drop; it stimulates osteoclasts to resorb bone and releasing calcium into the blood.

Chondroblasts

Cells that produce the extracellular matrix of cartilage.

Chondrocytes

Mature cartilage cells that reside in lacunae and maintain the cartilage tissue.

Avascular

A term describing tissue (like cartilage) that lacks a direct blood supply and must rely on diffusion for nutrients.

Aneural

A term describing tissue (like cartilage) that lacks nerve endings and thus has no direct sensation when damaged.

Hyaline cartilage

The most abundant and glassy-looking cartilage; it provides firm support and is found in articular cartilage, costal cartilages, and the nose.

Elastic cartilage

Cartilage containing many elastic fibers that allows it to tolerate distortion and return to its original shape; found in the outer ear and epiglottis.

Fibrocartilage

A strong, resilient cartilage with an abundance of Type I collagen fibers; found in intervertebral discs and the pubic symphysis.

Perichondrium

A double-layered membrane surrounding hyaline and elastic cartilage that resists outward expansion and provides nourishment.