Skeletal System

General vocabulary and key concepts for the Skeletal System, including bone structure, classification, development, and specific anatomical landmarks.

Hematopoiesis

The process of blood cell formation which occurs in the red bone marrow.

Long Bones

Bones that are long and narrow with expanded ends, such as the Radius or Tibia.

Short Bones

Cube-like bones where length equals width, including sesamoid (round) bones like the patella.

Flat Bones

Plate-like bones with broad surfaces, such as the ribs or bones of the cranium.

Irregular Bones

Bones with a variety of shapes that are usually connected to several other bones, like vertebrae or facial bones.

Epiphysis

The expanded end of a long bone.

Diaphysis

The shaft of a long bone.

Periosteum

A layer of dense connective tissue that encloses the bone.

Trabeculae

Branching bony plates that make up spongy (cancellous) bone.

Medullary cavity

A hollow chamber in the diaphysis that contains bone marrow.

Osteocytes

Mature bone cells.

Lacunae

Chambers occupied by osteocytes.

Canaliculi

Tiny passageways through which osteocyte cell processes exchange nutrients and wastes.

Osteon

The cylindrical unit of compact bone, also known as a Haversian system.

Red Bone Marrow

Tissue responsible for producing red blood cells, white blood cells, and platelets; remains in the adult skull, ribs, and sternum.

Yellow Bone Marrow

Tissue that stores fat and replaces red bone marrow with age; it does not produce blood cells.

Hydroxyapatite

Crystals of calcium phosphate that are the most abundant inorganic salt in the bone matrix, making up about $70\%$ of it.

Osteogenesis imperfecta

A hereditary collagen defect resulting in brittle bones and frequent fractures in fetuses.

Parathyroid hormone

A hormone that regulates blood calcium by resorbing bone to release calcium into the blood.

Calcitonin

A hormone that stimulates bone formation and the removal of calcium from the blood.

Axial Skeleton

One of the two main divisions of the skeleton containing 80 bones, including the skull, hyoid bone, vertebral column, and thoracic cage.

Appendicular Skeleton

The division of the skeleton containing 126 bones, including the pectoral girdle, upper limbs, pelvic girdle, and lower limbs.

Condyle

A rounded process that usually articulates with another bone, such as the occipital condyle.

Foramen

An opening through a bone that serves as a passageway for blood vessels, nerves, or ligaments.

Suture

An interlocking line of union between bones, such as the lambdoid suture.

Fontanel

A soft spot in the infantile skull where membranes cover the space between bones.

Intramembranous Ossification

The process of bone development where bones form between sheets of primitive connective tissue; common in flat skull bones and clavicles.

Endochondral Ossification

The process where bones form from hyaline cartilage models; how long bones and most of the skeleton develop.

Osteoblasts

Bone-forming cells that deposit bone matrix.

Osteoclasts

Cells that break down and resorb bone matrix.

Epiphyseal Plate

A band of cartilage between the ossification centers in a long bone where growth in length occurs.

Atlas

The first cervical vertebra (C1) which supports the head.

Axis

The second cervical vertebra (C2) around which the atlas pivots via the dens.

Sacrum

A triangular structure at the base of the vertebral column formed by 5 fused vertebrae.

Kyphosis

An exaggerated thoracic curvature of the spine, often called hunchback.

True Ribs

The first 7 pairs of ribs (vertebrosternal) that connect directly to the sternum.

Floating Ribs

The lower 2 pairs of ribs (vertebral) which have no connection to the sternum.

Pectoral Girdle

Consists of 2 clavicles and 2 scapulae; supports the upper limbs.

Acetabulum

The depression in the hip bone (os coxa) that receives the head of the femur.

Calcaneus

The tarsal bone that forms the heel.

Bone Remodeling

A lifelong process where between $10\%$ and $20\%$ of the skeleton is replaced annually by the opposing actions of osteoblasts and osteoclasts.

Fragility Fracture

A fracture that occurs after a fall from less than standing height, often a sign of osteoporosis.