Bones and Axial Skeleton

Vocabulary flashcards covering bone histology, anatomy, growth, skeletal divisions, and bone-related pathologies based on Chapter 5 lecture notes.

Osseous tissue

Also known as bone tissue, it is the major structural and supportive connective tissue in the body, categorized into compact and spongy bone.

Red marrow

Soft fatty tissue found in bone cavities that serves as the site for blood cell production.

Yellow marrow

Soft fatty tissue found in bone cavities used for fat storage.

Periosteum

A dense irregular collagenous connective tissue with a rich blood supply and neuronal axons that covers the outer surface of bones.

Perforating (Sharpey’s) fibers

Fibers that anchor the periosteum to the underlying bone.

Compact (Cortical) Bone

A dense, strong outer layer of bone that provides resistance to compression and twisting.

Trabeculae

A loosely-gathered meshwork of extensively-branched bone tissue found in spongy bone, lacking osteons and central canals.

Endosteum

A thin connective tissue layer that covers the trabeculae of spongy bone.

Epiphyses

The expanded, rounded ends of long bones containing abundant spongy bone and covered with hyaline cartilage.

Metaphysis

The narrow region between the diaphysis and epiphysis, serving as the major site of bone growth in the growth plate region.

Diaphysis

The long central axis or shaft of a bone, containing a thick compact bone layer and a nutrient foramen.

Epiphyseal Plate

A region of hyaline cartilage between the epiphysis and diaphysis responsible for lengthwise growth during childhood.

Epiphyseal Line

The remnant of the growth plate seen in adults after the cartilage ossifies and growth stops.

Inorganic matrix

The component of osseous tissue (about 65%) made primarily of hydroxyapatite ($Ca_5(PO_4)_3OH$) that provides strength and resistance to compression.

Organic matrix

The component of osseous tissue (about 35%) consisting of collagen fibers and osteoid that provides flexibility.

Osteoid

The unmineralized organic bone matrix secreted by osteoblasts, consisting of collagen strands (tropocollagen), proteoglycans, and glycoproteins.

Osteogenic cells

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

Osteoblasts

Bone-forming cells that secrete osteoid and eventually mature into osteocytes once surrounded by matrix.

Osteocytes

Mature bone cells located in lacunae that maintain the bone matrix and act as stress or strain sensors.

Osteoclasts

Multinucleated cells derived from macrophages responsible for bone resorption by breaking down the matrix.

Resorption bays

Shallow depressions on the bone surface where active osteoclasts settle to break down bone tissue.

Calcitonin

A hormone released by the thyroid gland in response to high plasma calcium levels, triggering calcium salt deposition in bone.

Parathyroid Hormone (PTH)

A hormone released by the parathyroid glands during low plasma calcium levels to stimulate osteoclast activity and calcium resorption.

Osteon

The small, tightly-packed functional unit of compact bone containing a central canal.

Canaliculi

Small canals that connect adjacent lacunae, allowing communication and nutrient diffusion between osteocytes.

Endochondral ossification

The process of bone formation where hyaline cartilage is replaced by bone tissue, forming most of the skeleton.

Intramembranous ossification

The process of bone development from a fibrous membrane, primarily forming flat bones like those of the skull.

Zone of proliferation

The region in the epiphyseal plate where chondrocytes divide rapidly and form stacks, contributing to bone lengthening.

Appositional growth

The process by which bones increase in diameter through the addition of bony tissue at the outer surface by osteoblasts in the periosteum.

Axial skeleton

Bones located within the long axis of the body, including the skull, hyoid bone, vertebral column, ribs, and sternum.

Appendicular skeleton

Bones of the body's limbs, including the pectoral and pelvic girdles.

Sesamoid bones

Small, flat, and oval-shaped specialized bones found within tendons, such as the patellae.

Foramen

A hole in a bone through which structures such as nerves or blood vessels pass.

Condyle

A rounded end of a bone that fits into a fossa or facet of another bone at a joint.

Sella turcica

A feature of the sphenoid bone that houses the pituitary gland.

Cribriform plate

A part of the ethmoid bone that forms the roof of the nasal cavity and contains foramina for olfactory neurons.

Hyoid bone

The only bone in the body that does not articulate with any other bone, serving as an attachment site for muscles involved in swallowing.

Atlas (C1)

The first cervical vertebra, which lacks a body and a spinous process, articulating with the occipital condyles.

Axis (C2)

The second cervical vertebra, characterized by the dens (odontoid process) on the superior surface of its body.

Wolff’s Law

The principle stating that bones adapt and are remodeled based on the compressive force or load placed on them.

Reduction

The treatment for fractures involving the realignment of broken bone ends, which can be closed (manual) or open (surgical).

Osteoporosis

A bone disease characterized by osteoclast activity outpacing osteoblast activity, often associated with a loss of estrogen and decreased bone density.