Osteogenic Cell
-what is it
-where is it found
-Stem cell that differentiates into osteoblasts.
-Found in the inner layer of the periosteum and endosteum.
Osteroblast
-what is it
- what does it do
-where is it found
-Cell that forms new bone matrix (Osteogenesis).
-Secretes proteins and adds calcium.
- Found on the exterior surface of the bone.
Osteocyte
-what is it
-how is it formed
-Mature bone cell that maintains existing bone tissue.
-Formed when an osteoblast gets trapped in the matrix within a lacuna.
Osteoclast
-what is it
-what does it release
- how is it found
-Cell that breaks down and recycles bone matrix (Osteolysis).
-Releases calcium and other minerals.
-Found at the endosteum to increase the medullary cavity size.
Epiphyseal Plate
Site of bone length growth (prior to puberty). Cartilage is formed on the epiphyseal side and replaced by bone (ossified) on the diaphyseal side. (bone structure)
Appositional Growth
Mechanism for bone width growth. Osteoblasts add new matrix to the exterior surface of the bone.(bone structure)
Endosteum
The inner lining of the medullary cavity where osteoclasts are active for bone resorption and remodeling.(bone structure)
Epiphyseal Line
The remnant of the epiphyseal plate after puberty, formed when it calcifies and stops length growth.(bone structure)
Endochondral Ossification
Replaces a Hyaline Cartilage template. Forms most bones, including long bones.
Intramembranous Ossification
Replaces a Mesenchymal Membrane template. Forms flat bones like the skull, face, clavicles, and sternum.
Primary Ossification Center
The first area of bone development, located in the center of the diaphysis of a long bone.
Fontanelles
The “soft spots” in an infant’s skull that solidify through intramembranous ossification.
Hematoma Formation
The first step of fracture repair: a large blood clot forms at the fracture site due to broken blood vessels.
Callus Formation
The second step of fracture repair: Fibrocartilage is formed by phagocytes and osteoblasts to bridge the broken bone ends.
Bone Remodeling
The final step of fracture repair: The fibrocartilage callus is replaced by bone tissue, and osteoclasts and osteoblasts reshape the bone back to normal.
Compound (Open) Fracture
A fracture where the bone breaks the skin, carrying a higher risk of infection.
Parathyroid Hormone (PTH)
Released when blood calcium falls (hypocalcemia). Stimulates osteoclasts to break down bone and release calcium into the blood.
Calcitonin
Released when blood calcium rises (hypercalcemia). Inhibits osteoclasts, keeping calcium within the bone.
Growth Hormone
Released from the pituitary gland; directly impacts cell division and growth at the epiphyseal plate.
Osteoporosis
A condition in older adults where osteoclast activity exceeds osteoblast activity, leading to reduced bone density and increased fracture risk.
Simple (Closed) Fracture
Bone does not break the skin
Ossification
the process of replacing an existing template (membrane or cartilage) with bone tissue.
Thyroxine (Thyroid Gland)
Stimulates endochondral ossification and increases osteoblast function.
Estrogen & Testosterone (Ovaries/Testes)
Cause the pubertal “growth spurt.” Elevated levels after puberty cause the calcification of the epiphyseal plate into the epiphyseal line, stopping further length growth and height gain.
