skeletal system and how bone grows

Mineral Storage:

stores 99% of the body's calcium and ~90% of its phosphorus in the extracellular matrix

Hematopoiesis

Blood cell production (red blood cells, white blood cells, platelets) takes place in red bone marrow

Energy Storage

Yellow bone marrow stores fat (triglycerides in adipocytes) within the medullary cavity

what is diaphysis

the central shaft

what is epiphyses

two expanded ends

medullary cavity

the hollow interior containing marrow

Osteogenic Cells

Mesenchymal stem cells; the only bone cells capable of dividing/replicating

Osteoblasts

Bone-building cells that secrete osteoid (uncalcified matrix); as they become trapped in matrix, they mature into osteocytes

Osteocytes

Mature bone cells housed in lacunae that maintain mineral balance and sense mechanical tension

Osteoclasts

Large, multinucleated cells (derived from monocytes/macrophages) that break down/resorb bone matrix

hyaline cartilage

Most common; smooth, avascular, covers joint ends (articular cartilage) to reduce friction, and forms growth plates

Fibrocartilage

Rich in dense collagen fibers to withstand heavy pressure/shoc

elastic cartilage

rarest, provides flexible support

Intramembranous Ossification

Mesenchymal stem cells convert directly into bone without a cartilage precursor; forms flat bones of the skull, facial bones, and clavicle

Endochondral Ossification

Hyaline cartilage models are gradually replaced by bone; forms long bones, vertebrae, and pelvis

where does the longitudinal growth occur?

epiphyseal plate

what are the 4 function zones of the epiphyseal plate in bone growth

Reserve Zone: Anchors plate; non-dividing chondrocytes

Proliferation Zone: Chondrocytes rapidly divide via mitosis

Hypertrophic Zone: Older cells enlarge as matrix calcifies

Calcification Zone: Dead chondrocytes leave calcified matrix for osteoblasts to ossify

stops when the plate completely ossifies into amn epiphyseal line

how does the bone grow wide?

appositional growth: occurs throughout life
Osteoblasts deposit new bone on the outer surface, while osteoclasts resorb bone along the medullary cavity

what is Parathyroid Hormone (PTH)

Released during hypocalcemia (low blood calcium)
Stimulates osteoclasts to break down bone and release calcium into the bloodstream, and reduces calcium loss in urine

what is calcitonin

released during hypercalcemia (high blood calcium)

stimulates osteoblasts to store excess calcium by building bone matrix

Growth Hormone (GH)

Stimulates chondrocyte proliferation at growth plates and increases calcium absorption