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Lecture 6

PNB 2264 Lecture Notes - Lecture 6: Ehlers–Danlos Syndromes, Intramembranous Ossification, Endochondral Ossification

Physiology and Neurobiology
Course Code
PNB 2264
John Redden

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PNB 2264 Lecture 6– Ossification, Tissue Transformation, Cell Death and Regeneration
Models of ossification (building new bone)
Intramembranous ossification (making bone where it did not exist before)
Stem cell (osteoprogenitor cell) based
Ossification center forms in mesenchyme, osteoid undergoes
calcification, and woven bone and surrounding periosteum form
Responsible for building flat, wide bones (flat bones of the skull, some
facial bones) and repairing fractures
Endochondral ossification (converting cartilage to bone)
Growth takes place inside metaphysis (growth plate), which contains
Gaps are present until cartilage has fully converted to bone (around 18-20
Looking for the presence or absence of these gaps can reveal the
age of an individual
Older chondrocytes not undergoing mitosis move towards shaft
Old chondrocytes die off (due to being avascular), and are replaced by
osteoblasts, which move upward toward epiphysis
Pathology examples
Ehlers Danlos Syndrome (EDS)
Caused by mutations in collagen fibers
Severity and specific impacts can vary
May cause extreme flexibility in joints and skin
May lead to arthritis later in life
Stone Man Disease (FOP)
Caused by a genetic mutation in a gene associated with bone growth and
Causes bone to develop where tissue should be, following damage to a
specific tissue (bone regeneration in response to tissue damage)
Tissue transformations
Metaplasia: the abnormal replacement of one tissue type with another
Stone Man Disease (FOP) is an example
Barretts Esophagus: a condition in which squamous epithelium
replaces ciliated epithelium
Caused by smoking or vaping
Often a precursor to cancer
Hypertrophy: cell growth without additional cell division (cells increase in size
but not quantity)
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