Lecture 11 Study Questions PDF

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Study Questions Lecture 11 Objectives: • Describe (order) how bones form in the embryo through Endochondral & Intramembranous ossification • Define the role of bone cells in bone formation and growth • Relate bone formation processes to bone remodeling processes, including how the endosteum and periosteum contribute Take Home Messages • Bone forms in two ways: intramembranous and endochondral ossification • Intramembranous ossification replaces mesenchyme tissue with bone • Endochondral ossification involves replacing an avascular cartilaginous model with a highly vascular bony model • A bone (organ) cannot grow through interstitial growth without cartilage – calcification prevents interstitial osseous tissue growth • Endochondral ossification continues throughout adolescence at growth plates • Sex hormones affect rate of bony formation causing growth plate to close and bones to cease growing in length • Bone remodels throughout life due to activity at endosteal and periosteal surfaces Big Picture: 1. Is bone vascular? yes 2. Is cartilage vascular? no 3. During ossification, one tissue type is replaced by ___bone______. Details: 1. From what embryonic tissue do all connective tissues arise? mesenchyme 2. In the process of intramembranous ossification: a. Bone replaces what type of existing tissue? Connective tissue b. What are the steps of intramembranous ossification (you do not need to know absolute numbers, but instead know what step precedes another)?  Mesenchymal cells differentiate into osteoblasts  Osteoblasts deposit osteoid that later calcifies into bone.  Small units of bone unite into trabeculae. Osteoblasts and osteoclasts surround the developing bone, forming the periosteum  Periosteum deposits compact bone and remodels trabeculae c. What is an ossification center? It is the site where bone begins to form in the shaft of a long bone or the body of an irregular bone- primary ossification center. The site where bone formation continues after beginning in the long shaft or body of the bone, is an epiphysis- secondary ossification center. d. Intramembranous ossification occurs in which bones of the body? The clavicle, mandible and may flat bones of the skull. 3. Regarding cartilaginous structures: a. What is a mature cartilage cell called? chondrocytes b. How does cartilage obtain its nutrients for growth (is cartilage vascular)? Cartilage is avascular and obtain its nutrients from blood vessels in the perichondrium and surrounding connective tissues. 4. In the process of endochondral bone formation:

a. Bone replaces what type of existing tissue? Cartilage b. What are the broad steps of endochondral ossification? How are chondrocytes, osteoblasts & osteoclasts involved?  bone collar forms around hyaline cartilage  cartilage in the center of the diaphysis calcifies and then develops cavities  the periosteal bud invades the internal cavities and spongy bone begins to form  the diaphysis elongates and a medullary cavity forms as ossification continues. Secondary ossification centers appear in the epiphyses in prep for step 5  the epiphyses ossify. Hyaline cartilage remains only in the epiphyseal plates and articular cartliages. c. Why must cartilage die before blood vessels can invade? Because cartilage is avascular and doesn’t allow blood vessels to invade d. Why must blood vessels arrive before bone can form? the blood vessels deliver the osteoblasts to form the bone. e. What is the difference between the primary and secondary ossification centers in terms of location on bone? Which ossification center forms first? Primary ossification center is the first to start ossifying in prenatal development in the central part of the developing bone (diaphysis) and in irregular bones it is in the body of the bone. Secondary appears after the primary. 5. Is the bone in your adult skeleton the same bone you had when you were born? What is the relationship between osteoblasts, osteoprogenitor (osteogenic) cells, osteocytes and osteoclasts in this process of constant remodeling? No your bones when you were born were mainly cartilage. Clinical Correlations: 1. Which do you think would be more detrimental to the development of the femur, a mid-shaft fracture or a fracture of the growth plate? Why?...