anim_bone_formation_answer_key.doc

Intramembranous & Endochondral Ossification To complete this worksheet, select: Module: Support and Movement Activity: Animations Title: Bone Formation Complete the following worksheet and add it to your notes. Define ossification. Is the process by which bone forms within an individual. An embryo has the beginnings of its skeleton in regions made up of loose mesenchymal cells that provide the guide for future bone formation. Ossification is the process that replaces these progenitor cells with bone tissue. Where does intramembranous ossification occur? Intramembranous ossification occurs at the flat bones of the skull and mandible. Intramembranous Ossification Explain how ossification centers form during intramembranous ossification. Include each of the following: A. Mesenchymal cells at the centers of ossification, mesenchymal cells receive specific chemical commands to group together and differentiate into the next type of cells. B. Osteogenic cells mesenchymal cells transform into osteogenic cells which are destined to give rise to bone cells.. C. Osteoblasts osteogenic cells further differentiate into these bone-building cells that synthesize and secrete collagen fibers and other organic compounds to form extracellular matrix. D. Osteoid (bone matrix) this is the uncalcified material secreted by the osteoblasts. How do trabeculae form which leads to spongy bone formation? Spongy bone grows as the bone matrix develops into thin columns of bone (trabeculae) that interconnect to form a lacy network of bone with intervening spaces. How does red bone marrow develop? Blood & lymphatic vessels growing into the surfaces of the newly formed trabeculae of the spongy layer provide the basis for red bone marrow. Red bone marrow is a highly vascularized connective tissue. Where does the periosteum form? This is a layer of connective tissue that forms on the outer surface of the bone. Where does compact bone frequently replace spongy bone and where does spongy bone remain? Compact bone usually replaces the outer layer of spongy bone. The center remains spongy bone. Define sutures and fontanels. What is the function of each? Sutures are immovable joints in the skull made of fibrous tissue found in adults. Fontanels are spaces in the infant skull filled with dense connective tissue commonly called soft spots. These allow the infant’s head to pass through the birth canal and allow for brain growth as the infant matures. Endochondral Ossification Endochondral ossification is the replacement of cartilage with bone. Describe the formation of the cartilage model. Include each of the following: a. Mesenchymal cells Embryonic connective tissue cells aggregate into clusters and differentiate into chondroblasts. b. Chondroblasts cells that secrete cartilage matrix to form the cartilage model. Contrast interstitial and appositional growth of the cartilage model. Interstitial growth of cartilage is growth from within the tissue and results in increases in length. Appositional growth adds bone tissue from the surfaces and results in increases in width and thickness. Describe events during cartilage model formation. Include each of the following: a. nutrient artery penetration this occurs during the development of the ossification center of endochondral ossification when an arterial vessel penetrates the bone from the perichondrium, thereby increasing the availability of nutrients to the surrounding cells. b. Osteogenic cells and osteoblasts Nutrient artery penetration stimulates nearby osteogenic cells to differentiate into osteoblasts. c. Contrast the perichondrium and the periosteum. Perichondrium is the connective tissue on the surface of cartilage while periosteum is the connective tissue on the surface of bone. Describe (step 2) growth of the cartilage model. Include each of the following: Chondroblasts within the perichondrium secrete cartilage matrix causing growth of the cartilage model within the fetus. Two types of cartilage growth happen. Interstitial growth reinforces the cartilage model to develop lengthwise while appositional growth causes cartilage thickness at the periphery. Describe (step 3) bone collar and periosteum formation. A nutrient arterial vessels inserts into the perichondrium and provide an increase of nutrients to the surrounding cells. This increase of nourishment stimulates the osteogenic cells to mature into osteoblasts. Osteoblasts secrete bone matrix under the perichondrium to create a thin structure of bone called the bone collar. Once this bone creation occurs, the perichondrium is now referred to as periosteum. Describe (step 4) primary ossification center formation. a. Nutrient deprival This happens when the bone collar prevents diffusion of nutrients to the interior cartilage area. b. Osteoblast carrying capillaries As the cartilage in the interior area disintegrate due to a lack of nutrients, capillaries penetrate into the interior, bringing with them osteoblasts that begin to lay down bone matrix. c. What occurs at the primary ossification center the replacement of the cartilage matrix with bone matrix is the primary event that happens at the primary ossification center. d. Osteoblasts building spongy bone trabeculae as the osteoblasts release bone matrix, these fuse together to form trabeculae, which is the structural unit of spongy bone. Describe events of (step 5) remodeling. Include each of the following: Medullary cavity formation As cartilage breaks down in the interior, spaces form and merge into a single central cavity. . b. Capillaries and red bone marrow the medullary cavity becomes filled with nutrient-carrying capillaries and red bone marrow connective tissue. c. Diaphysis formation bone matrix is secreted and creates the central bony shaft called the diaphysis. Describe secondary ossification center formation. Include each of the following: a. When does this happen? This occurs at the time of birth. b. Blood vessels entering the cartilaginous epiphysis initiate secondary ossification centers. c. How does secondary ossification differ from primary ossification? Secondary ossification always occurs following the primary ossification process and does not result in the formation a medullary cavity. d. Why does the interior of the epiphysis remain spongy? Due to the missing medullary cavity the inside of the epiphysis remain spongy. Describe articular cartilage and epiphyseal plate formation. Include the following: a. Hyaline (articular) cartilage (location and function) – Due to the effect of secondary ossification, a thin layer of hyaline cartilage is deposited on the surface of the epiphysis. This articular cartilage acts to reduce friction & shock within the articulating surfaces of the joint. b. Epiphyseal plate location and function – The hyaline cartilage that remains between the primary and secondary ossification centers forms the epiphyseal plate and allows the diaphysis to lengthen until puberty.