ESS 205 Anatomy and Physiology Lecture 11Outline of Last Lecture I. Structure of Compact Bonea. PartsII. Histology of Spongy boneIII. Cells of Osseous TissueIV. Matrix of Osseous TissueV. Bone DisordersOutline of Current LectureVI. Bone MarrowVII. Intramembranous OssificationVIII. Endochondral Ossification a. Secondary Ossification Centersb. MetaphysisIX. Bone Growth and RemodelingX. Physiology of Bone Tissuea. Wolffs LawCurrent Lecture1. Bone marrow is the soft tissue that occupies the medullary cavity if a long bone or the space of trabeculae of spongy bone. There are two types of marrow; red and yellow.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.a. Red bone marrow looks like thick blood. It is hemopoietic and a mesh of reticularfibers and immature cells. Red bone marrow is found in the sternum, ribs, vertebrae, pelvic girdle and proximal heads of femur and humerus in adultsb. Yellow bone marrow is a fatty marrow of long bones in adults. As the human agesthe yellow marrow turns into reddish, gelatinous jelly. 2. There are two types of bone growth in fetus’s and infants. The first is intramembranous ossification. This type of ossification only produces flat bones of the skull and sternum. Itis a fibrous membrane that develops directly into the bone. There is a four step process for intramembranous ossification:a. 1. Mesenchyme condenses into a sheet of soft tissue and eventually will become the periosteum. This then transforms into a soft network of trabeculae.b. 2. Osteoblasts gather on the trabeculae to form osteoid tissue (uncalcified bone).This calcium phosphate is deposited into matrix and transforms osteoblasts into osteocytes. The periosteum is now formed. c. 3. Osteoclasts remodel the center to contain marrow spaces. The ends continue to form trabeculae. d. 4. Osteoblasts remodel the surface forming compact bone3. The next type of ossification is endochondral ossification. It has a cartilage phase that the previous type of ossification does not have. Majority of bones are developed from this process. Six step process:a. Step 1 is the synthesis of the cartilage during development that will become into bone at some pointb. Step 2 is the formation of primary ossification center, bony collar, and periosteum. c. Step 3 is vascular invasion which forms the primary marrow cavity (primary ossification center turns in to primary marrow cavity). The appearance of a secondary ossification center also develops.d. Step 4 is the bone AT birth. There is an enlarged primary marrow cavity and the appearance of secondary marrow cavity turns into one epiphysis.e. Step 5 is the bone of a child. The epiphyseal plates are at the distal ends of the long bones. f. Step 6 is the adult bone. It has a single marrow cavity with a closed epiphyseal plate. 4. The second ossification center forms in the epiphyses near time of birth. The secondary center gets transformed into spongy bone. The hyaline cartilage remains on the joint surface and articular cartilage, junctions of diaphysis and epiphysis, and each of the epiphyseal plate that has a metaphysis. 5. The Metaphysis is a transitional zone between the head and shaft of developing long bones. There are five zones:a. Zone of reserve cartilage= hyaline cartilageb. Zone of proliferation= chondrocytes multiply to form columns of flat lacunaec. Zone of hypertrophy=cell enlargementd. Zone of calcification= mineralization of matrixe. Zone of bone deposition= chondrocytes of die and columns fill with osteoblasts. Osteons formed and spongy bone is created. 6. Bone Growth and Remodeling happens throughout life. Humans that are active or athletes have a greater bone density and mass of bone. Bone grows either appositional meaning growth of width or interstitial meaning growth of length. In appositional growth there is a deposit of new bone at the surface. Osteoblasts lay down matrix in layers parallel to outer surface and then the osteoclasts dissolve old bone on the inner surface. When this happens the bone marrow cavity also widens. **If one outpaces the other than various bone deformities occur. 7. Physiology of bone tissue is dynamic and active all life long. They are small scale changes. Every week the bone recycles 5-7% of our bone mass. Each day a half a gram ofcalcium may leave or enter the skeleton (IMPORTANT FACT). Spongy bone is replaced every 3-4 years and compact bone is replaced every 10 years or so. As stated before bone tissue is always remodeling. When bones are injured or strength is need there are mineral deposits of calcium and phosphate. Our diet is a contributing factor to the minerals we consume. Bone resorption (dissolving) happens via osteoclasts. Bone remodeling can be performed by hormones, and gravitational forces such as wolffs law.a. Wolff’s Law is where the bone accommodates the forces applied to it by altering its amount and distribution of mass. Long bones are thickest midway along diaphysis. Curved bones are thickest where tend to buckle. The trabeculae form struts along lines of compression. Large bony projections occur where heavy active muscles attach. Because bone remodeling is based on the amount of Ca and Pi depositions and resorption the calcium and phosphate homeostasis is vitally