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Skeletal System Notes .docx

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Ryerson University
PLN 103
Nick Bellissimo

Physiology: Skeletal System 10/18/2012 8:36:00 AM Characteristics of Bone Tissue: Dense matrix, containing: Deposits of calcium deposits Osteocytes (bone cells) within lacunae organized around blood vessels Canaliculi Forms pathways for blood vessels (blood supply for bones) Exchange nutrients and wastes (by diffusion) Periosteum Covers the outer lining of bone Consists of outer fibrous and inner cellular layers Bone Matrix contains minerals Two thirds of bone matrix is calcium phosphate, Ca3(Po4) Matrix proteins One third of bone matrix is protein fibers, collagen Bone cells make up 2% of bone mass Bone contains four types of cells Osteocytes 3 main things: matrix (less fluid then in other tissue types), canniculae extend from one osteo site to the next, helps with communication Osteoblasts Osteoprogenitor osteoclasts Osteocytes, mature bone cells that maintain bone matrix Found in been layers (lamellae) of matrix Connect by cytoplasmic extensions through canaliculi in amllae Do not divide Two major functions 1. To maintain protein and mineral content of matrix 2. Help repair damaged bone Osteoblast are the immature bone cells that secrete matrix compounds Overtime mature into osteocytes Osteoid is the matrix produced by osteoblasts but not yet calcified to form bone Osteoprogenitor cells Messenchymal (loose connective tissue) stem cells that divide to produce osteoblasts Located in the endosteum, the inner layer of periosteum (membrane) Main function- to assist in fracture repair bone injury Osteoclasts much bigger than the other Secrete acids and protein digesting enzymes Giant, multinucleate cells (50 or more) Dissolve bone matrix and release stored minerals (osteolysis) Homeostasis Bone building (by osteoblasts) and bone recycling (by osteoclasts) must balance More breakdown than building, bones become weak Exercise, particularly weight bearing exercise, causes osteoblasts to build bone Long Bone Compact Bone o Structure o Osteon is the basic unit o Osteocytes are arranged in concentric lamellae o Around a central canal containing blood vessels o Perforating canals o Perpendicular to the central canal o Carry blood vessels into bone and marrow Circumferential Lamellae o Lamellae wrapped around the long bone (like a sheet that wraps around) o Bonds osteons together No binding = weaker bone. Provides structural integrity Lamellae- sheets of connective tissue and structural fiber (collage fibers in particular) These collagen fibers strengthen bone by being wrapped around in a different direction, crisscrossing provides structural support to bone Functional unit of compact bone is the osteon The structure of spongy bone Does not have osteons The matrix forms an open network of trabeculae Trabeculae have no blood vessels The space between trabeculae is filled with red bone marrow Which has blood vessels Forms red blood cells And supplies nutrients to osteocytes RBC, WBC and platelets (blood clotting )are all in the red bone marrow When born, bone marrow is red Yellow bone marrow (turns yellow over time) In some bones, spongy bone holds yellow bone marrow Is yellow because it stores fat Weight bearing Bones The femur transfers weight from hip joint to knee joint Causing tension on the lateral side of the shaft And compression on the medial side Compact bone is covered with a membrane Periosteum on the outside Covers all bones except parts enclosed in joint capsules Made up of an outer, fibrous layer and an inner, cellular layer Perforating fibers: collagen fibers of the periosteum Connect with collagen fibers in bone And with fibers of joint capsules; attach tendons, and ligaments Functions of Periosteum 1. Isolates bone from surrounding tissues 2. Provides a route for circulatory and nervous supply 3. Participates in bone growth and repair Osteoblasts and osteoprogenator cells have to be there to repair Whats the difference between circumferential lamellae and concentric lamellae? Test question Compact bone is covered with a membrane Endosteum on the inside an incomplete cellular layer lines the medullary (marrow) cavity covers trabeculae of spongy bone lines central canals contains osteoblasts, osteoprogenitor cells and osteoclasts active in bone growth and repair Bone Development Human bones grow until about age 25 Osteogenesis Bone formation Ossification The process of replacing other tissues with bone Calcification The process of depositing calcium salts Occurs during bone ossification see powerpoint Endochondral ossification look in textbook for figure 6-10 Ossifies Appositional Growth Compact bone thickens and strengthens long bone with layers of circumferential lamellae Diameter increases due to appositional growth 1. Cells of the inner layer of the periosteum differentiate into osteoblasts 2. Osteoblwasts become surrounded by matrix and differentiate into mature osteocytes
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