Bones Lecture - Bone Anatomy and Physiology PDF

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Bone Anatomy and Physiology ...

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Bone Types, Structure, & Ossification Functions 1) Supports the body weight a) Attachment sites for soft tissues and organs b) Works with muscles to maintain body position c) Cartilage, joints, ligaments, and CT 2) Storage of minerals a) Calcium and phosphorus b) Remodeling and reshaping to metabolic needs 3) Blood cell production a) Red marrow- produce red and white blood cells b) Yellow marrow- lipid reserve for energy 4) Protection a) Ribs, skull, pelvis, etc. 5) Leverage a) Ability to move appendages Bone (osseous tissue) - Supporting CT type - Specialized cells - Matrix of extracellular protein fibers and ground substance - Osteocytes - main cell type in bone - Macroscopic features of a long bone - Appreciate with naked eye - Epiphyses: i. Expanded portions at each end ii. Epiphyseal line: Lines between epiphysis and diaphysis iii. Covered by articular cartilage - Diaphysis: surrounds the bone marrow cavity - Metaphysis: junction of diaphysis and epiphysis - Types of tissue i. Compact bone - Solid - Found in diaphysis - Osteon: functional unit of CB - Osteocytes arranged in circular lamellae around a canal - Canal contains blood vessels and nerves - Found in all bone surfaces except inside joints capsules - Limb bones withstand forces from each end

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Spongy bone - Network of bony rods or struts separated by spaces - Less dense - Found in epiphysis - No osteons - Lamellae form rods or plates (trabeculae) - Creates an open network - Space between trabeculae is filled with red bone marrow - Located where bones are not heavily stressed - Lighter - Protects cells of red bone marrow - Periosteum: i. Outer surface of bone ii. Thin layer - Endosteum: i. Cellular layer that lines marrow cavity ii. Active during bone growth Microscopic features of the bone - Osteocytes i. Bone cells ii. Sit in lacunae (small pockets) - Lamellae i. Narrow sheets of calcified matrix ii. Lacunae reside in between these sheets - Canaliculi i. Small channels that radiate through the matrix ii. Contain cytoplasmic extensions and osteocytes

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Bone cell Types - Osteocytes i. Mature bone cells ii. Live in lacunae between lamellae iii. Connect by cytoplasmic extensions through canaliculi iv. Do not divide v. Functions: - Maintain bone structure - Help repair bone - Osteoclast i. Giant, multinucleated cells ii. Secretes acids and protein-digesting enzymes iii. Dissolve bone matrix and release stored minerals (osteolysis) iv. Regulates calcium and phosphate concentrations in body fluids - Osteoblast i. Immature bone cells that secrete matrix compounds to create new bone ii. Osteoid - Matrix produced by osteoblasts - Not yet calcified to form bone iii. When surrounded by calcified bone they become osteocytes Ossification - Process of replacing other tissues with bone cartilage and connective tissues

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Intramembranous- bone develops within sheets or membranes of CT 1. Ossification centers appear in the fibrous CT membrane a. Increase in vascularity b. CT stem cells change into osteoblasts 2. Bone matrix is secreted within the fibrous membrane and calcifies a. Osteoblasts begin to secrete osteoid- calcifies within a few days b. Trapped osteoblasts change into osteocytes Endochondral- bone replaces existing cartilage

Endochondral Ossification: bone replaces existing cartilage - Most bones form this way - Ossification of existing hyaline cartilage - Cartilage develops first: miniature models of future bone Step 1: - chondrocytes at the center of growing cartilage enlarge - Die to slower diffusion of nutrients - Leave cavities in the cartilage - Surrounding matrix begins to calcify Step 2: - Bone formation first starts at shaft surface - Blood vessels invade perichondrium - Cells of inner layer of perichondrium change into osteoblasts - Cover the cartilage in a thin layer of bone Step 3: - Blood vessels penetrate the cartilage bringing in fibroblasts - Fibroblasts become osteoblasts - Osteoblasts replace cartilage with spongy bone in center of shaft (primary ossification center) - Bone development proceeds toward each end of bone Step 4: - Bone lengthens - Osteoclasts break down some of the spongy bone creating a bone marrow cavity - Cartilage at ends continue to enlarge increasing length of bone - Osteoblasts from shaft continuously invade epiphyseal cartilage - New cartilage is added in front of … Step 5: - Blood vessels invade the epiphyses - Osteoblasts form secondary ossification centers - Epiphyses fill with spongy bone - Thin cap of original cartilage remains exposed to the joint cavity: articular cartilage

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Bone shaft and epiphyses are still separated by a plate Epiphyseal cartilage persists as long as the rate of cartilage growth keeps pace

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Growth hormone ○ Bone growth accelerates dramatically Epiphyseal line ○ Former location of epiphyseal cartilage Epiphyseal closure ○ End of epiphyseal growth ○ Timing varies from bone to bone and person to person

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Appositional Growth - Diameter of bone enlarges on the outer surface as the bone elongates - Cells of the periosteum develop into osteoblasts and produce matrix

Requirements for normal bone growth - Dietary source of calcium and phosphate salts - Vitamins C, A, B12 - Calcitonin, parathyroid hormones - Hormones involved in calcium metabolism -

Calcitriol

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Helps absorb calcium and phosphorus from digestive tract Synthesis requires vitamin D3 (from diet or sun exposure) Growth hormone, thyroxine Estrogens, androgens

Process of Remodeling: - Mature Skeleton - Maintenance, dependent on stresses on bone - Replaces mineral reserves - Recycles and renews bone matrix - Osteocytes, osteoblasts, and osteoclasts - Turnover rate varies - Deposition is greater than removal, bones get stronger - Removal is faster than replacement, bones get weaker Heteroplastic Ossification - Formation of bone outside of the skeleton - Bones formed by this process in non-human animals include: - Os penis of dog - Os rostris (rostral bone) of pig

Skeleton as a Calcium reserve - Mineral portion= 62% of bone weight - Calcium is the most abundant mineral of the body - Calcium ions are vital to: - Membranes - Neurons - Muscle cells (especially heart) - Contains parathyroid glands - Increases calcium ion levels by: - Stimulating osteoclasts - Increasing intestinal absorption of calcium - Decreasing calcium excretion at __ - Calcitonin - Secreted by C cells (parafollicular cells) in thyroid gland - Decreases calcium ion levels by:

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Inhibiting osteoclasts activity Decreasing calcium secretion at kidneys

Fractures - Cracks or breaks - Physical stress, extreme loads or sudden impacts - Named according to: - External appearance - Location - Nature of crack or break - Types of fractures: - Closed: completely internal - Open fractures (compound): project through the skin - Transverse fractures: breaks through the shaft of the long bone across its long axis - Spiral fractures: produced by twisting stresses along length of the bone - Greenstick fractures: typically in young animals - Comminuted fractures: shattered bone in many small fragments Repair of Fractures - Healing depends on: - Blood supply to bone - Ability to form osteoblasts (which produces new bone) - Parts of the bones with low blood supply, and with little periosteum and endosteum, will heal very slowly Steps of repair: Step 1: Fracture Hematoma forms a large blood clot Step 2: stem cells of periosteum and endosteum undergo mitosis and an internal callus forms Step 3: cartilage of the external callus is replaced by bone and ends of fracture are now held firmly in place Step 4: swelling initially marks the location of the fracture and fragments and calluses will be gone...