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Bone cells
Quiz by Amy Kirby
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Bone growth and remodeling New bone development is balanced with bone resorption Haversian systems are continually being replaced Bone is resorbed from one area and added to another to meet changing stresses placed on it (e.g., weight, posture, fractures) Normal growth dependent on sufficient proteins, minerals, vitamins (A, C, D) and influenced by hormones (growth, thyroid, estrogen/testosterone) Bone is capable of repair because it contains osteoprogenitor cells in the periosteum, endosteum, and bone marrow and is very well vascularized Metabolic role of bone (contains 99% of bodyâs total calcium in crystals) Transfer calcium from crystals to interstitial fluid and into blood Hormonal Parathyroid - stimulates osteoblasts to secrete osteoclast-stimulating factor thus promoting resorption Calcitonin - inhibits osteoclast activityOSTEOGENESIS OF BONE (INTRAMEMBRANOUS VS. ENDOCHONDRAL) Intramembranous ossification (most flat bones of skull) Occurs w/in condensations of embryonic mesenchymal cells Differentiate into osteoblasts (takes place in primary ossification center) which surround capillaries Osteoid matrix is produced and then calcified forming trabeculae (islands of bone) of woven (primary) bone; its surface is surrounded by osteoblasts Trabecular growth leads to the fusion of adjacent ossification centers which gradually produce layers of compact bone that encloses spongy (cancellous) boneCOVERINGS OF BONE SURFACE Periosteum: Outer layer of Type I collagen fibers and fibroblasts Sharpeyâs (perforating) fibers penetrate the bone matrix and bind periosteum to bone Inner layer of osteoprogenitor cells and osteoblasts Functions: Provide nutrition for osseous tissue Supply osteoblasts for repair or appositional bone growth Endosteum - lines internal cavities (and trabeculae) within bone 1 layer of flat osteoprogenitor cells, osteoblasts, and some connective tissuePerichondrium is vascularized & bone collar formed Perichondrium becomes periosteum with osteoblasts which secrete bone matrix (collar blocks nutrients from reaching chondrocytes) Primary ossification center produced Chondrocytes enlarge,compress matrix (into trabeculae), calcify matrix (release enzymes and osteocalcin), die & leave large empty lacunae (cavity); periosteal bud brings osteoprogenitor cells & osteoblasts which lay down bone (woven) matrix on septa of cartilage matrix Osteoclasts resorb calcified cartilage/bone complex and enlarge cavity which fills with bone marrow; bone replaces cartilage along diaphysisOsteocytes (maintain matrix; help regulate bone remodeling) Surrounded by matrix and located (singly) in a lacunae (pl.) Cytoplasmic processes are housed in matrix canaliculi (where exchange of metabolites occurs with other cells. They act as sensors detecting mechanical stresses on bone.Primary ossification center produced Chondrocytes enlarge,compress matrix (into trabeculae), calcify matrix (release enzymes and osteocalcin), die & leave large empty lacunae (cavity); periosteal bud brings osteoprogenitor cells & osteoblasts which lay down bone (woven) matrix on septa of cartilage matrix Osteoclasts resorb calcified cartilage/bone complex and enlarge cavity which fills with bone marrow; bone replaces cartilage along diaphysisZones in epiphyseal cartilage (regions of cellular activity) Zone 1: Zone of Resting cartilage Zone 2: Zone of proliferating cartilage Chondrocytes aligned as aggregates in lacunae Zone 3:Zone of hypertrophic cartilage Cells enlarge; matrix compressed into bands Zone 4: zone of calcified cartilage Cells calcify the matrix (hydroxyapatite crystals formed); undergo apoptosis Zone 5: Zone of ossification Vessels invade region; osteoblasts deposit osteoid on calcified spicules of cartilage forming woven bone; remodeled as lamellar boneNutrition, Metabolism, and Body Temperature Regulation. Nutrient is a substance that promotes normal growth, maintenance, and repair. Major nutrients are carbohydrates, lipids, and proteins. Other nutrients include vitamins and minerals (and technically speaking, water).Complex carbohydrates (starches) are found in bread, cereal, flour, pasta, nuts, and potatoes .Simple carbohydrates (sugars) are found in soft drinks, candy, fruit, and ice cream.Glucose is the molecule ultimately used by body cells to make ATP.Neurons and RBCs rely almost entirely upon glucose to supply their energy needs.Excess glucose is converted to glycogen or fat and stored .The most abundant dietary lipids, triglycerides, are found in both animal and plant foods.Essential fatty acids â linoleic and linolenic acid, found in most vegetables, must be ingested. Dietary fats help the body to absorb vitamins, a major energy fuel of hepatocytes and skeletal muscle, and a component of myelin sheaths and all cell membranes. Lipids functions in smooth muscle contraction, control of blood pressure and inflammation. Cholesterol stabilizes membranes and is a precursor of bile salts and steroid hormones. The dietary requirements for lipids are higher for infants and children than for adults. The American Heart Association suggests that fats should represent less than 30% of oneâs total caloric intake, saturated fats should be limited to 10% or less of oneâs total fat intake, and daily cholesterol intake should not exceed 200 mg. Complete proteins that meet all the bodyâs amino acid needs are found in eggs, milk, milk products, meat, and fish.Incomplete proteins are found in legumes, nuts, seeds, grains, and vegetables. Essential amino acids are the building blocks for nonessential amino acids. Protein supply for nonprotein nitrogen-containing substances. Daily intake should be approximately 0.8g/kg of body weight. All amino acids needed must be present at the same time for protein synthesis to occur. Protein will be used as fuel if there is insufficient carbohydrate or fat available. The rate of protein synthesis equals the rate of breakdown and loss. Anabolic hormones accelerate protein synthesis. Vitamins are organic compounds needed for growth and good health. They are crucial in helping the body use nutrients and often function as coenzymes. Only vitamins D, K, and B are synthesized in the body; all others must be ingested. Water-soluble vitamins (B-complex and C) are absorbed in the gastrointestinal tract . Vitamin B12 additionally requires gastric intrinsic factor to be absorbed. Fat-soluble vitamins (A, D, E, and K) bind to ingested lipids and are absorbed with their digestion products. Vitamins A, C, and E also act in an antioxidant cascade. There are seven minerals are required in moderate amounts . These are calcium, phosphorus, potassium, sulfur, sodium, chloride, and magnesium. Dozens are required in trace amounts. Minerals work with nutrients to ensure proper body functioning. Calcium, phosphorus, and magnesium salts harden bone.