Literatura científica selecionada sobre o tema "Resorption (Physiology)"

Bone remodelling is important to maintain the skeletal physiology. Bone loss with aging and hormonal pathologies may be result ofaltered bone remodelling leading to osteoporosis. Even in presence of existing therapies, there is an unmet clinical need to look forideal alternatives that would stimulate bone formation and keep resorption in check. Adiponectin and its derivatives could be a possiblecandidate for such therapy. Orally active small molecule AdipoR agonists may be a proposed solution for this.

Pregnant women present different changes in the skeletal system, such as the increase in calcium throughout this period, there are also small reductions in bone density. Orthodontic tooth movement is based on the principles of tissue resorption and formation at the level of the surrounding bone and periodontal ligament. It should be noted that there are multiple factors that affect the speed of this type of movement. During pregnancy and lactation, certain alterations in orthodontic dental movement may be perceived, caused by changes in bone homeostasis, alterations in tooth resorption and observed bone deposition. In this article we will cover topics such as the physiology and history of pregnancy, as well as the analysis of various articles related to orthodontic dental movement in pregnant women.

Osteoclasts are multinucleated cells that resorb bone by extrusion of protons and proteolytic enzymes. They display marked heterogeneity in cell size, shape, and resorptive activity. Because high resorptive activity in vivo is associated with an increase in the average size of osteoclasts in areas of greater resorption and because of the importance of proton extrusion in resorption, we investigated whether the activity of the bafilomycin A1-sensitive vacuolar-type H+-ATPase (V-ATPase) and amiloride-sensitive Na+/H+ exchanger differed between large and small osteoclasts. Osteoclasts were obtained from newborn rabbit bones, cultured on glass coverslips, and loaded with the pH-sensitive indicator 2′,7′-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF). Intracellular pH (pHi) was recorded in single osteoclasts by monitoring fluorescence. Large (≥10 nuclei) and small (≤5 nuclei) osteoclasts differed in that large osteoclasts had a higher basal pHi, their pHi was decreased by bafilomycin A1 addition or removal of extracellular Na+, and the realkalinization upon readdition of Na+ was bafilomycin A1 sensitive. After acid loading, a subpopulation of large osteoclasts (40%) recovered by V-ATPase activity alone, whereas all small osteoclasts recovered by Na+/H+ exchanger activity. Interestingly, in 60% of the large osteoclasts, pHi recovery was mediated by both the Na+/H+ exchanger and V-ATPase activity. Our results show a striking difference between pHi regulatory mechanisms of large and small osteoclasts that we hypothesize may be associated with differences in the potential resorptive activity of these cells.

The decrease in cancellous bone formation after estrogen treatment is generally thought to be coupled with a prior decrease in bone resorption. To test the possibility that estrogen has rapid tissue-specific actions on bone metabolism, we determined the time course (1–32 h) effects of diethylstilbestrol on steady-state mRNA levels for immediate-response genes, extracellular matrix proteins, and signaling peptides in the proximal tibial metaphysis and uterus by using Northern blot and RNase protection assays. The regulation of signaling peptides by estrogen, although tissue specific, followed a similar time course in bone and uterus. The observed rapid decreases in expression of insulin-like growth factor I, a growth factor associated with bone formation; decreases in mRNA levels for bone matrix proteins; evidence for reduced bone matrix synthesis; failure to detect rapid increases in mRNA levels for signaling peptides implicated in mediating the inhibitory effects of estrogen on bone resorption (interleukin-1 and -6) as well as other cytokines that can increase bone resorption; and the comparatively long duration of the bone remodeling cycle in rats indicate that estrogen can decrease bone formation by a mechanism that does not require a prior reduction in bone resorption.

We investigated potential sex differences in bone resorption and the conservation of whole body bone mass in 24-week-old Sprague-Dawley rats maintained on a 1.0% calcium diet and then fed diets containing 0.02, 0.5, 1.0, or 1.75% calcium for 31 days. Lowering dietary calcium from 1.00% to 0.02% doubled whole skeleton bone resorption (urinary 3H-tetracycline loss). Female rats were more sensitive to calcium stress, exhibiting the maximal resorptive response when fed the 0.5% calcium diet, whereas the 0.02% calcium diet was required to elicit this response in males. Despite the evidence of increased bone resorption, whole skeleton mass was unchanged in females and was significantly increased in males, indicating that switching to even the 0.02% calcium diet did not result in an overt loss of total body bone mass. Compared with controls, the skeleton mass of females (97 ± 1.4%) maintained on the 0.02% calcium diet was significantly lower than males (107 ± 2.4%), again suggesting a greater impact of calcium deficiency in females. The calculation of the average percentage growth of selected individual bones in male rats indicated a proportional increase in bone mass between the axial and appendicular skeleton of approximately +4% and +18% in animals maintained on 0.02 and 1.75% diets, respectively. By comparison, female rats consuming the 0.02% calcium diet showed an average 14% loss in axial bone and 7.5% gain in appendicular bone mass. The results indicate increased sensitivity to dietary calcium deficiency in female rats which involves a significant loss in axial bone mass not observed in male rats maintained under similar dietary conditions.Key words: skeleton bone mass, calcium diet, 3H-tetracycline, axial, appendicular, gender, sex.

Calcitonin was discovered as a peptide hormone that was known to reduce the calcium levels in the systemic circulation. This hypocalcemic effect is produced due to multiple reasons such as inhibition of bone resorption or suppression of calcium release from the bone. Thus, calcitonin was said as a primary regulator of the bone resorption process. This is the reason why calcitonin has been used widely in clinics for the treatment of bone disorders such as osteoporosis, hypercalcemia, and Paget’s disease. However, presently calcitonin usage is declined due to the development of efficacious formulations of new drugs. Calcitonin gene-related peptides and several other peptides such as intermedin, amylin, and adrenomedullin (ADM) are categorized in calcitonin family. These peptides are known for the structural similarity with calcitonin. Aside from having a similar structure, these peptides have few overlapping biological activities and signal transduction action through related receptors. However, several other activities are also present that are peptide specific. In vitro and in vivo studies documented the posttreatment effects of calcitonin peptides, i.e., positive effect on bone osteoblasts and their formation and negative effect on osteoclasts and their resorption. The recent research studies carried out on genetically modified mice showed the inhibition of osteoclast activity by amylin, while astonishingly calcitonin plays its role by suppressing osteoblast and bone turnover. This article describes the review of the bone, the activity of the calcitonin family of peptides, and the link between them.

Bone remodeling is essential for the repair and replacement of damaged and old bone. The major principle underlying this process is that osteoclast-mediated resorption of a quantum of bone is followed by osteoblast precursor recruitment; these cells differentiate to matrix-producing osteoblasts, which form new bone to replace what was resorbed. Evidence from osteopetrotic syndromes indicate that osteoclasts not only resorb bone, but also provide signals to promote bone formation. Osteoclasts act upon osteoblast lineage cells throughout their differentiation by facilitating growth factor release from resorbed matrix, producing secreted proteins and microvesicles, and expressing membrane-bound factors. These multiple mechanisms mediate the coupling of bone formation to resorption in remodeling. Additional interactions of osteoclasts with osteoblast lineage cells, including interactions with canopy and reversal cells, are required to achieve coordination between bone formation and resorption during bone remodeling.

Amniotic fluid (AF) volume regulation is dependent on a balance between fluid production and fluid resorption. We examined the effects of reduced AF volume on AF production by fetal urine and resorption by fetal swallowing and the response of these parameters to AF volume replacement. Eight time-dated pregnant ewes (125 +/- 1 days gestation) were studied before (day 1) and after (day 3) AF and fetal urine drainage. Drainage resulted in a significant decrease in AF volume (415 +/- 89 to 157 +/- 36 ml). Fetal urine osmolality increased (139 +/- 10 to 286 +/- 33 mosmol/kgH2O), while urine flow did not change significantly (0.31 +/- 0.04 to 0.23 +/- 0.06 ml/min), resulting in nonsignificant increases in osmolar, sodium, and chloride excretions. Fetal electromyographic swallowing activity decreased 30% (1.0 +/- 0.1 to 0.7 +/- 0.1 swallows/min; P < 0.05), while net esophageal flow decreased 74% (0.31 +/- 0.12 to 0.07 +/- 0.04 ml/min; P < 0.05). On day 4, 0.15 M NaCl (500 ml; 37 degrees C) was administered into the AF over 30 min. During the 2 h after reinfusion, urine flow (0.29 +/- 0.07 to 0.40 +/- 0.09 ml/min) and osmolar sodium and chloride excretion significantly increased, though fetal swallowing activity and esophageal flow did not change. Thus the ovine fetus responded to reduced AF volume by maintaining AF production and decreasing AF resorption. In response to AF replacement, urine flow increased while fetal swallowing activity did not change, consistent with an intramembranous pathway for fetal AF resorption.

Osteoclasts generate a massive acid flux to mobilize bone calcium. Local extracellular acidification by polarized vacuolar-type H(+)-ATPase, balanced by contralateral HCO3-(-)Cl- exchange to maintain physiological intracellular pH, is theorized to drive this process. It follows that extracellular pH, PCO2, or HCO3- concentration ([HCO3-]) should impact bone matrix dissolution. However, the effects on bone resorption of the concentrations of these ions or their transmembrane gradients are unknown. Furthermore, because bone management is a vital process, regulatory feedback may minimize such effects. Thus a complex relationship between bone resorption and pH, PCO2, and [HCO3-] is expected but requires experimental determination. We measured bone resorption by isolated avian osteoclasts while varying these parameters across the physiological range. Bone degradation increased 50% from pH 7.3 to 6.7, whether achieved by changing [HCO3-] (2.3-38 mM) at constant HCO3- or PCO2 (15-190 mmHg) at constant [HCO3-]. However, at constant pH, changing PCO2 and [HCO3-] within physiological limits did not affect bone resorption. In contrast, total HCO3- removal at pH 7.4 reduced bone degradation by rat or avian osteoclasts substantially, confirming that normal acid secretion requires HCO3-. These observations support a model coupling osteoclastic bone resorption to proton and HCO3- transport but indicate that [HCO3-] is not rate limiting under physiological conditions. Extracellular pH changes affect osteoclastic bone resorption measurably, but not dramatically, at physiological [HCO3-].

In 1932 Beck and Marshall defined root resorption as the destruction of formed tooth structure. Root resorption results in the loss of substance from dentine or cementum and can present as either a physiological or pathological process. Physiological root resorption can occur in both deciduous and permanent dentition. Root resorption of the deciduous dentition is a normal and essential physiological process that facilitates natural exfoliation. Pathological resorption is an inflammatory process that is triggered by numerous factors. Root resorption following orthodontic treatment is intimately associated with the biological processes that occur during tooth movement. To date, the mechanism of orthodontically induced inflammatory root resorption (henceforth referred to as OIIRR) has not been fully understood. The pathological process is related to local injury of the periodontal ligament associated with the removal of hyalinised tissue. This process has been found to take place when local areas of the periodontal ligament are overcompressed. The phenomenon is widely known as OIIRR and is often unpredictable; it is an inevitable pathological consequence of orthodontic tooth movement that compromises the success of orthodontic treatment. The incidence of OIIRR ranges from 73% to 100% in recent studies} and its prevalence has been shown to increase with orthodontic treatment. Experimental research concludes that all human teeth develop resorption lacunae on the pressure side of the root surface shortly after application of orthodontic forces.

Bones are multifunctional passive organs of movement that supports soft tissue and directly attached muscles. They also protect internal organs and are a reserve of calcium, phosphorus and magnesium. Each bone is covered with periosteum, and the adjacent bone surfaces are covered by articular cartilage. Histologically, the bone is an organ composed of many different tissues. The main component is bone tissue (cortical and spongy) composed of a set of bone cells and intercellular substance (mineral and organic), it also contains fat, hematopoietic (bone marrow) and cartilaginous tissue. Bones are a tissue that even in adult life retains the ability to change shape and structure depending on changes in their mechanical and hormonal environment, as well as self-renewal and repair capabilities. This process is called bone turnover. The basic processes of bone turnover are: • bone modeling (incessantly changes in bone shape during individual growth) following resorption and tissue formation at various locations (e.g. bone marrow formation) to increase mass and skeletal morphology. This process occurs in the bones of growing individuals and stops after reaching puberty • bone remodeling (processes involve in maintaining bone tissue by resorbing and replacing old bone tissue with new tissue in the same place, e.g. repairing micro fractures). It is a process involving the removal and internal remodeling of existing bone and is responsible for maintaining tissue mass and architecture of mature bones. Bone turnover is regulated by two types of transformation: • osteoclastogenesis, i.e. formation of cells responsible for bone resorption • osteoblastogenesis, i.e. formation of cells responsible for bone formation (bone matrix synthesis and mineralization) Bone maturity can be defined as the completion of basic structural development and mineralization leading to maximum mass and optimal mechanical strength. The highest rate of increase in pig bone mass is observed in the first twelve weeks after birth. This period of growth is considered crucial for optimizing the growth of the skeleton of pigs, because the degree of bone mineralization in later life stages (adulthood) depends largely on the amount of bone minerals accumulated in the early stages of their growth. The development of the technique allows to determine the condition of the skeletal system (or individual bones) in living animals by methods used in human medicine, or after their slaughter. For in vivo determination of bone properties, Abstract 10 double energy X-ray absorptiometry or computed tomography scanning techniques are used. Both methods allow the quantification of mineral content and bone mineral density. The most important property from a practical point of view is the bone’s bending strength, which is directly determined by the maximum bending force. The most important factors affecting bone strength are: • age (growth period), • gender and the associated hormonal balance, • genotype and modification of genes responsible for bone growth • chemical composition of the body (protein and fat content, and the proportion between these components), • physical activity and related bone load, • nutritional factors: – protein intake influencing synthesis of organic matrix of bone, – content of minerals in the feed (CA, P, Zn, Ca/P, Mg, Mn, Na, Cl, K, Cu ratio) influencing synthesis of the inorganic matrix of bone, – mineral/protein ratio in the diet (Ca/protein, P/protein, Zn/protein) – feed energy concentration, – energy source (content of saturated fatty acids - SFA, content of polyun saturated fatty acids - PUFA, in particular ALA, EPA, DPA, DHA), – feed additives, in particular: enzymes (e.g. phytase releasing of minerals bounded in phytin complexes), probiotics and prebiotics (e.g. inulin improving the function of the digestive tract by increasing absorption of nutrients), – vitamin content that regulate metabolism and biochemical changes occurring in bone tissue (e.g. vitamin D3, B6, C and K). This study was based on the results of research experiments from available literature, and studies on growing pigs carried out at the Kielanowski Institute of Animal Physiology and Nutrition, Polish Academy of Sciences. The tests were performed in total on 300 pigs of Duroc, Pietrain, Puławska breeds, line 990 and hybrids (Great White × Duroc, Great White × Landrace), PIC pigs, slaughtered at different body weight during the growth period from 15 to 130 kg. Bones for biomechanical tests were collected after slaughter from each pig. Their length, mass and volume were determined. Based on these measurements, the specific weight (density, g/cm3) was calculated. Then each bone was cut in the middle of the shaft and the outer and inner diameters were measured both horizontally and vertically. Based on these measurements, the following indicators were calculated: • cortical thickness, • cortical surface, • cortical index. Abstract 11 Bone strength was tested by a three-point bending test. The obtained data enabled the determination of: • bending force (the magnitude of the maximum force at which disintegration and disruption of bone structure occurs), • strength (the amount of maximum force needed to break/crack of bone), • stiffness (quotient of the force acting on the bone and the amount of displacement occurring under the influence of this force). Investigation of changes in physical and biomechanical features of bones during growth was performed on pigs of the synthetic 990 line growing from 15 to 130 kg body weight. The animals were slaughtered successively at a body weight of 15, 30, 40, 50, 70, 90, 110 and 130 kg. After slaughter, the following bones were separated from the right half-carcass: humerus, 3rd and 4th metatarsal bone, femur, tibia and fibula as well as 3rd and 4th metatarsal bone. The features of bones were determined using methods described in the methodology. Describing bone growth with the Gompertz equation, it was found that the earliest slowdown of bone growth curve was observed for metacarpal and metatarsal bones. This means that these bones matured the most quickly. The established data also indicate that the rib is the slowest maturing bone. The femur, humerus, tibia and fibula were between the values of these features for the metatarsal, metacarpal and rib bones. The rate of increase in bone mass and length differed significantly between the examined bones, but in all cases it was lower (coefficient b <1) than the growth rate of the whole body of the animal. The fastest growth rate was estimated for the rib mass (coefficient b = 0.93). Among the long bones, the humerus (coefficient b = 0.81) was characterized by the fastest rate of weight gain, however femur the smallest (coefficient b = 0.71). The lowest rate of bone mass increase was observed in the foot bones, with the metacarpal bones having a slightly higher value of coefficient b than the metatarsal bones (0.67 vs 0.62). The third bone had a lower growth rate than the fourth bone, regardless of whether they were metatarsal or metacarpal. The value of the bending force increased as the animals grew. Regardless of the growth point tested, the highest values were observed for the humerus, tibia and femur, smaller for the metatarsal and metacarpal bone, and the lowest for the fibula and rib. The rate of change in the value of this indicator increased at a similar rate as the body weight changes of the animals in the case of the fibula and the fourth metacarpal bone (b value = 0.98), and more slowly in the case of the metatarsal bone, the third metacarpal bone, and the tibia bone (values of the b ratio 0.81–0.85), and the slowest femur, humerus and rib (value of b = 0.60–0.66). Bone stiffness increased as animals grew. Regardless of the growth point tested, the highest values were observed for the humerus, tibia and femur, smaller for the metatarsal and metacarpal bone, and the lowest for the fibula and rib. Abstract 12 The rate of change in the value of this indicator changed at a faster rate than the increase in weight of pigs in the case of metacarpal and metatarsal bones (coefficient b = 1.01–1.22), slightly slower in the case of fibula (coefficient b = 0.92), definitely slower in the case of the tibia (b = 0.73), ribs (b = 0.66), femur (b = 0.59) and humerus (b = 0.50). Bone strength increased as animals grew. Regardless of the growth point tested, bone strength was as follows femur > tibia > humerus > 4 metacarpal> 3 metacarpal> 3 metatarsal > 4 metatarsal > rib> fibula. The rate of increase in strength of all examined bones was greater than the rate of weight gain of pigs (value of the coefficient b = 2.04–3.26). As the animals grew, the bone density increased. However, the growth rate of this indicator for the majority of bones was slower than the rate of weight gain (the value of the coefficient b ranged from 0.37 – humerus to 0.84 – fibula). The exception was the rib, whose density increased at a similar pace increasing the body weight of animals (value of the coefficient b = 0.97). The study on the influence of the breed and the feeding intensity on bone characteristics (physical and biomechanical) was performed on pigs of the breeds Duroc, Pietrain, and synthetic 990 during a growth period of 15 to 70 kg body weight. Animals were fed ad libitum or dosed system. After slaughter at a body weight of 70 kg, three bones were taken from the right half-carcass: femur, three metatarsal, and three metacarpal and subjected to the determinations described in the methodology. The weight of bones of animals fed aa libitum was significantly lower than in pigs fed restrictively All bones of Duroc breed were significantly heavier and longer than Pietrain and 990 pig bones. The average values of bending force for the examined bones took the following order: III metatarsal bone (63.5 kg) <III metacarpal bone (77.9 kg) <femur (271.5 kg). The feeding system and breed of pigs had no significant effect on the value of this indicator. The average values of the bones strength took the following order: III metatarsal bone (92.6 kg) <III metacarpal (107.2 kg) <femur (353.1 kg). Feeding intensity and breed of animals had no significant effect on the value of this feature of the bones tested. The average bone density took the following order: femur (1.23 g/cm3) <III metatarsal bone (1.26 g/cm3) <III metacarpal bone (1.34 g / cm3). The density of bones of animals fed aa libitum was higher (P<0.01) than in animals fed with a dosing system. The density of examined bones within the breeds took the following order: Pietrain race> line 990> Duroc race. The differences between the “extreme” breeds were: 7.2% (III metatarsal bone), 8.3% (III metacarpal bone), 8.4% (femur). Abstract 13 The average bone stiffness took the following order: III metatarsal bone (35.1 kg/mm) <III metacarpus (41.5 kg/mm) <femur (60.5 kg/mm). This indicator did not differ between the groups of pigs fed at different intensity, except for the metacarpal bone, which was more stiffer in pigs fed aa libitum (P<0.05). The femur of animals fed ad libitum showed a tendency (P<0.09) to be more stiffer and a force of 4.5 kg required for its displacement by 1 mm. Breed differences in stiffness were found for the femur (P <0.05) and III metacarpal bone (P <0.05). For femur, the highest value of this indicator was found in Pietrain pigs (64.5 kg/mm), lower in pigs of 990 line (61.6 kg/mm) and the lowest in Duroc pigs (55.3 kg/mm). In turn, the 3rd metacarpal bone of Duroc and Pietrain pigs had similar stiffness (39.0 and 40.0 kg/mm respectively) and was smaller than that of line 990 pigs (45.4 kg/mm). The thickness of the cortical bone layer took the following order: III metatarsal bone (2.25 mm) <III metacarpal bone (2.41 mm) <femur (5.12 mm). The feeding system did not affect this indicator. Breed differences (P <0.05) for this trait were found only for the femur bone: Duroc (5.42 mm)> line 990 (5.13 mm)> Pietrain (4.81 mm). The cross sectional area of the examined bones was arranged in the following order: III metatarsal bone (84 mm2) <III metacarpal bone (90 mm2) <femur (286 mm2). The feeding system had no effect on the value of this bone trait, with the exception of the femur, which in animals fed the dosing system was 4.7% higher (P<0.05) than in pigs fed ad libitum. Breed differences (P<0.01) in the coross sectional area were found only in femur and III metatarsal bone. The value of this indicator was the highest in Duroc pigs, lower in 990 animals and the lowest in Pietrain pigs. The cortical index of individual bones was in the following order: III metatarsal bone (31.86) <III metacarpal bone (33.86) <femur (44.75). However, its value did not significantly depend on the intensity of feeding or the breed of pigs.

This chapter discusses the anatomy and physiology of the bone, including mineralization, and outlines techniques in bone remodelling. It describes formation and resorption hormonal markers that are part of the bone remodelling cycle, such as procollagens and serums. It describes how diagnostic measures in these formation markers are increased for focal bone disorders like Paget’s disease, fibrous dysplasia, osteomalacia, bone metastases, myeloma, primary hyperparathyroidism, thyrotoxicosis, and acromegaly. The chapter also discusses osteoporosis, including causes, symptoms, and treatment options. Clinical suggestions for bone diagnoses and diseases are provided, based on dual-energy X-ray absorptiometry (commonly abbreviated as DXA), plain radiography, and bone biopsy. The chapter also defines osteogenesis imperfecta and describes its epidemiology and management. In addition, it outlines sclerosing bone disorders such as osteopetrosis, pycnodysostosis, and hyperostosis type Worth, as well as fibrodysplasia ossificans progressive.