peak bone mass

Examples of peak bone mass in the following topics:

• Osteoporosis

  • Weight-bearing exercise such as walking helps maintain bone strength.
  • Osteoporosis is a disease of the bones that leads to an increased risk of fracture.
  • In osteoporosis, the bone mineral density (BMD) is reduced, bone microarchitecture deteriorates, and the amount and variety of proteins in bone is altered.
  • The three main mechanisms by which osteoporosis develop are an inadequate peak bone mass (the skeleton develops insufficient mass and strength during growth), excessive bone resorption, and inadequate formation of new bone during remodeling.
  • Its main consequence is the increased risk of bone fractures.

• Bone Remodeling and Repair

  • Bone remodeling is the replacement of old bone tissue by new bone tissue.
  • It involves the processes of bone deposition or bone production done by osteoblasts and bone resorption done by osteoclasts, which break down old bone.
  • Bone turnover rates, the rates at which old bone is replaced by new bone, are quite high, with five to seven percent of bone mass being recycled every week.
  • Bones that are not subject to normal everyday stress (for example, when a limb is in a cast) will begin to lose mass.
  • Compact bone is added to create bone tissue that is similar to the original, unbroken bone.

• Bone Scans

  • Bone scans are a special type of nuclear scanning test that is often used to find bone cancer or bone inflammation.
  • Cells easily break free from the tumor mass and are carried in the lymph system to other areas of the body where they begin growing new tumors.
  • A bone scan is a nuclear scanning test to find certain abnormalities in bone that are triggering the bone's attempts to heal.
  • A nuclear bone scan is a functional test, which means it measures an aspect of bone metabolism or bone remodeling .
  • Nuclear bone scans are not to be confused with the completely different test often termed a "bone density scan," DEXA or DXA, which is a low exposure X-ray test measuring bone density to look for osteoporosis and other diseases where bones lose mass, without any bone re-building (osteoblastic) activity.

• Bone Repair

  • These processes culminate in a new mass of heterogeneous tissue that is known as the fracture callus.
  • The next phase is the replacement of the hyaline cartilage and woven bone with lamellar bone.
  • Substitution of the woven bone with lamellar bone precedes the substitution of the hyaline cartilage with lamellar bone.
  • This new lamellar bone is in the form of trabecular bone.
  • The remodeling process continues with substitution of the trabecular bone with compact bone.

• Stages of Bone Development

  • Bone tissue is a type of dense connective tissue.
  • They are responsible for the formation of the diaphyses of long bones, short bones, and certain parts of irregular bones.
  • Approximately 10% of the skeletal mass of an adult is remodeled each year.
  • The bone remodeling period refers to the average total duration of a single cycle of bone remodeling at any point on a bone surface.
  • Bone tissue is removed by osteoclasts, and then new bone tissue is formed by osteoblasts.

• Exercise and Bone Tissue

  • If loading on a particular bone increases, the bone will remodel itself and have time to become stronger to resist that sort of loading.
  • If the loading on a bone decreases, the bone will become weaker due to turnover.
  • It is less metabolically costly to maintain and there is no stimulus for continued remodeling that is required to maintain bone mass .
  • In females, growth is characterized by increased estrogen levels and increased mass and strength of bone relative to that of muscle; whereas in men, increases in testosterone fuel large increases in muscle, resulting in muscle forces that coincide with a large growth in bone dimensions and strength .
  • For these reasons, walking could be an appropriate approach to prevent osteoporosis and maintain bone mass.

• Isotopes

  • Since a mass spectrometer separates and detects ions of slightly different masses, it easily distinguishes different isotopes of a given element.
  • The five peaks in this spectrum demonstrate clearly that natural bromine consists of a nearly 50:50 mixture of isotopes having atomic masses of 79 and 81 amu respectively.
  • Thus, the bromine molecule may be composed of two 79Br atoms (mass 158 amu), two 81Br atoms (mass 162 amu) or the more probable combination of 79Br-81Br (mass 160 amu).
  • Fragmentation of Br2 to a bromine cation then gives rise to equal sized ion peaks at 79 and 81 amu.
  • For example, the small m/z=99 amu peak in the spectrum of 4-methyl-3-pentene-2-one (above) is due to the presence of a single 13C atom in the molecular ion.

• Characteristics of Mass Spectra

  • The most intense ion is assigned an abundance of 100, and it is referred to as the base peak.
  • Most of the ions formed in a mass spectrometer have a single charge, so the m/z value is equivalent to mass itself.
  • The initial diagrams below are followed by a partial fragmentation analysis and peak assignment.
  • The molecular ion is also the base peak, and the only fragment ions are CO (m/z=28) and O (m/z=16).
  • A similar bond cleavage in cyclopropane does not give two fragments, so the molecular ion is stronger than in propane, and is in fact responsible for the the base peak.

• Aging and the Endocrine System

  • In the developing human body, GH from the anterior pituitary gland stimulates production and release of IGF-I by the liver, which is then transported in the blood to stimulate growth of muscle and bone.
  • Declines in pituitary GH secretion are associated with loss of skeletal muscle mass, increased adiposity, and other detrimental effects of aging in elderly humans.
  • With aging, there is a decrease in the amount of circulating GH and consequently IGF-I which results in weaker bones with a low bone mineral density (BMD).
  • In addition to lower circulating amounts of IGF-I, the responsiveness of the bone to this protein has been shown to decrease in animal models.
  • DHEA peaks in the mid-20's and then gradually declines with aging (termed adrenopause) and can reach as low as 5% of its original level.

• Nuclear Binding Energy and Mass Defect

  • This energy has mass, which is removed from the total mass of the original particles.
  • Mass defect (Md) can be calculated as the difference between observed atomic mass (mo) and that expected from the combined masses of its protons (mp, each proton having a mass of 1.00728 amu) and neutrons (mn, 1.00867 amu):
  • Mass must be in units of kg.
  • As such, there is a peak at iron-56 on the nuclear binding energy curve.
  • The rationale for this peak in binding energy is the interplay between the coulombic repulsion of the protons in the nucleus, because like charges repel each other, and the strong nuclear force, or strong force.