FACT OR FICTION ? • YOUR SKELETON REPLACES ITSELF EVERY 1O YEARS
BONE IS A LIVING TISSUE!
Bone as a Tissue • Connective tissue with a matrix hardened by minerals (calcium phosphate) • Individual bones consist of bone tissue, marrow, blood, cartilage and periosteum • Continually remodels itself • Functions of the skeletal system • support, protection, movement, electrolyte balances,acid-base balance, and blood formation
THE FUNCTIONS OF BONE • Support the body with a by providing a frame • Protect softer tissues by shielding or encasing them • Provide points of attachment for muscles, so that the skeleton can act as levers as forces are generated by muscles. . • Houses blood-producing stem cells, and • Stores inorganic minerals necessary for bioreactions in the body. Also, stored in bone are lipids.
HUMAN SYSTEMS MAINTAIN HOMEOSTATSIS
Negative Feedback Mechanisms The net effect of the response to the stimulus is the SHUT OFF the original stimulus OR reduce its intensity.
Negative Feedback This is the Most common control mechanism!When Levels of hormone in blood or body return to Normal levels homeostasis shuts off loop at the hypothalamus and pituitary ( Most common Negative Feedback Loop)
Positive Feedback The initial stimulus does NOT cause a switch to be “shut off”. Rather, a CASCADE of more ON switches in response to the initial response occurs. Examples: Giving Birth and Blood Clotting
Bone Homeostasis Parathyroids regulate the homeostasis of blood calcium When blood calcium is low Osteoclasts tap into reserves and Bone is “demineralized” Calcium ions is released into blood Too much calcium in the blood? This hormone causes the deposition of Calcium into the bone matrix by osteoblasts
Homeostasis: the maintenance of • By releasing PO4 ions into the blood pH is balanced. • When blood Ca levels are low; it is taken from the bone; maintain blood Ca levels.
ANATOMY of a BONE
Spongy Bone • It may appear that the trabeculae are arranged in a haphazard manner, but they are organized to provide maximum strength similar to braces that are used to support a building. The trabeculae of spongy bone follow the lines of stress and can realign if the direction of stress changes.
Compact Bone • Compact or cortical bone, is made up many rod-like units called osteons or Haversian systems which run longitudinally within the bone. Haversian systems have a central Haversian canal which carries blood and lymphatic vessels and nerve branches.
General Features of Bones • Shaft (diaphysis) = cylinder of compact bone • marrow cavity (medullary cavity) lined with endosteum (osteogenic cells and reticular connective tissue) • Enlarged ends (epiphyses) • spongy bone covered by compact bone • enlarged to strengthen joint and attach ligaments • Joint surface covered with articular cartilage • Shaft covered with periosteum • outer fibrous layer of collagen • inner osteogenic layer of bone forming cells • Epiphyseal plate (growth plate)
Matrix of Osseous Tissue • Dry weight = 1/3 organic and 2/3 inorganic matter • Organic matter • collagen, glycosaminoglycans, proteoglycans and glycoproteins • Inorganic matter • 85% hydroxyapatite • 10% calcium carbonate • other minerals (fluoride, potassium, magnesium) • Combination provides for strength and resilience • minerals resist compression; collagen resists tension • bone adapts by varying proportions
This is the form that Calcium Phosphate takes on in bone tissue. Calcium Phosphate Ca3(PO4)2 accounts for 2/3 weight of bone. Calcium Phosphate interacts with Ca(OH)2 to form Ca10(P04)6(OH)2 ( hydroxyapatite) Hydroxyapatite forms crystal that form plates and rods that lock with the collagen fibers of bone matrix. This allows for a flexable, yet shatter-resistant nature of bone . What is Hydroxyapatite?
Maybe Superior to Concrete! • Better than concrete INDEED! • As bone is able to REMODEL itself and repair itself after injury. • REMODELING: replacing old bone with new bone. Remodeling also allows bone to respond to changes in mechanical forces
During childhood, the long bones (in the arms, legs, and back) grow at the ends of the bones, whereas the flat bones (such as the skull) have a different pattern of growth.
THE CELLS OF BONE