bone tissue

6 basic functions of bone tissue

1. SUPPORT- provide frameworkfro the body by supporting soft tissues and providing points of attachment or most or most of the skeletal muscles 2. PROTECTION- protect many internal organs such as brain and spinal cord in addition the heart lungs and reproductive organs are given some degree of protection 3. MOVEMENT- most skeletal muscles attach to bones. when the muscles contract they pull on bones and movement is produced 4. MINERAL HOMEOSTASIS- bone tissue stores minerals particularly calcium and phosphorus. releases the minerals in bone matrix to maintain critical mineral balances 5. BLOOD CELL PRODUCTION- in all bones of the infant and certain bones of the adult, a connective tissueknown as red marrow produces blood cells by the process of hematopoiesis 6. STORAGE OF ENERGY-in some bones, yellow bone marrow stores lipidds, creating an important energy reserve for the body

parts of LONG BONE

DIAPHYSIS- shaft or long main portion EPIPHYSIS- the end portions. each epithysis is covered with articulating cartilage METAPHYSIS- region of mature bones where the diaphysis meets the epiphysis EPIPHYSEAL PLATE- in a growing bone, formed of hyaline cartilage divided into four zones of cells. ARTICULAR CARTILAGE- a thin layer of hyaline cartilage covering the articular surfaces of the epipyseal at a joint MEDULLARY CAVITY- space within the bone containing either red or yellow bone marrow. red bone marrow consists of blood precursors while yellow marrow consists of adipose tissue. PERIOSTEUM- double layered C.T. surrounding the bone and except where the articular cartilage is present. it is divided into outer fibrous and inner osteogenic layer ENDOSTEUM- single layer of osteoprogenitor cells lining the medullary cavity

3 parts of PERIOSTEUM

FIBROUS PERIOSTEUM- outer fibrous layer of the periosteum composed of dense irregular C.T. containing blood vessels, lymphatics, and nerves that pass onto the bone OSTEOGENIC PERIOSTEUM- the inner osteogenic layer of the periosteum contains elastic fibers and various bone cell types, particularly osteoprogenitor cells, that give rise to new osteoblasts when stimulated PERIOSTEAL PERIOSTEUM- fxns in bone growth, repair, and nutrition. in addition, it provides attachment points for skeletal muscles

BONE CELL TYPES

OSTEOPROGENITOR CELLS- immature quiscent cells lining the bone surfaces. when stimulate, they enter mitosis, giving rise to a new cell type called osteoblast OSTEOBLAST- once differentiated lose their mitotic ability and begin producing new bone matrix in a process known as osteogenesis OSTEOCYTES- are mature bone cells embedded in bone matrix, are incapable of mitosis, and probably do not secrete new matrix. OSTEOCLASTS- reside scattered along the endosteal surfaces. fxn in a process known as bone reabsorption, the destruction of bone matrix. this process is required for normal bone function.

REMODELING: bone homeostasis

REMODELING IS THE ONGOING REPLACEMENT OF OLD BONE TISSUE BY NEW BONE TISSUE. occurs as a delicate balance btwn bone reabsorption by osteoclasts and bone formation by osteoblasts. REMODELING ACCOMPLISHES 1. changes the way bone matrix resists stress 2. removes worn or injured bone 3. provides a resorvoir for body calcium

HISTOLOGY OF COMPACT BONE

VOLKSMANN CANAL- a minute passageway by means of which blood vessels and nerves from the periosteum of a bone penetrate into compact bone, HAVERSIAN CANAL- a circular channel running longitudinally in the center of an osteon of mature compact bone. contains blood and lymphatic vessels and nerves CONCENTRIC LAMELLAE- rings of calcified bone matrix surrounding the haversian canals of compact bone LACUNAE- "little lake" a small hollow space within bone matrix wherein resides an osteocyte. located between concentric lamellae CANALICULUS- a small channel or canal connecting two lacunae in compact bone. each caniliculus contains a cellular process of an osteocyte. OSTEON- basic unit of structure in adult compact bone consists of a central canal ith lamellae of matrix, lacunae, osteocytes, and caniliculi INTERSTITIAL LAMELLAE-fragments of older compact bone found btwn the newer osteons. partially destroyed during bone replacement

BONES ROLE IN CALCIUM HOMEOSTASIS

blood calcium levels are very tighty controlled between 9.5-10.5 mg% hormones parathyroid(PTH) and calcitonin(CT) as well as vitamin D are the principal regulators of blood calcium concentrations. control is regulated by a NEGATIVE FEEDBACK SYSTEM that regulated the amt of calcium in the blood. if it calcium levels drop too low- 1. the controlled condition is blood calcium which dropped below 9.5 mg% 2. parathyroid gland cells detect the lowered calcium concentration. this serves as input into the control center for the feedback system 3. the parathyroid gland cells respond to the input from the receptors by secreting parathyroid hormone into the blood. this is the output system! 4. the response to these effects is an increase in blood calcium levels and return to homeostasis as levels return to 9.5-10.5 mg% and feedback systen turns off PTH HAS 3 TARGETS (EFFECTORS)- 1. inc. bone reabsorption 2. inc. calcium reabsorption by kidneys 3. inc. absorption of calcium by the gut CALCITONIN(CT) has opp. effect when calcium levels get above 10.5 CT is secreted by throid gland causes 2 things to happen: 1. stops osteolysis and stimulates osteoblasts to create new bone matrix that will have to be calcified. 2. tells the kidneys to stop reabsorbing calcium, therefore allowing the excess calcium to leave the body in the urine. =net result is that blood calcium levels drop back into normocalcemia

SPONGY BONE

consists of lamellae(layers) of bone matrix arranged in an irregulat latticework of thin plates of bone called trabeculae. The spaces between the trabeculae are a part of the medullary cavity of the bone.

COMPACT BONE

contains very few spaces. the layers of bone matrix are packed together tightly forming osteons (haversian systems). It forms the external layer of all bones, providing protection and support and helps the long bone resist the stress of weight applied to them.

BONE MATRIX

matrix of bone contains an abundance of mineral salts embedded into homeogeneous framework of extracellular materials. 3 MAIN COMPONENTS OF BONE MATRIX: 1. tricalcium phosphate 2. ground substance 3. collagen fibers OSSIFICATION- the mineral salt, tricalcium phosphate, is deposited into the framework of ground substance and collagen fibers, they crystallize and the tissue ossifies. COLLAGEN FIBERS PROVIDE: PLIABILITY-bend freely without breaking and adjust to various conditions AND TENSILE STRENGTH- greatest longitudinal force a substance can bear without tearing apart___to resist being stretched or pulled apart. the mineral salts are crystallized onto the collagen fibers giving bone its hardness