4Four Bone TypesLong bones – extended longitudinal axis and expanded and often uniquely shaped articular ends.Examples are the femur and humerusShort Bones – cube- or box-shaped structure, which are about as broad as they are long.Examples include the wrist (carpals) and ankle (tarsal) bones
5Flat bones – generally broad and thin with a flattened and often curved surface. Examples include some skull bones, scapulae, ribs, and sternumIrregular Bones – often clustered in groups and come in various shapes and sizes.Examples include the vertebral bones that form the spine and facial bones
7Parts of a Long Bone Diaphysis – main shaftlike portion Epiphyses – both ends of a long bone have a bulbous shape that provides generous space near the joints for stability and muscle attachment.Articular Cartilage – thin layer of hyaline cartilage that covers joint epiphyses and acts as a cushion.
8Periosteum – Dense, white fibrous membrane that covers bone except at joint surfaces Medullary (marrow) cavity – tubelike hollow space in the diaphysis of a long bone. In adults it is filled with fatty yellow marrow.Endosteum – thin epithelial membrane that lines the medullary cavity of long bones.
10Bone (Osseous) Tissue Connective tissue Consists of cells, fibers, and extracellular matrixExtracellular components are hard and calcifiedMatrix is more abundant that the bone cells
11Composition of Bone Matrix Inorganic Salt are responsible for the hardness of bone.Hydroxyapatite – composed of calcium and phosphateOrganic Matrix – composite of collagenous fibers and a mixture of protein and polysaccharides called ground substance.
12OsteoporosisAge related skeletal disease that is characterized by loss of bone mineral density, increased bone fragility, and susceptibility to fracturesMore common in womenMay lose 4% - 8% of their bone density on a yearly basis
14Microscopic Structure of Bone Compact bone contains many cylinder-shaped structural units called osteons, or Haversian systems.Each osteon surrounds a canal that runs lengthwise through the bone.
15Main Structures of the Osteon Lamellae – concentric, cylinder shaped layers of calcified matrix.Lacunae – small spaces containing fluid and bone cellsCanaliculi – ultrasmall canals radiating in all directions from the lacunae that connects them to each other and the Haversian canal
16Haversian canal – Extends lengthwise through the center of each Haversian system; contains blood vessels, lymph vessels and nervesVolkmann’s canals – run perpendicular to Haversian canals
19Cancellous Bone There are no osteons in cancellous bone Consists of needle-like bony spicules called trabeculae.Bone cells are found within the trabaculaeNutrients are delivered and wastes removed by diffusion
21Types of Bone CellsOsteoblasts – synthesize and secrete a specialized organic matrix called osteoid, that is an important part of the ground substance of bone. (bone forming cells)Osteoclasts – giant multinucleate cells that are responsible for the active erosion of bone minerals. (bone reabsorbing cells)
22Osteocytes – mature, non-dividing osteoblasts that have become surrounded by matrix and now within a lacunae.
25Bone Marrow Soft, diffuse connective tissue called myeloid tissue. Site of blood cell productionFound in medullary cavities of certain long bones and in the spaces of some spongy bones.
26Red Marrow & Yellow Marrow In a child’s body, virtually all of the bones contain red marrow.Red marrow produces red blood cells.As an individual ages red marrow is replaced by yellow marrow.Yellow marrow has become saturated with fat and is no longer active in blood cell production.
28Functions of Bone Support – supporting framework of body Protection – protect delicate structures such as the brainMovement – joints act as levers and allow movement in conjuction with muscular systemMineral Storage – major reservoir for calcium, phosphorus, and certain other mineralsHematopoiesis – blood cell formation
29Regulation of Blood Calcium Levels 98% of body calcium is stored in boneOsteoblasts remove calcium from bloodOsteoclasts break down bone and calcium levels in the blood increasesCalcium is important for normal blood clotting, nerve impulses, and muscle contraction
30Calcium in the BodyCalcium that is consumed is absorbed through the intestinesCalcium is stored and released from bone tissueThe kidneys eliminate extra calcium and absorb calcium from urine if blood calcium levels get too low.
31Parathyroid HormoneWhen calcium levels fall below their “set point,” osteoclasts are stimulated to increase the rate of bone matrix breakdown.Calcium is released into the blood until the level returns to normal.
32Vitamin D (Calcitriol) Acts to increase blood calcium levelsFacilitates the absorption of calcium in the small intestines
33Calcitonin Functions to reduce blood calcium levels Enhances excretion of calcium in urineInhibits osteoclasts
35Development of BoneBefore birth, the skeleton consists of cartilage and fibrous structures shaped like bones.Cartilage is replaced with calcified bone matrixThe combined action of osteoblast and osteoclasts to make bone is known as osteogenesis
45Bone Growth and Resorption Bone growth is from the combined action of osteoclasts and osteoblastsOsteoclasts break down bone to enlarge the diameter of the medullary cavity.Osteoblasts from the periosteum build new bone around the outside of the bone