4 Long Bone – Macroscopic Anatomy Epiphysis (end)covered with hyaline cartilagecompact bone forms exteriorspongy bone forms interiorcontains epiphyseal line/plateDiaphysis (middle)center composed of the medullary cavity containing yellow or red marrow. Marrow helps produce red blood cells.Fig 7.1
6 Microscopic AnatomyOsteon = circular structure organized around blood vesselsOsteocyte = bone cellsBone matrix = hard calcium-based material between cellsFig 7.3
7 Tissue Types – Compact Bone FunctionsHard and provides stability, framework, protectionStructureMatrix has hard mineral structure, based on calciumCells and matrix are arranged in regular, concentric patternCompact Bone
8 Tissue Types – Spongy Bone FunctionsLightens total bone weight and provides space for bone marrowStructureMatrix is softer mineral, less organized and less of itEmpty spaces between matrix structure are filled with bone marrowSpongy (cancellous) Bone
10 Tissue Types – Hyaline Cartilage FunctionsProvides soft and smooth covering to end of bone (articular surface)Helps provide smooth and easy movement between bones (at joints)Provides the starting material for new bone growthStructureMatrix is gelatinous with fibers and is evenly distributed between the cellsCells (chrondocytes) are found in pairs within capsules called lacunaeHyaline Cartilage
11 Bone Cells OSTEOCYTES = “bone” “cells” BONE IS NEVER AT REST = OSTEOBLASTS“bone builders” which depositcalcium into bonesOSTEOCLASTS“bone crushers” which breakdown bone to release calcium whenNeededBONE IS NEVER AT REST =homeostasis!!!
12 Bone Physiology Living bones perform the following processes: FormationStarts as an embryo, continues through fetal development and after birthGrowthOccurs from before birth through maturityRemodelOld matrix is removed and replaced with new matrixRepairDamaged bones will heal and return to normal structure
14 Bone Physiology – Formation Fetal bones are made of hyaline cartilageAs cartilage cells die, they are replaced with spongy bone in diaphysisAfter birth, spongy bone invades diaphysisCompact bone replaces spongy bone in diaphysisHyaline cartilage remains on epiphyseal surface and in growth plateFig 7.5
15 Epiphyseal plate -cartilage band indicates ossification is occurring and spongy bone is being deposited
17 Bone Physiology - Repair Hemotoma, a mass of clotted blood, forms at the fracture site.A fibrous callus forms, and cartilage matrix is secreted.Spongy bone forms to replace cartilage.Bone remodeling occurs to remove excess material and replace compact bone.
18 Bone Physiology - Remodeling Bone matrix is inorganic and breaks down over timeSpecific bone cells (osteoclasts) remove old, broken matrixOther bone cells (osteoblasts) re-make/deposit new matrixThe entire skeleton is re-modeled every 7-10 yearsRemodeling slows with age, elderly people have thinner bones and are more susceptible to broken bones as a result
19 Aging and Bone TissueThere are two principal effects of aging on bone tissue:1) Loss of bone massResults from the loss of calcium from bone matrixThe loss of calcium from bones is one of the symptoms in osteoporosis2) BrittlenessResults from a decreased rate of protein synthesisCollagen fibers gives bone its tensile strengthThe loss of tensile strength causes the bones to become very brittle and susceptible to fracture
21 CalcitoninReleased by cells of the thyroid gland in response to high blood [Ca2+].Calcitonin acts to “tone down” blood calcium levels.Calcitonin causes decreased osteoclast activity which results in decreased break down of bone matrix and decreased calcium being released into the blood.Calcitonin also stimulates osteoblast activity which means calcium will be taken from the blood and deposited as bone matrix.Notice the thyroid follicles on the right. The arrow indicates a C cell
22 Parathyroid HormoneReleased by the cells of the parathyroid gland in response to low blood [Ca2+].Causes blood [Ca2+] to increase.PTH will bind to osteoblasts and this will cause 2 things to occur:The osteoblasts will decrease their activity and they will release a chemical known as osteoclast-stimulating factor.Osteoclast-stimulating factor will increase osteoclast activity.Osteoclasts will begin breaking down bone in order to increase Ca 2+ into the blood.