DCAP PPT Chapter 6 Bone Tissue Functions of
DCAP PPT Chapter 6 Bone Tissue
Functions of Bones
Bone marrow ¨ Aka myeloid tissue ¨ Yellow bone marrow – Fat storage – Found in medullary canal of long bones ¨ Red bone marrow – Found in spongy bone (ends of long bones, flat bones, irregular bones) – Hematopoiesis (formation of all blood cells)
Types of Bone Tissue
Cortical bone tissue ¨ Arranged in OSTEONS/ Haversian system – Repeated structural units ¨ Provide strength by providing a weight bearing surface ¨ Contains a series of openings that permit exchange of materials between osteocytes (& other bone cells) and the blood.
Osteon parts & functions ¨ Central/Haversian canal – central canal of each osteon – runs down the long axis of the bone ¨ Perforating/Volkmann’s canal – runs perpendicular to the Haversian canals – these are the communicating pathways from outside the bone to inside the bone ¨ Both provide passageways for BV & nerves
Types of Lamellae ¨ Lamellae – concentric rings or circles of matrix ¨ Circumferential lamellae – Rings that surround entire bone – Located deep to periosteum
Types of Lamellae ¨ Concentric lamellae: – rings of calcified extracellular matrix that surround the central canal – function to resist torsion stress (twisting) on bone tissue ¨ Interstitial lamellae: – Fragments from old osteons – located between new osteons – Function to provide strength
Osteon parts & functions ¨ Lacunae – tiny cavities within the matrix – location of osteocytes ¨ Canaliculi – tiny canals that radiate out from Haversian canals to all lacunae
Osteon diagram – cross section
osteocytes ¨ Lacunae, osteocytes, & canaliculi
Osteon diagram – sagittal section
Cancellous(spongy) bone tissue aka: Trabecular Bone ¨ Main structures are the trabeculae - irregularly arranged columns of lamellae – arranged along stress lines to provide strength & resist physical stress ¨ Lacunae – tiny cavities within the matrix – location of osteocytes ¨ Canaliculi – tiny canals that radiate out from lacunae & contain interstitial fluid – Location of bone marrow & BV
More dense trabeculae due to more stress on that area
Types of Bone Tissue Cortical Trabecular ¨ 80% of skeleton ¨ 20% of skeleton ¨ Strongest bone tissue – ¨ Light weight bone more dense ¨ Resists torsion stress from movement ¨ Resists mechanical stress from weight ¨ Osteons – less dense ¨ Spaces contain bone marrow & blood vessels ¨ Trabeculae
Lab Info Cortical Bone Trabecular Bone
BONE TISSUE CELLS
Blasts, Clasts & Cytes
BONE TISSUE COMPOSITION
Composition of bone tissue ¨ Osseous CT with hard ECM & widely distributed cells ¨ ECM – approximately 25% water, 25% collagen fibers, and 50% crystallized mineral salts (mainly Ca. PO 4) – Formed by process of calcification
Organic portion: 35% of mass ¨ The organic portion consists of the bone cells and the osteoid ¨ The Bone cells are the: – Osteocytes – Osteoblasts – Osteoclasts – FYI: There also osteoprogenitor cells that are the precursers to blasts & cytes. They are derived from mesenchyme & found on all bone surfaces.
Osteoid ¨ is produced by the osteoblasts ¨ It consists of ground substance (proteoglycans and glycoproteins) & collagen fibers produced by CT cells ¨ Its function is to provide the bone with tensile strength and resilience – in other words, to make the bone a little flexible & compressive
Inorganic matrix: 65% of mass ¨ The inorganic matrix consists of inorganic salt compounds mainly: – Hydroxyapatites: Calcium & phosphorus salt compounds ¨ Function to provide structure due to hardness that resists compression
Human Skeletons – dark color
Types of Bones
Long Bone Structure Know the descriptions & functions from your notes, as well as, the diagrams.
Lab Info Hyaline cartilage Fibrocartilage
Bone ¨ Bone is very vascular with multiple arteries, veins & capillaries ¨ Bone has an extensive nerve supply and lots of sensory nerve endings
BONE DEVELOPMENT
Terms ¨ Osteogenesis/Ossification – formation of bone – Endochondral – bone replaces cartilage – Intramembranous – bone develops directly from mesenchyme or fibrous CT ¨ Calcification – deposition of calcium salts (can occur in other tissue types)
Endochondral ossification
Intramembranous ossification
TYPES OF BONE GROWTH
Types of growth ¨ Longitudinal growth – bone growth in length at epiphyseal plates (till plates ossify) ¨ Appositional growth – bone growth in diameter (throughout life) – Known as remodeling ¨ These 2 types work together to make the bones long enough & strong enough
Regulation of bone growth ¨Bone is a dynamic and active tissue. They are constantly being remodeled according to the activities that we do. ¨Main factor = Ca levels in blood ¨Ca imp for bone strength but also for nervous & muscular system to work correctly!!!
Regulation by hormonal feedback ¨ Purpose: to maintain optimal ionic calcium levels in blood – This is your body’s TOP priority!!! ¨ A main factor that affects what our bone tissue does is our blood calcium level – Optimum blood Ca 2+ level = 9 -11 mg/100 ml of blood – Calcium ions are VERY important for muscle & nervous function – our body cares more about this level than it does our bone strength!!
Regulation by hormonal feedback ¨ PTH (parathyroid gland) – activated when Ca levels in blood are too low – (hypocalcemia) - promotes calcium reabsorption – Calcium will go from bone to blood ¨ Calcitonin (thyroid gland) activated when Ca levels in blood are too high – (hypercalcemia) - promotes calcium deposition – Calcium will go from blood to bone
Regulation by mechanical stress ¨ Purpose: keep bones strong – This is the secondary purpose ¨ Wolff’s law states that bones will grow according to the stresses placed upon them – Simply stated, bone grows in response to mechanical stress so as to produce an anatomical structure best able to resist the applied stress. – So activities that compress bones and pull on muscles which pull on bones can make bones stronger
How they work together to regulate ¨ PTH & calcitonin (hormones) determine WHEN the remodeling will occur – Primary purpose = Ca 2+ regulation in blood ¨ The Mechanical stresses determine WHERE the remodeling will occur – Secondary purpose = where will the calcium ions be deposited or reabsorbed from
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