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2.  Functions of Bone and Skeletal System  Structure of Bone  Histology of Bone Tissue  Blood and Nerve Supply of Bone  Bone Formation  Bone’s Role in Calcium Homeostasis  Exercise and Bone Tissue  Aging and Bone Tissue 2

3.  Support  Protection  Assistance in Movement  Mineral Homeostasis  Blood Cell Production  Triglyceride Storage 3

4. 4 Support  Structural framework of the body Supports soft tissues Provides attachment points for tendons of skeletal muscle Protection  Protects important internal organs  For example… Cranium protects brain Vertebrae protects spinal cord Ribs protect lungs and heart

5. 5 Assistance in Movement  Skeletal muscle attaches to bone Skeletal muscle contraction pulls on bone producing movement Mineral Homeostasis  Bone tissue stores several minerals Acts to serve as a reservoir of critical minerals  Calcium (99% of body’s content)  Phosphorus

6. 6 Blood Cell Production  Red bone marrow produces (Hemopoiesis) Red blood cells White blood cells Platelets Triglyceride Storage  Yellow bone marrow Triglycerides stored in adipose cells  Serves as a potential chemical energy reserve

7.  Diaphysis  Epiphysis  Metaphysis Epiphyseal growth plate  Articular cartilage Perforating fibers  Periosteum  Medullary cavity  Endosteum 7 Long Bone Anatomy (Humerus)

8.  Extracellular matrix surrounding widely separated cells  Matrix 25% water 25% collagen fibers 50% crystallized mineral salts  The most abundant mineral salt found in bone is calcium phosphate 8

9.  A process called calcification is initiated by bone-building cells called osteoblasts  Mineral salts are deposited and crystalize in the framework formed by the collagen fibers of the extracellular matrix  Bone’s flexibility depends on collagen fibers 9

10.  Four types of cells are present in bone tissue  Osteogenic cells  Undergo cell division; the resulting cells develop into osteoblasts  Osteoblasts  Bone-building cells  Synthesize extracellular matrix of bone tissue  Osteocytes  Mature bone cells  Exchange nutrients and wastes with the blood 10

11.  Osteoclast Functions:  Release enzymes that digest the mineral components of bone matrix (resorption)  Regulate blood calcium level 11

12.  Bone may be categorized as either:  Compact  Spongy 12

13.  Compact Bone  Resists the stresses produced by weight and movement  Components of compact bone are arranged into repeating structural units called osteons or Haversian Systems or Haversian Canals  Osteons consist of a central (Haversian) canal with concentrically arranged lamellae, lacunae, osteocytes, and canaliculi.  The result is a structure that resembles a tree trunk cut in half. 13

14.  Osteon  Central canals run longitudinally through bone  Around the central canals are concentric lamellae Rings of calcified matrix (like the rings of a tree trunk)  Between the lamellae are small spaces called lacunae which contain osteocytes  Radiating in all directions from the lacunae are tiny canaliculi filled with extracellular fluid 14

15.  Osteon  Canaliculi connect lacunae, forming a system of interconnected canals Providing routes for nutrients and oxygen to reach the osteocytes  The organization of osteons changes in response to the physical demands placed on the skeleton 15

16.  Spongy Bone  Lacks osteons  Lamellae are arranged in a lattice of thin columns called trabeculae Spaces between the trabeculae make bones lighter Trabeculae of spongy bone support and protect the red bone marrow Hemopoiesis (blood cell production) occurs in spongy bone 16

17.  Spongy Bone  Within each trabecula are lacunae that contain osteocytes  Osteocytes are nourished from the blood circulating through the trabeculae  Interior bone tissue is made up primarily of spongy bone  The trabeculae of spongy bone are oriented along lines of stress helps bones resist stresses without breaking 17

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19.  Bone is richly supplied with blood  Periosteal arteries accompanied by nerves supply the periosteum and compact bone  Epiphyseal veins carry blood away from long bones  Nerves accompany the blood vessels that supply bones  The periosteum is rich in sensory nerves sensitive to tearing or tension 19

20.  The process by which bone forms is called ossification  Bone formation occurs in four situations:  1) Formation of bone in an embryo  2) Growth of bones until adulthood  3) Remodeling of bone  4) Repair of fractures 20

21.  Formation of Bone in an Embryo  Cartilage formation and ossification occurs during the sixth week of embryonic development  Bone formation follows one of two patterns Intramembranous ossification Flat bones of the skull and mandible are formed in this way “Soft spots” that help the fetal skull pass through the birth canal later become ossified forming the skull Endochondral ossification The replacement of cartilage by bone Most bones of the body are formed in this way including long bones 21

22. 1 Blood capillary Ossification center Mesenchymal cell Osteoblast Collagen fiber Development of ossification center Mandible Flat bone of skull 1 Blood capillary Ossification center Mesenchymal cell Osteoblast Osteocyte in lacuna Canaliculus Osteoblast Newly calcified bone matrix Development of ossification center Calcification Mandible Flat bone of skull 2 Collagen fiber 1 Blood capillary Ossification center Mesenchymal cell Osteoblast Development of ossification center Calcification Mandible Flat bone of skull 2 Collagen fiber Osteocyte in lacuna Canaliculus Osteoblast Newly calcified bone matrix Mesenchyme condenses Blood vessel Spongy bone trabeculae Osteoblast Formation of trabeculae 3 1 Blood capillary Ossification center Mesenchymal cell Osteoblast Mesenchyme condenses Blood vessel Spongy bone trabeculae Osteoblast Periosteum Spongy bone tissue Compact bone tissue Development of ossification center Calcification Formation of trabeculae Development of the periosteum Mandible Flat bone of skull 3 4 2 Collagen fiber Osteocyte in lacuna Canaliculus Osteoblast Newly calcified bone matrix 22

23.  Growth in Length  The growth in length of long bones involves two major events:  1) Growth of cartilage on the epiphyseal plate  2) Replacement of cartilage by bone tissue in the epiphyseal plate 23

24.  Osteoclasts dissolve the calcified cartilage, and osteoblasts invade the area laying down bone matrix  The activity of the epiphyseal plate is the way bone can increase in length  At adulthood, the epiphyseal plates close and bone replaces all the cartilage leaving a bony structure called the epiphyseal line 24

25.  Growth in Thickness  Bones grow in thickness at the outer surface  Remodeling of Bone  Bone forms before birth and continually renews itself  The ongoing replacement of old bone tissue by new bone tissue  Old bone is continually destroyed and new bone is formed in its place throughout an individual’s life 25

26.  A balance must exist between the actions of osteoclasts and osteoblasts  If too much new tissue is formed, the bones become abnormally thick and heavy  Excessive loss of calcium weakens the bones, as occurs in osteoporosis  Or they may become too flexible, as in rickets and osteomalacia 26

27. 1 Development of cartilage model Hyaline cartilage Perichondrium Proximal epiphysis Distal epiphysis Diaphysis 1 Development of cartilage model Growth of cartilage model 2 Hyaline cartilage Uncalcified matrix Calcified matrix Perichondrium Proximal epiphysis Distal epiphysis Diaphysis 1 Development of cartilage model Development of primary ossification center Growth of cartilage model 23 Hyaline cartilage Uncalcified matrix Calcified matrix Nutrient artery Perichondrium Proximal epiphysis Distal epiphysis Diaphysis Periosteum Primary ossification center Spongy bone 1 Hyaline cartilage Calcified matrix Periosteum (covering compact bone) Uncalcified matrix Calcified matrix Medullary cavity Nutrient artery and vein Nutrient artery Perichondrium Proximal epiphysis Distal epiphysis Diaphysis Development of cartilage model Development of primary ossification center Development of the medullary cavity Growth of cartilage model Periosteum Primary ossification center 234 Spongy bone Uncalcified matrix 1 Development of cartilage model Development of primary ossification center Development of the medullary cavity Growth of cartilage model 234 Hyaline cartilage Calcified matrix Periosteum (covering compact bone) Uncalcified matrix Calcified matrix Medullary cavity Nutrient artery and vein Nutrient artery Perichondrium Proximal epiphysis Distal epiphysis Diaphysis Periosteum Primary ossification center Secondary ossification center Nutrient artery and vein Uncalcified matrix Epiphyseal artery and vein Development of secondary ossification center 5 Spongy bone Uncalcified matrix 1 Articular cartilage Spongy bone Epiphyseal plate Secondary ossification center Nutrient artery and vein Uncalcified matrix Epiphyseal artery and vein Formation of articular cartilage and epiphyseal plate Development of secondary ossification center Development of cartilage model Development of primary ossification center Development of the medullary cavity Growth of cartilage model 234 56 Hyaline cartilage Uncalcified matrix Calcified matrix Periosteum (covering compact bone) Uncalcified matrix Calcified matrix Medullary cavity Nutrient artery and vein Nutrient artery Perichondrium Proximal epiphysis Distal epiphysis Diaphysis Periosteum Primary ossification center Spongy bone 27

28.  Normal bone metabolism depends on several factors  Minerals  Large amounts of calcium and phosphorus and smaller amounts of magnesium, fluoride, and manganese are required for bone growth and remodeling  Vitamins  Vitamin A stimulates activity of osteoblasts  Vitamin C is needed for synthesis of collagen  Vitamin D helps build bone by increasing the absorption of calcium from foods in the gastrointestinal tract into the blood  Vitamins K and B12 are also needed for synthesis of bone proteins 28

29.  Hormones  During childhood, the hormones most important to bone growth are growth factors (IGFs), produced by the liver IGFs stimulate osteoblasts, which in turn promote cell division at the epiphyseal plate, and enhance protein synthesis  Thyroid hormones also promote bone growth by stimulating osteoblasts  Insulin promotes bone growth by increasing the synthesis of bone proteins 29

30.  Hormones  Estrogen and testosterone cause a dramatic effect on bone growth Cause of the sudden “growth spurt” that occurs during the teenage year Promote changes in females, such as widening of the pelvis Shut down growth at epiphyseal plates  Parathyroid hormone, calcitriol, and calcitonin are other hormones that can affect bone remodeling 30

31.  Fracture Types  Open (compound) fracture The broken ends of the bone protrude through the skin  Closed (simple) fracture Does not break the skin  Comminuted fracture The bone is splintered, crushed, or broken into pieces  Greenstick fracture A partial fracture in which one side of the bone is broken and the other side bends  Impacted fracture One end of the fractured bone is forcefully driven into another  Pott’s fracture Fracture of the fibula, with injury of the tibial articulation  Colles’ fracture A fracture of the radius in which the distal fragment is displaced  Stress fracture A series of microscopic fissures in bone 31

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33.  Calcium and phosphorus needed to strengthen and harden new bone after a fracture are deposited only gradually and may take several months  The repair of a bone fracture involves the following steps  1) Formation of fracture hematoma Blood leaks from the torn ends of blood vessels, a clotted mass of blood forms around the site of the fracture  2) Fibrocartilaginous callus formation Fibroblasts invade the fracture site and produce collagen fibers bridging the broken ends of the bone  3) Bony callus formation Osteoblasts begin to produce spongy bone trabeculae joining portions of the original bone fragments  4) Bone remodeling Compact bone replaces spongy bone 33

34. Compact bone Spongy bone Periosteum Fracture hematoma Fracture hematoma Bone fragment Osteocyte Red blood cell Blood vessel Formation of fracture hematoma Phagocyte Osteon 1 Phagocyte Osteoblast Fibroblast Fibrocartilaginous callus Collagen fiber Chondroblast Cartilage Fibrocartilaginous callus formation 2 Compact bone Spongy bone Periosteum Fracture hematoma Fracture hematoma Bone fragment Osteocyte Red blood cell Blood vessel Formation of fracture hematoma Phagocyte Osteon 1 Bony callus Spongy bone Osteoblast Bony callus formation Osteocyte 3 Compact bone Spongy bone Periosteum Fracture hematoma Fracture hematoma Bone fragment Osteocyte Red blood cell Blood vessel Formation of fracture hematoma Phagocyte Osteon 1 Phagocyte Osteoblast Fibroblast Fibrocartilaginous callus Collagen fiber Chondroblast Cartilage Fibrocartilaginous callus formation 2 Spongy bone Osteoblast Osteoclast New compact bone Bony callus formationBone remodeling Osteocyte 34 Compact bone Spongy bone Periosteum Fracture hematoma Fracture hematoma Bone fragment Osteocyte Red blood cell Blood vessel Formation of fracture hematoma Phagocyte Osteon 1 Phagocyte Osteoblast Fibroblast Fibrocartilaginous callus Collagen fiber Chondroblast Cartilage Fibrocartilaginous callus formation 2 Bony callus 34

35.  Bone is the body’s major calcium reservoir  Levels of calcium in the blood are maintained by controlling the rates of calcium resorption from bone into blood and of calcium deposition from blood into bone  Both nerve and muscle cells depend on calcium ions (Ca 2+ ) to function properly  Blood clotting also requires Ca 2+  Many enzymes require Ca 2+ as a cofactor 35

36.  To review the different types of fractures, their descriptions and accompanying radiographs and/or drawings, visit the following sites:  http://www.rush.edu/rumc/page-P07392.html http://www.rush.edu/rumc/page-P07392.html  http://www.nlm.nih.gov/medlineplus/ency/imagep ages/1096.htm http://www.nlm.nih.gov/medlineplus/ency/imagep ages/1096.htm  http://orthoinfo.aaos.org/fact/thr_report.cfm?threa d_id=125&topcategory=about%20orthopaedics http://orthoinfo.aaos.org/fact/thr_report.cfm?threa d_id=125&topcategory=about%20orthopaedics

37.  Actions that help elevate blood Ca 2+ level  Parathyroid hormone (PTH) regulates Ca 2+ exchange between blood and bone tissue PTH increases the number and activity of osteoclasts PTH acts on the kidneys to decrease loss of Ca 2+ in the urine PTH stimulates formation of calcitriol a hormone that promotes absorption of calcium from foods in the gastrointestinal tract 37

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39.  Actions that work to decrease blood Ca 2+ level  The thyroid gland secretes calcitonin (CT) which inhibits activity of osteoclasts  The result is that CT promotes bone formation and decreases blood Ca 2+ level 39

40.  Bone tissue alters its strength in response to changes in mechanical stress  Under stress, bone tissue becomes stronger through deposition of mineral salts and production of collagen fibers by osteoblasts  Unstressed bones diminishes because of the loss of bone minerals and decreased numbers of collagen fibers  The main mechanical stresses on bone are those that result from the pull of skeletal muscles and the pull of gravity  Weight-bearing activities help build and retain bone mass 40

41.  The level of sex hormones diminishes during middle age, especially in women after menopause  A decrease in bone mass occurs  Bone resorption by osteoclasts outpaces bone deposition by osteoblasts  Female bones generally are smaller and less massive than males  Loss of bone mass in old age has a greater adverse effect in females 41

42.  There are two principal effects of aging on bone tissue:  1) Loss of bone mass Results from the loss of calcium from bone matrix The loss of calcium from bones is one of the symptoms in osteoporosis  2) Brittleness Results from a decreased rate of protein synthesis Collagen fibers gives bone its tensile strength The loss of tensile strength causes the bones to become very brittle and susceptible to fracture 42

43.  Osteoporosis: A decrease in the amount and strength of bone tissue owing to decreases in hormone output. In osteoporosis, bone resorption outpaces bone formation. This cause bones to become fragile and more likely to break. If not prevented or if left untreated, osteoporosis can progress painlessly until a bone breaks. These fractures occur typically in the hip, spine, and wrist.  Any bone can be affected, but of special concern are fractures of the hip and spine which almost always requires hospitalization and major surgery. It can impair a person's ability to walk unassisted and may cause prolonged or permanent disability or even death. Spinal or vertebral fractures can also cause loss of height, severe back pain, and deformity

44.  Paget’s disease causes a malfunction in the normal process of bone remodeling. When an area of bone is destroyed in a person with Paget’s disease, the bone that replaces it is soft and porous. Soft bone can be weak and easily bend, leading to shortening of the affected part of the body.  The bone replacement also takes place very quickly and excess bone may be formed. This can cause the bone to get larger, be painful and break easily.

45.  Bone affected by Paget’s disease tends to have more blood vessels than normal. This causes an increase in the blood supply to the area, and as a result the area may feel warmer than usual.  The disease can affect any bone but more commonly affects the spine, pelvis, skull, femur and the tibia.  Paget’s disease can lead to other medical conditions including osteoarthritis, kidney stones and heart disease.  Paget’s disease is also called osteitis deformans. It is named after Sir James Paget, an English doctor who first described the disease in 1876.  How common is Paget’s disease?  The exact number of people with Paget’s disease is not known.  Men are more likely to be affected by Paget’s disease than women.  It usually affects people over age 40.  Paget’s disease is estimated to affect 3% of people over 40. However the exact number is not known because many people who have it do not know it. It occurs all over the world but is more prevalent in some areas, such as in Europe and Australia.  It tends to affect men more than women, and usually those over the age of 40.

46.  What are the warning signs of Paget’s disease?  Because Paget’s disease comes on slowly many people do not know they have it.  If you have Paget’s disease the first warning sign may be pain in or over a bone.  The area may feel extra warm.  You may feel also feel tired.  If Paget’s disease affects the bones in a leg, the shape of the bone may change and your legs may bend or bow out.  If it affects the skull, your head may get bigger. It can also cause you to have trouble hearing.  Paget’s disease can cause your bones to break more easily.  Often Paget’s affects only one or two bones.  In many cases, Paget's disease takes a very mild course and a person with it may not have any symptoms. Those who do have symptoms may be affected in various ways.  If you have Paget’s disease your bones may break easily because they are weakened. Your bones may also bend, and if your leg bones are affected you may notice that your legs bow, or a leg may appear to shrink. If your spine is involved, you may feel pain in your back. If the bones in your spine bend or grow larger than usual this can put pressure on your nerves, and you may feel pain or numbness in other areas of your body also.  If Paget’s disease affects your skull, your head may increase in size from front to back. Hearing loss may result if there is involvement of some of the small bones in the middle ear or pressure is placed on the nerves related to hearing.  In late stages of the disease, your hip joint may become damaged if the bones of your pelvis have been involved.  Usually only one or a few bones are affected. However, the disease can be widespread and affect all bones. Because of the increased number of blood vessels in bones affected by Paget’s disease your heart has to work harder to pump blood to them. If many bones are affected this can cause strain on your heart and lead to other problems. 46

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