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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
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Support Protection Assistance in Movement Mineral Homeostasis Blood Cell Production Triglyceride Storage
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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
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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
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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
Diaphysis Epiphysis Metaphysis
Epiphyseal growth plate Articular cartilage
Perforating fibers Periosteum Medullary cavity Endosteum
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Long Bone Anatomy (Humerus)
Extracellular matrix surrounding widely separated cellsMatrix
25% water25% collagen fibers50% crystallized mineral salts
The most abundant mineral salt found in bone is calcium phosphate
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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
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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
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Osteoclast Functions: Release enzymes that digest the mineral components of
bone matrix (resorption) Regulate blood calcium level
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Compact BoneResists the stresses produced by weight and
movementComponents 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.
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OsteonCentral canals run longitudinally through boneAround 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 osteocytesRadiating in all directions from the lacunae are
tiny canaliculi filled with extracellular fluid
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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
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Spongy BoneLacks osteonsLamellae 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
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Spongy BoneWithin each trabecula are lacunae that contain
osteocytesOsteocytes are nourished from the blood
circulating through the trabeculaeInterior bone tissue is made up primarily of
spongy boneThe trabeculae of spongy bone are oriented along
lines of stresshelps bones resist stresses without breaking
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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
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The process by which bone forms is called ossification
Bone formation occurs in four situations:1) Formation of bone in an embryo2) Growth of bones until adulthood3) Remodeling of bone4) Repair of fractures
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Formation of Bone in an EmbryoCartilage 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 ossificationThe replacement of cartilage by boneMost bones of the body are formed in this way including
long bones
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1
Blood capillary
Ossification center
Mesenchymal cell
Osteoblast
Collagen fiber
Development of ossification center
Mandible
Flat boneof skull
1
Blood capillary
Ossification center
Mesenchymal cell
Osteoblast
Osteocyte in lacuna
Canaliculus
Osteoblast
Newly calcified bonematrix
Development of ossification center
Calcification
Mandible
Flat boneof skull
2
Collagen fiber
1
Blood capillary
Ossification center
Mesenchymal cell
Osteoblast
Development of ossification center
Calcification
Mandible
Flat boneof skull
2
Collagen fiber
Osteocyte in lacuna
Canaliculus
Osteoblast
Newly calcified bonematrix
Mesenchymecondenses
Blood vessel
Spongy bonetrabeculae
Osteoblast
Formation of trabeculae3
1
Blood capillary
Ossification center
Mesenchymal cell
Osteoblast
Mesenchymecondenses
Blood vessel
Spongy bonetrabeculae
Osteoblast
Periosteum
Spongy bone tissue
Compact bone tissue
Development of ossification center
Calcification Formation of trabeculae
Development of the periosteum
Mandible
Flat boneof skull
3
4
2
Collagen fiber
Osteocyte in lacuna
Canaliculus
Osteoblast
Newly calcified bonematrix
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Growth in Length The growth in length of
long bones involves two major events:1) Growth of cartilage
on the epiphyseal plate2) Replacement of
cartilage by bone tissue in the epiphyseal plate
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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
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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
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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
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1 Development ofcartilage model
Hyalinecartilage
Perichondrium
Proximalepiphysis
Distalepiphysis
Diaphysis
1 Development ofcartilage model
Growth ofcartilage model
2
Hyalinecartilage
Uncalcifiedmatrix
Calcifiedmatrix
Perichondrium
Proximalepiphysis
Distalepiphysis
Diaphysis
1 Development ofcartilage model
Development ofprimary ossificationcenter
Growth ofcartilage model
2 3
Hyalinecartilage
Uncalcifiedmatrix
Calcifiedmatrix
Nutrientartery
Perichondrium
Proximalepiphysis
Distalepiphysis
Diaphysis
Periosteum
Primaryossificationcenter
Spongybone
1
Hyalinecartilage
Calcifiedmatrix
Periosteum(covering compact bone)
Uncalcifiedmatrix
Calcifiedmatrix
Medullarycavity
Nutrientartery and vein
Nutrientartery
Perichondrium
Proximalepiphysis
Distalepiphysis
Diaphysis
Development ofcartilage model
Development ofprimary ossificationcenter
Development ofthe medullarycavity
Growth ofcartilage model
Periosteum
Primaryossificationcenter
2 3 4
Spongybone
Uncalcifiedmatrix
1 Development ofcartilage model
Development ofprimary ossificationcenter
Development ofthe medullarycavity
Growth ofcartilage model
2 3 4
Hyalinecartilage
Calcifiedmatrix
Periosteum(covering compact bone)
Uncalcifiedmatrix
Calcifiedmatrix
Medullarycavity
Nutrientartery and vein
Nutrientartery
Perichondrium
Proximalepiphysis
Distalepiphysis
Diaphysis
Periosteum
Primaryossificationcenter
Secondaryossificationcenter
Nutrientartery and vein
Uncalcifiedmatrix
Epiphysealartery andvein
Development of secondaryossification center
5
Spongybone
Uncalcifiedmatrix
1
Articular cartilage
Spongy bone
Epiphyseal plate
Secondaryossificationcenter
Nutrientartery and vein
Uncalcifiedmatrix
Epiphysealartery andvein
Formation of articular cartilageand epiphyseal plate
Development of secondaryossification center
Development ofcartilage model
Development ofprimary ossificationcenter
Development ofthe medullarycavity
Growth ofcartilage model
2 3 4
5 6
Hyalinecartilage
Uncalcifiedmatrix
Calcifiedmatrix
Periosteum(covering compact bone)
Uncalcifiedmatrix
Calcifiedmatrix
Medullarycavity
Nutrientartery and vein
Nutrientartery
Perichondrium
Proximalepiphysis
Distalepiphysis
Diaphysis
Periosteum
Primaryossificationcenter
Spongybone
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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
VitaminsVitamin A stimulates activity of osteoblastsVitamin C is needed for synthesis of collagenVitamin 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
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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
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HormonesEstrogen 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
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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
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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
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Compact boneSpongy bone
Periosteum
Fracture hematoma
Fracturehematoma
BonefragmentOsteocyte
Red bloodcell
Blood vessel
Formation of fracture hematoma
Phagocyte
Osteon
1
Phagocyte
Osteoblast
Fibroblast
Fibrocartilaginouscallus
Collagen fiber
Chondroblast
Cartilage
Fibrocartilaginous callus formation2
Compact boneSpongy bone
Periosteum
Fracture hematoma
Fracturehematoma
BonefragmentOsteocyte
Red bloodcell
Blood vessel
Formation of fracture hematoma
Phagocyte
Osteon
1
Bony callus
Spongy bone
Osteoblast
Bony callus formation
Osteocyte
3
Compact boneSpongy bone
Periosteum
Fracture hematoma
Fracturehematoma
BonefragmentOsteocyte
Red bloodcell
Blood vessel
Formation of fracture hematoma
Phagocyte
Osteon
1
Phagocyte
Osteoblast
Fibroblast
Fibrocartilaginouscallus
Collagen fiber
Chondroblast
Cartilage
Fibrocartilaginous callus formation2
Spongy bone
OsteoblastOsteoclast
New compactbone
Bony callus formation Bone remodeling
Osteocyte
3 4
Compact boneSpongy bone
Periosteum
Fracture hematoma
Fracturehematoma
BonefragmentOsteocyte
Red bloodcell
Blood vessel
Formation of fracture hematoma
Phagocyte
Osteon
1
Phagocyte
Osteoblast
Fibroblast
Fibrocartilaginouscallus
Collagen fiber
Chondroblast
Cartilage
Fibrocartilaginous callus formation2
Bony callus
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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 boneBoth nerve and muscle cells depend on calcium
ions (Ca2+) to function properlyBlood clotting also requires Ca2+
Many enzymes require Ca2+ as a cofactor
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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.nlm.nih.gov/medlineplus/ency/imagep
ages/1096.htm http://orthoinfo.aaos.org/fact/thr_report.cfm?
thread_id=125&topcategory=about%20orthopaedics
Actions that help elevate blood Ca2+ levelParathyroid hormone (PTH) regulates
Ca2+ exchange between blood and bone tissuePTH increases the number and activity of
osteoclastsPTH acts on the kidneys to decrease loss of
Ca2+ in the urinePTH stimulates formation of calcitriol a
hormone that promotes absorption of calcium from foods in the gastrointestinal tract
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Actions that work to decrease blood Ca2+ level
The thyroid gland secretes calcitonin (CT) which inhibits activity of osteoclasts
The result is that CT promotes bone formation and decreases blood Ca2+ level
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Bone tissue alters its strength in response to changes in mechanical stressUnder 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
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The level of sex hormones diminishes during middle age, especially in women after menopauseA decrease in bone mass occursBone resorption by osteoclasts outpaces bone
deposition by osteoblasts Female bones generally are smaller and less
massive than malesLoss of bone mass in old age has a greater
adverse effect in females
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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
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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
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.
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.
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.
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Copyright 2009 John Wiley & Sons, Inc.Portions of the above presentation are copywrited by John Wiley & Sons, Inc. For those portions, all rights reserved. Reproduction or translation of those portions beyond that
permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be
addressed to the Permission Department, John Wiley & Sons, Inc. The Publishers assumes no responsibility for errors, omissions, or damages caused by the use of theses
programs or from the use of the information herein.