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THE SKELETAL SYSTEM: THE SKELETAL SYSTEM: OVERVIEWOVERVIEW

I.I. INTRODUCTIONINTRODUCTION The organs of the skeletal system The organs of the skeletal system

include the bones and the structures include the bones and the structures that connect bones to other that connect bones to other structures, including ligaments, structures, including ligaments, tendons, and cartilages.tendons, and cartilages.

The adult skeleton is composed of The adult skeleton is composed of 206 separate bones.206 separate bones.

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Division of skeleton Division of skeleton

– Axial skeletonAxial skeleton Includes the bones of:Includes the bones of: skull, vertebral column, and rib cage.skull, vertebral column, and rib cage. These bones are involved in protection, support, These bones are involved in protection, support,

and carrying other body parts.and carrying other body parts.

– Appendicular skeletonAppendicular skeleton Bones of upper & lower limbs and the girdles Bones of upper & lower limbs and the girdles

(shoulder bones and hip bones) that attach them (shoulder bones and hip bones) that attach them to the axial skeleton.to the axial skeleton.

Involved in locomotion and manipulation of the Involved in locomotion and manipulation of the environment.environment.

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AXIAL SKELETONAXIAL SKELETON

AppendicularAppendicular SKELETONSKELETON

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AXIAL SKELETONAXIAL SKELETON

1) Skull: 28 irregular shaped bones 1) Skull: 28 irregular shaped bones from the skull.from the skull.

The skull consists of two major The skull consists of two major division:division:

a)a) Cranium is formed by eight bones.Cranium is formed by eight bones.

b)b) Face is formed by fourteen bones.Face is formed by fourteen bones.

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AXIAL SKELETONAXIAL SKELETON

2) VERTEBRAL COLUMN2) VERTEBRAL COLUMN

Divided into 5 main regionsDivided into 5 main regions

1.1. Cervical spine (7)Cervical spine (7)

2.2. Thoracic spine (12)Thoracic spine (12)

3.3. Lumbar spine (5) Lumbar spine (5)

4.4. Sacrum (5)Sacrum (5)

5.5. Coccyx (4)Coccyx (4)

The 5 sacrum The 5 sacrum vertebrae and 4 coccyx vertebrae and 4 coccyx vertebrae are fused to form vertebrae are fused to form one solid bone.one solid bone.

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Cervical, Thoracic, Lumbar, Cervical, Thoracic, Lumbar, Sacrum Sacrum

and Coccyxand Coccyx

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AXIAL SKELETONAXIAL SKELETON

THORAXTHORAX 12 pairs of ribs12 pairs of ribs Joined to thoracic Joined to thoracic

vertebraevertebrae Top 10 ribs joined Top 10 ribs joined

to sternumto sternum Remaining two Remaining two

have “free” ends – have “free” ends – ‘floating’‘floating’

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APPENDICULAR SKELETONAPPENDICULAR SKELETON

Forms mainly the Forms mainly the extremities of the extremities of the body and their body and their connections to the connections to the axial skeletonaxial skeleton

Consists ofConsists of

- limbs (arms & legs)- limbs (arms & legs)

- shoulder and pelvic - shoulder and pelvic girdlesgirdles

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Bone Bone ClassificationClassification

4 types of bones:4 types of bones:– Long Bones Long Bones

Much longer than they Much longer than they are wide.are wide.

All bones of the limbs All bones of the limbs except for the patella except for the patella (kneecap), (kneecap), and the and the bones of the wrist and bones of the wrist and ankle.ankle.

Consists of a shaft plus 2 Consists of a shaft plus 2 expanded ends.expanded ends.

– Short BonesShort Bones Roughly cube shaped.Roughly cube shaped. Bones of the wrist and the Bones of the wrist and the

ankle.ankle.

Femur

Carpal Bones

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Bone ClassificationBone Classification

Types of bones:Types of bones:– Flat BonesFlat Bones

Thin, flattened, and Thin, flattened, and usually a bit curved.usually a bit curved.

Scapulae, sternum, Scapulae, sternum, (shoulder blades), ribs (shoulder blades), ribs and most bones of the and most bones of the skull.skull.

– Irregular BonesIrregular Bones Have weird shapes that Have weird shapes that

fit none of the 3 previous fit none of the 3 previous classes.classes.

Vertebrae, hip bones, 2 Vertebrae, hip bones, 2 skull bones ( sphenoid skull bones ( sphenoid and the ethmoid bones).and the ethmoid bones).

Sternum

Sphenoid Bone

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Parts of long bone Parts of long bone

1) diaphysis: main shaft like structure, 1) diaphysis: main shaft like structure, its hollow cylindrical shape, its its hollow cylindrical shape, its functions of providing strong support functions of providing strong support bone.bone.

2) epiphysis: both end of long bone, 2) epiphysis: both end of long bone, epiphysis have a bulbous shape that epiphysis have a bulbous shape that provide generous space near joint. provide generous space near joint.

For muscle attachment and give For muscle attachment and give stability of joint.stability of joint.

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Parts of long boneParts of long bone

3) articular cartilage thin layer of hyaline 3) articular cartilage thin layer of hyaline cartilage that covers joint surface.cartilage that covers joint surface.

4) Periosteum: dense white fibrous 4) Periosteum: dense white fibrous membrane that cover bone except at membrane that cover bone except at joint surface and anchoring bone to joint surface and anchoring bone to muscles.muscles.

5) Marrow cavity: a tubelike hollow space 5) Marrow cavity: a tubelike hollow space in the diaphysis of long bone.in the diaphysis of long bone.

6) endosteum: a thin epithelial 6) endosteum: a thin epithelial membrane that line the medullry cavity.membrane that line the medullry cavity.

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Long Long Bone Bone

StructureStructure

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Composition of bone matrix Composition of bone matrix

1)1) Inorganic saltsInorganic salts: the hardness of bone : the hardness of bone result from the deposition of high result from the deposition of high specialized chemical crystal of calcium and specialized chemical crystal of calcium and phosphorous called hydroxyapatite, the phosphorous called hydroxyapatite, the process called calcification in addition to process called calcification in addition to mg, Na, sulphate and fluoride.mg, Na, sulphate and fluoride.

2)2) Organic substance:Organic substance: collagenous fiber and collagenous fiber and mixture protein and poly saccarids called mixture protein and poly saccarids called ground substance, provide support and ground substance, provide support and adhesion between cellular and fiberous.adhesion between cellular and fiberous.

Chondroitin and glucosamine are required Chondroitin and glucosamine are required for repair and maintenance of bone and for repair and maintenance of bone and cartilage.cartilage.

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Composition of bone matrixComposition of bone matrix

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11. Osteoblasts. Osteoblasts Bone-forming cells Bone-forming cells

found in all bone found in all bone surfaces surfaces Bone-building Bone-building cells.cells.

Synthesize and secrete Synthesize and secrete collagen fibers and other collagen fibers and other organic components of organic components of bone matrix. bone matrix.

serve as a framework for serve as a framework for the deposition of the deposition of calcium and phosphate calcium and phosphate calcificationcalcification

The blue arrows indicate the osteoblasts. The yellow arrows indicate the bone matrix they’ve just secreted.

Types of bone cellsTypes of bone cells

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Types of bone Types of bone cellscells

22. Osteoclasts. Osteoclasts Giant multinucleate Giant multinucleate

cellscells Responsible for the Responsible for the

active erosion of active erosion of bone mineralsbone minerals

Contain large Contain large numbers of numbers of mitochondria and mitochondria and lysosomeslysosomes

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Types of bone cellsTypes of bone cells

3. Osteocytes3. Osteocytes——mature, nondividing mature, nondividing osteoblast surrounded by matrix, osteoblast surrounded by matrix, lying within lacunae lying within lacunae

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Bone MarrowBone Marrow

Specialized type of soft, diffuse Specialized type of soft, diffuse connective tissue; called connective tissue; called myeloid myeloid tissuetissue

Site for the production of blood cellsSite for the production of blood cells Found in medullary cavities of long Found in medullary cavities of long

bones and in the spaces of spongy bones and in the spaces of spongy bonebone

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Microscopic Structure of Compact BoneMicroscopic Structure of Compact Bone

– Contains many cylinder-Contains many cylinder-shaped structural units shaped structural units calledcalled osteons, osteons, oror Haversian systemsHaversian systems

– Four types of structures Four types of structures make up each osteon:make up each osteon: LamellaLamella——concentric, concentric,

cylinder-shaped layers of cylinder-shaped layers of calcified matrixcalcified matrix

LacunaeLacunae——small spaces small spaces containing tissue fluid in containing tissue fluid in which bone cells are which bone cells are located between hard located between hard layers of the lamellalayers of the lamella

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Microscopic Structure of Microscopic Structure of Compact BoneCompact Bone

CanaliculiCanaliculi——ultrasmall ultrasmall canals radiating in all canals radiating in all directions from the directions from the lacunae and connecting lacunae and connecting them to each other and them to each other and to the Haversian canalto the Haversian canal

Haversian canalHaversian canal——extends lengthwise extends lengthwise through the center of through the center of each osteon and contains each osteon and contains blood vessels and blood vessels and lymphatic vesselslymphatic vessels

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Microscopic Structure of Microscopic Structure of Compact BoneCompact Bone

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Bone MarrowBone Marrow

Two types of marrow are present during a Two types of marrow are present during a personperson’’s lifetime:s lifetime:– Red marrowRed marrow

Found in virtually all bones in an infantFound in virtually all bones in an infant’’s or childs or child’’s s bodybody

Functions to produce red blood cellsFunctions to produce red blood cells

– Yellow marrowYellow marrow As an individual ages, red marrow is replaced by As an individual ages, red marrow is replaced by

yellow marrowyellow marrow Marrow cells become saturated with fat and are no Marrow cells become saturated with fat and are no

longer active in blood cell productionlonger active in blood cell production

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Bone MarrowBone Marrow

The main bones in an adult that still The main bones in an adult that still contain red marrow include the ribs, contain red marrow include the ribs, bodies of the vertebrae, the humerus, bodies of the vertebrae, the humerus, the pelvis, and the femurthe pelvis, and the femur

Yellow marrow can alter to red marrow Yellow marrow can alter to red marrow during times of decreased blood during times of decreased blood supply, such as with anemia, exposure supply, such as with anemia, exposure to radiation, and certain diseasesto radiation, and certain diseases

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Functions of BoneFunctions of Bone SupportSupport——bones form the framework of the body bones form the framework of the body

and contribute to the shape, alignment, and and contribute to the shape, alignment, and positioning of the body partspositioning of the body parts

ProtectionProtection——bony bony ““boxesboxes”” protect the delicate protect the delicate structures they enclosestructures they enclose

MovementMovement——bones with their joints constitute bones with their joints constitute levers that move as muscles contractlevers that move as muscles contract

Mineral storageMineral storage——bones are the major reservoir bones are the major reservoir for calcium, phosphorus, and other mineralsfor calcium, phosphorus, and other minerals

HematopoiesisHematopoiesis——blood cell formation is carried blood cell formation is carried out by myeloid tissueout by myeloid tissue

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Regulation of Blood Calcium Regulation of Blood Calcium LevelsLevels

Skeletal system (cont.)Skeletal system (cont.)– Homeostasis of calcium ion Homeostasis of calcium ion

concentration essential for the following:concentration essential for the following: Bone formation, remodeling, and repairBone formation, remodeling, and repair Blood clottingBlood clotting Transmission of nerve impulsesTransmission of nerve impulses Maintenance of skeletal and cardiac muscle Maintenance of skeletal and cardiac muscle

contractioncontraction

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Regulation of Blood Calcium Regulation of Blood Calcium LevelsLevels

Mechanisms of calcium homeostasisMechanisms of calcium homeostasis– Parathyroid hormoneParathyroid hormone

Primary regulator of calcium homeostasisPrimary regulator of calcium homeostasis Stimulates osteoclasts to initiate breakdown Stimulates osteoclasts to initiate breakdown

of bone matrix and increase blood calcium of bone matrix and increase blood calcium levelslevels

Increases renal absorption of calcium from Increases renal absorption of calcium from urineurine

Stimulates vitamin D synthesisStimulates vitamin D synthesis

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Mechanisms of calcium homeostasis Mechanisms of calcium homeostasis (cont.)(cont.)– CalcitoninCalcitonin

Protein hormone produced in the thyroid glandProtein hormone produced in the thyroid gland Produced in response to high blood calcium Produced in response to high blood calcium

levelslevels Stimulates bone deposition by osteoblastsStimulates bone deposition by osteoblasts Inhibits osteoclast activityInhibits osteoclast activity Far less important in homeostasis of blood Far less important in homeostasis of blood

calcium levels than parathyroid hormonecalcium levels than parathyroid hormone

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Fracture TypesFracture Types

– Open (compound) Open (compound) bone ends penetrate bone ends penetrate the skin.the skin.

– Closed (simple) Closed (simple) bone ends don’t bone ends don’t penetrate the skin.penetrate the skin.

– Spiral Spiral ragged break caused by ragged break caused by excessive twisting forces. Sports excessive twisting forces. Sports injury/Injury of abuseinjury/Injury of abuse

– Greenstick Greenstick bone breaks incompletely. bone breaks incompletely. One side bent, one side broken. Common One side bent, one side broken. Common in children whose bone contains more in children whose bone contains more collagen and are less mineralizedcollagen and are less mineralized

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Clinical Clinical ConditionsConditions

OsteomalaciaOsteomalacia– Literally “soft bones.”Literally “soft bones.”– Includes many disorders in which Includes many disorders in which

osteoid is produced but osteoid is produced but inadequately mineralized.inadequately mineralized.

Causes can include insufficient Causes can include insufficient dietary calciumdietary calcium

Insufficient vitamin D Insufficient vitamin D fortification or insufficient fortification or insufficient exposure to sun light.exposure to sun light.

RicketsRickets– Children's form of osteomalaciaChildren's form of osteomalacia– More detrimental due to the fact More detrimental due to the fact

that their bones are still growing.that their bones are still growing.– Signs include bowed legs, and Signs include bowed legs, and

deformities of the pelvis, ribs, and deformities of the pelvis, ribs, and skull.skull.

What about the above x-ray is indicative of rickets?

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Clinical Clinical ConditionsConditions

OsteomyelitisOsteomyelitis– Inflammation of Inflammation of

bone and bone bone and bone marrow caused by marrow caused by pus-forming bacteria pus-forming bacteria that enter the body that enter the body via a wound (e.g., via a wound (e.g., compound fracture) compound fracture) or migrate from a or migrate from a nearby infection.nearby infection.

– Fatal before the Fatal before the advent of antibiotics.advent of antibiotics.

Clinical Clinical ConditionsConditions

OsteoporosisOsteoporosis– Osteoporosis is a Osteoporosis is a

disease that thins disease that thins and weakens the and weakens the bones to the point bones to the point that they become that they become fragile and break fragile and break easily. Women and easily. Women and men with men with osteoporosis most osteoporosis most often break bones in often break bones in the hip, spine, and the hip, spine, and wrist, but any bone wrist, but any bone can be affected. You can be affected. You can't "catch" can't "catch" osteoporosis or give osteoporosis or give it to someone else.it to someone else. 3535

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Any Any questions ???questions ???

The endThe end