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The human skeleton consists of both fused and individual bones supported and supplemented by

ligaments, tendons, muscles and cartilage. It serves as a scaffold which supports organs, anchors

muscles, and protects organs such as the brain, lungs and heart. The biggest bone in the body is

the femur  in the thigh, and the smallest is the stapes bone in the middle ear . In an adult, the skeleton

comprises around 30-40% of the total body weight,[1]and half of this weight is water.

Fused bones include those of the pelvis and the cranium. Not all bones are interconnected directly:

there are three bones in each middle ear  called the ossicles that articulate only with each other.

The hyoid bone, which is located in the neck and serves as the point of attachment for thetongue,

does not articulate with any other bones in the body, being supported by muscles and ligaments.

Sitting, standing,walking,picking up a pencil and taking a breath all involve the skeletal system, we

have no rigid framework to support the soft tissues of the body and no system of joints an levers so

critical for movement.

Skeleton is derived from a Greek word meaning dried. Despite of this concept of the skeleton as dryand nonliving, the skeletal system actually consists of dynamic, living tissues that are capable of 

growth, detect pain stimuli, adapt to stress and undergo repair after injury.

1. Functions of The Skeleton

The skeleton serves six major functions.

Support

The skeleton provides the framework which supports the body and maintains its shape. The pelvis and

associated ligaments and muscles provide a floor for the pelvic structures. Without the ribs, costal

cartilages, and the intercostal muscles, the lungs would collapse. Cartilage provides a firm yet flexible

support within certain structures such a s the nose, external ear, thoracic cage and trachea. Ligaments

are strong bands of fibrous connective tissue that attach to bones and hold them together.

Movement

The joints between bones permit movement, some allowing a wider range of movement than others,

e.g. the ball and socket joint allows a greater range of movement than the pivot joint at the neck.

Movement is powered by skeletal muscles, which are attached to the skeleton at various sites on

bones. Muscles, bones, and joints provide the principal mechanics for movement, all coordinated by

the nervous system. Skeletal muscles are attaché to bones by tendons, which are strong bands of 

connective tissues. Contraction of the skeletal muscles moves the bones producing body movements.

Protection

The skeleton protects many vital organs:

The skull protects the brain, the eyes, and the middle and inner ears.

The vertebrae protect the spinal cord.

The rib cage, spine, and sternum protect the lungs, heart and major  blood vessels.

The clavicle and scapula protect the shoulder .

The ilium and spine protect the digestive and urogenital systems and the hip.

The patella and the ulna protect the knee and the elbow respectively.

The carpals and tarsals protect the wrist and ankle respectively.

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Blood cell production

The skeleton is the site of  haematopoiesis, which takes place in red bone marrow. Marrow is found in

the center of long bones that gives rise to blood cells and platelets.

Storage

Bone matrix can store calcium and is involved in calcium metabolism, and bone marrow can

store ironin ferritin and is involved in iron metabolism. However, bones are not entirely made of 

calcium,but a mixture of chondroitin sulfate and hydroxyapatite, the latter making up 70% of a bone.

Endocrine regulation

Bone cells release a hormone called osteocalcin, which contributes to the regulation of blood

sugar (glucose) and fat deposition. Osteocalcin increases both the insulin secretion and sensitivity, in

addition to boosting the number of  insulin-producing cells and reducing stores of fat

2.Types of Bones

*Compact bone –

compact bone, also called cortical bone, dense bone in which the bony matrix is solidly filled

with organic ground substance and inorganic salts, leaving only tiny spaces (lacunae) that contain

the osteocytes, or bone cells. Compact bone makes up 80 percent of the human skeleton; the

remainder is cancellous bone, which has a spongelike appearance with numerous large spaces and

is found in the marrow space (medullary cavity) of a bone. Both types are found in most bones.

Compact bone forms a shell around cancellous bone and is the primary component of the long bones

of the arm and leg and other bones, where its greater strength and rigidity are needed.

Mature compact bone is lamellar, or layered, in structure. It is permeated by an elaborate system of 

interconnecting vascular canals, the haversian systems, which contain the blood supply for the

osteocytes; the bone is arranged in concentric layers around these canals, forming structural units

called osteons. Immature compact bone does not contain osteons and has a woven structure. It forms

around a framework of collagen fibres and is eventually replaced by mature bone in aremodeling

process of bone resorption and new bone formation that creates the osteons.

os·te·o·cyte ( s t -

-s t )

n.

 A branched cell embedded in the matrix of bone tissue.

osteonthe basic unit of structure of compact bone, comprising a haversian canal and its concentrically

arranged lamellae. Called also haversian system.

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CLASSIFICATION OF BONE

Long boneFrom Wikipedia, the free encyclopedia

Parts of a long bone

The long bones are those that are longer than they are wide, and grow primarily by elongation of 

the diaphysis, with anepiphysis at the ends of the growing bone. The ends of epiphyses are

covered with a hyaline cartilage ("articular cartilage"). The longitudinal growth of long bones is a

result of endochondral ossification at the epiphyseal plate. Bone growth in length is stimulated by

the production of growth hormone(GH), a secretion of the anterior lobe of the pituitary gland.

The long bones include the femurs, tibias, and fibulas of the legs, the humeri, radii, and ulnas of the

arms, metacarpals andmetatarsals of the hands and feet, and the phalanges of the fingers and

toes. The long bones of the human leg comprise nearly half of adult height. The other primary

skeletal component of height is the spine and skull.

The outside of the bone consists of a layer of connective tissue called the  periosteum. Additionally,

the outer shell of the long bone is compact bone, then a deeper layer of  cancellous bone(spongy

bone) which contains red bone marrow. The interior part of the long bone is the medullary

cavity with the inner core of the bone cavity being composed of (in adults) of yellow marrow.

Short bones

Definition

Short bones in the human body are cubelike -- the length, width, and height measurementsare all about the same.

Short bones include the carpal bones (hands, wrist) and tarsal bones (feet, ankles).

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Flat boneFrom Wikipedia, the free encyclopedia

Flat bones are those bones which are found where the principal requirement is either extensive

protection or the provision of broad surfaces for muscular attachment. These bones are expanded

into broad, flat plates,[1] as in the cranium (skull), the ilium (pelvis), sternum, rib cage, the sacrum

and the scapula.

These bones are composed of two thin layers of  compact bone enclosing between them a variable

quantity of cancellous bone,[1] which is the location of red bone marrow. In an adult, most red blood

cells are formed in flat bones.

In the cranial bones, the layers of compact tissue are familiarly known as the tables of the skull; the

outer one is thick and tough; the inner is thin, dense, and brittle, and hence is termed the vitreous

table.[1]

The intervening cancellous tissue is called the diploë, and this, in certain regions of the skull,

becomes absorbed so as to leave spaces filled with air (air-sinuses) between the two tables.[1]

The flat bones are: the occipital, parietal, frontal, nasal, lacrimal, vomer , scapula, os coxæ (hip

bone),sternum, and ribs.[1]

Irregular boneFrom Wikipedia, the free encyclopedia

The irregular bones are bones which, from their peculiar form, cannot be grouped as long

bone, short bone, flat bone or sesamoid bone. Irregular bones serve various purposes in the body,

such as protection of nervous tissue (such as the vertebrae protect the spinal cord), affording

multiple anchor points for skeletal muscle attachment (as with the sacrum), and

maintainingpharynx and trachea support, and tongue attachment (such as the hyoid bone). They

consist of cancellous tissue enclosed within a thin layer of compact bone.

The irregular bones are:

the vertebræ, sacrum, coccyx, temporal, sphenoid, ethmoid, zygomatic,maxilla, mandible, palatine,

inferior nasal concha, and hyoid.

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Sesamoid boneFrom Wikipedia, the free encyclopedia

In anatomy, a sesamoid bone is a bone embedded within a tendon.

Sesamoids are found in locations where a tendon passes over a joint, such as the hand, knee, and

foot. Functionally, they act to protect the tendon and to increase its mechanical effect. The

presence of the sesamoid bone holds the tendon slightly farther away from the center of the joint

and thus increases itsmoment arm. Sesamoid bones also prevent the tendon from flattening into

the joint as tension increases and therefore also maintain a more consistent moment arm through a

variety of possible tendon loads. This differs from menisci, which are made of cartilage and rather 

act to disperse the weight of the body on joints and reduce friction during movement.

sutural bone variable and irregularly shaped bones in the sutures between the bones of the skull

BONE DIVISIONS

1. The human skeleton is made of 206 bones and divided in to axial skeleton

and appendicular skeleton

 Axial skeleton (80 bones)

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Skull

(i) Cranial bones - 8 flattened bones, which are tightly inter locked forming abrain box or cranium. Brain is protected in it.

8 Cranial Bones: 1 x Ethmoid Bone1 x Frontal Bone1 x Occipital Bone2 x Parietal Bones1 x Sphenoid Bone2 x Temporal Bones

(ii) Facial bones -14 bones from the front part of the skull (Nose, hard palateand lower jaw).

14 Facial Bones: 2 x Inferior Nasal Conchae2 x Lacrimal Bones1 x Mandible2 x Maxillae (pl.); Maxilla (sing.)2 x Nasal Bones2 x Palatine Bones1 x Vomer 2 x Zygomatic Bones

(iii)Hyoid bone - 1 bone placed at the floor of the buccal cavity.

(iv)Middle car bones - 3 pairs (malleus, incus, stapes) located in the mid{dle}ear of both sides.

Bones of the Cranium

 

Ethmoid Floor of the cranium, inferior to thefrontal bone and anterior to thesphenoid.Non-technically: Centre of the face,

behind the nose.

Forms part of the nasal cavity and theorbits.Main support structure of the nasalcavity

  Frontal Forehead, extending down to form the

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upper surfaces of the orbits. Anterior roof of the skull.

  Occipital Back and base of the cranium, formsthe back of the skull.Non-technically: Lower back of thehead.

The occipital condyles (roundedsurfaces at the base of the occipitalbone) articulate with the atlas (firstvertebra of the spine), enablingmovement of the head relative to thespine.

Has a large opening called the ForamenMagnus which the spinal cord passesthrough.

  Parietal Top and sides of the cranium, posterior roof of the skull.

 

Sphenoid  Anterior to the temporal bones andforms the base of cranium - behind theorbitals.Consists of a body, two "wings" and two"pterygoid processes" (not labelled ondiagrams) that project downwards.

 Articulates with the frontal, parietal andtemporal bones.

  Temporal Sides of the skull, below the parietalbones, and above and behind the ears

 

Bones of the Face

  Hyoid In the neck, below the tongue (held inplace by ligaments and musclesbetween it and the styloid process of thetemporal bone).

Supports the tongue, providingattachment sites for some tonguemuscles, and also some muscles of theneck and pharynx.(Commonly fractured duringstrangulation, so studied in autopsies if strangulation suspected.)

  Lacrimal Behind and lateral to the nasal bone,

also contribute to the orbits.(Smallest bones in the face.)

Contain foramina for the nasolacrimal

ducts (tear ducts).

  Mandible Known as the lower jaw bone. Alsoforms the chin and sides of the face.(Largest, strongest facial bone.)

Bone into which the lower teeth areattached.The only moveable facial bone; motionof this bone is necessary for chewingfood (the first stage of the digestionprocess).Each side of the mandible has a condyleand a coronoid process. The condylearticulates with the temporal bone toform the temporomandibular joint.

  Maxilla Upper jaw bone, which also forms thelower parts of the orbits.

Bone into which the upper teeth areattached.Each maxilla contains a maxillary sinusthat drains fluid into the nasal cavity.

  Nasal Pair of small oblong bones that form thebridge and roof of the nose.

 

Palatine Back of the roof of the mouth (hence notillustrated above). Small "L-shaped"bones.

Form the bottom of the orbitals andnasal cavities, and also the roof of themouth.

  Turbinator   Also known as TurbinateBone and Nasal Concha. These terms

refer to any of three thin bones that formthe sides of the nasal cavity (notillustrated in the diagrams above).

Form the nasal cavities.

  Vomer  Thin roughly triangular plate of bone onthe floor of the nasal cavity and part of the nasal septum.

Separates the nasal cavities into left andright sides.

  Zygomatic  Also known as Zygoma and Malar Bone.Commonly (non-medically) referred toas theCheek Bone because it forms theprominent part of the cheeks. Also

contributes to the orbits.

 Articulates with the frontal, maxilla,sphenoid and temporal bones.

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 Vertebral column

It is situated on the mid-dorsal line and forms an axis to which all other parts of the skeleton remain attached. It is made of 26 small bones called vertebrae. Theyare grouped in to five types:

 Atlas is the first vertebra and the skull rests on it

 Axis is the second vertebra. The skull and Atlas together rotates on the axis.

• Cervical -Consists of 7 vertebrae of the neck region.

• Thoracic-Consists of 12 vertebrae of the thoracic region.

• Lumbar-consists of 5 vertebrae of abdominal region.

• Sacral - consists of 1 vertebra of the hip region (5 vertebrae fused to formone piece).

• Coccyx-consists of 1 vertebra and represents a vestigial tail (4 vertebraefused to form one piece).

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Sternum

It is also called as the breast bone and is a flat and narrow bone of approximately15cms in length. It is situated along the mid{dle} line of the thorax (chest).

 

Ribs

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Ribs have two facets, which articulate ventrally to the sternum and dorsally to thethoracic vertebrae.

12 pairs of ribs are classified as follows:

• 1-7 pairs: True ribs as they are directly attached to the sternum.

• 8-10 Pairs: False ribs as they are not directly attached to the sternum butthrough the true ribs.

• 11-12 Pairs: Floating ribs as they are very short and are not connected to thesternum

The thoracic vertebrae, ribs and sternum together form the 'rib cage' and provideprotection to the heart and lungs

The Pectoral (Shoulder) Girdle

Composed of two bones

Clavicle—collarbone

Scapula—shoulder blade

These bones allow the upper limb to have exceptionally free

movement

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Pectoral girdle

Each half of the pectoral girdle consists of a clavicle and a scapula, clavicle is along bone with two curves. Scapula forms the shoulder blade. There is a ridge

called spine is present diagonally across the triangular body of the scapula with aprocess called acromion It articulates with the clavicle. Below acromion process isa depression called glenoid cavity, which articulates with the head of the humerus.

 Appendicular skeleton (126 bones)

It consists of fore limbs, hind limbs, pectoral girdle and pelvic girdle.

Each fore-limb has 30 bones (fig 5.6).

Humerus (upper arm) = 1

Radius & ulna (lower arm) = 2

Carpals (wrist) = 8

Metacarpals (Palm) = 5

Phalanges (fingers) = 14

Each hind-limb has 30 bones (fig 5.7)

Femur (thigh bone-longest bone of the body) = 1

Tibia & fibula (shank) = 2

Patella (knee cap) = 1

Tarsal (ankle) = 7

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Metatarsals (foot) = 5

Phalanges (toes) = 14

The appendicular skeleton (126 bones) is formed by the pectoral girdles (4), the upper limbs (60), the

pelvic girdle (2), and the lower limbs (60). Their functions are to make locomotion possible and toprotect the major organs of locomotion, digestion, excretion, and reproduction

Girdle bones provide a connection between the axial skeleton and limbs. Eachgirdle is formed of two halves.

Pelvic girdle

Each half of the pelvic girdle consists of ileum, ischium and pubis. Ileum is thelargest where as pubis and ischium are inferior and are situated anteriorly and

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posteriorly. Acetabulum is a cavity formed at the point of fusion of the threebones. The head of femur articulates with acetabulum. The pubis of the two sidesarticulate at the median line to form the pubic symphysis. Between the pubis andischium is an opening for the passage of blood vessels and nerves called obturatorforamen.

Conditions & Disorders of the Skeletal System

• 1. Types of Fractures (and their causes)

A fracture is breakage of a bone, this breakage may be complete or incomplete.

1. Simple

A clean break of the bone with little or no break in the overlying skin.

2. Greenstick 

An incomplete break of the bone in which part of the outer shell (cortex) remains

intact.This occurs particularly in children, who have more flexible bones than adults.

3. Compound (also known as "Open")

A broken bone that pierces the overlying skin.

4. Comminuted

A fracture in which the bone is broken into more than two pieces.

A crushing force is usually responsible and there is extensive injury to surrounding

soft tissues is common.

5. Impacted

A fracture in which the bones involved are driven into each other.

6. Complicated

A broken bone that also involves damage to other organs - in addition to broken

Bone(s) and possibly also broken skin. An example is a broken rib that punctures a

lung.

2. Postural Deformities (in Vertebral Column)

1. Kyphosis

Excessive outward curvature of the spine, causing hunching of the back.

2. Lordosis

Inward curvature of the spine.

Some lordosis in the lumbar and cervical regions of the spine is normal.

Exaggerated lordosis may occur in adolescence - possibly as a result of faulty

 posture, or due to disease affecting the vertebrae and spinal muscles.

3. Scoliosis

Lateral (sideways) deviation of the spine.

Scoliosis may be caused by congenital or acquired abnormalities of the vertebrae,

muscles, and/or nerves.

Treatment may involve the use of spinal braces and, in cases of severe deformity.

surgical correction by fusion or osteotomy.

 

3. Other Skeletal Conditions (and their causes and effects)

Condition  Cause Effect

Arthritis Over 200 diseases may cause

arthritis, including:

Swelling, warmth, redness of the

overlying skin, pain, restriction of 

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motion.Inflammation

of one or more

 joints

osteoarthritis

rheumatoid arthritis

gout

tuberculosis, and other 

infections.

Osteo

Arthritis

Osteo-arthritis is due to wear of 

the articulatory cartilage, and may

lead to secondary changes in theunderlying bone..

The joints are painful and stiff with

restricted movement.

Degenerative joint disease

 

Rheumatoid

Arthritis

Rheumatoid Arthritis is a disease

of the synovial lining of joints:

The joints are initially painful,

swollen, and stiff and are usually

affected symmetrically.

As the disease progresses the

ligaments supporting the joints are

damaged and there is erosion of the

 bone, leading to deformity of the

 joints. Tendon sheaths can be

affected, leading to tendon rupture.

(The second

most

common

form of arthritis,

after osteo

arthritis)

 

Bone Cancer Bone cancer may occur as a

secondary cancer from, for 

example, prostate cancer 

Damage to stem cells (the cause of 

leukaemia).

Gout Gout is caused by a defect in uricacid balance in the metabolism -

resulting in an excess of the acid

and its salts (urates) which then

accumulate in the bloodstream and

 joints, respectively.

Gout can result in attacks of acutegouty arthritis, chronic destruction of 

the joints, and deposits of urates

(tophi) in the skin and cartilage -

especially of the ears.

Osteoporosis Infection, injury and synovitis can

cause localized osteoporosis of 

adjacent bone.

Bones that are brittle and liable to

fracture.Loss of bone

tissue.

 

Rickets Rickets is a childhood condition

caused by insufficient vitamin D

and Calcium

Bow legs.

Childhood

disease

 

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SKELETAL DISORDERS

1. Growth and development

1.1Giantism

Is a condition of abnormally increased size that usually

involves excessive endochondral growth at the epiphyseal

plates of long bones

1.2Dwarfism

 The condition in which a person is abnormally small, may

result from improper growth in the epiphyseal plates

1.3Osteogenesis Imperfecta

Osteo – bone

Genesis – production

A group of genetic disorders producing very brittle bones that

are easily fractured occurs because insufficient collagen is

formed.

Collagen normally strengthens bones and makes them

flexible.

In severe cases, prenatal fractures of the limbs often occur in

the fetus. These fractures usually heal in poor alignment,

causing the limbs to appear bent and shortened. In less severe

cases the disease first becomes apparent during childhood.

1.4Rickets ( to twist, bones become twisted)

Is a condition involving growth retardation resulting from

nutritional deficiencies either in minerals (calcium and

phosphate) necessary for normal ossification or in vitamin D,

which is necessary for calcium and phosphate absorption. The

condition results in bones that are soft , weak, and easily

broken.

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Rickets most often occurs in children who receive inadequate

amounts of sunlight. (Necessary for vitamin D production by

the body) and whose diets are deficient in vitamin D.

2. Bacterial Infections

2.1Osteomyelitis

Osteo – bone

Myelos – marrow

It is – inflammation

Is bone inflammation that often results from bacterial infection

and it can lead to complete destruction of the bone

Staphylococcus

Staphyle – a bunch of grapes

Kokkos – a berry

 These describe the organization and shape of the bacterium

Staphylococcus is introduced into the body through wounds

2.2Tuberculosis – is primarily a lung disease, but it can also

affect bones

3. Decalcification

3.1Osteomalacia ( adult rickets)

Osteo – bone

Malakia – softness

 This is the softening of bones, results from calcium depletion

from bones.

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If the bod has an unusual need if calcium (e.g pregnancy when

fetal growth requires large amounts of calcium) , it may be

removed from the mother’s bones, which consequently soften

and weaken. this can result from vitamin D deficiency.

3.2Osteoporosis

Osteo – bone

Poros – pore

Osis – condition

Result from the reduction in the overall quantity of bone tissue

4. Tumors

 There are many types of bone tumors with a wide range of resultant

bone defects

 Tumors maybe benign or malignant.

Malignant – may metastasize (spread) to other parts of the body or may

result from metastasizing tumors elsewhere