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The Skeletal System. Dr. S. Nishan Silva (MBBS). Under the Skeletal System. Function Classification Histology Formation Gross Anatomy. Function of the Skeletal System. Support- framework that supports body and cradles its soft organs Protection- for delicate organs, heart, lungs, brain

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Dr s nishan silva mbbs

The Skeletal System

Dr. S. Nishan Silva

(MBBS)


Under the skeletal system

Under the Skeletal System

  • Function

  • Classification

  • Histology

  • Formation

  • Gross Anatomy


Dr s nishan silva mbbs

Function of the Skeletal System

  • Support- framework that supports body and cradles its soft organs

  • Protection- for delicate organs, heart, lungs, brain

  • Movement- bones act as levers for muscles

  • Mineral storage- calcium & phosphate

  • Blood cell formation- hematopoiesis


Functions

Functions:

Support

The bones of the legs, pelvic girdle, and vertebral column support the weight of the erect body.

The mandible (jawbone) supports the teeth.

Other bones support various organs and tissues.


Dr s nishan silva mbbs

2.Protection

The bones of the skull protect the brain.

Ribs and sternum (breastbone) protect the lungs and heart.

Vertebrae protect the spinal cord

Movement

Skeletal muscles use the bones as levers to move the body.


Dr s nishan silva mbbs

Reservoir for minerals and adipose tissue

99% of the body’s calcium is stored in bone.

85% of the body’s phosphorous is stored in bone.

Adipose tissue is found in the marrow of certain bones

Hematopoiesis

Blood cell formation.

All blood cells are made in the marrow of certain bones


Dr s nishan silva mbbs

Types of Bones

  • Long Bones- metacarples, metatarsals, phelangies, humerus, ulna, radius, tibia, fibula

  • Short Bones- carpals, tarsals

  • Flat Bones- rib, scapula, skull, sternum

  • Irregular Bones- vertebrae, some facial bones

  • Sesamoid- patella


Classification of bones

CLASSIFICATION of BONES

1.long bones = length is greater than breadth

= consists of shaft (diaphysis) &

two extremities (epiphysis)

diaphysis = filled with yellow marrow

= cylindrical, large space or canal at the center

= periosteum

epiphysis = made up of cancellous tissue

e.g.: femur, humerus, tibia, fibula, radius, ulna, phalanges

Membranes: 1. periosteum

2. endosteum


Bone classification

Bone Classification

Long Bones

Much longer than they are wide.

All bones of the limbs except for the patella (kneecap),

and the bones of the wrist and ankle.

Consists of a shaft plus 2 expanded ends.

Your finger bones are long bones even though they’re very short


Classification of bones cont n

CLASSIFICATION of BONES cont’n.

2. short bones = cuboidal in shape

= spongy bone with thin coat of compact bone

= sesamoid bone -- short bone embedded in a

tendone.g.: patella

e.g.: carpals (wrist), tarsal (ankle) bones

3. flat bones = broad or elongated flat plates

= for protection & muscle attachments

composition: 2 thin layers of compact tse. enclosing

a thin layer of spongy bone

e.g.: bones of the skull, sternum, ribs, scapula


Dr s nishan silva mbbs

2. Short Bones

Roughly cube shaped.

Bones of the wrist and the ankle.


Dr s nishan silva mbbs

Flat Bones

Thin, flattened, and usually a bit curved.

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

Sternum


Classification of bones cont n1

CLASSIFICATION of BONES cont’n.

4. Irregular bones = all other bones not assigned to the previous groups

e.g.: vertebrae

pelvic bones

bones of the base of the skull


Dr s nishan silva mbbs

4. Irregular Bones

Have weird shapes that fit none of the 3 previous classes.

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

Sphenoid Bone


Dr s nishan silva mbbs

Bone Classification


Dr s nishan silva mbbs

Bone

65% mineral

35% organic

Calcium Phosphste

Hydroxy-apatite

90%

Type 1

Collagen

10%

Other matrix proteins

Lipids

Phospholipids

Proteoglycants

etc


Bone cells

Bone Cells

  • Osteoblasts

    • Synthesize matrix; type 1 collagen

  • Osteocytes

    • Control extra-cellular calcium and phosphorus

  • Osteoclasts

    • Synthesize acid phosphatase and hydrogen ions

    • Remove bone minerals and matrix


  • Bone cells1

    Bone Cells

    Bone tissue is a type of connective tissue, so it must consist of cells plus a significant amount of extracellular matrix.

    Bone cells:

    Osteoblasts

    Bone-building cells.

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

    Initiate the process of calcification.

    Found in both the periosteum and the endosteum


    Dr s nishan silva mbbs

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


    Dr s nishan silva mbbs

    2. Osteocytes

    Mature bone cells.

    Osteoblasts that have become trapped by the secretion of matrix.

    No longer secrete matrix.

    Responsible for maintaining the bone tissue.

    The osteocyte is “trapped” within the pink matrix


    Dr s nishan silva mbbs

    3.Osteoclasts

    Huge cells derived from the fusion of as many as 50 monocytes (a type of white blood cell).

    Cells that digest bone matrix – this process is called bone resorption and is part of normal bone growth, development, maintenance, and repair.

    Concentrated in the endosteum.


    Dr s nishan silva mbbs

    Bone Matrix:

    Consists of organic and inorganic components.

    Organic component consists of several materials that are secreted by the osteoblasts:

    Collagen fibers and other organic materials

    These (particularly the collagen) provide the bone with resilience and the ability to resist stretching and twisting


    Dr s nishan silva mbbs

    Inorganic component of bone matrix

    Consists mainly of 2 salts: calcium phosphate and calcium hydroxide.

    Bone also contains smaller amounts of magnesium, fluoride, and sodium.

    These minerals give bone its characteristic hardness and the ability to resist compression.


    Dr s nishan silva mbbs

    Anatomy of a Long Bone

    spongy bone

    Proximal

    epiphysis

    compact bone

    Endosteum

    diaphysis

    epiphyseal line

    yellow marrow

    Sharpey’s fibers

    Distal

    epiphysis

    periosteum

    hyaline cartilage


    2 types of bone

    2 Types of Bone

    Compact bone

    Spongy bone


    Classification of bones1

    CLASSIFICATION of BONES

    • According to structure

      1. compact = solid mass; dense & hard

      = forms the outer layer of bone structure

      = functional unit --- Haversian system

      2. cancellous or spongy = contain spaces filled with bone marrow

      = incomplete Haversian system


    Long bone structure

    Long Bone Structure

    Shaft plus 2 expanded ends.

    Shaft is known as the diaphysis.

    Consists of a thick collar of compact bone surrounding a central marrow cavity

    In adults, the marrow cavity contains fat - yellow bone marrow


    Dr s nishan silva mbbs

    Expanded ends are epiphyses

    Thin layer of compact bone covering an interior of spongy bone.

    Joint surface of each epiphysis is covered with a type of hyaline cartilage known as articular cartilage. It cushions the bone ends and reduces friction during movement.


    Dr s nishan silva mbbs

    The external surface of the entire bone except for the joint surfaces of the epiphyses is covered by a double-layered membrane known as the periosteum

    Periosteum is richly supplied with nerve fibers, lymphatic vessels and blood vessels.

    These enter the bone of the shaft via a nutrient foramen.


    Dr s nishan silva mbbs

    Periosteum is connected to the bone matrix via strong strands of collagen

    Internal bone surfaces are covered with a delicate connective tissue membrane known as the endosteum.

    Covers the trabeculae of spongy bone in the marrow cavities and lines the canals that pass through compact bone.

    Contains both osteoblasts and osteoclasts.


    Microscopic structure of compact bone

    MICROSCOPIC STRUCTURE OF COMPACT BONE


    Haversian system

    Haversian System

    osteon

    osteocyte

    • Osteon with central haversian canal containing

      • Cells

      • Vessels

      • Nerves

    • Volkmann’s canal

      • Connects osteons

    Picture courtesy Gwen Childs, PhD.

    Haversian canal

    Volkmann’s canal


    Dr s nishan silva mbbs

    Spider-shaped osteocytes occupy small cavities known as lacunae at the junctions of the lamellae.

    Hairlike canals called canaliculi connect the lacunae to each other and to the central canal.

    Canaliculi allow the osteocytes to exchange nutrients, wastes, and chemical signals to each other via intercellular connections


    Bones animation

    Bones - Animation


    Another classification for types

    Another Classification for -Types

    • Lamellar bone

      • Normal, mature, structured

  • Woven bone

    • Weak, fragile, immature, randomly organized

    • Ex

      • Bones in newborns

      • Fracture repair callus

      • Bone tumors


  • Classification of bones cont n2

    CLASSIFICATION of BONES cont’n.

    • According to location

      A X I A L

      skull22

      hyoid 1

      ossicles 6

      vertebrae26

      ribs & sternum 25_

      80


    Classification of bones cont n3

    CLASSIFICATION of BONES cont’n.

    • According to location

      APPENDICULAR

      Upper ExtremitiesLower Extremities

      clavicle2hip bone 2

      scapulae2femur 2

      humerus2patella 2

      radius2tibia 2

      ulna2fibula 2

      carpals 16tarsals 14

      metacarpals 10metatarsals 10

      phalanges 28__phalanges 28__

      64 62


    Dr s nishan silva mbbs

    Table. 6.2


    Gross anatomy of a long bone

    GROSS ANATOMY OF A LONG BONE


    Blood supply

    Blood Supply

    • Long bones have three blood supplies

      • Nutrient artery (intramedullary)

      • Periosteal vessels

      • Metaphyseal vessels

    Periosteal

    vessels

    Nutrient

    artery

    Metaphyseal

    vessels

    Figure adapted from Rockwood and Green, 5th Ed


    Nutrient artery

    Nutrient Artery

    • Normally the major blood supply for the diaphyseal cortex (80 to 85%)

    • Enters the long bone via a nutrient foramen

    • Forms medullary arteries up and down the bone


    Periosteal vessels

    Periosteal Vessels

    • Arise from the capillary-rich periosteum

    • Supply outer 15 to 20% of cortex normally

    • Capable of supplying a much greater proportion of the cortex in the event of injury to the medullary blood supply


    Metaphyseal vessels

    Metaphyseal Vessels

    • Arise from periarticular vessels

    • Penetrate the thin cortex in the metaphyseal region and anastomose with the medullary blood supply


    Bone marrow

    Bone Marrow

    soft tissue occupying the medullary cavity of a long bone, the spaces amid the trabeculae of spongy bone, and the larger haversian canals.

    There are 2 main types: red & yellow.

    Red bone marrow = blood cell forming tissue = hematopoietic tissue


    Bone marrow1

    Bone Marrow

    • Bone marrow is the spongy tissue in the cavities of the bones.

    • It is the blood cell ‘factory’ – it makes blood cells.

    • Healthy bone marrow releases blood cells into the blood stream when they are mature and when our body needs them.

      • The different blood cells made inside bone marrow are:

    • Red blood cells that carry oxygen around the body

    • Around 2.6 million red blood cells are produced each second by the bone marrow to replace those worn out and destroyed by the liver.

    • White blood cells that make up the body's immune system

      • Platelets which are needed for clotting.

  • Cancer of the blood is called…….

  • …leukaemia, where many more white blood cells are made than are needed. These cancerous white blood cells take over our blood!


  • Bone remodeling steps

    Bone Remodeling - Steps

    • (i) Resorption: stimulated osteoblast precursors release factors that induce osteoclast differentiation and activity. Osteoclasts remove bone mineral and matrix, creating an erosion cavity.

    • (ii) Reversal: mononuclear cells prepare bone surface for new osteoblasts to begin forming bone.

    • (iii) Formation: successive waves of osteoblasts synthesize an organic matrix to replace resorbed bone and fill the cavity with new bone.

    • (iv) Resting: bone surface is covered with flattened lining cells. A prolonged resting period follows with little cellular activity until a new remodelling cycle begins


    Dr s nishan silva mbbs

    Bone Remodelling


    Dr s nishan silva mbbs

    Axial Skeleton


    Dr s nishan silva mbbs

    Appendicular Skeleton


    Axial skeleton

    AXIAL SKELETON

    I.SKULL

    = skeleton --- head & face

    = flattened & irregular

    = united by joints (sutures)

    cranium -- skull minus mandible

    calvarium -- skull after the bones of the face have been removed

    cavities: a. Cranial - contains the brain

    b. Orbital - contains eyeball

    & accessory organs

    c. nasal


    Dr s nishan silva mbbs

    The skull

    8 sutured bones in cranium

    Facial bones: 13 sutured bones, 1 mandible

    Cranium

    encases brain

    attachments for muscles

    sinuses


    Anterior skull

    frontal bone

    glabella

    supraorbital foramen

    Anterior Skull

    infraorbital foramen

    zygomatic bone

    mandibular symphysis

    maxillary bone

    alveolar fossa

    mental foramen

    mandible


    Fig 6 11

    Fig. 6.11


    Sutures

    Sutures

    Sutures are the tight connections between skull bones

    In the adult skull , the skull bones are unable to move or separate due to this tight connections

    In infant skull this sutures are not well formed and the skull bones are mobile which facilitates the delivery of the baby


    Cranium

    Cranium

    frontal bone

    coronal suture

    parietal bone

    sagittal suture

    lambdoidal

    suture

    occipital bone


    Lateral skull

    Lateral Skull

    squamosal

    suture

    lacrimal

    bone

    temporal

    bone

    external acoustic

    meatus

    mandibular condyle

    In mandibular fossa

    (TMJ joint)


    Lateral skull1

    Lateral Skull

    zygomatic arch

    sphenoid

    bone

    coronoid process

    sutural bone

    mastoid process

    styloid process

    ramus

    angle

    body

    mandible


    Fig 6 14

    Fig. 6.14


    Internal skull

    Internal Skull

    cribriform plate

    crista galli

    lesser wing

    greater wing

    optic canal

    sella turcica

    intenal acoustic meatus

    jugular foramen


    Fig 6 15

    Fig. 6.15


    Ventral skull

    Ventral Skull

    palatine process

    sphenoid bone

    palatine bone

    vomer bone

    styloid process

    temporal bone

    mastoid process

    external occipital

    protuberance

    occipital bone


    Occipital bone

    Occipital bone

    carotid

    canal

    jugular

    foramen

    occipital

    condyle

    foramen magnum


    Divisions of the bones of the skull

    Divisions of the bones of the skull

    • Cerebral / cranial bones / brain case (8 bones)

      unpaired (4)paired (4)

      1. occipital 1. parietal

      2. frontal 2. temporal

      3. sphenoid

      4. ethmoid

      b.Facial or visceral cranium

      paired (12)unpaired (2)

      a. Nasal a. Vomer

      b. Lacrimal b. Mandible

      c. Maxilla

      d. Zygomatic / malar / cheek bones

      e. Palatine

      f. Inferior nasal concha or turbinate


    Frontal bone

    Frontal bone

    Forms the forehead

    Roof of the orbit

    articulates with parietal, sphenoid, lacrimal, nasal, ethmoid, zygomatic and maxilla

    Contain 2 air filled cavities. ( frontal sinuses)


    Parietal bones

    Parietal bones

    Part of the superior and lateral surfaces of the cranium

    -articulate with each other – sagittal suture

    -articulate with occipital, frontal,

    temporal and sphenoid bones


    Temporal bone

    Temporal bone

    Forms wall of jugular foramen

    Associated with ear canal

    Special parts

    - zygomatic process

    -forms cranial portion of the Tempero Mandibular joint

    -inferior to zygo. process – mandibular fossa (mandibular condyle)

    - inferior aspect – mastoid process

    - inferior and medial to the MP – styloid process


    Occipital bone1

    Occipital bone

    Part of the base of the skull

    articulates with parietal, temporal and sphenoid

    Surrounds the foramen magnum

    Occipital condyles articulate with Atlas – 1st cervical vertebra


    Dr s nishan silva mbbs

    The uppermost portion of the human respiratory system, the nose is a hollow air passage that functions in breathing and in the sense of smell. The nasal cavity moistens and warms incoming air, while small hairs and mucus filter out harmful particles and micro-organisms. This illustration depicts the interior of the human nose.


    Facial bones

    Facial Bones

    Nasal (2) Maxillae (2) Zygomatic (2)

    Mandible (1) Lacrimal (2) Palatine (2)

    Inferior nasal conchae (2) Vomer (1)


    Anterior skull1

    frontal bone

    glabella

    supraorbital foramen

    Anterior Skull

    infraorbital foramen

    zygomatic bone

    mandibular symphysis

    maxillary bone

    alveolar fossa

    mental foramen

    mandible


    Sinuses

    Sinuses

    Frontal Sinus

    Ethmoid Sinus

    Sphenoid Sinus

    Maxillary Sinus

    • Warm and moisten air

    • Lighten the skull

    • Enhance voice resonance


    Fig 6 13

    Fig. 6.13


    Frontal sinus pathologies

    Frontal sinus pathologies


    Paranasal sinuses

    Paranasal Sinuses

    frontal sinus

    ethmoid sinus

    maxilary sinus

    sphenoid sinus


    Fontanelles

    Fontanelles

    These are seen in new borns

    At birth the junction between skull bones covered with a membrane

    This allows the expansion and growth of the brain

    Later they become ossified ( bone formation)


    Fontanelle

    Fontanelle

    = membrane filled spaces found in the skull of

    newborn infants

    e.g.:1. anterior = largest

    2. posterior

    3. anterolateral (sphenoidal)

    4. posterolateral (mastoid)


    Dr s nishan silva mbbs

    Allows for

    growth


    Hydrocephalus

    Hydrocephalus


    Axial skeleton1

    AXIAL SKELETON

    • HYOID BONE

      = small U-shape; lies in front of the neck

      = base of the tongue is attached

      = lies between mandible & thyroid cartilage

      II. OSSICLES

      = small bones of the ear

      a. Stapes (stirrup)2

      b. Incus (anvil)2

      c. Malleus (hammer)2


    Hyoid

    Hyoid +

    external

    acoustic

    meatus

    temmporal

    mandibular

    joint

    Hyoid bone


    Mandible

    Mandible

    lower jaw carries teeth

    only freely movable bone of the skull

    moving articulations with temporal bone


    Fig 6 16

    Fig. 6.16


    Orbit

    Orbit


    Bones forming the walls of the orbit

    Bones forming the walls of the orbit

    Roof - frontal

    lesser wing of sphenoid

    Medial wall – maxilla

    lacrimal

    ethmoid

    sphenoid

    Floor – maxilla

    zygomatic

    palatine


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