dr. s. nishan silva (mbbs)

Under the Skeletal System

• Function• Classification• Histology• Formation• Gross Anatomy

• 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:1. 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.

2.Protection • The bones of the skull protect the brain.• Ribs and sternum (breastbone) protect

the lungs and heart.• Vertebrae protect the spinal cord

3. Movement • Skeletal muscles use the bones as levers

to move the body.

3. 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 bones4. Hematopoiesis

• Blood cell formation.• All blood cells are made in the marrow of

certain 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

1.1. long boneslong bones = length is greater than breadth = length is greater than breadth = consists of shaft (diaphysis) & = consists of shaft (diaphysis) &

two extremities (epiphysis)two extremities (epiphysis)

diaphysis diaphysis = filled with yellow marrow = filled with yellow marrow= = cylindrical, large space or canal at the cylindrical, large space or canal at the

centercenter = = periosteumperiosteumepiphysis epiphysis = made up of cancellous tissue = made up of cancellous tissue

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

MembranesMembranes: : 1. periosteum1. periosteum2. endosteum2. endosteum

Bone Classification

1. 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.2. 2. short bonesshort bones = cuboidal in shape = cuboidal in shape

= spongy bone with thin coat of compact bone= spongy bone with thin coat of compact bone= = sesamoid bonesesamoid bone -- short bone embedded in a -- short bone embedded in a

tendontendone.g.: patellae.g.: patellae.g.: carpals (wrist), tarsal (ankle) bonese.g.: carpals (wrist), tarsal (ankle) bones

3. flat bones3. flat bones = broad or elongated flat plates = broad or elongated flat plates= for protection & muscle attachments= for protection & muscle attachmentscomposition: 2 thin layers of compact tse. enclosingcomposition: 2 thin layers of compact tse. enclosing

a thin layer of spongy bonea thin layer of spongy bonee.g.: bones of the skull, sternum, ribs, scapulae.g.: bones of the skull, sternum, ribs, scapula

2. Short Bones• Roughly cube shaped.• Bones of the wrist and the ankle.

3. 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’n.

4. Irregular bones4. Irregular bones = all other bones not assigned = all other bones not assigned to the previous groupsto the previous groups

e.g.: e.g.: vertebraevertebraepelvic bones pelvic bones bones of the base of the skullbones of the base of the skull

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

Bone

65% mineral 35% organic

Calcium Phosphste Hydroxy-apatite

90%Type 1

Collagen

10%Other matrix proteins

LipidsPhospholipidsProteoglycants

etc

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 Cells• Bone tissue is a type of connective tissue, so it

must consist of cells plus a significant amount of extracellular matrix.

• Bone cells:1. 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

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

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

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.

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

• 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.

Distalepiphysis

Proximal epiphysis

diaphysis

yellow marrow

epiphyseal line

periosteum

compact bone

spongy bone

Endosteum

hyaline cartilage

Sharpey’s fibers

2 Types of Bone

Compact bone

Spongy bone

CLASSIFICATION of BONES

• According to structureAccording 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• 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

• 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.

• 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.

• 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

Haversian System• Osteon with

central haversian canal containing– Cells – Vessels– Nerves

• Volkmann’s canal – Connects

osteons

Picture courtesy Gwen Childs, PhD.

osteon

Haversian canal

osteocyte

Volkmann’s canal

• 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

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’n.• According to locationAccording to location

A X I A LA X I A L

skullskull 2222hyoidhyoid 1 1ossiclesossicles 6 6vertebraevertebrae 2626ribs & sternum ribs & sternum 25_ 25_

8080

CLASSIFICATION of BONES cont’n.• According to locationAccording to location

APPENDICULARAPPENDICULARUpper ExtremitiesUpper Extremities Lower ExtremitiesLower Extremities

clavicleclavicle 22 hip bonehip bone 2 2scapulaescapulae 22 femurfemur 2 2humerushumerus 22 patellapatella 2 2radiusradius 22 tibiatibia 2 2ulnaulna 22 fibulafibula 2 2carpalscarpals 16 16 tarsalstarsals 14 14metacarpals 10metacarpals 10 metatarsals metatarsals 10 10phalanges phalanges 28__ 28__ phalanges phalanges 28__ 28__

6464 62 62

Table. 6.2

GROSS ANATOMY OF A LONG BONE

Blood Supply

• Long bones have three blood supplies– Nutrient artery

(intramedullary)– Periosteal vessels– Metaphyseal vessels

Nutrient artery

Metaphysealvessels

Periosteal vessels

Figure adapted from Rockwood and Green, 5th Ed

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• 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

• Arise from periarticular vessels• Penetrate the thin cortex in the

metaphyseal region and anastomose with the medullary blood supply

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 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 Marrow

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

Bone Remodelling

AXIAL SKELETONI.I. SKULLSKULL

= skeleton --- head & face= skeleton --- head & face= flattened & irregular= flattened & irregular= united by joints (sutures)= united by joints (sutures)

cranium cranium -- skull minus mandible-- skull minus mandiblecalvarium calvarium -- skull after the bones of the -- skull after the bones of the

face have been removed face have been removed

cavities:cavities: a. Cranial - contains the brain a. Cranial - contains the brain b. Orbital - contains eyeball b. Orbital - contains eyeball

& accessory organs& accessory organs c. nasalc. nasal

The skull8 sutured bones in craniumFacial bones: 13 sutured bones, 1 mandible

Craniumencases brainattachments for musclessinuses

Anterior Skull

frontal bonefrontal bone

supraorbital supraorbital foramenforamen

zygomatic bonezygomatic bone

maxillary maxillary bonebone

alveolar fossaalveolar fossa

infraorbital infraorbital foramenforamen

glabella

mental foramenmental foramenmandiblemandible

mandibular mandibular symphysissymphysis

Fig. 6.11

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 frontal bonefrontal bone

parietal boneparietal bone

occipital boneoccipital bone

lambdoidallambdoidal suturesuture

sagittal suturesagittal suture

coronal suturecoronal suture

Lateral Skull

lacrimallacrimalbonebone

temporaltemporalbonebone

squamosalsquamosalsuturesuture

mandibular condylemandibular condyleIn mandibular fossaIn mandibular fossa

(TMJ joint)(TMJ joint)

external acousticexternal acousticmeatusmeatus

angleangle

coronoid coronoid processprocess

zygomatic archzygomatic arch

mastoid processmastoid process

styloid processstyloid process

sphenoid sphenoid bonebone

bodybodyramusramus

mandiblemandibleLateral Skull

sutural sutural bonebone

Fig. 6.14

crista gallicrista gallicribriform platecribriform plate

intenal intenal acoustic acoustic meatusmeatus

greater winggreater winglesser winglesser wing

optic canaloptic canalsella turcicasella turcica

jugular foramenjugular foramen

Internal Skull

Fig. 6.15

Ventral Skullpalatine processpalatine process

palatine bonepalatine bone

vomer bonevomer bone

mastoid processmastoid process

styloid processstyloid process

external occipitalexternal occipitalprotuberanceprotuberance

sphenoid bonesphenoid bone

temporal bonetemporal bone

occipital boneoccipital bone

Occipital bone

occipitaloccipitalcondylecondyle

jugularjugularforamenforamen

carotidcarotidcanalcanal

foramen magnumforamen magnum

Divisions of the bones of the skull

a.a. Cerebral / cranial bones / brain case (8 bones)Cerebral / cranial bones / brain case (8 bones)unpaired (4)unpaired (4) paired (4)paired (4) 1. occipital1. occipital 1. parietal 1. parietal 2. frontal2. frontal 2. temporal 2. temporal 3. sphenoid3. sphenoid 4. ethmoid4. ethmoid

b.b. Facial or visceral craniumFacial or visceral craniumpaired (12)paired (12) unpaired (2)unpaired (2) a. Nasala. Nasal a. Vomer a. Vomer b. Lacrimalb. Lacrimal b. Mandible b. Mandible c. Maxillac. Maxilla d. Zygomatic / malar / cheek bonesd. Zygomatic / malar / cheek bones e. Palatinee. Palatine f. Inferior nasal concha or turbinatef. Inferior nasal concha or turbinate

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– 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– 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 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

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

Nasal (2) Maxillae (2) Zygomatic (2)Mandible (1) Lacrimal (2) Palatine (2)

Inferior nasal conchae (2) Vomer (1)

Anterior Skull

frontal bonefrontal bone

supraorbital supraorbital foramenforamen

zygomatic bonezygomatic bone

maxillary maxillary bonebone

alveolar fossaalveolar fossa

infraorbital infraorbital foramenforamen

glabella

mental foramenmental foramenmandiblemandible

mandibular mandibular symphysissymphysis

• Warm and moisten air• Lighten the skull• Enhance voice resonance

Frontal Sinus

Ethmoid SinusSphenoid Sinus

Maxillary Sinus

Sinuses

Fig. 6.13

Frontal sinus pathologies

Paranasal Sinuses

frontal sinusfrontal sinus

ethmoid sinusethmoid sinus

maxilary sinusmaxilary sinus

sphenoid sinussphenoid sinus

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 = membrane filled spaces found in the skull of= membrane filled spaces found in the skull of

newborn infantsnewborn infants

e.g.:e.g.: 1. 1. anterior anterior = largest= largest2. 2. posterior posterior

3. anterolateral (sphenoidal)3. anterolateral (sphenoidal)4. posterolateral (mastoid)4. posterolateral (mastoid)

Allows forgrowth

Hydrocephalus

AXIAL SKELETONI.I. HYOID BONE HYOID BONE

= small U-shape; lies in front of the neck= small U-shape; lies in front of the neck= base of the tongue is attached= base of the tongue is attached= lies between mandible & thyroid cartilage= lies between mandible & thyroid cartilage

II. II. OSSICLESOSSICLES= small bones of the ear= small bones of the ear

a. Stapes (stirrup)a. Stapes (stirrup) 22b. Incus (anvil)b. Incus (anvil) 22c. Malleus (hammer)c. Malleus (hammer) 22

Hyoid boneHyoid bone

temmporaltemmporalmandibularmandibular

jointjoint

external external acousticacousticmeatusmeatus

Hyoid +

Mandible• lower jaw carries teeth• only freely movable bone of the skull• moving articulations with temporal bone

Fig. 6.16

Orbit

Bones forming the walls of the orbit

• Roof - frontal lesser wing of sphenoid• Medial wall – maxilla lacrimal ethmoid sphenoid• Floor – maxilla zygomatic palatine