SKELETAL SYSTEM

 SKELETAL SYSTEM

SKELETAL SYSTEM : Includes bones and cartilage's

• Forms the main support and shape to the body

BONES

• Highly specialised connective tissues
• Made up of organic and inorganic components

Functions of Bone 

• Gives support to the body 
• Protect the soft organs
• Movement due to attached skeletal muscle
• Helps in storage of mineral and fat 
• Blood cell formation 
• Bone marrow has reticuloentheial cell which take part in immune system.

Classification of bone 

1. According to shape    

• Long bones

• It has a long elongated shaft
• 2 expanded ends

• Short bones

• They are smaller in size
• Shape is usually cuboid , scaphoid or trapezoid
• Eg: carpal and tarsal bone

• Flat bone

• Resemble shallow plates 
• Form boundaries for certain body cavity
• Eg: sternum , scapula , ribs 

• Irregular bone

• Irregular in shape
• Eg: vertebrae , hip bone , bone of base of skull.

• Pneumatic bone

• Certain irregular bones containing large air space
• Lined with epithelium
• Eg: maxilla , sphenoid , ethmoid etc

• Sesamoid bone

• Bony nodules found embedded in the tendons
• No periostem
• No medullary cavity 
• Eg: patella in quadriceps femeoris
• Pesiform in flexor carpi ulnaris

1. According to development

• Membranous bones 

• Ossify in membranes
• Intra membranous or mesenchymal ossification
• Eg: Bones of vault of skull facial bone.

• Cartilaginous bones

• Ossify in cartilage
• Intra cartilaginous or endochordal ossification

• Membrano cartilaginous bone

• Ossify partly  in membrane and partly in cartilage

1. According to region

• Axial bone 

• Includes skull, vertebral coloumn

• Appendicular bone 

• Includes bones of limbs

1. According to the structure

• Microscopically

• Compact bone 
• Dense in texture

• Cancellous bone ( spongy or trabecular bone)

• Seen in the 2 ends of long bones

Division of skeletal system

AXIAL SKELETON	APENDICULAR SKELETON
Skull- cranium : 8                Face : 14	Pectoral girdles - clavicle : 2.                Scapula : 2
Hyoid bone : 1	Upper extremities : 60,humerus , ulna , radius, carpals, metacarpals,phalanges
Auditory ossicles : 3 in each ear	Pelvic girdles - hip bone : 2
Vertebral column : 26
Sternum : 1
Ribs : 24

Gross structure of an adult long bone

Shaft : it is composed of periosteum , cortex and medullary cavity.

• Gives strength to withstand all mechanical stress.

• Periosteum

• Thick fibrous membrane covering the bone.
• Made up of an outer fibrous layer and an inner cellular layer

• Medullary cavity

• Filled with bone marrow

• Types

1. Red bone marrow
2. Yellow bone marrow

Epiphysis

⁃ ⁃ 2 ends and tips of long bone which ossify from secondary centre are called epiphysis

• Types

1. Pressure epiphysis , eg : head of humerus
2. Traction epiphysis , eg : tronchatas of femurs
3. Atavistic epiphysis , eg : coracoid process of scapula
4. Aberrant epiphysis , eg : head of the metacarpal

Diaphysis

• It is elongated shaft of long bone . Ossify from the primary centre.

Metaphysis

• Epiphysial end of diaphysis
• It is the zone of active growth richly supplied by arteries

Blood supply of bone

• Nutrient artery
• Epiphysial artery
• Metaphysial artery
• Periosteal artery

Periosteal arteries:

• Numerous beneath the muscular and ligament attachment 
• They varify beneath the periosteum supplies 1/3rd of the calex

Ossification of bone

Ossification is the process of bone formation

2 types

1. Intra membrane ossification

• Bone developed from mesoderm

1. Intracartilagenous ossification

• Mesodermal stage passes through cartilaginous stage by chondrification