basic about human skeleton for medical students which will help to make their strong concept about osteology

1. “BASIC INTRODUCTION”
HUMAN SKELETON
DEPARTMENT OF RACHNA SHARIR
(ANATOMY)
SAMCH INDORE (MP)

2.  Skeleton includes =
bones + cartilages.
 It forms the main
supporting framework
of the body.
 It is primarily designed
for a more effective
production of
movements by the
attached muscles.

3. BONES
 Synonym – Os (Latin)
Osteon (Greek)
 It consists – 1/3rd of organic part (connective tissue)
& 2/3rd of inorganic part (ca salts)
 Inorganic calcium salts - calcium phosphate,
calcium carbonate & others salts.
 Inorganic salts make it regid & hard.
 Organic connective tissues – like collagen fibers
make is tough & flexible (resilient)

4.  Bone is very much a living tissue. it is highly
vascular.
Functions :-
 Give shape & support to the body.
 Provide surface for attachment of muscles, tendons &
ligaments etc.
 Protect internal body organs.
 Bone marrow manufactures RBCs.
 Store calcium & phosphorus (97% of the body part)
 Bone marrow contains R.E.S.

5. DIVISION OFTHE SKELETALSYSTEM
Total bones - (206)
AXIAL SKELETON (80 bones)
 SKULL –
Cranium – 8
Facial – 14
Hyoid – 1
Ear ossicles – 6
VERTEBRAL COLUMN - 26
THORAX –
Sternum – 1
Ribs - 24

6. APPENDICULAR SKELETON (126 bones)
PECTORAL GIRDLES
Clavicle – 2
Scapula – 2
UPPER EXTREMITIES
Humerus – 2
Ulna – 2
Radius – 2
Carpals – 16
Metacarpals – 10
Phalanges - 28
PELVIC GIRDLES
Pelvic (hip) bone – 2
LOWER EXTREMITIES
Femur – 2
Fibula – 2
Tibia – 2
Patella – 2
Tarsals - 14
Metatarsals – 10
Phalanges - 28

8. CLASSIFICATION OF BONES
1. According to shape –
a) Long Bones
b) Short Bones
c) Flat Bones
d) Irregular Bones
e) Pneumatic Bones
f) Sesamoid Bones
g) Accessory Bones.
2. Developmental classification -
3. Regional classification -
4. Structural classification -

9. According to shape
 Long bones – It has an elongated shaft (diaphysis)
& two expanded ends (epiphysis).
a) Typical long bones – It has one shaft & two
secondary epiphysis(ends). Exa - humerus, radius,
ulna, femur, tibia, fibula.

10. b) Short long bones (miniature) – have only one
epiphysis.
exa. - metacarpals & phalanges.
c) Modified long bones – have no medullary cavity.
Exa. - clavicle

11.  Short bones – their shape is usually cuboid
(cube like) & scaphoid (boat shape).
Exa. tarsals & carpal bones.
 Flat bones – resemble shallow plates.
Exa. bones in the vault of the skull, sternum,
ribs, scapula.
 Irregular bones – irregular in shape. Exa. -hip
bones, bones in the base of the skull etc.

12.  Pneumatic bones - certain irregular bones
contain large air spaces lined by epithelium.
i.e. maxilla, sphenoid, ethmoid etc.
 Sesamoid bones – These are bony nodules found
embedded in the tendon or joint capsules. They
have no periosteum & ossify after birth.
i.e. Patella, pisiform, flabella, riders bone

13.  Accessory bones – Not always present. These
may occur as ununited epiphyses developed
from extra centres of ossification. i.e. sutural
bones of the skull etc.

14. Developmental classification
1.
 Membrane (dermal) bones :-
ossify in membrane (intra-membranous ossification) Exa. -
bones of the vault of the skull & facial bones
 Cartilaginous bones :-
offify in cartilage (intracartilaginous or endochondral
ossification) exa. - bones of the limbs, vertebral column &
thoracic cage
 Membrano-cartilaginous bones :-
ossify partly in membrane & partly in cartilage.
exa. – clavicle, mandible, occipital , temporal, sphenoid
2.
 Somatic bones :- comprised of calcified connective tissue.
Exa. most of the bones
 Visceral bones :- few bones developed from pharyngeal
arches. exa.- hyoid bone, part of mandible, ear ossicles

15. Regional Classification
 Axial skeleton:
Skull
Vertebral column
Thoracic cage.
 Appendicular skeleton:
Pelvic girdle
Pectoral girdle
Bones of the limbs
(upper & lower)

16. Structural Classification
1. Macroscopically
a) Compact bone
b) Cancellous or spongy
or trabecular bone
2. Microscopically
a) Lamellar bone
b) Woven bone
c) Fibrous bone
d) Dentine
e) Cement

17.  Compact bone – it is
dense in nature but is
extremely porous.
• It is best developed in the
cortex of the long bones
• This is an adaptation to
bending & twisting
forces.
 Cancellous/spongy/trab
ecular bone –
• It is open in texture.
• It is made up of a
meshwork of trabeculae
(rods & plates) b/w
which are marrow
containing spaces.
• This is an adaptation to
compressive forces.

19. GROSS STRUCTURE OF AN ADULT BONE
1. Shaft : It is composed of –
a) Periosteum (outer most ) – it is a thick fibrous
membrane covering the surface of the bone.
• It is made up of an outer fibrous layer & an inner
cellular layer (osteogenic nature).
b) Cortex – is made up of a compact bone
c) Medullary cavity (inner most) – lined by endosteum.
Osteoblast situated in it.
• Cavity is filled with red & yellow bone marrow
2. The two ends : These are made up of cancellous
bone covered with hyaline (articular) cartilage.

21. Parts OfAYoung Growing Bone
 There four parts of a young bone:
1. Epiphysis:
• The end & tips of a bone.
2. Diaphysis :
• Elongated shaft of a long bone.
3. Metaphysis :
• Epipysial end of a diaphysis.
4. Epiphysial plates :
• it separates epiphysis from
metaphysis.

22. Blood Supply of bones :
 Arterial supply:
a) Nutrient artery
b) Periosteal arteries
c) Epiphysial arteries
d) Metaphysial arteries
 Venous drainage:
• Numerous & large in
cancellous red marrow

23. Fornation of bones (Ossification)
• All bones are of mesodermal origin.
• The process of bone formation is called ossification.
• There are two methods of bone formation –
a) Intramembranous ossification (mesenchymal)
b) Endochondral ossification (intracartilaginous )
• Ossification takes place by centers of ossification.
• The center of ossification may be-
1) Primary centres - forms diaphysis
2) Secondary centres - forms epiphysis
• Fusion of epiphysis with diaphysis starts at puberty
& is complete by the age of 25 years.

24. A) Intramembranous Ossification
 It is direct conversion
of mesenchymal
tissue into bone.
 Formed bones are
called membranous
(dermal) bones.
 Example- bones of
the vault of skull &
facial bones.

25. Steps of bone formation
(Intramembranous ossification):
1) Mesenchymal condensasion
2) Conversion into a fibrous membrane
3) Osteoblast & osteoid formation
4) Mineralization of osteoid
5) Conversion of osteoblast to osteocyte &
formation of woven bone.
6) Progressive bone formation
7) Remoudeling into lamellar bone

26. B) Endochondral Ossification
 Here mesenchymal
cells differentiate
into cartilage cells
that are later
replaced by bone.
 Bones formed in
this way are
therefore called
cartilage bones.
 Example- bones of
the limbs,
vertebral column
& thoracic cage.

27. Steps of bone formation
(Endochondral ossification):
1) Mesenchymal condensation
2) Cartilaginous model
3) Cartilage cell hypertrophy
4) Calcification of intercellular matrix
5) Vascularization of cartilaginous matrix
6) Osteoid & lamella formation
7) Formation of trabeculae.

28. Growth of a long bone
 In length – by multiplication of cells in the
epiphysial plate of cartilage.
 In thickness – by multiplication of cells in the
deeper layer of periosteum.
 Appositional growth/ surface accretion – the
deposition process by osteoblasts in which the
bone grow by deposition of new bone on the
surface & at the end.
 Remodelling – to maintain the shape of the bone
the unwanted bone must be removed by osteoclast
this process is called remodelling. This is how
marrow cavity increase in size.

29. Medicolegal aspects of the skeletal
system
 When a skeleton or isolated bones are
received for medicolegal examination, one
should be able to determine:
a) Whether the bones are human or not
b) Whether they belong to one or more persons
c) The age of the individual
d) The sex
e) The stature
f) The time & cause of the death.

30. Clinical (applied) anatomy :
 Fractures
 Rickets
 Osteoporosis
 Osteomalacia
 Bone marrow tumour
 Bone marrow biopsy etc.