Skeletal system

Dr. Adarsh Sahu

Assistant Professor-I
Amity Institute of Pharmacy
Amity University Rajasthan
 INTRODUCTION
The skeletal system consists of bones and
structures that form joints. It includes:
•Bone tissue for structural support.
•Cartilage to cushion joints.
•Fibrous connective tissue, which forms
ligaments connecting bones together.
• These elements work together to provide
strength, flexibility, and protection for the
body.
•A bone is made of several different tissues:
•Osseous tissue (bone tissue).
•Cartilage.
•Dense connective tissue.
•Epithelium.
•Adipose tissue (fat).
•Nervous tissue.
•Due to this complexity, each bone is considered an
organ.
•Functions Of Bones:
a. Support, Protection & Movement:

1. Gives shape to the body.

2. Supports body weight.

3. Protects sensitive parts of the body.

b. Blood Cell Formation:

The red bone marrow found in the connective

tissue of certain bones is the site of blood cell
production.
c. In-organic Salt Storage:
• Functions as a storage depot for many of the body needs.
• For example: (Calcium, Potassium, Sodium etc).
d. Triglyceride storage
• Yellow bone marrow consists mainly of adipose cells, which
store triglycerides.
• The stored triglycerides are a potential chemical energy
source.
• In a new born, all bone marrow is red, and in involved in
hemopoiesis.
 Types Of Bones:
Types On The Basis Of Shape:
There are 6 basic types which are
mentioned below:

1. Long Bones.
2. Short Bones.
3. Flat Bones.
4. Irregular Bones.
5. Pneumatic Bones.
6. Sesamoid Bones.
 Fig. Femur, Long Bone.
1. Long Bones:
These bones typically have an elongated shaft and
two expanded ends one on either side of the shaft. The shaft
is known as diaphysis and the ends are called epiphyses.
Examples: Humerus, femur etc.
 2. Short Bones:
These bones are short in posture and can be of any shape.
Examples: The carpal and tarsal bones.

Fig. Carpal Bones, Short Bones. Fig. Tarsal Bones, Short Bones.
3. Flat Bones:
These bones are flat in appearance.
Examples: Scapula, Ribs, Sternum etc.

Fig. Scapula, Flat Bone.

Fig. Sternum & ribs, Flat bones.

 4. Irregular Bones:
These bones are completely
irregular in shape.
Examples: vertebrae, hip bone and
bones in the base of skull.

Fig. Hip bone, Irregular bone.

Fig. 1st & 2nd Cervical of vertebra,
Irregular bone.
5. Pneumatic Bones:
Pneumatic bones can also be categorized under
the irregular bones.
The characteristic difference is the presence of large air
spaces in these bones which make them light in weight
and thus they form the major portion of skull
Examples: Sphenoid, Ethmoid, Maxila etc.

Fig. Sphenoid, Ethmoid, Maxila , Pnematic Bones.

 6.Sesamoid Bones:
These are in the form of nodules
embedded in tendons and joint capsules.
Examples: Patella, Pisiform, Fabella etc.

Fig. Patella, Sesamoid Bone.

Sesamoid bones protect tendons
from excessive wear and tear, and
they often change the direction of
pull of a tendon, which improves
the mechanical advantage at a
joint
Fig. Pisiform, Sesamoid Bone.
B. On The Basis Of Region:
It is divided into two types, they are:
1. Axial Skeleton.
2. Appendicular Skeleton.
1. Bones Of Axial Skeleton:
These bones forms the axial 22 bones
skeleton of the human body.
Bones of skull (22),
Thoracic cage (25) & Vertebral
Column (26)
80 bones in the head, neck, and trunk

Fig. Bones of Axial Skeleton.

1. Skull: (Front pot se cranial)
The skull is composed of 22 bones and is divided
into two main parts: the cranium and the facial bones.
1. Cranial Bones (8 total)
These bones encase and protect the brain.
•Frontal Bone (1): Forms the forehead and the roof of the orbits
(eye sockets).
•Parietal Bones (2): Form the top and sides of the cranium.
•Occipital Bone (1): Forms the back and base of the skull,
containing the foramen magnum through which the spinal cord
passes.
•Temporal Bones (2): Located on the sides of the skull, containing
structures like the ear canal and the mastoid process.
•Sphenoid Bone (1): A butterfly-shaped bone that spans the width
of the skull and forms part of the base of the cranium and the orbits.
•Ethmoid Bone (1): A light, spongy bone located between the eyes,
forming part of the nasal cavity and the orbits.
2. Facial Bones (14 total)
 2. Facial Bones (14 total)
These bones form the structure of the face and support the teeth.
•Nasal Bones (2): Small bones that form the bridge of the nose.
•Maxillae (2): The upper jawbones, which also form part of the orbits and the
hard palate.
•Zygomatic Bones (2): Known as the cheekbones, they also form part of the
orbits.
•Palatine Bones (2): Form the posterior part of the hard palate and part of the
nasal cavity.
•Lacrimal Bones (2): Small bones forming part of the inner eye socket.
•Inferior Nasal Conchae (2): Curved bones that project from the lateral walls
of the nasal cavity.
•Vomer (1): Forms the lower part of the nasal septum, which divides the nasal
cavity.
•Mandible (1): The lower jawbone, the only moveable bone of the skull.
 3. Hyoid bone
• The hyoid bone is a U-shaped bone located in the anterior
neck, between the mandible (jawbone) and the larynx (voice
box).
• It is unique because it does not articulate (connect) with any
other bone in the body.
Functions:
•Supports the tongue by providing attachment sites for tongue
muscles.
•Anchors muscles of the neck and pharynx.
•Keeps the larynx open, assisting in breathing and speech.
The hyoid bone and the cartilage of the larynx and trachea are
often fractured during strangulation, making it significant in
forensic investigations
 4. Auditory aussicles

• The ear ossicles are three tiny bones located in the middle
ear, essential for hearing.
• They are the smallest bones in the human body and form a
chain that transmits sound vibrations from the eardrum to the
inner ear.
The Three Ossicles:
1.Malleus (Hammer):
1. Attached to the eardrum.
2. Transmits vibrations from the eardrum to the incus.
2.Incus (Anvil):
1. Receives vibrations from the malleus and passes them to
the stapes.
3.Stapes (Stirrup):
1. The smallest bone in the body.
2. Connects to the oval window of the inner ear, transmitting
vibrations to the fluid-filled cochlea for sound processing.
5.
 Vertebral Column

During early development, the vertebral column contains 33

vertebrae. As a person grows, several vertebrae in the sacral and
coccygeal regions fuse, resulting in 26 vertebrae in adults.
1.Cervical (7 vertebrae): Located in the neck region.
2.Thoracic (12 vertebrae): Positioned posterior to the thoracic
(chest) cavity.
3.Lumbar (5 vertebrae): Found in the lower back region.
4.Sacrum (1 bone): Formed by the fusion of 5 sacral vertebrae.
5.Coccyx (1 bone): Typically made of 4 fused coccygeal
vertebrae.
The cervical, thoracic, and lumbar vertebrae are movable, while
the sacrum and coccyx are immobile.
Functions
•Support: The vertebral column supports the weight of the
head and trunk.
•Protection: It encases and protects the spinal cord, which
runs through the vertebral canal.
•Movement: Provides flexibility and a range of motion in
different directions.
•Posture: Helps maintain an upright posture and balance.
 The thoracic cage (also known as the rib cage) is a bony
structure that protects vital organs in the thoracic cavity, such as
the heart and lungs, and plays a crucial role in respiration.
Here's an overview:
 Structure of the Thoracic Cage
• Components:
• Ribs (12 pairs):

• True Ribs (1–7): Directly attach to the sternum via their

own costal cartilages.
• False Ribs (8–10): Indirectly attach to the sternum
through the cartilage of the rib above.
• Floating Ribs (11–12): Do not attach to the sternum and
end in the posterior abdominal musculature.
• Sternum:
• Manubrium: The upper part of the sternum, connecting
with the clavicles and the first pair of ribs.
• Body: The long central part of the sternum, to which the
ribs attach.
• Xiphoid Process: A small, cartilaginous structure at the
lower end of the sternum, which ossifies with age.
• Protection: It shields vital organs such as the heart, lungs,

and major blood vessels from injury.

• Support: Provides attachment points for muscles involved in

breathing, the neck, back, and upper limbs.

• Respiration: The thoracic cage expands and contracts during

breathing, allowing the lungs to fill with air.

• Stability: It maintains the structure of the thoracic cavity and

supports the upper body.

Fig. Upper limb, Clavicle & Scapula Fig. Lower limb, Pelvic Girdle
Girdle bones of Appendicular Skeleton. bones of Appendicular Skeleton.

2.Bones Of Appendicular Skeleton:

These bones forms the Appendicular skeleton of
the human Body.
Examples: bones of the limbs and girdles of limbs.
 I. Pectoral gridle (4)

•Definition: The pectoral girdle (shoulder girdle) connects the upper

limbs to the trunk.
•Components: Consists of two bones – the clavicle and scapula.

1. Clavicle (Collarbone): (2)

•S-shaped long bone.
•Connects the manubrium of the sternum to the scapula (acromion).
•Provides structural support and keeps the upper limb away from the
thorax for mobility.

2. Scapula (Shoulder Blade): (2)

•Triangular, flat bone.
•Articulates with the clavicle at the acromion and with the humerus at
the glenoid cavity.
 II. Upper limbs

•Definition: The upper limb is the region extending from the

shoulder to the hand.
•Subdivisions: Shoulder, arm (brachium), forearm
(antebrachium), and hand.
1.Humerus: Bone of the upper arm. 2
2.Radius: Lateral bone of the forearm (thumb side). 2
3.Ulna: Medial bone of the forearm (little finger side). 2
4.Carpals: 8 small bones in the wrist. 16
5.Metacarpals: 5 bones forming the palm. 10
6.Phalanges: Bones of the fingers (3 in each finger, 2 in the 28
thumb).
 III. Pelvic gridle (2)
Definition: The pelvic girdle (hip bone) is the bony structure that
connects the lower limbs to the trunk.
•Components: Consists of two hip bones (coxal bones), the sacrum,
and the coccyx.
•Function: Provides support for the body's weight during standing and
walking and protects the pelvic organs.

•Each hip bone is formed by the fusion of three bones:

1.Ilium
2.Ischium
3.Pubis
•The two hip bones join anteriorly at the pubic symphysis and
posteriorly with the sacrum at the sacroiliac joints.
Pelvic Girdle Gender Differences
•Male Pelvis:
• Narrower and more robust.
• Pubic arch angle less than 90°.
• Heart-shaped pelvic inlet.
•Female Pelvis:
• Wider and shallower to facilitate childbirth.
• Pubic arch angle greater than 90°.
• Oval-shaped pelvic inlet.

Functions of the Pelvic Girdle

•Support: Transmits weight from the upper body to
the lower limbs.
•Protection: Encloses and protects organs like the
bladder, intestines, and reproductive organs.
•Attachment Point: Provides attachment points for
muscles of the lower limb and trunk.
 IV. Lower limb

•Definition: The lower limb is the part of the body that includes the
leg, from the hip to the toes, and supports movement and balance.
•Subdivisions: Thigh, leg, and foot.
•Main Functions: Support, locomotion, and balance.

Key Bones:
1.Femur: The thigh bone and the longest, strongest bone in the body. 2
2.Patella: The kneecap, a small bone protecting the knee joint. 2
3.Tibia: The shin bone, the larger of the two bones in the lower leg. 2
4.Fibula: The smaller bone located alongside the tibia in the lower leg. 2
5.Tarsals: 7 bones that form the ankle. 14
6.Metatarsals: 5 bones forming the middle part of the foot. 10
7.Phalanges: The toe bones 15
(each toe has 3, except the big toe with 2).
D. On The Basis Of
Structure:

They are sub divided into two parts, which are:

1. Macroscopic Approach.
2. Microscopic Approach.
1. Macroscopic Approach:
a. Compact Bone:
Compact bone is dense in
texture but is extremely porus.
Example: In the cortex of
long bones.

•Made of osteons (Haversian

systems) with osteocytes in rings.
•Contains blood vessels in
Haversian canals.

Fig. Macroscopic structure of the

cortex of femur(Long Bone).
b. Cancellous OR Spongy Bone:
• The part of bone where there is more empty space and
less bone tissue. Example: The inner part of Long Bones.
•Contains osteocytes, matrix, and blood vessels in a porous
structure.
•Often houses red bone marrow, producing blood cells.

Fig. The Macroscopic Structure of the inner part of

Femur(Long Bone).
2. Microscopic Approach:

Fig. Microscopic structure of Fetus of Human.

a. Fibrous Bone:
These have more fibers in them. Also known as
immature bones.
Example: Found only in fetus, sockets of alveolar
bones and sutures of the skull.
Fig. Microscopic structure of Lamellar arranged in piles in a cancellous bone.

b. Lamellar Bone:
Most of the mature human bones, whether compact or
Cancellous, are composed of thin plates of bony tissue called lamellae.
Example: Formed on the periosteal
surface of diaphysis.
c. Woven Bone:
Occurs initially in fetal bones. In adults woven bone
is created after fractures.
Example: Seen in fetal bone, fracture repair and in
cancer of bone.

Fig. Microscopic structure of Woven bone.

 d. Cementum and Dentine:
Cementum is a specialized calcified
substance covering the
root of a tooth. It hardens to act as an adhesive glue.
Dentine is
one of the hard tissues of the teeth which
constitutes most of its bulk.
Example: Occur in teeth.

Fig. Dentine of a tooth. Fig. The Cementum of a human tooth.

 Do you know?
• Hyaline cartilage is the most abundant cartilage.
• By age 25 the skeleton is completely hardened.
• 206 bones make up the adult skeleton (20% of body mass)
• 80 bones of the axial skeleton
• 126 bones of the appendicular skeleton

• The largest bone in the human skeleton is Femur.

• Babies are born with about 300 bones.
• Almost a third of bones of babies eventually fuse together to
form the 206-bone skeleton of an adult.