SKELETAL SYSTEM

OVERVIEWFunctionsClassification of bonesBone structureMicroscopic structure of boneFormation of boneJoints

Functions of bone• Bones and cartilage together forms the

skeletal• system performing several functions.• 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.

Functions of bone2.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.

Functions of bone4. 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.4.Hematopoiesis All blood cells are made in the marrow

of certain bones.

Classification of BonesThere are 206 bones in the human

body.They are divided into two large groups: I. Axial skeleton

Forms long axis of the body.Includes the bones of the skull,

vertebral column, and rib cage.Involved in protection, support, and

carrying other body parts.

II. Appendicular skeletonBones of upper & lower limbs and

the girdles (shoulder bones and hip bones) that attach them to the axial skeleton.

Involved in locomotion and manipulation of the environment.

Classification of Bones

Classification of Bones

Four types of bones based on shapes: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.

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

Classification of Bones Types of bones:

3. Flat Bones Thin, flattened, and usually a bit

curved. Scapulae, sternum, (shoulder

blades), ribs and most bones of the skull.

4. Irregular Bones Have weird shapes that fit none of

the three previous classes. Vertebrae and hip bones.

Structure of BoneBones are organs and are composed of

multiple tissue types. Bone tissue (osseous tissue).Fibrous connective tissue.Cartilage.Vascular tissue.Lymphatic tissue.Adipose tissue.Nervous tissue.

Bone StructureExternally bone is covered by a thin layer

of dense connective tissue known as Periosteum.

It is a double-layered membrane• Covers entire external surface of bone

except for joints.• Outer fibrous layer is dense irregular

connective tissue containing fibroblast.• Inner cellular layer contains

osteoprogenitor cells and osteoblasts.• Below compact bone lies more porous and

light weight bone-spongy or cancellous bone.

Bone structureIt is a thin layer found just inside the compact

bone. The centre of the bone shaft is hollow-

Medullary Cavity. This contains both red and yellow bone

marrow

The centre of the bone shaft is hollow-Medullary Cavity.

This contains both red and yellow bone marrow

Endosteum • Delicate connective tissue membrane

covering internal surfaces of bone• Covers the trabeculae of spongy bone in

the marrow cavities and lines the canals that pass through compact bone.

• Contains both osteoblasts and osteoclasts.

Structure of Bone

Bone cells

Bone consist of cells and extracellular matrix.

A. Bone cells1. 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

Bone cells2. Osteocytes

Mature bone cells. Osteoblasts that have become

trapped by the secretion of matrix. No longer secrete matrix. Responsible for maintaining the

bone tissue.

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3. Osteoprogenitor Cells • Mesenchyme stem cells that divide to

produce osteoblasts• Are located in inner, cellular layer of

periosteum• Assist in fracture repair

4. Osteoclasts Giant, mutlinucleate cells Secrete acids and protein-digesting

enzymes Dissolve bone matrix and release

stored minerals Concentrated in the endosteum. Are derived from stem cells that

produce macrophages

Bone Matrix

Consists of organic and inorganic components.

Organic component • Consists of several materials that are

secreted by the osteoblasts.• Mainly consist of 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 • Consists mainly of two salts: calcium

phosphate and calcium hydroxide that interact to form a compound called hydroxyapatite.

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

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

Structure of Long Bone Long bone consist of a diaphysis and an

epiphysis.Diaphysis

Tubular shaft that forms the axis of long bones

Composed of compact bone that surrounds the medullary cavity (central marrow cavity)

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

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http://www.wbais.org/~usalant/Gallery/Anatomy_physiology/Skeletal/images/long_bone_shaft.jpg

Structure of Long Bone Epiphyses

Expanded ends of long bonesExterior is compact bone, and the

interior is spongy boneJoint surface is covered with articular

(hyaline) cartilage that cushions the bone ends and reduces friction during movement.

Microscopic Structure of Compact Bone

In cross section, compact bone is seen to consists of tightly packed multiple cylindrical structural units -osteons or haversian systems.

They are arranged parallel to one another along the long axis of a compact bone.

Osteons/Haversian systemsEach osteon consists of a single central

canal, known as a haversian canal, surrounded by concentric layers of calcified bone matrix (lamella).

Haversian canals are interconnected with one another via Volkmann's canals.

Between the lamella are present concentric rings of fluid filled spaces-lacuna containing osteocytes.

Tiny hair-like channels/canaliculi extend from lacuna through which osteocytes communicate and receive nutrients.

Haversian canals allow the passage of blood vessels, lymphatic vessels, and nerve fibers.

Structure of Bone

Haversian canal system

Microscopic Anatomy of Microscopic Anatomy of BoneBone

Compact Bone

Microscopic Structure of Bone: Compact Bone

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