skeletal system

Know Your Skeletal System

# Outlines

• Brief anatomy

• Organization of the bones

• Types of bones

• Joints

– Fibrous joints

– Cartilaginous joints

– Synovial joints or diarthrosis and its types

BRIEF ANATOMY

Bone Development & others on its behalf....Bone, Whom am I?

I am a specialized connective tissue. By providing a rigid skeleton, I give the all-important shape to the human beings. I am proud to be entrusted the job of protecting vital structures like brain, lungs and heart.

I am the largest store-house of the all important mineral(i.e. calcium) in the body.I am also concerned with hemopoiesis(formation of blood with all its components). I give attachment to the muscles& enable them to act on the joints by acting as a lever for their action. I am made-up of 30% organic material(mainly type I collagen) & 70% mineral(calcium hydroxyapatite).

Remember my Job then?!

• Protection of vital organs

• Support to the body

• Hemopoiesis

• Movement and locomotion

• Mineral storage

How do I start developing?

My development begins with the condensation of the mesenchyme in the embryo. There are certain exceptions

like the vault of the skull (membranous ossification), the clavicle (mixed ossification) & the mandible (Meckel’s

cartilage). From this condensation, I rapidly form a cartilaginous model. Between the cartilaginous bone and plates, I form small clefts for the future joints. During this

period of 12 weeks, I am particularly vulnerable to teratogenic influences.

As early as the fifth week of intrauterine life, I develop a primary centre of ossification, which gradually replaces

this cartilage model to bone by a process of endochondral ossification. During the late fetal stages or early few years of life, I develop secondary centers of ossification.

Growth plate, which keeps the primary and secondary centers of ossification separated from each other until skeletal maturity, helps me grow longitudinally and

I increase my width from the growth of the thickened periosteum. In addition, I keep remodeling myself from the fetal stage to the adult stage. Only the rate varies (50%

during the first two years of life and 5% per year thereafter until adulthood).

To sum this up!

• Bone development starts as a condensation of mesenchyme.

• Later a cartilaginous model develops.

• There are two types of ossification, endochondral and membranous.

• There are three types of bone cells.

About Osteon

Now let me tell you how exactly I am made-up of internally. I am made-up of many units called “osteon”. I have three types of cells, osteoblasts that form the bone, osteoclasts which remove the bone

and are concerned with remodeling, osteocytes, which are the resting cells. These cells are present in the lamellae, which surround concentrically the Volkmann’s canal (which has the nutrient vessel) & each lamellae is interconnected by the canaliculi through which the nutrients pass. Osteoblasts lay down uncalcified matrix,which is subsequently calcified as true bone. These various osteons

amalgamate to form large haversian systems, loosely woven in the medullary bone and densely packed in the cortical shell.

Now having known my intrinsic structure, you will be interested to know that I have two major portions, medulla and the cortex.

About Medulla

Medulla is my softer counterpart and has the dual role of structure and storage. It stores more than 95% of body’s calcium & is a storehouse for other minerals too. The other important component of the medulla is the marrow between the medullary

bone lattices. This is the source from where the RBCs & WBCs originate. Initially present throughout, it confines itself to the metaphyseal regions of the long

bones and in some flat bones like pelvis, rib, etc. as age advances & is replaced by a fatty white marrow.

The medulla plays the structural role by its

trabecular organization along maximal lines of stress and clearly identifies itself into compression & traction trabeculae.

About Cortex

Cortex gives me the remarkable strength, which you all admire particularly during compression. Its periosteal cover allows remodeling throughout life.

It also gives attachments to ligaments, tendons & muscles through the Sharpe’s fibers.

Remember about medulla

• Softer portion.

• Stores 95 percent of body calcium.

• Marrow is the other important component.

• Also plays a structural role.

# About General Structure

Now let me explain to you my general structure. I have an epiphysis and epiphysis plate (which disappears with growth), metaphysis and diaphysis.

Epiphysis is an expanded portion at the end develops usually under pressure and forms a support for the joint surface. It is easily affected by developmental problems like epiphyseal dysplasias,trauma, overuse, degeneration and damaged blood supply.The result is distorted joints due to avascular necrosis and degenerative changes.

Growth plate (physis) though mechanically weak it helps longitudinal growth. It responds to growth and sex hormones. It is affected by conditions like osteomyelitis, tumor, slipped epiphysis resulting in short stature or deformed growth or growth arrest.

Metaphysis is concerned with remodeling of bone. It is the cancellous portion and heals readily. It gives attachment to ligament and tendons. It is vulnerable to develop osteomyelitis, dysplasias and tumors

resulting in distorted growth & altered bone shapes.

Diaphysis is a significant compact cortical bone which is strong in compression and which gives origin to muscles. It forms the shafts of the bones. Healing is slow when compared to metaphysis. In remodeling, it can remodel angulations but not rotation. It may develop fractures, dysplasias, infection and rarely tumors.

Remember

Parts of a bone

• Epiphysis

• Physis (growth plate)

• Metaphysis

• Diaphysis

ORGANIZATION OF THE BONES

We are 206 in number and are grouped into two

subdivisions namely:

1. Axial skeleton—80 bones.

2. Appendicular skeleton—126 bones.

Axial skeleton forms the upright axis of the body & the appendicular skeleton forms the appendages and girdles that attach them to the axial skeleton.

Out of this 206, some of us are short & some

are long. We have different shapes. The shape & size depend upon the functions attributed to us.

TYPES OF BONES

Long bones :These serve as levers for the muscle action, e.g. femur,tibia, etc.

Short bones: These are generally cube-shaped and are found in areas where limited movements are required. Their primary role is to provide strength.

Flat bones:These consist of parallel layers of compact bone separated by a thin layer of cancellous bone tissue, e.g. scapula, skull, etc.

Irregular bones:These have a peculiar and irregular shape and are unique in their appearance and functions, e.g. pelvic bones.

Sesamoid bones: These are small, rounded or triangular bones, which develop within the substance of a tendon or fascia. Their name is derived from their resemblance to “sesame seeds”, e.g. patella (largest and most definitive of the sesamoid bones)

Remember

Types of bones

• Long bones

• Short bones

• Flat bones

• Irregular bones

• Sesamoid bones

The above bones are arranged in two groups

• Axial—80 bones

• Appendicular—126 bones

Thus, my duty is to serve you to the best of my ability, so that you lead a healthy skeletal life. Much depends on you in keeping me in a proper shape.

You need to take good nutritious diet rich in calcium and vitamins to keep me healthy. Proper exercises, protection against injuries and infection enhance my efficiency in serving you, but there are certain

inherent problems in me in which you can do precious little. 

Congenital problems, hormonal problems, metabolic problems, tumor conditions, etc. are some of these.

However, the above problems are troublesome I develop them infrequently. Nevertheless, the problem that poses a serious threat to my integrity is injuries due to trauma. As a child, you are more playful and more prone to fall and this breaks me

quite often. As an adult, you are more prone for road traffic accidents (RTAs) and this subjects me to a plethora of different varieties of forces causing many complexes, grotesque and bizarre breaks.

Though you pride in the fast-paced life of yours, I grieve at my misfortune and at my vulnerability to these vast array of incriminating forces, which overcome me putting you out of action for months.

As you age, my faithful friends, proteins and minerals gradually desert me. I cannot provide you the same strength as earlier. In this phase, even trivial forces (pathological fractures) easily overcome me. I am sad that I cannot provide you the same privileges as before but I hope you can realize that

I am not being unfaithful to you, but I am made helpless by situations beyond anybody’s control.

# Bones in the axial skeleton
Skull
   • Cranium---8
   • Face----14
Vertebral column
 • Cervical vertebrae--- 7
 • Thoracic vertebrae--- 12
  • Lumbar vertebrae ----5
   • Sacrum ---1 (5 fused bones)
   • Coccyx ---1 (3-5 fused bones)
Sternum ----1
Ribs ----24 (12 pairs)
Hyoid---- 1
Ear ossicles
    • Malleus ---2
    • Incus ----2
    • Stapes--- 2
Total -----------80
#Bones of the appendicular skeleton
Shoulder girdle
   • Clavicle---- 2
   • Scapula---- 2
Upper extremities
   • Humerus ----2
  • Ulna----- 2
  • Radius---- 2
  • Carpals ---16
 • Metacarpals ---10
 • Phalanges--- 28
Hip girdle
  • Os coxa ---2
Lower extremity
   • Femur--- 2
   • Fibula--- 2
  • Tibia ---2
  • Patella ---2
  • Tarsal ---14
 • Metatarsals ---10
 • Phalanges--- 28
Total ------126
#So,Axial+Appendi=80+126=206

ABOUT JOINTS

A joint exists where two or more skeletal components, whether bone or cartilage, come together to meet. Without joints in between the bones, your whole body would be rigid & immobile. The existence of these joints makes movement of the body parts possible. 

Joints are classified into 3 major groups:

1. FIBROUS JOINT OR SYNARTHROSIS

These are immovable joints, e.g. sutures of the skull.

In these, there are three varieties:

   A. Syndesmosis: This is characterized by a dense fibrous

membrane that binds the articular bone surfaces very

closely and tightly to each other, e.g. distal

tibiofibular joint.

 B. Sutures: True sutures are found in the skull. Here the adjoining bone margins are united into rigid, jagged interlocking processes, e.g. sagittal suture of the skull.

  C. Gomphosis: Here a conical peg or projection that fits into a socket, e.g. teeth and sockets of jawbones.

2. CARTILAGINOUS JOINTS OR AMPHORTHOSIS

These are slightly movable joints with either hyaline or fibro cartilage in between. Two varieties are described:

   A. Synchondroses: Here hyaline cartilage is posed in between, e.g. articulations between rib and sternum.

  B. Symphysis: Here the fibrocartilage is interposed in between and is usually found in the midline of the body, e.g. pubic symphysis.

3. SYNOVIAL JOINTS OR DIARTHROSIS

These form the majority of the joints in the body.

They have between the bones, a synovial or joint cavity. They form the most mobile joints in the body & hence are more prone for injuries.

It consists of a fibrous joint capsule that helps to hold the articulating bones together. The synovial membrane lines the joint space and secretes the synovial fluid.This fluid serves to lubricate the joints & provides nourishment for the articular cartilage.

The articular cartilage is formed by the hyaline cartilage, which is a unique type of connective tissue formed by specialized cells called chondrocytes.

Types of Synovial Joints

   A. Uniaxial joints: These permit movement in only one plane and one axis. In this, there are two types:

     I. Hinge joints: Here movement takes place around a horizontal axis, e.g. elbow joint.

   II. Pivot joints: Here movement takes place around a vertical axis that permits rotation, e.g.atlantoaxial joint.

 B. Biaxial joints: Here movement occurs in two planes and two axes that are at right angles to each other.

Two types are described:

   I. Saddle joint: Here the articular surface is concave in one direction and convex in the other while the articular surface of the opposing bone is exactly the opposite, e.g. carpometacarpal joint at the base of

the thumb.

 II. Condyloid joint: In this, an oval condyle fits into an elliptic socket or cavity, e.g. radiocarpal joints.

 C. Multiaxial joints: Here there are two or more axes of rotation and movement takes place in three or more planes. Two varieties are described:

  I. Ball and socket joint: In this a ball-shaped head of one fits into a concave socket of another bone. Of all the joints in the body, these provide the widest, most

free range of movements in almost any direction or plane, e.g. hip joint, shoulder joint, etc. 

  II. Gliding joints: These are numerous, gliding movements occur in all planes, e.g. joints between the carpal and tarsal bones, and all the joints between the articular processes of the vertebrae.