Ribs and Rib Cage– Class 11 | Chapter – 20 | Biology Short Notes Series PDF

Ribs and Rib Cage: The bony framework of the thoracic cavity is known as the ribs. They are flat, narrow and curved strips of bones that are found in all vertebrates. It is attached to the vertebrae dorsally, and ventrally to the breast bone (sternum) to form the rib cage.

Ribs and Rib Cage Structure

Generally, there are twelve pairs of ribs found in humans. A typical rib anatomy has the following components – a costal groove, tubercle, neck, shaft and a head with two articular facets. The first, second, tenth, eleventh and twelfth ribs are somewhat an exception and differ slightly from the typical ribs.

The first rib has two costal grooves, one articular facet and is wide and short. The second rib is long and thin. The tenth rib consists of only once articular facet. And lastly, the eleventh and twelfth ribs have no neck and only one articular facet.

In a typical rib, one of the articular surfaces joins with the face of the vertebrae and the other with the transverse process of the vertebrae. The neck is a narrow area behind the head of the rib and the remainder is called the shaft.

The ribs attach to the thoracic vertebrae on the back and are numbered accordingly 1-12. For example, the first rib is attached to the first thoracic vertebrae (T1). On the front side, the ribs are attached to what is called a breastbone or a sternum by costal cartilage forming a sternocostal joint.

Types of Ribs

Based on the attachment to the sternum, there are three types of ribs –

  • True Ribs: These ribs articulate directly with the sternum by costal cartilages. First to seventh ribs are true ribs. These ribs articulate with the sternum by forming a sternocostal joint.
  • False Ribs: These ribs indirectly articulate with the sternum because their costal cartilages are attached to the costal cartilage of the seventh rib. Eight, ninth and tenth ribs are false ribs. These are also called vertebrochondral ribs.
  • Floating Ribs: These ribs do not articulate with the sternum at any point. Eleventh and twelfth ribs are floating ribs.

Rib Cage – Human Body

A Rib cage is a bony structure which is attached to the vertebral column and sternum in humans and it is helpful in the protection of heart and lungs.

In human body, the rib cage is a basket-like structure that is formed from the ribs and their corresponding attachments to the sternum and vertebral column. The rib cage structure houses two vital organs, the lungs and the heart and provides them with bony protection from outside injury and trauma.

The rib cage is expansible and semi-rigid in nature. The expansive property allows the cage to expand during activities such as breathing. The three false ribs and the two floating ribs help the cage to expand and also facilitates the movement of diaphragm for respiration.

There are 12 pairs of ribs. Each rib is a thin flat bone connected dorsally to the vertebral column and ventrally to the sternum. It has two articulation surfaces on its dorsal end and is hence called bicephalic. First, seven pairs of ribs are called true ribs. Dorsally, they are attached to the thoracic vertebrae and ventrally connected to the sternum with the help of hyaline cartilage. The 8th, 9th, and 10th pairs of ribs do not articulate directly with the sternum but join the seventh rib with the help of hyaline cartilage. These are called vertebrochondral (false) ribs.  The last 2 pairs (11th and 12th) of ribs are not connected ventrally and are, therefore, called floating ribs. Thoracic vertebrae, ribs, and sternum together form the rib cage

The human rib cage acts as a component of the human respiratory system. It encloses the thoracic cavity that contains the lungs. An inhalation occurs when the muscular diaphragm present at the floor of the thoracic cavity contracts and flattens, while the contraction of intercostal muscles lifts the rib cage up and out.

The expansion of the thoracic cavity is driven in three planes they are:

  • The vertical

  • The anteroposterior

  • The transverse

The vertical plane is extended by the help of the contracting diaphragm and the abdominal muscles relaxs to accommodate the downward pressure that is supplied to the abdominal viscera by the contracting diaphragm. The greater extension can be achieved by the diaphragm itself moving down rather than flattening of domes. The second plane is expanded by a movement known as the ‘pump handle’ to the anteroposterior region.

The circumference of the normal adult human rib cage during inhalation expands by 3 to 5 cm.

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By Team Learning Mantras