Human rib cage

For other uses, see Rib cage.

Human rib cage
The human rib cage. (Source: Gray's Anatomy of the Human Body, 20th ed. 1918.)
Latin	cavea thoracis
Dorlands/Elsevier	rib cage

The human rib cage, also known as the thoracic cage, is a bony and cartilaginous structure which surrounds the thoracic cavity and supports the pectoral girdle, forming a core portion of the human skeleton. A typical human rib cage consists of 24 ribs, the sternum, costal cartilages, and the 12 thoracic vertebrae. It, along with the skin and associated fascia and muscles, makes up the thoracic wall and provides attachments for the muscles of the neck, thorax, upper abdomen, and back.

Respiratory function

The human rib cage is a component of the human respiratory system. It encloses the thoracic cavity, which contains the lungs. An inhalation is accomplished when the muscular diaphragm, at the floor of the thoracic cavity, contracts and flattens, while contraction of intercostal muscles lift the rib cage up and out.

Another way the thoracic cavity can expand during inhalation is called belly breathing. This also involves a contraction of the diaphragm, but the lower ribs are stabilized so that when the muscle contracts, rather than the central tendon remaining stable and lifting the ribs up, the central tendon moves down, compressing the sub-thoracic cavity and allowing the thoracic cavity and lungs room to expand downward.

These actions produce an increase in volume, and a resulting partial vacuum, or negative pressure, in the thoracic cavity, resulting in atmospheric pressure pushing air into the lungs, inflating them. An exhalation results when the diaphragm and intercostal muscles relax, and elastic recoil of the rib cage and lungs expels the air.

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

Rib anatomy

The parts of the rib.

All ribs are attached in the back to the thoracic vertebrae.

The upper seven true ribs (costae verae, vertebrosternal ribs, I-VII). are attached in the head to the sternum by means of costal cartilage. Due to their elasticity they allow movement when inhaling and exhaling.

The 8th, 9th, and 10th ribs are called false ribs (costae spuriae, vertebrochondral ribs, VIII-X), and join with the costal cartilages of the ribs above.^{[citation needed]}The 11th and 12th are also sometimes referred to as false ribs.

The 11th and 12th ribs are known as floating ribs (costae fluitantes, vertebral ribs, XI-XII), as they do not have any anterior connection to the sternum.

The spaces between the ribs are known as intercostal spaces; they contain the intercostal muscles, nerves, and arteries.

The human rib parts:

• The Head is the end of a rib closest to the vertebral column,it articulates with the corresponding vertebrae to make the Costovertebral joints.
• The neck is the flattened portion which extends lateralward from the head.
• The tubercle is an eminence on the posterior surface that articulates with the transverse process to make the costotransverse joint.
• The angle is a bending part.
• The Costal groove is a groove between the ridge of the internal surface of the rib and the inferior border.

Atypical ribs

Surface projections of the organs of the trunk, with ribs labeled at left. The ribs may be used for orientation for locating internal organs such as the heart, lung lobes and spleen.

The atypical ribs are the 1st, 2nd, 10th, 11th and 12th.

• The first rib is a shaft that is wide and nearly horizontal and has the sharpest curve of the seven true ribs. Its head has a single facet to articulate with the first thoracic vertebra (T1). It also has two grooves for the subclavian vessels, which are separated by the scalene tubercle. The first rib forms the superior thoracic aperture together with the manubrium and T1.

• The second rib is thinner, less curved, and longer than the first rib. It has two facets to articulate with T2 and T1, and a tubercle for muscles to attach to.

• The 10th has only a single articular facet on its head.

• The 11th and 12th ribs have only one facet on their head; the 11th and 12th ribs are short with no necks or tubercles and terminate in the abdominal wall before fusing with the costal cartilages.

Number of ribs

The number of ribs (24; twelve on each side) was noted by the Flemish anatomist Vesalius in his key work of anatomy De humani corporis fabrica in 1543, setting off a wave of controversy, as it was traditionally assumed from the Biblical story of Adam and Eve that men's ribs would number one less than women's. Variations in the number of ribs occur. About 1 in 200-500 people have an additional cervical rib, and there is a female predominance. Intrathoracic supernumerary ribs are extremely rare.

Medical issues

Rib fractures are the most common injury to the rib cage. These most frequently affect the middle ribs. When several ribs are injured, this can result in a flail chest.

Abnormalities of the rib cage include pectus excavatum ("sunken chest") and pectus carinatum ("pigeon chest"). Bifid or bifurcated ribs, in which the sternal end of the rib is cleaved in two, is a congenital abnormality occurring in about 1.2% of the population. The rib remnant of the 7th cervical vertebra on one or both sides is occasionally replaced by a free extra rib called a cervical rib, which can cause problems in the nerves going to the arm.

Rib removal is the surgical excision of ribs for therapeutic or cosmetic reasons.

Rib cage development & testosterone

In males, expansion of the ribcage is caused by the effects of testosterone during puberty. Thus, males generally have broad shoulders and expanded chests, allowing them to inhale more air to supply their muscles with oxygen.

Additional images

Anterior surface of sternum and costal cartilages.   X-ray image of human chest, with ribs labeled.   Thoracic cage.   Side view of human rib cage. Seen are the 5-12 ribs under lean muscle.

See also

• Terms for bones
• Terms for anatomical location
• Articulation of head of rib

References

• Clinically Oriented Anatomy, 4th ed. Keith L. Moore and Robert F. Dalley. pp. 62–64
• Principles of Anatomy Physiology, Tortora GJ and Derrickson B. 11th ED. John Wiley and Sons, 2006. ISBN 0-471-68934-3
• De Humani Corporis Fabrica: online English translation of Vesalius' books on human anatomy.

External links

• Anatomy at MUN thorax/cage
• Diagram at mhhe.com