The Ribs

The ribs are a vital component of the human skeletal system, forming the rib cage that protects the organs in the thoracic cavity, primarily the heart and lungs. The rib cage also plays a crucial role in respiration, as it expands and contracts with the movement of the diaphragm during breathing.

1.0Introduction

• The average person is born with 24 ribs—12 on each side. The ribs are located in the thoracic cage and thorax, along with their costal the s and the sternum. Each rib is made up of a few different components: the head, the neck, the tubercle, the angle, and the body.
• Their length increases from 1st to 7th rib and then diminishes from above downwards.
• The ribs lie one above the other and the spaces between them are known as 'Intercostal spaces'.
• The ribs are obliquely placed so that the intercostal spaces are deeper in front than behind.

2.0Classification

• True Ribs 1st to 7th - They are connected in front through costal cartilages with the sternum.
• False Ribs 8th to 12th - Vertebro-chondral Ribs: The cartilages of 8th. 9th and 10th ribs are joined each to the cartilage of the rib just above.
• Floating Ribs: 11th and 12th. They are free at their anterior ends.
• Typical: The ribs which present common features.
• Atypical: The ribs which present special features. They are 1st, 2nd, 10th, 11th and 12th ribs.

Also Check: Bones in the human skeleton

3.0Typical Ribs

(i) Curved

(ii) Angulated: The angle lies about 2.5 inches from the tubercle.

(iii) Twisted: Such that the two ends will not touch a horizontal surface.

Parts of Rib

• Anterior end
• Posterior end
• Shaft

Anterior End - Recognised by the presence of a small cup-shaped depression which articulates with the lateral end of the corresponding costal cartilage.

Posterior End - It consists of (1) Head (2) Neck (3) Tubercle

Head

• Bears 2 small facets separated by a transverse ridge called ‘Crest’.
• Larger lower facet articulates with the body of numerically corresponding vertebrae. Upper facet articulates with the vertebra above.
• The crest lies opposite the intervertebral disc.

Neck 

• Flat portion adjoining the head; about 1 inch long.
• Lies in front of the transverse process of numerically corresponding vertebra.
• It possesses: 2 surfaces: Anterior and Posterior.

2 borders: Upper and lower.

Tubercle 

• Situated on the posterior surface of the rib, at the junction of neck and shaft.
• Consists of 2 parts 

1. Medial articular part: bears an oval facet to articulate with the transverse process of numerically corresponding vertebra.
2. Lateral non-articular part: rough; 

Shaft 

• Thin and flat. 
• It is curved, bent and twisted on itself.
• It possesses : 2 surfaces : External and Internal.

2 borders : Superior and Inferior.

External surface

• Convex and smooth
• A rough ridge crosses this surface at some distance from the tubercle, indicating the posting of angle.

Internal surface 

• Smooth
• Has a groove (costal groove) along its lower border, limited, above by a ridge.

Superior border 

• Rounded
• It has got an inner and an outer lip behind.

Inferior border 

• Sharp border
• Forms lower margin of costal groove.
• Gives origin to External intercostal muscle.

4.0Atypical Ribs

1. First Rib

Distinguishing features 

• No twist.
• No angle as it is merged with the tubercle.
• No costal groove.
• Most curved.
• Shortest of all ribs.
• Broad and flat from above downwards.
• Single facet on the head

Head 

• Small and circular.
• Bears one nearly rounded facet for articulation with the upper part of the side of the body of 1st thoracic vertebra.

Neck 

• Rounded; faces upwards, backwards and laterally.

Tubercle 

• Thick and prominent.
• Faces upwards and backwards.
• Coincides with the angle.
• Has an oval facet for articulation with the transverse process of 1st thoracic vertebra.

Shaft 

• It possesses: 2 surfaces: (i) Superior, (ii) Inferior.

2 borders: (iii) Outer, (iv) Inner.

Superior surface:

• (i) Rough and irregular.
• (ii) Crossed by 2 oblique shallow grooves separated from each other by an ill-defined ridge. This ridge ends at the inner border of the rib in a small projection called ‘scalene tubercle’.

Interior surface : 

• (i) Smooth surface.
• (ii) Does not bear a costal groove.
• (iii) Related to pleura.

Outer border : 

• (i) Convex.

Inner border : 

• (i) Concave.
• (ii) Bears the scalene tubercle near its center.

Anterior end 

• Largest and thickest of all ribs.
• Articulates with 1st costal cartilage through which it is connected to sternum.

2. Second Rib

Distinguishing features 

• It has no twist-so both ends of this rib touch any plane surface upon which it is kept.
• It has a slight angle which lies close to the tubercle.
• It is about twice as long as the 1st rib.
• Head is small and bears 2 facets.
• Neck is small.
• Tubercle is divided into articular and nonarticular parts; the non articular part is smaller.
• Surfaces are External and Internal.

i. External surface : 

(i) faces upwards and slightly outwards.

(ii) It is convex.

(iii) Has a rough impression behind its middle.

ii. Internal surface : 

(i) Smooth and concave.

(ii) Faces downwards and slightly inwards.

(iii) There is a short costal groove at its posterior part.

3. Tenth Rib

• The head bears a single articular facet which articulates with the facet near the upper border of the body of the 10th thoracic vertebra .
• Other features are the same as in typical ribs.

4. Eleventh Rib

• The head bears only one large articular facet which articulates with the 11th  thoracic vertebra .
• It doesn’t possess a neck or tubercle.
• No articulation with the transverse process of 11th  thoracic vertebra .
• The Coastal groove on the internal surface is faint and shallow.
• It has a slight angle.
• Anterior end is pointed.

5. Twelfth Rib

• It has no angle.
• It has no twist.
• It has no neck, no tubercle and no coastal groove.
• It has a single large articular facet on the head which articulates with the 12th  thoracic vertebra ; no articulation with the transverse process.
• Anterior end is pointed.
• Shaft possesses: 2 surfaces : (i) External (ii) Internal

2 borders : (iii) Upper (iv) Lower

5.0Ribcage/Thoracic cage

Ribs form a large part of the thoracic wall and are connected behind to the vertebral column; in front the upper 7 pairs articulate through costal cartilages with the sternum; they form the anterior, posterior and lateral walls creating  a bony cage for protection of lungs and heart known as thoracic cage or rib cage.

6.0Functions of Ribs

• Protection: They protect vital organs in the thoracic cavity, including the heart and lungs, from injury.
• Support: Ribs provide structural support to the chest wall, helping to maintain the shape of the thoracic cavity.
• Respiration: Ribs play a crucial role in the mechanics of breathing. When the diaphragm contracts, the ribs move outward and upward, allowing the lungs to expand and fill with air.
• Attachment: They serve as attachment points for muscles involved in respiration and movements of the upper body.
• Blood Cell Production: The bone marrow inside the ribs can produce red and white blood cells, contributing to the body’s hematopoietic system.

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