LUNGS

                                                                                                          

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ave you ever wondered how do you take the air  inside and throw outside of your body?

Have you ever thought of what are Lungs in reality and how do they look, or how do they function! We will answer all of such questions in this blog of lung anatomy.

 This is an artistic illustration of lungs which shows all the basic anatomical things you must consider in order to understand it completely.

Lungs are one of the vital organs in our body that we must know and is the most commonly affected organ.

Both the lungs are situated in the cavity which is present in the thorax. A thorax is a cavity which is present between below the neck and the abdomen.

The Thoracic cavity is formed by the following structures –

Anterior – Sternum and xiphoid process

Posterior – bodies of 12 thoracic vertebrae

Superior – Thoracic inlet

Inferior – Diaphragm

and on both sides by the ribs.

          Fig 1.0 – boundaries of thorax

        Right Lung is 700 gm in weight, whereas the left lung is 50 – 100 gm less in weight and weighs approximately 600 – 650 gm.

Young lungs are pinkish - brown in colour which gradually become black over the due course of time because of accumulation of carbon particles.

Each lung is shaped like a cone with a top called APEX and a bottom, Each lung has three borders namely anterior, posterior and inferior. Also each lung as 2 surfaces one costal and other mediastinal(facing the heart). Each lung is covered in a thin membrane that acts like a sac and is called  as pleura.

Pleura is divided into 2 parts, Parietal pleura – the one covering the ribs; and the Visceral pleura – the one that covers the lungs like a stocking, i.e. hugs the surface of the lungs. This creates a gap in between the two pleurae and is called as the pleural cavity which is filled with a fluid called as pleural fluid.

                            

Fig 1.1 – Pleural cavity and Lungs

The top of the Lung reaches out into the neck, out of the Thoracic cavity like a mountain and thus called the Apex of the lung. It reaches approximately 2.5 cm above the 1^st rib and thus becomes one of the part for investigations.  

Fig 1.2 – Apex of Lungs (seen from the thoracic inlet)

The figure 1.2 Shows the apex of the lungs and can be clearly seen that it is reaching out of the 1^st rib.

Each lung has three fissures running all along their surfaces that divide them into smaller segments called as lobes.

The right lung as 2 fissures; horizontal fissure and oblique fissure; running across the whole lung that divides it into 3 lobes; Superior lobe, Middle lobe, Inferior lobe. Whereas the left lung has is divided into 2 lobes; Superior and Inferior lobe; by horizontal fissure. This is because the left lung has to accommodate the heart and its apex, this having 2 lobes and one notch called as the cardiac notch, which can be seen in the picture below.

        

Fig 1.3 – Lobes and notches of lungs

This cardiac notch is nothing but a part of anterior border of left lung.

The costal surface of the lung is the part which corresponds to the surface that is in contact with the ribs. Thus, it is covered by the pleura and pleural fluid to prevent frictional heating and acts as a shock absorber for the lungs.

The part of the lungs that faces towards the heart is called as the medial surface or mediastinal surface. 

  

A detail image can be seen in this specimen which was taken from a cadaver[Fig 1.4]

                          

Fig 1.4 – Mediastinal surface of lung (courtesy of Kenhub)

This mediastinal surface of he lung as opening that leads pathways in and out of the lungs. This is also called as the root of the lung. The root of the lung contains the following things ….

Bronchus, Pulmonary artery, Pulmonary veins, lymphatics, and fatty tissue. (as shown in the image 1.5)

Fig 1.5 contents of root of lungs as seen from behind (source: Teach me anatomy)

This area is clinically important as knowledge of this area helps us to understand the lobes of lung and its extent and further division inside the lung.

As the bronchus enters the lung it divides into more branches and forms segments inside the lungs. These segments along with the artery and its bronchial correspondent is called as a bronchopulmonary segment.

There are total of ten bronchopulmonary segments in each lung and are located in the lobes.

Each segment is pyramidal in shape and its apex is directed towards the root of the lungs.

These bronchopulmonary segments are individual respiratory units, and thus their knowledge helps us in surgeries like Lobectomy, where we remove the diseased lobe out of the lung.

Fig 1.6 bronchopulmonary segments of lungs.

Sometimes if there is infection in these segments, they remain confined to them except in Tuberculosis, where it can spread from one segment to another (will be discussed separately).

Lungs receive the arterial supply from the bronchial artery. Right bronchial artery arises from either of the 3^rd posterior intercostal artery or the upper left bronchial artery. Left bronchial artery arises from the descending thoracic aorta (as seen in following images)

These images show the locations of the arteries arising from the aorta and supply the lungs.

There are 2 bronchial veins on each side, where they drain into the intercostal veins of the azygous veins, but majority of it is drained via the pulmonary veins.

Fig 1.7 Venous drainage of lungs

The lungs are innervated by Parasympathetic fibres of Vagus (10^th cranial nerve) which gives motor branches to bronchial muscles and secretory innervation to the mucous glands in the bronchial tree. Sympathetic innervation is from the 2^nd to 5^th spinal segments that oppose the function of Vagus.

Fig 1.8 Innervation of lung (Source: the comical anatomist)