What are Lungs ? Structure, Surface, Blood Supply

There are two lungs on each side of the midline in the thoracic cavity. The area between the two lungs is the mediastinum occupied by heart great vessels, trachea, right and left bronchioles, oesophagus,lymph node, lymph vessels and nerves .

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The lungs are cone shape and are described as hav­ing an apec and a base two surface :

1. Costal sur­face
2. Medi­al surface

The Apex is round­ed and extend­ed up to the root of the neck for about 1 inch­es above the mid clav­i­cle. The base os con­cave and semi­lu­nar in shape and is relat­ed to upper sur­face of the diaphragm. The costal sur­face is con­cave and have rough tri­an­gu­lar shaped area called hilum or hilus at the lev­el of 5^th , 6^th and 7^th tho­racic vertebrae. 

The struc­ture which form the root of the lungs enter and leave at the hilum they are.

1. One bronchus
2. One pul­monary artery 
3. Two pul­monary veins 
4. Lymph ves­sels
5. Parasym­pa­thet­ic and sym­pa­thet­ic nerves
6. Bronchial veins
7. Bronchial arter­ies
8. Lym­phat­ic glands

Struc­ture

On exam­i­na­tion lungs feels spongy and if a por­tion is dropped into water it will float because of air which it contain.

The right is divid­ed into three dis­tinct lobes:

1. Supe­ri­or
2. Mid­dle
3. Infe­ri­or

Left lungs is divid­ed into two lobes

1. Supe­ri­or
2. Infe­ri­or

Pleu­ra :- Tt is a serous mem­brane which con­sist of two lay­ers.

1. Vis­cer­al pleura
2. Pari­etal pleura 

The vis­cer­al pleu­ra from the out­er cov­er­ing of the lungs which enclos­es the lungs com­plete­ly except at the hilum.

The pari­etal pleu­ra lines the infe­ri­or of the chest wall and upper sur­face of diaphragm. There is the pres­ence of a thin film of serous flu­id between the two pleu­ra suf­fi­cient to pre­vent fric­tion between them dur­ing breathing 

Inte­ri­or of the lungs : 

The lungs are com­posed of bronchi and small­er air pas­sage alve­oli, con­nec­tive tis­sue blood ves­sels, lymph ves­sels and nerves, left lungs is divid­ed into two lobes and right lung into three lobes. Each lobe is made up of large no alve­oli and three bronchioles . 

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The lobes are com­posed of :

1. Ter­mi­nal bronchioles 
2. Res­pi­ra­to­ry bronchioles 
3. Alve­o­lar
4. Alve­oli

1. As the air pas­sage sub­di­vid­ed there struc­ture under goes a grad­ual changes. The car­ti­lage becomes irreg­u­lar in size. And shape and at last dis­ap­pears. The walls become thin­ner until mus­cle and con­nec­tive tis­sue are replace by a sin­gle larg­er of duct and alve­oli. The cells between the epithe­li­um cells in the alve­oli secrets phos­pho­lipid sur­fac­tants which reduces the sur­face ten­sion between the col­lapsed walls of dis­tal air pas­sage and alveoli.

Pulmonary Blood supply:

Pulmonary artery divides into two right and left. Each branch carries deoxygenated blood to each lungs with in the lungs . Each pulmonary artery divides into many branches . which finally end in a dense capillary network around the walls of alveoli and of capillaries each consists of only one layer flattened epithelial cells. The exchange of gases between air and in the alveoli and blood in the capillaries take place across these two find membranes. The pulmonary capillaries join up eventually become two pulmonary vein in each lung. They leave the lungs at the hilum and convey oxygenated blood to the LA of the heart. The innumerable blood capillaries and vessels in the beings are supported by connective tissue.