Lungs

Respiratory organs include the lungs. They are found in the thorax, on each side of the mediastinum.

The lungs' job is to keep the blood oxygenated. It's done by bringing oxygen-poor blood in the pulmonary capillaries into close contact with fresh, inspired air.

Position and Relationships in the Human Body

According to Breatnach (1984), the lungs are located in the thoracic cavity on each side of the mediastinum. The visceral and parietal pleura encircle each lung and constitute the pleural cavity.

The lung root - a collection of structures entering and leaving the lungs – suspends them from the mediastinum. Several mediastinal structures can be found along the medial surfaces of both lungs:

Left Lung:

Heart

Arch of aorta
Thoracic aorta
Oesophagus

Right Lung:

Oesophagus
Heart
Inferior vena cava
Superior vena cava
Azygous vein

Structures in the lung

The lungs resemble a cone in form, with a pointed tip, a flat bottom, and three distinct surfaces. Because of the heart's location in the chest, the left lung is somewhat smaller than the right one..

The following structures are found in each lung:

The blunt tip of the lung's superior end is known as the apex. It extends through the neck's floor from the first rib level upwards.

The inferior surface of the lung that rests on the diaphragm is referred to as the base.

Fissures in the lung separate the two or three lobes.

They face different parts of the thorax according on how many surfaces there are. Costal, medial, and diaphragmatic are the terms used to describe these three types of tendons.

The anterior, inferior, and posterior margins are the three boundaries of the lungs.

Lobular Structure

According to Ernst (2004), lobular anatomy differs between the right and left lungs.

The superior, middle, and inferior lobes of the right lung make up the lung's three lobes. There are two fissures that separate the lobes:

The oblique fissure is slightly more than an angle between the inferior and superoposterior borders of the lung; it terminates at the posterior lung boundary.

The horizontal fissure connects the 4th rib to the oblique fissure, running horizontally from the sternum.

An oblique fissure separates the superior and inferior lobes of the left lung.

The image below shows the divisions between the right and left lungs:

Right lung:

Superior lobe

Apical
Posterior
Anterior

Middle Lobe

lateral
Medial

Inferior Lobe

Superior
Medial basal
Anterior basal
Lateral basal
Posterior basal

Left Lung

Superior Lobe

1&2 Apical/Posterior

3 Anterior

Lower Division (Lingular)

4 Superior Lingua

5 Inferior Lingua

Inferior Lobe

6 Superior

7&8 Anterior Medial Basal

9 Lateral basal

10 Posterior basal

Respiratory and Conducting Zones

There is a conducting zone and a respiratory zone in the respiratory system, both of which serve different purposes. Non-gas-exchanging organs and structures comprise the respiratory system's conductor zone. The respiratory zone is where gas exchange takes place.

Conducting Zone

The conducting zone's primary duties are to provide a passage for incoming and outgoing air, remove debris and viruses from that air, and warm and humidify that air. Another purpose performed by several buildings in the conducting zone is to conduct electricity. In the nasal passageways, for example, the epithelium is critical for odor perception, and in the lungs, the bronchial epithelium can help break down certain airborne toxins.

Respiratory Zone

Respiratory structures, as opposed to those in the conducting zone, directly contribute to gas exchange. The respiratory zone begins at the junction of the terminal bronchioles with a respiratory bronchiole, the tiniest form of bronchiole, which subsequently leads to an alveolar duct, which opens into a cluster of alveoli.

Structures of the Lungs

Structure of the walls. Squamous epithelial cells make up the vast majority of the alveolar walls.

Pores in the alveoli (the lungs). When feeder bronchioles are congested or otherwise closed, alveolar pores provide as an alternate pathway for air to reach the alveoli.

Membrane of the respiratory system. The respiratory membrane (air-blood barrier) is made up of the alveolar and capillary walls, their fused basement membranes, and a few elastic fibers. It allows gas (air) to pass through on one side and blood to flow through on the other.

Cells in the alveoli called macrophages. Alveolar macrophages, sometimes known as "dust cells," are remarkably adept in picking up bacteria, carbon particles, and other debris as they go in and out of the alveoli.

Cuboidal Cells. Along with epithelial cells, which compose the majority of alveolar walls, chunky cuboidal cells also exist. These cells generate an essential lipid (fat) component known as surfactant, which coats gas-exposed alveolar surfaces and plays a vital role in lung function.

Alveolar Lining

The alveolar lining is extraordinarily thin (0.35 to 2.5 microns). When compared to a red blood cell, the alveolar lining is very small since the RBC is 7 microns in diameter, meaning that RBC cannot pass through the alveolar lining. This quality then promotes rapid transfer of gas across the membrane. The alveolar lining is made up of two types of cells: the Type 1 Pneumocytes (flat cells involved in gas exchange) and the Type II Cells (cuboidal cells) which are the source of the surfactant, a substance that reduces surface tension and keeps the alveoli from collapsing.

References:

Breatnach, E. American Journal of Roentgenology, 1984; vol 142: pp 903-906.

Ernst, A. American Journal of Respiratory and Critical Care Medicine, 2004; vol 169: pp 1278-1297.

Mason, R. Murray & Nadel's Textbook of Respiratory Medicine 4th Edition, Elsevier Saunders, 2005.

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