Are the organs of respiration.

They are located in the thorax, either side of the mediastinum

Each lung is surrounded by a pleural cavity, which is formed by the visceral and parietal pleura.

The are suspended from the mediastinum by the lung root- a collection of structures entering and leaving the lungs.

The medial surfaces of both lungs lie in close proximity to several mediastinal structures.

LEFT LUNG

Heart

Arch of aorta

Thoracic aorta

Esophagus

RIGHT LUNG

Esophagus

Heart

Inferior vena cava

Superior vena cava

Azygous vein

They are roughly cone shaped, with an apex, base, three surfaces and three borders.

The left lung is slightly smaller than the right- due to the presence of the heart.

Each lung consist of

Apex

Base

Lobes

Surfaces

Borders

The blunt superior of the lung

Projects upwards, above the level of the 1st rib and into the floor of the neck.

BASE

The inferior surface of the lung, which sits on the diaphragm

The right lung has three lobes

Superior

Middle

Inferior

The lobes are divided from each other by two fissures

Oblique fissure

Horizontal fissure

The left lung has superior and inferior lobes, separated by oblique fissure.

The mediastinal surface,

faces the lateral aspect of the middle mediastinum

The hilum is located on this surface

The diaphragmatic surface

Rests on the dome of the diaphragm, and has concave shape.

This concavity is deeper in the right lung, due to the higher position of the right dome overlying the liver.

The costal surface

It faces the internal surface of the chest wall.

The anterior border

Formed by the convergence of the mediastinal and coastal surfaces

The inferior border

Separate the base of the lung from the costal and mediastinal surfaces

The posterior border

It is formed by the coastal and mediastinal surface meeting posterioly

The lung root is a collection of structures that suspends the lung from the mediastinum.

Each root contains a bronchus, pulmonary artery, two pulmonary veins, bronchial vessels, pulmonary plexus of nerves and lymphatic vessels.

All these structures enter or leave the lung via the hilum- a wedge shaped area on its mediastinal surface.

Supplied with deoxygenated blood by the paired pulmonary arteries.

Once the blood has received oxygenation, it leaves the lungs via four pulmonary veins ( two for each lung)

Bronchial arteries which arise from descending aorta supply oxygenated blood to the lung structures.

The bronchial veins provide venous drainage.

The right bronchial vein drains into the azygos vein

The left drains into the accessory hemiazygos vein.

Derived from the pulmonary plexuses

Parasympathetic

Derived from vagus nerve

Stimulate secretion from the bronchial glands, contraction of the bronchial smooth muscle, and vasodilation of the pulmonary vessels

Sympathetic

Derived from sympathetic trunks

Stimulate relaxation of the bronchial smooth muscle, and vasoconstriction of the pulmonary vessels.

Visceral afferent

conduct pain impulses to the sensory ganglion of the vagus nerve.

Superficial (subpleural)

Drains the lung parenchyma

Deep

Drains the structures of the lung root

Refers to the serous membranes that line the lungs and thoracic cavity.

They permit efficient and effortless respiration.

STRUCTURE OF THE PLEURAE

Consists of a serous membrane- a layer of simple squamous cells(mesothelium) supported by connective tissue.

Each pleurae can be divided into two parts

Visceral pleura- covers the outer surface of the lungs, and extends into the interlobar fissures.

Parietal pleura- covers the internal surface of the thoracic cavity.

These two parts are continuous with each other at the hilum of each lung.

The space between the viscera and parietal pleura is known as pleural cavity, which contains a small volume of serous fluid

Major function of pleural fluid

It lubricates the surfaces of the pleurae

Produces a surface tension