The Pleurae, and the LungsThe thoracic cavity consists of the fascia, the Muscle Layer, and the main building block of the human body the Bones. The bones that make up the thoracic wall are the 12 Rib pairs, the Sternum, and the 12 Thoracic Vertebrae. The inside of the thoracic cavity is divided into 3 main parts:

2 radiolucent areas (dark areas) called the Pulmonary cavity (referring to the lung), each of these cavities contains a lung and a Pleura, the pleura is the membrane that covers the lung (the lining of the lungs)In the middle of the two radiolucent area is a radiopaque (light) cavity, this contains the heart, the heart’s lining membrane (Pericardium), and some major arteries. This area (behind the sternum) is referred to as the Mediastinum. This area also contains the esophagus, trachea, the Aorta and the Vena Cava.

The Pleurae:

Any organ that moves inside the body is covered by a protective tissue membrane; the duty of these membranes is mainly Protection of the organ, and Reducing the Friction produced when the organ shifts. The Lungs are constantly moving; during inhalation they expand, and during Exhalation the lungs collapse, (the heart is also constantly moving 60~90 times per minute depending on the pumping rate) during all these movements these organs are in constant contact with each other, this continuous friction would cause severe tearing to the organs, which brings us to the Membranes which act as lubricants between these organs greatly reducing the friction. In the lungs this protective membrane is called the Pleura, and in the heart it is known as the Pericardium.

These membranes are basically a fluid filled sac surrounding the lung, Similar to pushing your fist into a water filled balloon (allowing the balloon to surround your fist). This continuous sac has two layers:

Visceral layer- The “inner” layer of the Pleura which is in contact with the lung. (visceral means related to organs)Parietal layer- the “outer” layer of the organs, the one that is in cintact with the thoracic wall mainly the ribs and muscles. (parietal means related to the wall)

*Remember that the Pleural membrane is ONE CONTINUOUS MEMBRANE, but with two layers. The space between these layers is called the Pleural Cavity.

The Pulmonary cavity contains > Lungs & Pleura

The Pleural cavity contains> Fluid that separates Pleura layers.

Lateral to the lung is the thoracic wall (as well as costal), medially is the heart & esophagus, and inferiorly there is the diaphragm. So the parietal pleuron lines the thoracic wall (costal wall) mediastinum and the diaphragm. (Use the slide pictures to help you understand this.)

Parietal wall Surfaces:

The Parietal wall has 4 main surfaces:

1- Costal surface of the Pleura which is opposite to the ribs and the intercostal muscles.

2- Mediastinal surface medially (inside) towards the heart.3- Diaphragmatic surface superior the diaphragm.4- There is also another part of the Pleura called the Cervical Pleura, which covers the

apex of the lung (it reaches to the root of the neck), about 2~3 centimeters above the clavicle bone, this is a very dangerous and exposed region any injury to this area could easily be fatal.

A Pleural Recess is a gap/space that is formed between pleural reflections.

a- CostoDiaphragmatic recess- a space between the costal and diaphragmatic parietal pleura, this recess is cause by gravity; the pleural cavity is filled with fluid, which is pulled down to the bottom of the pleural lining by gravity causing it to “pool up” in the empty space beneath the lungs, Mostly during exhalation (the lung collapses

creating a larger gap for the fluid to go). During Inhalation the lung expands forcing the fluid out of this gap and spreading throughout the pleural cavity once again.

b- CostoMediastinal recess- Gap that forms between the Costal and the Medaistinal pleura, this is a much smaller recess than the CostoDiaphragmatic, the left sides CostoMediastinal recess is larger than the right sides.

Nerve Supply to the Pleura:

The blood supply and nerve supply for the parietal pleura comes from the thoracic wall, and the visceral pleura gets its blood supply from the lungs, (each pleura gets it supply form the part it’s exposed to). The Visceral Pleura gets a autonomic nerve supply from the lungs; specifically the bronchial arteries and veins, but it has no somatic nerves therefore it is insensitive (feels no pain).

Note: the Bronchial Artery is different than the Pulmonary Artery, the Bronchial artery feeds the lung it’s blood supply (for the lungs use “nutritioning” [lungs are living tissue and need oxygen as well]) meanwhile the Pulmonary artery (leave the heart from the right ventricle, and return to the left atrium) sends oxygen to the lung so it can be oxygenated

The costal Parietal surface is fed by the Intercostal Bundle (Arteries, veins and nerves or VAN), the diaphragmatic nerve is supplied by the Phrenic Nerve, which descends all the way from the neck to the mediastinal surface of the pleura and then to then onto the diaphragmatic, Any injury to the Phrenic nerve could lead to paralysis of the diaphragm = no respiration.

So the Phrenic nerve supplies both the Costal pleura and the Diaphragmatic Pleura.

Injuries to visceral pleura will not be felt but any injury to the parietal surface will cause pain

Abnormalities in the Pleura:

Any foreign substance entering into the pleural cavity is called an abnormality, (blood entering the pleural cavity and mixing with the fluid). These usually occur because of any injury to the lung area (fractured or broken ribs can puncture the pleural cavity).

1- Nemothorax- entrance of air into the pleural cavity, raising the pressure of the cavity leading to the collapsing of the lung and difficulty in breathing

2- Hemothorax- Blood seepage into the pleural cavity3- Hydrothorax- Accumulation of pleural fluid In the cavity, usually the fluid stays at

the bottom of the cavity and is not re-circulated.

4- Chylothorax- Accumulation of Lymph in the pleural cavity.

The proper treatment for all 4 cases is removal of the liquid “drainage” by a process called Thoracentesis, this includes inserting a needle/tube through the thoracic wall into the pleural cavity, passing through the skin, fasciae, all 3 Intercostal muscles (external, internal, innermost), through the endothoracic fasciae and through the parietal wall into the pleural cavity.

While carrying out Thoracentesis you must go above the rib, because going from below may lead to injuring the Intercostal VAN (vein artery, and nerve), instead you go above the rib (even though there are some collateral branches of the Intercostal VAN above the rib; but they are much smaller than the main intercostal VAN, to avoid these braches insert the needle about one finger width above the rib. Usually the needle is inserted at Rib number 5 and below, because beneath the 7th rib is the CostoDiaphragmatic recess where all the fluid is accumulated.

The Lungs

Lungs are the vital organs of respiration, functioning in the oxygenation of blood. The lungs color changes as we grow; in newborns the lungs are pink because they are newly formed tissue, however as we grow older dust particles and pollution accumulate on the wall of the lungs darkening them. Each lungs has an Apex and 3 surfaces: Costal (facing the ribs and the intercostal muscles), Mediastinal (in the middle), And Diaphragmatic (above the diaphragm). The apex of the lungs extends 2.5 centimeters above the clavicle into the root of the neck, the right lung is larger than the left lung because the heart is slightly shifted to the left taking up space form the left lung, however the left lung is longer because the liver is beneath the right lung forcing it to be shorter.

The right lung consists of three lobes (parts), easily separated from each other they are:

I. Superior lobeII. Middle lobe (usually the smallest lobe)

III. Inferior lobe

all 3 lobes are separated by fissures:1- Oblique fissure- (slanted) starts from the 6th costal cartilage

anteriorly and slants until it reaches the 2nd thoracic vertebrae, this lobe separates the inferior lobe from the superior and middle lobe.

2- Horizontal fissure- usually at level with the 4th costal cartilage and passes horizontally until it meets the oblique fissure at the mid-axillary –line (area beneath the arm pit/shoulder), separates the middle lobe form the superior lobe.

The left lung is separated into 2 Lobes by One Fissure, Upper lobe and Lower Lobe by an oblique fissure which also starts from the 6th costal cartilage anteriorly and slants until it reaches the 2nd thoracic vertebrae. However since the Heart compresses against the left long it “snags” some of the lung area away leaving what we called a Cardiac Notch, beneath this notch is a tongue shaped protrusion called the lingual (part of the superior lobe of the left lung).

Root and Hylum:

The Root of an organ is the artery/nerve/vein that enters the organ, meanwhile the Hylum is the area where the root passes inside the organ. The roots if the lung is Pulmonary artery, bronchi, and the Pulmonary vein, passing through the lungs mediastinal surface. (ex: root of the kidney is the renal artery, renal vein, and the ureter).

In the left lung the most superior structure is the pulmonary artery, the most inferior is the Pulmonary Vein and the most posterior is the Bronchi.

In the right lung the bronchus is wider than in the left lung (because it splits into 3 instead of 2, one per each lung lobe), so it pushes the artery from the most superior position to the most anterior, and the bronchi remains most posterior and the Vein remains most inferior.

The Trachea:

In the neck we have the Larynx (throat) and behind the pharynx, the larynx ends at C6 to become the trachea which is Anterior to the esophagus. The trachea is composed of “C” shaped hyaline cartilage rings attached posteriorly to a smooth muscle called trachealis (remember that smooth muscles are involuntary, found in hollow tubes[intestines, arteries] causing them to contract), contraction of the trachealis causes broncho-spasms also known as Asthma, which causes difficulty in breathing, people with this condition are usually given anti-histamines through an inhaler which leads to the relaxation of the trachealis muscle allowing the patient to breathe normally. The trachea begins

from the 6th vertebrae and ends at the sterna angle (level of T4~T5), where it splits into right and left bronchus. The right Bronchus is more vertical and wider than the left bronchus (vertical narrow), this means that incase of inhalation of a foreign object it most commonly disrupts the right (wider)

bronchus.

If ignorance is bliss, this lesson would appear to be a deliberate attempt to deprive me of happiness, the pursuit of which is my unalienable right according to the Declaration of Independence. I therefore assert my patriotic prerogative to not know this material. I’ll be out in the playground. ~Calvin

By: Ali Hassan Al-Qudsi