Thorax Lab 2A

Lab 2A: Remove Heart and Lungs

Learning objectives

Observe the orientation of the heart as it sits in the thorax.
Identify the great vessels of the pulmonary and systemic circulations.
Remove the heart and lungs from the thorax while preserving all of the nearby structures.
Be able to distinguish between the right and left isolated lungs by their distinctive features. Identify the trachea and primary bronchi. Be able to list the structures contained within the hilum of the lung.

Short List of Structures - 2A

Removal of the Heart and Lungs

Before you begin...

During this lab we will be removing the heart and lungs from the posterior mediastinum either...

1) as a single unit that will eventually be separated (more difficult; as seen in the dissection video)

2) separate pieces (easier)

Before dissecting, identify again the phrenic nerves and attempt to preserve them by leaving them behind in the thorax as you remove the heart and lungs.

Mobilize the lungs by running your hands around and behind them, breaking any adhesions between the parietal and visceral pleurae with your fingers. Take care with sharp edges of the cut ribs. Healthy lungs are completely free to move around in the pleural cavities, but in older or ill individuals there may be extensive adhesions between the visceral and parietal pleurae (the result of inflammation of the pleura, a condition called pleurisy or pleuritis). If there is extensive pleural fluid in your cadaver's thorax, you may need to scoop some of it out to clear your field of view.

1) Removal as a single unit

Any structures that you cut should first be isolated and identified, do not cut blindly! Take care to preserve the phrenic nerves as you make the following cuts. Transect the following structures, in the following locations:

The ascending aorta, about 1 cm from the heart.
The superior vena cava, 2cm superior to its union with the right atrium.
The inferior vena cava, as inferiorly as possible. Avoid cutting the diaphragm!
The trachea, superior to the split between the left and right primary bronchi.

Now we can begin to remove the heart and lungs:

To preserve the phrenic nerves, pull one laterally and try to get it positioned lateral to its adjacent lung. The phrenic nerves are located medial to the lungs in life, so this will require a combination of pulling laterally and tucking a lung under the nerve medially. Have a member of your group hold the lung so that you can begin removing the connective tissue connecting the heart to the mediastinum.

2) Removal as separate pieces

The ascending aorta, about 1 cm from the heart.
The superior vena cava, 2cm superior to its union with the right atrium.
The inferior vena cava, as inferiorly as possible. Avoid cutting the diaphragm!
The trachea, superior to the split between the left and right primary bronchi.

Now you will need to separate the heart from the lungs.

Cut along the dotted lines in the figure below to separate the heart and lungs. Cut the pulmonary arteries and veins approximately mid-way along their lengths, so that they can be identified at both the heart and the lungs.

You may keep the trachea intact and the two lungs attached to one another by the trachea, or divide the trachea slightly off the midline to get a better view of the carina.

Anterior view of the cardiopulmonary unit. The dashed lines indicate the approximate location of cuts made to separate the heart from the lungs.

Once you have completed the previous steps for either method #1 or #2...

Use blunt dissection with your fingers, and scissor-spreading, to break the remaining connections between the heart/lung unit and the posterior mediastinum shown generally by the black dotted lines on the figure in the right. This step can be challenging - take your time and ask for help from the teaching staff if necessary. You will need to cut:

Azygos vein (see the image to the right)
Portions of the pericardium that interfere with removal both surrounding the heart and attaching it to the diaphragm
Small nerves of the cardiopulmonary plexus
- A lot of this plexus is actually made up of branches of the vagus nerves and the post-ganglionic sympathetic neurons that go from the sympathetic chain ganglia to the heart and lungs.

But, be careful not to cut these structures:

Esophagus (abdomen is next block, lets not open it up yet)
Descending Aorta (the aortic arch was already cut)
Phrenic nerves

You’ll also see the ligamentum arteriosum joining the pulmonary trunk to the arch of the aorta. You’ll have to cut this structure to remove the pulmonary vessels along with the heart and lungs, so make sure everyone gets a good look at it before it’s gone.

Remove the heart and lungs as a single unit or in three separate pieces from the thoracic cavity.

Examining the Heart and the Lungs

Before you begin...

Now that the heart and lungs are detached from the posterior mediastinum and removed from the thoracic cavity, it’s time to examine them as a cardiopulmonary unit. Then we will separate the cardiac and pulmonary components of this unit if you have not done so already.

Posterior view

Clean any adipose and connective tissue on the posterior surface of the cardiopulmonary unit to view the left and right inferior pulmonary vv. Scissor-spread along the veins a short distance into the lung tissue and you’ll see that the veins branch repeatedly. These branches are all tributaries to two of the four pulmonary veins that bring oxygenated blood from the lungs to the left atrium. The superior pulmonary veins are anterior to the bronchi and are easier to see from an anterior view.

Clean up the trachea and the left and right primary bronchi. The trachea is made up of multiple C-shaped cartilaginous arches that hold the airway open. Scissor-spread along the bronchi a short distance into the lung tissue. As with the pulmonary veins, you’ll see that the bronchi branch repeatedly as they move into the lung. The results of the first branching are the secondary bronchi (lobar bronchi), and secondary bronchi branch to form tertiary bronchi.

Posterior view of the cardiopulmonary unit

Airways

Look down into the trachea and you’ll see a structure at the split into left and right primary bronchi called the carina (“keel”). The carina is a cartilaginous ridge that projects into the trachea at the split between the left and right primary bronchi.

The carina is a cartilaginous structure at the point of the split of the trachea into the left and right primary bronchi.

Anatomy of the airways

Clinical correlation: Intubation and Aspirated Bodies

When you put in an endotracheal tube you need to know where the end of the tube is relative to the carina. If the tube is distal to the carina you’re only ventilating one lung (that’s bad). You should also note that the passage from the trachea into the right primary bronchus is a fairly straight shot, while the left primary bronchus is at more of an angle to the trachea (because it has to go over the heart). One of the results of these differing angles is that an aspirated body tends to go into the right primary bronchus.

Anterior view

Clean the pulmonary trunk on the anterior surface of the cardiopulmonary unit and follow its split into the left and right pulmonary arteries. As you did with the veins and airways, follow the pulmonary arteries into the lung tissue to see that they split repeatedly as they enter the lungs. Look for the left and right superior pulmonary veins slightly inferior and posterior to the pulmonary arteries.

We’ve completed the examination of the heart and lungs as a single unit. Now it’s time to separate the heart from the lungs if you have not done so already.

Separating the Heart from the Lungs

Skip this step if you opted to remove the heart and lungs as separate pieces from the thoracic cavity.

You may keep the trachea intact and the two lungs attached to one another by the trachea, or divide the trachea slightly off the midline to get a better view of the carina.

Anterior view of the cardiopulmonary unit. The dashed lines indicate the approximate location of cuts made to separate the heart from the lungs.

HELPFUL HINTS

Orient yourself when looking at the lungs in isolation. Note that the anterior border of the lung is thin and pointed, while the posterior border of the lung is rounded. Also note contact impressions from the ribs.

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