Introduction

In this lab, you will examine the muscles of respiration, lungs, heart, and roots of the great vessels. The lungs function for the exchange of oxygen and carbon dioxide between the alveoli and the blood.  Our muscles of respiration allow us to inhale and exhale by expanding and diminishing the space in our thoracic cavity and, in turn, our lungs. The heart pumps blood throughout our body, carrying oxygen and nutrients to our tissues, carrying waste products away from our tissues, and much more.

Lab Activities

Activity 1: Muscles of Respiration: 

Watch the videos in Canvas using the digital atlas and view the images in the Abrahams‘ and Netter’s atlases to explore the muscles of respiration.

• Identify the following muscles of respiration (superficial to deep). The angle (orientation) of the fibers can help you understand how they work to elevate or depress the ribs (except the diaphragm).
  • External intercostals: Elevate ribs with passive inhalation
  • Internal intercostals: Depress the ribs with forced exhalation
  • Serratus posterior superior: Elevate the ribs with forced inhalation
  • Serratus posterior inferior: Depress the ribs with forced exhalation
  • Diaphragm: Expands and increases the vertical dimension of the thoracic cavity, Increases pressure in the abdominopelvic cavity

Activity 2: Heart Tissue

Watch the videos on Canvas exploring the anatomy of the heart. The wet organs were all cut at autopsy to allow the pathologists to search for disease in the tissues. Smaller cuts sequentially along the outside surface of the heart were made to investigate the condition of the coronary arteries. The coronary arteries are usually surrounded by adipose tissue. The typical human heart weighs between 200-375g. You can also explore the anatomy of the heart in the Abrahams‘ and Netter’s atlases (Netter’s starts on page 4 and continues to page 5).

• Observe the external features of the heart. In the region of the atria, notice a pouch-like structure. This is called the auricle, and there is one present on each atrium.
• Look inside the right atria and view the septum between the left and right atria. Observe a small oval indent on the septum. This is the fossa ovalis. Prior to birth, there is no need for blood to go to the lungs for oxygenation because the fetus receives oxygen from the mother’s circulation. The fossa ovalis is open in the fetus, then called the foramen ovalis. As a result, blood is able to bypass pulmonary circulation and go straight from the right atrium to the left atrium and into systemic circulation. It closes shortly after birth, but the small oval indent, the fossa ovalis, remains.
• Observe the ventricles.
• Observe the structures of the internal features of the heart.
  • The right (tricuspid) and left (bicuspid, mitral) atrioventricular (AV) valves prevent backflow from the ventricles into the atria. The pulmonary and aortic semilunar valves prevent backflow from the pulmonary arteries and aorta into the right and left ventricles, respectively. You should note whether or not it appears that the valve is near an artery or separating the atria and ventricles. You can also differentiate an AV valve from a semilunar valve by determining if the chordae tendineae are attached to it. The chordae tendineae prevent the AV valves from prolapsing (collapsing backward) into the atria.
  • The projections from the heart wall that attach to the chordae tendineae are the papillary muscles. They provide support to prevent prolapse of the AV valves.
  • The muscular ridges on the walls of the ventricles are called the trabeculae carneae. Their function is not well-understood.
  • Also, observe the interventricular septum separating the right and left ventricles.
• Observe the great vessels entering and leaving the heart. The aorta leaves the left ventricle, while the pulmonary trunk leaves the right ventricle. The aorta has thicker walls than the pulmonary trunk. The superior and inferior vena cava both carry deoxygenated blood to the right atrium, while the pulmonary veins carry oxygenated blood to the left atrium. They will appear as holes in the right atrium.
• Note that the left and right coronary arteries branch off of the ascending aorta just after it leaves the heart. The other vessels do not have any immediate branches.
• Identify the coronary vessels that supply the heart walls with blood.
  • Right coronary artery – Brach off of the aorta
    • Right marginal artery 
    • Posterior interventricular artery (posterior descending artery, PDA)
  • Left coronary artery – Brach off of the aorta
    • Anterior interventricular artery (left anterior descending, LAD)
    • Circumflex artery
  • Great cardiac vein – runs with the anterior interventricular artery
  • Middle cardiac vein – runs with the posterior interventricular artery 
  • Small cardiac vein – runs with the marginal artery
  • Coronary sinus – collects blood from all of the cardiac veins 

Activity 3: Respiratory system tissue

Watch the videos in Canvas examining the respiratory tissue: the lungs, bronchi, and trachea. Also, explore these structures in the Abrahams‘ and Netter’s atlases.

• The right lung has three lobes: Inferior, superior, and middle. These are separated by the oblique and horizontal fissures. The way that the lungs are cut in the videos makes it hard to see the lobes and fissures, but you can view these in the atlases.

• Observe the hilum on the medial aspect of the lungs. By the end of the unit, you will observe several organs that have a hilum. This is where neurovascular structures, and sometimes other structures, enter or leave an organ. In the lungs, you can observe bronchi, arteries, and veins in this location. The bronchi are thicker with sturdy walls as a result of the cartilage in their walls. Arteries have thicker walls than the veins, and this will be evident in the hilum as well.

The orientation of these structures as they enter/leave the hilum is consistent and can tell you if you are looking at a right or left lung. You can use the mnemonic “RALS”.

• • In the Right lung, the pulmonary artery will be Anterior to the main bronchi.
  • In the Left lung, the pulmonary artery is located Superior to the main bronchi.
• Observe a cut internal section of a lung and examine the appearance of the alveoli. The lungs will look somewhat like a very condensed sponge, which is a result of the alveoli.
• Observe the trachea and primary (main) bronchi. Cartilaginous rings help to maintain the lumen (open portion) of this tube so that our airway does not collapse. Also, notice the point where the trachea splits into the primary bronchi. The point at which the split is called the carina. The image at the right is taken from within the trachea looking down at the bronchi.
• Observe the diaphragm. Notice how thin this muscle is. Also, notice its domed shape extending upward into the thoracic cavity.
• Observe the phrenic nerve in the atlas images. The phrenic nerve descends through the thoracic cavity and innervates the diaphragm. It originates from the C3, C4, and C5 spinal roots. Remember, C3, C4. C5 keeps the diaphragm alive.

Activity 4: the THORACIC CAVITY IN CROSS-SECTION

Watch the video in Canvas on the cross-sectional anatomy of the thoracic cavity. It is important to understand what these structures look like in cross-section, as that is how the structures are viewed in many radiology images.

Activity 5: Thoracic Radiology

Watch the radiology presentation in Canvas on the thoracic cavity. You will see X-Ray imaging, Echo imaging, and CT imaging of the thoracic cavity. The slides will also be available to you to use as a study tool. In anatomy, we frequently use our knowledge of structures around a given structure to identify that structure. There is an example of this in the introductory video on Canvas for this lab. Practice using that method here. You might find it helpful to take notes about your thought process as you do this to help you remember your cues for identifying certain structures.

X-Ray

• Lungs
• Heart
• Liver
• Ribs
• Vertebrae

Echocardiogram (echo) – Heart

• Atria
• Ventricles
• Right atrioventricular (tricuspid) valve
• Left atrioventricular (bicuspid/mitral) valve
• Pulmonary semilunar valve
• Aortic semilunar valve
• Interventricular septum
• Papillary muscles

CT

• Lungs
• Heart
• Aorta
• Liver
• Vertebrae

Wrap up and Clinical CoNNECtions 

For our clinical connections for this lab, we will discuss two heart conditions: myocardial infarction (heart attack) and enlargement of the heart. The clinical connection video is posted on the course Canvas page.