Module 6 The Thorax

Pectoralis Major

responsible for 4 primary actions. The first of these actions is the medial rotation of each humerus. An example is rotating the humerus from an anatomic position with the palms facing anteriorly and ending with the palms facing posteriorly. The second action for which the pectoralis major is responsible is flexion, or forward elevation, of the humerus. The third action of the pectoralis major is adduction of the humerus. Adduction of the humerus involves bringing the arm down from a position straight out at your side to be parallel to the main axis of the body. The fourth and final role of the pectoralis major muscle is to keep the arm attached to the body.

The Female Breast

can be divided into 3 components: subcutaneous, mammary and retromammary. Starting anteriorly, the first layer of the breast deep to the skin is the subcutaneous component, which is typically composed of subcutaneous fat, or adipose tissue.

Glandular Tissue

Breast milk is formed in the glandular tissue. Glandular tissue is made up of the terminal duct lobule units and the excretory, or lactiferous, ducts. Surrounding the nipple is a circular pigmented area called the areola. The areola is made up of sebaceous glands that provide lubrication during breast feeding.

Articular Processes

Each vertebra contains 2 superior and 2 inferior articular processes. The articular processes are located above and below the junction of the pedicle and lamina. Each process is coated with hyaline cartilage and articulates with the opposite process of the adjacent vertebra. In other words, the superior articular process forms a joint with the inferior articular process of the vertebra above it. These joints are called the zygoapophyseal, or facet, joints. Like most joints, the facet joints can break down with age, causing irritation and osseous overgrowth, a common condition known as facet arthropathy.

The Posterior Intercostal Arteries

Eleven _________________________________________ extend laterally along the inferior borders of the ribs. The first and second, or highest, intercostal arteries arise from the subclavian arteries, while the remaining 9 originate from the back of the thoracic aorta. They supply the space between adjacent ribs, called the intercostal space, with oxygenated blood. It's important to note that the intercostal arteries travel along the inferior borders of the ribs. When performing interventional procedures that require access to the pleural cavity, the practitioner should slide the needle or other instrument over the superior border of the rib to limit the chances of injuring the intercostal artery.

Aortic Arch

In most people, 3 branches originate from the _____________________: the brachiocephalic artery, the left common carotid artery and the left subclavian artery. The brachiocephalic artery further divides into the right subclavian and right common carotid arteries. The subclavian arteries run under each clavicle and supply oxygenated blood to each arm.

The Trapezius Muscles

Like the rhomboid muscles, the ____________________________also take their name from geometry. They resemble a trapezoid, which is a diamond-shaped quadrilateral

Pulmonary Arteries

Not all arteries carry oxygenated blood. One exception to this rule is the pulmonary arteries. The pulmonary arteries carry deoxygenated blood from the heart to the lungs. The main pulmonary trunk arises from the right ventricle and then bifurcates into the right and left pulmonary arteries. The right and left pulmonary ateries can be seen on the image on this slide. Also note the location of the aortic arch as it relates to the pulmonary arteries.

Intervertebral Foramina

Small recesses above and, more prominently, below each pedicle are called vertebral notches. When the spine is in anatomic alignment, the inferior notches of a superiorly situated vertebra combine with the superior notches of an inferiorly adjoining vertebra to form the intervertebral foramina. The intervertebral foramina allow the nerves and vessels to pass to and from the spinal column.

The Sternum

The manubrium is the most superior section of the ________________and laterally receives the cartilages of the first and second ribs. On the superior border of the manubrium is a small indentation called the suprasternal notch, or jugular notch. The superior border of the manubrium articulates with the clavicles, and inferiorly, the manubrium articulates with the body of the sternum. In most people, you can palpate a bony ridge at this articulation, although in others the articulation may be rounded, making it harder to feel. The lateral borders of the sternum articulate with the third through seventh ribs. Inferiorly, the body of the sternum articulates with the third and final portion of the sternum, the xiphoid process. The xiphoid process is a small bony protrusion that extends inferiorly from the body of the sternum.

The Surface Lines

The midsternal, or midsagittal, line evenly divides the body into right and left halves. The lateral sternal lines run vertically along both lateral borders of the sternum. The vertical line that runs through the midpoint of each clavicle is called the midclavicular, or mammary, line. Lateral to the midclavicular line is the midaxillary line, which extends vertically through the axilla, or armpit, along the lateral border of the thorax. The transpyloric line extends horizontally at a level midway between the suprasternal notch of the sternum and the superior border of the symphysis pubis. The transpyloric line transects the pylorus of the stomach, costal cartilages of the ninth ribs and the first lumbar vertebra. The transpyloric line forms the lower border of the top 3 regions formed by the Addison planes.

The Ribs

The most superior 7 of the pairs are considered true ribs, with the first pair having a more flattened and C-shaped appearance. True ribs directly articulate with the sternum via the costal cartilages. The remaining 5 sets of ribs are called false ribs. The first 3 of these sets, or ribs 8 to 10, are connected indirectly with the sternum by costal cartilages that converge with the costal cartilages from more superior levels on their way to the sternal articulation. Ribs 11 and 12 are called floating ribs because they don't connect to the sternum.

Costal Cartilages

The ribs are attached to the sternum by the costal cartilages. These structures are made of hyaline cartilage and arise from the anterior ends of the first through tenth ribs. In ribs 1 through 7, they connect the rib directly to the sternum. In ribs 8 through 10, they arch superiorly, connecting the rib to the inferior border of the costal cartilage above it.

Veins of the Thorax

The subclavian veins unite bilaterally with the internal jugular veins, which drain blood from the head and neck, to form the brachiocephalic, or innominate veins. In contrast to the single brachiocephalic artery, there are bilateral brachiocephalic veins. The brachiocephalic veins unite to form the superior vena cava, which is commonly known by its abbreviation SVC.

The Vertebral Body

The typical _______________________- is divided into anterior and posterior elements. The anterior element, called the vertebral body, makes up the majority of each vertebra. The superior and inferior borders of each vertebral body have a raised outer rim with a rough, flattened recess that provides an attachment point for the intervertebral discs. Multiple tiny foramina are located anteriorly and posteriorly for the passage of the vertebral vessels.

The Thoracic Diaphragm

a thin sheet-like muscle that extends across the bottom of the rib cage and divides the thoracic and abdominal cavities. The diaphragm originates circumferentially from the costal cartilages and the lumbar vertebrae and inserts into the central tendon of the diaphragm.

Intervertebral Discs

are located between the vertebral bodies. Each intervertebral disc is made up of 3 parts: the nucleus pulposus, the annulus fibrosus and the paired vertebral endplates. The intervertebral disk provides cushioning, acts as a ligament to hold the vertebral bodies together and works as a joint to provide movement to the spine.

The Sternal Angle

corresponds to the superior border of the second ribs. Once you locate the second ribs, it's easy to count and locate the rest of the ribs. The second reason the sternal angle is important is that is corresponds to the level of the bifurcation of the trachea into the right and left mainstem bronchi. Finally, the sternal angle corresponds to the superior border of the atria of the heart. This landmark also coincides horizontally with the level of the fifth thoracic vertebral body.

Addison Planes

divide the inferior chest, abdomen and pelvis into 9 regions. These planes are useful in clinical medicine because particular disease processes can present as pain or tenderness in specific areas.

The Trachea

extends inferiorly from the larynx although some sources consider the larynx to be a part of the trachea. The trachea extends inferiorly to approximately the level of the fifth thoracic vertebral body and bifurcates into the right and left mainstem bronchi, which distribute air to each lung. This bifurcation is called the carina and is an easily recognizable structure on chest radiographs.

The Male Breast

has the same basic structure and contains the same type of breast tissue as the female breast. The difference is that during puberty, male breast tissue does not grow and remains barely noticeable, whereas the female breast tissue begins developing.

Thoracic Vertebrae

have a typical vertebral appearance with 2 differences: the costovertebral and costotransverse facets. Each thoracic vertebra articulates with a pair of ribs in 2 places per rib. The head of each rib articulates with the vertebral body along the posterolateral border at the costovertebral facet. The tubercle of each rib articulates with the anterolateral border of each transverse process at the costotransverse facet.

The Pectoralis Minor Muscle

is a thin triangular muscle located underneath the pectoralis major muscle. Similar to the pectoralis major muscle, it has 3 points of origin: the upper outer borders of the third, fourth and fifth ribs. The fibers also converge to 1 insertion point, attaching with a flat tendon at the upper inner border of the coracoid process of the scapula. The pectoralis minor muscle pulls the scapula inferiorly and medially toward the thorax, a motion that forces the inferior tip of the scapula posteriorly.

The Lung

is divided into 3 parts, but only the right lung has 3 lobes. Fissures separate the upper, middle and lower lobes of the right lung. The upper lobe is divided from the middle lobe by the horizontal, or minor, fissure. The horizontal fissure extends along the level of the fourth rib and intersects the oblique fissure. The oblique, or major, fissure extends posteriorly from about the level of the second thoracic spinous process anteriorly to the level of the sixth costal cartilage, separating the upper lobe and middle lobe from the lower lobe. The left lung only has the oblique fissure, which separates the upper and lower lobes. The third part of the left lung is the lingula. The lingula, although not considered a lobe, is a tongue-like projection that arises from the lower portion of the upper lobe.

The Right Ventricle

is found in the lower medial portion of the heart. It receives deoxygenated blood from the right atrium during atrial contraction and ventricular relaxation. When the right ventricle contracts, it pushes the blood into the main pulmonary artery to travel to the lungs, where it is oxygenated. The oxygenated blood then returns to the heart via the left atrium.

The Left Ventricle

is located in the lower lateral portion of the heart. It receives oxygenated blood from the left atrium during atrial contraction and ventricular relaxation. During the contraction phase of the left ventricle, oxygenated blood is pushed into the aorta to travel throughout the body. An important note is that the left ventricular wall is typically thicker and more muscular because higher pressure is needed to deliver blood to the rest of the body.

The Left Atrium

is located in the upper lateral portion of the heart and receives the oxygenated blood from the pulmonary veins during the relaxation phase of the surrounding muscle. During the contraction phase, it pushes oxygenated blood into the left ventricle.

The Right Atrium

is located in the upper medial portion of the heart and receives deoxygenated blood from the superior and inferior vena cavae. The blood enters the right atrium during the relaxation phase of the surrounding muscle. During the contraction phase, the blood is then pushed into the right ventricle.

The Thymus Gland

is part of the immune system. It directs the T lymphocytes, which are the cells responsible for the adaptive immune system. T lymphocytes travel throughout the bloodstream and attack foreign bodies. The thymus is most active in the early stages of life. During the early teen years, the thymus atrophies and normal thymic tissue is replaced with adipose tissue.

The Heart

is the primary organ of the cardiovascular system. The 4 chambers of the heart are the right atrium, right ventricle, left atrium and left ventricle. The pericardium surrounds the heart. It is made up of 2 primary layers the fibrous pericardium and the serous pericardium. The serous pericardium is further divided into the visceral and parietal pericardial layers. Similar to the pleura that lines the lungs, the visceral pericardium lines the heart, and the parietal pericardium lines the inner fibrous pericardium. The function of the pericardium is to protect the heart from shock, as well as to lubricate the surface of the heart.