Thoracic+Wall,+Lungs+and+Pleura

=**Objectives**=


 * 1. Describe the boundaries and reference lines of the thoracic cavity and the skeletal components (thoracic cage) of the thoracic wall.**

The thoracic cavity contains the chest, or the upper part of the trunk. It is bound by the jugular arch and the clavicle, contains part of the anterior axillary fold, and the costal margin. The jugular notch is the depression above the clavicle and below the neck on the midline which can be palpated. The sternal angle is the fused join between the manubrium and the sternum. The intercostal spalces are teh spaces between the ribs. The breasts are the nipples and the surrounding areola. The costal margin is the cartilage connecting the lower ribs to the sternum. The infrasternal (subcostal) angle is formed at the bottom of the sternum at the xiphisternal joint. Lastly, the midclavicular line is an imaginary line drawn from about the the half point of the clavicle down.

The skeletal components contain the sternum, ribs, costal cartilages, and 12 thoracic vertebrae. The sternum contains the manubrium, the sternum body, and the xyphoid process. The costal cartilages connect the ribs to the manibrium/sternum.

The 12 pairs of ribs are divided up between the true, false, and floating ribs. Ribs 1-7 are true ribs that connect with the manibrium/sternum through costal cartilages and has its own articulation. Ribs 8-10 are false ribs that have fused costal cartilages that indirectly attach to the sternum. Ribs 11-12 are floating ribs that just have cartilage caps and don't attach to the sternum.

The superior thoracic aperture (thoracic inlet) is the opening at the top of the rib cage. It is bound by the T1 vertebrae posteriorly, 1st rib laterally, and manubrium anteriorily. The clavical is //not// part of the superior thoracic aperture. The inferior thoracic apeture is the openning at the bottom of the rib cage. It is bound posteriorly by the T12 vertebrae, 11th and 12th ribs posterior/laterally, and by the costal margins and xyphisternal joint lateral/anteriorly.


 * 2. What are the functions and surface landmarks associated with the thoracic cage**

See above for surface landmarks.

The functions associated with the thoracic cavity include: (1) Respiration (2) Protect viscera (heart/lungs) (3) Anchor point for skeletal muscles (upper extremity/connecting muscles)


 * 3. Describe the process of respiration and the associated movements of the thoracic wall.**

Movement of air into (inspiration) and out of (expiration) the lungs is called ventilation. Insipration requires an increase in the volume of the thoriacic cavity which produces a negative air pressure in the lungs, drawing air in.

Quiet respiration is caused by the diaphragm contracting and lowering the diaphragm, increasing the vertical dimension. It is done when there is not a high oxygen requirement since the volume changes are small. Active inspiration is done when other respiratory muscles contract to elevate the ribs and increase the transverse and anterior/posterior dimension. This increases the anterior-posterior dimension (elevating ribs) and transverse dimensions (rotating ribs) during high oxygen requirements. Elevating the ribs produces a pump handle movement while rotating the ribs produces a bucket handle movement.

Quite expiration is passive, relying on the elastin fibers in the thorax to recoil and force the air back out. In patients with emphysema, the elastin fibers are destoryed, preventing efficient quiet expiration. Active expiration uses contracting abdominal muscles to force the air out.


 * 4. Describe the anatomy of the breast. What is the clinical significance of the lymphatic drainage in this region?**

Breast is composed mostly of adipose tissue surrounding the mammary glands which are embedded into fatty lobules. The mammary glands connect with the lactiferous ducts which become dialated into lactiferous sinuses and exit through the nipple. The suspensory ligaments of cooper hold the cutaneous tissue aorund the lobules and connects it with teh subcutaneous connective tissue septa of the dermis. This produces the characteristic shape of the breasts and allows some movement of the breast independent from the chest wall. The retromammary space is a thin layer of connective tissue between the subcutaneous fat and glands of the breast and the fascia of pectoralis major.

The breast is innervated by the 4th-6th intercostal nerves which supply sympathetic and sensory fibers. It is vascularly supplied by 4 arteries: the tributaries of the internal thoracic artery, the pectoral branches of hte thoracromial artery, the lateral thoracic artery, and the posterior intercostal artery. Blood drains mostly from the axillary vein, with some from the internal thoracic vein.

Lymphatic drainage goes to axillary, clavicular, sternal, and phrenic lymph nodes. Most drainage goes to the axillary nodes because the glands in the breast are usually closest to the axilla (superior lateral quadrant).


 * 5. Describe intercostal mucles.**

The intercostal muscles include the external intercostal muscles/membrane that elevates the ribs. These mucles have fibers that run medially and becomes a membrane as it nears its ventral terminus. The internal intercostal muscles/membrane action is unclear. The innermost intercostal muscle/membrane functions in respiration but its function is also unclear. Both the fibers of the internal and innermost intercostal muscles run laterally. The internal intercostal muscles becomes a membrane as it nears its dorsal terminus while the innermost intercostal muscles become membranes at both the dorsal and ventral terminus.


 * 6. What nerves, arteries and veins supply the thoracic wall.**

The thoracic wall is supplied by the neurovascular bundle. Veins drain into the azygous system through the internal thoracic vein. Arteries supply blood from the posterior intercostal artery which is supplied byt eh thoracic aorta and the anterior intercostal artery which is supplied by the internal thoracic artery. Nerves from the ventral rami of T1-T12 become the subcostal nerves, dermatomes, and myotomes.


 * 7. Describe the arrangement of the intercostal nerve, artery, and vein within the intercostal space.**


 * 8. Describe the major anatomical compartments within the thoracic cavity: pleural cavities and the mediastinum.**