Thoracic cavity

Mediastinum The space in the thoracic cavity between the pleural sacs and behind the sternum. 

The heart is located in the center of the thoracic cavity. It sits directly above the muscles of the diaphragm, which separates the thorax from the abdomen, and lies beneath the sternum between the two lungs. The heart is enclosed and anchored in place by a double-walled fibrous sac referred to as the pericardium. The membranes of the pericardium produce a small amount of pericardial fluid that minimizes friction produced by the movement of the heart when it beats. To function mechanically as a pump, the heart must have ... 

Thoracic volume. The volume of the thoracic cavity increases during inspiration and decreases during expiration. 

Assisting the diaphragm with inspiration are the external intercostal muscles, which connect adjacent ribs. When the external intercostal muscles contract, the ribs are lifted upward and outward (much like a handle on a bucket). Therefore, contraction of these muscles causes an increase in the horizontal dimension of the thoracic cavity and a further increase in thoracic volume. The external intercostal muscles are supplied by the intercostal nerves. 

Deeper inspirations are achieved by more forceful contraction of the diaphragm and external intercostal muscles. Furthermore, accessory inspiratory muscles, including the scalenus and sternocleidomastoid muscles, contribute to this process. Located mainly in the neck, these muscles raise the sternum and elevate the first two ribs. As a result, the upper portion of the thoracic cavity is enlarged. 

The second factor is motion. The lung in the upper trunk (thoracic cavity) is encased by a lining membrane known as the visceral pleura. In fact, this is a dual membrane one membrane covers the lung and a second membrane lines the chest wall (the parietal pleura, see Fig. 3.1). Characteristics of the pleura are discussed later, but we mention this important tissue here because the movements of the lung are facilitated by the juxtaposition of the visceral and parietal pleura and the thin layer of fluid between them. 

The fluid in the lung tissues may drain either toward the pleura or toward the center of the thoracic cavity (Fig. 3.5). The pleural fluid returns through the lymphatics to the central thoracic cavity, where a duct opens into the venous circulation. Thus, the fluid transported from lung tissue is returned to the systemic blood circulation by the lymphatics. Alternatively, fluid can be transported directly by and into the central lymphatic system. 

Malignant mesothelioma, described more than 100 years ago, is a comparatively rare tumor that occurs in the pleura and peritoneum, membranes that surround the lungs, line the thoracic cavity, surround the gut, and line the abdominal cavity. The survival time of mesothelioma patients is often less than a year, in spite of chemotherapy and radiotherapy. Combined therapy and surgical resection in cases of early diagnosis, a treatment currently being tested, has produced a few long-term (more than five years) survivors (Ant-man, et ah, 1980 Antman et ah, 1983), usually in cases with peritoneal rather than pleural involvement. 

Pleurisy Inflammation of the pleura, the membranes that line all internal and external structures of the lung and thoracic cavity. 

In 1971 the National Academy of Science published a 40-page report, Asbestos The Need for and Feasibility of Air Pollution Controls, (Cooper, 1971) summarizing the illnesses associated with occupational exposure to asbestos and the risks of developing asbestosis, pleural calcifications, and cancers of the pulmonary and gastrointestinal tracts and thoracic cavity. Based on the evidence, the committee recommended control and reduction of dust containing fibrous inorganic materials in the workplace it also discussed nonoccupational exposure to asbestos. 

The thoracic cavity is opened by a ventral sagittal section to the left side of the sternum, cutting through the ribs. 

The thymus, lungs, and heart are first observed in situ in the thoracic cavity. 

Unlike the fixed rodent specimens, the skin and subcutaneous fat are removed from the non-rodent fetuses either before (minipigs) or after (rabbits) microdissection of the abdominal and thoracic cavities. The carcass is then processed for skeletal examination. The ventral abdominal wall is carefully removed. The forelimbs are pinned back on the cork board. 

This is very much like your lungs, by the way. As your diaphragm contracts, it reduces the pressure in the thoracic cavity to about 600 Pa below atmospheric pressure, and about 500 mL of air is drawn into your lungs. Note that we have used an idealized object (a frictionless piston) in this example. While such an object does not exist, it is frequently useful to incorporate such idealizations into working models to help us understand more complicated systems. Now, back to our frictionless piston with 2.5 L of air. How much work is done when the piston slides to a new volume of 3.0 L, assuming the pressure remains constant ... 

Robert Boyle reported that the volume of a fixed sample of gas is inversely related to pressure, as long as the temperature is constant. As the pressure increases, the volume decreases, and vice versa. This is the basis of breathing. During inspiration, the diaphragm muscle contracts and pulls downward, thereby increasing the volume of the thoracic cavity. The gas pressure in the lungs decreases to less... 

Fig. 2. Tracings of lung airflow, transpulmonary pressure, and lung volume changes during spontaneous breathing in a rat. Airflow was measured directly using a head-out plethysmograph chamber, while pleural pressure was measured using a pressure sensitive catheter placed into the esophagus within the thoracic cavity. The functional endpoints can be automatically calculated for each breath using a data acquisition and analysis software system.

Pleural pressure is measured chronically in conscious rats by surgically implanting a fluid-filled polyurethane catheter (length = 10 cm O.D. = 0.7 mm) attached to a pressure-sensitive radiotelemetry transmitter (Model TA11PA-C40, Data Sciences International, St. Paul, MN) beneath the serosal layer of the esophagus and within the thoracic cavity (see Figure 3). 

An easy one. You told me so a moment ago, but the condition of the corpse proves it. I returned my attention to my master. The stroke missed his heart and likely penetrated the aorta, accounting for the massive hemorrhage in the dorsal area. A heart wound would not have bled so much. He died of exsanguination and asphyxiation. I mean he bled to death, but he may have suffocated first, as his thoracic cavity filled with blood. The punctures are so tiny it would not be possible to remove the sword and replace it from the opposite direction without leaving evidence. I estimate that he died about nine o clock last night, but you can undoubtedly judge that more closely than I can, master. ... 

---