Thoracic Cavity Anatomy

Viscera of the Thoracic Cavity

• In a transverse section, the thoracic cavity is kidney-shaped.
• It is an oval space deeply indented posteriorly by the thoracic vertebral column as well as the heads and necks of the ribs articulating with it.
• The thoracic cavity is divided into three compartments: the right and left pulmonary cavities, housing the lungs and pleurae which mostly fill the cavity, and the mediastinum.
• The mediastinum lies between and separates the pulmonary cavities.
• It contains the heart, great vessels' thoracic portions, trachea, esophagus, thymus, and lymph nodes.
• Vertically, the mediastinum stretches from the superior thoracic aperture to the diaphragm, and from the sternum to the thoracic vertebral bodies front to back.

Pleurae, Lungs, Trachea, and Bronchial Tree

• Each right and left pulmonary cavity is lined by a pleural membrane (pleura) that also covers the external lung surface occupying these cavities.
• Visualizing the pleurae and lungs is possible by imagining a fist pushing into a partly inflated balloon.
• The inner balloon part close to the fist (representing the lung) corresponds to the visceral pleura, while the remaining outer balloon wall corresponds to the parietal pleura.
• The space between the balloon layers, filled with air here, is like the pleural cavity, which only contains a thin liquid film.
• Where the balloon's inner and outer walls meet at the wrist (representing the lung root) are continuous, as are the visceral and parietal pleurae that form the pleural sac.
• The lung sits outside the pleural sac but is contained within, similarly to how the fist is surrounded by the balloon but remains outside of it.
• The figure illustrates lung and pleura development: developing lungs invaginate into the pericardioperitoneal canals during the embryonic stage, which form the precursors of the pleural cavities.
• Lung buds are covered by invaginated coelomic epithelium, which turns into visceral pleura how the balloon covers the fist.
• Parietal pleura forms from the epithelium lining the pericardioperitoneal canal walls.
• Pleural cavities separate from the pericardial and peritoneal cavities during embryogenesis.

Pleura

• Each lung is enveloped by a serous pleural sac consisting of two continuous membranes: the visceral pleura, which forms the lung's shiny outer surface, and the parietal pleura, which lines the pulmonary cavities.
• The pleural cavity, a potential space between the pleura layers, contains a thin layer of serous pleural fluid.
• The pleural fluid lubricates pleural surfaces and allows them to slide smoothly over one another during breathing.
• Surface tension in the pleural fluid maintains lung surface contact with the thoracic wall.
• As a result, the lung expands and fills with air as the thorax expands.
• The visceral pleura (pulmonary pleura) intimately covers the lung, adhering to all its surfaces, including within the horizontal and oblique fissures.
• In a cadaver, the visceral pleura cannot be separated from the lung surface.
• It provides the lung with a smooth, slippery surface, allowing it to move freely over the parietal pleura.
• The visceral pleura becomes the parietal pleura at the lung hilum, where various structures forming the lung root (e.g., bronchi and pulmonary vessels) enter and exit.
• The parietal pleura lines the pulmonary cavities, attaching to the thoracic wall, mediastinum, and diaphragm.
• It is thicker than the visceral pleura and can be separated from the surfaces it covers during cadaveric and surgical dissections.
• The parietal pleura includes the costal, mediastinal, and diaphragmatic portions and the cervical pleura.

Parietal Pleura

• The costal part of the parietal pleura (costal or costovertebral pleura) covers the inner surfaces of the thoracic wall.
• It is separated from the thoracic wall's internal aspect (sternum, ribs, costal cartilages, intercostal muscles, intercostal membranes, and thoracic vertebrae sides) by the endothoracic fascia.
• This thin, extrapleural layer of loose connective tissue serves as a natural separation plane for surgically separating the costal pleura from the thoracic wall.
• The mediastinal part of the parietal pleura (mediastinal pleura) covers the mediastinum’s lateral aspects, the compartment separating the pulmonary cavities and their pleural sacs.
• The mediastinal pleura continues superiorly at the neck root as the cervical pleura, to connect anteriorly and posteriorly with the costal pleura, and from underneath with the diaphragmatic pleura.
• Above the lung root, it forms a continuous sheet from the sternum to the vertebral column passing anteroposteriorly.
• The mediastinal pleura reflects laterally at the lung root become continuous with the visceral pleura.
• The diaphragmatic portion of the parietal pleura (diaphragmatic pleura) covers the superior or thoracic face of the diaphragm on either side of the mediastinum, except along the costal attachments (origins) and where the diaphragm is connected to the pericardium surrounding the heart
• A thin and more elastic lamina of the endothoracic fascia, i.e. phrenicopleural fascia, attaches the diaphragmatic pleura to the muscular fibers of the diaphragm
• The cervical pleura covers the apex of the lung (the part of the lung that extends superiorly through the superior thoracic opening into the root of the neck).
• It is the superior continuation of the costal and mediastinal portions of the parietal pleura.
• A cup-shaped dome characterizes the cervical pleura, forming the pleural cap over the apex reaching approximately 2-3 cm above the middle third of the clavicle and at the level of the neck of the 1st rib.
• The cervical pleura is reinforced by a fibrous extension of the endothoracic fascia, the suprapleural membrane (Sibson's fascia).
• The membrane attaches to the inner edge of the 1st rib and the transverse process of vertebra C7.

Key Takeaways: Pleurae, Lungs, Trachea, and Bronchial Tree

• The thoracic cavity has three compartments
• Two bilateral pulmonary cavities partitioned by the central mediastinum
• Parietal pleurae membranously line the pulmonary cavities, reflecting around the lungs and roots, turning into the lung's intimately lining visceral pleura.
• The potential, empty cavity fluid-filled between creates a fluid film that keeps the lungs open.
• This pleural liquid prevents lung collapsing and supporting thoracic breathing expansion.
• Parietal pleura regions are named after underlying coverings: costal, mediastinal, diaphragmatic.
• Neck top extends to the neck roots forming the cup superior to thoracic rib bones including the part of the clavicle
• Parietal sensitive pleura in supplied by phrenic and intercostal nerves while lungs aren't
• Exterior throacic cavity's protrution by abdominal organs diaphragm create periferic groove along inferior margin
• Fluid collects within this space.

Lungs

• Lungs consist of vital organs for venous supply for gass exchange
• Air and blood enter the lungs from a root of artery veins connected by an artery on the primary branch of the hilum
• Pyramid shapes cover the outer surface and edge.
• There are 3 lobes left and right covered separately by horizonatal openings
• The left lobe presents depression that is anterior to a heartbeat

Bronchial Tree

• Structure identified by cartilage
• Trunk bifurcation level and shape varies: the right is vertical with a larger bore
• Bronchi and arteries travel with a common trajectory with each artery supply to the lung by second level and tertiary

Overview of the Mediastinum

• The mediastinum centrally between two lungs contains almost all organs
• Covering of pleural membrane, except lungs
• Superior throacic aperture to the diaphragm

Description of structure

• Composed of fluid and tissue
• Made of vascular lymph
• Elastic properties to alliw lung movement
• Divides upper lower mediastinum
• Inferior divided according to position like pericardia
• Other structures like organs like the espohagus passing
• Connected superiorly for supporting arteries

Pericardium

• Contains great vessel and heart
• 2 membranes that make a sack with outer later being fibrous to the connecting tendon
• Internal is a membrane that has various parts and vessels
• Composed with flat area connecting to areas in the diaphragm

Fundamental Points: General Vision of the Mediastinum and Pericardium

• The mediastinum acts like an inflatable container.
• The mediastinum moves in response to movement around it combined by gravity
• Upper region has traces upper of great vessels
• A middle is heart main portion.
• Pericardium sacs surround heart and vessels limited amount.
• Does not expand by connecting itself to organ and membrane
• The liquid prevents surface contact to support movememnt
• Causes sensation and referred pain

General Vision: Walls, Cavities, Regions and Planes.

• The abdominal cavity which is the first area is continuous and extends to the diaphram
• Does not contain own base
• Thoracic cage protected by localized abdominal organ
• Contains digestive and renal with the spllen

Localization of organs is split nine section via

• Sagittal transverse
• Passing upper and middle
• A palpabale point on the tube

Anatomical Definition

• Clinical quadrants defined by point like the vertebrae umbilical
• For general structure determine region

Pelvic Cavity

• Protect abdominal cavities that impact tissues
• Limit base by tendons
• Study separately since they are similar

Description of anatomy

• Muscular wall surrounding by pelvic muscles being and opening
• Curves surrounding bone
• Mechanical structure is affected by curves

Pelvic Fascia

• Connecting tissues for organs and muscules in between the regions

Type of structure

• Connected to the parietal and wall tissues
• Continuous in muscle and membrane

Tissue Structure

• The tissue envelopes a variety of organs
• Thick area that connects to areas between ligaments

Pélvic Regions

• Region bound by pelvis and thighs
• Area covered in the muscle
• Support different aspects in relation to bowel activity
• Region by the pelvis is important for connection to other organ
• Membranous tissue that cover organs and lines of muscles
• Contains fat within vessels acting to both bind and anchor the organ.