Thoracic Wall and Cavity Flashcards
What is the the main function of the thoracic wall?
to provide a mechanism for increasing the size of the thoracic cavity, which is essential for inspiration and expiration
What is the most important functions of the organs in the thorax?
delivery of O2 to cells of the body that they require for tissue metabolism and removal of the CO2 generated by metabolic activity.
T or F. Blood is never blue
T
Oxygenated arterial blood is bright red due to the color of what?
oxyhemoglobin.
Deoxygenated venous blood is dark red, due to the color of what?
deoxyhemoglobin. The level of O2 affects the color of blood, but the level of CO2 does not.
T or F. Gas exchange occurs as air passes through the pharynx, larynx, trachea, bronchi and bronchioles
F. These structures are collectively referred to as “dead space”, at least as far as gas exchange goes.
Where does gas exchange occur?
The alveolus. This is where hemoglobin that is contained within erythrocytes binds O2 that has diffused from the air space into the blood, and it is where CO2 is dissipated.
There are roughly 300 million total alveoli in the two lungs.
Gas exchange occurs through which structure of the alveolus?
the “respiratory membrane”
T or F. CO2 diffuses through tissues 10-fold faster than O2
T. Anything that causes the respiratory membrane to become wider will cause problems for the diffusion of oxygen.
CO2 diffuses through tissues 10-fold faster than O2, so the barriers are not as much of an issue in eliminating CO2.
What is stroke volume?
volume of blood pumped from ventricles with each beat
The inner aspect of the thoracic wall is lined by a fascial layer called what?
endothoracic fascia. The endothoracic fascia along with fascia of the diaphragm enclose a single thoracic cavity.
The thoracic cavity is further subdivided into what?
a centrally located mediastinum and two lateral thoracic spaces
What structures does the mediastinum contain?
the heart (and pericardium), the great vessels (e.g. aorta, superior vena cava) , trachea, esophagus, nerves and lymphatics
What structures do the lateral thoracic spaces contain?
pleural membranes and lungs
Describe the events associated with expiration
The intercostal muscles and various ancillary muscles attached to rib cage have relaxed and the ribs rotate downward anteriorly due largely to elastic recoil and gravity. The muscle fibers of the diaphragm have relaxed, so upward pressure from abdominal contents (due to their mass, to the attachments of the various organs to other structures, and to abdominal wall muscular contractions) pushes the diaphragm superiorly. Thus, the space within the thoracic cavity is becoming reduced in size. If the abdominal muscles contract while the diaphragm is relaxed, abdominal viscera will be pushed further superiorly and thoracic volume reduced further.
Describe how the size of the thoracic cavity is affected by inspiration
When inspiration begins, external intercostal muscles and ancillary muscles contract and the diaphragm contracts. The rib cage expands in all dimensions. In quiet breathing, thoracic cavity expansion can be accomplished largely by contraction of the diaphragm.
What are the to pleura of the lungs?
visceral and parietal
The visceral pleura is fused directly to the surface of the lung, while the parietal pleura is bound to the inner surfaces of the lateral thoracic spaces (e.g. thoracic wall, diaphragm, mediastinum). The pleural cavity is only the space inside the pleural sac.
T or F. The lungs lie in the pleural cavity.
F.
T or F. Normally, the pleural cavity is only a potential space filled with a few cc of pleural fluid, a lubricating fluid constantly produced by capillary fluid outflows and reabsorbed by lymphatic vessels.
T. Larger amounts of pleural fluid can accumulate as a result of disease, compromising lung function.
Note on the flow of structures from the larynx to the lungs
The trachea begins at the lower border of the larynx, descends in the midline into the superior mediastinum and ends by dividing into two 1° bronchi at the level of the sternal angle. The bronchi extend into the lateral thoracic spaces where they are continuous with the lungs and covered by pleural membranes
What are the divisions of the visceral pleura?
There are none (as opposed to the parietal pleura)
What are the divisions of the parietal pleura?
the cervical (apical) pleura fills the apex of the lateral thoracic space, rising slightly above the first rib
the mediastinal pleura is bound to the structures of the mediastinum
the diaphragmatic pleura is bound to the upper surface of the diaphragm
the costal pleura is bound to the inner aspect of the thoracic wall
Where is the costodiapragmatic recess located?
in the space between the visceral and parietal pleuras at the border of the diaphragmatic and costal portions of the parietal pleura.
When the thoracic wall expands and the diaphragm contracts, this space opens up, creating enough negative pressure for the lung to expand and begin to fill the space. Even in deep inspiration
Do the lungs ever completely fill the costodiaphragmatic space?
No
What is Pleurisy?
an inflammation of the pleural membranes. Pain from inflamed regions rubbing against each other can be severe and it is sensed through, for instance, intercostal nerve innervation of parietal pleura, not through visceral pleura which does not receive pain fibers.
T or F. As the lung expands into the spaces created by muscular contractions, the alveoli expand
T. When the lung collapses, the alveoli shrink to a much smaller size, no air exchange, reduced blood flow.
What is Boyle’s Law?
it says that if a certain space contains a given number of gas molecules and the space is expanded, the pressure inside the space will decrease. In contrast, if the space is decreased, pressure will increase. The pressure is due to the forces generated by molecules bouncing off each other.
So, as the alveolar spaces of the lungs enlarges, the pressure drops. The difference between the lowered pressure in the lungs and the higher pressure of the external environment forces air into the expanding space.
What type of fibers are abundant in the lungs?
elastic fibers bitches
What is the pressure of the pleural cavity at rest?
At rest, pleural cavity pressure is ~756 mm Hg, slightly less than the pressure within the lung, which is equal to atmospheric pressure (i.e. 760 mm Hg). This is not a big difference in pressure, but it is enough to keep the lung expanded, with the visceral pleura pressed up against the parietal pleura.
Describe pressures of the lungs and pleural cavity in relation to inspiration
When the thoracic wall expands, the parietal pleura is attached to it, so it expands along with the wall. This reduces the pressure in the pleural cavity a little bit more, because it is making the space larger. So, the pleural pressure is already lower than that within the lungs, but muscular contraction causes a further reduction in pressure. This greater negative pressure pulls on the visceral pleura and expands the lungs into recesses, such as the costodiaphragmatic recesses. Thus, pressure within the alveoli is reduced. At that point, the pressure outside is greater than in the lungs, so air is pushed into the alveoli, until equilibrium is established again.
When the muscles that expanded the thoracic cavity quit contracting, the size of the thoracic cavity begins to shrink, thus slightly increasing pressure in the pleural cavity and, consequently, in the alveoli, so air is forced out to, once again, establish equilibrium.
The phrenic nerve arises from which nerve root?
C4
The internal jugular veins join the subclavian veins behind what structure?
the sternoclavicular joints
The internal jugular veins join the subclavian veins behind the sternoclavicular joints, to form what?
the right and left brachiocephalic veins
The brachiocephalic veins join to form what?
SVC
the superior vena cava, which empties venous blood into what?
the right atrium
Immediately superior to the right atrium, what empties into the SVC and drains the posterior mediastinum?
the azygos vein
Do the major arteries supplying oxygenated blood to the head, neck and upper limbs generally lie posterior or anterior to the major veins of the superior mediastinum (i.e. the left and right brachiocephalic veins, etc)
posterior
The ascending aorta arises from what structure?
the left ventricle (It leaves the pericardium at roughly the plane of the sternal angle). Here, the name changes to the aortic arch
The aortic arch both begins and ends at the plane of the sternal angle, with the arch then becoming what?
the descending aorta
What are the branches of the ascending aorta?
only the right and left coronary arteries
What is the first branch of aortic arch?
the brachiocephalic trunk
the brachiocephalic trunk delivers blood to which structures?
It primarily delivers blood to the arm and head (arm-brachio, cephalic-head) on the right side.
NOTE: but it is not called the right brachiocephalic trunk. Just brachiocephalic trunk (because there is not a left brachiocephalic trunk)
Where does the brachiocephalic artery/trunk branch? Into what?
Posterior to the sternoclavicular joint (and posterior to the junction of internal jugular and subclavian veins), the brachiocephalic artery branches into the right subclavian and right common carotid arteries. .
What is the second branch of the aortic arch?
the left common carotid artery
What is the third branch of the aortic arch?
the left subclavian artery
What is the sole motor supply to the diaphragm?
the phrenic nerve (C4)
T or F. The phrenic nerves enter the superior thoracic aperture by passing anterior to the subclavian arteries and posterior to the subclavian veins
T.
What artery travels with the phrenic nerve?
The pericardiacophrenic artery (a branch of the internal thoracic artery)
As the internal thoracic artery approaches the inferior aspect of the thoracic wall, it divides into what?
the superior epigastric artery and the musculophrenic artery
Why is the visceral pleura not sensitive to pain or touch?
The visceral pleura is supplied with General Visceral Afferent innervation, but is not supplied with nerves for General Somatic sensation. So, the visceral pleura is not sensitive to pain or contact.
The cervical pleura receives sensory innervation from what sources?
phrenic and intercostal nerves
The mediastinal pleura receives sensory innervation from what sources?
phrenic nerves
The diaphragmatic pleura receives sensory innervation from what sources?
phrenic nerves in the central part of the diaphragm and from intercostal nerves in the peripheral part of the diaphragm
The costal pleura receives sensory innervation from what sources?
intercostal nerves
The vagus nerve (cranial nerve X) exits the skull along with the internal jugular vein and travels inferiorly in the neck between what two structures?
the internal jugular vein and internal carotid artery
T or F. Both the left and right vagus nerves lie just lateral to the phrenic nerves and both are between the major arterial and venous channels
T. However, their paths differ due to the asymmetric arterial branches coming off the aortic arch
Describe the route of the left vagus nerve
The left vagus follows the left common carotid artery to the aortic arch and crosses it anteriorly. Here, it gives off the left recurrent laryngeal nerve which hooks posteriorly under the inferior border of the arch
The recurrent laryngeal innervates which structures?
trachea and esophagus
Describe the route of the right vagus nerve
follows the internal and then common carotid arteries and passes anterior to the subclavian artery just behind the sternoclavicular joint. The right recurrent laryngeal hooks posteriorly under the inferior border of the right subclavian artery in the neck, just as the subclavian splits from the brachiocephalic trunk
Other than its point of origin, the right recurrent laryngeal nerve has essentially the same superior course as the left, lying in the groove between trachea and esophagus on its way to the larynx
The right vagus nerve continues through the superior mediastinum alongside the brachiocephalic trunk.
What structures attach to the manubrium?
the clavicle and the 1st rib
Which ribs are considered ‘true ribs’
1-7. These attach to the sternum directly
Which ribs are considered ‘false ribs’. Why?
Ribs 8-10 are called false ribs, because their cartilages attach to each other successively, and then to the 7th costal cartilage. The attachment of costal cartilages to each other creates a so-called costal arch demarcating the inferior border of the thoracic skeleton anteriorly and laterally.
Ribs 11-12 are called what? Why?
The 11th and 12th ribs have cartilaginous tips but they do not attach to the others. These are called floating ribs.
What are the muscles of the intercostal spaces?
external intercostal muscles, the internal intercostal muscles, and an incomplete layer called the innermost intercostals
A small number of innermost intercostal muscle bundles span three ribs and get a separate name. What is it?
subcostal muscles
What maintains the negative pressure of the pleural cavity?
lymphatics that drain the fluid produced by capillaries in the cavity
Where does the thoracic duct drain into systemic circulation?
just distal to the junction of the left subclavian and internal jugular veins (It is sucked in)
What is a pneumothorax?
if there is a hole in the thoracic wall due to a stab wound, as just one example of many possibilities, the intrapleural pressure could equilibrate with atmospheric pressure directly through the opening in the thoracic wall. The lung would then collapse due to its elasticity (lots of smooth muscle and elastic fibers)
What is a tension pneumothorax?
a flap of tissue or some other structure, acts as a one-way valve: air enters with inspiration, but does not exit during expiration. With each inspiration, additional air is brought into the space. This is much more of a medical emergency
What are the two most common sites for thoracentesis?
the 2nd intercostal space with the patient lying down for removal of air and the 6th intercostal space with the patient sitting up for the removal of fluid
What things are found at the sternal angle?
The second rib articulates with the sternum
The fibrous pericardium blends with the adventitia (outer layer of connective tissue) of the superior vena cava and ascending aorta
The azygos vein empties into the superior vena cava
The aortic arch begins and ends
The pulmonary trunk divides into right and left pulmonary arteries
The trachea divides into right and left 1° bronchi
