Oct 30 - Thorax and Mediasternum Flashcards
What is the role of the thoracic wall?
The thoracic wall, or ribcage, protects the contents of the thorax (lungs, heart, great vessels, liver, spleen)
Name the three components of the thoracic wall
12 thoracic vertebrae
12 pairs of ribs
Sternum
What does the sternum compose of?
Manubrium
Body
Xiphoid process
Where do you find the sternal angle?
At the level of the second rib
Describe the ribs of the thoracic wall
Each rib has a bony part (costo-) and a cartilage part (chondro-). All 12 pairs of ribs attach posteriorly to the vertebrae (mostly synovial joints). Most ribs show an inferior and medial costal groove to protect intercostal vessels and nerves
What are true ribs? How many are there?
The costal cartilages of true ribs articulate directly with the sternum. Ribs 1 through 7 are true ribs
What are false ribs? How many are there?
The costal cartilages of false ribs connect with with the cartilage of other ribs. Ribs 8 through 10 are false ribs
What are floating ribs? How many are there?
Floating ribs don’t articulate with the sternum. Ribs 11 and 12 are floating ribs
What happens to the ribs during inspiration?
The sternum is slightly elevated, increasing the anterior-posterior dimensions of the thoracic cavity. The lower ribs are elevated, increasing the transverse diameter of the thoracic cavity
What are the main two muscles of the thoracic wall involved in inspiration?
Scalenus muscles and the external intercostal muscles elevate the ribs
What are the main four muscles of the thoracic wall involved in expiration?
The internal intercostal muscles, the innermost intercostal muscles, the transverse thoracis muscle and the subcostal muscles depress the ribs
Describe the external and internal intercostal muscles?
The external intercostal muscles go from posterior to anterior downwards (hands in pockets direction) and the internal intercostal muscles are perpendicular to the external. There is a membrane between the external intercostal muscles and the sternum and between the internal intercostal muscles and the vertebral column
What innervates the muscles of the thoracic wall muscles? What innervates the scalenus muscles?
The thoracic wall muscles are innervated by the intercostal nerves. The scalenus muscles are innervated by the cervical plexus
What are the openings created by the ribcage?
The superior and inferior thoracic aperture
What closes the inferior thoracic aperture?
The diaphragm, separating the thorax and the abdominal cavity
Describe the diaphram
Dome-shaped, musculotendinous, thin muscle. Divides in two: the right and left hemidiaphragm joined by the central tendon. It originates from the xiphoid process and the anterior surfaces of L1-L3 and inserts in the central tendon
Which side of the diaphragm is bigger? Why?
The right hemidiaphragm is bigger because of the heart on the left side and the liver in the abdominal cavity on the right
The diaphragm separates incompletely the thoracic cavity from the abdominal cavity. What travels through?
The aorta (aortic aperture), the inferior vena cava (vena caval aperture) and the esophagus (esophageal aperture)
When is the diaphragm active (what is the role of the diaphragm?)
Principal muscle of respiration. Also active during coughing
What innervates the diaphragm?
The phrenic nerve (C3, C4, C5)
What are the two main arteries that supply blood to the thoracic wall?
The thoracic aorta and the subclavian artery
What two arteries do they intercostal arteries derive from?
The posterior intercostal arteries derive from the aorta and the anterior intercostal arteries derive from the internal thoracic artery (derived from the subclavian artery)
Describe the thoracic venous system
The inferior vena cava splits into the azygous vein, which collects blood from the right posterior intercostal veins then merges with the superior vena cava. The blood from the left posterior intercostal veins drains hemiazygous vein, which connects to the azygous vein. The internal thoracic vein collects blood from the anterior intercostal veins and merges with the superior vena cava
What do the ventral rami of the thoracic spine do?
They remain segmental (they don’t form plexuses). T1-T6 are considered intercostal nerves. T7-T12 are considered thoracoabdominal nerves. They provide motor innervation for the muscles of the thoracic and abdominal wall. They also provide sensory innervation for the dermatomes and costal parts of the diaphragm. Finally they provide sympathetic innervation for the skin (sweat glands, blood vessels)
What is special about the ventral ramus of T12?
It forms the subcostal nerve (antero-lateral abdominal region)
What do the second and third intercostal nerves do?
They give rise to the intercostobrachial nerves, which at the mid axillary line penetrate the serratus anterior muscle to enter the axilla and arm
What is at the level of T4
The nipples
What is at the level of T10?
The navel
Name the contents of the 11 intercostal spaces
Intercostal muscles (external, internal and innermost), blood vessels and nerves
Name the first layer of connective tissue deep to the ribs
The fascia endothoracica. It is attached to the ribs and the intercostal muscles and covers the thoracic cavity
What is between the two pleural layers?
Pleural fluid, which fill the pleural cavity
What is the pleura?
Serous epithelial layer with subepithelial connective tissue
Name the two continuous parts of the pleura
The parietal pleura, which attached to the endothoracic fascia and the visceral pleura, which is attached to the lung surface
How many pleural cavities are there?
Two, one for each lung. The two cavities are completely separate.
Besides separating the parietal and visceral layers, what is the role of the serous fluid?
To reduce the friction between the pleural layers during breathing
What happens if air enters the pleural cavity?
The lung will collapse
Name the parts of the parietal pleura
The mediastinal pleura, the costal pleura and the diaphragmatic pleura
Name the nerve supplies of the parietal pleura
The costal pleura is innervated by the intercostal nerves. The mediastinal and diaphragmatic pleura are innervated by the phrenic nerve
Which part of the pleura can sense pain
The parietal pleura. The visceral pleura has no pain receptors
What are the two parts of respiration?
Inspiration and expiration
Describe inspiration
Muscle actions increase the thoracic space in all three dimensions. Because the parietal pleura is attached to the thoracic wall, the lungs are forced to expand, decreasing the pressure within in the lungs below that of the atmosphere. Air passively rushes inwards (down the pressure gradient)
Describe expiration
It’s passive; the muscles of inspiration relax. The air in the lungs is forced to move out of the lungs because of the high elasticity and retractility of the lung tissue. Muscles of expiration work during forced expiration
How many lobes does the left lung have?
Two lobes. They are separated by the oblique fissure
How many lobes does the right lung have?
Three lobes. The horizontal fissure separates the superior and middle lobes and the oblique fissure separates the inferior lobe from the superior and middle lobes
What attaches the lungs to the heart and trachea?
The hilum/root of the lung
Name the contents within the hilum of the lung (8)
Pulmonary artery, pulmonary veins, bronchus, autonomous nerves, lymph nodes, bronchial arteries, bronchial veins, lymphatic vessels
What is the role of bronchial arteries/veins? How are they different from pulmonary arteries/veins
They supply the lungs with arterial blood required to function (and return it to the heart). They pulmonary arteries/veins go to the lungs to receive oxygen and return to the heart to be pumped to the body
What lung is more likely to receive foreign bodies during aspiration?
They will more likely be found in the right bronchus because the left bronchus is much more deviated laterally
How many bronchopulmonary segments does the right lung have?
10 bronchopulmonary segments
How many bronchopulmonary segments does the left lung have?
9 bronchopulmonary segments
Describe the lymphatic drainage of the lungs and bronchi
The subpleural and peribronchial lymphatics drain into the hilar nodes. The 3 lobes of the right lung and the inferior lob of the left lung drain into the right lymphatic duct. The superior lobe of the left lung drains into the left lymphatic duct
What type of lymph nodes drain lungs, heart and mediastinal organs
Tracheobronchial, retro- and partracheal lymph nodes
What is the mediastinum?
It is the space between the two pleural cavities. It’s largely occupied by the heart
Name the areas of the mediastinum
There’s the superior and inferior mediastinum. The inferior mediastinum can be further divided into anterior, middle and posterior. The middle inferior mediastinum is where the heart rests
Name the major organs of the mediastinum (8)
Trachea, esophagus, lymph vessels and nodes, thymus, greater vessels, heart and nerves
Name the major branches of the aorta (8)
Coronary arteries, the brachiocephalic trunk, the left common carotid artery, the left subclavian artery, the posterior intercostal arteries, bronchial arteries, esophageal arteries and the superior phrenic arteries
What is the origin of the phrenic nerve?
The cervical plexus (C3-C5)
The phrenic nerve supplies motor innervation of what?
The diaphragm
The phrenic nerve supplies sensory innervation of what?
The pericardium, the mediastinal and diaphragmatic parietal pleura, and the parietal peritoneum (the underside of the diaphragm
Where can you find the phrenic nerve? What are the benefits and the disadvantage to where it’s found?
It originates from the cervical plexus, on the ventral side of the anterior scalenus muscle, and descends anterior to the roots of the lungs and between the fibrous pericardium and the mediastinal pleura. This is beneficial in the case of spinal cord injury (has to be really high to effect the breathing). The disadvantage is it is easily injured
What is the vagus nerve?
It is cranial nerve 10. It’s the biggest parasympathetic nerve of the body.
Where does the vagus nerve run?
It runs posterior to the roots of the lung. The right and left vagal trunks are adjacent to the esophagus
What does the vagus nerve do?
It contributes to cardiac, esophageal and pulmonary autonomous nerve plexuses
What is the recurrent laryngeal nerve?
A branch of the vagus nerve. It courses lateral to the trachea
What does the recurrent laryngeal nerve do?
Provides motor innervation of most of the muscles of the larynx. Provides sensory innervation of the inferior larynx
How can lung cancer cause hoarsness?
Apical lung cancer may cause hoarsness resulting from invasion of the recurrent laryngeal nerve
What do sphlanchnic nerves innervate?
They innervate abdominal organs
Where do parasympathetic nerves derive from?
The vagus nerve
What do sympathetic and parasympathetic nerves contribute to?
Pulmonary, esophageal and cardiac plexuses
How do parasympathetic affect glands, bronchi and arterials?
They cause secretion in the glands, contraction of the smooth muscles in the bronchi and constriction of the arterials
How do sympathetics affect glands, bronchi and arterials?
They inhibit secretion in the glands, dilation of the smooth muscles and dilation of the arterials
How does the thoracic duct contribute to lymphatic drainage?
It drains lymph about 3/4 of the body. It drains into the left jugular-subclavian junction. It contains the chylomicrons of the small intestine
