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Anatomy - Thorax
Terms in this set (81)
What 5 regions does the Primitive Heart tube divide into?
1. Truncus arteriosus
2. Bulbus cordis
5. Sinus venosus
What is the septum primium? What structure appears in it's upper part?
It is a partition in the atrium, deviding it in two. It grows down to fuse with the endocardial cushions. Before fusion is complete, a hole appears called the foramen secundum.
What is the septum secundum?
It is a second, incomplete membrane that develops to the right of the septum primium but is never complete.
What is the foramen ovale?
It is the result of two overlapping defects in the septa. The spetum secundum acts as a valve like structure allowing blood flow from the right to the left side of the heart in the foetus.
What happens at birth with regards to the foramen ovale?
At birth, there is increased blood flow through the lungs and a rise in left atrial pressure causing the septum primium to be pushed across to close the formaen ovale.
What is the fossa ovalis?
It is a little dimple left from the fusion of the septum primum and septum secundum.
What does the sinus venosus become on the left vs. the right?
Left: 4 pulmonary veins
Right: 2 vena cava
How many pairs of arches does the truncus arteriosus give off?
What happens to the the 1st, 2nd and 5th pairs? What about the 3rd? What about the 4th? What about the 6h?
3: carotid artery
4: Right = subclavian artery
Left = aortic arch
6: Right = right pulmonary artery + connection to dorsal aorta disappears
Left = left pulmonary artery + connection with the aortic arch called the Ductus Arteriosus
What is the ductus arteriosus? What does it become in the adult?
A structure in embryo connecting the pulmonary trunk to the aorta.
In the adult, it closes and becomes the ligamentum arteriosum.
Why is the laryngeal nerve positioned differently on the left side compared to the right?
On the right side, because the connection to the dorasl aorta disappears and the 5th arch disappears as well, it goes and wraps around the 4th arch (ie. subclavian artery).
On the left, because the ductus arteriosus is present, the laryngeal nerve remains hooked around the sixth arch (ie. ligamentum arteriosum).
What is the ductus venosum? What does it become in the adult?
It is a foetal shunt. It allows blood to bypass the liver joining the umbilical vein (oxygenated blood) to reach the IVC and then the right atrium.
In the adult, it becomes the ligamentum venosum.
Name two congenital abnormalities that cause malposition of organs in the thorax.
Dextocardia: mirror image of normal anatomy in thorax.
Situs invertus: inversion of all viscera (including abdominal organs)
Name 4 left to right shunt congenital abnormalities.
1. Atrial septal defect (ASD)
2. Ventricular septal defect (VSD)
3. Patent ductus arteriosus (PDA)
4. Eisenmenger's Syndrome
Describe Atrial Septal Defect (ASD).
When the fusion between the septum primium and secundum does not take place (normally within 3 months).
Leads to shunting from the left to the right (left ventricle is stronger).
Describe Ventricular Septal Defect (VSD).
Most common abnormality.
When there is a defect in the muscular part of the septum. May need repair. Causes a left to right shunt.
Describe Patent Ductus Arteriosus.
When then ductus arteriosus doesn't close.
Blood flows from the aorta to the pulmonary artery as oygenated blood returns to the lungs.
Needs surgical correction as it may cause pulmonary hypertension if left alone. of note, AVOID the LEFT LARYNGEAL NERVE!
Describe Eisenmenger's Syndrome.
Consequence of either ASD, VSD or PDA. Due to the left to right shunt, pulmonary HTN develops and overtime becomes so present, that it causes reversed shunting with a right to left shunt.
Name the most important right to left shunt congenital abnormality. What are its 4 major signs?
2. Stenosed pulmonary outflow track
3. Overriding aorta
4. Right ventricular hypertrophy
Presents as cyanosis, because there is a right to left shunt with deoxygenated blood reaching the organs.
Describe Coarctation of the aorta.
Caused by an abnormality of the obliterative process of the ductus arteriosus leading to a stenosis of the aortic arch.
Signs: HTN in upper limbs, weak and delayed femoral pulses.
X-ray: enlarged intercostal arteries causing notching of the inferior border of the rib
What 4 parts fuse to form the diaphragm?
1. Septum transversum (fibrous central tendon)
2. Mesentry of the foregut
3. ingrowth from the body wall
4. Pleuroperitoneal membrane
Describe possible congenital diaphragmatic hernias.
1. Posterolateral hernia through the foramen of Bochdalek (pleuroperitoneal membrane)
2. Hernia through a deficiency of the whole central tendon
3. Hernia through the foramen of Morgagni anteriorly between xiphoid and costal margins
4. Hernia through a congenitally large oesophageal hiatus
What makes the thoracic cage?
1. Vertebral column
2. Ribs and intercostal spaces
3. Sternum and costal cartilage
Which ribs are 'true', 'false' and 'floating'?
True ribs: 1-7
False ribs: 8-10
Floating ribs: 11-12
Describe a typical rib.
Head with 2 articular facets for articulation with the corresponding vertebra
Neck to attach to the costotransverse liagement
Tubercle with a smooth facet to articulate with the transverse process of the corresponding vertebra
Shaft flattened from one side to side with an angle that marks the attachment of the erector spinae. The shaft has a subcostal grove in which the vessels and nerves lie (VAN = vein, artery, nerve)
If inserting a chest drain, would you go above or bellow a rib?
Above of course! To avoid the neurovascular bundle.
V = vein
A = artery
N = nerve
Superficial to deep: external, internal, VAN, innermost
Describe the anatomy of the 1st rib, the vasculature and nerve structures around it.
First rib: short, flat, most curved. Bears a prominent tubercle on the inner border for the insertion of scalenus anterior. In front of the scalenus tubercle, the sublavian vein crosses the rib, behind, there is the sublacian groove for the subclavian artery and lowest trunk of the brachial plexus.
What are the atypical ribs?
Remember, they have "1s and 2s"
Rib 2: less curved than 1
Rib 10: only one articular facet
Rib 11: shallow costal groove
Rib 12: no subcoastal groove, no angle
What are possible complications of rib fractures in general? On the left side compared to the right side?
Damage to underlying structure, leading to a pneumothorax or a haemothorax.
Left side: 9th, 10th and 11th fracture can damage the spleen
Right side: right lobe of liver
How would abnormal 'cervical ribs' present in a patient?
1. Arterial compression and embolization: the rib on the undersurface of the distal portion of the subclavian artery reduces the diameter of the vessel and allows eddy currents to form. Platelets aggregate and atheroma may develop in this region. This debris can be dislodged and flow distally within the upper limb vessels to block off blood flow to the fingers and the hand, a condition called distal embolization.
2. Compression of T1 nerve: the T1 nerve, which normally passes over rib I, is also elevated, thus the patient may experience a sensory disturbance over the medial aspect of the forearm, and develop wasting of the intrinsic muscles of the hand.
3. Compression of the subclavian vein: this may induce axillary vein thrombosis.
What type of cartilage makes costal cartilage?
Hyaline cartilage. Calcifies with age, leading to irregular areas of calcification on chest X-ray.
Describe the anatomy of the sternum. What 3 parts make the sternum?
1. Manubrium: articulates with the clavicle, the first and upper part of second costal cartilages and the body of the sternum forming the angle of Louis.
2. Body: receives most of the second, third and all the way to seventh costal cartilages.
3. Xiphoid process: small and cartilaginous
What important clinical points should be noted prior to splitting a sternum open during cardiothoracic surgery?
Directly posterior to the sternum lies the anterior mediastinum that can contain a retrosternal goitre, thymus or ectopic parathyroid tissue.
Describe the anatomy and epithelium of the trachea.
It is a fibroelastic lumen with U-shaped cartilaginous rings connected by smooth muscle (trachealis) extending from the lower border of the cricoid cartilage (6th cervical vertebra) and terminates into the 2 main bronchi (5th thoracic vertebra).
It is lined with columnar ciliated epithelium.
What are the anterior, lateral and posterior relations of the trachea in the neck?
Anterior: isthmus of the thyroid, inferior thyroid, veins, sternohyoid, sternothyroid
Lateral: lobes of thyroid gland, carotid sheath
Posterior: oesophagus, recurrent laryngeal nerves in the groove between the trachea and oesophagus
What are the anterior and posterior relations of the trachea in the thorax?
Anterior: brachocephalic artery and left common carotid artery, left brachiocephalic vein, thymus
Posterior: oesophagus, recurrent laryngeal nerves
What are the right sided relations of the trachea in the thorax?
Right side: vagus nerve, azygos vein, pleura
What are the left sided relations of the trachea in the thorax?
Left side: aortic arch, left common carotid artery, left
subclavian vein, left recurrent laryngeal nerve, pleura
Note: Rib 1 is wrong on diagram (it's the clavicle)
Describe the anatomy of the right and left main bronchi.
Right main bronchus: wider, shorter, more vertical, passes downwards and laterally behind the ascending aorta and SVC to enter the hilum of the lung, the pulmonary artery lies anterior to it.
It first divides outside the lung into an upper lobe bronchus and then, within the lung, into a middle and lower lobe bronchi.
Left main bronchus: passes downwards and laterally bellow the arch of the aorta, in front of the oesophagus and descending aorta.
It gives off no branches until it enters the hilum, and then divides into upper and lower lobe bronchi in the lung.
What may cause the trachea to be displaced? In which main bronchus are foreign objects more likely to lodge?
Pathological enlargement of surrounding structures such as the thyroid or the arch of the aorta.
Right main bronchus: wider and more vertical.
Describe a tracheostomy. Where do you aim to make your incision? How does this differ from a cricothyroidotomy?
Make a vertical incision downward from the cricoid cartilage passing between the cricoid cartilage and suprasternal notch (between tracheal rings 2-4). The incision goes through the skin, platysma and the pretracheal fascia is split longitudinally.
The isthmus of the thyroid gland will be encountered and may be retracted upwards or divided between clamps to expose the cartilages of the trachea. A longitudinal incision is then made to insert the tracheostomy tube.
What are the broad differences between the left and right lungs?
Right lung: larger than left, divided into 3 lobes with both an oblique and horizontal fissure.
Left lung: has only an oblique fissure, has an anterior cardiac notch, there is the lingula which is the equivalent of the middle lobe in the right lung that is positioned between the cardiac notch and the oblique fissure.
Which chief structures compose the roots of the right lung? How do the arrangement differ on the left side compared to the right side?
From above downwards:
Right lung root: upper lobe bronchus, pulmonary artery, right principal bronchus, lower pulmonary vein
Which chief structures compose the roots of the left lung? How do the arrangement differ on the left side compared to the right side?
From above downwards:
Left lung root: pulmonary artery, bronchus, lower pulmonary vein
How many bronchopulmonary segments are there for each lung?What supplies each segment? Is it possible to remove one individual segment on its own?
There are 10 bronchopulmonary segments for each lung.
Each segment is supplied by a segmental bronchus, artery and vein.
Yes its is.
Where does the pulmonary trunk arise from? Anterior to which structure does it divide into left and right branches?
It arises from the right ventricle. It is directed upwards in front of the ascending aorta and reaches the concavity of the aortic arch.
It divides into left and right branches anterior to the left main bronchus.
Note: on diagram, notice the left and right bronchial arteries that are branches of the descending aorta.
Describe the course of the right pulmonary artery.
It passes in front of the oesophagus and makes its way to the root of the right lung behind the ascending aorta and SVC.
At the root of the lung, it lies between the right main bronchus and the upper lobe bronchus.
Describe the course of the left pulmonary artery. What structures will you find here?
It arises from the pulmonary trunk and runs in front of the left main bronchus and descending aorta. You can find the ligamentum arteriosum here.
The left recurrent laryngeal nerve loops below the aortic arch in contact with the ligamentum arteriosum.
What are the two types of pleura in the lung? Are the left and right pleural cavities joined?
1. Visceral pleura: intimately related to the lung surface and is continuous with the parietal layer over the root of the lung
2. Parietal pleura: applied to the inner aspect of the chest wall, diaphragm and mediastinum.
No. The two pleural cavities are totally separate one from another.
Describe pleural and lung margins in relation to ribs.
- extends above the sternal end of the 1st rib
- 8th rib in mid clavicular line
- 10th rib in midaxillary line
- 12th rib at the lateral border of the erector spine muscles (back)
- apex is 2.5cm above the clavicle
- 6th rib in the midclavicular line
- 8th rib in the midaxillary line
- 10th rib at the lateral border of the erecotr spine muscles (back)
How may you injure the pleura when inserting a subclavian or internal jugular line? What about when opening the loin to approach the kidney or adrenal gland?
The pleura arise above the clavicle into the neck and can be injured.
The pleura descends below the medial extremity of the 12th rib and may be damaged during an incision.
What is the nerve supply to the visceral pleura, the parietal pleura and the diaphragmatic pleura? Which of these are sensitive to pain?
Visceral pleura: autonomic - vagus nerve (not sensitive to pain, only to stretch)
Parietal pleura: somatic - intercostal nerves (sensitive to pain). Pain may be referred to the abdomen (eg. right lower lobar pneumonia may irritate the parietal pleura and refer pain the the right lower abdomen, mimicking acute appendicitis)
Diaphragmatic pleura: phrenic nerve (sensitive to pain)
What are the 3 main openings in the diaphragm? What do they each transmit?
1. Aortic (not really an opening as it lies 'behind' the diaphragm): level of T12, transmits the abdominal aorta, the thoracic duct and the azygos vein.
2. Oesophageal: level of T10, transmits the oesophagus, the vagus nerves and branches of the left gastric artery and veins.
3. IVC opening: level of T8, transmits the IVC and right phrenic nerve.
Describe the anatomy of the diaphragm. What make the lateral and medial arcuate ligaments and what muscles are they related to?
Diaphragm is dome shaped with a peripheral muscular part and a central tendon. The muscular parts arise from the crura, arcuate ligaments, ribs and sternum.
Medial arcuate ligament: condensation of the fascia of psoas major.
Lateral arcuate ligament: condensation o the fascia over quadratus lumborum.
Where do the splanchnic nerves cross the diaphragm? What about the sympathetic trunk?
Greater and lesser splanchnic nerves pierce the crura.
The sympathetic chain passes behind the medial arcuate ligament lying on psoas major.
What is the nerve supply to the diaphragm? Why can irritation of the diaphragm present as shoulder pain?
Phrenic nerve (C3, C4, C5) is the sole motor nerve supply. Is also supplies sensory nerve supply to the central tendon of the diaphragm.
The periphery of the diaphragm is supplied by the six intercostal nerves.
C4 dermatome can be affected (shoulder) if the diaphragm and phrenic nerve are irritated.
How does phrenic nerve palsy present on examination and chest X-ray?
Dullness to percussion at the base of the lung with absent breath sounds on the affected side. On CXR, the diaphragm will be elevated and there will be paradoxical movement of the diaphragm on respiration.
Aetiology: malignancy/trauma and iatrogenic/ direct trauma/ infiltration/ neuromuscular disease/ inflammation/ direct compression
What is the difference between thoracic and abdominal breathing?
Thoracic: movements of the rib cage.
Abdominal: contraction of the diaphragm. When the muscular fibres contract the central tendon descends causing the negative intrapleural pressure to increase and expand the lungs.
Describe the heart's overall anatomy.
What are the 3 surfaces of the heart? What are the 3 borders of the heart?
1. Anterior: right atrium, right ventricle and narrow strip of the left ventricle, auricle of left atrium
2. Posterior: left ventricle, left atrium with 4 pulmonary veins
3. Inferior: right atrium with IVC entering it and lowe part of both ventricles
1. Right: right atrium with IVC and SVC
2. Inferior: right ventricle and apex of left ventricle
3. Left: left ventricle, auricle and atrium
What is the crista terminalis? What muscles originate from this? What about the fossa ovalis? In what heart chamber can you find these?
In the right atrium.
Crista terminalis: crest that separates the smooth walled posterior part of the atrium (derived from the sinus venosum) from the rougher area (due to pectinate muscles) derived from the true atrium.
Pectinate muscles: make up the right atrial appendage, they increase the power of contraction without increasing heart mass substantially
Note: these are different from the trabeculae carneae which are found on the inner walls of both ventricles
Fossa ovalis: remnant of the foetal foramen ovale
How many leaflets does each heart valve have?
Tricuspid: three, septal, anterior, posterior
Pulmonary: three semilunar cusps
Mitral: two, anterior (larger), posterior
Aortic: three, anterior, right, left posterior
Describe the conduction system of the heart.
Sinoatrial node (SA), atrioventricular (AV) node (B), AV bundle (C), bundle branches (D), Purkinje fibers (E)
Describe the anatomy of the right coronary artery and its branches.
Arises from the anterior sinus of the ascending aorta.
1. marginal branch along the lower border of the heart
2. posterior interventricular (posterior descending) branch - anastomoses with the corresponding branch from the left coronary artery
Describe the anatomy of the left coronary artery ad its branches.
Arises from the posterior aortic sinus.
1. anterior interventricular (left anterior descending) branch running down to the apex to anastomose with the posterior interventricular branch
2. circumflex: continues round to the left side of the heart and anastomoses with the terminal branches of the right coronary artery
What is 'left dominance' with regards to the heart? What about 'co-dominance'?
Left dominance: when the left coronary artery and circumflex and larger and longer and give off the posterior intraventricular artery before anastamosing with the right coronary artery that is small (10% of pop.)
Co-dominance: when the left and right coronary arteries have equal contribution to the posterior interventricular artery (10% pop.)
What coronary arteries supply the SA node in most people? What about the AV node?
60% - right coronary artery
40% - circumflex artery
90% - right coronary artery
10% - circumflex artery
What is the main venous drainage of the heart? What are it's 3 tributaries (venous branches)?
The coronary sinus: lies in the posterior AV groove, opens into the right atrium.
1. great cardiac vein (next to the anterior interventricular artery)
2. middle cardiac vein (next to the posterior interventricular artery)
3. small cardiac vein (next to the marginal artery)
What is the cardioinhibitor nerve supply to the heart?
What do the sensory nerve fibres from the heart travel through? Why is this clinically relevant?
They travel through the cardiac plexus, sympathetic chain and up to the dorsal root ganglia of T1-T4. Angina can cause pain referred to these dermatomes, in the inner aspect of the left arm.
Cardiac vagal afferent fibres synapse in the nucleus of the tractus solitarius (medulla) and then excite the cervical spinothalamic tract which explains neck and jaw pain in angina.
What three layers of soft tissue form the pericardium?
Parietal layer (1) lines the inner surface of the fibrous pericardium (2). It fuses with the adventitia of the great vessels at its apex. At its base, it fuses with the central tendon of the diaphragm.
Visceral layer (3) (epicardium) of the serous pericardium adheres to the heart and forms its outer covering.
Parietal + visceral = serous membrane
What are the anatomical relations of the fibrous pericardium?
Anterior: sternum, 3rd to 6th costal cartilages, thymus, anterior edges of lungs and pleura
Posterior: oesophagus, descending aorta, T5-8 vertebrae
Lateral: roots of the lungs, phrenic nerves, mediastinal pleura
Where does the transverse sinus lie?
After the pericardial sac is opened anteriorly, a finger can be passed through the transverse pericardial sinus posterior to the ascending aorta and pulmonary trunk and anterior to the SVC and left atrium.
By passing a surgical clamp or a ligature around these large vessels, inserting the tubes of a coronary bypass machine, and then tightening the ligature, surgeons can stop or divert the circulation of blood in these arteries while performing cardiac surgery, such as coronary artery bypass grafting.
What is the oblique sinus?
It is a space bounded by the pulmonary veins that forms a recess between the pericardium and the left atrium.
2 - Transverse sinus
5 - Oblique sinus
What happens if there is a sudden increase in pericardial contents? For example of blood?
Despite the fibrous pericardium being able to stretch over a long period of time (heart failure), if there is a sudden increase of contents, the pressure will increase and cause cardiac tamponade.
Note: pulsus paradoxus (abnormally large decrease in stroke volume, systolic blood pressure and pulse wave amplitude during inspiration.)
What is the surface anatomy of the heart?
Superior: line from the 2nd intercostal space (1.2 cm from sternal edge) to the 3rd right intercostal space9 1.2 cm from sternal edge)
Inferior: line from the 6th right intercostal cartilage (1.2cm from sternal edge) to 5th left intercostal space (9cm from the sternal edge)
Left border: curved line from left 2nd intercostal space (1.2cm from sternal edge) to 5th intercostal space (9cm from midline/ in the midclavicular line)
Right border: curved line 3rd right costal cartilage (1.2cm from sternal edge) to right 6th costal cartilage (1.2cm from sternal edge)
What is the angle of Louis? At what vertebral level does it lie? Why is this plane relevant?
Corresponds to the plane of T4, it is the sternal angle where the manubrium meets the body of the sternum.
The following occur at the level:
- commencement and termination of the aortic arch
- bifurcation of the trachea
- junction between the superior and inferior mediastinum
- second costosternal joint
- throracic duct runs from right to left
- ligamentum arteriosum lies on this plane
What are the boundaries and contents of the superior mediastinum?
Posterior: first 4 thoracic vertebrae
Above: root of neck
Below: inferior mediastinum (at level of the angle of Louis)
- lower end of the trachea
- thoracic duct
- aortic arch
- part of carotid and subclavian arteries
- upper part of SVC
- phrenica nd vagus nerves
- recurrent laryngeal nerves
- lymph nodes
- remnant of thymus gland
What are the boundaries and contents of the anterior mediastinum?
- part of thymus gland in children
- anterior mediastinal lymph nodes
What are the boundaries and contents of the middle mediastinum?
Anterior: anterior mediastinum
Posterior: posterior mediastinum
- great vessels
- phrenic nerves
- pericardiophrenic vessels
What are the boundaries and contents of the posterior mediastinum?
Anterior: pericardium, roots of lungs, diaphragm below
Posterior: vertebral column (4th to 12th thoracic vertebrae)
Above: plane from angle of Louis
- descending thoracic aorta
- vagus and splanchnic nerves
- azygos vein
- hemiazygos vein
- thoracic duct
- mediastina lymph nodes
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