T1 L2: Superior mediastinum Flashcards
Where is the division between the superior and inferior mediastinum?
At level T4/5 (the sternal angle or the transverse thoracic plane)
At what level does the trachea bifurcate?
Level T4/5
What structures are in the inferior anterior mediastinum?
None, it’s the space between the sternum and the heart
What structures are part of the inferior middle mediastinum?
The heart and the pericardium
What structures are part of the inferior posterior mediastinum?
Everything that isn’t in the inferior anterior or middle mediastinum
What is in the superior boundary of the superior mediastinum?
Superior thoracic aperture (connective tissue between the thorax and neck)
What is the inferior boundary of the superior mediastinum?
The transverse thoracic plane (T4/5)
What is the anterior boundary of the superior mediastinum?
The manubrium
What is the posterior boundary of the superior mediastinum?
T1-T4/5 vertebral bodies
What is the lateral boundary of the superior mediastinum?
The mediastinal pleura
What is the main function of the thymus gland?
T cells mature in the thymus
What 3 nodes drain the lymph from the thymus gland?
Parasternal, brachiocephalic and tracheobronchial nodes
Where are parasternal lymph nodes?
Either side of the sternum
Where are the brachiocephalic lymph nodes?
Near the brachiocephalic vein
Where are tracheobronchial lymph nodes?
At the hilum
What is the thymus gland replaced by after puberty?
By fat
What are the 3 branches of the arch of the aorta?
- Bronchiocephalic trunk
- Left common carotid artery
- Left subclavian artery
What arteries does the bronchiocephalic trunk branch off into?
The right subclavian artery (blood to right upper limbs) and the right common carotid artery (blood to the neck, head and brain)
What is the clinical importance of Virchow’s node?
It can indicate abdominal cancer but can sometimes be benign
What are the 2 branches of the ascending aorta?
The left and right coronary arteries
What are the 3 branches of the descending aorta?
The posterior intercostals, bronchial arteries and lumbar arteries
When do the left and right coronary arteries fill up?
Between ventricular contractions (during a contraction, blood is pushed up the arch of the aorta but some of it will fall back down and pool at the bottom of the closed aortic valve. This blood flows into the coronary arteries)
What are the different branches of the superior vena cava?
Firstly into the left and right brachiocephalic veins. Then each side bifurcates into a subclavian and internal jugular vein.
What is the ligamentum arteriosum?
It’s the embryological remnant of the ductus arteriosus (a duct connecting the pulmonary trunk and the arch of the aorta to allow the blood to bypass the immature lungs)
What is the trachealis muscle?
The muscle on the posterior trachea that allow food to pass down through the oesophagus
What is the longest lymphatic vessel in the body?
The thoracic duct
What is the thoracic duct?
Numerous lymph nodes associated with the descending (thoracic) duct
What are the origins of the phrenic nerve?
From the anterior rami of spinal nerves C3, C4 and C5.
What is the function of the phrenic nerve?
Motor supply to the diaphragm and sensory supply to the diaphragmatic and mediastinal pleura
Between what vessels does the phrenic nerve enter the superior mediastinum?
Between the brachiocephalic veins and subclavian arteries
How does the phrenic nerve pass the main bronchi?
Anteriorly
What is CNX?
Cranial nerve 10 (the Vagus nerve)
How does the Vagus nerve enter the superior mediastinum?
Between the brachiocephalic veins and subclavian arteries medially to the phrenic nerve
What is the recurrent laryngeal branch of the Vagus nerve?
The loop of the Vagus nerve that goes on to supply the larynx
How does the Vagus nerve pass the main bronchi?
Posteriorly
What is the function of the Vagus nerve?
Provides parasympathetic supply via the pulmonary, cardiac and oesophageal plexi
What is the first stage of cardiac development?
Angiogenic clusters form in the mesoderm and then canalise to form early blood vessels. 2 heart tubes form and pair up at about day 21
Why must the heart be one of the first major system to begin functioning in an embryo?
Because diffusion is lo longer efficient as the embryo gets bigger
What day of development does the heart usually begin to beat?
Day 22-23
What are Truncus arteriosus?
The primitive outflow vessels
What are Sinus Venosus?
The primitive inflow vessels
Why does the heart start to fold at day 23?
Because it gets too long for the pericardial cavity
What are the 4 divisions of a newly formed heart tube before folding?
Sinus Venosus, primordial atrium, primordial ventricle and Truncus arteriosus
What are the 2 cardiac features that allow the blood to bypass the lungs?
The foreman ovale and ductus arteriosus. Some blood must still reach the lungs to allow them to develop
How does blood reach the foeutus?
Through the umbilical vein
What is the foreman ovale?
The hole in the atrial septum that allows blood to go straight to the left atria an not the lungs
What is the ductus arteriosus?
Its a tube that connects the pulmonary trunk to the arch of the aorta. Most of the blood from the pulmonary trunk will travel through it and then to the rest of the body instead of the lungs
Describe the development of the foreman ovale
- An incomplete septum primum forms with an ostium primum
- An ostium secondum forms when the primum fuses
- The incomplete septum secundrum forms (the foreman ovale)
What is the ostium primum?
The incomplete part of the septum primum in the development of the foreman ovale
What is an interseptal defect?
It’s a hole in the heart that remains when the foreman ovale doesn’t fuse. (Normally as the foetus develops, the pressure between the atria evens out so the foreman ovale fuses)
How does blood flow through the the foreman ovale?
There is a high pressure in the right atrium because no blood is leaving through the pulmonary veins so blood travels down the pressure gradient
