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Thorax/Superior Mediastinum

*Today we will complete our last lecture in the thorax which is the superior mediastinum…

The superior mediastinum as we said superiorly is part of the superior thoracic ………… or we call it the thoracic inlet which is marked by the 1st rib.

Here the inferior boundry is an imaginary line or plane descending from the sternal angle until the lower margin of the T4…

Anteriorly it is bounded by the manubrium , so the structures within the space will be the topic of our lecture … So what is there ?? The roots of the great vessels are there ; the Aortic arch and the branches , S.vena cava and the veins that make it , the vagus

and phrenic nerves , trachea and esophagus…

Trachea & esophagus pass NOT only through the superior mediastinum, BUT through the inferior mediastinum as well…

So, let's start with them.…

Start talking about trachea cephalic veins, usually we will talk about artries ; we will talk about the main artry and then we will proceed with branches .. We start with the branches that make the main trunk because the flow of the blood is in that direction. So vein here is the S.vena cava , How is this vein formed ? It is formed by 2 merging cephalic veins(Right & left) . If you notice the left one is more horizontal, it lies posterior to the manubrium.

Q: How this brachiocephalic vein is made ?A: By another 2 smaller veins : 1- the internal jugular 2- the subclavian , right for right & left for left.

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Here is the left internal jugular which comes from the head and neck, and this is the subclavian vein(left subclavian vein) which drain blood from the upper limbs.

A student asked a question but I didn’t hear .. The answer was : the subclavian vein is shorter and more vertical.

Both brachiocephalic veins unite behind the 1st costal cartilage to make the S.vena cava , the internal jugular and the subclavian unite behind the sternoclavicular joint .

So let's talk about the S.vena cava: It starts behind the Rt. 1st costal cartilage and it ends in the right atrium at the level of the right 3rd costal cartilage.

Relations : what surrounds the structure .. so,1 -Anterior to the S.vena cava we have the right one and covering plurea

2 -Posterior we have the root of the right lung medial to it And u can see in the picture up we have the ascending Aorta and laterally we have the Rt.phrenic nerve and the Rt.lung . So. The lung is both Anterior & Lateral.

{OK, its confusing this why u need to study for 2-3 hours at your home y3ni .. =P}

For veins we have something called{treputaries ?}, it means: other veins that empty blood in that specific vein.{treputary ?} means ( rwafed ). The main {treputary ?}for the S.vena cava is the Azygos vein .

Also you can see in the picture up the azygos vein emptying in the S.vena cava (As I said the internal jugular & the subclavian veins unite behind the sternoclavicular joint, so if the clavicle is removed u can see the branches).

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Now, the next lecture we will talk about in the medtastinum is the Aorta. We have the Ascending , the Arch and the Descending.

We talked about the thoracic or the descending as part of the posterior mediastinum, we are talking about the ascending which is continuation of the left ventricle. And it goes in a superior direction to the right , this is why we call it the pathway that is taken by this artry,, it moves upward or superiorly and to the right until the right 2nd costal cartilage. At that level we will stop saying ascending Aorta , we will start saying Arch of aorta. Branches that are given off this this part just of the Rt & Lt coronary artries.

Note : Brachiocephalic , the common carotid and the subclavian artries all are from the Arch of aorta.…

Now we will talk about the arch of aorta. It's continuation of the ascending aorta. It starts behind the Rt.2nd costal cartilage.

What is the pathway? It is upward & backward .. or in other words Superio-Posterio direction to left side.

Where it terminates? Or where does we stop saying arch and start saying descending aorta? It is at the level of the T4 which corresponds to the sternal angle .

Relations as u can see it arches over so ,1-it lies over the left of the principle bronchus and the Rt. pulmonary artry .

2-It is crossed Anteriorly so, the veins pass Anteriorly to the aortic arch which is the phrenic nerve and the Lf vagus which is the only nerves that is seen in the mediastinum.

3 -on the right of the arch we have the trachea and the esophagus which slightly posterior to the right.

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Q: What branches are given off this part of the aorta?A: Brachiocephalic artry (it is on the right BUT we don’t say Rt. Brachiocephalic because we don’t have left one). Brachiocephalic is the largest branch of the aorta. It starts at the sternoclavicular joint and the Rt. Common carotid and the subclavian artries.Notice on the left side we DON’T have brachiocephalic artry . Immediately, from the arch of aorta (Lf. Common carotid & Lf. Subclavian artries) they arise immediately from the aortic arch.

This picture explain. The brachiocephalic artry it gives behind the sternoclavicular joint. It splits into the Rt. Common carotid & the Rt. Subclavian artry. Whereas in the left side immediately we have the Lf. Common carotid & the Lf. Subclavian .

We talked about the descending aorta and its branches in the last lecture , so we will jump to the Abdominal aorta.

Once the aorta , the same artry by leaving the thorax and enrtering the abdomen we will start calling it the Abdominal aorta. It will starts at the level of the aortic opening in the diaphragm which is in T12 & extends until L4. It ends by dividing into Rt. & Lf. Common iliac artries.

Now we have talked about the blood vessels and artries , we will talk about the nerves ( Vagus & Phrenic).

*Vagus nerve is a cranial nerve , btw both vagus & phrenic nerves we have Rt. And Lf. Parts…

Cranial nerve means: it arises immediately from the brain or the brain stem.

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Most of the fibers of this nerve is parasympathetic as I said many times. So, lets start talking about the Rt. Vagus.

It passes lateral to the trachea {as can u see in the pic}. It goes anterior to the root of the lung or posterior.

It goes posterior to the root of the Rt. Lung, it follows the path taken by the

esophagus. So it leaves the thorax by exiting through the esophageal opening which is located posterior to the esophagus.

It gives an important branch called recurrent laryngeal nerve that loops around the subclavian artry. So in this pic you can see the subclavian artry before it goes down it gives a branch we call it recurrent because it goes up after leaving the vagus nerve. It goes to the up to supply the larynx.

There is an important difference between the right & the left: - The Rt. Loops around the subclavian ,,, the Lf. Loops around the arch of aorta.

So, the Lf. Vagus descends between the Lf. Common carotid & Lf. Subclavian artries, it goes also behind the root of the left lung. Here it gives the Lf. Recurrent laryngeal nerve which loops around the arch of aorta and goes up to supply the larynx.

It also leaves the thorax through the esophageal opening and it is located anterior to the esophagus .

Let's talk about the Phrenic nerve. Its NOT a cranial nerve like most of the nerves in our bodies. It originates from the spinal cord(C3,C4,C5). This level is so important because any injury above or below it determins wether the patient will be able to breath or not. Scince phrenic nerve is the main innervations to the breathing

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muscles which is the diaphragm. So, which is more serious having the injury above at C2 (for example) or at C6?

A: C2, because no impulses will come from the brain to these segments so will have paralysis of the diaphragm .

*All of the motor supply to diaphragm. Sensory supply just for the central part of the diaphragm, pericardium and parts of the parietal pleura (mediastinal & diaphragmatic) and part of the peritoneum.

Q: what is the peritoneum ?A: it is a serous membrane because it is in the abdomen ; it lines the organs of the abdomen.Q: does the phrenic supply all the peritoneum ?

A: No, just the diaphragmtic part which lies below the diaphragm.

The Rt. Phrenic: it descends laterally to brachiocephalic and S. vena cava. It lies on the Rt. Side of the pericardium and it leaves the thorax through the caval opening.

Caval opening: opening through which the inferior vena cava passes from the abdomen to the thorax.

The Lf. Phrenic: it enteres left to the subclavian, it is superimposed on the vagus nerve, it passes lateral to the vagus nerve and anterior to the root of the left lung.So, this is one criteria to distinguish between the vagus and phrenic nerve in the …………..; one passes posterior to the root of the lung and the other passes anterior. Through which opening does this nerve exit? It has it's own opening (it is one of the diaphragm opening).

Trachea or the windpipe It's made of fibrocartilage so it's a ring of U-shaped fibrocartilage (not complete ring) and it is complete a circule posteriorly by a muscle called Trachialis muscule (it is a smooth muscle). This is one of the few places that the smooth muscle has a name because usually we don’t have names for the smooth muscles. We have the left main bronchus which is more horizontal and narrower , the Rt.main bronchus is more vertical and wider. This why when If you accidently inhale an object the ………….will go to the right side because of this.Relations of the Lf. bronchus:

1- Inferioir to the aortic arch2- Anterior to the esophagus.

Trachea relationships:1- Anterioir : Lf. Brachiocephalic vein & the manubrium.2- Posterior : esophagus & recurrent laryngeal nerve.3- Right side : we have the Rt. Vagus nerve & Azygos nerve.4- Left side : we have the aortic arch, Lf. Common carotid & subclavian artries

and Lf. Vagus nerve,

Note : Veins are Anterior to the Artries … Trachea Anterior to the Esophagus.Blood vessels loops above 1st rib.

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{By this we finish the S. mediastinum}

The abdominBefore talking about the abdominal cavity we will talk about the abdominal wall. It is made of layers same principle we had in the thorax.

Skin Fascia Muscle layer Super fascia deep fascia

And here we have a special layer called Transversalis. It lies between the parietal layer of the peritoneum and abdominal wall (because it is a serous membrane so there is parietal & vesciral pleura).

We have anterior wall. Lateral sometimes called flanks and posterior wall.The blood vessels, the muscles, the nerves are usually continuous with the anterior & lateral walls of the abdomin so why is that we use anterio-lateral abdominal wall; we talked about it as one unit.In the surface anatomy we can see a boundry between th Ant. & Lat. The lateral margin of the rectus abdominis muscle called linea semilunaris (betkoon 3la shkel ridge).When this muscle(in the middle) contract, it forms a ridge around it's Lat. Margin. It demarcates the boundry between the Ant. & Lat. Walls of the abdomin. It extends from the margin of the 9th costal cartilage of the pubic tubercle. The fascia or the aponorosis of the abdominal muscles that forms the lateral part they merge together in this line.

The boundaries of the anterio-lateral wall:1- Superior: xiphoid process & the costal margin of the 7th-10th costal cartilage.2- Inferior: inguinal ligament; extends between the Ant.-Sup. Iliac spine & the

pubic tubercle. (look at your book on the hipbone picture to familiarize yourself between these structures ).

The layers:Skin Superfascial fascia (it has 2 layers): Fatty layer: made of fat we call it Camper's fascia, it can be up to several inches in obese people. (we need this fascia). Membranous layer: called Scarpa's fascia.

Deep fascia: the fascia that encloses or inveses the muscles of the abdominal wall.These fascia of the muscles fuse in the lungs. The 1st line I just told u about it which is linea alba ; it is also a site of fusion of the aponorosis of the abdominal muscles.

We have a special fascial layer in the abdomin called Transversalis ; it is continuous with the endothoracic fascia

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Endo thoracic fascia: is a fascial layer that comes between the parietal pleura & the inner surface of the thoracic wall.Plus having extra peritoneal fat, if u open the abdomen looking at the vescira u will find variable amounts of fat depending on how obese person is.

Muscles of the Ant.-Lat. Wall:

Read table 4-1 in your textbook, basically most of that table are written in the slides it is just a nice summry that many help u in the exam. (u need to memorize it).

5 muscles : 3 lateral muscles & 2 anterior muscles

Are named by layers and fiber direction

2 of the muscles the fibers are directed obliquely so, we need to differentiate them:One is superfascial & the other is deeper.

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1- Superfascial: external oblique muscle.2- Deepfascial : internal oblique muscle.

The 3rd muscle has fibers orientated horizontally so it is called: transverses abdominus muscle and it is the deepest muscle of the 3 muscles.

The 2 anterior muscles: have vertical orientation they are the rectus abdominus muscle & a small one that is not present always called pyramidalis muscle

External oblique :The origin from the outer margin of the lower 8 ribs. The lateral portion is muscular and it goes Inferio-Medial direction, and as it goes anteriorly becomes aponorosis that is inserted mainly in the linea alba.

If u notice here, the margin of the aponorosis is free which is NOT attached to any other organ. It's folded on itself. So, it is thickened and we call this the Inguinal ligament which is the Inferior boundry of the abdominal wall.

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Inguinal Ligament.: Thickened backward reflection of the inferior border of external oblique aponeurosis that extends from anterior superior iliac spine to pubic tubercle.

Inguinal ligament is important because together with other fibers of the external oblique aponorosis it forms a ring or an opening we call it the Super fascial inguinal ring.There is a defect which normal in all of us so that the structures can pass from the abdomin through this opening.

Note : the spermatic cord in males & the round ligament in female passes through this opening.The round ligament comes from the Uterus.

Internal oblique :It has the opposite fiber direction. Most of the fibers NOT all of them goes opposite because one goes infero-medially & the other goes superior-medially, this means that the fibers of the external & internal oblique muscles are attract angles The angle between them is 90

The main origin is from the lumbar fascia in the back which is aponorosis + it's originated from the ant. 2-3rd of the iliac crest . Part of the ilium & the lateral 2-3rd part of the inguinal ligament.It is inserted in the margins of the lower 3 ribs; xiphoid process, linea alba, andsymphysis pubis. All of these are more or less structures toward the midline.

The last muscle in the lateral wall is the transverses abdominus. It runs horizontally. ** The main origin from the lumbar fascia . ** The main insertion is the linea alba .

- These muscles together help maintan the tune of our body, to protect the abdominal vescira, it helps in respiration and it help in other physiological preprocesses like: mecturation or defection .

Note: these muscles fuse Ant. But they are on the lateral aspect of the abdominal wall.

Now, we will talk about the 2 muscles from the Ant. Wall.* Rectus abdominus muscle: which is 4 fleshy parts, it is a muscular tissue, they are separated by 3 tendinous intersections.The 1st tendon lies on the level of the xiphoid process, the 3rd at the level of umbilicus and the 2nd between them. This muscle is enclosed by a something called rectus sheath : it's like a sac, that the muscle is put inside.

*** Remember that the aponorosis transverses & oblique muscle merge in 2 lines. 1st one is laterally (linea lonaris) so the aponorosis come together and they split in 2 parts to surround the abdominus muscle & again they fuse in the midline so, they make a sac in which the muscle is housed.

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Within this rectus sheath, we have another muscle that lies anterior to the rectus abdominus and posterior to the anterior wall of the rectus abdominus sheath it is called pyramidalis. It's NOT always present, it is triangular in shape or pyramidal in shape. The base is inserted in the pubic bone & the apex is inserted in the linea alba.

When the rectus sheath is removed and rectus abdominus is also removed what we are left with is the posterior aspuct of the rectus sheath.So, it's a fibrous structure as I said starts from the linea semilunaris in both sides they terminates in the linea alba. Now as I said it is made of the aponeurosis of the muscle which merge to the midline and splits to make this sac.

Q:What makes the anterior part of this sac?A: the external oblique & half of the internal oblique(we are talking about the aponorosis of these muscles NOT the muscle itself).The posterior part of this sac is made of the half of the internal oblique muscle & the transverses abdominus muscle, and then they merge in the midline as linea alba.

The 3 muscles of the aponeurosis come together to the semilonaris and then they split to encase the rictus abdominus muscle and they fuse again in linea alba .

* There is one exeption ; instead of splitting the fascial layers and surround the rectus abdominus muscle, they all go ant. Leaving the post. Aspect pair NOT covered. This infero-posterior disappearance is marked by the Arcuate line.

The Ant. Wall of the rectus sheath is longer than the post. Because at certain area all the fascial layers will go anterior leaving the posterior aspect pair uncovered . the 3 margins of the posterior part of the rectus sheath , we call it the arcuate line.

So this is how the orientation of fibers will be instead of splitting to surround the rectus abdominus all of them will go anteriorly and this level we call it the arcuate line …

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The End …

* Forgive me for any mistake ,, fi kza word ma sm3ton mnee7 so I'm sorry 3l t29eer .. I really did my best … enjoy it guyz ;p

Done by : Tuqa Al-Zoubi

*** merciiiiiiiii 4 u sister " nano " l2nek raj3ti ylli ktbto o sm3teli kteer sh'3lat ma knt same3ta mnee7 .. <3

*** also I will not 4get my best frnd ever " samoura al-omari " =)

Srsrt

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