In the Last Three Lectures We Already Discussed the Importance of the Thoracic Cage.

Transcription

1 -This Lecture Will Revise what we took in the last three lectures and will introduce the concept of the chest cavity ( Thoracic Cavity ) In the Last Three Lectures We Already Discussed the Importance of the Thoracic Cage. The Thoracic Cage is Made of Sternum Anteriorly. The Sternum is Made of 3 Parts which are : (1)Manubrium Sterni (2)Body of Sternum (3)Xiphoid Process. Posteriorly we had the Vertebral Column. The Vertebral Column is made of different Parts of Vertebrae but here we are concerned about the Thoracic Part of Vertebrae (T1-T12). Each Thoracic Vertebra has 2 major parts : (1)-Body (Anterior) (2)-Vertebral Arch (Posterior) And between them we have pedicles. Two adjacent vertebrae result in intervertebral foramen ( spinal nerves passes through it ) and we can see it from a lateral view. Three or four etc adjacent vertebrae result in Vertebral Canal ( Spinal Cord Passes through it). Between the Sternum Anteriorly and the Vertebral Column Posteriorly we have the Ribs ( we already discussed that ). Each Rib is Made of a : (1)head (2) neck

2 (3) tubercle (4) shaft -In the Inferior Border of the Shaft we have a groove, Costal Groove-. We Also Discussed the Muscles Between the Adjacent Ribs, which are the Intercostal muscles. Theses muscles are divided into three types : (1)-External Intercostal Muscles (2)-Internal Intercostal Muscles (3)-Innermost Intercostal Muscles. That s It!! These are the Main Structures of the wall of the Thoracic Cage. Lets Proceed. Wait (Loading 78%) Each Intercostal Space has its own nerve supply and venous drainage along with arterial blood supply. Each Intercostal Space contains a large single posterior intercostal artery. If you would design the blood supply for the thoracic cavity, you have to get the blood from Thoracic or Descending Aorta (Later on we will talk about the other parts of the aorta : Ascending and the Arch of the Aorta). The Descending Aorta as soon as it passes the diaphragm and goes inferiorly it s called Abdominal Aorta. Blood Supply : However, if you look here, the Arch of the Aorta arises behind the sternum and then goes down, so the area from the sternum till the upper part of the thoracic cavity doesn t have a Thoracic Aorta, in this case we have to look for another different blood Supply. {The Posterior intercostal arteries of the first two intercostals spaces} are branches from the superior intercostal artery which is a branch from the costocervical trunk ( Whether it s on the right or left side) of the subclavian artery. The arch of Aorta gives 3 Branches : 1-Brachiocephalic (Divides into the Right Subclavian artery and Right common carotid artery ) 2-Left common carotid artery 3-Left Subclavian Artery.

3 The posterior intercostals arteries of the lower nine intercostals spaces : Take blood from the Thoracic Aorta! 2+9=11 intercostal spaces!! Why 11? Because we don t have an intercostal space numbered 12! Duh! Ex. Under the first rib we have the first intercostal space and so So the Thoracic Aorta (Descending Aorta) is the Main blood supply for the intercostal spaces (Posteriorly)! Blood Supply For the Intercostal Spaces (Anteriorly) : o All What we have said so far was in the posterior area of the thoracic wall, as the Thoracic or descending aorta is close to the vertebral column. o Now the Major Blood Supply for the Anterior part of the Intercostal Spaces come from the Internal Thoracic Artery ( Internal Mammary Artery ) which is a branch from the 1 st part of subclavian artery. 1- The {Anterior Intercostal Arteries of the First Six Spaces} are branches from the Internal Thoracic Artery. 2- The Remaining anterior intercostal arteries are from the musculophrenic artery ( one of the terminal branches of the internal thoracic artery ). The Internal Thoracic Artery gives 2 terminal branches : ( around the sixth intercostals space ). (1)Musculophrenic Artery (2)Epigastric Artery To Summarize : We Have 2 Major sources of blood supply, that are the main blood supply for the thoracic cavity and lying within it. [Posteriorly] we have the Major Artery : Thoracic Aorta (Descending Aorta) which gives of posterior intercostal arteries. However, they are faced anteriorly by the anterior intercostal arteries from the Internal Thoracic ( Internal Mammary) Artery. They anastomose with each other

4 The Upper two Intercostal Spaces (The Aorta doesn t reach them) so they have to get their posterior blood supply by means of the subclavian artery through the costocervical trunk by the superior intercostal artery. The Venous Drainage : Of Course Obviously the venous drainage always accompany the arteries ( Taking also their names ). However, we have a space for the aorta but we don t have a corresponding vein for it. For Example in the Abdomen we have 2 major structures lying in front or along the vertebral column, one is called the abdominal aorta and next to it inferior vena cava. but you will not see this in the thoracic cavity! In the Thoracic Cavity we have no space! we got lungs, heart etc. that s why the design of the veins in the Thoracic Cavity is of two veins : 1-Azygos vein 2-Hemiazygos vein They Will Eventually receive venous drainage of structures within the Thoracic Cavity. So we have a descending aorta, but what veins correspond to it? They are the Azygos (right) and Hemiazygos(left) Veins. o The Corresponding posterior intercostal veins drain backward into the azygos or the hemiazygos veins. o The Corresponding anterior intercostals veins drain into the internal thoracic and musculophrenic veins. We Finished with the blood supply and venous drainage of the thoracic cavity!! Ohh Finally :D

5 Intercostal Nerves : Each Nerve which either you call them spinal nerves generally or you can name them intercostals nerves. If you name them intercostals nerves you have to bear in mind that you have 11 inercostal spaces. Ex. T1 you can call it intercostal, T2 Second Intercostal etc until you reach T11 which is intercostal nerve number 11. However, T12 we don t have intercostals space, that s why this nerve a unique nerve (Subcostal Nerve) Under the Rib Number 12! The Doctor Loves to name them Spinal Thoracic Nerves in order to get rid of confusion! These nerves comes from the anterior rami! Small Revision of the nervous system :P : Every Spinal nerve is made of posterior and anterior roots which come together along with a communicantes branch(from the sympathetic) and make a spinal nerve. Of course every spinal nerve is mixed (Sensory + Motor + Sympathetic(for the sweat glands and muscles for hair!!) ) At the Moment it(spinal Nerve) will emerge from the intervertebral foramen, there it will divide into two parts ( anterior and posterior). The Anterior is mixed ( Motor + Sensory + Sympathetic) and the Posterior Also! However, you wouldn t hear about from now on the posterior rami ( Cause it innervates the muscles of the back! So forget). Because all the muscles of your body that of concern of point of view of medical doctors are the upper and lower limb muscles which are supplied by the anterior primary rami بدها ذكاء) (ما!! Brachial Plexus, Lumbar Plexus and Sacral Plexus are all anterior primary rami! The Anterior Ramus of the 12 th spinal thoracic nerve (T12) lies in the abdomen and runs forward into the abdominal wall as the subcostal nerve. Each Intercostal Nerve enters an intercostal space (Between the Parietal Pluera and posterior intercostal membrane ( the continuation of the internal intercostal muscle towards the vertebral column ), then runs forward inferiorly to the intercostals vessels in the subcostal groove. The Function of intercostal nerve is to innervate the muscles ( Motor) then after that it becomes sensory for the skin. These nerves are segmental ( meaning every nerve innervates specific muscles and skin area ) so it s rare to use هون قعد الدكتور يهمهم و يحكي كالم غير مفهوم them all at once!! Forget

6 1-The First Six Nerves are distributed within their intercostal spaces, why?! Cause the Upper six ribs are considered true ribs forming true intercostals spaces. But beneath the sixth intercostal space, the remaining intercostal nerves as they approach the abdomen they will not find an intercostal space but the anterior abdominal wall, this is why the muscles of the anterior abdominal wall are supplied by the intercostal nerves number 7,8,9,10.. and so. until the inguinal ligament!! Forget 2-The 7 th to the 9 th intercostal nerves leave the anterior ends of there intercostal spaces by passing deep to costal cartilages to enter the anterior abdominal wall. 3-The 10 th and 11 th intercostal nerves sense the corresponding ribs are floating pass directly into the abdominal wall. Thoracic Cavity (Chest Cavity) : New Subject You should understand that there is a huge difference between the thoracic cavity and the thoracic cage. Who is bigger :P?? Of Course the thoracic cage. The Thoracic cavity is a part that occupies a part of the thoracic cage!! Shoo ya3nee?! :P.. Now the thoracic cage is larger than the thoracic cavity, the diaphragm divides the thoracic cage into 2 spaces (2 cavities), The Thoracic Cavity (Above) and Abdominal Cavity(Below). The Thoracic cage serves to protect the main important organs in the thoracic cavity (The Lungs and the Heart), ok. In the Abdominal Cavity under the diaphragm ( Which contains the liver, the spleen, part of the stomach, main blood supply and some part of kidneys ) all of these organs are partially or totally protected by the thoracic cage!! Confusing 9a7! Allah be3een.. ( الخالصة (. cage The Most Important organs of your body are protected by means of Thoracic Clinical Point : When a patient comes to you suffering from bleeding in the lower right area of the thoracic cage, you would be concerned about two things : Bleeding in the liver or the lungs or both ( Cause there are 2 cavities deep to the thoracic cage in that area ). Hope it s Clear the difference between the thoracic cavity and cage!

7 The Chest Cavity is bounded above by the chest wall and below by the diaphragm. It Extends upward into the root of the neck about one finger breadth. However, the two lungs are extending upward above the first rib and like pushing the root of the neck ( in the thoracic outlet ). so they ( the lungs ) emerges above the clavicle on each side. Sometimes the doctor who wants to listen to the apex of the lungs puts the stethoscope on the root of the neck. (So don t call him an idiot! lol ) The Main problem in this area (root of the neck above the clavicle) is getting a stab wound ( Like in Troy Movie :P), Cause the Lungs might be injured :S Allah yeb3edna. The Chest cavity is divided into (1) the Mediastinum : which is located in the median partition and contains the heart (2) 2 pleural cavities laterally located ; The Lungs are inside these pleural sacs. The Contents of the Mediastinum : In the Next Lecture Sorry Colleagues if there were any scientific or spelling mistakes. Excellence is not a singular act, but a habit. You are what you repeatedly do. Your Colleague, Ahmad Almusa