Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
2 Anatomy #01 د.محمد الحيدري 15-3-2016 ثائر شحادة وسعد العيطان Today we will start describing the cardiovascular system structurally. As we know by now, this system is a completely closed system, composed of a pumping station (the heart) of specialized muscle. Recall that we have 3 types of muscles in our body: 1- skeletal (motor control) 2- smooth (autonomic control) 3- cardiac (autonomic control) From this pumping station, vessels arise to distribute the blood to different regions of the body by a special circulation called the “systemic circulation”. Another smaller circulation aiming at oxygenating the blood after the consumption of oxygen in different types of tissues in the body is called the “pulmonary circulation”. The right atrium of the heart will receive deoxygenated blood from the body via vena cava and it is passed to the right ventricle which pumps blood to the pulmonary circulation to be oxygenated, and the left atrium of the heart will receive oxygenated blood from the lungs and it passes to the left ventricle to be pumped outside the heart to the systemic circulation. So a general rule is: any vessel approaching the heart is called a vein. Any vessel leaving the heart is called an artery, Regardless if it was oxygenated or not. e.g: - The aorta leaves the heart (oxygenated) Artery Blood flow in the heart - Pulmonary trunk leaves the heart (deoxygenated) Artery The whole cardiac muscle with its great vessels are located in the chest region in a position behind the sternum (retrosternal position). In clinical examination, we are going to see certain landmarks on the chest of a person and use them to examine the dimension or certain sounds of the heart. What is a sternum?... It’s a part of the axial skeleton, and it has 3 parts: - manubrium - body - xyphoid process So behind the sternum we have the whole heart with its coverings. Sternum 1|Page In the thoracic cavity, the major organs present are the lungs and the heart with the attached structures to them. In between the 2 lungs there is a space (imaginary space) called the mediastinum. And of course, this space has limits and boundaries. You may be asking, “How can we examine patients according to landmarks?” Well, let’s take the thoracic cage for example. The sternum is the central portion that receives cartilage costal attachments from the ribs. How many ribs are directly attached to the sternum? About 6 The ribs below these 6 are connected indirectly as they all merge into one subcostal cartilage. And we also have the last remaining floating ribs that are not attached to the sternum at all. (see the figure) Note: you can’t feel the 1st rib because it is located behind the clavicle So assume you want to hear someone’s heart with a stethoscope. You need to locate the best intercostal space to put your stethoscope on. We know that we have 6 ribs connected directly, but how can we feel them and count them? We can feel the junction between the body and the manubrium (sternal angle). At this angle that we could feel, the 2nd costal cartilage articulates, meaning that this is the 2nd rib. This means what’s above this rib is the 1st intercostal space, below it is the 2nd intercostal space. Let’s look at these 2 diagrams for the mediastinum. If we take a straight line from the sternal angle to the vertebral column, we are going to approach the intervertebral disk between T4-T5. And if we take another straight line from vertebra T1 to the jugular notch (at the tip of manubrium superiorly), 2|Page this will mark an oblique line above the thoracic cavity. This will mark a space which is called the mediastinum. We know that the diaphragm is a curved muscle sheath that comes from several attachments. In this sagittal section we can see that the diaphragm comes from the lower part of the sternum (Xiphisternal junction) and curves backward into a deeper attachment to the 1st and 2nd lumber vertebrae. Okay let’s break this diagram into pieces: The mediastinum! The lowest point is the diaphragm The highest point is the oblique line The line from the sternal angle to T4-T5 divides the mediastinum to superior and inferior parts. Inferior: from straight line to diaphragm Superior: from straight line to oblique line The Superior mediastinum receives mainly the great vessels emerging from the heart Inferior mediastinum is larger and occupies the heart and pericardium. let’s talk about the inferior mediastinum now cause it’s waaay more interesting than the lame superior one. The inferior mediastinum is subdivided into 3 regions: Anterior mediastinum Slightly deep Smallest in volume internal thoracic (internal mammary) 3|Page Middle mediastinum Not deep largest in volume Heart and pericardium Posterior mediastinum deepest large in volume Descending aorta So now we have subdivided the mediastinum into 4 regions: One above the horizontal line One below the horizontal line (3 parts (anterior, middle, posterior)) The whole heart, like any visceral structure in the body, is surrounded by a serous membrane for protection. Of course, the lungs also have a protective covering called the pleura, GIT (stomach to rectum part of it) is surrounded by the Peritoneum (some parts are not). The one that surrounds the heart is called the Pericardium. But, what exactly is this serous membrane? It is a covering composed of 2 layers, the visceral layer (against the viscera) and the parietal layer (against the outside). In between these 2 membranes is a small space filled with a fluid named after the name of the membrane (pleural fluid for lungs, peritoneal fluid for GIT). So it is called the pericardial fluid for the heart. This fluid will help in the movement and minimizes the friction to protect the heart. Now let’s make something clear. All these visceral organs in the body have these 2 membranes, but the heart has an extra outer layer (membrane) called fibrous pericardium. It is tougher than the parietal and visceral membranes and is located on the outer portion of the heart to protect and limit the expansion of the heart (so that the heart doesn’t blow up or burst from the pressure inside it). The fibrous pericardium is attached inferiorly to the diaphragm, but how is it attached and why? Well, let’s explain what the diaphragm is first. The diaphragm is a flat sheet of muscle which is a muscle of respiration. It acts during respiration by 4|Page If we want to blow a balloon, we Know it has a thin elastic wall. If you continue to blow it, it will blow up. But if you put the balloon in a paper bag and blow it, it will no. It will limit itself and you’ll reach a stage where you can’t blow it anymore; this is how fibrous pericardium acts. The balloon is the heart, and the paper bag is the fibrous pericardium contraction and relaxation. It also separates the thoracic and abdominal cavities. What is it made of? Is it all made of flesh (muscles tissue)? Nooo, we have a central tendon in the center of it (C shaped) which is not a muscle tissue, it is a tendinous structure. Tendinous structures are not a contractile tissue, so if you are running or performing exercise, the diaphragm moves up and down rapidly for respiration. But what exactly goes up and down? Only the fleshy part!! Okay? The tendinous part does not move up and down or it could at least slightly move. So the tendinous part will be fixed. Now let’s go back to our first question, how is the fibrous pericardium attached to the diaphragm? Via the central tendon Why? To fix the heart in its place and prevent it from moving up and down. But, what is the upper attachment for the fibrous pericardium to fix the heart in its place? The superior attachment will be to the roots of the great vessels, the “ascending aorta” and the “pulmonary trunk” to their adventitia (outer layer of the vessel). THE END 5|Page