I want to do a quick one on the Heart. I am going to be discussing the anatomy of the heart, the Coronary Circulation and the Pulmonary circulation. This is an anatomy post and not a physiology post, I will be doing a physiology post in the future. I have written post were touch the heart a little in the past and one of those posts is "Another Child Born With a Heart Defect || Acyanotic Congenital Heart Disease", you can read the post but I will be giving an extensive review on the Anatomy of the heart. Let's quickly discuss the anatomy of the heart, how oxygen-filled blood flows to the Myocardium of the heart, and the structures needed to send deoxygenated blood to the lungs and oxygenated blood back to the heart.
The heart is located at the mediastinum of the thorax and it is shifted to the two-thirds of the midsternal line. The heart weighs about 200 to 300 grams which are about the size of a fist. In the inner part of the heart is the tissue lining layer known as the endocardium, above the endocardium is a cardiac muscle tissue layer known as the Myocardium (the myocardium of the left ventricle is thicker than that of the right ventricle because it has to pump blood to supply the entire body), while the outer layer of the heart after the myocardium is the epicardium (visceral layer of the serous pericardium) Between the parietal layer of the serous pericardium and the epicardium is the pericardial cavity which is made of pericardial fluid. The outer part of the heart is the fibrous pericardium which is made up of dense fiber irregular connective tissues. The fibrous pericardium helps to protect the heart, helps to anchor the heart, and prevents overstretching causing an overfilling with blood. The heart has different chambers which include the atrial chamber which is at the top of the heart. It is regarded as Atrial because there are two Atrial (Atrium - singular). The Atrial is then divided into the right and the left atrium. The right atrium has three blood vessels bringing blood into it, and these blood vessels include the inferior vena cava, the superior vena cava, and the Coronary Sinus. In the right atrium, the scar of the foramen ovale which is present in infants is visible as the hole closes up to become scar tissue known as Fossa Ovalis. In the right atrium, there are nodule cells known as the Sinoatrial node (SA nodes). The left atrium gets blood from the lungs and these veins are the pulmonary veins (right and left pulmonary veins). Another chamber in the heart is the ventricle which are the right and the left ventricles. Dividing the atrial and the ventricles are valves, and in the right part of the heart is the tricuspid valve (right atrial valve), while the valve dividing the left atrial from the ventricle is the Bicuspid valve (mitral valve). The valve is made up of fibrous layers known as the zona fibrosa, zona spongiosa, and zona ventricularis. At the cups of the valves are collagen cords that anchor the valves known as chordae tendineae which are attached to the muscle of the heart known as the papillary muscles. The muscles and the collagen cord prevents the regurgitation of blood after passing through the valve by holding the valve tight. , , , , ,
The right ventricle pumps blood to the pulmonary trunk which I said previously is divided into two, the left and right pulmonary arteries. The pulmonary trunk and the right ventricle are separated by a valve known as the Pulmonary Semilunar valve, while the left ventricle is separated from the aorta known as the Aortic Semilunar valve. These valves prevent the backflow of blood to the ventricles. In the chamber of the ventricle, there is a separation of both ventricles known as the intraventricular septum (if the separation isn't there it can lead to a congenital disorder in the tetralogy of Fallot where there is shunting of blood from either of the ventricles). Between the left and right atrium is a separation known as the interatrial septum. The aorta starts with the Ascending aorta (quick clarity, your aorta isn't connected like a pipe descending down from the ventricle. If it was so, the heart wouldn't need to pump, and gravity would have done the job but the aorta is a valve that ascends before descending). The ascending aorta then goes to form an arch known as the aortic arch. In the aortic arch are three vesicle that come out from it, and they are; brachiocephalic artery (which splits into the right common coratid artery, and the right subcleavian artery), the left common coratid artery, and the left subclavian artery. The blood continues in the aorta to other systemic circulation.,
The Coronary circulation starts at the left ventricle where blood is pumped out through the aortic semilunar valve, then to the ascending aorta during the Systolic state which is the state where the heart constricts or pumps. The diastolic state is when the heart is relaxed and the heart is filled with blood. In diastole, the heart valve flaps shut to prevent blood from flowing back into the ventricle thereby allowing for the shunting of blood into the coronary circulation. While every other part of the body gets its blood supply when the heart constricts, the myocardium of the heart gets its blood when the heart is in diastole. The coronary artery is of two which are the right and the left coronary artery. The right coronary artery goes to the coronary sulcus to give branches which include the marginal artery (which supplies the right ventricle and the inferior part of the ventricle), and the posterior interventricular artery (which supplies the posterior aspect of the heart). The left coronary artery gives out two arteries which are the anterior interventricular artery (supplying the left ventricle, and the right ventricle muscles), and the Left Circumflex (which supplies the left atrium muscle and ventricle). Each of these arteries would split like other arteries that have arterioles, and capillaries which exchange blood with the muscle of the myocardium, and out of the myocardium, the blood goes to the venules which combine to become veins. From the Marginal artery, the vein formed is the small cardiac venule and then the Small cardiac vein. The blood from the Posterior interventricular artery is returned by the middle cardiac vein. The blood received by the myocardium of the heart from the anterior interventricular artery is returned by the Great Cardiac vein. Blood from the Left Circumflex is returned by the Posterior Vein of the Left Ventricle. These veins carry the blood to the coronary sinus which then to the right atrium and then to the right ventricle where the pulmonary circulation then begins., , , So let's quickly do the pulmonary circulation.
The pulmonary circulation takes blood from the right heart side to the lungs where oxygenation takes place, also CO2 is removed from the blood to the lungs where it is exhaled after which the blood is taken to the left side of the heart. The circulation of pulmonary circulation starts from the right ventricle where the blood moves through the pulmonary semilunar valve to the pulmonary trunk. The blood goes through the pulmonary trunk and then splits into the right and left pulmonary arteries. Keep in mind that the pulmonary artery carries deoxygenated blood. The pulmonary arteries carry blood to the lungs. In the lungs, they split to give pulmonary arterioles, then to the capillaries. From the capillaries, waste products, and CO2 are removed and blood becomes oxygenated through gaseous exchanges from the alveolar. From the pulmonary capillaries, they drain to the pulmonary venules. From the pulmonary venule, they come together to form the pulmonary veins which then take the blood from the lungs to the left side of the heart. The blood gets to the left atrium which then pumps the blood through the mitral valve to the left ventricle which then pumps the blood to the body through the Aorta., ,