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ANATOMY ANA 217 Cardiovascular System Auza, M I (BSc, MSc) Department of Human Anatomy Faculty of Basic Medical Sciences Bingham University, Karu  Cardiovascular System The cardiovascular system consists of the 1. Heart 2. Vascular system The primary fu...

ANATOMY ANA 217 Cardiovascular System Auza, M I (BSc, MSc) Department of Human Anatomy Faculty of Basic Medical Sciences Bingham University, Karu  Cardiovascular System The cardiovascular system consists of the 1. Heart 2. Vascular system The primary function of the heart is to pump blood through the arteries, capillaries, and veins. Blood transports oxygen and nutrients and has other important functions as well. The heart is the pump that keeps blood circulating properly.  Heart: Location The heart is located in the thoracic cavity between the lungs. This area is called the mediastinum. The base of the cone-shaped heart is uppermost, behind the sternum, and the great vessels enter or leave here. The apex (tip) of the heart points downward and is just above the diaphragm to the left of the midline. This is why we may think of the heart as being on the left side, because the strongest beat can be heard or felt here.  Heart: Pericardial Membranes The heart is enclosed in the pericardial membranes, of which there are three layers. The outermost is the fibrous pericardium, a loose fitting sac of strong fibrous connective tissue that extends inferiorly over the diaphragm and superiorly over the bases of the large vessels that enter and leave the heart. The endocardium is the lining of the chambers of the heart. The fibrous pericardium is the outermost layer. Layers of the wall of the heart and the pericardial membranes.  Heart: Pericardial Membranes The serous pericardium is a folded membrane; the fold gives it two layers, parietal and visceral. Lining the fibrous pericardium is the parietal pericardium. On the surface of the heart muscle is the visceral pericardium, often called the epicardium. Between the parietal and visceral pericardial membranes is serous fluid, which prevents friction as the heart beats.  Chambers of the Heart The heart is made up of four chambers The walls of the four chambers of the heart are made of cardiac muscle called the myocardium. The chambers are lined with endocardium, simple squamous epithelium that also covers the valves of the heart and continues into the vessels as their lining (endothelium). The important physical characteristic of the endocardium is not its thinness, but rather its smoothness. This very smooth tissue prevents abnormal blood clotting, because clotting would be initiated by contact of blood with a rough surface.  Chambers of the Heart The upper chambers of the heart are the right and left atria (singular: atrium), which have relatively thin walls and are separated by a common wall of myocardium called the interatrial septum. The lower chambers are the right and left ventricles, which have thicker walls and are separated by the interventricular septum  Right Atrium The two large caval veins return blood from the body to the right atrium. The superior vena cava carries blood from the upper body, and the inferior vena cava carries blood from the lower body. From the right atrium, blood will flow through the right atrioventricular (AV) valve, or tricuspid valve, into the right ventricle.  Right Atrium The tricuspid valve is made of three flaps (or cusps) of endocardium reinforced with connective tissue. The general purpose of all valves in the circulatory system is to prevent backflow of blood. The specific purpose of the tricuspid valve is to prevent backflow of blood from the right ventricle to the right atrium when the right ventricle contracts. As the ventricle contracts, blood is forced behind the three valve flaps, forcing them upward and together to close the valve.  Left Atrium The left atrium receives blood from the lungs, by way of four pulmonary veins. This blood will then flow into the left ventricle through the left atrioventricular (AV) valve, also called the mitral valve or bicuspid (two flaps) valve. The mitral valve prevents backflow of blood from the left ventricle to the left atrium when the left ventricle contracts. Another function of the atria is the production of a hormone involved in blood pressure maintenance.  Left Atrium When the walls of the atria are stretched by increased blood volume or blood pressure, the cells produce atrial natriuretic peptide (ANP), also called atrial natriuretic hormone (ANH). The ventricles of the heart produce a similar hormone called B-type natriuretic peptide, or BNP ANP decreases the reabsorption of sodium ions by the kidneys, so that more sodium ions are excreted in urine, which in turn increases the elimination of water. The loss of water lowers blood volume and blood pressure. ANP is an antagonist to the hormone aldosterone, which raises blood pressure.  Right Ventricle When the right ventricle contracts, the tricuspid valve closes and the blood is pumped to the lungs through the pulmonary artery (or trunk). At the junction of this large artery and the right ventricle is the pulmonary semilunar valve (or more simply, pulmonary valve). Its three flaps are forced open when the right ventricle contracts and pumps blood into the pulmonary artery. When the right ventricle relaxes, blood tends to come back, but this fills the valve flaps and closes the pulmonary valve to prevent backflow of blood into the right ventricle  Right Ventricle Projecting into the lower part of the right ventricle are columns of myocardium called papillary muscles. Strands of fibrous connective tissue, the chordae tendineae, extend from the papillary muscles to the flaps of the tricuspid valve. When the right ventricle contracts, the papillary muscles also contract and pull on the chordae tendineae to prevent inversion of the tricuspid valve. If you have ever had your umbrella blown inside out by a strong wind, you can see what would happen if the flaps of the tricuspid valve were not anchored by the chordae tendineae and papillary muscles.  Left Ventricle The walls of the left ventricle are thicker than those of the right ventricle, which enables the left ventricle to contract more forcefully. The left ventricle pumps blood to the body through the aorta, the largest artery of the body. At the junction of the aorta and the left ventricle is the aortic semilunar valve (or aortic valve). This valve is opened by the force of contraction of the left ventricle, which also closes the mitral valve.  Left Ventricle The aortic valve closes when the left ventricle relaxes, to prevent backflow of blood from the aorta to the left ventricle. When the mitral (left AV) valve closes, it prevents backflow of blood to the left atrium; the flaps of the mitral valve are also anchored by chordae tendineae and papillary muscles. All of the valves are also depicts the fibrous skeleton of the heart. This is fibrous connective tissue that anchors the outer edges of the valve flaps and keeps the valve openings from stretching. It also separates the myocardium of the atria and ventricles and prevents the contraction of the atria from reaching the ventricles except by way of the normal conduction pathway.  Anatomy Of The Heart Structure Description Epicardium Serous membrane on the surface of the myocardium Myocardium Heart muscle; forms the walls of the four chambers Endocardium Endothelium that lines the chambers and covers the valves; smooth to prevent abnormal clotting Right atrium (RA) Receives deoxygenated blood from the body by way of the superior and inferior caval veins Tricuspid valve Right AV valve; prevents backflow of blood from the RV to the RA when the RV contracts Right ventricle (RV) Pumps blood to the lungs by way of the pulmonary artery Pulmonary semilunar Prevents backflow of blood from the pulmonary artery to the RV when the RV relaxes valve Left atrium (LA) Receives oxygenated blood from the lungs by way of the four pulmonary veins Mitral valve Left AV valve; prevents backflow of blood from the LV to the LA when the LV contracts Left ventricle (LV) Pumps blood to the body by way of the aorta Aortic semilunar valve Prevents backflow of blood from the aorta to the LV when the LV relaxes Papillary muscles and In both the RV and LV; prevent inversion of the AV valves when the ventricles contract chordae tendineae Fibrous skeleton of the Fibrous connective tissue that anchors the four heart valves, prevents enlargement of the valve heart openings, and electrically insulates the ventricles from the atria  Coronary Vessels The right and left coronary arteries are the first branches of the ascending aorta, just beyond the aortic semilunar valve. The two arteries branch into smaller arteries and arterioles, then to capillaries. The coronary capillaries merge to form coronary veins, which empty blood into a large coronary sinus that returns blood to the right atrium. The purpose of the coronary vessels is to supply blood to the myocardium itself, because oxygen is essential for normal myocardial contraction. If a coronary artery becomes obstructed, by a blood clot for example, part of the myocardium becomes ischemic, that is, deprived of its blood supply. Prolonged ischemia will create an infarct, an area of necrotic (dead) tissue. This is a myocardial infarction, commonly called a heart attack.  The Vascular System The vascular system consists of the arteries, capillaries, and veins through which the heart pumps blood throughout the body. The major “business” of the vascular system, which is the exchange of materials between the blood and tissues, takes place in the capillaries. The arteries and veins, however, are just as important, transporting blood between the capillaries and the heart.  Arteries Arteries carry blood from the heart to capillaries; smaller arteries are called arterioles. The artery has three layers (or tunics) of tissues, each with different functions. Tunica intima Tunica media Tunica externa  Layers: Tunica intima The innermost layer, the tunica intima, is the only part of a vessel that is in contact with blood. It is made of simple squamous epithelium called endothelium. This lining is the same type of tissue that forms the endocardium, the lining of the chambers of the heart. Its extreme smoothness prevents abnormal blood clotting. The endothelium of vessels, however, also produces nitric oxide (NO), which is a vasodilator.  Layers: Tunica Media The tunica media, or middle layer, is made of smooth muscle and elastic connective tissue. Both of these tissues are involved in the maintenance of normal blood pressure, especially diastolic blood pressure when the heart is relaxed. The smooth muscle is the tissue affected by the vasodilator NO; relaxation of this muscle muscle tissue brings about dilation of the vessel. Smooth muscle also has a nerve supply; sympathetic nerve impulses bring about vasoconstriction.  Layers: Tunica Externa Fibrous connective tissue forms the outer layer, the tunica externa. This tissue is very strong, which is important to prevent the rupture or bursting of the larger arteries that carry blood under high pressure. The outer and middle layers of large arteries are quite thick. In the smallest arterioles, only individual smooth muscle cells encircle the tunica intima. The smooth muscle layer enables arteries to constrict or dilate. Such changes in diameter are regulated by the medulla and autonomic nervous system.  Veins Veins carry blood from capillaries back to the heart; the smaller veins are called venules. The same three tissue layers are present in veins as in the walls of arteries, but there are some differences when compared to the arterial layers. The inner layer of veins is smooth endothelium, but at intervals this lining is folded to form valves.  Anastomoses An anastomosis is a connection, or joining, of vessels, that is, artery to artery or vein to vein. The general purpose of these connections is to provide alternate pathways for the flow of blood if one vessel becomes obstructed. An arterial anastomosis helps ensure that blood will get to the capillaries of an organ to deliver oxygen and nutrients and to remove waste products. There are arterial anastomoses, for example, between some of the coronary arteries that supply blood to the myocardium. A venous anastomosis helps ensure that blood will be able to return to the heart in order to be pumped again. Venous anastomoses are most numerous among the veins of the legs, where the possibility of obstruction increases as a person gets older  Capillaries Capillaries carry blood from arterioles to venules. Their walls are only one cell in thickness; capillaries are actually the extension of the endothelium, the simple squamous lining, of arteries and veins. Some tissues do not have capillaries; these are the epidermis, cartilage, and the lens and cornea of the eye.  Capillaries: precapillary sphincters Blood flow into capillary networks is regulated by smooth muscle cells called precapillary sphincters, found at the beginning of each network. Precapillary sphincters are not regulated by the nervous system but rather constrict or dilate depending on the needs of the tissues. Because there is not enough blood in the body to fill all of the capillaries at once, precapillary sphincters are usually slightly constricted. In active tissue such as exercising muscle, that requires more oxygen, the precapillary sphincters dilate to increase blood flow. These automatic responses ensure that blood, will circulate where it is needed most.  Capillaries: Sinusoids Some organs have another type of capillary called sinusoids, which are larger and more permeable than are other capillaries. The permeability of sinusoids permits large substances such as proteins and blood cells to enter or leave the blood. Sinusoids are found in the red bone marrow and spleen, where blood cells enter or leave the blood, and in organs such as the liver and pituitary gland, which produce and secrete proteins into the blood.  Exchanges In Capillaries Capillaries are the sites of exchanges of materials between the blood and the tissue fluid surrounding cells. Some of these substances move from the blood to tissue fluid, and others move from tissue fluid to the blood.  Exchanges In Capillaries Gases move by diffusion, that is, from their area of greater concentration to their area of lesser concentration. Oxygen, therefore, diffuses from the blood in systemic capillaries to the tissue fluid, and carbon dioxide diffuses from tissue fluid to the blood to be brought to the lungs and exhaled.  Exchanges In Capillaries As blood enters capillaries from the arterioles, Blood pressure here is high (about 30 to 35 mmHg) and the pressure of the surrounding tissue fluid is much lower(about 2 mmHg). Because the capillary blood pressure is higher, the process of filtration occurs, which forces plasma and dissolved nutrients out of the capillaries and into tissue fluid. This is how nutrients such as glucose, amino acids, and vitamins are brought to cells.  Exchanges In Capillaries Blood pressure decreases as blood reaches the venous end of capillaries, but notice that proteins such as albumin have remained in the blood. Albumin contributes to the colloid osmotic pressure (COP) of blood; this is an “attracting” pressure, a “pulling” rather than a “pushing” pressure. At the venous end of capillaries, the presence of albumin in the blood pulls tissue fluid into the capillaries, which also brings into the blood the waste products produced by cells. The tissue fluid that returns to the blood also helps maintain normal blood volume and blood pressure. Diffusion of fluid molecules and dissolved substances between the capillary and interstitial fluid spaces.  Pathways Of Circulation The two major pathways of circulation are Pulmonary circulation Systemic circulation. Pulmonary circulation begins at the right ventricle, and systemic circulation begins at the left ventricle. Hepatic portal circulation is a special segment of systemic circulation that will be covered separately. Fetal circulation involves pathways that are only before birth and will also be discussed separately.  Pulmonary Circulation The right ventricle pumps blood into the pulmonary artery (or trunk), which divides into the right and left pulmonary arteries, one going to each lung. Within the lungs each artery branches extensively into smaller arteries and arterioles, then to capillaries. The pulmonary capillaries surround the alveoli of the lungs; it is here that exchanges of oxygen and carbon dioxide take place. The capillaries unite to form venules, which merge into veins, and finally into the two pulmonary veins from each lung that return blood to the left atrium. This oxygenated blood will then travel through the systemic circulation.  Systemic Circulation The left ventricle pumps blood into the aorta, the largest artery of the body. The branches of the aorta take blood into arterioles and capillary networks throughout the body. Capillaries merge to form venules and veins. The veins from the lower body take blood to the inferior vena cava; veins from the upper body take blood to the superior vena cava. These two caval veins return blood to the right atrium. Systemic arteries.  Systemic Circulation The aorta is a continuous vessel, it is divided into sections that are named anatomically: ascending aorta, aortic arch, thoracic aorta, and abdominal aorta. The ascending aorta is the first inch that emerges from the top of the left ventricle. The arch of the aorta curves posteriorly over the heart and turns downward. The thoracic aorta continues down through the chest cavity and through the diaphragm. the abdominal aorta continues below the level of the diaphragm to the level of the 4th lumbar vertebra, where it divides into the two common iliac arteries. Along its course, the aorta has many branches through which blood travels to specific organs and parts of the body.  Systemic Circulation The ascending aorta has only two branches: the right and left coronary arteries, which supply blood to the myocardium. The aortic arch has three branches that supply blood to the head and arms: the brachiocephalic artery, left common carotid artery, and left subclavian artery. The brachiocephalic (literally, “arm-head”) artery is very short and divides into the right common carotid artery and right subclavian artery. The right and left common carotid arteries extend into the neck, where each divides into an internal carotid artery and external carotid artery, which supply the head. The right and left subclavian arteries are in the shoulders behind the clavicles and continue into the arms.  Systemic Circulation As the artery enters another body area (it may not “branch,” simply continue), its name changes: The subclavian artery becomes the axillary artery, which becomes the brachial artery. See the branches of the carotid and subclavian arteries in the diagram  Systemic Circulation Some of the arteries in the head contribute to an important arterial anastomosis, the circle of Willis (or cerebral arterial circle), which is a “circle” of arteries around the pituitary gland (Fig. 13–6). The circle of Willis is formed by the right and left internal carotid arteries and the basilar artery, which is the union of the right and left vertebral arteries (branches of the subclavian arteries). The brain is always active, even during sleep, and must have a constant flow of blood to supply oxygen and remove waste products. For this reason there are four vessels that bring blood to the circle of Willis. From this anastomosis, several paired arteries (the cerebral arteries) extend into the brain itself.  Systemic Circulation The thoracic aorta and its branches supply the chest wall and the organs within the thoracic cavity. The abdominal aorta gives rise to arteries that supply the abdominal wall and organs and to the common iliac arteries, which continue into the legs. The common iliac artery becomes the external iliac artery, which becomes the femoral artery, which becomes the popliteal artery; the same vessel has different names based on location. The systemic veins drain blood from organs or parts of the body and often parallel their corresponding arteries.  Hepatic Portal Circulation Hepatic portal circulation is a subdivision of systemic circulation in which blood from the abdominal digestive organs and spleen circulates through the liver before returning to the heart. Blood from the capillaries of the stomach, small intestine, colon, pancreas, and spleen flows into two large veins, the superior mesenteric vein and the splenic vein, which unite to form the portal vein.  Hepatic Portal Circulation The portal vein takes blood into the liver, where it branches extensively and empties blood into the sinusoids, the capillaries of the liver. From the sinusoids, blood flows into hepatic veins, to the inferior vena cava and back to the right atrium.  Hepatic Portal Circulation Glucose from carbohydrate digestion is absorbed into the capillaries of the small intestine; after a big meal this may greatly increase the blood glucose level. If this blood were to go directly back to the heart and then circulate through the kidneys, some of the glucose might be lost in urine. However, blood from the small intestine passes first through the liver sinusoids, and the liver cells remove the excess glucose and store it as glycogen. The blood that returns to the heart will then have a blood glucose level in the normal range.  Hepatic Portal Circulation Another example: Alcohol is absorbed into the capillaries of the stomach. If it were to circulate directly throughout the body, the alcohol would rapidly impair the functioning of the brain. Portal circulation, however, takes blood from the stomach to the liver, the organ that can detoxify the alcohol and prevent its detrimental effects on the brain. Of course, if alcohol consumption continues, the blood alcohol level rises faster than the liver’s capacity to detoxify, and the well known signs of alcohol intoxication appear. As you can see, this portal circulation pathway enables the liver to modify the blood from the digestive organs and spleen. Some nutrients may be stored or changed, bilirubin from the spleen is excreted into bile, and potential poisons are detoxified before the blood returns to the heart and the rest of the body.  Fetal Circulation The fetus depends upon the mother for oxygen and nutrients and for the removal of carbon dioxide and other waste products. The site of exchange between fetus and mother is the placenta, which contains fetal and maternal blood vessels that are very close to one another The blood of the fetus does not mix with the blood of the mother; substances are exchanged by diffusion and active transport mechanisms.  Fetal Circulation The fetus is connected to the placenta by the umbilical cord, which contains two umbilical arteries and one umbilical vein (see Fig. 13–8). The umbilical arteries are branches of the fetal internal iliac arteries; they carry blood from the fetus to the placenta. In the placenta, carbon dioxide and waste products in the fetal blood enter maternal circulation, and oxygen and nutrients from the mother’s blood enter fetal circulation.  Fetal Circulation The umbilical vein carries this oxygenated blood from the placenta to the fetus. Within the body of the fetus, the umbilical vein branches: One branch takes some blood to the fetal liver, but most of the blood passes through the ductus venosus to the inferior vena cava, to the right atrium. After birth, when the umbilical cord is cut, the remnants of these fetal vessels constrict and become nonfunctional. The other modifications of fetal circulation concern the fetal heart and large arteries. Because the fetal lungs are deflated and do not provide for gas exchange, blood is shunted away from the lungs and to the body.  Fetal Circulation The foramen ovale is an opening in the interatrial septum that permits some blood to flow from the right atrium to the left atrium, not, as usual, to the right ventricle. The blood that does enter the right ventricle is pumped into the pulmonary artery. The ductus arteriosus is a short vessel that diverts most of the blood in the pulmonary artery to the aorta, to the body. Both the foramen ovale and the ductus arteriosus permit blood to bypass the fetal lungs. Just after birth, the baby breathes and expands its lungs, which pulls more blood into the pulmonary circulation. More blood then returns to the left atrium, and a flap on the left side of the foramen ovale is closed. The ductus arteriosus constricts, probably in response to the higher oxygen content of the blood, and pulmonary circulation becomes fully functional within a few days.  Function Of Circulation The function of the circulation is to service the needs of the body tissues: To transport nutrients to the body tissues To transport waste products away To conduct hormones from one part of the body to another And, in general, to maintain an appropriate environment in all the tissue fluids of the body for optimal survival and function of the cells.  Major Systemic Arteries: Branches of the Ascending Aorta and Aortic Arch Artery Branch of Region supplied Coronary a. Ascending aorta Myocardium Brachiocephalic a. Aortic arch Right arm and head Right common carotid a. Brachiocephalic a. Right side of head Right subclavian a. Brachiocephalic a. Right shoulder and arm Left common carotid a. Aortic arch Left side of head Left subclavian a. Aortic arch Left shoulder and arm External carotid a. Common carotid a. Superficial head Superficial temporal a. External carotid a. Scalp Internal carotid a. Common carotid a. Brain (circle of Willis) Ophthalmic a. Internal carotid a. Eye Vertebral a. Subclavian a. Cervical vertebrae and circle of Willis Axillary a. Subclavian a. Armpit Brachial a. Axillary a. Upper arm Radial a. Brachial a. Forearm Ulnar a. Brachial a. Forearm Volar arch Radial and ulnar a. Hand  Major Systemic Arteries: Branches of Thoracic Aorta Artery Region Supplied Intercostal a. (9 pairs) Skin, muscles, bones of trunk Superior phrenic a. Diaphragm Pericardial a. Pericardium Esophageal a. Esophagus Bronchial a. Bronchioles and connective tissue of the lungs  Major Systemic Arteries: Branches of Abdominal Aorta Artery Region Supplied Inferior phrenic a. Diaphragm Lumbar a. Lumbar area of back Middle sacral a.. Sacrum, coccyx, buttocks Celiac a. (see branches) Hepatic a. Liver Left gastric a. Stomach Splenic a. Spleen, pancreas Superior mesenteric a. Small intestine, part of colon Suprarenal a. Adrenal glands Renal a. Kidneys Inferior mesenteric a. Most of colon and rectum  Major Systemic Arteries: Branches of Abdominal Aorta Artery Region Supplied Testicular or ovarian a. Testes or ovaries Common iliac a. The two large vessels that receive blood from the abdominal aorta; each branches as follows: Internal iliac a. Bladder, rectum, reproductive organs External iliac a. Lower pelvis to leg Femoral a. Thigh Popliteal a. Back of knee Anterior tibial a. Front of lower leg Dorsalis pedis Top of ankle and foot Plantar arches Foot Posterior tibial a. Back of lower leg Peroneal a. Medial lower leg Plantar arches Foot  Major Systemic Veins: Head and Neck Veins Veins Joined Region Drained Cranial venous Internal jugular v. Brain, including reabsorbed CSF sinuses Internal jugular v. Brachiocephalic Face and neck v. External jugular v. Subclavian v. Superficial face and neck Subclavian v. Brachiocephalic Shoulder v. Brachiocephalic v. Superior vena Upper body cava Superior vena cava Right atrium Upper body  Major Systemic Veins: Arm and Shoulder Veins Veins Joined Region Drained Radial v. Brachial v.. Forearm and hand Ulnar v.. Brachial v.. Forearm and hand Cephalic v. Axillary v. Superficial arm and forearm Basilic v. Axillary v. Superficial upper arm Brachial v. Axillary v. Upper arm Axillary v. Subclavian v. Armpit Subclavian v. Brachiocephalic v. Shoulder  Major Systemic Veins: Trunk Veins Veins Joined Region Drained Brachiocephalic v. Superior vena cava Upper body Azygos v. Superior vena cava Deep structures of chest and abdomen; links inferior vena cava to superior vena cava Hepatic v. Inferior vena cava Liver Renal v. Inferior vena cava Kidney Testicular or ovarian Inferior vena cava and Testes or ovaries v. left renal v. Internal iliac v. Common iliac v. Rectum, bladder, reproductive organs External iliac v. Common iliac v. Leg and abdominal wall Common iliac v. Inferior vena cava Leg and lower abdomen  Major Systemic Veins: Leg and Hip Veins Veins Joined Region Drained Anterior and Popliteal v. Lower leg and foot posterior tibial v. Popliteal v. Femoral v. Knee Small saphenous v. Popliteal v. Superficial leg and foot Great saphenous v. Femoral v. Superficial foot, leg, and thigh Femoral v. External iliac v. Thigh External iliac v. Common iliac v. Leg and abdominal wall Common iliac v. Inferior vena cava Leg and lower abdomen Inferior vena cava Right atrium Lower body