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Date Published: November 2003
Welcome to "Anatomy and Physiology of the Cardiovascular System". Before beginning, please take a moment to read the course details.
Course Length: Approximately 3 hours. Your
time may vary based on modem speed, prerequisite knowledge and
other factors.
Prerequisites: None.
Date Published: November 2003
Valid Until: November, 2006
The cardiovascular system—the heart, veins, arteries, and blood—provides oxygen and nutrients to all the tissues of the body at the same time as it removes carbon dioxide and waste materials. This course, Anatomy and Physiology of the Cardiovascular System, is divided into four sections.
The first section, OVERVIEW OF THE CARDIOVASCULAR SYSTEM, describes the anatomy of the heart and introduces the three interconnected circulatory systems that provide tissues with oxygen, reoxygenate blood, and nourish the heart.
The second section, NORMAL CARDIAC PHYSIOLOGY, describes the mechanical and electrical events of the heart and explains cardiac output.
The third section covers RENAL ANATOMY AND PHYSIOLOGY. All the body’s blood passes through the kidneys, which filter out impurities and surplus nutrients. Since they control the body’s fluid volume, the kidneys exert a great deal of influence over the cardiovascular system and blood pressure.
The fourth section, BLOOD PRESSURE, describes how blood pressure is determined and the different mechanisms by which normal blood pressure is regulated.
The cardiovascular system—the heart, blood vessels, and blood—comprise three interconnected circulatory systems. It provides oxygen and nutrients to all body tissues, including the heart itself, and removes carbon dioxide and waste materials at the same time. All the body’s blood passes through the kidneys, which filter out impurities and surplus nutrients.
These are the objectives for this section
After you finish this section, you should be able to:
The heart is a hollow, muscular organ approximately the size of a fist. It is located roughly in the middle of the chest, between the lungs. It serves as the pump for the cardiovascular system, creating the pressure that moves blood continuously through the arteries and veins. This lesson describes the heart, its conductance system and the blood vessels that are part of the cardiovascular system.
The heart is divided into four chambers: two upper chambers called the left and right atria, and two lower chambers called the left and right ventricles.
These chambers collect blood and pump it to different parts of the body.
The atria are reservoirs for returning blood. The right atrium receives deoxygenated blood from the body, and the left atrium receives oxygenated blood from the lungs.
A combination of gravity and atrial contraction then propels blood from the atria into the ventricles. The right ventricle pumps blood into the pulmonary artery to the lungs, and the left ventricle pumps newly oxygenated blood into the aorta and throughout the body. Since the left ventricle pumps against a higher pressure, its walls are significantly thicker; the right ventricular wall is only about one third of the thickness of the left, and the atrial walls are thinner yet.
Four heart valves keep blood flowing in the proper direction.
Each valve consists of fibrous flaps or cusps that attach to the heart's walls. The atrioventricular valves or tricuspid and mitral valves separate the atria from the ventricles and prevent blood from flowing back into the atria when the ventricles contract.
The three leaflets of the tricuspid valve separate the right atrium and ventricle, while the two leaflets of the mitral or bicuspid valves separate the left atrium and ventricle.
The pulmonic and aortic valves each have three cusps. The pulmonary valve separates the right ventricle and the pulmonary artery, preventing backflow from the lungs into the heart. The aortic valve, between the left ventricle and the aorta, prevents backflow from the aorta. The heart's walls are composed of three layers surrounded by a thin membranous sac called the pericardium:
The pericardium acts as a protective barrier against damage and infection from adjacent organs.
The space between the pericardium and epicardium contains a small amount of pericardial fluid, which minimises friction as the heart beats and cushions the heart during physical activity.
The epicardium is a moist, smooth, protective external layer.
The myocardium, the thickest layer, is composed of striated muscle that can contract and conduct electrical impulses.
The endocardium is a thin layer of smooth, flat endothelial cells lining the interior of the heart, and is continuous with the endothelium of blood vessels.
Regular, rhythmic beating of the heart is maintained by electrical impulses which are spread through the heart by a specialised conduction system, initiating atrial and then ventricular contraction. This lesson shows the anatomical pathway of this electrical conduction system.
Regular, rhythmic beating of the heart is maintained by electrical impulses that stimulate myocardial cells to contract. These electrical impulses result from the flow of electrically charged molecules or ions in cardiac cells. Impulses are spread through the heart by a specialised conduction system, initiating atrial and then ventricular contraction. In a healthy heart, electrical impulses originate in the sinoatrial node, an area of modified myocardial tissue at the junction of the right atrium and the superior vena cava.
Each impulse spreads throughout the atria, initiating atrial contraction to the atrio-ventricular node, located near the base of the tricuspid valve. Impulses then move into the His-Purkinje system, conducting tissue that spreads impulses to ventricular cells, causing ventricular contraction. The His-Purkinje system consists of the bundle of His, which travels down the interventricular septum, and Purkinje fibres, which fan out into the ventricles.
The His-Purkinje system ensures that the ventricles contract simultaneously to efficiently expel blood through the aortic and pulmonary valves.
Blood has many functions in the body: it supplies tissues with oxygen and other nutrients, transports waste products for excretion, helps regulate temperature, and influences pH. This lesson introduces the systemic, pulmonary, and coronary circulatory systems.
Blood is composed of about 60% plasma, a yellowish liquid containing water, proteins, and electrolytes, and 40% formed elements. The formed elements of blood are red blood cells or erythrocytes, white blood cells or leucocytes, and platelets.
Erythrocytes, which impart the blood's characteristic red colour, contain haemoglobin, the compound responsible for transporting oxygen. Leucocytes are a variety of cells that help to defend the body against infection. Platelets help to initiate blood clotting to repair damaged blood vessels.
Two discrete circulatory patterns transport blood around the body.
Systemic circulation carries oxygenated blood to most body tissues, and returns deoxygenated blood to the right atrium.
Pulmonary circulation carries deoxygenated blood to the lungs and returns newly oxygenated blood to the left atrium.
An important part of the systemic circulation is the coronary circulation, which supplies the heart muscle with blood.