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The Cardiovascular System
Users will gain a basic knowledge of the cardiovascular system in terms of its structure, functions, and classification.
After completing this unit, users will be able to:
- name the major components of the cardiovascular system;
- explain the vital role of the cardiovascular system in maintaining homeostasis;
- describe briefly the structure of the heart and relate its functions;
- define some heart related terms such as cardiac cycle and heart rate;
- classify blood vessels based on their structure and function;
- relate briefly the physiology of blood circulation;
- define some blood related terms such as blood flow, pulse, and blood pressure; and
- name the two blood circuits that function differently.
Introduction to the Cardiovascular System
The cardiovascular system is sometimes called the blood-vascular or simply the circulatory system. It consists of the heart, which is a muscular pumping device, and a closed system of vessels called arteries, veins, and capillaries. As the name implies, blood contained in the circulatory system is pumped by the heart around a closed circle or circuit of vessels as it passes again and again through the various "circulations" of the body.
As in the adult, survival of the developing embryo depends on the circulation of blood to maintain homeostasis and a favorable cellular environment. In response to this need, the cardiovascular system makes its appearance early in development and reaches a functional state long before any other major organ system. Incredible as it seems, the primitive heart begins to beat regularly early in the fourth week following fertilization.
The vital role of the cardiovascular system in maintaining homeostasis depends on the continuous and controlled movement of blood through the thousands of miles of capillaries that permeate every tissue and reach every cell in the body. It is in the microscopic capillaries that blood performs its ultimate transport function. Nutrients and other essential materials pass from capillary blood into fluids surrounding the cells as waste products are removed.
Numerous control mechanisms help to regulate and integrate the diverse functions and component parts of the cardiovascular system in order to supply blood to specific body areas according to need. These mechanisms ensure a constant internal environment surrounding each body cell regardless of differing demands for nutrients or production of waste products.
The heart is a muscular pump that provides the force necessary to circulate the blood to all the tissues in the body. Its function is vital because, to survive, the tissues need a continuous supply of oxygen and nutrients, and metabolic waste products have to be removed. Deprived of these necessities, cells soon undergo irreversible changes that lead to death. While blood is the transport medium, the heart is the organ that keeps the blood moving through the vessels. The
normal adult heart pumps about 5 liters of blood every minute throughout life. If it loses its pumping effectiveness for even a few minutes, the individual's life is jeopardized. Click a topic below to learn more about the heart.
- Structure of the Heart
- Physiology of the Heart
Structure of the Heart
Physiology of the Heart
Blood is the fluid of life, transporting oxygen from the lungs to body tissue and carbon dioxide from body tissue to the lungs. Blood is the fluid of growth, transporting nourishment from digestion and hormones from glands throughout the body. Blood is the fluid of health, transporting disease fighting substances to the tissue and waste to the kidneys. Because it contains living cells, blood is alive. Red blood cells and white blood cells are responsible for nourishing and cleansing the body.
Without blood, the human body would stop working.
To learn more about blood, select a topic listed below to branch into a sub-section.
- Physiology of Circulation
- Circulatory Pathways
Physiology of Circulation
The blood vessels of the body are functionally divided into two distinctive circuits: pulmonary circuit and systemic circuit. The pump for the pulmonary circuit, which circulates blood through the lungs, is the right ventricle. The left ventricle is the pump for the systemic circuit, which provides the blood supply for the tissue cells of the body.
Pulmonary circulation transports oxygen-poor blood from the right ventricle to the lungs where blood picks up a new blood supply. Then it returns the oxygen-rich blood to the left atrium.
The systemic circulation provides the functional blood supply to all body tissue. It carries oxygen and nutrients to the cells and picks up carbon dioxide and waste products. Systemic circulation carries oxygenated blood from the left ventricle, through the arteries, to the capillaries in the tissues of the body. From the tissue capillaries, the deoxygenated blood returns through a system of veins to the right atrium of the heart.
The coronary arteries are the only vessels that branch from the ascending aorta. The brachiocephalic, left common carotid, and left subclavian arteries branch from the aortic arch. Blood supply for the brain is provided by the internal carotid and vertebral arteries. The subclavian arteries provide the blood supply for the upper extremity. The celiac, superior mesenteric, suprarenal, renal, gonadal, and inferior mesenteric arteries branch from the abdominal aorta to supply the abdominal viscera. Lumbar
arteries provide blood for the muscles and spinal cord. Branches of the external iliac artery provide the blood supply for the lower extremity. The internal iliac artery supplies the pelvic viscera.
Major Systemic Arteries
All systemic arteries are branches, either directly or indirectly, from the aorta. The aorta ascends from the left ventricle, curves posteriorly and to the left, then descends through the thorax and abdomen. This geography divides the aorta into three portions: ascending aorta, arotic arch, and descending aorta. The descending aorta is further subdivided into the thoracic arota and abdominal aorta.
Major Systemic Veins
After blood delivers oxygen to the tissues and picks up carbon dioxide, it returns to the heart through a system of veins. The capillaries, where the gaseous exchange occurs, merge into venules and these converge to form larger and larger veins until the blood reaches either the superior vena cava or inferior vena cava, which drain into the right atrium.
Most circulatory pathways in a fetus are like those in the adult but there are some notable differences because the lungs, the gastrointestinal tract, and the kidneys are not functioning before birth. The fetus obtains its oxygen and nutrients from the mother and also depends on maternal circulation to carry away the carbon dioxide and waste products.
The umbilical cord contains two umbilical arteries to carry fetal blood to the placenta and one umbilical vein to carry oxygen-and-nutrient-rich blood from the placenta to the fetus. The ductus venosus allows blood to bypass the immature liver in fetal circulation. The foramen ovale and ductus arteriosus are modifications that permit blood to bypass the lungs in fetal circulation.
Cardiovascular System: Unit Review
Here is what we have learned from this unit:
- The cardiovascular system consists of the heart, which is a muscular pumping device, and a closed system of vessels called arteries, veins, and capillaries.
- The vital role of the cardiovascular system in maintaining homeostasis depends on the continuous and controlled movement of blood through the thousands of miles of capillaries that permeate every tissue and reach every cell in the body.
- The heart is a muscular pump that provides the force necessary to circulate the blood to all the tissues in the body.
- Three layers of the heart are: the epicardium, the myocardium, and the endocardium.
- The four chambers of the heart are: the right atrium, the right ventricle, the left atrium, and the left ventricle.
- Two types of valves of the heart are the atrioventricular valves and semilunar valves.
- Blood flows from the right atrium to the right ventricle and then is pumped to the lungs to receive oxygen. From the lungs, the blood flows to the left atrium, then to the left ventricle. From there it is pumped to the systemic circulation.
- Specialized cardiac muscle cells that make up the conduction system of the heart coordinate contraction of the chambers.
- The pulmonary vessels transport blood from the right ventricle to the lungs and back to the left atrium.
- The systemic vessels carry blood from the left ventricle to the tissues in all parts of the body and then returns the blood to the right atrium.
- Substances pass through the capillary wall by diffusion, filtration, and osmosis.