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• The circulatory system is composed of three parts: the heart, the blood vessels, and the blood.
• There are two basic types of circulatory systems: open system, where the blood leaves the open-ended blood vessels like insects, and closed system, where the blood remains in the blood vessels like humans.
• Advantages of a closed circulatory system include faster delivery of nutrients to cells, increased blood flow to different organs, and more active organism.
• Blood vessels can be classified into three main types: arteries, veins, and capillaries.
• Arteries carry blood away from the heart, divide into smaller blood vessels called arterioles, have small lumens, thick elastic walls, and do not have valves.
• The blood in arteries is under high pressure and typically carries oxygenated blood.
• Blood flows in pulses in arteries.
• Veins carry blood to the heart, are smaller than arteries, have thin walls, large lumen, usually carry deoxygenated blood, and have valves.
• The blood in veins is under low pressure and the blood flows smoothly (no pulse).
• Capillaries are tiny, much branched vessels that carry blood from arteries to veins, their wall, the endothelium, is only one cell thick and permeable to water and small molecules, allowing dissolved substances to enter and leave the blood by diffusion.
• The heart has four valves at the exits of each heart chamber to ensure that blood flows through the heart in one direction only: the Tricuspid Valve between the right atrium and right ventricle, the Bicuspid Valve between the left atrium and the left ventricle, and the Semilunar valves located between the pulmonary artery and the right ventricle and the aorta and left ventricle.
• The electrical impulses then cause the ventricles to contract and blood is pumped out of the heart.
• The flow of blood through the heart is due to the alternate contraction and relaxation of heart muscle, known as the cardiac cycle.
• The pacemaker sends out electrical impulses which the walls of the right and left atria to contract, causing the atrial muscle to contract, forcing the blood through the tri- and bicuspid valves into the ventricles.
• More advanced animals have a two-circuit system.
• Blood pressure can be kept high to pump blood around the body to tissues and organs.
• Humans have a 2 circuit or double circulatory system: the Pulmonary Circuit which is the blood pathway from the heart to the lungs and back to the heart, and the Systemic Circuit which is the blood pathway from the heart all around the body and back to the heart.
• A portal system is a blood pathway that starts and ends in capillaries, for example, the hepatic portal system which starts in the capillaries of the small intestines and ends in the capillaries in the liver.
• If a coronary artery is blocked with fatty deposits, a person may suffer a heart attack, resulting in damage to the heart.
• The double circulation allows for the separation of oxygen rich and oxygen poor blood, allowing for efficient delivery of oxygen to the cells and maintaining a higher metabolic rate.
• The heart has two chambers on the right side and two chambers on the left side, separated by the septum which ensures that the deoxygenated blood on the right-hand side and the oxygenated blood on the left-hand side never mix.
• The heart wall is supplied with blood by the coronary arteries which branch from the aorta just above the semi lunar valves to the aorta.
• The heartbeat is controlled by a bundle of nerve tissue called the pacemaker, located in the wall at the top of the right atrium.
• Capillaries have no valves.
• Capillaries have the thickest walls of all blood vessels.
• A human heart is about the size of a clenched fist.
• Blood flows in pulses in arteries and veins, but flows smoothly in capillaries with no pulse.
• Veins carry blood to the heart.
• Arteries have thicker walls than veins.
• The heart is located in the thoracic or chest cavity, slightly to the left-hand side of the lungs.
• Muscle expands to allow increased blood flow through the vessel.
• Capillaries carry mostly oxygenated blood.
• Valves prevent the backflow of blood.
• The heart is surrounded by the pericardium, a double membrane filled with fluid, which allows friction-free movement when the heart is beating.
• The blood in capillaries is under very low pressure.
• The heart is made of cardiac muscle, which never fatigues (tires).
• Arteries carry blood away from the heart.
• Capillaries have the lowest blood pressure.
• Capillaries have the thinnest walls of all blood vessels, one cell thick.
• Capillaries connect arterioles to venules.