chapter 10 circulatory system

• circulatory system


  moves blood throughout the body. Nutrients and oxygen are carried in blood to all cells in the body. Carbon dioxide and other waste products of metabolism are carried away from cells to be excreted from the body. The circulatory system carries hormones from one part of body to target organs and tissues. It distributes heat throughout the body and maintains levels of body fluids. It helps defend the body against invading microorganisms. Our body has about 5.6 liters of blood. They circulates through the body three times every minute and travels a total of 19000km a day.
• arteries


  blood vessels that carry blood away from the heart. They are made of thick walls that are layers of connective tissues and muscle fibers. They have very thick walls to hold the high pressure within the arteries. They do not contain any valves. They bulge every time the heart beats, as blood surges from the heart and enters the arteries. This change in diameter is the pulse you can feel near your wrist and on either side of your neck.
• arterioles


  blood from the arteries passes into these smaller vessels. Much thinner walls than arteries. Made of elastic fibers and smooth muscles. Do not contain any valves. The blood in humans flows from the heart to arteries to arterioles to capillaries to venules to veins.
• autonomic nervous system


  controls motor nerves that maintain equilibrium. Regulates the diameter of the arterioles. Not under conscious control(we don't need to think about it).
• vasoconstriction


  when the blood passes into the smaller arterioles, the middle layer of the arterioles are composed of elastic fibers and smooth muscle. The diameter of these vessels is regulated by the autonomic nervous system. Nerve impulses cause smooth muscle in the arterioles to contract, reducing the diameter of the blood vessel. This constriction is called vasoconstriction. Vasoconstriction causes a reduction of blood flow to tissues.
• vasodilation


  the opposite of vasoconstriction. This is when the arterioles dilate(widen) increasing blood flow to the tissues.
• vasoconstriction and vasodilation


  When exercising, muscle cells need more O₂ and nutrients to get rid of more CO₂. Thus increased blood flow is needed by cells, causes increased vasodilation. As blood flow increases, blood pressure increase. Vasodilation is important because this widening of arterioles reduce high blood pressure. If blood pressure drops, arterioles constrict to increase blood flow and blood pressure. The body constantly maintains homeostasis by constricting and dilating to maintain healthy blood pressure.
• arteriosclerosis


  a degeneration of blood vessels caused by the accumulation of fat deposits in the inner wall, a group of disorders that cause the blood vessels to thicken, harden, and lose their elasticity. Arteriosclerosis is caused by an excess amount of fat in blood vessels that join together and stick to the walls of the arteries. This narrowing of the vessels leads to high blood pressure. Blood clots can form, blocking the artery, and cutting off blood flow. If this happens in the heart, this results in a heart attack.
• aneurysm


  a bulge in the wall of a weakened vessel. If it occurs in the brain, it can cause a stroke. If a blockage occurs in the coronary arteries, which supply blood to the heart, a heart attack may occur.
• cardiac catheterization


  a procedure where a thin tube, catheter, is threaded through a vessel to the heart. To analyze the amount of blockage, a dye is used to make the vessels visible on X-ray film. Doctors can study the blood flow or lack of flow due to the blockage.
• angioplasty


  a little balloon is placed inside a vessel and inflated. This compresses the plaque and opens up the vessel. A stent may be inserted to hold this blocked area open. By pass surgery may be necessary if the vessel is extensively blocked or damaged and cannot take the insertion of a stent.
• capillaries


  tiniest blood vessels, composed of a single layer of cells. Site of fluid and gas exchange between blood and body cells, they are so small that red blood cells must travel in single file through them. Capillaries are only two cells away from any one cell, capillary beds are easily destroyed by high blood pressure or any impact that can cause bruising.
• capillaries

  Capillaries carry oxygenated blood(appears red) to the tissues. O₂ diffuses from the capillaries into tissues. Deoxygenated blood appears purple - blue as it leaves capillaries and enters small veins called venules. Blood then passes back to the heart by ways of veins.
• bruising


  the internal bleeding of the blood coming from a capillary bed that has ruptured. The blood travels into the spaces between the tissues. This pooling of blood is visible under skin as a bruise.
• veins and venules


  capillaries merge and become larger vessels called venules. The walls of venules contain smooth muscle. Venules merge into veins, which have larger diameter. The diameter of the veins increases as they get closer to the heart. As the blood flows from the arteries to the arterioles to the capillaries, blood flow and blood pressure are reduced. By the time the blood reaches the venules, the pressure is not enough to get the blood back to the heart, especially from the leg.
• how does the body keep the blood flowing back to the heart?


  two methodes:

  1. veins contain one way valves which force the blood to move back in the direction of the heart. The valves prevent the blood flowing in the opposite direction.
  2. the skeletal muscles next to the veins contract and push on the veins to make the blood pressure high enough to make blood move back to the heart.
• heart


  muscular organ that pumps in order to circulate the blood throughout the body. Consists of 2 parallel pumps which are separated by the septum. The right side receives deoxygenated blood from the body tissues and pumps it to the lungs. The left side receives oxygenated blood from the lungs and pumps it to the body tissues.
• pulmonary circulatory system


  vessels that carry blood to and from the lung
• systemic circulatory system


  vessels that carry blood to and from the body tissues
• pulmonary arteries


  carry deoxygenated blood away from the heart
• pulmonary veins


  carry oxygenated blood to the heart
• atria


  thin walled chambers of the heart that receive blood from veins
• ventricles


  thick walled chambers of the heart that pump blood to the arteries
• aorta


  the largest artery in the body. It carries oxygenated blood leaving the heart to the body
• superior and inferior vena cava


  carries deoxygenated blood from the body and empties into the right atrium of the heart
• double circulation in mammals(humans)


  deoxygenated blood returns to the right side of the heart at the right atrium. Right atrium pumps to right ventricle which pumps the blood to the lungs. Oxygenated blood returns to the left side of the heart at the left atrium. Left atrium pumps to the left ventricle and aorta.
• order of circulation of blood


  superior/inferior vena cava ⟶ right atrium ⟶ right ventricle ⟶ pulmonary arteries ⟶ lungs ⟶ pulmonary vein ⟶ left atrium ⟶ left ventricles ⟶ aorta ⟶ arteries ⟶ arterioles ⟶ capillaries ⟶ venules ⟶ veins(superior and inferior vena cava)
• one way flow of blood through the heart


  the blood flows through the heart in one direction. This occurs because of the presence of valves. The lubb-dubb sound of the heart is caused by the closing of atrioventricular valves(AV) and semilunar valves.
• atrioventricular valves(AV)


  separate the atria from the ventricles. They prevent the blood in the ventricles from flowing back up into the atria when the ventricles contract.
• semilunar valves


  separate the ventricles form the arteries(pulmonary artery and aorta). They prevent the blood that has entered the arteries from flowing back into the ventricles.
• diastole


  heart relaxes, atria fill with blood. AV valves are open so when the atria contract, the ventricles fill with blood. Semilunar valves are closed.
• systole


  ventricles contract to pump blood out of the heart. AV valves are closed. Semilunar valves are open so blood can leave the heart.
• control of heart rate


  the heart is a myogenic muscle, it can contract without external nerve simulation. The heart rate of beating is set by the SA (sinoatrial) node. This is a bundle of specialized nerve and muscles located in the upper right atrium. It is the pacemaker and it sets the rate at approx. 70 beats per minutes.
• control of heart rate


  Nerve impulses travel from the SA node to a second node, the atrioventricular (AV) node. It serves as a conductor, passing nerve impulses via 2 large nerve fibers called Purkinje fibers through the septum toward the ventricles. Impulses along the outer walls of the ventricles back toward the atria. A wave of cardiac contraction follows the nerve pathway.
• sympathetic nervous system


  a division of the autonomic nervous system that prepares the body for stress
• parasympathetic nervous system


  a division of the autonomic nervous system that returns the body to normal resting levels following adjustments to stress
• control of heart rate


  both sympathetic and parasympathetic nervous system send signals from brain to the SA node, but the sympathetic nerves speed up the heart rate in preparation for a fight-or-flight response whereas the parasympathetic nerves reduce the heart rate to normal after a stress.
• diagnosing heart conditions

  • electrocardiograph - a technology used to diagnose heart conditions
  • electrocardiogram(ECG) - the electrical impulses in the heart are recorded on this device
  • P wave - the first impulse, used to pump the atria, is recorded as a small wave
  • QRS wave - the second impulse, used to pump the ventricles, is the largest wave
  • T wave - the last impulse represents the relaxation of the ventricles and is shown as a small wave
• ventricular fibrillation


  an uncontrolled heart rate. It is caused by toxin accumulation in the heart due to low levels of oxygen. The toxin, not the electric signals, causes the beating of the ventricles, causing wild beating of the heart.
• arrhythmia


  the term used by doctors to refer to irregular heartbeats. One cause is a blocked coronary artery. It delivers less blood and can cause the heart to beat in an irregular pattern.