The Human Body: Circulatory System/2nd Ed.

[Music] one heart 5 L of blood and some 96,000 km of blood vessels 60,000 Mi of them make up your circulatory system through it materials for energy growth and repair are moved to every living cell of your body and waste products are carried away this is a very complex job but what makes it all possible is one of Nature's simplest substances water your circulatory system works because of water water helps things move in your inner environment and in your outer environment the world outside you substances dissolve in water substances float in water and whether the water runs through pipes or out in the open the substances in it are moved from place to place water is a mover in your body water does the same kind of job moving floating and dissolve substances in your blood to and from all your living cells your blood flows because more than half of it is water the watery part of blood is plasma floating in this plasma are cellular and non-cellular substances most of the cells are red blood cells each a tiny cell without a nucleus red blood cells do a very specific job they deliver oxygen to all the other cells of your body they can do this because they contain an iron-based molecule called hemoglobin hemoglobin combines with oxygen in a weak chemical combination when hemoglobin does this it becomes bright red and this gives the cells their red color and so your blood looks red because of these blood cells in a single drop of blood there are some 250 million of them now besides carrying floating red blood cells with their load of oxygen watery blood plasma also carries dissolved substances to all your cells some of these dissolved substances are nutrients from your digestive system your blood delivers this food to your cells and in using it your cells give off waste products that your blood carries away one of these waste products carbon dioxide is also dissolved in the plasma for all this transporting of substances your blood has to be moving throughout your body something has to keep flowing rivers flow because of gravity the water moves from higher places to lower places in your body your River of blood flows in spite of gravity working with it sometimes but against it much of the [Music] time within your body your blood flows because of force exerted by a pump your heart the pumping action of your heart keeps your blood moving through all parts of your circulatory system your heart can work as a pump because it's a muscle a powerful muscle cardiac muscle fibers are arranged differently from the fibers and other muscles of your body these fibers are woven into a webike structure all muscles work by Contracting when they receive electrical impulses from your nervous system but because of the structure of cardiac muscle these electrical signals spread more rapidly through your heart than they do in other muscles this rapid spread of the signals allows the fibers of cardiac muscle to coordinate their contractions and produce the rhythmic squeezing that makes the heart a pump inside your heart there are four compartments or Chambers each upper chamber is called an Atrium in the wall of the right atrium there's a region of specialized tissue a node called the pacemaker the signal that makes the upper chamber Chambers contract originates here when the signal fires the Atria contract and blood is forced past two sets of valves that separate the top and bottom Chambers these valves control the flow of blood so it can go in Only One Direction out of the Atria and into the ventricles the lower chambers of the heart now a second node transmits the electrical signal from the Atria to The ventricle making them [Music] contract the force of their contraction opens the second set of valves and drives blood out of the heart into the arteries to follow two separate circuits the structure of the heart makes these two circuits [Music] possible on one circuit the blood that leaves the right ventricle goes into an artery that leads directly to the lungs then the blood returns to the heart and into the left atrium in the other circuit blood that leaves the left ventricle follows a considerably longer circuit through the body itself making contact with all the billions of your body's cells before it returns to the right atrium blood moving through the right chambers of the heart carries large amounts of carbon dioxide dissolved in the plasma and its red cells have given up some of their oxygen but when it makes the circuits through your lungs this Blood gives up carbon dioxide and picks up oxygen so the blood that returns from your lungs to the left chambers of your heart is oxygen rich it's this oxygen rich blood pumped out of your left ventricle and sent on its circuit through your body that nourishes your cells the pumping action of your heart keeps your blood moving through the two circuits simultaneously the movement is helped by the structure of your [Music] arteries artery walls have a number of layers of tissue a smooth single layer of cells lines the hollow interior this helps reduce friction between the moving blood and the artery wall over this lining is an elastic layer that stretches under the pressure of blood from each heartbeat then contracts this rebounding gives the blood a little squeeze and helps to move it along wrapped around this elastic layer are two layers of smooth involuntary muscle these muscles are controlled by nerve fibers whose signals cause the muscles to contract or relax changing the diameter of the artery and so controlling the amount of blood flowing through it and over the muscle layers is a tough layer of fiber that reinforces the artery walls against the blood pressure produced by the heart the artery that carries oxygen rich blood out of the heart's left ventricle and starts its circuit through the body is called the aorta the aorta branches quickly into many smaller arteries let's follow this series of branchings one of the arteries that branches off from the aorta carries blood to the muscles of the heart the heart can't make use of the food in Oxy oygen in the blood that passes through its Chambers it needs its own blood vessels for nourishment two other branches of the aorta run up the sides of your neck and carry nutrients and oxygen to your brain and two other branches move out toward your shoulders and then through your arms the main part of the aorta continues down behind the heart sending out branches to all your abdominal organs then the aorta divides again into two large branches one going to each kidney where some wastes are removed from the blood and still another division sends arteries down into each leg usually arteries are buried deep within your body occasionally they're near the surface of your skin so at places like your neck and your wrists you can feel a wave of increased pressure as the blood is pumped by your heart this pressure wave is what you call your pulse so your branching arteries direct the oxygen-rich nutrient-filled blood to different parts of your body the arteries divide again and again becoming finer and finer blood vessels as they thread their ways throughout your body bringing blood closer and closer to the individual cells eventually the arterial vessels become so thin that their diameter is only slightly larger than the diameter of red blood cells and the cells can move through them only one at a time now the vessels are called capillaries blood flows slows allowing the vital exchanges between your blood and your body cells to take place now a major task of your circulatory system gets done the nourishment of your body the weak chemical combination between the oxygen and the hemoglobin is broken in many of the red cells oxygen and nutrients pass through the walls of the capillaries out out of the blood and into the fluid that surrounds all your cells this watery fluid called lymph is very much like Plasma in fact it comes from the plasma passing through the capillary walls carrying the oxygen and the nutrients now the important exchange takes place between your cells and the lymph oxygen and nutrients pass from the lymph into your cells and carbon dioxide and other waste products pass from your cells into to the lymph and these wastes then pass out of the lymph back through the capillary walls and into the blood that is now traveling back to your heart but only part of the lymph that came out of the capillaries returns to them some lymph travels through the vessels of its own lymphatic system back toward the heart pushed Along by pressure from nearby arteries now the capillaries that are carrying the blood and its load of Wast from the cells merge into larger and larger blood vessels these are the veins of your body the walls of veins aren't as thick as the walls of arteries but they don't have to be blood pressure is lower and veins don't need a layer of muscles to help move the [Music] blood instead blood is squeezed back toward the Heart by nearby skeletal muscles valves along the length of the veins keep the blood moving in the proper direction the veins join into larger and larger vessels as they carry blood back toward your heart in your neck a pair of veins is joined by lymph vessels returning lymph to the blood this lymph becomes part of the circulatory system again in this region of your body gravity works with your Sur circulatory system helping to move blood from your head back to your heart finally all the veins merge into the upper right Chamber Of Your Heart from here the blood with its dissolved carbon dioxide will be pumped through the heart and back to the lungs and so the circuits go on the pacemaker constant signals keep your heart beating steadily but not all controls come from inside your heart your heart can also respond to signals from other parts of your body signals from nerve centers near your spinal cord can speed up the pacemaker signals and speed your heartbeat signals from your brain stem can slow it down when you exercise there's an increase in the amount of carbon dioxide dissolved in your blood this change signals your neres centers to speed up your heartbeat your heart can beat more than twice as fast as normal if necessary your body also produces a chemical activator the hormone adrenaline that can affect the rate of your heart's electrical signals excitement or fright will cause your adrenal glands to pour adrenaline into your blood and this will speed up your heartbeat the amount of blood that flows to different parts of your body can be regul regulated too depending on your body's special needs arteries that nourish your muscles send more blood to them when you're active and more blood flows to your digestive system after you've eaten when you're warm blood flow is directed toward the surface of your skin when you're cold it's directed away all this traffic control is accomplished by changes in the diameter of the arteries the muscles that are part of the artery walls can contract in one area and narrow the artery reducing the flow of blood to one part of your body or the muscles can relax and widen the artery allowing more blood to get through when there is damage to any part of the body blood flow to that part increases floating in the blood plasma along with the red cells are much smaller disk-shaped bits of protoplasm called platelets platelets help your blood clot clotting seals breaks in the circulatory system and Begins the repair process in the blood there are also various kinds of white blood cells these destroy and remove living and non-living substances that can cause infections and disease white cells are formed in lymph nodes located along the lymph vessel and these nodes also act as filters for microorganisms and foreign particles keeping them out of your bloodstream the health of all your body cells depends on your circulatory system and keeping it in motion is your heart beating slower faster steadily resting only briefly between beats as it sends the blood through its double circuit bringing nourishment and carrying away wastes from every corner of your internal world for your whole life your heart your blood and the vessels that travels through will feed and protect and repair the billions of tiny cells that are you [Music] me