One of the most indispensable organs in the body for blood circulation is the organ that is the carrier of oxygen, the lungs. Before a component of blood is pumped out of the heart to the body, it has to acquire oxygen from the lungs which is critical for every cell in the body to function. Blood from the head and arms enter the heart through the right auricle from the upper ( superior) vena cava . Blood from the trunk and legs enter the heart from the lower ( inferior) vena cava . The blood flow restricted by a valve is channeled to the right ventricle . It is then conveyed to the lungs via the pulmonary (pertaining to the lungs) artery (it is called an artery because it leads away from the heart) to obtain oxygen.
Having obtained oxygen in the lungs, blood is brought back to the left auricle through two pulmonary veins . (They are called veins because they lead to the heart).
After that it is pumped through the aorta to be dispersed to all segments of the body.
For Further information on the lungs go to the Respiratory System Page.
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The human body contains about 9.5 pints, 4.5 liters, 6 quarts of blood . This blood that circulates throughout the body is a sort of liquefied tissue of which about 80% is water. It is the medium through which the entire body is nourished and supported carrying nutrient molecules from digested foods, as well as carrying away harmful waste products such as carbon dioxide. It circulates the needed oxygen from the lungs. It also picks up hormones and uses custom distribution to deliver chemical messages to the organs it comes into contact with. As other organs interact with the blood it is in a constant flux of updating and extending its chemical composition. However, certain basic components can be identified in the blood despite its changing composition.
If blood is extracted from the body and it is left to sit for a period of time in a testube, it will divide into a transparent watery liquid with a yellowish hue on top and a dark red solid looking clump on the bottom.The watery liquid part is called plasma and makes up about 55 percent of the volume of blood. Plasma is over 90% water and enables our blood to navigate fast moving substances in solution and slow moving thicker substances in suspension. The majority of the contents of plasm except water is salt, proteins, and sugars or oxygen,wich has escaped red blood cells.
Platelets are very tiny vital blood components lacking nuclei and are one fourth of the size of red blood cells. As a matter of fact, platelets are not blood cells at all. Platelets travel with the blood and assist to prevent the organism from bleeding to death if it experiences even the smallest of wounds. They activates some of the first biochemical processes needed to clot blood. The change of blood from a fluid to a solid is called clotting .
Red blood Cells (erythrocytes) red corpuscles
These cells number in the trillions and are the greatest number of blood cells in the body. They carry oxygen, the most important substance needed by cells in the body, from the lungs. Red blood cells are produced in the in the red bone marrow ( tissues within the ends of the bone that replaces and produces the red blood cells and is the manufacturing site of white blood cells) of the interior of bones. As they mature, they lose their nuclei and become less like a cell and therefore their name changes to red corpuscles or erythrocytes . Because they have no nucleus, their life span is decreased to about 120 days (four months). As they die, the red marrow replaces them in enormous numbers at a rate of about a million a minute.The liver and spleen are also sites for red blood cell production.
Hemoglobin is a complex iron protein substance. It is the component of red blood cells which gives red blood cells their special oxygen carrying proficiency as well as their color. Although other substances in the body such as water and plasma can also carry oxygen, hemoglobin is unique in its oxygen carrying capacity because it increases by more than 50 times the quantity of oxygen it can carry.
White blood Cells (leukocytes) white corpuscles
White blood cells are diverse in shapes and sizes. Although they may be larger in size and rounder than the red blood cells, they are far less in number- a ratio of about 1:700. Unlike red corpuscles, white corpuscles or leukocytes have their nuclei. White blood cells are comprised of lymphocytes (white blood cells with round nuclei which are accountable for producing protective antibodies, agents responsible for immunity to an infectious disease), monocytes (white blood cells with ovoid or kidney shaped nuclei containing chromatin which carries DNA material), and granulocytes (white blood cells with band shaped nuclei containing granules).
All of the components of the white blood cells work to safeguard the body against sickness and combat infection as they increase in number when the body is under an infectious attack. Pus , a bevy of neutralized foreign bacteria and dead white cells, litter the area where the battle took place.The white blood cells can be compared to a computer virus program that identifies, seeks out, and increases in efficiency as it works to eliminate non-native culprits in your computer system that may slow down or destroy important files and documents. It carries its own utilities pack which allows for simple diagnosis and repairs. Defective cells are replaced without having to completely shut down or interrupt the system.This replacement of white blood cells can take place in a number of locations in the body: in the lymph nodes, in the intestinal tract , and in the spleen .
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Blood vessels are part of a closed extensive network of narrow elastic passageways whose main function is to circulate blood to all the far out places of the body. Without this wiring system of finger thick to microscopically slender cables and connectors of some 70,000 miles of blood vessels the blood would not be able to acquire and accumulate essentials for the nourishment and health of the entire body. There are two kinds of blood vessels: arterial arteries (carry blood away from the heart) and venous veins (carry blood toward the heart to be repumped).
Capillaries are minute blood vessels that allow oxygen and nutrients to traverse through their walls to all the body cells. The walls of the capillaries act as a semipermeable (authorizing passage only of certain molecules) membrane for the interchange of various substances between the blood and tissue fluid. They carry blood between the smallest arteries (arterioles ) and the smallest veins (venules ). Capillaries are so small
The tissue of arteries are tough on the outside, muscular in the middle, and smooth on the inside. Blood arrives at the heart muscles through two coronary (pertaining to the heart) arteries winding around the heart and that are about as wide as drinking straws. These arteries branch out from the aorta delivering freshly oxygenated blood to the right and left sides of the heart. The coronary arteries have been called the arteries of sudden death since a blood clot in their tubes can lead to a fatal heart attack.The aorta is the largest artery emerging from the left ventricle. It is the primary artery from which the arterial system wends. The aorta branches off into over 250 different named arteries dispersed throughout each part of the body- to name a few places, wrist, hand, testes, muscles of the neck, spinal cord, brain, stomach, scalp, and middle ear walls. Arteries are blood vessels in which blood flows away from the heart conveying oxygenated blood (blood with oxygen). The arteries experience continuing branching and decreasing of size, some with and some without channels connecting with other arteries. As they undergo this progressive branching and decrease in size they become know as arterioles (the microscopic arterial branch). When oxygenated blood reaches the arterioles, the capillaries begin their specialty.
Veins (Venae Cavae/Venules)
The two venae cavae are the largest veins in the body and are the veins which carry the deoxygenated blood to the right side of the heart.The tissues of the veins are thinner, less flexible, and less muscular than the arteries.They are the counterpart of the arteries. Like the arteries there are also over 250 different named veins dispersed throughout each part of the body - to name a few places, eyeball, lung, ankle, eyelid, foot, toe, and nose. Veins are blood vessels in which blood flows toward the heart conveying deoxygenated blood (blood that has given up most of its oxygen). At the transition site where arterial blood has flowed through the capillaries and has become venous blood, the returning deoxygenated blood moves through venules (the smallest vessels that collect blood from the capillary and join to form veins). As venules successively increase in size they become veins and move blood back to the heart where it will be begn its never ending pumping cycle.
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The heart is a core playing member of the circulatory network and can be described as a small 9 ounce or 30 gram cavernous fist sized intertwining muscle located behind the breastbone and centered perpendicular to the midline of the chest. Through its pumping action it helps to circulate blood through the body.The heart must be unceasingly supplied with rich fresh oxygen and used blood must be returned to the lungs for reoxygenation. It has a right and left side partitioned by a sinewy wall of muscle called a septum . Each side has two chambers. A healthy circulation depends to a large extent on the pipelines through which the blood and its components flow.Therefore to meet its need for fresh blood, the heart has its own circulation network, consisting of arteries and veins .
The upper chamber of the heart has two auricles , the right auricle and the left auricle. The auricles serve as a holding cache for blood that enters the heart. When the blood enters the right auricle, a valve closes after right auricle is full. Then, through a kind of trapdoor valve, blood is released from the right auricle into the right ventricle. When the right ventricle is full, and its outlet valve opens, the heart as a whole contracts-that is it pumps. When inundated with blood the left auricle propels its contents into the left ventricle. A valve closes between the left auricle and ventricle, and the heart pumps.
The lower chamber of the heart has two ventricles , the right ventricle and the left ventricle. The left ventricle has the responsibility of pumping blood to the entire body and therefore is somewhat bigger and more muscular than the right ventricle. It has an opening that blood flows through to the aorta (the central artery where blood circulation originates throughout the body).
Blood Pressure (Heartbeat)
On average, without strenuous exercise, the heart beats 72 times a minute for adults. Electrical waves pulsate through the heart causing the opening and closing of valves and muscular contractions of the ventricles. Each heartbeat has two main phases. Both auricles (atria) contract at the same time, forcing and squeezing out blood into the ventricles.This period of contraction is called systole.Then both ventricles contract (while the auricles relaxes and refill with blood) forcing and squeezing blood into the aorta.This period of relaxation is called diastole.
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