The following topics are covered in this segment:
Functions of the Blood - Blood is a liquid tissue that has three major functions; as a transportation, for regulation, and protection. Blood transports materials to and from all the cells of the body Wastes produced by the cells carried away in the blood to organs which remove the wastes. Blood acts as a regulator. Blood can absorb heat from warm areas of the body and releases the heat in cooler areas. The blood usually maintains a constant pH and water balance. Blood also protects the body. It holds specialized cells and chemicals that defend the body against diseases. Blood has the ability to clot, preventing the body from loosing large amounts of blood due to an injury.
The Components of the Blood - Because blood has many functions you might be able to conclude that the blood is composed of many different parts. The liquid part of the blood is called plasma. Plasma takes up about 55% of the total volume of the blood. The remaining 45% of the blood is made up of red blood cells, white blood cells, and platelets. An adult human has between four and six liters of blood in the body.
Plasma - Plasma is the clear liquid portion of the blood. 90% of plasma is water. The other 10% contains many types of molecules, including nutrients, glucose, vitamins, cellularwastes, salts, and proteins. There are three major types of proteins which exist in plasma. These are albumin, fibrinogen, and globulins. Each proteins has a specific function to perform. The albumin keeps water from leaving the blood and entering the surrounding cells by osmosis. It does this by helping to keep the concentration of the water within the blood the same as the concentration in the body tissues. The fibrinogen aids in the clotting of the blood. Some globulins transport proteins and other substances from one part of the body to the next. Other globulins are known as antibodies, which help to fight of infection. Antibodies are proteins that attach to and help destroy foreign substances in the body.
Red
Blood
Cells - These cells are red and carry oxygen and
carbon dioxide. They are present in huge numbers within the blood.
The human body conatins 30 trillion red blood cells, or approximately
5 million cells per cubic millimeter of blood. The red blood cells transport
oxygen from the lungs to the tissues in the body. They also carry carbon
dioxide from the body tissues to the lungs. In humans, the matured
red blood cells do not contain a nuclei. Their cytoplasm is filled
with an iron-containing protein called hemoglobin. Hemoglobin is the
substance that gives the blood its red colour. Human red blood cells
are constructed by bone marrow and have and
a average life span of up to 120 days. New cells are produced at the
same rate red blood cells are destroyed . This occurs at pace of about
2 million per second. The old red cells are removed from the body
by the spleen and liver and are then broken down. The iron from the
hemoglobin is then collected and reused.
When a person has an insufficient amount of hemoglobin or too few red blood cells, this is referred to as anemia. Both of these conditions lowers the amount of oxygen that can be carried throughout the blood. Anemia causes the cells not to recieve the proper amount of oxygen. This is a heriditary disorder, and is caused by an abnormal form of hemoglobin.
White Blood Cells - There is a variety of colorless blood cells which make the white blood cells, or known as leukocytes. These white blood cells are defenders for the body. They proect the body from bacteria and viruses, which are disease-causing organisms. Unlike red blood cells, the white blood cells contain a nucleus and are larger than the red blood cells. There are fewer white blood cells than white, but there are still about 60 billion in an adult human body. The bone marrow and lymphatic tissue produce approximately 1 million white blood cells every second. The white bloods cells are distribute themselves throughout the body by moving through the circulatory system. When there is an infection within the body, the white blood cells collect in the infected area and attack the foreign organisms.
There are five different types of white blood cells. The majority of them function to protect the body in some form. A portion of the white blood cells are what are called phagocytic(monocytes & neutrophils). They protect the body by fighting the bacterial invaders, and anything which does not belong in the body. The lymphocytes take care of the production of antibodies and the cells that destroy certain substances and uncommon cells. Usually, there are 7000 to 10 000 white blood cells present per cubic millimeter of blood. When an infection of the blood occurs, the numbers of white blood cells may increase to 30,000 or more per cubic millimeter. The phagocytic white blood cells eat the bacteria which they encounter. After these phagocytic cells eat the bacteria some of them die. This is what pus is when it forms around an infected area.
Platelets
- The part of the blood which is involved in the clotting
of blood. Platelets are formed when bits of cytoplasm are pinched.
Even though these bits of cytoplasm contain no nuclei, they surrounded
by a membrane. There about a total of 1.5 trillion platelets in the
blood of an adult human. There are about 300,000 platelets existing
in a cubic millimeter of blood. Their life lasts for about seven days and
are produced at about 200 billion per day.
Blood Clotting - Unless
blood is a free-flowing liquid it will not be able to circulate easily
throughout the body's blood vessels. However, in being a liquid it
could
cause a large variety of problems. If there was an injury that broke
a large blood vessel it could lead to a large loss of blood. This problem
is resolved by the complex mechanism of clotting. The clots form a
temporary barrier to prevent blood loss until the vessel walls have healed.
The Clotting Process - When a blood vessel is injured, platelets begin to collect near the injury, which forms a barrier known as the platelet plug. When the platelets come in contact with an injured area, they swell up, become sticky, and release certain chemicals.
Blood clotting requires many precise reactions to maintain a certain balance between quick and efficient clot formation. This balance has to be kept exact so that your blood will not clot at the wrong time.
Prothrombin and fribrinogen are two
proteins that are produced by the liver that are always present in the plasma
of the blood. The injured tissues and platelets release prothrombin
activator and calcium ions (Ca2+) to change prothrombin into the
enzyme thrombin. Then the thrombin splits two short amino acid chains
from each fibrinogen molecule. The ends of the fibrinogen then join
together, forming threads of fibrin.
These
fibrin
surround the platelet
plug in the damaged area of the blood vessel and provide the shape for the
clot. Red blood cells are present within the fibrin which makes the
clot appear red. After this the clot stops the bleeding, gets smaller,
and hardens. Over time the injury is repaired by the growth of new
cells which will replace the cells lost because of the injury. When
all the healing has finished an enzyme called plasmin in activated and dissolves
the fibrin clot.
Some Clotting Problems - There are many conditions which can cause the clotting process to be disrupted. People who have the hereditary disease haemophilia, lack the essential Factor VIII (Antihaemophilic Globulin, or AHG) of blood clotting. These people can recieve certain injections which will enable ther blood to clot properly. If you don't have enough platelets in the blood or lack vitamin K, this will reduce the ability to clot.
Blood Groups - The ABO grouping and the Rh factor are the most often used to determine blood type. The physician Karl Lansteiner determined that there were four major blood groups among humans. He designated them as A, B, AB, and O. This same system is used today. It is now a known fact that blood type is based on a type of glycoprotein present in the red blood cells. Type A blood has A-type glycoproteins, type B blood has B-type glycoproteins, type AB blood has both of these glycoproteins, and type O blood has neither of them. The A and B glycoproteins function as antigens, and they combine specifically with antibody molecules. When this kind of reaction occurs, the red blood cells agglutinate (join together). People who have type O blood are called universal donors. It can be given to anyone without fear of agglutination because it does not contain any antigens that could combine with anti-a or anti-b antibodies The name universal recipient is given to a person with type AB blood. AB blood does not have anti-a or anti-b antibodies that could combine with any antigens.
The Rh factors are another group of antigens found on the surface of red blood cells. They are called Rh factors simply because they were first discovered in rhesus monkeys. About 85% of humans are Rh+, which means they have Rh factors on their red blood cells. The remaining 15% of humans are Rh-, which means that they do not contain the Rh factor. These Rh factors may present a problem when a mother is Rh- and the baby is Rh+. If their blood is to mix and some of the Rh+ blood cells enter the mother's circulatory system, her immune system will from anti-Rh antibodies. In future pregnancies, these anti-Rh antibodies could enter the babies blood stream. If this were to happen and the baby was Rh-, the antibodies would destroy the babies red blood cells. This problem can be eliminated if the mother is given an injection of anti-Rh antibodies to destroy the baby's Rh+ cells shortly after the birth of each Rh+ child. This will prevent the mother's immune system from forming it's own antibodies.
The Immune System - Bacteria, viruses, and any other thing that may cause disease are called pathogens. The microorganisms exist almost everywhere in the environment, which means that you are exposed to these pathogens every day. Thankfully, humans have several defences against these various pathogens. The defenses keep your body's environment healthy most of the time.
First-Line Defenses - The body's first line of defense against pathogens uses mostly physical and chemical barriers such as sweat, skin, tears, mucus, stomach acid, and so on. Our skin and other membranes which line the body passages are fairly effective in keeping most pathogens out of the body. Mucus can trap pathogens, which are then washed away or destroyed by chemicals. Tears, sweat, and saliva have certain chemicals which can kill different pathogens.
Second-Line Defenses - If a pathogen is able to get past the body's first line of defense, and an infection starts, the body can rely on it's second line of defense. This will result in what is called an inflammatory response. This is a reaction that causes redness, heat, swelling, and pain in the area of infection. Redness and heat are due to cappilary dilation resulting in increased blood flow. Sweeling is caused by the passage of plasma from the blood stream and into the damaged tissue. The pain is mainly due to the tissue destruction, and to a lesser extent, the swelling.
Third-Line Defenses - Sometimes the second line of defense is still not enough and the pathogen is then heading for the body's last line of defense, the immune system. The immune system will recognize, attack, destroy, and remembers each foreign substance and pathogen that enters the body. It does this by making specialized cells and antibodies that makes the pathogens useless. Unlike the first line and second line defense the immune system determines between kinds of pathogens. For each type of pathogen, the immune system produces cells that are specific for that particular pathogen.
(Cancerous Cell)
The Immune Response - The immune system includes all parts of the body that help in the recognition and destruction of foreign materials. White blood cells, phagocytes and lymphocytes, bone marrow, lymph nodes, tonsils, thymus, and your spleen are all part of the immune system. Immunity is the body's abitlity to fight off foreign substances, viruses, or bacteria by producing antibodies or cells that can deactivate these foreign substances or cells. The hole idea of immunity is that the body is able to distinguish between its own substances or foreign substances. When the body recognizes foreign cells or molecules, it makes special antibodies or cells that attach to the pathogens and inactivate them. When these antibodies and special cells are produced it is called the immune response.
Types of Immunity - There are two types of immunity; active and passive. In the active immunity the body produces its own antibodies to defend against certain antigen. In the passive immunity the person is given the antibodies required to defend against the antigen. Passive immunity is only for a short period of about one month because the borrowed antibodies are destroyed by the body.
Active immunity may result from having a certain disease once and then getting it again. For some diseases a person usually only gets them once, such as the chicken pox. If a particular viruse that has been in the body before enters, the memory cells within the body tissue will produce antibodies or killer T cells. You may recieve active immunity through a vaccine. The vaccine consists of dead or weakened viruses or bacteria. These organisms can act as antigens but do not normally cause disease because they are weakened. When the vaccine enters the body, the immune system reacts to it the same way as it would to a pathogen. This way a person can actually develop immunity without even getting the disease.
Lymphocytes - Immunity
is the result of the action of two types lymphocytes, the B lymphocytes and
the T lymphocytes. The B and T cells are produced in the bone marrow. The
T cells mature in the tymus gland while the B cells mature in the bone
marrow. Millions of these matured B and T cells move through the
circulatory and lymphatic systems.
B and T cells have different functions. B cells produce antibodies that are secreted into the blood and lymph. Unlike B cells, the T cells do not produce antibodies. Instead the T cells just attack the cells that have antigens that they recognize. It has been estimated that during our lifetime, we will encounter a million different antigens, and our bodies need the same amount of lymphocytes to defend against them. There will always be a different type of lymphocyte for each possible antigen. None of these lymphocytes are supposed to attack the body's own cells. It very rarely may be possible that a lymphocyte will respond to the body's own proteins.
The Lymphatic System - Rather than a circulatory system, the lymphatic system is a one way system, and contains lymph veins and capillaries only. The lymphatic system begins with lymph veins and capillaries that lie near the blood capillaries. They take up any excess tissue fluid. Once the tissue fluid has entered the lymph capillaries it is called lymph. Lymph in humans moves through the lymph capillaries and vessels as a result of pressure applied by muscle contractions near the vessels. Valves prevent the lymph from flowing backwards. Lymph moves through smaller vessels that join to form larger vessels, which then goes into two major lymph ducts that empty into large blood circulatory veins of the shoulders near the heart.
The lymphatic system has several other functions. Lymph vessels known as lacteals are present within the intestinal villi. The products of fat digestion enter the lacteals and are carried in lymph vessels to enter the circulatory system. Lymph nodes are small round structures made out of lymphnoid tissue. Lymphocytes are packed into the spaces of a lymph node, which filters and traps bacteria and other debris, help keeping the blood clean. When there is a small infection, such as a sore throat, lymph nodes in that region may swell and become painful.
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