week 4 chpt 6,16 study

The cells that make up the formed elements of the blood arise from stem cells (cells from which specific body cells are formed). Two such stem cells are found in separate hematopoietic (blood-forming) compartments: myeloid (developed from bone marrow) and lymphoid (developed from the lymphatic system). Blood cells formed by myeloid stem cells include the red blood cells, platelets, granulocytes (neutrophils, eosinophils, and basophils), and monocytes. Blood cells formed by lymphoid stem cells include two different types of lymphocytes, B cells and T cells.

Erythrocytes (red blood cells, or RBCs) originate in the bone marrow and are the most numerous of all the blood cells. On average, a healthy adult has approximately 4.2 to 6.1 million red blood cells per cubic millimeter (mm?) of blood. The normal range varies, depending on a person's sex. RBCs average 7 to 8 micrometers (um) across their diameter, and their average volume is 90 femtoliters (fL). A femtoliter is 10-15 liter. At this size, about 18 million RBCs could sit on the head of a pin. When fully mature, erythrocytes resemble the shape of a doughnut without a hole. This appearance is referred to as biconcave because both sides of the red blood cell cave inward at the center. This shape allows flexibility, so that the RBCs can pass through blood vessels of various sizes, down to tiny capillaries, in order to perform their functions. 

Leukocytes, or white blood cells, are primarily responsible for destroying foreign substances, such as pathogens, and removing cellular debris. Leukocytes are not confined to vascular spaces when performing their duties. They can pass through capillaries' thin walls in a process known as diapedesis to better access the pathogens or other foreign invaders. Once white blood cells are near enough, they can surround and destroy the foreign substance through a process called phagocytosis. In phagocytosis, the leukocytes engulf, or "eat," foreign substances and/or cellular debris. Leukocytes are round and primarily clear, but they appear white because the light by which they are viewed is white. When stains are applied to leukocytes, they take on various colors based on the cell type. These stains will be explained further later in this chapter. The average adult has between 5000 and 10,000 white blood cells per cubic millimeter (mm?) of blood, unless an infection or other disorder is present. 

If 20 tubes of blood from different patients were lined up on a counter in the laboratory, they all would look very much alike, even though they may be very different. The naked eye is not capable of detecting the inherited identifying proteins on the surface of individual red blood cells, known as antigens. The ABO blood group consists of four blood types: A, B, AB, and O. They are distinguished from each other in part by their antigens and antibodies

Medical laboratory scientists identify these blood groups by testing for agglutination, the clumping of red blood cells. Agglutination occurs because the antigens on the surface of red blood cells bind to antibodies in plasma.

People with type A blood have antigen A on the surface of their red blood cells. They also have antibody B in their plasma. Type B People with type B blood have antigen B on the surface of their red blood cells. They also have antibody A in their plasma. If a person with type A blood is given type B blood, the antibody B in the recipient's bloodstream will bind with the red blood cells of the donor blood because those cells have antigen B on their surfaces. The donated-in this case type B-red blood cells are destroyed causing severe complications for the patient. This is why a person with type A blood should never be given type B blood (and vice versa). It can cause complications known as transfusion reactions, which are discussed later in this chapter. Type AB People with type AB blood have both antigens A and B on the surface of their red blood cells. They have neither antibody A nor antibody B in their plasma. People with type AB blood are sometimes called universal blood recipients because most of them can receive all ABO blood types. They lack antibodies A and B in their plasma, so there is no reaction with antigens A and B in the donor blood. On the other hand, because AB blood has no antibodies in the plasma to react with the recipient's antigens, people who have AB blood are considered universal plasma donors.

People with type O blood have neither antigen A nor antigen B on the surface of their RBCs. However, they do have both antibodies A and B in their plasma. Considering the ABO group only, people with type O blood are sometimes called universal donors because their red blood cells can be given to most people, regardless of the recipient's blood type. Type O blood will not cause a transfusion reaction when given to other people because it does not have the antigens to bind to antibody A or antibody

The Rh antigen is present on red blood cells and is classified separately from the ABO blood groups. The Rh antigen is assigned the letter D. The Rh antigen was first discovered in 1940 by Karl Landsteiner during his research with Rhesus monkeys, hence the name Rhesus factor and the abbreviation Rh. People who are Rh-positive have red blood cells with Rh antigens on the cell surface. People who are Rh-negative have red blood cells that do not have Rh antigens on the cell surface.

The Rh, or D, antigen is the next most important antigen after those in the ABO blood group because of the possible antibody reaction. Rh is tested by adding antibodies to the D antigen to a drop of patient blood. If agglutination occurs, the patient is Rh-positive. No agglutination indicates Rh-negative blood

A person who is Rh-negative, if given Rh-positive blood, will usually make antibodies that bind to the Rh antigens. If the Rh negative person is given Rh-positive blood a second time, the antibodies will bind to the donor cells and agglutination will occur. Because of this, the Rh factor must be considered during blood transfusions. O negative blood is truly the universal donor because it has no A, B, or D antigens that can cause the recipient to form antibodies.