BLOOD

I) Composition of Whole Blood

a) Blood is an example of a connective tissue.  If you will remember connective tissue consists of a ground substance (extracellular matrix), cells, and fibers (collagen, elastic and reticular fibers).  The ground substance of blood is the straw colored sticky liquid of the blood called plasma. It contains about 90% water along with over 100 different dissolved solutes including nutrients, gases, hormones, various wastes and products of cell activity, ions, and proteins. Collagen and elastic fibers are absent from blood, but dissolved fibrous proteins become visible as fibrin strands when blood clotting occurs. Whole blood also contains formed elements which are the red blood cells or erythrocytes which are used to transport oxygen and carbon dioxide, white blood cells or leukocytes (appears as the "buffy coat" a thin whitish layer present at the erythrocyte-plasma junction of a centrifuged whole blood sample)  which function in immunity along with blood platelets which are the noncellular components of the formed elements consisting of small membranous enclosed sacs of enzymes  used in the clotting process. The term whole blood therefore refers to the total combination of plasma and the formed elements.  

II) Characteristics of Whole Blood

a) Volume: 5-6 liters in males; 4-5 liters in females

b) Temperature: 100.4 degrees F (slightly higher than normal body temperature) from venipuncture, arterial puncture, or from peripheral capillaries.

c) Viscosity: Five times as viscous as water (blood really is thicker than water). It is very sticky and resistant to flow due to the cohesive nature between the proteins, formed elements and the water present in the blood.

d) pH: The average normal pH of the blood is 7.4 and can range from between 7.35 and 7.45 (the blood is slightly alkaline or basic).

III) Plasma Proteins

a) There are seven grams of protein in each 100 ml of plasma (5 times the concentration as that in interstitial fluid) and are the most abundant of the plasma solutes. They account for 8% by weight of the plasma volume.

b) The proteins in the plasma are large and globular which prevents them from leaving the capillaries. 

c) Three classes of plasma protein:

1) Albumin forms 60% of the plasma protein is formed by the liver and is the major contributor of of osmotic pressure  to maintain water balance between blood and tissue. Sodium is the other major solute contributing to blood osmotic pressure.  Albumin also acts as a carrier to shuttle  certain molecules through the circulation and is also an important blood buffer.  Buffers are chemical substances that maintain the normal pH level of the blood (7.35 to 7.45).  Buffers release hydrogen ions when pH begins to rise acting as an acid and acts to bind hydrogen ions when the pH begins to drop acting as a base.

2) Globulins form 35% of all plasma proteins and consist of two types: alpha and beta globulins which are also produced by the liver. Thyroid binding globulin for example binds and transports thyroid hormone. Both albumins and globulins attach to lipids (which include triglycerides  and steroids such as cholesterol) and transport them through the blood stream.  Lipids  are insoluble in water, but become soluble when  they bind with protein in a process called emulsification. Globulins that carry lipids are called lipoproteins.  There are four types of lipoproteins two of which are the most familiar: LDL and HDL (the two types of cholesterol).   Alpha and beta globulins are transport proteins that bind to small ions, hormones, fat soluble vitamins  and others that would normally be filtered out by the kidney.  The second type of globulin are gamma globulins (also called immunoglobulins) which are antibodies released by plasma cells during the immune response.  Gamma globulins also include the antibodies which determine blood typing.

3) Clotting proteins form 4% of all plasma proteins and include fibrinogen and prothrombin which are also produced by the liver.  When one removes the clotting proteins from the blood it is what we call serum.

4) Metabolic enzymes, antibacterial protein (such as complement protein and interferons used in the immune response), and protein based hormones make up other plasma proteins. 

***Albumin, alpha and beta globulin (transport proteins), and clotting proteins are made by the liver.  A blood sample can be analyzed for protein to determine whether the liver is functioning properly.

 IV) Erythrocytes (red blood cells) :

---are small cells shaped like biconcave discs which gives them a larger surface area for diffusion of oxygen and carbon dioxide to and from the plasma in the capillaries of the body tissues and lungs. The biconcave shape of an erythrocyte is maintained by a network of proteins especially one called spectrin which is a very deformable and gives erythrocytes a flexibility which enables them to change shape as they are pushed through capillaries with diameters smaller than theirs.

---They have no nucleus (anucleate, ribosomes, or mtochondria which means that they cannot  reproduce by mitosis, or synthesize proteins.  Also without mitochondria they cannot obtain energy anerobically.  This insures that any oxygen absorbed by the red blood cells is not stolen by the mitochondria.

---Hemoglobin is made of the protein globin bound to the red heme group. Globin consists of four polypeptide chains--two alpha chains  and two beta chains each bound to a separate heme group (four iron-heme groups present in each molecule of hemoglobin).  Each heme group can bind with an oxygen molecule so each hemoglobin molecule can carry four molecules of oxygen.  A red blood cell contains about 250 million hemoglobin molecules so each red blood cell can carry about 1 billion molecules of oxygen.  Oxygen is first dissolved in the plasma and some of the oxygen is taken to our tissues by plasma alone. Most of the oxygen is taken out of solution by the hemoglobin.  Much more oxygen can be carried to our body tissues in this way by removing the oxygen from the plasma into the hemoglobin molecules.  As more oxygen dissolves in the plasma it is taken out of solution by the hemoglobin allowing for more oxygen to dissolve in the plasma.  When oxygen binds to iron  in the capillaries of the lungs the hemoglobin which is now called oxyhemoglobin assumes a new three-dimensional shape and becomes bright red.   When oxygen is released at the body cells it returns to its former shape and and is called deoxyhemoglobin and appears dark red.  The released oxygen diffuses into the tissue fluid and into the tissue cells.   About 20% of the carbon dioxide transported in the blood combines with hemoglobin, but it binds to amino acids of globin rather than the heme group and is called carbaminohemoglobin.

---Erythrocytes are the major factor contributing to blood viscosity.  The percentage of whole blood occupied by cellular elements is called the hemocrit. Red blood cells outnumber white blood cells by 1000 to 1, so many times the hemocrit is called the VRRC (volume of red blood cells) or the PCV (packed cell volume). The hemocrit of men and women are different.  Males have about 5.4 million red blood cells per cubic millimeter and women about 4.8 cells per cubic millimeter. Male hormones stimulate the production of red blood cells.  There is about 2.5 trillion erythrocytes in the healthy adult.  Blood viscosity (hemocrit) can rise or fall with an increase or decrease in numbers of red blood cells and can result in the blood flowing slowly or more rapidly.  Dehydration increases the hemocrit due to a decrease in plasma volume and the blood flows more slowly. Internal bleeding or a decrease in red blood cell formation can also decrease the hemocrit.  Anemia can also be diagnosed through a low hemocrit.

---Erythrocytes have a very short life span of about 120 days.  They go through a lot of physical stress as they make a trip through the body ( a round trip through the circulatory system of a single red blood cell is 30 seconds). About 1% of our red blood cells are removed every day; more than two million enter the circulatory system each second (the newer blood cells entering to replace the dead ones at a comparable rate to maintain the average hemocrit. Too few erythrocytes leads to tissue hypoxia (oxygen deprivation).  Red blood cells are produced through a process called erythropoiesis.  This process is controlled hormonally (EPO-erythropoetin produced by the kidneys)  and requires adequate supplies of iron, amino acids and certain B complex vitamins ( vitamin B12  and folic acid-which are necessary for DNA synthesis- slight deficiencies in these vitamins reduce production of cell populations such as erythrocytes . EPO is released rapidly when the kidneys become hypoxic (inadequate oxygen supply) due to a drop in the normal blood oxygen levels that may occur due to hemorrhage, or excess blood cell destruction, reduced oxygen availability such as might occur during high altitudes or during pneumonia, or from increased tissue demands as that which occurs in those who engage in aerobic exercise.  Too many erythrocytes or excessive oxygen in the blood would decrease erythropoietin production .      (Figure 18.6)  

--- The red blood cells can actually die in two ways. They can rupture (hemolysis) in which case hemoglobin is lost through the urine. This happens when abnormally high amounts of red blood cells rupture resulting in the urine turning reddish brown, a condition called hemoglobinuria.  Normally only 10 % survive long enough to hemolyze. The liver, bone marrow and  the spleen produce phagocytic cells to engulf old worn out blood cells before they hemolyze. This occurs primarily in the spleen where the cells become trapped and fragmented in small circulatory channels.  The spleen is often called the "red blood cell graveyard".  Here the hemoglobin and red blood cells are removed from circulation for recycling in the following steps:

1) The globular proteins are broken down into individual amino acids (can be metabolized by phagocytic cells or released into the bloodstream)

2) The heme of the hemoglobin is split off from globin. Some of which is converted to biliverdin (green substance that appears in bad bruises). The biliveridin is then converted into bilirubin and released into the circulation. Bilirubin which is a yellow pigment binds with albumin for transport. Bilirubin is picked up by liver cells which is secreted (in bile) into the intestine. Here it is metabolized into urobilinogen and eventually leaves the body in feces as a brown pigment called stercobilin.  If bile ducts are ever blocked then a condition called Jaundice results.

4) Most of the heme or iron group is salvaged and stored for use later.  Iron can be stored in phagocytic cells or released into the bloodstream where it binds to transferrin a plasma protein as ferritin or hemosiderin.  Red blood cells developing in the bone marrow absorb amino acids and transferrins from the circulation to synthesize new hemoglobin molecules.   Excess transferens are removed and stored in the liver and the bone marrow along with the iron which is stored in special protein complexes.  (figure 18.7) 

****Females contain 2.4 grams of iron (Fe2+). About 1.9 grams are bound to their hemoglobin in red blood cells.  The iron reserves of females is only 1/2 of males (.5 grams)

***If dietary supplies are inadequate symptoms of iron deficiency appear. Too much iron in our diet can cause an excessive buildup in the liver and heart (excessive iron deposition in the heart is linked to heart disease). 

V) Red Blood Cell Formation

a) Red blood cell formation or erythropoiesis occurs in the myeloid tissue of the red bone marrow of vertebrate, the sternum, the ribs, the skull, the scapula, the pelvis, and proximal limb bones.

b) During sustained blood loss yellow marrow can be changed to red marrow.

c) Erythropoetin  (EPO)  increases mitosis of erythroblasts resulting in a speed up of hemoglobin synthesis, and maturation of red blood cells.   Red blood cell formation can occur by ten fold (30 million/second).  This only happens during severe blood loss. If EPO is given to a normal person red blood cell formation can rise to 65+ and cause heart failure. 

ERYTHROPOIESIS:

VI) BLOOD TYPES

a) Specific proteins are found in the cell membrane of red blood cells and are called surface antigens or agglutinogens which are determined genetically. There are 50 kinds of antigens known, but only  three determine blood types: A, B, and Rh.  Antibodies produced by leukocytes are present in the plasma that result in cross reactions or agglutination (resulting in hemolysis)  when opposing blood types are mixed are called Immunoglobins (antibodies) A, B, and the Rh antibody.

b) Rh Blood Groups: There are at least eight different types of Rh agglutinogens each of which is called an Rh factor. Only three of these, the C,D, and E antingens are common.  About 85% are Rh+ meaning their Red Blood Cells carry the Rh antigen.  Rh antibodies are not found normally in the plasma of an Rh- individual. If this person were to receive the Rh factor from a blood transfusion, then the immune system would begin producing Rh antibodies against the foreign protein.  Hemolysis doesn't occur the first time a transfusion is performed because it takes time for the body to react and start making antibodies, but during the second time and every time thereafter, a typical transfusion reaction occurs in which the recipient's antibodies attack and rupture the donor Red blood cells.

c) Women who are Rh- and carrying an Rh+ baby run into the same problem. The first such pregnancy results in a healthy baby, but the mother is sensitized by the Rh+ antigens that have passed into her bloodstream from the baby through the placenta and will form Rh antibodies unless treated with RhoGAM  before or after giving birth. RhoGAM is a serum containing anti-Rh agglutinins and agglutinates the Rh factor  thereby blocking the mother's immune response.  If the mother is not treated with RhoGAM, then her antibodies will cross through the placenta and destroy the RBCs producing a condition known as hemolytic disease of the newborn, or erythroblastosis fetalis.  The baby becomes anemic and hypoxic. Brain damage and even death may result unless transfusions are done before birth.  Without RhoGAM injections the second and third child can suffer from this condition

VII) Leukocytes (white blood cells)

a) contain no hemoglobin (not red

b) have a nucleus

c) defend the body from pathogens (immunity)

d) can move along blood vessels or among body cells by amoeboid movement

e) can migrate out of blood stream by diapedesis a process that occurs when they squeeze between cells in capillary walls 

f) They are attracted to chemical stimuli (positive chemotaxis) (pathogens, damaged tissue, and active leukocytes)

g) Some leukocytes (neutrophils, monocytes, and eosinophils) engulf pathogens or cellular debris by a process called phagocytosis  These include the microphages (neutrophils and eosinophils) and the macrophages (monocytes).

d) Consists of two groups: granulocytes and agranulocytes

VII) Granulocytes (spherical in shape, larger and short lived than erythrocytes, have lobed nuclei, are all photocytic, and have membrane bound cytoplasmic granules stain with Wright's stain) They include neutrophils and eosinophils  andbasophils.

a) Neutrophils

----most numerous of the white blood cells accounting for 50-70% of the WBC population----

---about twice the size of red blood cells---

---their granules are chemically neutral and difficult to stain; their granules take up both basic (blue) and acidic (red) dyes---

---have a dense contorted nucleus like beads of a chain (polymorphonuclear--nucleus consists of many shapes)---

---first to arrive at an injury site and are active phagocytes---

---They kill bacteria by a process called respiratory burst in which  the granules merge with the phagosome (food vacuole containing the bacteria) to produce toxic substances such as bleach and hydrogen peroxide. Neutrophils also die from the toxins shortly after engulfing 1-2 dozen bacteria and have a short life span of 12 hours----

---They release chemicals after dieing to attract other neutrophils to the site---

----Bacteria slayers; numbers increase dramatically when we have an infection such as during appendicitis and meningitis---  

b) Eosinophils

---account for 1-4% of all leukocytes and are about the size of neutrophils---

--- have a red nucleus that appears like an old-fashioned telephone receiver---

---have large coarse granules in the cytoplasm that stain red with acid dyes (eosin)---

---most important role is to protect us from parasitic worms such as flatworms(tapeworm and fluke), and roundworms (pinworms and hookworms). Eosinophils reside where one might encounter such parasites such as in the loose connective tissue of the skin, intestinal,or respiratory tract.  Parasites are too large to be phagocytized, so they release enzymes from their cytoplasmic granules and digest the parasites--

---They also act as phagocytes by engulfing bacteria and other microbes that the immune system has coated with antibodies---- 

c) Basophils

---the rarest of white blood cells averaging only 0.5% (1 in 200) of the leukocyte population---

---same size or smaller than neutrophils, and their cytoplasm contains large coarse histamine-containing granules which are stained easily with the basic dyes (basophil means base loving). Basophils are not phagocytic. They discharge the granules into the damaged area. The granules contain histamine and heparin.   Histamine is an inflammatory chemical that acts as a vasodilator (opens up blood vessels to increase blood flow to an area) and attracts other white blood cells to the inflamed site. Heparin aids in clotting the blood. Mast cells which are found in connective tissue also respond to these chemicals  and induce local inflammation. Mast cells are not leukocytes, but also function in the immune response.

---have a deep purple nucleus that is generally U or S shaped with two or three conspicuous constrictions--

VIII) Agranulocytes ( WBCs that lack visible cytoplasmic granules, have a nucleus that is characteristically spherical or kidney shaped) ( include lymphocytes and monocytes)

a) Lymphocytes

----Second most numerous of the leukocytes (20% of all the leukocytes); contains a large purple circular nucleus  that occupies most of the cell volume. The nucleus may be slightly indented and is surrounded by a thin rim of pale-blue cytoplasm (all of the cytoplasm is pushed to the inner side of the plasma membrane by the nucleus--

---Most lymphocytes (larger ones) are found in lymphoid tissues (lymph nodes, spleen....) where they function in immunity. Only a small number are ever found in the bloodstream (smaller ones).----

----Lymphocytes are of two types T cells  which act directly against virus infected cells and tumor cells, and B cells which give rise to plasma cells which produce antibodies (immunoglobins) into the blood.---  

b) Monocytes

---account for 4-8% of the leukocyte population and are the largest of the leukocytes---

---They have a U or kidney shaped nucleus which stains dark purple---

---Monocytes differentiate into macrophages when they enter the tissues from the bloodstream. Macrophages are very phagocytic and are crucial in protecting the body from viruses bacteria and they also activate the lymphocytes for the immune response. They increase in number during chronic infections such as tuberculosis---

--They are second to neutrophils in arriving at a wound site. As neutrophils die from phagocytizing bacteria, the monocytes phagocytize the neutrophils---

IX) Leukopoiesis (production of white blood cells) 

---hormonally stimulated by group of hormones called glycoproteins which include the  interleukins and colony stimulating factors called CSFs.  Macrophages and T lymphocytes produce these hormones with other selected cell types.  Interleukins are numbered (IL-3,IL-5....) while the CSFs are named for the leukocyte population that they stimulate (G-CSF stimulates the production of granulocytes)--

----Figure 18.11 illustrates the various stages of leukopoiesis. Note the cells arising from the hematocytoblast. The myeloid stem cell will give rise to the granulocytes (eosinophils, neutrophils, and basophil), and the monocytes which will change into macrophages in the tissues. The lymphoid stem cell will give rise to the lymphocytes in which some further differentiate into special types of lymphocytes  including plasma cells that produce antibodies.  Note also the differentiation that occurs along the myeloid stem line after division is complete following the promyelocyte stage. The nuclei distort and become arc like producing the band cell stage. Their nuclei further constrict to form the characteristic nucleus specific to each type of granuloctye before entering into the blood stream.--- 

--- Many stem cells also migrate to lymphoid tissue (thymus, spleen, lymph nodes) from the bone marrow and as a result lymphocytes are produced these organs as well as bone marrow--

X) Differential Count of WBC Population

----Average differential count of formed elements per microliter: 5.2 million red blood cells(range of 4.4-6.0 million), 7,000 white blood cells (range of 6,000-9,000), and 350,000 (range of 150,000-500,000) platelets.---

---Factors affecting WBC population would include pathogenic infection, allergic reactions, inflammation----

---Leukopenia results in an inadequate number of WBCs and leukocytosis an excessive number of WBCs. ----

XI) Platelets

----formed in bone marrow called megakaryocytes  which have a large lobe or ring shaped nucleus--

---They are not cells, but cell fragments consisting of continually shed membrane enclosed packets from the megakaryocytes which enter into the blood and are called platelets. ---

---They initiate the clotting process, and circulate for 10-12 days after production before being removed by phagocytosis---

---A low platelet count is called thrombocytopenia which results in inadequate platelet production or excessive platelet destruction. Symptons include bleeding in the digestive tract, skin, and even inside the central nervous system---

---A high platelet count is called thrombocytosis which results from an acceleration in platelet formation due to infection, inflammation or cancer.

XII) Hemostasis (Stopping of bleeding) 

Consists of Three major phases:

1) The vascular phase (begins within a few seconds after the injury)

---a decrease in blood vessel diameter (vasoconstriction) when cut by the reflexive contraction of the smooth muscles in the blood vessels--

---vascular spasm follows which lasts about 30 minutes which can slow or even  stop the loss of blood----

----membranes become sticky and in small capillaries may stop bleeding completely----

2) The Platelet Phase 

---platelets attach and can form a plug in the break in the vascular system----

3) Coagulation (clotting phase) 

---takes 15 seconds to several minutes and results in the conversion of fibrinogen and prothrombin (the two clotting proteins in plasma) into fibrin to form a net like structure which eventually forms into a clot--

---Includes the extrinsic, intrinsic, and common pathways----