Blood is a type of connective tissue, a fluid made of 4 major substances:

  • 1. Plasma - the liquid part that has not clotted (After clots have formed and been removed from the plasma only the SERUM is left.)
  • 2. Erythrocytes - Red blood cells
  • 3. Leukocytes - White blood cells
  • 4. Thrombocytes - Platelets



    Approx. 5 million RBC's, 7,500 WBC's, and 300,000 platelets are found in 1 drop of blood, approx 30 trillion RBC's in entire body.

    Blood = 8% of body weight, approx. 5-6 qts.(10-12 pints), pH of 7.4, temperature = 100 degrees Fahrenheit.

    Manufacture of Blood


    Myeloid tissue (red bone marrow) produces 2 million RBC's each second because RBC's live only about 120 days. Myeloid tissue, found in the sternum, ribs, hipbones, and clavicles, manufacture most of the blood except for some types of white blood cells which are produced in the lymphatic tissue.


  • 1. Transports: oxygen from lungs to cells; carbon dioxide from cells to lungs; nutrients from digestive system to cells; wastes from cells to kidneys, lungs, and sweat glands; hormones from endocrine glands to cells; enzymes to cells.
  • 2. Regulates: pH through buffers; normal body temperature through heat absorbing and cooling properties of its water content; water content of cells
  • 3. Protects against: blood loss by clotting; foreign microbes with immune system

  • Click here to learn about Charles Drew, inventor of the blood bank.

    Click here to go to Quiz 1

    RED BLOOD CELL FUNCTIONS: Transport oxygen - Unique structure and tremendous numbers give the RBC's a total surface area larger than a football field for absorbing oxygen.

    HEMOGLOBIN - an iron containing protein that combines with oxygen to form OXYHEMOGLOBIN which carries oxygen to the body. Each erythrocyte contains approx. 280 million molecules of hemoglobin.

    ANEMIA - a number of different conditions caused by an inability to carry sufficient oxygen to the body cells due to:

  • 1. inadequate number of erythrocytes (lost by hemorrhage or inadequate production (cancer, radiation))
  • 2. inadequate amount of hemoglobin




  • IRON DEFICIENCY ANEMIA - lack of iron in the diet causes lack of hemoglobin, lack of oxygen, lack of energy.
  • PERNICIOUS ANEMIA - caused by a defiency of RBC's due to lack of B12.
  • SICKLE CELL ANEMIA - caused by inheritance of an abnormal type of hemoglobin. When oxygen levels in blood fall, the defective hemoglobin crytallizes distorting the RBC into a sickle shape and blocking function.



    POLYCYTHEMIA - Almost the opposite of anemia; the red bone marrow produces too many RBC's.
    Blood Doping - An artificial way of raising red blood cell levels involving tranfusions by athletes to raise their level of RBC's and increase oxygen delivery to muscles (Illegal for competition and probably inadvisable anyway).

    HEMATOCRIT - A blood test that uses a centrifuge to separate and measure the different portions of blood.
    RBC's = 45% in normal blood
    Buffy Coat - made of WBC's and platelets
    Plasma = approx 50% of blood

    Click here to go to Quiz 2



  • 1. NEUTROPHILS - these are the most numerous of the PHAGOCYTES. They engulf and digest microbes.
  • 2. EOSINOPHILS - help protect the body from irritants that cause allergies. Also capable of phagocytosis.
  • 3. BASOPHILS - also help with allergic reactions, produce a chemical called HEPARIN which prevents clotting of blood.


  • 1. LYMPHOCYTES - protect against disease by producing an immunity to previous invaders. Will be discussed in the chapter on immunity.
  • 2. MONOCYTES - Monocytes digest (phagocytize) microbes




  • LEUKOPENIA - low white count (under 5,000/dl of blood) caused by diseases of the immune system
  • LEUKOCYTOSIS - abnormally high white count, usually because of infection
  • LEUKEMIA - malignant blood cancer that causes increase of leukocytes




    As platelets collect around an injured vessel, some break up and release PLATELET FACTORS which combine with PROTHROMBIN (a protein found in the plasma) to form THROMBIN (an enzyme) that changes FIBRINOGEN to FIBRIN, a gel-like fiber that catches RBC's and forms the clot.

    VITAMIN K - stimulates liver to increase production of prothrombin.

    THROMBUS - a blood clot
    THROMBOSIS - the condition of having a blood clot
    EMBOLUS - a dislodged clot
    EMBOLISM - the condition of having a dislodged blood clot

    Click here to go to a Multiple Choice Quiz on blood cells

    Click here to identify Leukocytes

    Click here to go to Quiz 3

    Click here to learn about Karl Landsteiner, discoverer of Blood types

    A = 41%
    B = 10%

    ANTIGEN - a substance that stimulates the production of antibodies
    ANTIBODY - a substance that reacts to an antigen, usually causing them to clump together
    AGGLUTINATE - clumping of antibodies and antigens

    The blood types are caused by the presence or absence of two types of proteins that act as antigens in the blood (see the chart below.) Those with the first protein are called Type A. Those with the second protein are called Type B. Some people have both and are called Type AB. Some people don't have either protein. They are called type O. Reactions between the antibodies and antigens of different blood types causes clumping (agglutination) of the cells.

    In addition to these blood types, blood type is identified as to the presence or absence of a blood protein called Rh factor. Those with the factor are said to be positive. Those without the factor are said to be negative (chart below.)


    A A Anti-B
    B B Anti-A
    AB A & B Neither A nor B
    O Neither A nor B Both Anti-A & Anti-B



    Rh positive Rh Antigen No Rh antibody
    Rh negative No Rh Antigen Can develop antibodies if exposed


    Rh FACTOR - an antigen found in 85% of human blood. The name Rh was chosen because it was first discovered in the blood of the Rhesus monkey. People without the factor (negative) do not have antibodies against the factor, but will develop them if exposed to Rh factor through blood transfusion or childbirth. 

    ERYTHROBLASTOSIS FETALIS - a disorder caused by the reaction of an Rh negative mother carrying an Rh positive child. It happens to the second positive child of an Rh negative mother and may cause death. This can be prevented if the mother receives a shot to prevent the production of antibodies after each birth. 


    The inheritance of blood is an example of a genetic condition known as multiple allelles. This means that it is a little more complicated than the simple dominant / recessive traits that we usually discuss. Blood types A and B are what is known as co-dominant. When both are inherited, both will be expressed. Neither is recessive to the other. Both A and B, however, are dominant to the inheritance of O, which is the lack or either A or B factor. 

    We use the lowercase letter i to represent the recessive type O. The genotypes (possible gene combinations) for blood type can be represented by the chart below:

    Blood Inheritance Chart

    BLOOD TYPE Possible Genotypes
    A AA or Ai
    B BB or Bi
    AB AB only
    O ii only

    Rh factor is inherited separately from blood type. The inheritance of Rh factor (positive) is dominant to the inheritance of negative (no Rh factor). 

    Click here to go to Multiple Choice Quiz on Blood Type

    Click here to go to Quiz 4