BLOOD CELLS

The circulatory system exists to transport the blood.
​The blood has 3 major components.

1. Blood Cells
   1. Red Blood Cells (Erythrocytes) 
   2. White Blood Cells (Leukocytes)
2. Platelets (Thrombocytes)
   1. Blood Clotting Factors
3. Blood Plasma
   1. The Liquid Background Substance of the Blood

Blood Plasma
​
​Blood plasma functions to transport nutrients, hormones, and proteins to the cells of the body. 

Thrombocytes (Platelets)

Thrombocytes (platelets) get their name from the Greek words for "clot" and "cell".  This name explains their function, which is to assist blood clotting at the site of injury, to prevent excessive bleeding. Another word for "clotting" is "coagulation". 

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THE RED BLOOD CELLS (ERYTHROCYTES)
    The proper name for Red Blood Cells is Erythrocytes. Red blood cells are short-lived and do not have a nucleus. The main function of the erythrocytes is to transport oxygen and nutrients to the cells of the body and to take away unwanted waste products and carbon dioxide from the cells.
     Red blood cells are easy to spot in histology due to the lack of the nucleus. 

   The red blood cells function to:

1. Deliver oxygen to the cells of the body.
2. Take away carbon dioxide from the cells.​

THE WHITE BLOOD CELLS (LEUKOCYTES)
    White blood cells come from hematopoietic stem cells found in bone marrow. Leukocytes are found everywhere in the body, including the blood of the circulatory system and the lymph of the lymphatic system. All white blood cells have nuclei and are easily distinguishable from red blood cells. 
    White blood cells are known as leukocytes. The general function of leukocytes is to protect the body against infectious diseases and foreign invaders. There are 6 types of leukocytes that fall into one of two categories. ​

Red blood cells are highly specialized for their function of as exchange. 2 of these can be seen in the red blood cell's physical features. 

1. The Concave Shape of the Red Blood Cell - Red blood cells have an unusual shape.  Their shape in concave, which means they inward.  This unique shape allows the red blood cells to have an increased surface area to maximize the rate of gas exchange. 
   
2. Red Blood Cells Are Anucleated - Mature red blood cells do not have a nucleus and do not divide! This means that the red blood cells do not need very much energy in order to live out their short, hard-working gas-toting lives. They need very little oxygen themselves, which means that they can carry even more oxygen to the cells of the body that depend on it!. 

There are 2 categories of white blood cells;

1. Granulocytes
2. Agranulocytes

  Granulocytes appear "speckled" or granulated, because they contain secretory vessels. The secretory vessels stain purple with the hematoxylin nuclear stain. ​

There are 3 types of granular white blood cells:  

1. Neutrophils 
2. Basophils
3. Eosinophils

There are 2 types of agranular white blood cells:

1. Lymphocytes
2. Mo​nocytes

Granulocytes

GRANULOCYTES

Agranulocytes

 Neutrophils

        Neutrophils are the most abundant type of white blood cell. They are the "first responders" of the immune system and defend against bacteria and fungi.  

    Neutrophils appear as though they have multiple nuclei. However their nucleus is made up of 3 to 4 lobes connected by a thin section.

Basophils

Eosinophils

Eosinophils are rare and  primarily target parasitic infections. Under the microscope they appear to have 2 lobes and stain very pink (due to the eosin stain).  ​

Lymphocytes

Monocytes

    Monocytes are large phagocytic white blood cells, known as macrophages. The nucleus will be large and "kidney-shaped", taking up most of the space in the cell. Monocytes (macrophages) are part of the body's innate nonspecific defensive cells, but also function to provide specific immunity long term.
   In their nonspecific defensive function, the macrophages are able to "eat" or engulf larger particles of debris, dead or damaged cells, pathogens or foreign invaders of the body. The macrophages are constantly on patrol to seek and destroy. They travel throughout the body using the circulatory system and are able to move through the capillary walls if they encounter any signs that an intruder has invaded or damage has occurred. 

    The macrophages also have a specific immune function in addition to the non-specific phagocytosis (engulfing) of unwanted entities. This specific immune function is acquired through the action first identifying a particle being "foreign", or not belonging to the body. It does this by identifying the major histocompatibility complex proteins (MHCs) on the surface of the particle. ​

​   Each person has their own unique signature MHCs, except for identical twins, that enables the cells of their immune system to identify the cells of the body, and to be able to distinguish those cells from bacteria, parasites, and viruses. Even the body's own cells that have become mutated or infected with a pathogen will often show evidence of the change as a change in the signaling sequence of the MHCs on the surface of those affected cells.. ​

    Monocytes have agranulated cytoplasm. Their nucleus contains only one oddly shaped lobe, that is large and takes up most of the space within the cell. The nucleus usually takes on a rather "kidney-bean" shaped. The nuclei of monocytes do not contain distinct lobes like we see with eosinophils, for example. 
    Monocytes (macrophages) that are stored in the spleen can be mobilized to the area of injury or infection in response to inflammation within approximately 8–12 hours. ​

Blood Disorders

Anemia

   Anemia is a blood disorder characterized by having an abnormally low number of red blood cells in your blood. The decreased amount of red blood cells can result in excessive bleeding or even death, depending of the severity of the disorder.
   In patients that are anemic, when an injury that causes bleeding occurs, the body will lose red blood cells faster than the body is able to replace them. 
 Anemia has several causes including malnutrition, vitamin B-12 deficiency, folic acid deficiency, or iron deficiency (the most common cause). Anemia can accompany many diseases, disorders and illnesses, including autoimmune disorders and exposure to environmental toxins.