Blood is a vital substance for our existence. Without it we would die. The blood is a fluid tissue. The reason it is called a tissue is that it has cells. Blood is a fluid but it has cells in which is why it is called a fluid tissue.

Composition of Blood:

plasmaBlood is composed of Plasma, Blood cells and the Platelets. The Plasma is a yellowish substance which is mostly composed of water and includes includes serum albumin, serum globulin, fribinogen and prothrombin. Other substances are mineral salts, hormones, excretory products and food molecules. Blood cells include white Blood cells and the red blood cells.

Red Blood cells:

The Blood cells are the leukocytes (white blood cells) and erythrocytes (the red blood cells). The Red blood cell is a spherical cell which has a biconcave at the center of its body. The center is much more thinner than the rest of the body of the cell. It has no nucleus. The red blood cells are produced by the bone marrow. The center of the red blood cell (erythrocytes) is composed of hemoglobin. The blood cellshemoglobin has iron in it and is red pigmented.

Note: Did you know that there are 5 million red blood cells present in each cubic centimeter of blood.

It helps to transport oxygen across the body. The hemoglobin combines with the oxygen from the lungs in pulmonary system. These two combine with loose connections and can easily be broken. The substance after the merge is then called the oxyhemoglobin. When the blood cells reach an area of low oxygen concentration the the oxygen molecules break loose and reach the cells of that area.

White Blood cell:

The white blood cells are of two types. The lymphocytes and the phagocytes. The Phagocytes are divided into subcategories. These are the monocytes and the white-cellpolymorph. Lymphocytes are like any other cell and has a nucleus. The Monocytes are bean shaped and have non granular cytoplasm. The Poly-morph have granular cytoplasm and its nucleus has lobes and is irregular in shape.

These cells are the protective cells which protect the body from any disease and bacteria which enters our body.


phagocytosisThis is the process in which the white blood cells ingest the bacteria and break it down. This process is called Phagocytosis.

The Immunity System:

When certain diseases enter the body it produces toxins which is harmful for the body. The lymphocytes produce an antibodies which destroys these toxins and can also get rid of the bacteria. The bacteria is then forced to clump together which is then called agglutination. The antibodies persist in the blood vessels for a long time which creates the immunity for the same disease or bacteria. This forms the immunity system.

This is why sometimes doctors may inject you with dead bacteria to activate the antibodiesantibodies forming an immunity.

Blood clot:

Blood clotting is essential for protecting from incoming diseases and from bleeding too much. This will take place when you get a scar or a cut.

What happens is that the blood platelets and the damaged blood vessels release an enzyme called thrombokinase. This breaks down the prothrombin found in the plasma. The new enzyme thrombin is made. Thrombin then breaks down the fibrinogin from the blood plasma and creates fibrin threads. These tangle the blood blood clotcells together and the whole combined structure is then called blood clot.

Note: For blood clotting Vitamin K and Calcium is required.

Note: People with hemophilia cannot blood clot which is why they can bleed to death by internal bleeding from smallest injury.

With this I conclude my article.

How Capillaries Supply Nutrient Molecules to Body Cells:

When the blood reaches the capillaries, the plasma with all the food molecules it has and the white blood cells diffuse through the capillary wall and dilute the tissue fluid.

Tissue fluid is the substance found between molecules. It is found in inter-molecular lymphdistances in minute spaces. The tissue fluid washes the cells. When this action occurs all the food molecules it contains from the plasma diffuses through the plasma membrane of the cell. This is how the cell is provided with food molecules. Inside the cells the mitochondria breaks these molecules down and produce energy i.e; respire.

The red blood cells do not pass through as they are not small enough to pass through the endothelial membrane of the capillaries. To prevent loss of too much liquid some of the water is absorbed by the capillaries while some tissue fluid is absorbed in the veins near the heart

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