Human Blood Circulatory System Definition:

The human blood circulatory system functions to transport blood and oxygen from the lungs to the various tissues of the body.

The heart, the lungs, and the blood vessels work together to form the circle part of the circulatory system.

Heart

The heart is one of the most important organs in the entire human body and human blood circulatory system. It is really nothing more than a pump, composed of muscle which pumps blood throughout the body, beating approximately 72 times per minute of our lives. It contains four chambers: two atria and two ventricles. Oxygen-poor blood enters the right atrium through a major vein called the vena cava. The blood passes through the tricuspid valve into the right ventricle.

Next, the blood is pumped through the pulmonary artery to the lungs for gas exchange. Oxygen-rich blood returns to the left atrium via the pulmonary vein. The oxygen-rich blood flows through the bicuspid (mitral) valve into the left ventricle, from which it is pumped through a major artery, the aorta. Coronary arteries supply the heart muscle with blood

Sinoatrial Node is called the pacemaker.

Blood

Blood is the medium of transport in the body. The fluid portion of the blood, the plasma, is a straw-colored liquid composed primarily of water. All the important nutrients, the hormones, and the clotting proteins as well as the waste products are transported in the plasma. Red blood cells and white blood cells are also suspended in the plasma. Plasma from which the clotting proteins have been removed is serum.

Red Blood Cells (RBC)

• Red blood cells are also called erythrocytes.
• These are disk-shaped cells produced in the bone marrow.
• Red blood cells have no nucleus, and their cytoplasm is filled with hemoglobin.
• Hemoglobin is a red-pigmented protein that binds loosely to oxygen atoms and carbon dioxide molecules.
• A red blood cell circulates for about 120 days and is then destroyed in the spleen.
• When the red blood cell is destroyed, its iron component is preserved for reuse in the liver.
• The remainder of the hemoglobin converts to bilirubin.This amber substance is the chief pigment in human bile, which is produced in the liver.
• Red blood cells commonly have immune-stimulating polysaccharides called antigens on the surface of their cells.
• Individuals having the A antigen have blood type A (as well as anti-B antibodies); individuals having the B antigen have blood type B (as well as anti-A antibodies); individuals having the A and B antigens have blood type AB (but no anti-A or anti-B antibodies); and individuals having no antigens have blood type O (as well as anti-A and anti-B antibodies).

White Blood Cells (WBC)

• White blood cells are referred to as leukocytes.
• They are generally larger than red blood cells and have clearly defined nucleus.
• They are also produced in the bone marrow and have various functions in the body.
• Certain white blood cells called lymphocytes are essential components of the immune system.
• Neutrophils and monocytes function primarily as phagocytes; that is, they attack and engulf invading microorganisms.
• About 30 percent of the white blood cells are lymphocytes, about 60 percent are neutrophils, and about 8 percent are monocytes.
• The remaining white blood cells are eosinophils and basophils.Their functions are uncertain; however, basophils are believed to function in allergic responses.

Platelets

• Platelets are small disk-shaped blood fragments produced in the bone marrow.
• They lack nuclei and are much smaller than erythrocytes. Also known technically asthrombocytes, they serve as the starting material for blood clotting.