Human Circulatory System and Vital Blood Functions

The Circulatory System

The circulatory system is responsible for delivering nutrients and oxygen to all cells, collecting the waste substances produced, and conducting these to the organs responsible for eliminating them.

Composition and Properties of Blood

Blood is a thick, viscous red liquid that circulates through the blood vessels, responsible for transporting substances. It is formed by a liquid part called plasma, where cells are in suspension: red blood cells, white blood cells, and platelets.

Blood Plasma

Plasma is a transparent yellow liquid in which blood cells float. It is composed of 90% water and 7% proteins, of which the most important factors are related to coagulation and antibodies related to defense against infections.

Red Blood Cells (Erythrocytes)

Red blood cells (also known as erythrocytes) are disc-shaped cells in the central part without a nucleus. Their role is the transport of oxygen from the lungs to all organs and tissues of the body.

Understanding Anemia

Anemia consists of a decreased number of red blood cells in the blood. It can have different origins, such as bleeding, inadequate production of red blood cells, or a diet poor in iron that prevents the manufacture of enough hemoglobin.

White Blood Cells (Leukocytes)

White blood cells are blood cells with a nucleus and a size slightly greater than that of red blood cells. Their mission is to defend the body against infections. There are three main types:

• Granulocytes: These feature granules in their cytoplasm and a nucleus with several lobes. They are phagocytic cells that distribute and engulf microorganisms.
• Lymphocytes: These have cytoplasm without granules and a large spherical nucleus that occupies much of the cell. Their function is to produce antibodies against the proteins of microbes that defend us.
• Monocytes: These are mobile, large cells without granules in the cytoplasm, featuring a large nucleus similar in shape to a kidney.

Platelets (Thrombocytes)

Platelets, also called thrombocytes, are very tiny compared to erythrocytes or leukocytes and have no nucleus. The mission of platelets is blood clotting, which occurs when a blood vessel rupture happens.

The Three Primary Functions of Blood

1. Transportation: Erythrocytes in the blood transport oxygen from the lungs to the cells and carbon dioxide from the cells to the lungs. Blood transports nutrients from the intestine to the cells. It transports all cellular waste products, such as nitrogen compounds, from the cells to the kidneys to be processed into urea. It also transports hormones from endocrine glands to the tissues where they act.
2. Defense: Blood defends the body against microorganisms; white blood cells destroy them through phagocytosis or antibodies. It protects the body when an injury occurs by forming clots to prevent blood loss and infection.
3. Temperature Regulation: Blood unifies the body temperature as it carries heat from organs like the liver. It acts as a coolant because the liquid distributes body heat throughout the body and allows for its fast dissipation.