Blood is a fluid that primarily consists of cells and a substance called plasma. It contains a substance called hemoglobin, which contains a pigment that is responsible for its red color.
It is extremely important that it is kept relatively clean and chemically balanced... In fact, this is the primary function of the kidney.
To the naked eye, blood may seem as just a red (and sometimes repulsive) fluid but it is much more than that. Its structure and composition provide some good insights into its function and importance to the body.
It has two main components - the plasma and the formed elements.
Plasma is a clear extracellular (outside the cells) fluid in which the various cells and platelets (collectively called formed elements) are suspended. The platelets are fragments of certain bone marrow cells. Plasma is a complex mixture of proteins, enzymes, nutrients, wastes, hormones, and gases.
Formed elements are visible structures with distinctive shapes. They are enclosed in plasma membrane. The two (2) main cells that comprise "formed elements" are red blood cells (erythrocytes) and white blood cells (leukocytes).
These formed elements are responsible for many important biological functions such as transporting nutrients, oxygen, and other important substances; defend the body against attacks by diseases; regulate and maintain the body's correct fluid balance.
Erythrocytes have two (2) main functions. They take oxygen from the lungs and deliver it to other tissues in the body and they pick up carbon dioxide from other tissues and take it to the lungs.
The primary function of leukocytes is to defend the body against pathogens (organisms that cause disease). The main pathogens that affect humans are bacteria and viruses.
Erythrocytes [eh-RITH-ro-sites] are made in the BONE MARROW. They look like little red disc, concave on both sides, and full of hemoglobin (or haemoglobin). The production of these cells is triggered by a hormone called erythropoietin [eh-RITH-ro-poy-EE-tin]. This hormone is secreted by the kidneys and liver, and through a series of complex biological processes, stimulates the bone marrow to produce these very important cells.
Erythrocytes are mainly responsible for transporting oxygen to tissues and taking carbon dioxide away. If for any reason these cells are not able to perform this function effectively, tissues and organs will be deprived of oxygen and will eventually die.
Leukocytes [LOO-ko-sites] contain no hemoglobin. They also differ from erythrocytes in that each leukocyte contains a nucleus. Leukocytes are formed in the BONE MARROW, SPLEEN, THYMUS, and LYMPH NODES. There are three types: granulocytes, lymphocytes, and monocytes.
Leukocytes are mainly responsible for defending the body against diseases. Granulocytes help combat bacterial and viral infections. Lymphocytes are responsible for long term immunity and destroy foreign bodies, either directly or through production of ANTIBODIES. Monocytes ingest bacteria and foreign bodies by a process called phagocytosis.
Basically, there are four different blood types: A, B, AB and O. These can be further subdivided into "Positive (+)" or "Negative (-)" categories.
On the surface of each cell are combinations of proteins, glyco-proteins and glyco-lipids. These form what is called antigens, which enable our immune system to distinguish our cells from foreign components. The different types are determined by these antigens. Cells with type 'A' antigens are classified as type A; cells with type 'B' antigens are classified as type B; cells with 'AB' antigens are classified as type AB, and cells without any of these antigens are classified as type O.
Types that are classified as "Positive" contain a property called Rh antigens. If there are no Rh antigens, it is classified as "Negative".
The different classifications are very important considerations for transfusions and transplants, since they are not all compatible with each other. Persons with type O, however, can donate to all of the different types and is sometime referred to as the universal donor. Individuals with type AB are sometimes referred to as universal recipients, because they can receive from any of the other types.
Blood plays more roles in the body than one might expect. Its main function is to transport cells, oxygen, nutrients and other essential molecules around the body. It is involved in immune defense, nutrition, respiration, thermoregulation (regulation of body temperature), water and pH balance, waste elimination, and internal communication. Its three (3) main functions are:
Blood has two (2) very important properties - viscosity and osmolarity. These two properties warrant special attention, since they impact directly on the blood's quality and ability to efficiently discharge its function.
Health is directly affected by the volume and concentration (chemical balance) of the blood. Its correct volume, concentration and quality are essential for optimal health. The kidneys work very hard to keep it free of toxins and help maintain its optimal quality.