Blood is a bodily fluid that plays several vital functions in animals. While humans have several types of blood cells, more than half is plasma – a solution primarily composed of water that also contains floating proteins. In addition to circulating the body’s blood cells, Plasma also distributes sugars and hormones, and removes waste such as carbon dioxide, urea, and lactic acid. Plasma also contains platelets (or thrombocytes), which form blood clots at wounds and cuts to preventive excessive bleeding.
Erythrocytes (or red blood cells) are the most common type of blood cell in humans. Red blood cells primarily transport dissolved oxygen throughout the body. These cells contain the iron-rich protein hemoglobin, which binds molecules of oxygen in the lungs’ alveoli – specialized sacks where carbon dioxide leaves the blood stream and oxygen enters.
When hemoglobin is bound with oxygen, it turns red (hence the cells’ red color). As oxygenated blood flows away from the heart in arteries, it delivers oxygen to tissues that require it. These tissues absorb oxygen at capillaries, the smallest of body’s blood vessels. The now deoxygenated blood turns blue, and flows back towards the heart in veins.
Leukocytes (or white blood cells) are the second type of blood cell, and work as part of the body’s immune system to defend the organism from disease and foreign materials. There are several types of white blood cells: lymphocytes are among the most common. They target specific germs and substances using antibodies, protein tags that mark a cell for elimination. Lymphocytes also eliminate virus-infected and tumor cells, and prevent the body’s immune system from attacking itself. Neutrophils are the most abundant leukocyte. These cells quickly flock to an injury and absorb bacteria and dead tissue. Neutrophils are the primary component in pus, hence it’s whitish-yellow coloring.
Each individual has a blood type, identified by the ABO blood system. ABO labels blood A, B, AB, or O, based on the proteins it contains. These proteins determine the kind of blood an individual can receive in a transfusion. For example, a person with AB blood can receive any type of blood, whereas someone with O blood can only receive more O blood. Blood types are further categorized based on whether or not they have Rh factor, named for the Rhesus monkey in which it was discovered. If your blood contains Rh factor, it’s positive; if not, it’s negative.
Receiving blood of the wrong type can lead to hemolysis – destruction of red blood cells – and death. Although blood might make you a little queasy, it’s definitely worth knowing a little about – it might even save your life one day.