Science, Tech, Math › Science 12 Interesting Facts About Blood Share Flipboard Email Print Science Picture Co/Getty Images Science Biology Basics Cell Biology Genetics Organisms Anatomy Physiology Botany Ecology Chemistry Physics Geology Astronomy Weather & Climate By Regina Bailey Biology Expert B.A., Biology, Emory University A.S., Nursing, Chattahoochee Technical College Regina Bailey is a board-certified registered nurse, science writer and educator. Her work has been featured in "Kaplan AP Biology" and "The Internet for Cellular and Molecular Biologists." our editorial process Regina Bailey Updated June 21, 2019 Blood is the life-giving fluid that delivers oxygen to the cells of the body. It is a specialized type of connective tissue that consists of red blood cells, platelets, and white blood cells suspended in a liquid plasma matrix. These are the basics, but there are many more surprising facts as well; for example, blood accounts for about 8 percent of your body weight and it contains trace amounts of gold. Intrigued yet? Read on below for 12 more fascinating facts. 01 of 12 Not All Blood Is Red Jonathan Knowles/Stone/Getty Images While humans have red colored blood, other organisms have blood of varying colors. Crustaceans, spiders, squid, octopuses, and some arthropods have blue blood. Some types of worms and leeches have green blood. Some species of marine worms have violet blood. Insects, including beetles and butterflies, have colorless or pale-yellowish blood. The color of blood is determined by the type of respiratory pigment used to transport oxygen via the circulatory system to cells. The respiratory pigment in humans is a protein called hemoglobin found in red blood cells. 02 of 12 Your Body Contains About a Gallon of Blood SHUBHANGI GANESHRAO KENE/Getty Images The adult human body contains approximately 1.325 gallons of blood. Blood makes up about 7 to 8 percent of a person's total body weight. 03 of 12 Blood Consists Mostly of Plasma JUAN GARTNER/Getty Images Blood circulating in your body is composed of about 55 percent plasma, 40 percent red blood cells, 4 percent platelets, and 1 percent white blood cells. Of the white blood cells in blood circulation, neutrophils are the most abundant. 04 of 12 White Blood Cells Are Necessary for Pregnancy Michael Poehlman/Getty Images It is well known that white blood cells are important for a healthy immune system. What is less known is that certain white blood cells called macrophages are necessary for pregnancy to occur. Macrophages are prevalent in reproductive system tissues. Macrophages assist in the development of blood vessel networks in the ovary, which is vital for the production of the hormone progesterone. Progesterone plays a critical part in the implantation of an embryo in the uterus. Low macrophage numbers result in reduced progesterone levels and inadequate embryo implantation. 05 of 12 There's Gold in Your Blood Seyfi Karagunduz/EyeEm/Getty Images Human blood contains metals atoms including iron, chromium, manganese, zinc, lead, and copper. You may also be surprised to know that blood contains small amounts of gold. The human body has about 0.2 milligrams of gold that is mostly found in the blood. 06 of 12 Blood Cells Originate From Stem Cells DAVID MACK/Getty Images In humans, all blood cells originate from hematopoietic stem cells. About 95 percent of the body's blood cells are produced in the bone marrow. In an adult, most of the bone marrow is concentrated in the breastbone and in the bones of the spine and pelvis. Several other organs help to regulate the production of blood cells. These include the liver and lymphatic system structures such as the lymph nodes, spleen, and thymus. 07 of 12 Blood Cells Have Different Life Spans Science Photo Library - SCIEPRO/Brand X Pictures/Getty Images Matured human blood cells have varying life cycles. Red blood cells circulate in the body for about 4 months, platelets for about 9 days, and white blood cells range from a few hours to several days. 08 of 12 Red Blood Cells Have No Nucleus DAVID MCCARTHY/Getty Images Unlike other types of cells in the body, mature red blood cells do not contain a nucleus, mitochondria, or ribosomes. The absence of these cell structures leaves room for the hundreds of millions of hemoglobin molecules found in red blood cells. 09 of 12 Blood Proteins Protect Against Carbon Monoxide Poisoning BanksPhotos / Getty Images Carbon monoxide (CO) gas is colorless, odorless, tasteless and toxic. It is not only produced by fuel-burning devices but is also produced as a by-product of cellular processes. If carbon monoxide is produced naturally during normal cell functions, why aren't organisms poisoned by it? Because CO is produced in much lower concentrations than seen in CO poisoning, cells are protected from its toxic effects. CO binds to proteins in the body known as hemoproteins. Hemoglobin found in blood and cytochromes found in mitochondria are examples of hemoproteins. When CO binds to hemoglobin in red blood cells, it prevents oxygen from binding to the protein molecule leading to disruptions in vital cell processes such as cellular respiration. At low CO concentrations, hemoproteins change their structure preventing CO from successfully binding to them. Without this structural change, CO would bind to the hemoprotein up to a million times more tightly. 10 of 12 Capillaries Spit Out Blockages in Blood shulz/Getty Images Capillaries in the brain can expel obstructive debris. This debris may consist of cholesterol, calcium plaque, or clots in the blood. Cells within the capillary grow around and enclose the debris. The capillary wall then opens up and the obstruction is forced out of the blood vessel into the surrounding tissue. This process slows down with age and is thought to be a factor in cognitive decline that occurs as we age. If the obstruction is not completely removed from the blood vessel, it can cause oxygen deprivation and nerve damage. 11 of 12 UV Rays Reduce Blood Pressure tomch / Getty Images Exposing a person's skin to the sun's rays reduces blood pressure by causing levels of nitric oxide to rise in the blood. Nitric oxide helps to regulate blood pressure by reducing blood vessel tone. This reduction in blood pressure could cut the risks of developing heart disease or stroke. While prolonged exposure to the sun could potentially cause skin cancer, scientists believe that very limited exposure to the sun could increase the risks of developing cardiovascular disease and related conditions. 12 of 12 Blood Types Vary by Population ERproductions Ltd / Getty Images The most common blood type in the United States is O positive. The least common is AB negative. Blood type distributions vary by population. The most common blood type in Japan is A positive.