The body has several mechanisms it uses to keep itself healthy and strong. Blood is one such mechanism. Blood tissue is a connective tissue that works to perform several functions. Among other functions, it transports oxygen and carbon dioxide for delivery and disposal and helps keep the blood's pH normal. It also helps to keep the body at the right temperature. Without the blood, human bodies could not live, function, or get rid of bodily wastes.
Blood tissue is a form of connective tissue, even though it is a fluid. It is sticky and red in color because it contains red blood cells. If blood were to be put in a centrifuge, it would separate into three distinct parts: the eythrocytes, the buffy coat, and the plasma. Eythrocytes are red blood cells, and the buffy coat, a gray substance, is made up of leukocytes and blood platelets. Plasma is a liquid the color of straw that contains over 100 different substances, such as vitamins and bodily waste products.
Even though it doesn't connect anything, blood is considered a connective tissue because it is made from mesenchyme and is comprised of blood cells suspended in liquid that is not alive. It transports oxygen and nutrients to cells, removes waste from cells, and transports hormones. The liquid also contains cells and other factors that help blood to clot and help to defend the body from invaders. It also contains substances that keep the pH of the body normal.
Red blood cells are the body's oxygen transport systems. They are not true cells, as they do not have a nuclei or organelles. Their color ranges from bright red to dark red, depending on how much oxygen they are carrying. In the lungs, the oxygen binds to hemoglobin, a protein with four iron-containing sites for oxygen to bind to. Hemoglobin is also what gives the cells their red color.
White blood cells, or leukocytes, are the defense army within the blood tissue. They are the only true cells in the blood and are not limited to the blood stream. When called to defeat an infection or to dispose of a dead cell, they can squeeze through openings in the vessel walls. There, they can move through amoeboid action, meaning that they sprout cytoplasmic extensions that can move them. Leukocytes, along with platelets, usually make up less than 1% of blood.
Platelets are actually cell fragments that help in blood clotting. When a tear occurs in the blood vessels, platelets stick to the exposed collagen at the site of injury. They produce fibrous protein that traps other blood cells in a clot that stops blood from flowing and helps to prevent excess blood loss. Some platelets also secrete substances that signal other platelets to the break, substances that constrict blood vessels, or substances that promote an inflammatory response. Once the clot is formed, the platelets contract and pull the opening back together, thus healing the break.
Most of the blood cells contained in blood tissue don't last very long. Red blood cells only last about 100-120 days before they are disassembled, recycled, and disposed of. Platelets last about 10 days if they do not need to clot blood. The bone marrow makes and releases blood cells into the blood on a regular basis to replace old blood cells. Thus, the tissue is constantly being restored.
