A person's blood carries oxygen to living cells and takes away their waste products. It also delivers immune cells to fight infection and contains platelets that form a plug in a damaged blood vessel to stop bleeding. Blood also transports nutrients throughout the body and returns carbon dioxide to the lungs to be exhaled.
Your blood is made up of straw-colored fluid (plasma), red and white blood cells, and platelets. Plasma is mostly water, but it also contains proteins (albumins, clotting factors, antibodies, enzymes, and hormones), sugars (glucose), and fat particles. Red and white blood cells are the main types of cells in your blood. They are both involved in forming blood clots and fighting infection, but white blood cells are more important in the former role. Platelets are colorless, cell-like fragments that help control blood clotting and prevent excessive bleeding after an injury.
A blood sample is usually analyzed by a doctor using a technique called a blood smear, which allows the physician to see individual cells in a sample of blood. Variations in the shape and size of cells may suggest a blood disorder. Blood disorders can be cancerous or noncancerous, and they can affect how long a person lives. Some blood disorders are chronic and do not cause any symptoms, but others can be life-threatening. In addition to its normal functions, your blood also transports substances that help the kidneys filter waste from the body and carries waste from the digestive tract into the large intestine for excretion.