Anemia: The condition of not having enough hemoglobin in the blood to carry oxygen to body cells.
Antibodies: Proteins that identify pathogens or other substances as being harmful; flow in blood; can destroy pathogens by attaching to the cell membrane of the pathogen.
Arteries: Blood vessels that carry blood away from the heart.
Atrioventricular (AV) valves: Valves that stop blood from moving from the ventricles back into the atria.
Atrium: One of the two small, thin-walled chambers on the top of the heart that blood first enters.
Blood: A body fluid that is a type of connective tissue; moves oxygen and other compounds throughout the body.
Blood clotting: The complex process by which blood forms solid clots.
Blood pressure: The force exerted by circulating blood on the walls of blood vessels.
Capillaries: The smallest and narrowest blood vessels in the body.
Cardiovascular system: The organ system that is made up of the heart, the blood vessels, and the blood.
Heart attack: Event that occurs when the blood supply to a part of the heart is blocked.
Hemophilia: A group of hereditary diseases that affect the body's ability to control blood clotting.
Hypertension: Also called high blood pressure; a condition in which a person’s blood pressure is always high;
Leukemia: Cancer of the blood or bone marrow; characterized by an abnormal production of blood cells, usually white blood cells.
Lymphatic system: A network of vessels and tissues that carry a clear fluid called lymph; includes lymph nodes, lymph ducts, and lymph vessels.
Plasma: The golden-yellow liquid part of the blood.
Platelets: Fragments of larger cells that are important in blood clotting.
Pulmonary circulation: The part of the cardiovascular system which carries oxygen-poor blood away from the heart to the lungs, and returns oxygen-rich blood back to the heart.
Red blood cells (RBCs) : Flattened disk-shaped cells that carry oxygen, the most common blood cell in the blood. Mature red blood cells do not have a nucleus.
Semilunar (SL) valves: Found in the arteries leaving the heart; prevents blood flowing back from the arteries into the ventricles.
Sickle cell disease: A blood disease that is caused by abnormally-shaped blood protein hemoglobin.
Stroke: A loss of brain function due to a blockage of the blood supply to the brain.
Systemic circulation: The portion of the cardiovascular system which carries oxygen-rich blood away from the heart to the body, and returns oxygen-poor blood back to the heart.
Veins: Blood vessels that carry blood back to the heart.
Ventricle: One of the two muscular V-shaped chambers that pump blood out of the heart.
White blood cells (WBCs): Nucleated blood cells that are usually larger than red blood cells; defend the body against infection by bacteria, viruses, and other pathogens.