The Circulatory System Part 1 Purpose of the System • The circulatory systems transports substances around the body. – It carries oxygen and nutrients to the cells – It carries wastes away from the cells – It transports substances (e.g., hormones) from one part of the body to another • It helps to regulate body temperature • It carries disease-fighting white blood cells and medicine to where they are needed. Parts of the System The circulatory system has three main components: • Heart • Blood vessels • Blood Together, the heart and the blood vessels make up the cardiovascular system Blood • An average adult contains 5 L of blood • Blood is a type of connective tissue because it links all cells and organs • It has two distinct components: Fluid component: • Called plasma • Consists of water and dissolved substances (gases, proteins, sugars, vitamins, minerals and waste products) Solid component: • Red blood cells, which carry oxygen • White blood cells, which fight disease • Platelets, which help blood to clot Plasma • A clear, yellowish fluid • 92% water, 7% proteins, 1% other dissolved substances and ions (sodium, potassium, chloride, bicarbonate) • Main proteins are albumin, globulins, fibrinogen Red Blood Cells • • • • • • • • • Also called erythrocytes Produced in the bone marrow Their function is to carry oxygen They live for about 120 days Make up about 44% of total blood volume Lack a nucleus Shaped like biconcave disks, which increases the surface area by 2030% for oxygen exchange Contain hemoglobin, a protein molecule containing iron, which can bind with oxygen Your hematocrit is a measure of what proportion of the blood is made up of red blood cells. A person with anemia has a low hematocrit and will feel tired. White Blood Cells • Also called leukocytes • Produced in the bone marrow • Much less numerous than red blood cells • Part of the body‘s response to infection • 1% of the total blood volume, but numbers may double when an infection is present • 5 types, all nucleated (see the diagram, above right) • Leukemia is a type of cancer in which abnormal white blood cells are produced and they crowd out normal cells, making it hard for them to function Fighting Disease • Some white blood cells destroy pathogens by phagocytosis – they engulf and then digest them • Others secrete a substance that attracts phagocytes Platelets • Also called thrombocytes • Membrane-bound fragments of cells formed when larger cells break apart in the bone marrow • No nuclei • Break down within 7 to 10 days in the blood • Play a key role in blood clotting How Blood Clots • The injured blood vessel releases a chemical signal that attracts platelets • Platelets rupture, releasing chemicals that cause a cascade of reactions that produce fibrin • Fibrin is an insoluble protein that forms a mesh over the injury site, preventing loss of blood cells and eventually forming a clot Blood Type • There are four basic blood types, depending on the antigen (A, B, AB, O) • An antigen is a protein attached to the surface of a red blood cell, which gives it its identity • Blood type is inherited, one allele from each parent • An antibody is a protein produced by the immune system to destroy a foreign antigen • If antigens and antibodies of the same type come together (e.g., by transfusion), they clump together (agglutination) and place the person at grave risk • People with Type O blood are universal donors • People with Type AB blood are universal receivers Rh Factor • The Rh factor is another antigen found on the red blood cell • Also inherited • 85% of Canadians are Rh-pos. They have the Rh antigen. • 15% are Rh-neg. They lack the Rh antigen. • People with Rh-neg blood can donate blood to Rh-pos people, but cannot receive it from them • When an Rh-neg woman becomes pregnant, she must receive an injection of gammaglobulin so she does not react against her baby if it has Rh-pos blood. This reaction harms the baby.
