Cardiovascular System

• Cardiovascular system


  Delivers oxygen and nutrients to the body tissues and carries away wastes such as carbon dioxide via blood
• Cardiovascular system


  • Major function is transportation
  • Uses blood as the transport vehicle
  • Carries oxygen, nutrients, cell wastes, hormones, and other substances vital for body homeostasis to and from the cell
  • Heart pumps blood throughout the body in blood vessels
  • Blood flow requires both the pumping action of the heart and changes in blood pressure
• If the cardiovascular system cannot perform its functions

  Wastes build up in the tissues, body organs fail to function properly, and then, once oxygen becomes depleted, they will die
• Blood


  • Transports substances such as oxygen and nutrients throughout the body and participants in processes such as clotting and fighting infections
  • Moved through the blood vessels by the pumping action of the heart
  • Fluid that contains red blood cells to carry oxygen, clotting proteins to stop bleeding, and white blood cells to fight infection
• Transportation via blood is the only way substances can be moved to distant body locations
• Clotting proteins are found only in blood—without them, a cut could be life-threating
• Blood


  • Unique, it is the only fluid tissue in the body
  • Has both solid and liquid components
• Plasma


  The liquid part of the blood, approximately 90% water, with over 100 different substances dissolved in it
• Plasma proteins


  • Made by the liver, except for antibodies and protein-based hormones
  • Serve a variety of functions such as transporting substances, distributing body heat, and contributing to the osmotic pressure of the blood
• Erythrocytes (Red Blood Cells)

  • Function primarily to carry oxygen to all cells of the body
  • Anucleate (without nucleus), literally "bags" of hemoglobin molecules
  • Hemoglobin transports most of the oxygen carried in the blood
  • Lack mitochondria and make ATP by anaerobic mechanism, so they do not use up any of the oxygen they are transporting, making them very efficient oxygen transporters
  • Small, flexible cells shaped like biconcave discs with depressed centers on both sides, providing a large surface area relative to their volume for gas exchange
  • Number of RBCs in the circulation vary, normally about 5 million cells per cubic millimeter of blood, but the amount of hemoglobin in the bloodstream is more important for oxygen transport
• A single red blood cell contains 250 million hemoglobin molecules of oxygen, so each of these tiny cells carry about 1 billion molecules of oxygen
• Decrease in the oxygen-carrying ability of the blood

  Anemia
• Anemia may be the result of

  Lower-than-normal number of RBCs, or abnormal or deficient hemoglobin content in the RBCs
• Sickle cell anemia (SCA)

  • The body does not form normal hemoglobin, instead, abnormal hemoglobin is formed that becomes spiky and sharp when either oxygen is unloaded or the oxygen content in the blood decreases below normal
  • This change in hemoglobin causes the RBCs to become sickled (crescent-shaped), rupture easily, and dam up small blood vessels, interfering with oxygen delivery and causing extreme pain
• Excessive or abnormal increase in the number of erythrocytes

  Polycythemia
• Polycythemia


  • May result from bone marrow cancer or be a normal physiologic response to living at high altitudes
  • The major problem is increased blood viscosity, which causes blood to flow sluggishly in the body and impairs circulation
• Leukocytes (White blood cells)


  • Crucial to body defense, contain nuclei and organelles, able to slip into and out of the blood vessels (diapedesis)
  • Form a protective, movable army that helps defend the body against damage by bacteria, viruses, parasites, and tumor cells
  • Can locate areas of tissue damage and infection by responding to certain chemicals (positive chemotaxis) and moving through the tissue spaces by amoeboid motion
• Whenever WBCs mobilize for action


  The body speeds up their production, and as many as twice the normal number of WBCs may appear in the blood within a few hours
• Leukocytosis


  An increase in WBC count, generally indicates that a bacterial or viral infection is stewing in the body
• Leukopenia


  An abnormally low WBC count, commonly caused by certain drugs, such as corticosteroids and anti-cancer agents
• In leukemia


  The bone marrow becomes cancerous, and huge numbers of WBCs are turned out rapidly, but the immature WBCs are incapable of carrying out their normal protective functions, so the body becomes prey for disease-causing bacteria and viruses, and severe anemia and bleeding problems result
• WBC classifications


  • Granulocytes
  • Agranulocytes
• Platelets


  • Not technically cells, but fragments of bizarre multinucleate cells called megakaryocytes
  • Needed for the clotting process that stops blood loss from broken blood vessels
• Hematopoiesis (Blood cell formation)


  • Occurs in the red bone marrow, or myeloid tissue
  • All the formed elements arise from a common stem cell, the hemocytoblast, which forms two types of descendants - the lymphoid stem cell and the myeloid stem cell
• Formation of Red Blood Cells

  1. RBCs are unable to synthesize proteins, grow, or divide

  2. As they age, RBCs become rigid and begin to fall apart in 100 to 120 days

  3. Their elements are eliminated by phagocytes in the spleen, liver, and other body tissues, and the iron is bound to protein as ferritin and secreted into the intestine by liver cells

  4. Lost blood cells are replaced more or less continuously by the division of hemocytoblasts in the red bone marrow

  5. The rate of erythrocyte production is controlled by the hormone erythropoietin, produced mainly by the kidneys
• Formation of White Blood Cells and Platelets

  1. Leukocytes and platelets production is stimulated by hormones like colony stimulating factors (CSFs) and interleukins, which prompt red bone marrow to turn out leukocytes and enhance their protective abilities

  2. The hormone thrombopoietin accelerates the production of platelets from megakaryocytes
• Hemostasis


  • The process of stopping bleeding when a blood vessel breaks
  • Involves a series of reactions starting with platelet adhesion and aggregation, followed by activation of the clotting cascade, and eventually regeneration of the endothelium and breakdown of the clot
• Placing a sterile gauze over a cut or applying pressure to a wound


  Speeds up the clotting process by providing a rough surface for platelet adhesion and increasing the release of tissue factor locally
• Undesirable clot formation


  A clot that develops and persists in an unbroken blood vessel is called a thrombus, which may prevent blood flow and lead to tissue death if it breaks off as an embolus
• Bleeding disorders


  Caused by platelet deficiency or deficits of clotting factors, leading to abnormal bleeding and conditions like thrombocytopenia and hemophilia
• Blood groups and transfusions

  • RBCs bear genetically determined proteins (antigens) that identify each person as unique
  • Antibodies in the plasma can recognize and attach to RBCs bearing different surface antigens, causing agglutination and clogging of small blood vessels
  • There are over 30 common RBC antigens in humans, so each person's blood can be classified into different blood groups
• Antigens


  Substances that the body recognizes as foreign and stimulates the immune system to mount a defense against
• Antibodies


  Recognizers present in plasma that attach to RBCs bearing surface antigens different from those on the patient-recipient's RBCs to clump, a phenomenon called agglutination, which leads to the clogging of small blood vessels throughout the body
• Common RBC antigens in humans

  • Over 30
• Blood groups that cause the most vigorous transfusion reactions

  • ABO
  • Rh
• Development of the circulatory system in the embryo

  1. Entire circulatory system develops early

  2. Many sites of blood cell formation before birth

  3. By 7th month, fetus's red marrow becomes the chief site of hematopoiesis

  4. Embryonic blood cells circulating in newly formed blood vessels by day 28 of development

  5. Fetal blood cells gradually replaced by RBCs containing more typical hemoglobin A after birth
• Physiologic jaundice


  Jaundice that generally causes no major problems, caused by fetal RBCs being destroyed so fast that the immature liver cannot get rid of the body's hemoglobin breakdown products fast enough
• Heart


  • Approximately the size of a person's fist
  • Hollow, cone-shaped
  • Weighs less than a pound
  • Snugly enclosed within the inferior mediastinum
  • Flanked on each side by the lungs
  • Apex directed downward the left hip and rests on the diaphragm, at the level of the fifth intercostal space
  • Broad posterosuperior aspect, or base, from which the great vessels of the body emerge, points toward the right shoulder and lies beneath the second rib
• Pericardium


  Sac that encloses the heart, made up of three layers: fibrous pericardium, parietal layer of serous pericardium, and visceral layer of serous pericardium (epicardium)
• Heart walls


  Composed of three layers: epicardium, myocardium, and endocardium