Cardiovascular System

• Cardiovascular System

  The system responsible for the circulation of blood throughout the body
• Three Components of the Cardiovascular System

  • Blood
  • Heart and Blood Vessels
• Hematology

  The study of blood, blood forming tissues and blood disorders

  
• Blood (Connective Tissue)


  Consists of materials suspended in the plasma

  
• Functions of Blood

  • Transportation
  • Regulation
  • Protection

  
• Blood

  • Transports oxygen and carbon dioxide between lungs and tissues
  • Transports absorbed nutrients from GIT to liver and other cells
  • Transports hormones from endocrine glands to target cells
  • Transports waste products from cells to excretory sites (liver, kidney, skin)
  • Transports heat throughout the body
• Blood

  • Regulates pH via buffers
  • Regulates body temperature by carrying excess heat to skin for dissipation or by vasoconstricting to conserve heat
  • Regulates osmotic pressure by maintaining blood protein and electrolyte levels
• Blood

  • Provides immunity through blood proteins (complement and interferons)
  • Provides immunity through phagocytic blood cells
  • Provides immunity through blood cells that produce antibodies
  • Helps maintain homeostasis by clotting to prevent blood loss
• Physical Characteristics of Blood

  • Blood is denser than water
  • When centrifuged, forms layers - red blood cells at the bottom, plasma at the top, and leukocytes/platelets in the middle (buffy coat)
  • Hematocrit is the percentage of blood sample that is erythrocytes
  • Polycythemia is an abnormally high hematocrit, can indicate dehydration
  • Low hematocrit indicates anemia, can result in increased cardiac output

  
• Plasma

  • 90% water
  • Contains nutrients, gases, hormones, waste products, electrolytes, and proteins
  • Plasma proteins are the most abundant plasma solute
  • Plasma proteins can function as carriers for other nutrients, act in immunity, and help in blood clotting
  • Liver synthesizes most plasma proteins

  
• Formed Elements of Blood

  • Red Blood Cells (Erythrocytes)
  • White Blood Cells (Leukocytes)
  • Platelets

  
• Erythrocytes (Red Blood Cells)

  • Biconcave discs
  • Flexible and able to deform to move through capillaries
  • Mammals lack nucleus and organelles, unable to reproduce, must produce ATP due to lack of mitochondria
  • Avian erythrocytes are nucleated

  
• Erythrocyte Life Cycle

  1. Live about 120 days

  2. Damaged RBCs are removed by phagocytic macrophages in the spleen, liver and bone marrow

  3. Hemoglobin is separated into heme and globin

  4. Globin is hydrolyzed into amino acids to be used in new protein synthesis

  5. Iron from heme binds to transferrin and is transported to be stored in muscle fibers, liver cells, and macrophages in the spleen

  6. Leftover iron is converted to biliverdin and then bilirubin

  7. Bilirubin is transported to the liver and secreted into bile, then converted to stercobilin and urobilin

  
• Leukocytes (White Blood Cells)


  • Only blood cells that are true cells, containing a nucleus and organelles
  • Do not contain hemoglobin
  • Important component of the immune system
  • Make up 1% of the blood volume

  
• Leukocyte Emigration

  1. Endothelial cells display cell adhesion molecules called selectins

  2. Leukocytes have cell adhesion molecules called integrins that recognize selectins, causing them to line up along the inner surface of capillaries (margination)

  3. Leukocytes move out of the capillaries through diapedesis

  4. Leukocytes migrate via amoeboid action following a chemical signal produced by damaged tissue (positive chemotaxis)

  5. Neutrophils and macrophages become phagocytized and ingest bacteria and dispose of dead matter
• Types of Granulocytes

  • Neutrophils
  • Eosinophils
  • Basophils
• Neutrophils

  • 50-70% of white blood cells
  • Twice as large as other WBCs
  • Cytoplasm is pale lilac with very small granules
  • Some granules are lysosomes containing hydrolytic enzymes, others contain antibiotic-like proteins called defensins
  • Polymorphonuclear leukocytes with a nucleus containing three to six lobes
  • First to leave the bloodstream in response to chemotaxis
  • Attracted to and phagocytize bacteria and some fungi

  
• Eosinophils

  • 2-4% of all white blood cells
  • Large, uniformly sized granules that stain red-orange
  • Granules contain digestive enzymes but lack enzymes that digest bacteria
  • Function against parasitic worms
• Basophils

  • 0.5-1% of white blood cells (rarest)
  • Slightly smaller than neutrophils
  • Contain histamine-filled granules that stain dark purple
  • When bound to IgE, release histamine which causes vasodilation and attracts other WBCs

  
• Types of Agranulocytes

  • Lymphocytes
  • Monocytes
• Lymphocytes

  • 25% of the white blood cells
  • Contain large dark-purple staining nucleus
  • Responsible for cellular immunity and humoral immunity

  
• Monocytes

  • Have a kidney or horseshoe-shaped nucleus
  • Contain very small blue-gray-staining granules that are lysosomes
  • After leaving the bloodstream, become macrophages, some of which become fixed macrophages in the lungs and liver

  
• Platelets

  • Consist of plasma membranes containing numerous vesicles but no nucleus
  • When there is a tear in a blood vessel, platelets coalesce at the site and form a platelet plug
• Hemopoiesis/Hematopoiesis

  1. Formation of new blood cells

  2. Prior to birth, begins in yolk sac, later occurs in liver, spleen, thymus and lymph nodes of the fetus

  3. After birth, occurs in red bone marrow

  
• Pluripotent Cells

  • Myeloid stem cells within the red bone marrow can proliferate or differentiate into different red blood cells, platelets, monocytes, neutrophils, eosinophils and basophils
  • Lymphoid stem cells begin in red bone marrow and finish differentiation in lymphatic tissue to form white blood cells

  
• Hemostasis

  • A series of responses that stop bleeding
  • Involves vascular spasms, platelet plug formation, and blood clotting
  • If bleeding is not stopped, can lead to hemorrhage and blood loss
• Platelets in Hemostasis

  • Release ADP, ATP, Ca2+, serotonin, and enzymes that produce thromboxane A2
  • Provide fibrin stabilizing factor to strengthen blood clots
  • Release platelet-derived growth factor involved in proliferation of vascular endothelial cells, vascular smooth muscle fibers, and fibroblasts

  
• Platelet Plug Formation

  1. Platelet adhesion to exposed collagen fibers in damaged vessel wall

  2. Platelet release reaction, liberating vesicular contents

  3. Platelet aggregation due to ADP release making adjacent platelets sticky

  4. More platelets gather at the site forming the platelet plug
• Blood Clotting


  1. Involves a series of chemical reactions resulting in the formation of insoluble fibrin threads that trap other blood cells and elements

  2. Thrombosis is the formation of a clot in an unbroken blood vessel

  3. Thrombus is the clot itself

  4. Embolus is the movement of a clot, air bubble, fat, or debris through the bloodstream

  
• Stages of Blood Clotting

  1. Intrinsic and extrinsic pathways produce prothrombinase

  2. Prothrombinase catalyzes the conversion of prothrombin to thrombin

  3. Thrombin catalyzes the conversion of fibrinogen into insoluble fibrin

  
• Extrinsic Pathway

  • Quicker and fewer steps than intrinsic pathway
  • Damaged tissue releases tissue factor (TF) or thromboplastin, which initiates the formation of prothrombinase in the presence of Ca2+

  
• Intrinsic Pathway

  • All the factors necessary for blood clotting are present in the blood
  • Relies on the production of PF3, a phospholipid associated with the external surface of aggregated platelets
  • Also results in the production of factor X

  
• Common Pathway

  • Both the intrinsic and extrinsic pathways use a common pathway after the activation of factor X
  • Prothrombin is converted to thrombin by prothrombinase
  • Thrombin then catalyzes the conversion of fibrinogen to fibrin
  • Activated factor XIII catalyzes the polymerization of cross-linked fibrin

  
• Oxygen diffuses from the alveoli into the bloodstream through the walls of capillaries surrounding them.
• Gas exchange occurs at the alveoli, which are small air sacs located within the lungs.
• The respiratory system consists of the nose, trachea, bronchi, bronchioles, alveolar ducts, and alveoli.
• Prothrombin is converted to thrombin by prothrombinase


  1. Thrombin then catalyzes conversion of fibrinogen to fibrin

  2. Activated Factor XIII catalyzes polymerization of cross-linked fibrin
• Vitamin K

  • Syntheses of clotting factors II, VII, IX and X by hepatocytes
  • Synthesized by bacteria in large intestine, absorbed through intestinal wall with other lipids
• Clot retraction and repair

  1. Actin and myosin begin to contract

  2. Platelet pulls on surrounding fibrin strands, squeezes serum from the clot and pulls ruptured edges of vessels together

  3. Platelets release Factor XIII to strengthen fibrin clot
• Clot retraction and repair

  1. PDGF release degranulating platelets

  2. Fibroblasts form a connective tissue sheath over the injured area