Physiology

• Functions of the Circulatory System


  • Transportation
  • Regulation
  • Protection
• Substances transported by the Circulatory System

  • Respiratory: Transport O2 and CO2
  • Nutritive: Carry absorbed digestion products to the cells
  • Excretory: Carry metabolic wastes to kidneys and lungs to be excreted
• Regulatory functions of the Circulatory System

  • Hormonal: Carry hormones to target tissues to perform their functions
  • Temperature: Diversion of blood from deeper to more superficial cutaneous vessels or vice versa
• Protective functions of the Circulatory System

  • Clotting Mechanism: protects against blood loss when vessels are damaged
  • Immune Function Performed by Leukocytes that protect against pathogens

  
• Components of the Cardiovascular System

  • Blood
  • Blood Vessels
  • Heart

  
• Blood


  Composed of cellular portion called formed elements (cells and cell fragments) suspended in a liquid called plasma

  
• The total blood volume in the average-size adult is about 5 liters
• Formed elements


  Constitute approximately 45% of the total blood volume
• Plasma


  Accounts for the remaining 55% of the total blood volume

  
• Hematocrit


  The volume percentage (vol%) of red blood cells (RBCs) in blood

  
• Normal hematocrit range


  • 36% to 46% in women
  • 41% to 53% in men

  
• Plasma


  Straw-colored liquid consisting of water and dissolved solutes: Ions, metabolites (ex. Glucose), hormones, antibodies
• Plasma proteins


  • Albumins
  • Globulins
  • Fibrinogen

  
• Albumin


  Accounts for 60-80% of plasma proteins, produced by the liver, provides the colloid osmotic pressure needed to draw water from interstitial fluid to capillaries, maintains blood pressure & volume

  
• Globulins


  Grouped into three subtypes: Alpha globulins, Beta globulins, and Gamma globulins. Alpha & beta globulins are produced by the liver and function in transporting lipids and fat soluble vitamins. Gamma globulins are antibodies produced by lymphocytes and function in immunity.
• Fibrinogen


  Constitutes 4% of plasma proteins, produced by the liver, important clotting factor converted into insoluble threads of fibrin during the clotting process
• Serum


  The fluid from clotted blood, does not contain Fibrinogen

  
• Formed elements


  • Erythrocytes, or red blood cells
  • Leukocytes, or white blood cells
  • Platelets

  
• Erythrocytes


  Flattened biconcave discs, lack nuclei and mitochondria and other organelles increasing the oxygen‐carrying capacity, have a relatively short circulating life span of only about 120 days
• Hemoglobin


  The oxygen‐carrying protein in erythrocytes, composed of a protein called globin bound to the iron‐containing pigments called haem, each hemoglobin molecule transports four molecules of oxygen
• Formation of RBCs


  1. Erythroblasts undergo development in the red bone marrow to form red blood cells

  2. During maturation, red blood cells lose their nucleus and organelles and gain more haemoglobin molecules

  3. Mature red blood cells do not have a nucleus; their life span is approximately 120 days

  4. Destroyed RBCs are replaced each time to maintain the balance
• Erythropoietin


  A hormone produced by the kidneys that stimulates the production of red blood cells in the bone marrow, its production and release is through a negative feedback system
• Types of Leukocytes


  • Granulocytes (neutrophils, eosinophils, basophils)
  • Agranulocytes (monocytes, lymphocytes)

  
• Leukocytes


  Unlike red blood cells, white blood cells have nuclei and they are able to move out of blood vessel walls into the tissues, their life span can be from a few days to years

  
• Platelets


  Smallest of formed elements, fragments of large cells called Megakaryocytes found in bone marrow, lack nuclei, capable of amoeboid movement, survive for about 5-9 day before destroyed in liver and spleen
• Platelets


  Play a vital role in blood loss by the formation of platelet plugs, which seal the holes in the blood vessels and release chemicals that aid blood clotting

  
• Components of Haemostasis


  • Vasoconstriction
  • Platelet aggregation
  • Coagulation
• Vasoconstriction


  Results from contraction of the smooth muscle of the vessel wall, restricts blood flow through small blood vessels

  
• Platelet aggregation


  Platelets adhere to the exposed collagen fibers of the damaged blood vessels and release chemicals that make other platelets stick, forming a platelet plug
• Coagulation


  The complicated process of blood clotting that occurs if platelet aggregation and vasoconstriction cannot stop the bleeding, involves clotting factors synthesized in the liver

  
• RBC Antigens


  Markers on the surface of red blood cells, the major group is the ABO system

  
• ABO Blood Types


  A has A antigens, B has B antigens, AB has both A and B antigens, O has neither A nor B antigens
• Antibodies in ABO system

  Blood group A has anti-B antibodies, B has anti-A, AB has no antibodies, O has both anti-A and anti-B
• Rh Factor


  Another group of antigens found on RBCs, if a person has the Rh antigen they are Rh positive, if they do not have it they are Rh negative
• Transfusion errors can lead to blockage of small blood vessels and cause hemolysis which may damage the kidneys and other organs

  
• Rh- mother may produce antibodies against the Rh+ blood of the fetus, causing erythroblastosis fetalis (Haemolytic disease of newborn)