Circulatory

• Blood composition


  Suspension of blood elements (RBC, WBC, platelets) in blood plasma
• Blood


  • Females have around 4-5 litres
  • Males have around 5-6 litres
  • pH of 7.35-7.45
  • No artificial substitute for human blood to date
• Blood separation


  Blood elements can be separated from blood plasma using centrifugal force
• Plasma


  • Transports nutrients from gut/liver to cells
  • Transports excretory products from liver to kidneys
  • Transports hormones from endocrine glands to tissues/organs
  • Contains dissolved proteins that regulate osmotic concentration and act as antibodies
  • Distributes heat to all tissues
• Erythrocytes (Red Blood Cells)

  • Transport oxygen from lungs to respiring cells
  • Transport carbon dioxide from respiring cells to lungs
  • Very small with biconcave disc shape to increase surface area/volume ratio for rapid diffusion of O2
  • Contain haemoglobin which combines with O2 to form oxyhaemoglobin
  • Have no nucleus or mitochondria to allow more space for haemoglobin
• Leucocytes (White Blood Cells)


  • Lymphocytes have major roles in immune system including forming antibodies
  • Phagocytes ingest bacteria and cell fragments
  • Granulocytes have granules and lobed nuclei to fight foreign bodies by phagocytosis
  • Agranulocytes lack granules and defend body against harmful effects
• Thrombocytes (Platelets)


  • Part of blood clotting mechanism, clump together to form a plug and stop bleeding
  • Promote blood coagulation by providing prothrombin and other clotting factors
  • Enhance vasoconstriction to reduce blood flow to damaged region
• Hematopoiesis (Blood cell production)


  1. Production of all types of blood cells, including formation, development and differentiation

  2. Normally occurs in bone marrow and lymphatic tissues in adults
• Erythropoiesis (Red blood cell production)

  1. Occurs in bone marrow

  2. Increased by erythropoietin hormone secreted by kidneys in response to decreased oxygen levels or increased physical activity

  3. Erythrocytes live for about 120 days
• ABO blood group system

  • Based on presence or absence of antigens A and B on red blood cells
  • Antibodies to missing antigens occur naturally in serum
• Rhesus (Rh) blood group system

  • D antigen is the most important, red cells with D antigen are Rh D positive, those without are Rh D negative
  • Antibodies to Rh antigens do not occur naturally but can be produced by sensitization
• Universal red cell donor has Type O negative blood
• Universal red cell recipient has Type AB positive blood
• Universal plasma donor has Type AB blood
• Rh-negative pregnant woman


  If fetus inherits Rh-positive blood from father, mother can become sensitized and produce Rh antibodies, causing haemolytic disease of newborn
• A person with Rh-negative blood who makes Rh antibodies is called "Rh sensitized"
• Circulatory system


  Main transport system in mammals
• Circulatory system


  • A closed system of the heart and blood vessels
  • The heart pumps blood
  • Blood vessels allow blood to circulate to all parts of the body
• Function of circulatory system

  Deliver oxygen and nutrients and to remove carbon dioxide and other waste products
• Types of blood vessels

  • Arteries
  • Arterioles
  • Capillaries
  • Veins
  • Venules
• Blood vessels


  • Consist of three layers (tunics)
  • Capillary only has a layer of endothelium
• Arteries


  • Strongest of the blood vessels
  • Carry blood away from the heart
  • Under high pressure
  • Arterioles are small branches of arteries
• Arteries


  • Muscular walls can constrict (vasoconstriction) to increase blood pressure or dilate (vasodilation) to decrease blood pressure
• Veins


  • Carry blood back into the heart
  • Blood under no pressure
  • Venules are small vessels formed when capillaries merge
• Veins


  • Blood has no pressure and does not move very easily
  • Use the milking action of muscles to help move blood
  • Have valves to prevent backflow
• Capillaries


  • Smallest, only about one cell layer thick
  • Branches of arterioles
  • Connect arterioles to venules
  • Serve as site for exchange of respiratory gases, nutrient and wastes
• Capillary beds


  • Consist of vascular shunts and true capillaries
  • Precapillary sphincters help regulate flow of blood into capillary beds
• Heart


  • Located in the mediastinum
  • About the size of a loose fist
  • Slightly left of the midline
  • Pointed apex directed toward left hip
  • Bordered laterally by the lungs, posteriorly by the vertebral column, anteriorly by the sternum
  • Rests on the diaphragm inferiorly
• Pericardium


  • Consist of 2 sacs
  • Outer sac is fibrous tissue
  • Inner sac is double layer of serous membrane
  • Pericardial fluid fills the space between the layers
• Pericardium


  • Tough sac that prevents the heart from being overstretched or overfilled with blood
  • Protects and anchors the heart
  • Allows the heart to work in a relatively friction-free environment
• Layers of heart wall

  • Epicardium
  • Myocardium
  • Endocardium
• Heart wall layers


  • Epicardium is the outermost layer and contains connective tissue and fat
  • Myocardium is the middle layer and is primarily cardiac muscle
  • Endocardium is the innermost layer and is thin and smooth
• Heart chambers


  • Four chambers - Atria (receiving chambers) and Ventricles (discharging chambers)
  • Septum separates right and left atria, right and left ventricles, and atria and ventricles
  • Right and left side act as separate pumps
• Pulmonary circulation


  Right side of heart pumps deoxygenated blood into lungs and oxygenated blood returns to left side
• Systemic circulation


  Left side of heart pumps oxygenated blood to other parts of body and deoxygenated blood returns to right side
• Heart valves


  • Atrioventricular valves (Bicuspid and Tricuspid)
  • Semilunar valves (Pulmonary and Aortic)
• Heart valves


  • Allow blood to flow in only one direction
  • Held in place by chordae tendineae
  • Open as blood is pumped through and close to prevent backflow
• Blood in the heart chambers does not nourish the myocardium
• Coronary circulation


  The heart has its own nourishing circulatory system with coronary arteries and cardiac veins
• Cardiac cycle


  1. Systole (contraction of heart muscle)

  2. Diastole (relaxation of heart muscle)