1. General plan
    1. parts
      1. Propulsive organ- heart
      2. Atertial system - distribution and pressure reservoir
      3. Capillaries - transfer of gases, metabolic products
      4. Venous system - volume reservoir and return of blood
    2. Open Circulation (earthworms, mollusks)
      1. Heart to artery to open space (hemocoel); bathes tissues directly via small channels
      2. Low pressures, high blood volume (20-40% of body volume)
      3. Some control over flow and distribution of hemolymph (blood), but not much - limits movement
      4. Insects don't use circulation for oxygen transfer, so they aren't limited as other animals are
    3. Closed Circulation
      1. Heart to arteries to capillaries to veins to heart
      2. Low volume (5-10% of body volume)
      3. High blood pressure (maintained by arteries)
      4. Better and faster control of oxygen delivery to tickets (so faster movement is possible)
      5. Blood can be filtered (by kidney) as a result of pressure
      6. Lymphatic system - returns fluid to blood
  2. The heart
    1. Electrical aspects
      1. AP is started at the pacemaker cells (sinoatrial and atrio-ventricular nodes), SA and AV nodes
      2. Spreads via Gap junctions
      3. SA node cells are neurogenic (in invertebrates), requiring CNS input, or myogenic (invertebrates and vertebrates) as a result of the pacemaker cells
      4. Cardiac pacemaker potentials
        1. Always cycling - no stable resting potential
        2. Slow depolarization (resulting from decreasing K current) during diastole leads to AP (systole)
        3. ACh (parasympathetic) slows heart
        4. NE (sympathetic) increases heart rate
        5. Autonomic NS affects:
          1. Heart rate (chronotropism)
          2. Force of contraction (inotropic effects)
          3. Speed of conduction (dromotropic effects)
      5. Action potentials (fig 12-7)
        1. Longer AP's (100's of ms) and refractory periods, therefore there are no summation of contractions
        2. Longer AP's are due to increased Ca 2+ influx, a delayed K+ influx and longer refractory period of Na channels (but this is a minor effect in relation to the others)
      6. Electrical transmission (fig 12-8)
        1. In mammals, signal spreads from SA to atria to AV to ventricles (SA and AV are slow conductions)
        2. Bundle of His and Purkinje fibers spread depolarization to ventricle, from the inner lining to the outer wall
    2. Cornonary Circulation - heart needs oxygen
      1. Decreased flow during systole
      2. As heart works harder, more ATP is broken down, causing an increase in adenosine concentrations which dialates cardiac vessels
    3. Mechanical Properties of the Heart
      1. Cardiac Output (CO=SV x HR)
        1. HR = heart rate
        2. SV= stroke volume (volume of blood ejected per beat; end diastolic volume - end systolic volume)
          1. Diastolic factors = venous filling pressure, atrial pressure of contraction, distensibilty of ventricular wall, time for filling ventricle
          2. Systolic factors = pressure of ventricular contraction, pressure in outflow area (in aortic and pulmonary arteries)
          3. Increased heart rate does not decrease stroke volume, because blood is emptied from the heart faster, decreasing ejection time (not just filling time)
  3. Mechanics
    1. Heart cycle (mammalian heart)- fig 12-11
      1. Atria contracts, tops of ventricle
      2. Ventricle starts contraction (all valves are closed), pressure rises rapidly
      3. Ventricle contracts with valves open, pressure finishes rising then begins to fall, volume falls
      4. Aortic/pulmonary valves close, mitral and tricuspid valves open, venous blood flows back in
    2. Work done by the heart (fig 12-12)
      1. Work = difference in pressure x flow
      2. Pressure = 2y/r; y = wall tension, r = radius of heart
      3. Maintenance of pressure requires more work for a larger heart, therefore "A small heart is a happy heart" because it works less.
    3. Pericardium
      1. Compliant - found in mammals/higher animals, lubricates and protects heart
      2. Non-compliant (fig 12-13) - found in lower animals (mollusks); contraction of the ventricle creates a lower pressure which helps fill the atria
    4. Comparative Morphology
      1. 1 atrium, 1 ventricle - fish (water breathing fish have gills and systemic circulation in series)
      2. 2 atria, 1 ventricle - amphibians (frogs) - blood mixes, but can change amount of blood flowing to pulmonary and systemic sides
      3. 2 atria, partial division of ventricle (leaky four chamber) - noncrocodilian reptiles (snakes, turtles) - blood mixes less
      4. 2 atria, 2 ventricles with shunt - crocodilian reptiles (shunt from pulmonary to systemic systems)
      5. 2 atria, 2 ventricles - mammals and birds - no mixing of blood, but must make sure that blood flow is balanced (ie won't work well if blood is not returning to atria at same rate it is being pumped out)
  4. Hemodynamics
    1. Laminar flow - silent, flowing, uses less energy (blood near the edges/walls doesn't move)
    2. Turbulent flow - noisy, uses more energy, not parallel to the axis of flow
    3. Pressure and flow (figs 12-24 and 12-26)
      1. Flow is from areas of high to areas of low pressure
      2. Pressure is reduced by resistance
      3. Poiseuille's law: Q=[(P1 - P2) P r4] / (8 L h )
        1. Q = flow
        2. P1 and P2 = pressures at two different points
        3. r = radius of tube (blood vessel)
        4. L = length between P1 and P2
        5. h = viscosity of blood
      4. Because vessels are compliant, (veins more than arteries), Poiseuille's law doesn't work perfectly, best predictor for terminal arteries and veins
      5. Flow is normally laminar or oscillatory laminar, but can become turbulent. (Don't want turbulent flow because it is more likely to cause blood clots, etc.) Flow can be predicted by the Reynold's number (this is wrong in the book). The greater the Reynold's number, the more likely turbulent flow (more than 3000, turbulence is almost always present; less than 2000, flow is laminar)
        1. Re= p2rQ/h
        2. p= density of fluid
        3. r=radius of vessel
        4. Q = flow
        5. h = viscosity of blood
  5. Peripheral Circulation (fig 12-27)
    1. Arteries
      1. Purpose
        1. Transfer blood from heart to capillaries
        2. Pressure reservoir
        3. Produces a more even flow
        4. Allows for control of blood distribution
      2. Closer to the heart, vessels are more elastic
      3. Farther from the heart, vessels are more rigid (less muscle)
      4. Blood pressure is affected by surroundings - more pressure around vessels, decreases transmural pressure differences and decreases flow - less pressure around vessels, increases transmural pressure differences and increases flow
      5. Gravity and body position relative to flow - giraffe (fig 12-33)
        1. Head up - lower vessels constrict, high aortic pressure
        2. Head down - lower vessels dilate, lower aortic pressure
    2. Venous System
      1. Purpose
        1. Return blood to heart
        2. Volume reservoir (high volume, lower pressures)
      2. Larger diameter, easily stretched
      3. Flow of blood dependent upon contraction of skeletal muscles and diaphragm in conjunction with the heart (cannot constrict vessels enough to return to blood to heart without help from these muscles)
      4. Contain pocket valves to ensure blood flow is in one direction
      5. Countercurrent exchangers - terminal veins and arteries lie next to each other (current flowing in opposite directions), exchanging heat, gases, etc.
    3. Capillaries
      1. Just big enough for a red blood cell (RBC) to slip through
      2. Site of gas/ metabolic exchange
      3. Flow controlled by precapillary and arteriole sphincters
      4. Can contain up to 14% of blood, but only 1/3- 1/2 are open at a time, so only 5-7% is usually here
      5. Three types (fig 12-37)
        1. Continuous - least permeable, found in skeletal muscle, nervous tissue, etc
        2. Fenestrated - medium permeability - only large proteins and RBC can't filter through, found in kidneys, gut
        3. Sinusoidal - most permeable, found in liver, bone marrow, spleen, lymph nodes, adrenal cortex (places where large proteins/RBC need to enter/exit the system)
      6. Pressure differences at beginning and end of capillaries causes fluid to filter into and out of interstitial spaces (fig 12-39)
  6. Lymphatic System
    1. Collects fluid from interstitial spaces and returns it to blood via the thoracic duct
    2. Pathway which allows fats and high weight molecular proteins to enter the blood
  7. Circulation and Immune Response (fig 12-41)
    1. Circulation and lymphatic systems circulate leukocytes (white blood cells - WBC) which are responsible for the immune response
    2. Response
      1. Recognition - lymphocytes
      2. Marking - antibodies
      3. Destruction - lymphcytes, neutrophils, macrophages
    3. Series of interactions with vessels allows leukocytes to leave the circulation and reach infected tissues
  8. Regulation of Circulation (fig 12-43)
    1. Baroreceptors- measure blood pressures at different points in the circulations
    2. Chemoreceptors - measure oxygen, carbon dioxide, and pH in the blood
    3. Mechanoreceptors and thermoreceptors also affect flow and blood pressure
    4. Medullary Cardiovascular Center - integrates input from all sources, then stimulates the pressor center (sympathetic) or depressor center (parasympathetic) to bring values back to their set point