Chapter 25: Circulation

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Review questions

Background from Introductory Biology Courses

  1. Human Anatomy and Physiology
    1. Online Learning Center for Hole's Human Anatomy & Physiology
      1. chapter 15 resources 
      2. chapter/quizzes/ch15
      3. check out the other resources such as the study outline, flash cards, animations, etc.
      4. use the other course tools for chapter 15
  2. On-Line Biology Book by M. J. Farabee 
    1.  Circulatory System
      1. vertebrate cardiovascular system
      2. Vertebrate vascular systems
      3. The heart
      4. the vascular system
  3. Kimball's Biology Pages
    1. Anatomy of the Circulatory System from Kimball's Biology Pages
    2. Heartbeat from Kimball's Biology Pages
  4. This is what you should have learned in high school about circulation, from Jim Buckley, Edwards-Knox Central School, Russell, New York.  Try Mr. Buckley's quiz on human circulation and the quiz on the human heart for his high school students.
  5. more detailed information from Frank Orme, Chabot College Human Physiology  Class notes on the Cardiovascular system, Circulation and Heart as a Pump 




  • your heart and how it works from the American Heart Association
  • the heart from the Franklin Institute
  • to learn more about the circulatory system try this site from HUMAN ANATOMY On-Line.  click on the pictorial representation of the cardiovascular system.  Once in, explore the many features of the site.  Try the animation of the beating heart.  Click on the markers on the images to learn more.  Use this site to gain more information about other organ systems.


    • vena cavae --> right atrium tricuspid (AV) valve  --> right ventricle  -->  semilunar valve  -->  pulmonary arteries  -->  pulmonary capillaries  -->  pulmonary veins  -->  left atrium.
    • left atrium  -->  bicuspid (AV) valve  -->  left ventricle  -->  semilunar valve  --> aorta  --> coronary arteries, carotid subclavian, mesenteric, renal, iliac arteries, etc.  -->  arterioles  -->  capillaries  -->  venules  -->  veins  -->  inferior & superior vena cavae -->  right atrium.




image courtesy of BIODIDAC


  1. Circulatory System
  2. Functional Connections
    1. Accepts oxygen, nutrients, and other substances, immune cells, signaling cells, from the respiratory, digestive, immune, and endocrine systems and delivers them to cells
    2. accepts carbon dioxide and wastes from cells and delivers them to respiratory and urinary systems for disposal
  3. Limits of Diffusion
    1. Unicellular organisms and some small metazoans lack circulatory systems and rely on diffusion to transport molecules
    2. Diffusion can be rapid over small distances, but is very slow over large distances
    3. Large animals move fluid through their bodies by bulk flow
  4. Figure 25.1 The human heart
  5. Pressure patterns in the Heart
    1. Systole
    2. Diastole
    3. Ventricular Filling and Emptying
      1. The two ventricles contract simultaneously
  6. Cardiac Output
    1. Cardiac output (CO or Q): amount of blood the heart pumps per unit time (mL/min)
    2. Stroke volume (SV): amount of blood the heart pumps with each beat (mL/beat)
    3. Heart rate (HR): rate of contraction (beats/min)
    4. CO = HR X SV
    5. Bradycardia
    6. Tachycardia
  7. Ventricular Pressure
    1. Resistance in the pulmonary circuit is low
    1. Figure 4.2 The heart as a pump: The dynamics of the left side of the human heart
      1. The heart cycle is divided into five phases  
      2. animation showing the phases

    1. The cardiac cycle from Wikipedia. Image by DestinyQx

  8. The diagram shows the synchronous changes in
    1. Electrocardiogram  
    2. Blood pressure of the left ventricle, left atrium, and aorta
    3. Closing and opening of valves
    4. Ventricular volume
    5. Ventricular outflow
  9. Figure 25.2 The heart as a pump: The dynamics of the left side of the human heart (Part 1)
  10. Sound patterns in the Heart
    1. Lub (or lubb)
    2. Dub (or dupp)
    3. heart murmur: valve does not close properly, blood flows backward
  11.  Control of Contraction
    1. Vertebrate hearts are myogenic
      1. autonomic nervous system controls heart rate, but heart muscles are self excitable
      2. Cardiomyocytes produce spontaneous rhythmic depolarizations
      3. heart cells beat on own when separated from nervous system
      4. atricular or ventricular muscle mass contracts in unison.
    2. Pacemaker - cells with the fastest intrinsic rhythm
      1. sinoatrial (SA) node
  12. Figure 25.4 The conducting system and the process of conduction in the mammalian heart
  13. The MYOGENIC conducting system in the mammalian heart
    1. Pacemaker (S-A node)
    2. Atrioventricular node
    3. Atrioventricular bundle (Bundle of His)
  14. The Initiation and Spread of Depolarization During a Heartbeat
    1. Depolarization begins in the Sinoatrial node and spreads outward through atrial muscle
    2. SA node is the PACEMAKER
    3. hypopolarized muscle cells
  15. The Initiation and Spread of Depolarization During a Heartbeat
    1. internodal pathways connect the SA node to the atrioventricular (A-V) node
    2. spread into the A-V node is delayed.  
  16. The Initiation and Spread of Depolarization During a Heartbeat (Part 3)
    1. depolarization spreads into the ventricles along the conducting system (Bundles of His and Purkinje fibers)
  17. The Initiation and Spread of Depolarization During a Heartbeat (Part 4)
    1. depolarization of cells throughout the ventricular myocardium leads to forceful ventricular contraction.
  18. Spread of cardiac excitation:
  19. Conducting Pathways
  20. Figure 25.6 Electrocardiography (Part 1)
  21. Fig. 25.6 Electrocardiogram:  EKG / ECG
    1. Electrocardiography
  22.  Electrocardiogram (ECG or EKG)
    1. P wave
    2. QRS complex:
    3. T wave:
  23. Frank-Starling Law of the Heart
    1. an increase in end-diastolic volume results in a more forceful contraction of the ventricle and an increase in Stroke Volume
  24. Gravity Effects
    1. Hydrostatic pressure
    2. Higher pressure at tissues below heart & lower pressures at tissues above heart
    3. .Animals must compensate for positional effects
  25. Fig. 25.7b Positional Effects & Gravity
    1. Blood pressure varies when standing or prone
  26. Species differences
    1. Giraffe has Mean Arterial Pressure = 220 mm Hg
  27. Overview of Circulation
    1. .Most metazoans larger than a few cells use circulatory systems
      1. Blood: A fluid that circulates through the system
      2. Pump (Heart) or propulsive structures
      3. Vasculature: A system of tubes, channels, or spaces
    2. Not all animals have cardiovascular systems, e.g., sponge
  28. Components of Circulatory Systems
    1. Circulatory systems move fluids by increasing the pressure of the fluid in one part of the body
    2. The fluid flows through the body down the resulting pressure gradient
  29. Types of Fluid
    1. Interstitial fluid:  extracellular fluid that directly bathes the tissues
    2. Blood:  fluid that circulates within a closed circulatory system
    3. Lymph:  fluid that circulates in the secondary (lymphatic) system of vertebrates
    4. Hemolymph:  fluid that circulates within an open circulatory system
  30. Open Circulatory Systems
    1. Circulatory fluid comes in direct contact with the tissues in sinuses (Arthropods, most mollusks)
  31. Closed Circulatory Systems
    1. Circulatory fluid remains within the blood vessels and does not come in direct contact with the tissues (vertebrates, cephalopods, some annelids)
  32. The conduits: blood vessels
    1. Arteries and Veins have elastic walls and smooth muscle
    2. arteries have thick, strongly muscled walls (except in pulmonary system)
    3. veins have thinner walls and valves
    4. capillaries have very thin walls with no muscle or elastic
  33. Birds and Mammals
    1. Four chambered heart: two atria and two ventricles
    2. Systemic and pulmonary circuits are completely divided
    3. Allows pressure to be different in the two circuits
  34. Fig 25.10 The circulatory plan in mammals and birds
  35. Fig 25.12a Blood flow in the human systemic vasculature
    1. Volume of blood flowing through vessels always equals output of heart.
    2. Progressive increase in total cross-sectional area from the aorta (0.8 cm2) to the capillaries (600 cm2)
    3. Decrease from capillaries to vena cava (1 cm2)
    4. Cross-sectional area of venous system is larger than that of arterial system
  36. Cross-sectional Area
    1. Flow velocity is highest in large-diameter transport vessels
    2. Flow velocity is slowest in capillary beds
    3. Velocity increases after passing through the capillaries
  37. Average Blood Pressure
    1. Blood pressure is highest and varies most in the left ventricle
    2. .Blood pressure decreases away from heart as x-sectional area increases.
    3. Blood pressure drops rapidly in arterioles due to high resistance
    4. .Pressure drops on whole journey from about 100 mm Hg in arteries to 20 mm in capillaries to 2 mm in veins
  38. Flow in Vertebrate Circulatory Systems
    1. When x-sectional area decreases in venules, the pressure does not return due dissipation due to friction with capillaries.
    2. The velocity of blood is highest in the arteries (high pressure), lowest in the capillaries (large cross-sectional area), and intermediate in the veins (lower pressure and cross-sectional area)
  39. Figure 25.13 Fluid exchange across mammalian systemic capillary walls: The Starling-Landis hypothesis
  40. Capillary Filtration
    1. fluid exchange between capillaries and interstitial fluid space
    2. Net Filtration Pressure (NFP)
      1. Blood pressure forces fluid out of capillaries (hydrostatic pressure)
  41. Fluid Exchange, cont.
    1. colloidal osmotic pressure (plasma proteins) draws water back into the capillaries
  42. Exchange of Material From the Plasma to the Interstitial Fluid of Surrounding Cells
    1. fluid moves out near arterial side and in on venous side
    2. .Usually outflow exceeds inflow.
    3. This creates lymph which travels through lymphatic system which eventually dump the fluid back into larger veins
  43. The Lymphatic System
    1. The lymphatic system collects the filtered fluid and returns it to the circulatory system
    2. Lymphatic veins and ducts contain valves to prevent backflow
  44. Moving Blood Back to the Heart
    1. Blood in veins is under low pressure
    2. Two major pumps assist in moving blood back to the heart: .Skeletal muscle and Respiratory pumps
  45. Evolution of Circulatory Systems
    1. First evolved to transport nutrients
    2. Very early on they began to serve a respiratory function
    3. Closed systems evolved independently in jawed vertebrates, cephalopods, and annelids
  46. Figure 25.14 The circulatory plan in gill-breathing fish
    1. Closed system
    2. Single circuit
    3. Some fish have accessory hearts in the tail
  47. Fig 25.19 Typical circulatory plans of the major vertebrate groups, plotted on a phylogenetic tree of the groups
  48. Amphibians and Reptiles
    1. Like lungfish, the heart is only partially divided; two atria and one ventricle except
    2. Crocodilians have a completely divided ventricle
  49. Figure 25.20 Blood flow in the heart ventricles and the systemic and pulmonary arteries of crocodilian reptiles
  50. Mollusks
    1. All have hearts and some blood vessels
    2. Most have open systems
    3. Only cephalopods have closed systems
  51. Arthropods
    1. All have one or more hearts and some blood vessels
    2. All have open systems
  52. Arthropods
    1. Insects and arachnids have a relatively simple open circulatory system, but high metabolic rates
    2. tracheal system for most gas transport


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