The Mammalian Heart by dfsdf224s


									S E C T I O N
                                            The Mammalian Heart


Describe the pathway of
circulation through the
mammalian heart.
Identify the major
compartments of the heart and
its associated blood vessels.
Design a feedback diagram to
illustrate how the heartbeat is
Explain how personal choices
can affect the functioning of
the heart.

Figure 9.24 This heart is about
to be transplanted into a patient
needing a new heart.

Imagine you are an engineer, and a client asks you                     to adjust quickly — and without any conscious
to design a pump that will push fluid through a                         controls — to demands for an increase or decrease
closed system. It may seem like a simple task, until                   in the pressure of fluid within the system. It must
you see the client’s specifications. This pump must                     be able to pump in two directions at once, without
work constantly, day after day, pumping about                          mixing the fluid travelling in the two directions. It
70 times per minute, or approximately                                  must have a life expectancy of about 80 years
90 000 times per day. With each beat, it must be                       without any major repairs or part replacements
able to pump fluid through about 160 000 km of                          (assuming it is well cared for). To top it off, it must
vessels. It must maintain a steady flow, but be able                    be compact — about the size of your fist. As an

                                  left common
         brachiocephalic          carotid artery
         artery                                    left subclavian                     superior
superior                                           artery                              vena cava                        left pulmonary
vena cava                                                                                                     aorta     arteries
                                                   left pulmonary    pulmonary
                                                   arteries          arteries
 right                                                                                                                  pulmonary
 pulmonary                                         pulmonary         right                                              trunk
 arteries                                          trunk             pulmonary                                          left pulmonary
                                                   left pulmonary    veins                                              veins
 right                                             veins
                                                                     right atrium                                       left atrium
                                                   left atrium                                                          semilunar
                                                                     atrioventricular                                   valves
 right atrium                                      left cardiac
                                                   vein              valve                                              atrioventricular
 right coronary                                                                                                         valve
 artery                                                              right ventricle                                    left
 right ventricle                                                                                                        ventricle
        inferior                                                                    inferior
        vena cava                                  apex
                                                                                    vena cava              septum
   A An external view of the human heart. The left ventricle            B An internal view of the human heart. Note the thick
     is more muscular than the right, giving the heart a                  septum or wall separating the right and left ventricles.
     lopsided shape.

Figure 9.25

                                                                                                   Transport and Circulation • MHR       303
 engineer you would find this project daunting, and            The left ventricle has the thickest walls, since it
 yet these are only some of the features of the               must force blood the greatest distance.
 human heart.                                                    A series of valves prevents blood from flowing
    As you saw in Section 9.1, the heart of a mammal          the wrong way through the cardiac cycle. On both
 is divided into four chambers: a right and left              sides of the heart, the atrium and ventricle are
 atrium, and a right and left ventricle. Blood enters         separated from one another by a set of three valves
 the heart through the atria, and leaves the heart            called atrioventricular valves. These are also
 through the ventricles. The two atria contract               known as tricuspid valves because each valve has
 simultaneously, and the two ventricles contract              three parts or cusps.
 simultaneously shortly afterward. This double pump              Between the left ventricle and the aorta, and
 action forces the blood through the cardiac cycle.           between the right ventricle and the pulmonary
    As the blood returns from the body, it is                 artery, other valves work to prevent blood from
 collected in a vein called the superior vena cava,           being sucked back into the heart when the ventricle
 which flows into the right atrium. When the atria             relaxes after forcing blood out of the heart. When
 contract, the right atrium pumps the blood into the          you listen to a heartbeat through a stethoscope, the
 right ventricle. When the ventricles contract, the           classic “lub-dup” sound you hear is caused by the
 right ventricle then pumps blood from the heart out          opening and closing of these valves. The softer
 to the lungs through the pulmonary artery. The               “lub” is the sound of the atrioventricular valves
 oxygenated blood returns to the heart through the            closing, while the louder, sharper “dup” is the
 pulmonary veins, which are blood vessels that                sound of the valves between the ventricles and the
 enter the left atrium. When the atria contract again,        arteries snapping shut following the contraction of
 the left atrium pumps the blood into the left                the ventricles.
 ventricle. When the ventricles contract, the left
 ventricle pumps the blood out through the aorta to                                         PLAY
 the systemic circulatory system.                               To view an animation of the function of the heart and the
                                                                pathway of cardiac circulation, refer to your Electronic
           oxygenated blood        deoxygenated blood
                                   to lungs                     Learning Partner.
           to body

                                                              Control of the Heartbeat
                                                              You can probably hold your breath for more than a
                                                              minute, and yet you cannot hold your pulse even
                                                blood         for a single beat. Your heart continues beating
  deoxygenated                                  from lungs    regularly if you are knocked unconscious, and may
  blood from                                                  even continue beating for a while after you die. In
  body                                                        fact, a heart kept in a saline solution of the correct
                                                              composition may beat for a long time. The impulse
                                                              that triggers the heartbeat actually originates from
                                                              within the heart itself. A bundle of specialized
                                                              muscle tissue, located in the wall of the right
 Figure 9.26 The flow of blood through the heart. Note that
 the atria contract at the same time, and the ventricles      atrium, stimulates the muscle fibres to contract and
 contract at the same time. Thus, only two contractions are   relax rhythmically. This tissue is called the
 required to force blood through all four chambers.           sinoatrial node, or the S-A node. More commonly,
                                                              the S-A node is known as the pacemaker.
    The contraction of each chamber of the heart
 produces a certain amount of pressure. The atria,                                  BIO             FACT
 which only have to push blood into the adjacent
                                                                The first artificial pacemaker was invented by Canadian
 ventricles, have relatively thin walls and do not              John Hopps in 1950. Hopps was conducting experiments
 generate much force. The ventricles, on the other              with body temperature when he discovered that artificial
 hand, have thicker, muscular walls that can push               stimulation could restart regular contractions in a heart that
 blood out through blood vessels and capillary beds             had stopped beating after being chilled. Hopps used this
 in the pulmonary and systemic circulatory systems.             information to design a large external pacemaker.

304     MHR • Internal Systems and Regulation

                               Atrial         Ventricular
                      depolarization          repolarization

                                        R                                                                               R
Voltage (mV)

                                                T                                                                           T
                                  P                                                                             P
                                      Q                                                                             Q
                                          S                                                                             S

                                 0 0.1 0.2 0.3

Figure 9.27 An electrocardiogram records the electrical         ventricles recover from the contraction, the small spike at T
activity measured by an electrocardiograph. The small           shows the electrical repolarization that precedes the next
voltage increase from P to Q shows the electrical               firing of the S-A node. The repolarization of the atria cannot
depolarization that accompanies the contraction of the atria.   be measured, because it takes place at the same time as
The large spike from Q to S shows the depolarization that       the depolarization of the ventricles.
accompanies the contraction of the ventricles. As the

Recording the Heart Rate                                        a sudden strong electrical current to the heart.
The S-A node generates an electrical impulse that               After the fibrillation has stopped, the S-A node
spreads over the two atria and makes them contract              may be able to initiate a regular heartbeat again.
simultaneously. As the atria contract, the impulse
                                                                Chemical Regulators
reaches another node called the atrioventricular, or
                                                                When you are relaxed, your S-A node fires
A-V, node. This node, located near the atria on the
                                                                regularly, probably around 70 times a minute. This
partition between the two ventricles, transmits the
                                                                firing rate adjusts, however, to meet your body’s
electrical impulse over the walls of the ventricles
                                                                needs. When you run to catch a bus, the increased
to start their contraction. The change in voltage
                                                                activity in your muscles produces a faster rate of
produced by these electrical signals can be
                                                                cellular respiration. This leads to an increase in the
measured using a device called an electro-
                                                                amount of carbon dioxide in your blood. Receptors
cardiogram (ECG). The tracing produced by an
                                                                in your blood vessels transmit this information to
electrocardiogram is called an electrocardiograph.
                                                                the medulla oblongata (the part of your brain that
   Figure 9.27 shows a typical ECG tracing. To take
                                                                plays a role in controlling the rate of respiration).
the tracing, a doctor or technician will place
                                                                As shown in Figure 9.28, the medulla oblongata
electrodes on the skin over the heart. The
                                                                sends impulses along the nervous system causing
electrodes transmit signals to an instrument that
                                                                the release of a chemical called noradrenaline.
measures the electrical changes in the heart muscle.
                                                                When it reaches the S-A node, noradrenaline makes
   In a normal ECG reading, the small voltage
                                                                the node fire more rapidly.
increase marked as P shows the electrical
                                                                   Once you have boarded the bus and found a
depolarization that accompanies the contraction of
                                                                seat, your heart gradually slows down again until it
the atria. The large spike from Q to S shows the
                                                                resumes its resting rate. This response is also
depolarization that accompanies the contraction of
                                                                controlled by the medulla oblongata. A fast heart
the ventricles. As the ventricles recover from the
                                                                rate leads to an increase in blood pressure, since
contraction, the small spike at T shows the
                                                                blood is being pumped more quickly through the
electrical repolarization that precedes the next
                                                                vessels. Receptors in the blood vessels sense the
firing of the S-A node. The repolarization of the
                                                                increase in blood pressure and carry this
atria cannot be measured because it takes place at
                                                                information to the medulla oblongata. In turn, the
the same time as the depolarization of the ventricles.
                                                                medulla oblongata causes the nervous system to
   Some conditions, such as a drug overdose, can
                                                                release a substance called acetylcholine (see Figure
cause the ventricles to start contracting randomly.
                                                                9.29). This chemical slows the firing of the S-A node.
This condition is known as ventricular fibrillation.
Fibrillation can sometimes be stopped by applying

                                                                                        Transport and Circulation • MHR         305
                                                                         conditions produce what is called a “fight or flight”
                                                                         response — a physiological change that prepares
                                                                         the body for anticipated activity including attack,
                                                                         defence, or escape. As the heart rate increases, so
                                                                         does blood flow to the muscles, resulting in more
                                                  medulla                oxygen being delivered to the muscle cells.
  spinal cord
                                                  heart rate             Cardiac Output and Fitness
                                                                         The amount of blood pumped by the heart is often
                                                                         referred to as the cardiac output. This is a measure
                                                                         of the volume of blood pumped from each ventricle
                                                                         per unit of time. Therefore, it is also a measure of
                                                                         the level of oxygen delivery to the body, and an
                                                                         indicator of the total level of work the muscles
                                                                         can perform.
                                                    left atrium
                                                                            Two factors affect the cardiac output. These are
                                                                         the heart rate and the stroke volume. Stroke
 sino-auricular                                     left ventricle
                                                                         volume is the amount of blood forced out of the
                                                                         heart with each heartbeat. Cardiac output can be
      right atrium
                                                                         calculated as
  right ventricle                                                             cardiac output = stroke volume × heart rate
                                                                            The average person has a stroke volume of about
 Figure 9.28 While the firing of the S-A node happens                     70 mL and a resting heart rate of about 70 beats per
 spontaneously, the rate of firing can be temporarily                     minute, for a cardiac output of about 4900 mL/min.
 increased or decreased by chemical messengers. The                      Remember that the average person has about 5 L of
 release of these chemicals is controlled by the medulla
                                                                         blood in the body. This means that for the average
 oblongata in the brain.
                                                                         person, the total volume of blood in the body
                                                                         circulates through the heart about once every
    Physical activity is not the only trigger for an
                                                                         five minutes.
 increased heart rate. Your nervous system releases
                                                                            Table 9.6 shows the relationship between stroke
 adrenaline when you are nervous, angry, or excited,
                                                                         volume, heart rate, and cardiac output. In this table
 or after a sudden shock or sharp pain. All of these

                                                                                              vagus nerve

       electrode                                                     B When Loewi passed the saline solution
                                                                       collected from the first heart through the
                                                                       second heart, the second heart also
  A Loewi removed the hearts from two anesthetized                     slopped. Loewi concluded that since there
    frogs and passed a saline solution through each                    was no physical connection between the
    heart to keep them beating. He then electrically                   hearts, the nerve must have secreted a
    stimulated the vagus nerve of one of the hearts.                   chemical inhibitor that was carried to the
    This caused the heartbeat to slow down and                         second heart in the saline solution. This
    eventually stop.                                                   substance was later shown to be acetylcholine.

 Figure 9.29 An experiment conducted by a German scientist in 1921 demonstrated
 that chemicals are involved in the control of the heart rate. Loewi and a colleague
 later received a Nobel prize for their work.

306       MHR • Internal Systems and Regulation
individual C is exceptionally fit, having a very high               it takes for your heart rate to return to its resting
stroke volume. C can maintain the same level of                    level following physical activity. The recovery time
oxygen delivery at a much lower heart rate than the                will diminish as you become more fit.
less fit individual B. This means that C’s heart is
working more efficiently than B’s. A low resting                                           FAST FORWARD
heart rate is considered an indicator of physical                    You should not exercise at your maximum heart rate.
fitness because it means that stroke volume is high.                  Instead, aim for a target level of about 80% of this rate.
                                                                     For tips on determining your maximum heart rate and on
Table 9.6
Relationship between stroke volume, heart rate,                      exercising to promote cardiovascular fitness, turn to
and cardiac output                                                   Chapter 10, Section 10.5.

                   Cardiac      Stroke volume      Heart rate
  Individual    output mL/min      mL/beat         beats/min       Stroke Volume and Fitness
      A             4900               70              70          Two sets of factors affect stroke volume. The first
                                                                   set affects how easily the heart fills with blood,
      B             4900               50              98
                                                                   while the second set affects how readily the heart
      C             4900              140              35          empties again. The first set of factors include the
      D             9800               70             140          volume of blood returning to the heart from the
                                                                   veins and the distensibility, or stretchiness, of the
                                                                   ventricles. The second set includes the strength of
                      BIO           FACT                           the ventricular contraction and the pressure
                                                                   exerted by the artery walls.
  Elite endurance-trained athletes such as Olympic cross-
                                                                      Regular cardiovascular exercise will increase the
  country skiers have demonstrated resting heart rates as low
                                                                   resting stroke volume of your heart. Cardiovascular
  as 30 beats per minute. The maximum cardiac output in
                                                                   exercise enlarges the ventricular chambers,
  such individuals may reach 40 L per minute – 8 times that
  of an average person!                                            increases the distensibility of the ventricles and
                                                                   strengthens the ventricle walls. As a result, the
                                                                   heart develops more power to push blood out with
Heart Rate and Fitness                                             each contraction. Strength training such as
Your maximum heart rate is the highest heart rate                  weightlifting, on the other hand, may simply
you can attain during an all-out physical effort. This             increase the thickness of the ventricle walls. This
value will diminish as you get older. Maximum                      may actually limit stroke volume by reducing the
heart rate does not appear to be related to fitness.                elasticity of the ventricles. A good exercise program
The more important indicator is the length of time                 will include regular cardiovascular activity.

    MINI        LAB

Measuring Recovery Rates                                           Modification: After recording your resting heart rate, sit very
                                                                   quietly and breathe deeply. Try to relax your body and mind
In this lab you will see how long it takes your heart to return
                                                                   as much as you can. After a few minutes, record your pulse
to its resting rate following a short period of exercise. If you
                                                                   rate again to see if you have managed to bring your heart
have a physical condition that makes it unadvisable for you
                                                                   rate down to below your usual resting rate. Then measure
to exercise vigorously, try the modification described below.
                                                                   your heart rate at one-minute intervals until your heart
Find your pulse either at the wrist or under your jawbone.         returns to its resting rate. Plot the results on a graph.
Record your pulse rate for 15 s and multiply this number by
four to determine your resting heart rate. You may wish to
do this twice to ensure an accurate measurement. Record            Describe the shape of the graph you have produced.
the number. Now have a partner time you while you do               Compare your results with other members of the class.
jumping jacks or another vigorous activity for one full            Provide an explanation for the differences you see. What do
minute. Immediately after you finish, measure your pulse           you think these results tell you about your level of fitness?
rate again and record this number. Measure your pulse rate         Explain.
at one-minute intervals until your heart returns to its resting
rate. Plot the results on a graph.

                                                                                            Transport and Circulation • MHR       307
    Stroke volume also increases while you exercise.
 The more fit you are, the greater will be the

                                                             stroke volume (mL)
 increase in stroke volume. Table 9.7 shows the                                   200
 relationship between resting and maximum stroke
 volumes for individuals of different fitness levels.
 Heart Defects                                                                     50
 A newborn baby will sometimes have a distinct
 bluish tinge. This is a sign that not enough oxygen                                    untrained trained       elite
 is reaching the body. Such “blue babies” may have                                                          endurance
 one or more congenital heart defects. Some of the                                                            trained
 more common defects include problems in the
                                                             Table 9.7 The difference between resting (green bars) and
 walls dividing the chambers of the heart, in the
                                                             maximum stroke volume (purple bars) increases with
 valves, or in the structure of the blood vessels near       physical fitness.
 the heart.

            Investigation                         9 • A                                                         SKILL FOCUS

                                                                                                                Performing and recording
       The Heart Rate of Daphnia                                                                                Analyzing and interpreting
       Although Daphnia is commonly called a water flea, it is actually a
                                                                                                                Communicating results
       crustacean rather than an insect. You will be able to see the heart of
       this animal through its transparent skin, and will be able to gauge the
       effects of various substances on its heart rate.

       Pre-lab Questions                                                          adrenaline solution          chloroform (very small
                                                                                  magnesium sulphate             amount)
         How will substances in the environment reach
                                                                                    (Epsom salts)              ice water
         the heart of a crustacean to cause a change in
         its heart rate?                                                          Procedure
         What effect will a change in the heart rate of a
                                                                                   1. Place a single healthy Daphnia on the
         crustacean have on its circulatory system?
                                                                                      microscope slide and examine it under low-
                                                                                      power magnification with a microscope. See
                                                                                      if you can count the number of heartbeats in
       How can you compare the effects of different                                   a one minute interval. If so, record this figure.
       substances on the heart rate of a single animal?
                                                                                   2. Gently lift the cover slip slightly and inject a
       Prediction                                                                     drop or two of ice water. It may be necessary
                                                                                      first to blot up the existing water in the well.
       Predict how you would expect a change in
                                                                                      Record any change you see in the heart rate.
       temperature to affect the activity level of a
                                                                                      If you have not been able to count the heart
                                                                                      rate, simply note whether the ice water caused
       CAUTION: Be careful when using chloroform
                                                                                      an increase or decrease in the heart rate, or
                                                                                      whether there was no noticeable effect.
                                                                                   3. Repeat the procedure several times, adding
                                                                                      any or all of the following substances:
                                                                                      adrenaline solution, ASA, magnesium
       several live daphnia         medicine dropper
                                                                                      sulphate, chloroform.
       microscope slide (with a     cover slip
         small well or concavity)   ASA (such as Aspirin™)                         4. Prepare a table compiling your observations.

308    MHR • Internal Systems and Regulation
   A septal defect is a hole in the septum, the wall     failure of the valve to close properly results in
that separates the right and left ventricles. This       blood being drawn back into the heart after a
defect allows oxygenated and deoxygenated blood          contraction. A heart murmur takes its name from
to mix in the heart. Such mixing may also happen         the characteristic whooshing or rasping sound
when a small fetal blood vessel connecting the           caused by the blood escaping from the valve. This
aorta and the pulmonary artery does not close            sound can be heard with a stethoscope. A heart
properly at birth. Both of these conditions can          murmur is not necessarily a problem. Physicians
usually be treated with surgery.                         grade heart murmurs according to their severity
   Another relatively common congenital defect is        and according to the location of the valve defect.
a heart murmur, a condition that occurs when one         The location can be determined by identifying
or more of the heart valves does not open or close       when the murmur is heard in relation to the
properly. A failure of the valve to open readily         different elements of the heartbeat.
restricts the flow of blood from the heart, while a

                                                          response give to the animal? Assuming that
                                                          the mammalian heart responds to a drop in
                                                          temperature in the same way, how could
                                                          knowledge of this response be used to
                                                          increase the success rates of heart surgery?

                                                       Exploring Further
                                                        6. Daphnia, a very small crustacean, has a
                                                           heart rate much faster than your own. If you
Post-lab Questions                                         were able to measure the heart rate of your
                                                           daphnia, calculate the ratio of your own
 1. Which substances caused a change in the
                                                           resting heart rate to the daphnia’s. Why
    daphnia’s heart rate? Explain how you think
                                                           would such a small animal have such a fast
    these substances worked.
                                                           heart rate? Would you expect the heart rate
 2. ASA is said to “thin” the blood because it             of large animals to be, on average, slower
    prevents platelets from sticking together.             than that of small animals? Explain.
    Explain how this characteristic might have
                                                        7. This investigation provides information
    contributed to the result you saw.
                                                           about factors that affect the heart rate of a
 3. Another classmate points out that your                 small crustacean. How much can this
    experiment lacks a control. Could this affect          information contribute to scientists’
    the validity of the conclusions you may                knowledge of the factors that affect the
    draw from your findings? Explain. What                  hearts of other animals, including a fish or a
    control could be set up for this experiment?           mammal? Conduct research to determine the
                                                           structure and function of the heart of a
 4. Compare your findings with those of others
                                                           daphnia, and compare this to what you
    in your class. Are all the findings consistent?
                                                           know about the structure and function of the
    If not, explain what factors may have
                                                           human heart. In what ways are the two
    produced any variations.
                                                           similar? How do they differ? Using this
Conclude and Apply                                         information, write a brief report explaining
                                                           whether or not the data gathered from this
 5. What effect did the ice water have on the
                                                           investigation could help to predict what
    heart rate? What advantage could this
                                                           might happen in another organism.

                                                                              Transport and Circulation • MHR   309
                                                                        The most common heart valve defect is mitral
                                                                     valve prolapse, a condition in which the flaps of
                                                                     the mitral valve (Figure 9.30) close unevenly,
                                                                     allowing blood to flow backwards from the left
                                          mitral valve               ventricle into the left atrium. This condition is
                                                                     thought to affect between five to 15% of the
                                                                     population of North America. It is not usually a
                                                                     serious condition, although it does require regular

 Figure 9.30 The mitral valve is located between the left
 atrium and left ventricle.

  Biology At Work

      Pathology: Investigating                                       undergoing open-heart surgery, a heart transplant, or a
                                                                     bypass graft operation. He must report on the procedure
      Medical Questions
                                                                     that was done and draw a conclusion about why the
                                   Dr. Jagdish Butany seldom         patient died. He tries to make sure that nothing went
                                   has a dull moment. His            wrong in the surgical procedures or in the patient’s
                                   workday includes a variety of     treatment at any other time.
                                   responsibilities: practicing
                                   regular pathology, serving as     Research
                                   Chief of Autopsy Services at      Dr. Butany considers research to be a very enjoyable part
                                   the University Health             of his work. He publishes reports and presents his
                                   Network/Toronto General           findings at meetings all over the world. He is particularly
                                   Hospital, conducting              interested in artificial cardiovascular devices, such as the
                                   research, and teaching at the     artificial heart valve. Manufacturers consult him about
                                   University of Toronto’s           new heart valves and other cardiac devices that are being
                                   medical school. With so many      developed for human use. Usually, Dr. Butany works with
                                   obligations, he must juggle       manufacturers in the testing stage, when the device is
      Dr. Jagdish Butany           priorities so no one suffers.     implanted into animals. It is essential to know how well
                                   Doing the work he likes,          the device is working and how it can be improved.
      doing it well, and doing it on time are among Dr. Butany’s     Dr. Butany must use his skills as a pathologist to come
      biggest challenges.                                            up with definitive answers to these important questions.

      Responsibilities                                               Rewards
      Pathology is a branch of medicine that studies disease         A career in pathology, according to Dr. Butany, is a huge
      by examining tissues and body fluids obtained during           challenge. Clinical colleagues ask for his advice when
      surgery or autopsy. Ontario law states that any tissue a       diagnosing a disease and when planning a course of
      surgeon removes must be sent for pathological                  treatment. He is rewarded by his confidence in his work
      examination. Dr. Butany first examines the tissue visually     and by the opportunity to make a significant contribution
      and records a description of his findings. He then has         to the well-being of the patient. His work as a pathologist
      microscope slides made of sections of the tissue, and          gives him an extraordinary sense of fulfilment.
      examines the slides in order to make a diagnosis. On
      rare occasions, the diagnosis may be that the tissue is        Career Tips
      normal. More commonly, Dr. Butany will diagnose a              Becoming a pathologist requires a strong background in
      lesion, which is an abnormal change in the tissue. His         biology and biochemistry, as well as good detective skills.
      report will mention the lesion, describe it, and (when         If you are drawn to solving medical mysteries, you can
      possible) explain its significance and how it relates to the   contact the pathology department of your local hospital
      patient’s symptoms.                                            to learn more about the education and other qualifications
                                                                     you will need to pursue work in this field.
      Dr. Butany’s specialty is cardiovascular pathology. He
      performs autopsies on patients who have died after

310        MHR • Internal Systems and Regulation
     SECTION             REVIEW

1.    K/U Arrange the following into the order by which      7.      K/U            Study the normal ECG trace shown below.
     blood flowing through the cardiac cycle encounters           (a) What effect does the increase in voltage at R
     them: pulmonary artery, pulmonary vein, aorta,                   have on the ventricles of the heart?
     superior vena cava, right atrium, left atrium, right
                                                                  (b) Describe what the trace might look like during
     ventricle, left ventricle.
                                                                      ventricular fibrillation.
2.    K/U Explain how noradrenaline and acetylcholine are
     involved in the regulation of the heart rate.
3.    I Can an ECG reading provide information about a

                                                                  Voltage (mV)
     person’s cardiac output? Explain and give examples.                         0.5
                                                                                                  P           T
4.   C   Copy the following illustration in your notebook.
     Use arrows to show the flow of oxygenated and                                                    Q
     deoxygenated blood. Indicate the source and desti-                                                   S
     nation for each of these blood supplies.

                                                             8.    MC In one form of congenital heart defect, the major
                                                                  blood vessels are transposed. That is, the aorta is
                                                                  connected to the right ventricle, and the pulmonary
                                                                  artery is connected to the left ventricle. At the same
                                                                  time, a hole exists in the septum separating the right
                                                                  and left sides of the heart.
                                                                  (a) Draw a diagram to explain how this defect will
                                                                      affect the flow of blood through the heart, and
                                                                      explain the implications for the efficiency of
                                                                      oxygen delivery in the body.
                                                                  (b) How would you expect the ECG reading for an
                                                                      individual with this heart defect to differ from the
                                                                      ECG reading of a normal individual? Explain.

5.    C Prepare a drawing and a set of up to four flash
                                                                                 UNIT PROJECT PREP
     cards that you could use to explain to a Grade 1
     class why regular exercise is good for the heart.       If you have decided to study a heart disorder in your
                                                             Unit 3 Project, draw a labeled diagram showing which
6.    I Plot a graph of your heart rate versus time over a
                                                             heart structures are affected by the disorder. Include a
     24 h period. Account for any variations in the shape
                                                             note explaining what effect the disorder will have on the
     of the curve.
                                                             flow of blood through the heart.

                                                                                                Transport and Circulation • MHR   311

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