AP Biology Lab 10: Circulatory System Physiology Lab
In order for a cell to survive, it must be in a favorable environment that is rich in nutrients and
oxygen for respiration, with a low concentration of waste produced by cellular metabolism. In lower
animals, such as sponges, this is achieved entirely by water flowing across body membranes. More
advanced body systems, such as are found in humans, require a more complex system to transport fluids
and maintain a favorable extracellular environment.
Like all vertebrates, humans have a closed circulatory system, which consists of a network of
blood vessels and a muscular, pumping heart that pushes blood through arteries and veins. This network of
blood vessels is divided into two distinct circuits: they systemic and pulmonary circulatory systems.
Pulmonary circulation carries oxygen depleted blood to the lungs and returns oxygen-rich blood to the
heart. The systemic circulation then distributes this oxygenated blood to the tissues of the body.
When the metabolic rate of tissues increases, as it does during exercise, the demand for oxygen
and nutrients increases along with it. To satisfy this increase in demand, the circulatory system adapts in a
number of ways: heart rate, arterial pressure, and breathing rate increase, and blood flow to muscle tissue
increases while decreasing in other tissues.
In order for the blood pumped by the heart to reach the cells of body tissues, there must be
considerable pressure in the arteries and arterioles. This pressure is determined by the rate of blood flow
through, and the resistance in, the arterioles. Blood pressure is at its highest when the heart is actively
contracting; this is referred to as systolic pressure. Diastolic blood pressure, lower than the systolic value,
occurs when the heart is at rest. A common, “normal” blood pressure might be 120/70, which means that
the pressure during systole is 120 mm Hg, and pressure during diastole is 70 mm Hg. The range of normal
blood pressure is dependent on heredity, sex, age, and environmental factors.
Blood pressure is measured using a sphygmomanometer and a stethoscope. By applying pressure
to the blood vessels of the upper arm with a cuff of the sphygmomanometer, and listening for the sounds of
Korotkoff (Korotkoff sounds) with the stethoscope, the systolic and diastolic pressure can be determined.
The sounds of Korotkoff, named for the man who discovered them, occur when the arm cuff of the
sphygmomanometer is pumped high enough to restrict bleed flow to the artery. As the cuff valve is
released, the pressure eventually reaches a point equal to systolic pressure. When this happens, blood is
forced through the compressed artery and the vibrations of the artery walls become audible with the
stethoscope as a distinct tapping noise. As the pressure continues to lessen, the sounds change. Five
distinct phases (Table 1) occur, with the final phase being a disappearance of sound altogether. This is
equivalent to the diastolic pressure. The sounds of Korotkoff usually become audible around 120 mm Hg.
Systolic pressure can be noted when the sounds begin, and diastolic pressure when the sounds stop.
The baroreflex or baroreceptor reflex is one of the body's homeostatic mechanisms for maintaining
blood pressure. It provides a negative feedback loop in which an elevated blood pressure reflexively causes
heart rate and thus blood pressure to decrease; similarly, decreased blood pressure depresses the baroreflex,
causing heart rate and thus blood pressure to rise.
Phase 1 Tapping (systolic)
Phase 2 Murmur which may be heard after the tapping (10 to 15 mm Hg lower
than phase 1)
Phase 3 Reappearance of only tapping
Phase 4 Muffling
Phase 5 Disappearance of sounds (diastolic)
Heart rate, and its change under different conditions, is a measurement of an individual’s physical
fitness. Exercise makes the heart more efficient, able to pump more blood with each contraction. The
amount of blood the heart pumps with each beat is referred to as stroke volume. A person in good physical
shape will have a higher stroke volume and a lower resting heart rate.
Maximum heart rate, a constant for a particular age group, is also an indicator of fitness.
Individuals who are not in very good shape will reach the maximum heart rate at a lower level of exertion
than a person of the same age who exercises regularly. Likewise, well conditioned people will show a
smaller increase in cardiac rate with exercise, and they will also return to their resting heart rate much more
quickly than people who are not in good shape.
Unlike mammals, the rate of metabolism and physiological mechanisms of “cold-blooded”, or
ectothermic (poikilothermic), animals is dependent on the temperature of the organism’s environment.
Although most biochemical reactions taking place in their bodies occur faster at higher temperatures, the
effect is quite noticeable as the metabolic rate, as well as the rate of activity, of animals such as reptiles
increases dramatically between 5° and 35° C. This increase in metabolism is expressed in terms of the
value “Q10”. Q10 is defined as the ratio of the metabolic rate of an organism at one temperature as compared
to the metabolic rate at a temperature 10° C lower.
An ideal organism for study of an ectotherm’s rate of metabolism is the Amphipod, due to its
varied habitats and easily studied anatomy. Although the complex muscular system obscures some of the
Amphipod’s smaller anatomical features, the essential parts of most organ systems can be easily
distinguished. The simple foot-ball-shaped heart is readily visible behind the head on the dorsal side of the
animal. Its heart rate is variable with water temperature, making it easy to alter the Amphipod’s heart rate
and observe the changes.
Investigating Heart Rate in Amphipoda
1. Obtain two depression slides. Tear a small portion of a
cotton ball off, and place it in the center well of one of the
2. Place several Amphipods on the cotton fibers with a pipet.
Cover the Amphipods with a second depression slide. Bind
the two slides together with rubber bands, wrapping the
rubber band once between the slides so the subject is not
3. Fill a Petri dish with room-temperature water (20°C), 1 cm
deep. Place the slides in the dish, and allow to sit for at least
one minute to equilibrate.
4. Place the entire dish on the stage of a microscope. Let the Petri dish sit until the contents settle.
5. Locate the largest Amphipod on the slide. Find the heart of the specimen, dorsal to the dark line of the
6. Practice measuring the heart rate. Have one partner keep track of the time while the other observes the
Amphipod. Count the number of times the heart beats over a period of 15 seconds. Multiply this number by
four to determine the heart rate per minute. Record the data in a table that looks similar to the Amphipod
Heart Rate Table below, in your quadrille.
Table:Amphipod Heart Rate
Temperature (°C) Heartbeats per Minute
7. Remove the slides and empty the Petri dish of the water. Fill the dish with ice water (10°C) and place the
slides in the dish. Let the preparation acclimate as before on the stage of the microscope.
8. Again locate and view a single Amphipod. Measure its heart rate at this temperature. Record the data in
your quadrille in the data table.
9. Gradually add warm water to the Petri dish, keeping track of the temperature with a digital thermometer. As
indicated in the table, take a heart rate measurement once the temperature reaches 30°C give, or take.
Remove water as necessary, using a pipette.
10. Stop taking heart rate measurements when the Amphipod’s heart rate stops changing, or when you can no
longer measure the heart rate of the specimen. Record the data in the table.
11. Calculate the Q10 for Amphipod heart rate and metabolism. Q10 represents the change in metabolic rate (or
rate of any chemical reaction) between two temperatures 10°C apart, indicating the effect of this temperature
change on the organism. A Q10 of 2 means that for a rise in temperature of 10°C, the metabolic rate will
double. This is simply a means we can quantify our observations and have some good quantitative data. Q10
can be calculated as follows:
Q10 = Rate at the higher temperature divided by rate at the lower temperature
Q10 = [k2/k1]
k1 = heart rate at t1
k2 = heart rate at t2
12. Plot the data from your table in a graph in your quadrille.
1. If the Amphipod heart rate experiment were performed on an endothermic organism, what results
would you expect? Explain.
2. The maximum heart rate of a conditioned athlete and a person in poor shape, both the same age,
are approximately the same. True or false? Explain.
3. Create a double bubble (NOT A VENN DIAGRAM!!!) that shows similarities and differences
between endothermy and ectothermy.