HW8. Circulatory Systems - Due Friday 4/15/2011
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should meet before completing the assignment. However, you must write your answers
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1. Compare and contrast the circulatory system in mammals vs. the xylem in angiosperm trees
with respect to the following characteristics. Use the assigned textbook readings and the GAE
pdf to answer the questions on the following page.
1A. The nature of the overall circulatory system (open, closed, or flow-through) and the
molecules, substances, and/or cells carried in the circulatory fluid (2 pts)
Mammal –
Tree -
1B. The nature of the pump, its mode of action, and its energy source (2 pts)
Mammal –
Tree -
Fluid flow problems: Use the information about the variables affecting bulk flow in the
Hagen-Poiseuille equation to answer the following questions.
2. No extra cheese, please! Coronary arteries are responsible for supplying oxygenated blood
to heart muscle. The radius of typical open artery is 1.5 mm. Coronary heat disease is caused by
the arteriosclerosis, i.e., the deposition of plaque along the arterial walls. In a patient with a
“mild” case of coronary arteriosclerosis, plaque may line the walls so that it reduces the radii of
the open lumens of these arteries to 1.0 mm.
2A. Assuming that all other variables affecting blood flow remain the same, then determine the
ratio of blood flow in a patient having the occluded arteries described above vs. a healthy
individual having 100% open arteries. Explain your reasoning, and show your calculations. (3
pts)
2B. Do the same calculation for a patient having occluded coronary arteries with open radii of
0.5 mm (2 pts)
2C. Using the physical relationships described in the Hagen-Poiseuille equation, explain to this
patient why his body might try to compensate for the increased resistance in his occluded
coronary arteries by an increase in his blood pressure (2 pts)
2D. What might be the biological consequences if the patient’s body were to make that simple
physical adjustment to the increased resistance to blood flow? For additional information,
refer to: www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001502 (2 pts)
3. So Few for So Much! A large tree adds a new growth ring of xylem cells for conducting water
every year. The so-called diffuse-porous woods, such maples and magnolias, develop many
xylem vessels of intermediate radius, or 40 um. On other hand, oaks, elms, and other ringporous woods develop fewer xylem vessels of greater radius, or 80 um. Let’s assume that all
features of the conducting vessels are identical in these trees, except for the different radii of
their vessels.
In a new growth ring, a maple tree can develop 10,000 new vessels with a radius of 40 um.
How many vessels of 80 um radius would have to develop in a new growth ring of an oak tree
to have an equal rate of xylem flow as in the maple? Explain your reasoning, and show your
calculations. (2 pts)