Download Q28: The graph below shows normal breathing in a

BIOL 220, Summer 2014: Study Questions for Week 3
Q28: The graph below shows normal breathing in a healthy human volunteer. Is X equal to 0,
greater than 0, or less than 0? Explain.
A28: X must be greater than 0 (typically it is around 150 mL) because you can't empty your
ventilatory system (trachea, bronchi, etc.) of all air. This air that remains in your ventilatory
system is called the dead space.
Q29: Find the points in the textbook figure below (45.26) at which left AV and aortic valves open
and close. How do you know? Where in relation to these points would the start of the QRS
complex occur?
A29: The AV valve opens when the atrial pressure exceeds the ventricular pressure and closes
when the ventricular pressure exceeds the atrial pressure. The aortic valve opens when the
ventricular pressure exceeds the aortic pressure and closes when the aortic pressure exceeds
the ventricular pressure. Since the QRS complex represents depolarization of the ventricles, it
will start slightly before the ventricle actually contracts, and thus before the ventricular pressure
rises above aortic pressure – at about 0.45 seconds, according to the X axis of the graph.
Q30: A certain valve in the heart is open during the P wave, is closed during the QRS complex,
and re-opens after the T wave. Where is this valve?
A30: It must be an AV valve (which closes during ventricular contraction). From the information
given, we cannot tell whether it is on the left or right side of the heart (mitral valve or tricuspid
valve, respectively -- but you don’t need to memorize these terms).
BIOL 220, Summer 2014: Study Questions for Week 3
Q31: The graph below shows blood pressure measurements recorded at 2 blood vessels. Curve
A is for a major systemic artery; what kind of vessel is represented by curve B?
A31: B is essentially constant, not fluctuating according to the cardiac cycle, so it must
represent the pressure toward the end of a capillary or in a vein.
Q32: You come upon a half of a pig heart with blood vessels still attached, but it is not labeled
as the left half or the right half, and no other hearts or heart pieces are there to compare it to.
How can you tell whether you have the left heart or the right heart?
A32: Many answers are possible here. One approach is to see whether the vessels leading to
the atrium look more like the venae cavae (plural of vena cava; right) or pulmonary veins (left)
and whether the vessel emerging from the ventricle looks more like the pulmonary artery (right)
or aorta (left). You could also check for the presence/absence of the moderator band (present
only in the right ventricle), see whether the AV valve has 3 leaflets (right) or 2 (left), etc.
Q33: Let’s say that the blood entering the pulmonary capillaries has a PO2 of 40 mm Hg and a
PCO2 of 45 mm Hg, and that the air in the nearest alveoli has a PO2 of 120 mm Hg and a PCO2 of
20 mm Hg. Which will be faster: the initial diffusion of O2 out of the alveoli, or the initial diffusion
of CO2 into the alveoli? Explain.
A33: Since this is a question about diffusion rates, you should think of the Fick equation.
Surface area (A) and diffusion barrier thickness (D) are the same for both gases; the diffusion
constant (k) is not the same for both, but similar, as both are small, nonpolar gases. The main
difference is that O2 has a much larger partial pressure gradient than CO2 (104 minus 40 mm
Hg vs. 45 minus 40 mm Hg), so O2 will diffuse faster.
Q34: The graph below is a plot of force exerted by the diaphragm muscle over time. Assuming
that this diaphragm is operating in a normal, healthy human, draw graphs of chest cavity
pressure and lung volume over this same time period.
BIOL 220, Summer 2014: Study Questions for Week 3
A34: The increases in force represent contraction of the diaphragm, which increases chest
cavity volume, decreasing chest cavity pressure and increasing lung volume. Thus, the peaks in
force should correspond to low points in chest cavity pressure (perhaps a minimum of 752-754
mm Hg, down from a high of 756-758 or so) and peak lung volumes.
Q35: The coronary circulation delivers blood to the working heart muscle. The cardiac veins
often have a PO2 of about 25 mm Hg. What fraction of the oxygen carried by the coronary
arteries is extracted by the coronary tissue? Use the figure below from your textbook.
A35: The coronary arteries, like other arteries, normally have a PO2 of about 100 mm Hg,
corresponding to near-complete saturation of hemoglobin (~97%). Based on curves like the one
above from your textbook, a PO2 of 25 mm Hg corresponds to a hemoglobin saturation of about
22%. 97% minus 22% equals about 75% of the arterial oxygen getting extracted by the coronary
tissue.
Q36: What would be the physiological consequences of blocking red blood cells'
chloride/bicarbonate exchanger (antiporter), which moves bicarbonate in and out of red blood
cells?
BIOL 220, Summer 2014: Study Questions for Week 3
A36: The blocking agent would greatly limit the amount of CO2 that could be removed from the
tissues and exhaled at the lungs. This is because much more CO2 can be transported by the
blood if the red blood cells convert it to carbonic acid (H2CO3), which then dissociates into H+
and HCO3-, with the latter then exiting the red blood cells via the exchanger. Without this
exchanger, only a limited amount of CO2 could be converted into H+ and HCO3- before the
intracellular buildup of HCO3- would, according to Le Chatelier's Principle, prevent further CO2
conversion. And when this blood returned to the lungs, only a limited amount of CO2 would be
there to be released.
Q37. When we ascend to high
altitudes, we increase our
production of a compound called
2,3-bisphosphoglycerate (BPG).
The presence of this compound
in the blood shifts the oxygenhemoglobin curve as shown at
right. Does BPG increase,
decrease, or not change
hemoglobin's affinity for
oxygen?
A37: BPG decreases affinity.
Q38: If we assume an arterial
PO2 of 80 mm Hg (due to the
high altitude) and a tissue
capillary PO2 of 40 mm Hg,
calculate what percentage of the
hemoglobin would give up oxygen to the tissues for both curves (normal and high-BPG curve).
Show your work.
A38:
Normal: (all #s are approximate)
High BPG: (all #s are approximate)
Arterial hemoglobin saturation = ~95%
Arterial hemoglobin saturation = ~92%
End-tissue hemoglobin saturation = ~55%
End-tissue hemoglobin saturation = ~35%
Net delivery to tissues = 95% minus 55%
Net delivery to tissues = 92% minus 35%
equals 40%
equals 57%
Q39: Based on your answer to #38, do high BPG levels help, hurt, or not affect our ability to
work at high altitude? Briefly explain your logic.
A39: Since net oxygen delivery to tissues is higher for the high-BPG curve (57% vs 40%), high
BPG seems beneficial to us at high altitude.
Q40: If capillaries' average PO2 is 40 mm Hg as they exit the body's tissues (muscles, GI tract,
skin, etc.), what is the approximate PO2 in the pulmonary artery? Briefly explain.
A40: The pulmonary artery PO2 is also 40 mm Hg because no oxygen is extracted or added on
the way back from the tissues. (Oxygen transfer only occurs at the capillaries.)
Q41: Your textbook says, "A frog lowers the floor of its throat, increasing the volume there and
thus drawing in air from the atmosphere though the nasal passages and into the oral cavity. The
animal then closes the nasal passages and contracts it throat muscles. These actions increase
the pressure on the air in the oral cavity and force it into the lungs." How is this fundamentally
different from the way we humans ventilate our lungs?
BIOL 220, Summer 2014: Study Questions for Week 3
A41: Frogs use positive pressure ventilation to inflate the lungs, i.e., pressurized air is forced
into them. In contrast, humans use negative pressure ventilation, i.e., the less-than-atmospheric
pressure in the cavity surrounding the lungs causes the lungs to inflate.
Q42: Is "Neurotransmitter X" in the graph below more likely to be acetylcholine or
norepinephrine? Explain.
A42: Acetylcholine promotes the relaxation of the smooth muscles surrounding blood vessels,
thus increasing the diameter of the vessels and lowering blood pressure, consistent with the
graph above. Acetylcholine also slows heart rate, which also lowers blood pressure.
Q43: The data table below is from B. Nielsen et al., Journal of Physiology 1992. These
researchers measured forearm blood flow before and at the end of exercise on a stationary
bicycle. They studied both heat-acclimated and non-acclimated subjects under hot and cool
conditions. Why was forearm blood flow greater in hot conditions than cool conditions? And why
did forearm blood flow increase during exercise even though the forearm wasn't being
exercised?
A43: In hot conditions, the body sends more blood to the skin so that heat can be dissipated
from the surface of the body. Exercise served to accentuate the thermal stress, so more blood
flow went to the forearm during exercise to get rid of more heat.