Download Key - Creighton Biology

Name: __________________________
Biology 449 - Animal Physiology
Spring 2006
Midterm 2 - Key
Fill in your scantron form as follows. This is worth 1 point:
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

Write and bubble in your name in the upper left (last name first).
Follow any additional instructions provided in class.
Sign your form in the upper right.
Multiple choice: As always, choose the best answer for each multiple-choice question.
Answer on your scantron form. Each question is worth 3 points.
1. Steroid hormones activate
a.
b.
c.
d.
e.
ligand-gated ion channels.
G-protein pathways.
membrane-bound enzymes.
intracellular receptors that activate enzymes.
intracellular receptors that affect gene expression.
2. Thyroid stimulating hormone
a.
b.
c.
d.
e.
is released in response to corticotropin releasing hormone.
promotes the release of corticotropin releasing hormone.
is released in response to thyrotropin releasing hormone.
promotes the release of thyrotropin releasing hormone.
None of the above is true.
3. Which of the following is not a neurohormone?
a.
b.
c.
d.
e.
Gonadotropin releasing hormone
Growth hormone releasing hormone
Oxytocin
Prolactin
All of these are neurohormones.
4. An often observed phenomenon in island ecology is that when large species colonize an
island they tend to evolve to be smaller. (For example, fossilized remains of dwarf elephants
have been found on the Mediterranean islands of Crete and Sicily.) What might the
physiological basis for this evolutionary change be?
a.
b.
c.
d.
e.
Hyporesponsiveness to growth hormone
Hyposecretion of growth hormone
Hypersecretion of growth hormone
a and b
a and c
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5. Which of the following are characteristics of skeletal muscle cells?
a.
b.
c.
d.
e.
They are striated, connected by gap junctions, and contract relatively quickly.
They are striated, connected by gap junctions, and contract relatively slowly.
They are striated, multinucleated, and contract relatively quickly.
They are not striated, are connected by gap junctions, and contract relatively slowly.
They are not striated, are multinucleated, and contract relatively quickly.
6. During cross-bridge cycling in a sarcomere, the event that occurs the closest in time before
myosin binds to actin is
a.
b.
c.
d.
e.
ATP binds to myosin.
myosin releases ADP and inorganic phosphate.
myosin changes configuration to a high-energy state.
myosin changes configuration to a low-energy state.
myosin breaks its connection with actin.
7. A muscle will shorten
a.
b.
c.
d.
e.
whenever cross-bridge cycling occurs.
as soon as the latent period ends.
during the entire period known as the “contraction time.”
during the entire period known as the “50% relaxation time.”
whenever the force produced by the muscle exceeds the force opposing shortening.
8. The best definition of a motor unit is
a.
b.
c.
d.
e.
“all the fibers in a particular muscle.”
“all the fibers of a particular fiber type in a muscle.”
“all the fibers activated at the same time within a muscle.”
“all the fibers innervated by a single motor neuron.”
“a single muscle fiber.”
9. Depolarization of the pacemaker cells of the sinoatrial node in the heart requires
a.
b.
c.
d.
e.
sympathetic input.
parasympathetic input.
hormonal activation.
a and b.
None of the above.
10. The mammalian blood circulatory system is best described as
a.
b.
c.
d.
e.
a single pump circuit.
two circuits in series.
two circuits in parallel.
four circuits in series.
four circuits in parallel.
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11. The elasticity of the walls of the arteries is important because
a.
b.
c.
d.
e.
it keeps blood flowing in one direction.
it allows the vessels to bend as the limbs and torso move.
it maintains arterial blood pressure during diastole.
it helps prevent the formation of plaques along the vessel walls.
it allows the arterial system to hold a greater blood volume than the venous system.
12. According to Starling’s Law of the Heart, an increase in venous return to the heart causes an
increase in stroke volume because
a. increased venous return is associated with an increase in epinephrine release.
b. increased venous return increases the pressure in the ventricles before systole begins.
c. increased ventricular volume is sensed by stretch receptors that activate sympathetic
pathways.
d. increased stretching of the heart muscle causes it to contract with more force.
e. increased venous return reduces the blood pressure on the arterial side of the
circulatory system.
13. The velocity of blood flow is greatest in the
a.
b.
c.
d.
e.
arteries.
arterioles.
capillaries.
veins.
Blood velocity is the same in all regions of circulatory system.
14. If one region of the body, such the skeletal musculature, exhibits vasodilation in order to
increase local blood flow, which of the following would best describe the normal response?
a.
b.
c.
d.
e.
Increased cardiac output and/or vasoconstriction in other regions.
Increased cardiac output and/or vasodilation in other regions.
Decreased cardiac output and/or vasoconstriction in other regions.
Decreased cardiac output and/or vasodilation in other regions.
No cardiovascular response would be necessary.
15. In a young man taking breaths with a tidal volume of 300 ml, about what percentage of the
air reaching the alveoli would be fresh air?
a.
b.
c.
d.
e.
0%
20%
50%
80%
95%
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16. Imagine a person with lungs that had zero elasticity. Compared to a normal person, the
muscular force required for breathing by this bizarre individual would be
a.
b.
c.
d.
e.
more for inhalation and less for exhalation.
less for inhalation and more for exhalation.
more for both inhalation and exhalation.
less for both inhalation and exhalation.
about the same for both inhalation and exhalation.
17. If nitrogen has a solubility in water of 0.1 ml / liter·torr, and the concentration of nitrogen in
a volume of water is 10 ml/liter, then the partial pressure of the nitrogen in the water is
a.
b.
c.
d.
e.
1 torr
10 torr
100 torr
1000 torr
The partial pressure cannot be determined from this information.
18. The tendency of a gas to diffuse from one location to another is ultimately determined by
a.
b.
c.
d.
e.
the concentration difference between the locations.
the gas fraction difference between the two locations.
the gas volume difference between the two locations.
the partial pressure difference between the locations.
the solubility difference between the locations.
19. Carbon dioxide is transported in the blood as a dissolved gas, by combining with H2O (to
form bicarbonate ion), and by combining with
a.
b.
c.
d.
e.
amino acids.
carbonic acid.
carbonic anhydrase.
heme groups.
2,3-DPG.
20. During heavy breathing, such as occurs during exercise, the muscles responsible for
inhalation and exhalation are activated mainly by the
a.
b.
c.
d.
e.
central pattern generator of the medulla.
dorsal respiratory group of the medulla.
ventral respiratory group of the medulla.
dorsal respiratory group of the hypothalamus.
ventral respiratory group of the hypothalamus.
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Short answer: Write a concise answer to each of the following questions. Your answers
should fit in the spaces provided. Diagrams may be used but must be accompanied by
written explanations. Each question is worth 8 points.
21. Two questions on the stress response:
a. Describe or diagram the hormonal pathway associated with the stress response. Be sure to
provide the full name of each hormone and the feedback loop(s) that control hormone
release.
An increase in stress promotes the increased release of corticotropin releasing hormone by
the hypothalamus. This promotes increased adrenocorticotropic hormone release by the
anterior pituitary, which triggers increased release of cortisol by the adrenal cortex. The
effects of cortisol may ultimately help to reduce stress, and thus cortisol levels, but the main
feedback loops controlling cortisol level are the negative effects of the increased cortisol
levels on the release of CRH and ACTH.
b. What are the physiological effects of increased release of the main stress hormone?
Cortisol helps maintain energy delivery to tissues by promoting the mobilization of fats, as
well as the breakdown of proteins (in large part for use in gluconeogenesis). Cortisol also
suppresses the immune and inflammatory responses, presumably to help conserve energy.
22. Describe the process of excitation-contraction coupling in muscle – that is, how does an
action potential initiated on the sarcolemma (muscle cell membrane) ultimately cause the
muscle to produce force? You description should include the mechanism that controls
whether or not cross-bridge cycling can occur, but you do not need to discuss the molecular
events of the cross-bridge cycling process itself.
Once initiated, an action potential spreads across the sarcolemma, including the transverse
or T-tubules that invaginate deeply into the muscle. The change in voltage in the T-tubules
causes the integral protein dihydropyridine to change conformation. This conformation
change in turn changes the conformation of the associated ryanodine receptors, which are
calcium channels in the sarcoplasmic reticula immediately adjacent to the T-tubules. The
conformation change in ryanodine opens the calcium channels, allowing calcium ions to
move down their concentration gradient from the SR into the sarcoplasm. Once in the
sarcoplasm, the calcium diffuses into the myofibrils, where it binds to the troponin complex
on the thin filaments. This binding causes troponin to change conformation, moving the
tropomyosin molecules that cover the myosin binding sites on the actin of the thin filament
when the muscle is at rest. The movement allows myosin heads to bind with actin so that
cross-bridge cycling can occur. (Once AP’s end, calcium is no longer released from the SR,
and the active transport of calcium back into the SR reduces calcium levels in the
sarcoplasm. This causes troponin and tropomyosin to return to their resting configurations.)
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23. The mammalian heart contains two sets of valves, the atrioventricular and the semilunar.
Indicate when in the cardiac cycle each set of valves opens and closes and explain why they
open or close at that time.
At the start of ventricular systole (contraction), the AV valves are open because atrial
pressure is higher than ventricular pressure, and the SL valves are closed because arterial
pressure is higher than ventricular pressure. As contraction begins, ventricular pressure
increases until it exceeds atrial pressure, causing the AV valves to close. Ventricular
pressure builds further (during isovolemic contraction) until it exceeds arterial pressure and
causes the SL valves to open and blood to be ejected from the ventricle. As the ventricle
enters diastole (relaxation), ventricular pressure starts to fall. When it drops below arterial
pressure (which is maintained by arterial elasticity), the SL valves close, and when it drops
below atrial pressure, the AV valves open. (Once the AV valves open, blood begins entering
the ventricles from the atria through the rest of diastole, with atrial contraction contributing
an additional volume of blood at the end of ventricular diastole.)
24. Two questions on circulation:
a. Describe the process of active hyperemia (i.e. local control of vasodilation).
Tissues with insufficient blood flow will show increased levels of CO2 and H+, and decreased
levels of O2. In response to this, endothelial cells of the arterioles in these tissues release
nitric oxide, which diffuses to adjacent smooth muscle cells of the arterioles. This paracrine
signal triggers relaxation of the smooth muscle, resulting in vasodilation and increasing
blood flow to the downstream capillaries.
b. For each of the following, indicate the route taken by the substance as it moves from
capillary blood to interstitial fluid.
Oxygen – Diffuses directly through the membranes of endothelial cells.
Na+ – Moves through pores between the endothelial cells.
Small proteins – Carried across the endothelial cells in vesicles.
Water – Moves through pores between the endothelial cells.
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25. The following questions relate to the oxygen affinity of hemoglobin.
Oxygen Saturation Curve
120
% HbO2
100
80
60
40
20
0
0
10
20
30
40
50
60
70
80
90
100
110
120
PO2
a. How low would PO2 have to drop for the hemoglobin to reach 20% saturation?
PO2 would have to reach about ~13 torr for Hb to be 20% saturated.
b. There are a few locations in the body where blood passes through two capillary beds before
returning to the heart. If a volume of blood passed through one capillary bed with PO2 = 40
torr and then passed through a second one with PO2 = 20 torr, about how much oxygen (in
terms of percent total carrying capacity) would be offloaded at the second capillary bed?
(Show your work.)
At 40 torr, Hb is about 77% saturated, so blood would leave the first capillary bed and thus
enter the second capillary bed at that saturation. At ~20 torr, Hb is about ~32% saturated,
so the amount of O2 unloaded would be the difference between these values, or ~45%.
c. Add to the graph a right-shifted oxygen saturation curve, such that the hemoglobin saturation
at PO2 = 40 torr is 65% and at PO2 = 30 torr is 40%.
See blue line on graph
d. Describe three mechanisms associated with increased muscular activity that can cause a
right-shift in the oxygen saturation curve of hemoglobin.
An increase in H+ concentration will cause a right-shift (the Bohr effect). This can be due to
both increased carbon dioxide (which increases H+ through the bicarbonate pathway) or
increased lactic acid.
Increased CO2 can cause a right-shift through non-H+-based effects on Hb (primarily the
formation of carbamino compounds with the globins).
Increases in temperature also cause a reduction in the oxygen affinity of Hb.
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