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Inquiry Questions

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Self Test

1). Which of the following best describes hormones?
    a). Hormones are relatively unstable and work only in the area adjacent to the gland that produced them.
    b). Hormones are stable, long-lasting chemicals released from glands.
    c). All hormones are lipid-soluble.
    d). Hormones are chemical messengers that are released into the environment.
Answer: b

2). The receptor for steroid hormones lies
    a). in the cytoplasm.
    b). within the plasma membrane.
    c). within the nuclear envelope.
    d). in the blood plasma.
Answer: a

3). Second messengers are activated in response to
    a). steroid hormones.
    b). thyroxine.
    c). peptide hormones
    d). all of these.
Answer: c

4). _________________ regulates the kidney's retention of water. Its secretion is suppressed by alcohol.
    a). Prolactin
    b). Oxytocin
    c). Thyroxine
    d). Vasopressin (ADH)
Answer: d

5). Which of the following hormones is not released by the anterior pituitary?
    a). melanocyte-stimulating hormone
    b). gonadotropin-releasing hormone
    c). thyroid-stimulating hormone
    d). growth hormone
Answer: b

6). ___________________ hormone stimulates the adrenal cortex to produce several of its hormones.
    a). Follicle-stimulating
    b). Luteinizing
    c). Adrenocorticotropic
    d). Growth
Answer: c

7). Parathyroid hormone acts to ensure that
    a). calcium levels in the blood never drop too low.
    b). sodium levels in urine are constant.
    c). potassium levels in the blood don't escalate.
    d). the concentration of water in the blood is sufficient.
Answer: a

8). The adrenal cortex releases ________________, which stimulates Na+ reabsorption by the kidneys.
    a). epinephrine
    b). aldosterone
    c). glucose
    d). cortisol
Answer: b

9). Individuals with type I diabetes
    a). lack ß cells in the islets of Langerhans.
    b). produce enough insulin but lack functional receptors on their cells.
    c). can control their diabetes with diet and exercise.
    d). All of these are correct.
Answer: a

10). The hormone melatonin, which is involved in skin blanching in lower vertebrates, is released from the
    a). anterior pituitary gland.
    b). melanocytes.
    c). pineal gland.
    d). suprachiasmatic nucleus of the hypothalamus.
Answer: c

Test Your Visual Understanding

1). A goiter results when the thyroid gland becomes enlarged. The figure above shows the regulation of thyroxine secretion, with the different steps in the process numbered. Indicate which numbered step or steps are disrupted in the process that leads to the formation of a goiter, and explain why this happens and what results.
Answer: The appearance of a goiter is the result of overstimulation of the thyroid gland, which causes it to continually grow. There are two different steps in the regulation pathway that can lead to overstimulation: the inhibition of steps 6 or 7. Under normal conditions, the production of thyroxine has a negative effect on further stimulation of the thyroid gland. This is called negative feedback inhibition. When the production of thyroxine is interrupted, the hypothalamus will stimulate the anterior pituitary gland, which in turn stimulates the thyroid gland to produce more thyroxine. When enough thyroxine is produced, the negative feedback inhibition steps are followed. If thyroxine is not produced, there is no negative feedback, no shutting down of the pathway. Therefore, the hypothalamus and the anterior pituitary continue to stimulate the thyroid. Eventually, the thyroid becomes enlarged, resulting in a goiter.
Applying Your Knowledge

1). The adrenal medulla secretes epinephrine in response to stimulation from the sympathetic division of the autonomic nervous system. Epinephrine triggers the fight or flight response in the body, which causes an increase in the heart rate. In a person at rest, the heart beats about 72 beats per minute and moves about 70 ml of blood per beat. Epinephrine causes the heart rate to double and the volume per beat to triple.
    a). How much blood is moved per minute in a resting heart and in a hormone-stimulated heart?
    b). As a percentage, how much more blood is moved by a hormone-stimulated heart compared to a resting heart?
Answer:
    1a). In a resting heart: 72 beats/min x 70 ml/beat = 5,040 ml/min or 5.04 liters/min
In a stimulated heart: 144 beats/min x 210 ml/beat = 30,240 ml/min or 30.24 liters/min
    1b). As a percentage the stimulated heart pumps 500% more blood:
(30.24 - 5.04) / 5.04 = 5.0 or 500%

2). Suppose that two different organs, such as the liver and heart, are sensitive to a particular hormone (such as epinephrine). The cells in both organs have identical receptors for the hormone, and hormone-receptor binding produces the same intracellular second messenger in both organs. However, the hormone produces different effects in the two organs. Explain how this can happen.
Answer: The same hormone can affect two different organs in different ways because the second messengers triggered by the hormone, have different targets inside the cell because the cells have different functions. Epinephrine affects the cells of the heart by increasing metabolism so that their contractions are faster and stronger. However, liver cells do not contract and so the second messenger in liver cells triggers the conversion of glycogen into glucose. That is why hormones are so valuable but also economical to the body. One hormone can be produced, one receptor can be made, and one second messenger system can be used, but there can be two different targets inside the cell.

3). Many physiological parameters, such as blood Ca++ concentration and blood glucose levels, are controlled by two hormones that have opposite effects. What is the advantage of achieving regulation in this manner instead of by using a single hormone that changes the parameters in one direction only?
Answer: Hormones such as thyroxine, whose effects are slower and have a broader range of activity, a negative feedback system using one hormone adequately controls the system. However, for certain parameters that have a very narrow range and change constantly within that range, a regulatory system that uses "up" and "down" regulation is desirable. Too much or too little Ca++ or glucose in the blood can have devastating effects on the body and so those levels must be controlled within a very narrow range. To rely on negative feedback loops would restrict the quick "on" and "off" responses needed to keep the parameters in a very narrow range.







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