Download Answers to Mastering Concepts Questions

Answers to Mastering Concepts Questions
25.1
1. What is the overall function of an endocrine system?
The endocrine system is a communication system in an animal’s body.
2. Describe the relationships among endocrine glands, hormones, and target cells.
Endocrine glands are the organs responsible for producing and secreting hormones,
which are the biochemicals that travel through the blood. Target cells have receptors for
the hormone and respond when exposed to the hormone.
25.2
1. Describe the actions of water- and lipid-soluble hormones.
The water-soluble hormones interact with receptors on the cell membrane, whereas lipidsoluble hormones bind to receptors within the cytoplasm or nucleus of the target cells.
2. Why do water-soluble hormones usually act faster than lipid-soluble hormones.
Water-soluble hormones usually act faster than lipid-soluble hormones because they
activate chemical cascades within the cell. In contrast, lipid-soluble hormones cross cell
membranes. The hormone may enter the nucleus and bind to a receptor on DNA, or it
may bind to a receptor in the cytoplasm before traveling to the nucleus to interact with
DNA. Either way, the hormone triggers the production of proteins, which takes more
time than just triggering the activation of chemicals that are already present within the
cytoplasm.
25.3
1. How does the hypothalamus interact with the posterior and anterior pituitary glands?
The hypothalamus controls secretions from the pituitary gland. Releasing hormones from
the hypothalamus stimulate the secretion of anterior pituitary hormones, and inhibiting
hormones from the hypothalamus inhibit the secretion of anterior pituitary hormones. In
addition, the hypothalamus secretes hormones that are then stored in the posterior
pituitary.
2. List the names and functions of the hormones released by the posterior and anterior
pituitary glands.
The posterior pituitary releases oxytocin, which stimulates smooth muscle contraction in
the uterus and mammary glands. The posterior pituitary also releases ADH, which
promotes water conservation in the kidney. The anterior pituitary secretes GH to
stimulate tissue growth, prolactin to stimulate milk production, TSH to stimulate the
release of thyroid hormones, ACTH to stimulate the release of glucocorticoid hormones
from the adrenal cortex, FSH and LH to stimulate sex hormone release, and endorphins to
act as pain killers at receptors in the brain.
25.4
1. What are the three hormones produced in the thyroid, and what are their functions?
Thyroid hormones include:
- thyroxine: increases the rate of metabolism in cells
- triiodothyronine: increases the rate of metabolism in cells
- calcitonin: increases the rate at which calcium is deposited in bone
2. What is the function of parathyroid hormone (PTH)?
PTH increases calcium levels in blood and tissue fluid by increasing calcium release from
bones, and by increasing calcium absorption into the blood from the digestive tract and
kidneys.
3. How do the functions of hormones secreted by the adrenal cortex and adrenal medulla
differ?
Hormones secreted by the adrenal cortex (glucocorticoids and mineralocorticoids)
suppress the immune system, are important in the body’s response to prolonged stress,
and maintain blood volume and salt balance. Hormones secreted by the adrenal medulla
(epinephrine and norepinephrine) are important in the body’s response to short-term
stress. They increase the heart rate, breathing rate, blood flow, and blood glucose, and
shunt blood toward the brain and muscles.
4. Describe the opposing roles of insulin and glucagon.
Insulin removes glucose from the bloodstream by stimulating cells to absorb it. Glucagon
stimulates liver cells to release glucose into the bloodstream.
5. How do darkness and light affect melatonin secretion?
Darkness stimulates melatonin production in the pineal gland, whereas light inhibits
melatonin synthesis.
25.5
1. Which organs contain target cells for FSH and LH?
The testes and the ovaries contain receptors for FSH and LH.
2. What are the functions of estrogen, progesterone, and testosterone?
Estrogen regulates the menstrual cycle and promotes the development of female
secondary sex characteristics. Progesterone regulates the menstrual cycle and maintains a
pregnancy. Testosterone maintains male secondary sex characteristics and promotes
sperm development.
25.6
1. How did the researchers test the hypothesis that the number of ADH receptors in the
brain’s reward area influences pair-bonding?
The researchers inserted ADH receptor genes into the reward area of the brains of male
voles. Control voles had a different gene injected into the same area, or ADH receptor
genes injected into a different area of the brain. All of the voles spent time with females,
but they did not mate. The males were then subjected to partner preference tests. The
males that had more ADH receptors spent more time with their partner than males with
fewer ADH receptors.
2. Could the researchers have drawn the same conclusions if they had omitted one of the
control groups? Why or why not?
No. If they had not included both controls, they would not have been able to determine
whether the main factor influencing pair-bonding was the stimulation of the reward area
of the brain or the addition of ADH receptors.
Answers to Write It Out Questions
1. How does the endocrine system interact with the circulatory system?
The endocrine system interacts with the circulatory system by releasing hormones into
the bloodstream.
2. A queen honeybee secretes a substance from a gland in her mouthparts that inhibits the
development of ovaries in worker bees. Is this substance most likely a hormone, a
neurotransmitter, or a pheromone (see chapter 24)? Cite a reason for your answer.
The chemical would most likely be a pheromone, which is a communication molecule
that transmits signals to other individuals. Hormones and neurotransmitters are
communication molecules that act within the body of a single organism.
3. What prevents a hormone from affecting all body cells equally?
A hormone exerts a physiological effect only on target cells that have specific receptors
for the hormone.
4. Many dairy operators inject their cows with bovine growth hormone to stimulate milk
production. Cite two reasons that bovine growth hormone might not stimulate growth in
people drinking the milk.
Bovine growth hormone would probably not interact with receptors on target cells in
humans, because bovine growth hormone probably has a slightly different shape than
human growth hormone. In addition, bovine growth hormone in milk could be destroyed
in a person’s digestive system and never enter the bloodstream.
5. How do hormones regulate their own levels?
Negative feedback loops ensure that the levels of a hormone in the bloodstream are not
too high or too low.
6. Compare and contrast the endocrine and nervous systems.
The nervous and endocrine systems both interact to maintain homeostasis, and both rely
on chemicals for communication (i.e. neurotransmitters and hormones). The nervous
system acts faster and more locally than the endocrine system.
7. Sketch the mechanisms of water-soluble and lipid-soluble hormone function.
[Answer will be visual. Refer to figure 25.2.]
8. List the hormones released from the posterior pituitary and the anterior pituitary.
The posterior pituitary releases antidiuretic hormone (ADH) and oxytocin. The anterior
pituitary gland releases growth hormone, prolactin, follicle-stimulating hormone (FSH),
luteinizing hormone (LH), thyroid-stimulating hormone (TSH), and adrenocorticotropic
hormone (ACTH).
9. How are the pituitary and adrenal glands each really two glands in one?
The pituitary gland has both an anterior and posterior portion, each with different
functions and made of different types of tissue. The adrenal gland has a medulla that
secretes different hormones from the adrenal cortex.
10. Which hormone(s) match each of the following descriptions?
a. Produced by a woman who is breast feeding
b. Causes fatigue if too little is present
c. Causes increase in blood calcium level
d. Causes decrease in blood glucose level
e. Synthetic steroids mimic the muscle-building effects of this hormone
(a) prolactin; (b) insulin and thyroxine (metabolism is affected); (c) parathyroid hormone
(PTH); (d) insulin; (e) testosterone
11. Describe how thyroxine, triiodothyronine, TSH, and TRH interact.
When levels of thyroxine and triiodothyronine are low, the hypothalamus releases TRH,
which stimulates cells in the anterior pituitary gland to secrete TSH. TSH travels in the
bloodstream and stimulates cells in the thyroid gland to produce and secrete thyroxine
and triiodothyronine.
12. Ancient Egyptian doctors treated goiters with seaweed, not realizing that it was the
iodine in the seaweed that was reversing the condition. Why would iodine help cure a
goiter?
Iodine is needed by the thyroid to produce the thyroid hormones. Low iodine is the cause
of the swollen thyroid gland.
13. Why would a physician counsel a patient with high blood pressure to try to reduce the
amount of stress in his or her life?
In response to stress, the adrenal medulla releases epinephrine and norepinephrine, both
of which elevate blood pressure and heart rate. Also, the adrenal cortex releases
glucocorticoids in response to long-term stress. Glucocorticoids, such as cortisol,
constrict blood vessels, increasing blood pressure.
14. Sleep deprivation increases cortisol concentrations in the blood. Why would sleep
deprivation be associated with increased risk of illness?
Secretion of the steroid hormone cortisol suppresses the immune system.
15. Consult chapter 24 and this chapter to create a chart comparing hormones with
neurotransmitters. Include the distance over which each is active, the connection between
the cell releasing signals and the receiving cell, the response speed, and the duration of
the response.
Characteristic
Distance
Connection between
releasing and receiving cell
Response speed
Duration of response
Neurotransmitter
The synaptic cleft
A synapse
Hormone
Throughout the body
Bloodstream
Fractions of a second
Fractions of a second
Minutes, hours, or days
Prolonged
16. In healthy adults, the concentration of glucose in blood is approximately 80 to 110
milligrams per deciliter (mg/dl). After a carbohydrate-rich meal, however, the
concentration may spike to 140 mg/dl.
a. Describe the hormonal action that returns blood glucose to normal.
b. What is the name for the condition in which the glucose concentration drops
below 70 mg/dl?
c. What is the name for the condition in which the glucose concentration before a
meal is 130 mg/dl or higher?
(a) After a meal, blood glucose levels rise, stimulating the release of insulin from the
pancreas. The insulin signals body cells to absorb the glucose, lowering the blood glucose
levels and ending the release of insulin. (b) Blood glucose levels below 70 mg/dl are
referred to as hypoglycemia. (c) Blood glucose levels above 130 mg/dl are referred to as
hyperglycemia.
17. Search the Internet for a diabetes risk test. What actions can you take to reduce your
risk of type 2 diabetes?
The two main actions you can take to prevent type 2 diabetes are eating healthy and
increasing exercise, both of which promote weight loss.
18. How might insulin-producing stem cells transplanted to the pancreas help people with
type 1 diabetes? Would the same treatment help people with type 2 diabetes?
In type 1 diabetes, cells in the pancreas do not produce insulin when stimulated. The
insulin-producing stem cells would correct this disorder. In type 2 diabetes, however,
beta cells produce insulin, but the body’s cells do not respond to it. The stem cell
treatment would not help in this case.
19. Identify the target cells and effects of FSH, LH, estrogen, progesterone, and
testosterone.
FSH targets cells in the ovaries and testes to stimulate sperm and egg production. LH
targets cells in the ovaries and testes to produce the sex hormones. Estrogen targets the
uterus and brain to regulate menstruation and secondary sex characteristics. Progesterone
targets the uterus to prepare for pregnancy and to regulate menstruation. Testosterone
targets cells in the embryo to stimulate male development. Testosterone also targets cells
in the body, maintaining secondary sex characteristics and sperm production in males.
20. An endocrine disruptor is a molecule that either mimics or blocks the activity of a
hormone. Propose a way to test the hypothesis that:
a. a pesticide such as atrazine is an endocrine disruptor.
b. endocrine disruptors have caused declines in human sperm counts.
c. microwaving foods in plastic containers releases chemicals that act as endocrine
disruptors.
[Answers will vary, but each experiment should include a treatment group, a control
group, and standardized variables.]
Answers to Pull It Together Questions
1. Describe a negative feedback loop that controls hormone secretion.
Thyroid hormones are regulated by a negative feedback loop. When the hypothalamus
detects low concentrations of thyroid hormone, it increases secretion of thyroid releasing
hormone (TRH). When the anterior pituitary detects TRH, it increases secretion of
thyroid stimulating hormone (TSH), which increases the release of hormones from the
thyroid gland. If the concentration of thyroid hormone becomes too high, the
hypothalamus decreases secretion of TRH, which decreases the anterior pituitary’s
secretion of TSH. In turn, TSH decreases the release of hormones from the thyroid gland.
2. What brain structure connects the endocrine and nervous systems?
The hypothalamus is part of the forebrain. It is intimately connected with the pituitary
gland, which connects the brain with the endocrine system.
3. Describe the relationships among the hypothalamus, pituitary, and other endocrine
glands.
The hypothalamus receives signals from the bloodstream and the brain. It sends neural
and hormonal signals to the pituitary gland, which is just below the hypothalamus. The
pituitary gland relays regulatory signals to other endocrine glands, including the
pancreas, adrenal gland, thyroid gland, pineal gland, and testes or ovaries. These glands
respond to signals from the hypothalamus and pituitary, releasing their own hormones.