Download Answers to Mastering Concepts Questions

Answers to Mastering Concepts Questions
Chapter 30
30.1
1. The endocrine system is a communication system in an animal’s body.
2. The endocrine and nervous systems differ in the rate of communication. Neural communication
is practically instantaneous, while endocrine communication is much slower and longer-lasting.
3. In a negative feedback loop, the buildup of the product of a process causes its own production
to slow or stop. In a positive feedback loop, the buildup of the product causes its own production
to increase. Positive feedback loops are self reinforcing.
4. Hormones are different from neurotransmitters in that hormones circulate throughout the body
rather than being secreted only into the gap between two cell membranes. Hormones are
different from paracrine secretions in that hormones affect target cells at sites that are distant
from where they are produced. Also, hormones travel in the bloodstream. Pheromones are
communication molecules, similar to hormones, but their target cells are within the body of
another individual instead of within the body of the organism that produces them.
30.2
1. A hormone will only affect certain target cells that have receptors for them.
2. The role of second messengers is to act within the cell to activate the enzymes that produce
the hormone’s effects.
3. Peptide hormones usually act faster than steroid hormones because they activate chemical
cascades within the cell. In contrast, steroid hormones cross cell membranes and may enter the
nucleus and bind to a receptor on DNA. This will trigger the production of proteins. Or the steroid
may bind to a receptor in the cytoplasm and the combination travels to the nucleus to interact with
DNA. Either process takes more time than just triggering the activation of chemicals that are
present within the cytoplasm in inactive forms.
30.3
1. The hypothalamus controls secretions from the pituitary gland. Releasing hormones from the
hypothalamus stimulate the secretion of 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. Tropic hormones released by the pituitary include FSH, LH, TSH, and ACTH.
3. ADH helps maintain the composition of body fluids. Oxytocin stimulates smooth muscle
contraction and has a role in affection, bonding, and social recognition in both sexes. Both ADH
and oxytocin are produced by the hypothalamus and stored in the posterior pituitary.
4. The hormones produced by the anterior pituitary and their functions are:
- GH: stimulates production of growth factors that promote growth of tissues throughout the body
- prolactin: stimulates milk secretion
- FSH: in females stimulates follicle development, oocyte maturation, and release of estrogen; in
males stimulates sperm production
- LH: in females promotes ovulation and secretion of progesterone; in males stimulates secretion
of testosterone
- TSH: stimulates the secretion of thyroid hormones
- ACTH: stimulates the secretion of glucocorticoids from the adrenal cortex and secretion of
insulin from the pancreas
30.4
1. 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. PTH increases calcium levels in blood and tissue fluid by causing more calcium to be absorbed
by the digestive tract and kidneys.
3. Hormones secreted by the adrenal cortex (glucocorticoids and mineralcorticoids) 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. Both insulin and glucagon affect the level of glucose in the blood, but they have opposite
effects. Insulin removes glucose from the bloodstream by stimulating cells to absorb it. Glucagon
stimulates liver cells to release glucose into the bloodstream.
5. Darkness stimulates melatonin production, whereas light inhibits melatonin synthesis in the
pineal gland.
30.5
1. In both sexes, GnRH stimulates the anterior pituitary to release FSH and LH into the
bloodstream. In males, these hormones arrive at the testes, where FSH stimulates the early
stages of sperm formation and LH completes the process and stimulates cells to make
testosterone. In females, when FSH and LH arrive at the ovaries, they stimulate oocyte
maturation and division, growth of ovarian follicles, and ovulation.
2. Estrogen promotes the development of female secondary sex characteristics and inhibits
secretion of GnRH from the hypothalamus. Progesterone maintains a pregnancy. It also inhibits
secretion of GnRH from the hypothalamus, which inhibits the production of LH and FSH.
Testosterone produces male secondary sex characteristics and inhibits the production of LH and
FSH.