37.E: The Endocrine System (Exercises)
37.1: Types of Hormones
There are three basic types of hormones: lipid-derived, amino acid-derived, and peptide. Lipid-derived hormones are structurally similar to cholesterol and include steroid hormones such as estradiol and testosterone. Amino acid-derived hormones are relatively small molecules and include the adrenal hormones epinephrine and norepinephrine. Peptide hormones are polypeptide chains or proteins and include the pituitary hormones, antidiuretic hormone (vasopressin), and oxytocin.
Review Questions
A newly discovered hormone contains four amino acids linked together. Under which chemical class would this hormone be classified?
- lipid-derived hormone
- amino acid-derived hormone
- peptide hormone
- glycoprotein
- Answer
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C
Which class of hormones can diffuse through plasma membranes?
- lipid-derived hormones
- amino acid-derived hormones
- peptide hormones
- glycoprotein hormones
- Answer
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A
Free Response
Although there are many different hormones in the human body, they can be divided into three classes based on their chemical structure. What are these classes and what is one factor that distinguishes them?
- Answer
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Although there are many different hormones in the human body, they can be divided into three classes based on their chemical structure: lipid-derived, amino acid-derived, and peptide hormones. One of the key distinguishing features of the lipid-derived hormones is that they can diffuse across plasma membranes whereas the amino acid-derived and peptide hormones cannot.
Where is insulin stored, and why would it be released?
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Secreted peptides such as insulin are stored within vesicles in the cells that synthesize them. They are then released in response to stimuli such as high blood glucose levels in the case of insulin.
37.2: How Hormones Work
Hormones cause cellular changes by binding to receptors on target cells. The number of receptors on a target cell can increase or decrease in response to hormone activity. Hormones can affect cells directly through intracellular hormone receptors or indirectly through plasma membrane hormone receptors. Lipid-derived (soluble) hormones can enter the cell by diffusing across the plasma membrane and binding to DNA to regulate gene transcription.
Review Questions
A new antagonist molecule has been discovered that binds to and blocks plasma membrane receptors. What effect will this antagonist have on testosterone, a steroid hormone?
- It will block testosterone from binding to its receptor.
- It will block testosterone from activating cAMP signaling.
- It will increase testosterone-mediated signaling.
- It will not affect testosterone-mediated signaling.
- Answer
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D
What effect will a cAMP inhibitor have on a peptide hormone-mediated signaling pathway?
- It will prevent the hormone from binding its receptor.
- It will prevent activation of a G-protein.
- It will prevent activation of adenylate cyclase.
- It will prevent activation of protein kinases.
- Answer
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D
Free Response
Name two important functions of hormone receptors.
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The number of receptors that respond to a hormone can change, resulting in increased or decreased cell sensitivity. The number of receptors can increase in response to rising hormone levels, called up-regulation, making the cell more sensitive to the hormone and allowing for more cellular activity. The number of receptors can also decrease in response to rising hormone levels, called down-regulation, leading to reduced cellular activity.
How can hormones mediate changes?
- Answer
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Depending on the location of the protein receptor on the target cell and the chemical structure of the hormone, hormones can mediate changes directly by binding to intracellular receptors and modulating gene transcription, or indirectly by binding to cell surface receptors and stimulating signaling pathways.
37.3: Regulation of Body Processes
Hormones have a wide range of effects and modulate many different body processes. The key regulatory processes that will be examined here are those affecting the excretory system, the reproductive system, metabolism, blood calcium concentrations, growth, and the stress response.
Review Questions
Drinking alcoholic beverages causes an increase in urine output. This most likely occurs because alcohol:
- inhibits ADH release
- stimulates ADH release
- inhibits TSH release
- stimulates TSH release
- Answer
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A
FSH and LH release from the anterior pituitary is stimulated by ________.
- TSH
- GnRH
- T 3
- PTH
- Answer
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B
What hormone is produced by beta cells of the pancreas?
- T 3
- glucagon
- insulin
- T 4
- Answer
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C
When blood calcium levels are low, PTH stimulates:
- excretion of calcium from the kidneys
- excretion of calcium from the intestines
- osteoblasts
- osteoclasts
- Answer
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D
Free Response
Name and describe a function of one hormone produced by the anterior pituitary and one hormone produced by the posterior pituitary.
- Answer
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In addition to producing FSH and LH, the anterior pituitary also produces the hormone prolactin (PRL) in females. Prolactin stimulates the production of milk by the mammary glands following childbirth. Prolactin levels are regulated by the hypothalamic hormones prolactin-releasing hormone (PRH) and prolactin-inhibiting hormone (PIH) which is now known to be dopamine. PRH stimulates the release of prolactin and PIH inhibits it. The posterior pituitary releases the hormone oxytocin, which stimulates contractions during childbirth. The uterine smooth muscles are not very sensitive to oxytocin until late in pregnancy when the number of oxytocin receptors in the uterus peaks. Stretching of tissues in the uterus and vagina stimulates oxytocin release in childbirth. Contractions increase in intensity as blood levels of oxytocin rise until the birth is complete.
Describe one direct action of growth hormone (GH).
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Hormonal regulation is required for the growth and replication of most cells in the body. Growth hormone (GH), produced by the anterior pituitary, accelerates the rate of protein synthesis, particularly in skeletal muscles and bones. Growth hormone has direct and indirect mechanisms of action. The direct actions of GH include: 1) stimulation of fat breakdown (lipolysis) and release into the blood by adipocytes. This results in a switch by most tissues from utilizing glucose as an energy source to utilizing fatty acids. This process is called a glucose-sparing effect. 2) In the liver, GH stimulates glycogen breakdown, which is then released into the blood as glucose. Blood glucose levels increase as most tissues are utilizing fatty acids instead of glucose for their energy needs. The GH mediated increase in blood glucose levels is called a diabetogenic effect because it is similar to the high blood glucose levels seen in diabetes mellitus.
37.4: Regulation of Hormone Production
Hormone production and release are primarily controlled by negative feedback. In negative feedback systems, a stimulus elicits the release of a substance; once the substance reaches a certain level, it sends a signal that stops further release of the substance. In this way, the concentration of hormones in blood is maintained within a narrow range.
Review Questions
A rise in blood glucose levels triggers release of insulin from the pancreas. This mechanism of hormone production is stimulated by:
- humoral stimuli
- hormonal stimuli
- neural stimuli
- negative stimuli
- Answer
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A
Which mechanism of hormonal stimulation would be affected if signaling and hormone release from the hypothalamus was blocked?
- humoral and hormonal stimuli
- hormonal and neural stimuli
- neural and humoral stimuli
- hormonal and negative stimuli
- Answer
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B
Free Response
How is hormone production and release primarily controlled?
- Answer
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Hormone production and release are primarily controlled by negative feedback. In negative feedback systems, a stimulus causes the release of a substance whose effects then inhibit further release. In this way, the concentration of hormones in blood is maintained within a narrow range. For example, the anterior pituitary signals the thyroid to release thyroid hormones. Increasing levels of these hormones in the blood then feed back to the hypothalamus and anterior pituitary to inhibit further signaling to the thyroid gland.
Compare and contrast hormonal and humoral stimuli.
- Answer
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The term humoral is derived from the term humor, which refers to bodily fluids such as blood. Humoral stimuli refer to the control of hormone release in response to changes in extracellular fluids such as blood or the ion concentration in the blood. For example, a rise in blood glucose levels triggers the pancreatic release of insulin. Insulin causes blood glucose levels to drop, which signals the pancreas to stop producing insulin in a negative feedback loop.
Hormonal stimuli refer to the release of a hormone in response to another hormone. A number of endocrine glands release hormones when stimulated by hormones released by other endocrine organs. For example, the hypothalamus produces hormones that stimulate the anterior pituitary. The anterior pituitary in turn releases hormones that regulate hormone production by other endocrine glands. For example, the anterior pituitary releases thyroid-stimulating hormone, which stimulates the thyroid gland to produce the hormones T 3 and T 4 . As blood concentrations of T 3 and T 4 rise they inhibit both the pituitary and the hypothalamus in a negative feedback loop.
37.5: Endocrine Glands
Both the endocrine and nervous systems use chemical signals to communicate and regulate the body's physiology. The endocrine system releases hormones that act on target cells to regulate development, growth, energy metabolism, reproduction, and many behaviors. The nervous system releases neurotransmitters or neurohormones that regulate neurons, muscle cells, and endocrine cells.
Review Questions
Which endocrine glands are associated with the kidneys?
- thyroid glands
- pituitary glands
- adrenal glands
- gonads
- Answer
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C
Which of the following hormones is not produced by the anterior pituitary?
- oxytocin
- growth hormone
- prolactin
- thyroid-stimulating hormone
- Answer
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A
Free Response
What does aldosterone regulate, and how is it stimulated?
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The main mineralocorticoid is aldosterone, which regulates the concentration of ions in urine, sweat, and saliva. Aldosterone release from the adrenal cortex is stimulated by a decrease in blood concentrations of sodium ions, blood volume, or blood pressure, or an increase in blood potassium levels.
The adrenal medulla contains two types of secretory cells, what are they and what are their functions?
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The adrenal medulla contains two types of secretory cells, one that produces epinephrine (adrenaline) and another that produces norepinephrine (noradrenaline). Epinephrine is the primary adrenal medulla hormone accounting for 75–80 percent of its secretions. Epinephrine and norepinephrine increase heart rate, breathing rate, cardiac muscle contractions, and blood glucose levels. They also accelerate the breakdown of glucose in skeletal muscles and stored fats in adipose tissue. The release of epinephrine and norepinephrine is stimulated by neural impulses from the sympathetic nervous system. These neural impulses originate from the hypothalamus in response to stress to prepare the body for the fight-or-flight response.