BIOL 252 Human Anatomy & Physiology II – Module 1
Exam: The Endocrine System
SECTION I: OVERVIEW OF THE ENDOCRINE SYSTEM AND HORMONE
CHEMISTRY
1. Define the endocrine system and explain its primary role in the human body.
Answer: The endocrine system is a collection of ductless glands and tissues that
synthesize and secrete chemical messengers called hormones directly into the
bloodstream. Its primary role is to maintain homeostasis by regulating growth,
development, metabolism, reproduction, electrolyte balance, and the body's response to
stress.
2. Contrast the endocrine system with the nervous system in terms of speed of
response, duration of effect, and method of communication.
Answer: The nervous system communicates via electrical impulses through neurons,
produces rapid but short-lived responses, and targets specific cells through synapses.
The endocrine system communicates via chemical hormones through the bloodstream,
produces slower but longer-lasting responses, and can affect widespread target cells
throughout the body.
3. Define the term "hormone."
Answer: A hormone is a chemical messenger produced by an endocrine gland or
specialized tissue that is secreted into the blood and travels to distant target cells where
it exerts a specific regulatory effect.
4. What is a "target cell," and what determines whether a cell will respond to a particular
hormone?
,Answer: A target cell is any cell that possesses specific receptors for a given hormone.
Only cells with the correct receptor protein will bind the hormone and respond to its
signal.
5. Name the three major chemical classifications of hormones and provide at least two
examples of each.
Answer: (a) Amino acid-based hormones, which include amines (epinephrine,
norepinephrine, thyroid hormones), peptides (ADH, oxytocin), and proteins (insulin,
growth hormone). (b) Steroid hormones, which are derived from cholesterol (cortisol,
aldosterone, estrogen, testosterone, progesterone). (c) Eicosanoids, which are derived
from arachidonic acid (prostaglandins, leukotrienes).
6. Which chemical class of hormones is lipid-soluble and can therefore cross the cell
membrane to bind intracellular receptors?
Answer: Steroid hormones and thyroid hormones.
7. Which chemical class of hormones is water-soluble and therefore cannot cross the
cell membrane, requiring cell-surface receptors?
Answer: Amino acid-based hormones (peptides, proteins, and most amines except
thyroid hormones).
8. Explain the difference between an endocrine gland and an exocrine gland, and
provide one example of each.
Answer: Endocrine glands are ductless and secrete hormones directly into the blood
(e.g., the thyroid gland). Exocrine glands secrete their products through ducts onto body
surfaces or into body cavities (e.g., sweat glands, salivary glands).
9. What is a "paracrine" signal, and how does it differ from an endocrine signal?
Answer: A paracrine signal is a chemical messenger that acts on nearby cells without
entering the bloodstream. An endocrine signal (hormone) enters the bloodstream and
travels to distant target cells.
, 10. What is an "autocrine" signal?
Answer: A chemical messenger that acts on the same cell that secreted it.
SECTION II: MECHANISMS OF HORMONE ACTION
11. Describe the mechanism of action of a water-soluble hormone acting through a
second messenger system.
Answer: The water-soluble hormone (first messenger) binds to a receptor on the target
cell's plasma membrane. This activates a G-protein, which in turn activates an
intracellular enzyme (such as adenylate cyclase). The enzyme produces a second
messenger (such as cAMP) inside the cell. The second messenger activates protein
kinases, which phosphorylate specific intracellular proteins to produce the cellular
response.
12. What enzyme converts ATP into cyclic AMP (cAMP)?
Answer: Adenylate cyclase.
13. What enzyme breaks down cAMP to terminate the hormone signal?
Answer: Phosphodiesterase (PDE).
14. Name three different second messengers used in cell signaling.
Answer: Cyclic AMP (cAMP), inositol triphosphate (IP3), and diacylglycerol (DAG).
15. Describe the mechanism of action of a lipid-soluble (steroid) hormone.
Answer: The steroid hormone diffuses across the target cell's plasma membrane and
binds to an intracellular receptor (usually in the cytoplasm or nucleus). The hormone-
receptor complex enters the nucleus (if not already there), binds to a specific DNA
response element, and directly activates or represses gene transcription. This leads to
the production of new mRNA and new proteins that produce the cellular response.
Exam: The Endocrine System
SECTION I: OVERVIEW OF THE ENDOCRINE SYSTEM AND HORMONE
CHEMISTRY
1. Define the endocrine system and explain its primary role in the human body.
Answer: The endocrine system is a collection of ductless glands and tissues that
synthesize and secrete chemical messengers called hormones directly into the
bloodstream. Its primary role is to maintain homeostasis by regulating growth,
development, metabolism, reproduction, electrolyte balance, and the body's response to
stress.
2. Contrast the endocrine system with the nervous system in terms of speed of
response, duration of effect, and method of communication.
Answer: The nervous system communicates via electrical impulses through neurons,
produces rapid but short-lived responses, and targets specific cells through synapses.
The endocrine system communicates via chemical hormones through the bloodstream,
produces slower but longer-lasting responses, and can affect widespread target cells
throughout the body.
3. Define the term "hormone."
Answer: A hormone is a chemical messenger produced by an endocrine gland or
specialized tissue that is secreted into the blood and travels to distant target cells where
it exerts a specific regulatory effect.
4. What is a "target cell," and what determines whether a cell will respond to a particular
hormone?
,Answer: A target cell is any cell that possesses specific receptors for a given hormone.
Only cells with the correct receptor protein will bind the hormone and respond to its
signal.
5. Name the three major chemical classifications of hormones and provide at least two
examples of each.
Answer: (a) Amino acid-based hormones, which include amines (epinephrine,
norepinephrine, thyroid hormones), peptides (ADH, oxytocin), and proteins (insulin,
growth hormone). (b) Steroid hormones, which are derived from cholesterol (cortisol,
aldosterone, estrogen, testosterone, progesterone). (c) Eicosanoids, which are derived
from arachidonic acid (prostaglandins, leukotrienes).
6. Which chemical class of hormones is lipid-soluble and can therefore cross the cell
membrane to bind intracellular receptors?
Answer: Steroid hormones and thyroid hormones.
7. Which chemical class of hormones is water-soluble and therefore cannot cross the
cell membrane, requiring cell-surface receptors?
Answer: Amino acid-based hormones (peptides, proteins, and most amines except
thyroid hormones).
8. Explain the difference between an endocrine gland and an exocrine gland, and
provide one example of each.
Answer: Endocrine glands are ductless and secrete hormones directly into the blood
(e.g., the thyroid gland). Exocrine glands secrete their products through ducts onto body
surfaces or into body cavities (e.g., sweat glands, salivary glands).
9. What is a "paracrine" signal, and how does it differ from an endocrine signal?
Answer: A paracrine signal is a chemical messenger that acts on nearby cells without
entering the bloodstream. An endocrine signal (hormone) enters the bloodstream and
travels to distant target cells.
, 10. What is an "autocrine" signal?
Answer: A chemical messenger that acts on the same cell that secreted it.
SECTION II: MECHANISMS OF HORMONE ACTION
11. Describe the mechanism of action of a water-soluble hormone acting through a
second messenger system.
Answer: The water-soluble hormone (first messenger) binds to a receptor on the target
cell's plasma membrane. This activates a G-protein, which in turn activates an
intracellular enzyme (such as adenylate cyclase). The enzyme produces a second
messenger (such as cAMP) inside the cell. The second messenger activates protein
kinases, which phosphorylate specific intracellular proteins to produce the cellular
response.
12. What enzyme converts ATP into cyclic AMP (cAMP)?
Answer: Adenylate cyclase.
13. What enzyme breaks down cAMP to terminate the hormone signal?
Answer: Phosphodiesterase (PDE).
14. Name three different second messengers used in cell signaling.
Answer: Cyclic AMP (cAMP), inositol triphosphate (IP3), and diacylglycerol (DAG).
15. Describe the mechanism of action of a lipid-soluble (steroid) hormone.
Answer: The steroid hormone diffuses across the target cell's plasma membrane and
binds to an intracellular receptor (usually in the cytoplasm or nucleus). The hormone-
receptor complex enters the nucleus (if not already there), binds to a specific DNA
response element, and directly activates or represses gene transcription. This leads to
the production of new mRNA and new proteins that produce the cellular response.
