,Part I: Foundational Physiologic Unit VII: Hematologic and Lymphatic System
Concepts Chapter 22: Review of Hematologic System
Development, Structure, and Function
Unit I: The Cell Chapter 23: Hematologic and Lymphatic System
Disorders
Chapter 1: Cellular Biology, Regulation, and Control
Mechanisms Unit VIII: Nervous System
Chapter 2: Cellular and Tissue Physiology
Chapter 3: Bioenergetics and Body Metabolism
Chapter 24: Review of Nervous System Development,
Chapter 4: Body Fluid Homeostasis
Structure, and Function
Chapter 25: Central Nervous System Disorders
Unit II: Genetics and Genomics Chapter 26: Peripheral Nervous System Disorders
Chapter 27: Disorders of the Special Senses
Chapter 5: Basic Genetics Chapter 28: Mental Health Disorders
Chapter 6: Patterns of Inheritance, Mitochondrial
Inheritance, Epigenetics, and Selected Associated Unit IX: Musculoskeletal System
Disorders
Chapter 29: Review of Musculoskeletal Development,
Unit III: Inflammation, Immunity, Infection, and Structure, and Function
Cancer Biology Chapter 30: Muscle and Tendon Disorders
Chapter 31: Bone and Joint Disorders
Chapter 7: Innate Immunity and Inflammation
Chapter 8: Adaptive Immunity Unit X: Endocrine System
Chapter 9: Infectious Processes and Body Responses
Chapter 10: Abnormal Cell Growth and Cancer Biology Chapter 32: Review of Endocrine Structure, Function,
and Interactions
Part II: Pathophysiology of Disorders Chapter 33: Disorders of the Hypothalamus, Pituitary
Glands, and Adrenal Glands
Within Specific Body Systems Chapter 34: Disorders of the Thyroid Gland and the
Parathyroid Glands
Unit IV: Cardiovascular System Chapter 35: Glycemic Control and Diabetes Mellitus
Chapter 11: Review of Cardiovascular Development, Unit XI: Disorders of Immunity
Structure, and Function
Chapter 12: Vascular Disorders Chapter 36: Disorders of Reduced Immune Function
Chapter 13: Cardiac Disorders Chapter 37: Hypersensitivity and Autoimmune Disorders
Chapter 14: Congenital Heart Disease Across the Lifespan
Chapter 15: Shock and Multiple Organ Dysfunction
Syndrome Unit XII: Integumentary System
Chapter 38: Review of Integumentary Development,
Unit V: Pulmonary System
Structure, and Function
Chapter 39: Integumentary System Disorders
Chapter 16: Review of Pulmonary Structure,
Development, and Function
Chapter 17: Congenital, Obstructive, and Restrictive Unit XIII: Digestive System
Pulmonary Disorders
Chapter 18: Infectious Pulmonary Disorders and Lung Chapter 40: Review of Gastrointestinal Development,
Cancer Structure, and Function
Chapter 41: Disorders of the Mouth, Throat, Esophagus,
and Stomach
Unit VI: Renal-Urinary System
Chapter 42: Disorders of the Small Intestine, Large
Intestine, Pancreas, and Hepatobiliary System
Chapter 19: Review of Renal System Structure,
Development, and Function
Chapter 20: Urinary Tract Disorders Unit XIV: Reproductive Systems
Chapter 21: Kidney Disorders
,Chapter 43: Review of Reproductive System
Development, Structure, Function, and Sex Chromosome
Abnormalities Chapter 46: Sexually Transmitted Infections
Chapter 44: Common Disorders of the Female Chapter 47: Physiology and Pathophysiology of the
Reproductive System Breast
Chapter 45: Male Reproductive Disorders
,UNIT I: THE CELL
CHAPTER 1: Cellular Biology, Regulation, and Control Mechanisms
Section 1: Foundational Structure, Function, and Homeostatic Regulation
1. Which cellular mechanism primary functions to maintain a negative resting membrane
potential in excitable tissues under basal conditions?
A. Active transport of sodium out of the cell and potassium into the cell via Na+/K+-ATPase
B. Passive efflux of potassium through non-gated leak channels
C. Rapid influx of calcium through voltage-gated ion channels
D. Facilitated diffusion of chloride ions down an electrochemical gradient
Answer: A
Rationale: The Na+/K+-ATPase pump actively moves 3 sodium ions out of the cell for every 2
potassium ions brought into the cell against their respective concentration gradients using ATP
hydrolysis. This electrogenic transport mechanism maintains the intracellular negative charge
and resting membrane potential necessary for excitable tissue function.
2. A patient experiencing acute intracellular acidosis undergoes a shift in cellular membrane
transport dynamics. Which transport process relies directly on the sodium concentration
gradient established by primary active transport to move hydrogen ions out of the cell?
A. Receptor-mediated endocytosis
B. Simple diffusion
C. Secondary active transport
D. Primary active transport
Answer: C
Rationale: Secondary active transport (specifically antiporters or exchangers such as the
Na+/H+ exchanger) uses the potential energy stored in the electrochemical gradient of
sodium—which is generated by the primary active Na+/K+-ATPase pump—to drive hydrogen
ions out of the cell against their concentration gradient.
,3. What is the primary functional significance of epithelial cell polarity achieved through apical
and basolateral membrane domain specialization?
A. Facilitation of multidirectional bulk movement of intracellular organelles
B. Vectorial transport of solutes and fluid across tissue barriers
C. Enhanced structural elasticity during mechanical tissue deformation
D. Unrestricted lateral diffusion of membrane-bound signal receptors
Answer: B
Rationale: Epithelial cell polarity establishes distinct apical and basolateral plasma membrane
domains separated by tight junctions. This spatial segregation of specific channels, transporters,
and enzymes allows epithelial sheets to perform directional (vectorial) transport of ions,
nutrients, and water between external environments and internal compartments.
4. Which cellular process is specifically responsible for degrading damaged organelles and long-
lived proteins to maintain intracellular metabolic homeostasis during periods of nutrient
deprivation?
A. Autophagy
B. Phagocytosis
C. Exocytosis
D. Pinocytosis
Answer: A
Rationale: Autophagy is a lysosomal degradation pathway wherein the cell sequesters its own
damaged organelles, protein aggregates, and cytoplasmic components into double-membrane
vesicles (autophagosomes) that fuse with lysosomes. This process cleanses cellular debris and
recycles amino acids and energy during metabolic stress, distinguishing it from phagocytosis,
which targets extracellular pathogens and foreign debris.
Section 2: Membrane Physiology, Signaling, and Receptor Mechanics
5. A patient receiving chronic high-dose beta-1 adrenergic agonist therapy for heart failure
exhibits a progressive decline in therapeutic responsiveness. Which receptor-level adaptation
accounts for this phenomenon?
,A. Increased receptor affinity resulting from conformational stabilization
B. Receptor upregulation driven by increased transcription factor activity
C. Homologous desensitization and endocytic receptor downregulation
D. Enhanced coupling efficiency between the receptor and G-protein subunits
Answer: C
Rationale: Continuous or excessive exposure to an agonist induces receptor phosphorylation by
G-protein-coupled receptor kinases (GRKs), leading to arrestin binding, functional uncoupling
from G-proteins (desensitization), and subsequent endocytosis (downregulation) of the receptor.
This reduces the density of functional surface receptors, causing pharmacologic tolerance.
6. During the depolarization phase of an action potential in a nerve axon, which channel event
directly drives the rapid reversal of membrane potential toward positive values?
A. Closing of inactivation gates on voltage-gated Na+ channels
B. Efflux of potassium through voltage-gated K+ channels
C. Influx of chloride through ligand-gated Cl- channels
D. Opening of activation gates on voltage-gated Na+ channels
Answer: D
Rationale: When the threshold potential is reached, voltage-gated sodium channels open their
activation gates rapidly, causing a massive influx of sodium ions down both an electrical and
chemical gradient. This inward positive current causes the rapid depolarization overshoot
toward positive potential values.
7. Which structural component of the extracellular matrix (ECM) provides tensile strength to
tissues and prevents mechanical tearing under physical stretch?
A. Proteoglycans
B. Fibronectin
C. Collagen fibers
D. Elastin fibers
Answer: C
,Rationale: Collagen forms triple-helical protein fibers that exhibit high tensile strength,
protecting tissues against mechanical disruption under stretch. Proteoglycans provide
compressive resistance, while elastin imparts recoil capacity.
8. Which cell-adhesion system is anchored internally to intermediate filaments and provides
strong intercellular mechanical adhesion in tissues subjected to severe physical stress, such as
the myocardium?
A. Gap junctions
B. Tight junctions
C. Adherens junctions
D. Desmosomes
Answer: D
Rationale: Desmosomes (maculae adherentes) connect adjacent cells via cadherin family
proteins and are anchored intracellularly to keratin or desmin intermediate filaments. This
complex distributes mechanical force across cell sheets, preventing cell separation under
structural stress in tissues like the skin and cardiac muscle.
Section 3: Etiology, Pathophysiology, and Clinical Correlation
9. An APRN evaluates a patient with suspected cell-adhesion pathway failure causing mucosal
blistering. Pathophysiologically, the loss of hemidesmosomal integrity results in which structural
impairment?
A. Disruption of direct electrical coupling between adjacent cells
B. Breakdown of the paracellular barrier to macromolecular diffusion
C. Dissolution of the actin cytoskeleton within epithelial apical borders
D. Detachment of epithelial basal cells from the underlying basement membrane
Answer: D
Rationale: Hemidesmosomes anchor the basal surface of epithelial cells to the extracellular
matrix of the underlying basement membrane (via integrins). Loss or autoimmune destruction of
hemidesmosomal components disrupts this cell-matrix junction, causing the epithelium to peel
away from the basement membrane and form subepithelial blisters.
,10. Which systemic response demonstrates a positive feedback control loop operating in human
physiology?
A. Maintenance of core body temperature via shivering thermogenesis
B. Generation of the luteinizing hormone (LH) surge prior to ovulation
C. Control of plasma glucose concentration through insulin secretion
D. Regulation of arterial blood pressure via the carotid baroreceptor reflex
Answer: B
Rationale: The pre-ovulatory LH surge operates via positive feedback: rising estrogen levels
produced by the developing follicle signal the hypothalamus and pituitary to release increased
amounts of GnRH and LH, which in turn stimulates further estrogen release until ovulation
occurs. Baroreceptor, insulin, and thermoregulatory systems operate via negative feedback to
maintain stability.
11. A patient presenting with muscle weakness and cardiac dysrhythmias is found to have
severe hyperkalemia. Mechanistically, how does an elevated extracellular potassium
concentration alter neuronal excitable membrane dynamics?
A. It increases the magnitude of the driving force for outward potassium current during resting
conditions.
B. It depolarizes the resting membrane potential, bringing it closer to threshold and initially
increasing excitability followed by inactivation of sodium channels.
C. It blocks voltage-gated potassium channels, preventing repolarization completely.
D. It hyperpolarizes the resting membrane potential, driving it further from threshold.
Answer: B
Rationale: Elevating extracellular potassium concentration decreases the chemical gradient
across the cell membrane, reducing potassium efflux and shifting the resting membrane
potential toward a less negative (depolarized) state. While this initially brings the cell closer to
firing threshold, persistent depolarization keeps voltage-gated sodium channels in an
inactivated state, ultimately impairing action potential propagation and driving muscle weakness
and conduction block.
12. How does chronic exposure to an antagonist affect target cell receptor populations over
time?
,A. Receptor upregulation occurs, increasing target cell sensitivity to endogenous ligands upon
antagonist withdrawal.
B. Internalization and lysosomal degradation of receptors increase.
C. Receptor binding affinity permanently decreases due to conformational decay.
D. Receptor downregulation occurs to prevent overstimulation.
Answer: A
Rationale: Blockade of cell-surface receptors by a chronic antagonist deprives the cell of normal
ligand signaling. In response, the cell transcribes and inserts additional receptors into the
membrane (upregulation). When the antagonist is abruptly withdrawn, the increased receptor
density makes the cell hypersensitive to endogenous ligands.
Section 4: Process Sequences, Diagnostics, Matrix Correlations, and Calculations
13. [Ordered Response] Sequence the molecular events involved in G-protein-coupled
receptor (GPCR) activation and signaling from ligand binding to second-messenger initiation.
1. Dissociation of the G-alpha subunit from the G-beta/gamma complex
2. Binding of an extracellular signaling ligand to the GPCR
3. Activation of effector enzymes (e.g., adenylyl cyclase) to generate second messengers
4. Conformational shift causing GDP-to-GTP exchange on the G-alpha subunit
Answer: 2, 4, 1, 3
Rationale: Ligand binding (2) induces a conformational change in the GPCR that promotes
exchange of bound GDP for GTP on the heterotrimeric G-alpha subunit (4). GTP binding triggers
dissociation of the G-alpha subunit from the G-beta/gamma complex (1). The GTP-bound G-
alpha subunit then interacts with downstream effector enzymes like adenylyl cyclase or
phospholipase C to generate second messengers (3).
14. [Ordered Response] Sequence the phases of a cardiac action potential in ventricular
myocytes starting from resting membrane state through repolarization completion.
1. Rapid influx of sodium causing sharp depolarization (Phase 0)
2. Inward calcium current balancing outward potassium current to form a plateau (Phase 2)
3. Resting membrane potential maintained by potassium leak and ion pumps (Phase 4)
4. Transient early repolarization driven by inactivation of sodium channels and brief
potassium efflux (Phase 1)
5. Rapid repolarization mediated by sustained outward potassium efflux (Phase 3)
, Answer: 3, 1, 4, 2, 5
Rationale: The resting state is Phase 4 (3). Phase 0 (1) is rapid depolarization driven by voltage-
gated sodium channels. Phase 1 (4) is brief early repolarization. Phase 2 (2) represents the
plateau phase where inward calcium current balances outward potassium movement. Phase 3
(5) is rapid repolarization driven by delayed rectifier potassium channels until Phase 4 is
restored.
15. [Calculation / Fill-in-the-Blank] Calculate the approximate equilibrium potential (in mV) for
potassium (E(K+)) across a neuronal membrane at 37°C using the simplified Nernst equation:
E(K+) = -61 × log10([K+](in)/[K+](out))
Given an intracellular potassium concentration [K+](in) = 140 mEq/L and an extracellular potassium
concentration [K+](out) = 4.0 mEq/L. Round to the nearest whole number.
Answer: -94 mV
Rationale: [K+](in) / [K+](out) = .0 = 35. The log10(35) ≈ 1.544. Multiplying -61 × 1.544 = -94.18
mV, which rounds to -94 mV. This negative value represents the electrical gradient needed to balance the
outward chemical concentration gradient of potassium.
16. [Fill-in-the-Blank] What specific enzyme deficiency serves as the primary pathophysiologic
cause of Gaucher disease, leading to the accumulation of glucocerebroside within tissue
macrophages?
Answer: Glucocerebrosidase
Rationale: Gaucher disease is an autosomal recessive lysosomal storage disorder caused by
mutations in the GBA1 gene resulting in deficiency of the lysosomal enzyme beta-
glucocerebrosidase (glucosylceramidase). Without this enzyme, lipid substrates accumulate
within lysosomes of monocytes and macrophages (Gaucher cells).
17. [Matching / Matrix] Match the membrane transport mechanism with its defining functional
characteristic.
Transport
Primary Functional Characteristic
Mechanism
A. Requires ATP hydrolysis directly to transport solutes against an
1. Simple Diffusion
electrochemical gradient
Concepts Chapter 22: Review of Hematologic System
Development, Structure, and Function
Unit I: The Cell Chapter 23: Hematologic and Lymphatic System
Disorders
Chapter 1: Cellular Biology, Regulation, and Control
Mechanisms Unit VIII: Nervous System
Chapter 2: Cellular and Tissue Physiology
Chapter 3: Bioenergetics and Body Metabolism
Chapter 24: Review of Nervous System Development,
Chapter 4: Body Fluid Homeostasis
Structure, and Function
Chapter 25: Central Nervous System Disorders
Unit II: Genetics and Genomics Chapter 26: Peripheral Nervous System Disorders
Chapter 27: Disorders of the Special Senses
Chapter 5: Basic Genetics Chapter 28: Mental Health Disorders
Chapter 6: Patterns of Inheritance, Mitochondrial
Inheritance, Epigenetics, and Selected Associated Unit IX: Musculoskeletal System
Disorders
Chapter 29: Review of Musculoskeletal Development,
Unit III: Inflammation, Immunity, Infection, and Structure, and Function
Cancer Biology Chapter 30: Muscle and Tendon Disorders
Chapter 31: Bone and Joint Disorders
Chapter 7: Innate Immunity and Inflammation
Chapter 8: Adaptive Immunity Unit X: Endocrine System
Chapter 9: Infectious Processes and Body Responses
Chapter 10: Abnormal Cell Growth and Cancer Biology Chapter 32: Review of Endocrine Structure, Function,
and Interactions
Part II: Pathophysiology of Disorders Chapter 33: Disorders of the Hypothalamus, Pituitary
Glands, and Adrenal Glands
Within Specific Body Systems Chapter 34: Disorders of the Thyroid Gland and the
Parathyroid Glands
Unit IV: Cardiovascular System Chapter 35: Glycemic Control and Diabetes Mellitus
Chapter 11: Review of Cardiovascular Development, Unit XI: Disorders of Immunity
Structure, and Function
Chapter 12: Vascular Disorders Chapter 36: Disorders of Reduced Immune Function
Chapter 13: Cardiac Disorders Chapter 37: Hypersensitivity and Autoimmune Disorders
Chapter 14: Congenital Heart Disease Across the Lifespan
Chapter 15: Shock and Multiple Organ Dysfunction
Syndrome Unit XII: Integumentary System
Chapter 38: Review of Integumentary Development,
Unit V: Pulmonary System
Structure, and Function
Chapter 39: Integumentary System Disorders
Chapter 16: Review of Pulmonary Structure,
Development, and Function
Chapter 17: Congenital, Obstructive, and Restrictive Unit XIII: Digestive System
Pulmonary Disorders
Chapter 18: Infectious Pulmonary Disorders and Lung Chapter 40: Review of Gastrointestinal Development,
Cancer Structure, and Function
Chapter 41: Disorders of the Mouth, Throat, Esophagus,
and Stomach
Unit VI: Renal-Urinary System
Chapter 42: Disorders of the Small Intestine, Large
Intestine, Pancreas, and Hepatobiliary System
Chapter 19: Review of Renal System Structure,
Development, and Function
Chapter 20: Urinary Tract Disorders Unit XIV: Reproductive Systems
Chapter 21: Kidney Disorders
,Chapter 43: Review of Reproductive System
Development, Structure, Function, and Sex Chromosome
Abnormalities Chapter 46: Sexually Transmitted Infections
Chapter 44: Common Disorders of the Female Chapter 47: Physiology and Pathophysiology of the
Reproductive System Breast
Chapter 45: Male Reproductive Disorders
,UNIT I: THE CELL
CHAPTER 1: Cellular Biology, Regulation, and Control Mechanisms
Section 1: Foundational Structure, Function, and Homeostatic Regulation
1. Which cellular mechanism primary functions to maintain a negative resting membrane
potential in excitable tissues under basal conditions?
A. Active transport of sodium out of the cell and potassium into the cell via Na+/K+-ATPase
B. Passive efflux of potassium through non-gated leak channels
C. Rapid influx of calcium through voltage-gated ion channels
D. Facilitated diffusion of chloride ions down an electrochemical gradient
Answer: A
Rationale: The Na+/K+-ATPase pump actively moves 3 sodium ions out of the cell for every 2
potassium ions brought into the cell against their respective concentration gradients using ATP
hydrolysis. This electrogenic transport mechanism maintains the intracellular negative charge
and resting membrane potential necessary for excitable tissue function.
2. A patient experiencing acute intracellular acidosis undergoes a shift in cellular membrane
transport dynamics. Which transport process relies directly on the sodium concentration
gradient established by primary active transport to move hydrogen ions out of the cell?
A. Receptor-mediated endocytosis
B. Simple diffusion
C. Secondary active transport
D. Primary active transport
Answer: C
Rationale: Secondary active transport (specifically antiporters or exchangers such as the
Na+/H+ exchanger) uses the potential energy stored in the electrochemical gradient of
sodium—which is generated by the primary active Na+/K+-ATPase pump—to drive hydrogen
ions out of the cell against their concentration gradient.
,3. What is the primary functional significance of epithelial cell polarity achieved through apical
and basolateral membrane domain specialization?
A. Facilitation of multidirectional bulk movement of intracellular organelles
B. Vectorial transport of solutes and fluid across tissue barriers
C. Enhanced structural elasticity during mechanical tissue deformation
D. Unrestricted lateral diffusion of membrane-bound signal receptors
Answer: B
Rationale: Epithelial cell polarity establishes distinct apical and basolateral plasma membrane
domains separated by tight junctions. This spatial segregation of specific channels, transporters,
and enzymes allows epithelial sheets to perform directional (vectorial) transport of ions,
nutrients, and water between external environments and internal compartments.
4. Which cellular process is specifically responsible for degrading damaged organelles and long-
lived proteins to maintain intracellular metabolic homeostasis during periods of nutrient
deprivation?
A. Autophagy
B. Phagocytosis
C. Exocytosis
D. Pinocytosis
Answer: A
Rationale: Autophagy is a lysosomal degradation pathway wherein the cell sequesters its own
damaged organelles, protein aggregates, and cytoplasmic components into double-membrane
vesicles (autophagosomes) that fuse with lysosomes. This process cleanses cellular debris and
recycles amino acids and energy during metabolic stress, distinguishing it from phagocytosis,
which targets extracellular pathogens and foreign debris.
Section 2: Membrane Physiology, Signaling, and Receptor Mechanics
5. A patient receiving chronic high-dose beta-1 adrenergic agonist therapy for heart failure
exhibits a progressive decline in therapeutic responsiveness. Which receptor-level adaptation
accounts for this phenomenon?
,A. Increased receptor affinity resulting from conformational stabilization
B. Receptor upregulation driven by increased transcription factor activity
C. Homologous desensitization and endocytic receptor downregulation
D. Enhanced coupling efficiency between the receptor and G-protein subunits
Answer: C
Rationale: Continuous or excessive exposure to an agonist induces receptor phosphorylation by
G-protein-coupled receptor kinases (GRKs), leading to arrestin binding, functional uncoupling
from G-proteins (desensitization), and subsequent endocytosis (downregulation) of the receptor.
This reduces the density of functional surface receptors, causing pharmacologic tolerance.
6. During the depolarization phase of an action potential in a nerve axon, which channel event
directly drives the rapid reversal of membrane potential toward positive values?
A. Closing of inactivation gates on voltage-gated Na+ channels
B. Efflux of potassium through voltage-gated K+ channels
C. Influx of chloride through ligand-gated Cl- channels
D. Opening of activation gates on voltage-gated Na+ channels
Answer: D
Rationale: When the threshold potential is reached, voltage-gated sodium channels open their
activation gates rapidly, causing a massive influx of sodium ions down both an electrical and
chemical gradient. This inward positive current causes the rapid depolarization overshoot
toward positive potential values.
7. Which structural component of the extracellular matrix (ECM) provides tensile strength to
tissues and prevents mechanical tearing under physical stretch?
A. Proteoglycans
B. Fibronectin
C. Collagen fibers
D. Elastin fibers
Answer: C
,Rationale: Collagen forms triple-helical protein fibers that exhibit high tensile strength,
protecting tissues against mechanical disruption under stretch. Proteoglycans provide
compressive resistance, while elastin imparts recoil capacity.
8. Which cell-adhesion system is anchored internally to intermediate filaments and provides
strong intercellular mechanical adhesion in tissues subjected to severe physical stress, such as
the myocardium?
A. Gap junctions
B. Tight junctions
C. Adherens junctions
D. Desmosomes
Answer: D
Rationale: Desmosomes (maculae adherentes) connect adjacent cells via cadherin family
proteins and are anchored intracellularly to keratin or desmin intermediate filaments. This
complex distributes mechanical force across cell sheets, preventing cell separation under
structural stress in tissues like the skin and cardiac muscle.
Section 3: Etiology, Pathophysiology, and Clinical Correlation
9. An APRN evaluates a patient with suspected cell-adhesion pathway failure causing mucosal
blistering. Pathophysiologically, the loss of hemidesmosomal integrity results in which structural
impairment?
A. Disruption of direct electrical coupling between adjacent cells
B. Breakdown of the paracellular barrier to macromolecular diffusion
C. Dissolution of the actin cytoskeleton within epithelial apical borders
D. Detachment of epithelial basal cells from the underlying basement membrane
Answer: D
Rationale: Hemidesmosomes anchor the basal surface of epithelial cells to the extracellular
matrix of the underlying basement membrane (via integrins). Loss or autoimmune destruction of
hemidesmosomal components disrupts this cell-matrix junction, causing the epithelium to peel
away from the basement membrane and form subepithelial blisters.
,10. Which systemic response demonstrates a positive feedback control loop operating in human
physiology?
A. Maintenance of core body temperature via shivering thermogenesis
B. Generation of the luteinizing hormone (LH) surge prior to ovulation
C. Control of plasma glucose concentration through insulin secretion
D. Regulation of arterial blood pressure via the carotid baroreceptor reflex
Answer: B
Rationale: The pre-ovulatory LH surge operates via positive feedback: rising estrogen levels
produced by the developing follicle signal the hypothalamus and pituitary to release increased
amounts of GnRH and LH, which in turn stimulates further estrogen release until ovulation
occurs. Baroreceptor, insulin, and thermoregulatory systems operate via negative feedback to
maintain stability.
11. A patient presenting with muscle weakness and cardiac dysrhythmias is found to have
severe hyperkalemia. Mechanistically, how does an elevated extracellular potassium
concentration alter neuronal excitable membrane dynamics?
A. It increases the magnitude of the driving force for outward potassium current during resting
conditions.
B. It depolarizes the resting membrane potential, bringing it closer to threshold and initially
increasing excitability followed by inactivation of sodium channels.
C. It blocks voltage-gated potassium channels, preventing repolarization completely.
D. It hyperpolarizes the resting membrane potential, driving it further from threshold.
Answer: B
Rationale: Elevating extracellular potassium concentration decreases the chemical gradient
across the cell membrane, reducing potassium efflux and shifting the resting membrane
potential toward a less negative (depolarized) state. While this initially brings the cell closer to
firing threshold, persistent depolarization keeps voltage-gated sodium channels in an
inactivated state, ultimately impairing action potential propagation and driving muscle weakness
and conduction block.
12. How does chronic exposure to an antagonist affect target cell receptor populations over
time?
,A. Receptor upregulation occurs, increasing target cell sensitivity to endogenous ligands upon
antagonist withdrawal.
B. Internalization and lysosomal degradation of receptors increase.
C. Receptor binding affinity permanently decreases due to conformational decay.
D. Receptor downregulation occurs to prevent overstimulation.
Answer: A
Rationale: Blockade of cell-surface receptors by a chronic antagonist deprives the cell of normal
ligand signaling. In response, the cell transcribes and inserts additional receptors into the
membrane (upregulation). When the antagonist is abruptly withdrawn, the increased receptor
density makes the cell hypersensitive to endogenous ligands.
Section 4: Process Sequences, Diagnostics, Matrix Correlations, and Calculations
13. [Ordered Response] Sequence the molecular events involved in G-protein-coupled
receptor (GPCR) activation and signaling from ligand binding to second-messenger initiation.
1. Dissociation of the G-alpha subunit from the G-beta/gamma complex
2. Binding of an extracellular signaling ligand to the GPCR
3. Activation of effector enzymes (e.g., adenylyl cyclase) to generate second messengers
4. Conformational shift causing GDP-to-GTP exchange on the G-alpha subunit
Answer: 2, 4, 1, 3
Rationale: Ligand binding (2) induces a conformational change in the GPCR that promotes
exchange of bound GDP for GTP on the heterotrimeric G-alpha subunit (4). GTP binding triggers
dissociation of the G-alpha subunit from the G-beta/gamma complex (1). The GTP-bound G-
alpha subunit then interacts with downstream effector enzymes like adenylyl cyclase or
phospholipase C to generate second messengers (3).
14. [Ordered Response] Sequence the phases of a cardiac action potential in ventricular
myocytes starting from resting membrane state through repolarization completion.
1. Rapid influx of sodium causing sharp depolarization (Phase 0)
2. Inward calcium current balancing outward potassium current to form a plateau (Phase 2)
3. Resting membrane potential maintained by potassium leak and ion pumps (Phase 4)
4. Transient early repolarization driven by inactivation of sodium channels and brief
potassium efflux (Phase 1)
5. Rapid repolarization mediated by sustained outward potassium efflux (Phase 3)
, Answer: 3, 1, 4, 2, 5
Rationale: The resting state is Phase 4 (3). Phase 0 (1) is rapid depolarization driven by voltage-
gated sodium channels. Phase 1 (4) is brief early repolarization. Phase 2 (2) represents the
plateau phase where inward calcium current balances outward potassium movement. Phase 3
(5) is rapid repolarization driven by delayed rectifier potassium channels until Phase 4 is
restored.
15. [Calculation / Fill-in-the-Blank] Calculate the approximate equilibrium potential (in mV) for
potassium (E(K+)) across a neuronal membrane at 37°C using the simplified Nernst equation:
E(K+) = -61 × log10([K+](in)/[K+](out))
Given an intracellular potassium concentration [K+](in) = 140 mEq/L and an extracellular potassium
concentration [K+](out) = 4.0 mEq/L. Round to the nearest whole number.
Answer: -94 mV
Rationale: [K+](in) / [K+](out) = .0 = 35. The log10(35) ≈ 1.544. Multiplying -61 × 1.544 = -94.18
mV, which rounds to -94 mV. This negative value represents the electrical gradient needed to balance the
outward chemical concentration gradient of potassium.
16. [Fill-in-the-Blank] What specific enzyme deficiency serves as the primary pathophysiologic
cause of Gaucher disease, leading to the accumulation of glucocerebroside within tissue
macrophages?
Answer: Glucocerebrosidase
Rationale: Gaucher disease is an autosomal recessive lysosomal storage disorder caused by
mutations in the GBA1 gene resulting in deficiency of the lysosomal enzyme beta-
glucocerebrosidase (glucosylceramidase). Without this enzyme, lipid substrates accumulate
within lysosomes of monocytes and macrophages (Gaucher cells).
17. [Matching / Matrix] Match the membrane transport mechanism with its defining functional
characteristic.
Transport
Primary Functional Characteristic
Mechanism
A. Requires ATP hydrolysis directly to transport solutes against an
1. Simple Diffusion
electrochemical gradient
