Physiology is the science of how living systems work, from cells to organs and whole bodies. It explains how neurons signal, muscles contract, and the heart, lungs, kidneys, and hormones coordinate to keep internal conditions stable. By measuring flows of energy, fluids, and signals, physiology links structure to function and predicts responses to stress, exercise, and environment. Its principles guide medicine, training, and design of technologies that support human health. It underpins health. Please note that the questions require knowledge and not all questions are the same difficulty level. Ready for my physiology answers?

The chief ionic determinant of the resting membrane potential in most neurons is:
A) Na⁺ permeability

B) K⁺ permeability

C) Ca²⁺ permeability

D) Cl⁻ permeability
Answer: B.

Explanation: High resting K⁺ conductance makes E_K dominate V_rest.

Define equilibrium (Nernst) potential.
Answer: The membrane potential at which an ion’s net flux is zero.
Explanation: Electrical and chemical driving forces balance.

(True/False) The Na⁺/K⁺ pump directly sets the resting membrane potential.
Answer: False.

Explanation: It indirectly maintains gradients; V_rest mainly reflects passive K⁺ permeability.

Which transport shows saturation kinetics?
A) Simple diffusion

B) Channel diffusion

C) Facilitated diffusion (carrier)

D) Osmosis
Answer: C.

Explanation: Carriers have a finite V_max.

Osmolarity vs. tonicity?
Answer: Osmolarity = total solute concentration; tonicity = effect on cell volume.
Explanation: Tonicity depends on effective osmoles.

Increasing extracellular K⁺ will:
A) Hyperpolarize

B) Depolarize

C) No change

D) Make V_rest equal E_Na
Answer: B.

Explanation: Reduces K⁺ gradient → less negative V_rest.

Osmosis requires:
A) Ion channels

B) ATP

C) Semipermeable membrane + solute gradient

D) Vesicular transport
Answer: C.

Explanation: Water moves down its chemical potential.

Gibbs–Donnan effect?
Answer: Non-diffusible ions on one side skew ion distribution and osmotic pressure.
Explanation: Maintains electroneutrality with unequal ion spreads.

Absolute refractory period is due to:
A) K⁺ channels open

B) Na⁺ channel inactivation

C) Ca²⁺ influx

D) Na⁺ channel closed (resting)
Answer: B.

Explanation: Inactivated Na⁺ channels cannot reopen until reset.

Saltatory conduction—what & why faster?
Answer: APs “jump” node to node on myelinated axons.

Explanation: ↑membrane resistance, ↓capacitance.

Opening which channel produces an IPSP in many CNS neurons?
A) Na⁺

B) Ca²⁺

C) Cl⁻

D) Nonselective cation
Answer: C.

Why: Cl⁻ influx tends to hyperpolarize/stabilize.

(True/False) Myelination increases axonal membrane capacitance.
Answer: False.

Explanation: It decreases capacitance, speeding conduction.

Temporal summation?
Answer: Multiple inputs from the same synapse summate over time.
Explanation: Postsynaptic potentials overlap.

NMJ transmitter removal primarily by:
A) Reuptake

B) Diffusion

C) Acetylcholinesterase

D) Endocytosis
Answer: C.

Explanation: AChE rapidly hydrolyzes ACh.

A Gs-coupled receptor first activates:
A) Phospholipase C

B) Adenylyl cyclase

C) Guanylyl cyclase

D) Tyrosine kinase
Answer: B.

Why: Gs → ↑cAMP via adenylyl cyclase.

Ionic driving force definition?
Answer: V_m − E_ion.
Explanation: Determines direction/magnitude of ion current.

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Ca²⁺ for skeletal muscle contraction primarily comes from:
A) ECF

B) SR

C) Mitochondria

D) T-tubule lumen
Answer: B.

Explanation: Depolarization couples to SR release via RyR.

Troponin–tropomyosin role?
Answer: Ca²⁺ binds troponin C → moves tropomyosin → exposes actin sites.
Explanation: Enables cross-bridge cycling.

(True/False) ATP binding to myosin is needed for cross-bridge detachment.
Answer: True.

Explanation: Rigor ends when ATP binds.

Maximal active tension occurs at:
A) Very short

B) Optimal

C) Very long

D) Independent of length
Answer: B.

Explanation: Best actin–myosin overlap.

Tetanic fusion occurs because:
Answer: Ca²⁺ remains elevated; repeated stimuli summate force.
Explanation: Insufficient time for sequestration.

Cardiac refractory period is long due to:
A) Na⁺ window current

B) L-type Ca²⁺ plateau

C) K⁺ inward rectifier

D) Cl⁻ current
Answer: B.

Explanation: Plateau prolongs AP → long refractory.

Smooth muscle contraction is triggered by:
A) Troponin

B) Calmodulin → MLCK

C) Titin

D) DHP receptor alone
Answer: B.

Explanation: Ca²⁺–calmodulin activates MLCK.

Isometric vs. isotonic?
Answer: Isometric: tension ↑, length constant; Isotonic: length changes at ~constant load.
Explanation: Different mechanical constraints.

A motor unit is:
A) One myofibril

B) One motor neuron + all its fibers

C) One sarcomere

D) All muscles in a limb
Answer: B.

Explanation: Functional innervation unit.

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Frank–Starling law:
A) ↑Afterload → ↑SV

B) ↑Preload → ↑SV

C) ↑HR → ↓SV

D) ↑Contractility → ↓SV
Answer: B.

Explanation: Greater EDV stretches fibers → more force.

MAP (approximate) = ?
Answer: MAP ≈ DBP + 1/3 Pulse Pressure.
Explanation: Systole occupies ~1/3 of cycle at rest.

(True/False) Arterioles are the main site of adjustable resistance.
Answer: True.

Explanation: Largest pressure drop occurs here.

Flow sensitivity to radius (Poiseuille):
A) r

B) r²

C) r³

D) r⁴
Answer: D.

Explanation: Small radius changes greatly affect flow.

Vascular compliance?
Answer: ΔVolume/ΔPressure; veins are more compliant.
Explanation: Thin walls and low tone.

High-pressure baroreceptors are in:
A) Carotid sinus & aortic arch

B) Atria

C) Ventricles

D) Pulmonary artery
Answer: A.

Explanation: Stretch-sensing sites for rapid reflexes.

Isovolumetric contraction:
A) All valves open

B) All valves closed

C) AV open only

D) Semilunar open only
Answer: B.

Explanation: Pressure rises at constant volume.

Pulse pressure = ? Influenced by?
Answer: PP = SBP − DBP; ↑stroke volume & ↓arterial compliance increase PP.
Explanation: Determines systolic–diastolic gap.

Fastest intrinsic pacemaker:
A) AV node

B) Purkinje

C) SA node

D) His bundle
Answer: C.

Explanation: Highest spontaneous phase-4 depolarization.

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Primary driver of ventilation at rest:
A) PaO₂

B) PaCO₂ (via H⁺ in CSF)

C) BP

D) Temp
Answer: B.

Explanation: Central chemoreceptors dominate.

Surfactant: made by? effect?
Answer: Type II pneumocytes; reduces surface tension → ↑compliance.
Explanation: Stabilizes alveoli.

(True/False) End-expiratory intrapleural pressure is positive.
Answer: False.

Explanation: It’s subatmospheric (negative).

At FRC:
A) Lungs recoil inward > chest wall

B) Outward > inward

C) Balanced

D) Both zero
Answer: C.

Explanation: Static equilibrium volume.

Dead space?
Answer: Ventilated but non-perfused (or non-exchanging) air; includes anatomic (+ alveolar if any).
Explanation: Doesn’t contribute to gas exchange.

O₂ content of blood depends most on:
A) Dissolved O₂

B) Hb concentration & saturation

C) Alveolar humidity

D) CO₂
Answer: B.

Explanation: Hb carries the bulk of O₂.

Hypoventilation effect on PaCO₂:
A) ↓

B) ↑

C) No change

D) Unpredictable
Answer: B.

Explanation: Alveolar ventilation and PaCO₂ are inversely related.

Regional V/Q in upright lung?
Answer: Apex: higher V/Q; base: lower V/Q.
Explanation: Gravity affects perfusion > ventilation.

Surfactant primarily:
A) Decreases compliance

B) Increases collapsing pressure

C) Reduces surface tension

D) Thickens alveolar membrane
Answer: C.

Explanation: Lowers work of breathing.

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Ideal GFR marker (freely filtered, not handled):
A) PAH

B) Inulin

C) Creatinine (exact)

D) Glucose
Answer: B.

Explanation: Gold-standard filtration tracer.

Starling forces at the glomerulus determine what?
Answer: Net filtration pressure → GFR.
Why: Balance of hydrostatic & oncotic pressures.

(True/False) Most filtered Na⁺ is reabsorbed in the proximal tubule.
Answer: True.

Explanation: Bulk reabsorption site.

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ADH promotes water reabsorption by inserting:
A) AQP1 in PCT

B) AQP2 in collecting duct

C) NKCC2 in TAL

D) Na⁺/K⁺-ATPase in CD
Answer: B.

Explanation: V2-receptor → AQP2 apical insertion.

Countercurrent multiplier function?
Answer: TAL creates hyperosmotic medulla to concentrate/dilute urine downstream.
Explanation: Enables water extraction in CD.

Aldosterone on principal cells:
A) ↓Na⁺ reabsorption

B) ↑Na⁺ reabsorption & ↑K⁺ secretion

C) ↑Cl⁻ secretion

D) ↑HCO₃⁻ reabsorption
Answer: B.

Explanation: Genomic effects increase ENaC/Na⁺-pump activity.

Afferent arteriole constriction:
A) ↑GFR

B) ↓GFR

C) No effect

D) ↑RPF, ↓GFR
Answer: B.

Explanation: Lowers glomerular capillary pressure.

Transport maximum (T_m)?
Answer: Maximal reabsorptive (or secretory) rate when carriers saturate (e.g., glucose).
Explanation: Explains threshold phenomena.

Macula densa senses:
A) K⁺

B) NaCl in distal tubule

C) Urea

D) Glucose
Answer: B.

Explanation: Regulates tubuloglomerular feedback.

Acid–Base & Body Fluids (61–70)

Principal extracellular buffer:
A) Phosphate

B) Hemoglobin

C) Bicarbonate

D) Proteins
Answer: C.

Explanation: Open CO₂/HCO₃⁻ system with respiratory control.

Henderson–Hasselbalch (bicarbonate system)?
Answer: pH = pK_a + log( [HCO₃⁻] / (0.03 × PaCO₂) ).
Explanation: Links pH to kidneys (HCO₃⁻) and lungs (CO₂).

(True/False) Lungs directly change plasma bicarbonate to compensate.
Answer: False.

Explanation: Lungs change CO₂; kidneys handle HCO₃⁻.

Increasing alveolar ventilation generally:
A) Lowers pH

B) Raises PaCO₂

C) Raises pH

D) No effect on pH
Answer: C.

Explanation: ↓PaCO₂ → ↓[H⁺] → ↑pH.

Osmolarity vs. osmolality?
Answer: Osmolarity = osmoles/L; osmolality = osmoles/kg solvent.
Explanation: Osmolality is temperature-independent.

Plasma osmolality is determined mainly by:
A) Proteins

B) Na⁺ and its anions (± glucose, urea)

C) K⁺

D) Ca²⁺
Answer: B.

Explanation: Na⁺ salts dominate ECF solutes.

Infusing isotonic saline primarily expands:
A) ICF only

B) ECF only

C) Both equally

D) Plasma only
Answer: B.

Explanation: Na⁺ is ECF-restricted effective osmole.

Effective osmoles?
Answer: Solutes that do not freely cross membranes and thus shift water (e.g., Na⁺).
Explanation: Create tonic gradients.

Most important intracellular buffers:
A) Proteins and phosphate

B) Bicarbonate

C) Calcium salts

D) Ammonia
Answer: A.

Explanation: Abundant intracellularly; Hb in RBCs.

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GI slow waves originate from:
A) Vagus

B) Skeletal muscle

C) Interstitial cells of Cajal

D) Paneth cells
Answer: C.

Explanation: Gut pacemaker cells.

Gastrin actions?
Answer: ↑Gastric H⁺ secretion, ↑mucosal growth, ↑motility.
Explanation: Hormone of gastric phase.

(True/False) Pancreatic acinar cells secrete bicarbonate.
Answer: False.

Explanation: Ductal cells secrete HCO₃⁻; acini secrete enzymes.

Secretin is released by acid in duodenum and:
A) ↓Pancreatic HCO₃⁻

B) ↑Pancreatic HCO₃⁻

C) Contracts gallbladder

D) ↑Gastric acid
Answer: B.

Explanation: Neutralizes chyme.

CCK functions?
Answer: Contracts gallbladder, ↑pancreatic enzymes, relaxes Oddi, slows gastric emptying.
Explanation: Optimizes fat digestion.

Most overall nutrient absorption occurs in:
A) Duodenum

B) Jejunum

C) Ileum

D) Colon
Answer: B.

Explanation: Large surface area & transporters.

Migrating motor complex (MMC) occurs during fasting and is triggered by:
A) Gastrin

B) Secretin

C) Motilin

D) VIP
Answer: C.

Explanation: Housekeeping motility.

ENS plexuses?
Answer: Myenteric (Auerbach): motility; Submucosal (Meissner): secretion/blood flow.
Explanation: Intrinsic neural control.

Bile salts mainly:
A) Digest proteins

B) Form micelles for lipid absorption

C) Buffer gastric acid

D) Increase iron uptake
Answer: B.

Explanation: Amphipathic emulsifiers reabsorbed in ileum.

Steroid hormones typically act by:
A) cAMP

B) IP₃/DAG

C) Nuclear receptors altering transcription

D) Ion channels
Answer: C.

Explanation: Lipophilic → intracellular receptors.

Peptide vs. steroid hormones—storage/transport?
Answer: Peptides stored in vesicles, circulate free; steroids made on demand, circulate bound to proteins.
Explanation: Solubility differences.

(True/False) Posterior pituitary synthesizes ADH/oxytocin.
Answer: False.

Explanation: Synthesized in hypothalamus; released from posterior pituitary.

Insulin receptor type:
A) GPCR

B) Ligand-gated channel

C) Receptor tyrosine kinase

D) Nuclear receptor
Answer: C.

Explanation: Autophosphorylation/IRS signaling.

Hormone permissiveness?
Answer: One hormone enhances the effect of another (e.g., thyroid hormones permissive for catecholamines).
Explanation: Increases receptor number/signaling.

TRH → TSH → thyroid hormones is an example of:
A) Long-loop feedforward

B) Hypothalamo–pituitary–target axis

C) Ultrashort loop only

D) Paracrine reflex
Answer: B.

Explanation: Classic HPT axis.

A classic cAMP-mediated hormone is:
A) PTH

B) Aldosterone

C) Thyroxine

D) Insulin
Answer: A.

Explanation: PTH uses Gs → adenylyl cyclase.

Negative feedback example in HPT axis?
Answer: T₃/T₄ inhibit TRH and TSH release.
Explanation: Stabilizes hormone levels.

Receptor up-regulation example:
A) Fewer receptors after high ligand

B) More uterine oxytocin receptors near term

C) Fewer insulin receptors with fasting

D) None
Answer: B.

Explanation: Sensitizes uterus for labor.

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Ovulation is triggered by the surge of:
A) FSH

B) LH

C) Prolactin

D) Progesterone
Answer: B.

Explanation: LH surge induces follicular rupture.

Menstrual cycle phases & dominant hormones?
Answer: Follicular (estrogen), Luteal (progesterone).
Explanation: Ovarian hormone patterns define phases.

(True/False) Sperm acquire motility in the epididymis.
Answer: True.

Explanation: Maturation and storage site.

Sertoli vs. Leydig primary responses:
A) Sertoli–LH; Leydig–FSH

B) Sertoli–FSH; Leydig–LH

C) Both to FSH

D) Both to LH
Answer: B.

Explanation: FSH supports spermatogenesis; LH stimulates testosterone.

Capacitation?
Answer: Functional maturation of sperm in female tract enabling acrosome reaction.
Why: Alters membrane and motility.

Basal body temperature rises post-ovulation due to:
A) Estrogen

B) Progesterone

C) LH

D) Inhibin
Answer: B.

Explanation: Thermogenic effect of progesterone.

Early maintenance of the corpus luteum is by:
A) FSH

B) Prolactin

C) hCG

D) Oxytocin
Answer: C.

Explanation: hCG mimics LH support.

Oxytocin’s main roles?
Answer: Uterine contraction (parturition) and milk ejection (let-down).
Explanation: Acts via Gq/IP₃–Ca²⁺ in target tissues.