Concours de fin de PACES — Médecine Vétérinaire (Université d'Antananarivo)

Under anaerobic conditions in mammalian erythrocytes or working skeletal muscle fibers, what is the net yield of ATP generated per molecule of glucose oxidized via the glycolytic pathway?

• A1 ATP
• B2 ATP
• C4 ATP
• D32 ATP

What is the net ATP yield from the complete beta-oxidation and subsequent aerobic oxidation (via the citric acid cycle and electron transport chain) of one molecule of palmitic acid (C16:0)?

• A106 ATP
• B129 ATP
• C96 ATP
• D140 ATP

In the hepatic urea cycle of domestic mammals, which enzyme catalyzes the initial rate-limiting step inside the mitochondrial matrix, requiring N-acetylglutamate as an essential allosteric activator?

• AOrnithine transcarbamylase
• BArgininosuccinate synthetase
• CArginase
• DCarbamoyl phosphate synthetase I

In the fluid mosaic model of mammalian plasma membranes, what is the primary role of cholesterol in modulating membrane fluidity across physiological temperatures?

• AIt binds to extracellular ligands to trigger secondary messenger cascades
• BIt acts as a bidirectional fluidity buffer, restraining phospholipid movement at high tem…
• CIt forms covalent cross-links between transmembrane protein alpha-helices to rigidify the…
• DIt creates active hydrophilic pores allowing passive water and electrolyte transit

During the synthesis of secretory and lysosomal proteins in domestic animal cells, which ribonucleoprotein particle recognizes the hydrophobic N-terminal signal sequence and halts translation until docking onto the rough endoplasmic reticulum?

• ARibophorin I
• BClathrin coatomer
• CSignal Recognition Particle (SRP)
• DProteasome 26S

Which specific biochemical modification added in the cis-Golgi apparatus targets newly synthesized acid hydrolases to the lysosome rather than the constitutive secretory pathway?

• AC-terminal KDEL peptide signal addition
• BUbiquitin polymerisation via Lys48 linkages
• CGPI anchor attachment to the C-terminus
• DPhosphorylation of mannose residues to mannose-6-phosphate (M6P)

In the eukaryotic cell cycle, the Maturation-Promoting Factor (MPF) that triggers the transition from the G2 phase into mitosis (M phase) is a heterodimer composed of which two molecules?

• ACyclin B and CDK1 (Cdc2)
• BCyclin D and CDK4/6
• CCyclin E and CDK2
• DCyclin A and CDK2

In the intrinsic (mitochondrial) pathway of apoptosis in mammalian cells, which event directly triggers the assembly of the apoptosome in the cytosol?

• ABinding of Fas ligand (FasL) to the Fas death receptor (CD95)
• BRelease of cytochrome c from the mitochondrial intermembrane space into the cytosol and i…
• CDirect nuclear translocation of caspase-8 to cleave chromatin
• DInhibition of the transcription factor p53 by MDM2

Which type of epithelium lines the luminal surface of the mammalian trachea and primary bronchi, functioning in the mucociliary clearance apparatus?

• ASimple squamous epithelium
• BStratified squamous non-keratinized epithelium
• CPseudostratified ciliated columnar epithelium with goblet cells
• DTransitional epithelium (urothelium)

Which fibrillar collagen type is the predominant structural protein providing tensile strength in domestic animal tendons, ligaments, and dense regular connective tissues?

• ACollagen type I
• BCollagen type II
• CCollagen type III
• DCollagen type IV

In the histological structure of mammalian compact (cortical) bone, what microscopic channels connect adjacent lacunae containing osteocyte dendritic processes, enabling nutrient exchange and mechanosensation?

• AVolkmann's canals
• BHaversian canals
• CSharpey's fibers
• DCanaliculi

During endochondral ossification of mammalian long bones, where does the primary center of ossification first appear?

• AIn the articular cartilage lining the epiphyseal extremity
• BIn the center of the diaphysis (shaft)
• CWithin the epiphyseal growth plate (physis) zone of resting cartilage
• DWithin the proximal epiphysis exclusively

Which mechanism of exocrine secretion is characteristic of sebaceous glands in the skin of domestic mammals, in which the entire glandular cell disintegrates to release its lipid-rich product?

• AMerocrine (eccrine) secretion
• BApocrine secretion
• CHolocrine secretion
• DParacrine secretion

During mammalian nuclear DNA replication, which enzyme is responsible for joining the adjacent Okazaki fragments on the lagging strand by catalyzing phosphodiester bond formation between adjacent 3'-OH and 5'-phosphate groups?

• ADNA ligase
• BDNA helicase
• CDNA topoisomerase I
• DRNA primase

Which post-transcriptional processing event in eukaryotic cells involves the excision of non-coding intronic sequences from primary pre-mRNA transcripts by snRNP complexes?

• A5' 7-methylguanosine capping
• B3' Polyadenylation
• CRNA editing via deamination
• DSpliceosomal pre-mRNA splicing

According to Francis Crick's Wobble Hypothesis, non-canonical (wobble) base-pairing during ribosomal translation occurs between which two positions?

• AThe 1st base (5' end) of the codon and the 3rd base (3' end) of the anticodon
• BThe 3rd base (3' end) of the codon and the 1st base (5' end) of the anticodon
• CThe 2nd base of the codon and the 2nd base of the anticodon
• DThe Shine-Dalgarno sequence and the 16S ribosomal RNA

In a classic Mendelian dihybrid test-cross between an individual heterozygous for two unlinked autosomal genes with complete dominance (AaBb) and a homozygous recessive individual (aabb), what is the expected phenotypic ratio among the offspring?

• A9:3:3:1
• B3:1
• C1:1:1:1
• D1:2:1

Using the Nernst equation at mammalian body temperature (37°C, where 2.303 RT/F ≈ 61.5 mV): if the intracellular potassium concentration [K+]in is 145 mmol/L and the extracellular potassium concentration [K+]out is 4.5 mmol/L, what is the potassium equilibrium potential (E_K)?

• A+61.5 mV
• B-92.7 mV
• C-65.0 mV
• D+15.0 mV

According to the Goldman-Hodgkin-Katz (GHK) voltage equation, why does the resting membrane potential of a mammalian nerve fiber (~ -70 mV) sit much closer to the K+ equilibrium potential (-90 mV) than to the Na+ equilibrium potential (+60 mV)?

• AExtracellular sodium ions are completely bound to plasma albumin and cannot permeate the…
• BVoltage-gated sodium channels are permanently inactivated at negative voltages
• CThe resting membrane permeability to potassium (P_K) is approximately 20 to 100 times gre…
• DThe Na+/K+-ATPase pumps 3 K+ ions inward for every 2 Na+ ions extruded

In electrophysiology, the space (length) constant (lambda) of an unmyelinated axon is defined by the formula lambda = sqrt(r_m / r_i). What biological change will increase lambda, allowing local subthreshold graded potentials to spread farther along the fiber?

• AAn increase in membrane resistance (r_m) or a decrease in internal axoplasmic resistance…
• BA decrease in axon diameter reducing cross-sectional area
• CA massive opening of resting chloride channels in the membrane
• DAn increase in axoplasmic viscosity without altering membrane channels

During the initiation of a neuronal action potential, what biophysical event constitutes the regenerative positive-feedback loop known as the 'Hodgkin cycle'?

• AHyperpolarization activating delayed rectifier potassium channels
• BCalcium extrusion via the plasma membrane Ca2+-ATPase pump
• CChloride influx hyperpolarizing the axon hillock
• DDepolarization opening voltage-gated Na+ channels, causing Na+ influx, which triggers fur…

Standard isotonic saline solution (0.9% w/v NaCl) used in veterinary fluid therapy contains 9.0 g of NaCl (molar mass = 58.44 g/mol) dissolved in 1.0 L of sterile water. Assuming complete dissociation into Na+ and Cl- ions (osmotic coefficient i = 2.0), what is the calculated theoretical osmolarity of this solution?

• A154 mOsm/L
• B308 mOsm/L
• C616 mOsm/L
• D280 mOsm/L

Using the Starling equation for transcapillary fluid exchange: Net Filtration Pressure (NFP) = (P_c - P_if) - sigma * (pi_c - pi_if). In a skeletal muscle capillary bed where capillary hydrostatic pressure (P_c) = 32 mmHg, interstitial hydrostatic pressure (P_if) = -1 mmHg, plasma oncotic pressure (pi_c) = 25 mmHg, interstitial oncotic pressure (pi_if) = 2 mmHg, and reflection coefficient sigma = 1.0, what is the net filtration pressure?

• A+10 mmHg (favoring fluid filtration into the interstitium)
• B-10 mmHg (favoring fluid reabsorption into the capillary)
• C+6 mmHg (favoring fluid filtration into the interstitium)
• D+33 mmHg (favoring fluid filtration into the interstitium)

Which circulating plasma protein contributes approximately 75% to 80% of total plasma colloid osmotic (oncotic) pressure in domestic mammals?

• AFibrinogen
• BAlpha-1-acid glycoprotein
• CAlbumin
• DImmunoglobulin G (IgG)

According to the Hagen-Poiseuille relationship for laminar fluid flow in cylindrical vessels, vascular resistance (R) is inversely proportional to which power of the internal vessel radius (r)?

• ADirectly proportional to r
• BInversely proportional to r^2
• CInversely proportional to r^3
• DInversely proportional to r^4

In a biological study measuring serum calcium concentrations in a herd of dairy cows, the sample size is increased from n = 25 to n = 100 while the population standard deviation (sigma) remains constant. How does the Standard Error of the Mean (SEM) change?

• AIt remains unchanged
• BIt is halved (reduced by 50%)
• CIt is reduced to one-fourth (reduced by 75%)
• DIt doubles

In inferential statistics applied to veterinary clinical trials, what is a Type I error (alpha error)?

• ARejecting the null hypothesis (H0) when it is actually true (a false positive conclusion)
• BFailing to reject the null hypothesis (H0) when it is actually false (a false negative co…
• CThe probability of correctly rejecting a false null hypothesis (statistical power = 1 - b…
• DSelecting an unrepresentative sample due to confounding bias

A diagnostic screening test for bovine viral diarrhea (BVD) is evaluated in a cohort of 200 cattle. By reference standard, 50 cattle are truly infected and 150 are uninfected. The test identifies 45 true positives and 135 true negatives. What are the diagnostic sensitivity and specificity of this test?

• ASensitivity = 90%; Specificity = 67.5%
• BSensitivity = 75%; Specificity = 90%
• CSensitivity = 90%; Specificity = 90%
• DSensitivity = 100%; Specificity = 85%

A single intravenous bolus dose of 500 mg of an antibacterial agent is administered to a 25 kg domestic dog. By back-extrapolation of the monoexponential elimination curve to time zero, the initial plasma concentration (C0) is determined to be 20 mg/L. What is the apparent volume of distribution (Vd) of this drug in liters and in L/kg?

• AVd = 10 L (0.4 L/kg)
• BVd = 25 L (1.0 L/kg)
• CVd = 50 L (2.0 L/kg)
• DVd = 2.5 L (0.1 L/kg)

A veterinary drug follows first-order elimination kinetics with an elimination half-life (t1/2) of 4.0 hours and an apparent volume of distribution (Vd) of 20 L. What is the total body clearance (Cl) of this drug?

• A0.80 L/h
• B5.00 L/h
• C13.86 L/h
• D3.47 L/h

A pharmacokinetic trial compares oral and intravenous formulations of a therapeutic agent in horses. An intravenous dose of 100 mg produces an Area Under the Curve (AUC_IV) of 50 mg*h/L. An oral dose of 200 mg produces an Area Under the Curve (AUC_oral) of 60 mg*h/L. What is the absolute oral bioavailability (F) of the drug?

• A60% (F = 0.60)
• B30% (F = 0.30)
• C120% (F = 1.20)
• D50% (F = 0.50)

Who originally conceptualized the 'milieu intérieur' (internal environment) as an extracellular fluid bath that shields living cells from environmental fluctuations, establishing the foundation of modern animal physiology?

• AWalter Cannon
• BClaude Bernard
• CErnest Starling
• DAugust Krogh

In a healthy adult domestic mammal of normal body condition, what proportion of total body weight is typically composed of water (Total Body Water, TBW)?

• AApproximately 60%
• BApproximately 20%
• CApproximately 40%
• DApproximately 85%

According to the fundamental physiological partition of body water (the 60-40-20 rule), how is Total Body Water (TBW) partitioned between the intracellular (ICF) and extracellular (ECF) fluid compartments?

• AICF contains 1/3 of TBW (~20% body weight); ECF contains 2/3 of TBW (~40% body weight)
• BICF and ECF each contain exactly 1/2 of TBW (~30% body weight each)
• CICF contains 90% of TBW (~54% body weight); ECF contains 10% of TBW (~6% body weight)
• DICF contains 2/3 of TBW (~40% body weight); ECF contains 1/3 of TBW (~20% body weight)

The Extracellular Fluid (ECF) compartment (~20% of body weight) is further subdivided into interstitial fluid and blood plasma. What is their approximate proportional distribution?

• AInterstitial fluid is 25% of ECF (5% body weight); Plasma is 75% of ECF (15% body weight)
• BInterstitial fluid is 50% of ECF (10% body weight); Plasma is 50% of ECF (10% body weight)
• CInterstitial fluid is approximately 75% to 80% of ECF (~15% body weight); Plasma is appro…
• DInterstitial fluid is 95% of ECF (19% body weight); Plasma is 5% of ECF (1% body weight)

Which of the following biological fluids is categorized as part of the transcellular fluid compartment?

• ACerebrospinal fluid (CSF), synovial fluid, and aqueous humor
• BBlood plasma inside the aortic arch
• CInterstitial fluid bathing skeletal muscle myocytes
• DCytosol within hepatocytes

In the indicator dilution principle used to determine fluid compartment volumes (V = (Q - E) / C), which property is an essential requirement for an ideal indicator substance?

• AIt must be actively transported across cell membranes and metabolized within 5 minutes
• BIt must disperse homogeneously only throughout the compartment being measured, remain non…
• CIt must bind irreversibly to intracellular structural proteins
• DIt must be cleared exclusively by rapid biliary excretion

To measure the extracellular fluid volume in a bovine calf, a bolus of 1000 mg of inulin is injected intravenously. During the 2-hour equilibration period, 100 mg of inulin is excreted in the urine. At equilibrium, the inulin concentration in plasma is measured at 50 mg/L. What is the calculated Extracellular Fluid (ECF) volume of the calf?

• A20.0 L
• B10.0 L
• C18.0 L
• D22.2 L

An Evans Blue dye dilution measurement in a small ruminant determines a plasma volume of 3.0 L. A microhematocrit centrifuge measurement gives a packed cell volume (PCV / hematocrit) of 40% (0.40). What is the total blood volume of this animal?

• A5.0 L
• B4.2 L
• C7.5 L
• D1.8 L

In a sheep, Total Body Water (TBW) is measured using antipyrine dilution and equals 30.0 L. Extracellular fluid (ECF) volume is measured using sodium thiocyanate dilution and equals 10.0 L. What is the calculated Intracellular Fluid (ICF) volume?

• A40.0 L
• B15.0 L
• C10.0 L
• D20.0 L

If an animal's Extracellular Fluid (ECF) volume is 16.0 L (measured via inulin) and its Plasma Volume is 4.0 L (measured via radiolabeled 131I-albumin), what is the calculated Interstitial Fluid (ISF) volume?

• A20.0 L
• B12.0 L
• C4.0 L
• D8.0 L

Which ions constitute the predominant cation and predominant anion in mammalian extracellular fluid (plasma and interstitial fluid)?

• ASodium (Na+) and Chloride (Cl-)
• BPotassium (K+) and Phosphate (HPO4 2-)
• CCalcium (Ca2+) and Bicarbonate (HCO3-)
• DMagnesium (Mg2+) and Sulfate (SO4 2-)

How does the Gibbs-Donnan equilibrium affect the distribution of diffusible monovalent electrolytes between blood plasma and interstitial fluid across the capillary wall?

• ADiffusible cations and anions achieve exactly identical concentrations in plasma and inte…
• BDiffusible anions (Cl-) are slightly higher in plasma, while diffusible cations (Na+) are…
• CDiffusible cations (Na+) are slightly higher in plasma (~5%), while diffusible anions (Cl…
• DElectrolyte movement across the capillary endothelium is governed exclusively by primary…

What fluid shift occurs between body fluid compartments immediately following the rapid intravenous infusion of hypertonic saline (3.0% NaCl) in a domestic animal?

• AWater moves from ECF into ICF, causing cellular swelling and ECF contraction
• BSolutes move rapidly into cells until intracellular sodium equals extracellular sodium
• CNo fluid shift occurs because the capillary endothelium is impermeable to water
• DWater shifts by osmosis from the intracellular fluid (ICF) into the extracellular fluid (…

In the circulating plasma of domestic mammals, in what form is calcium present in the physiologically active state that directly regulates neuromuscular excitability, cardiac contractility, and enzyme function?

• ACalcium bound to circulating albumin
• BFree ionized calcium (Ca2+), representing approximately 50% of total plasma calcium
• CCalcium complexed with citrate, phosphate, and bicarbonate
• DCalcium precipitated as hydroxyapatite crystals

What is the exact stoichiometric ratio of ions transported across the plasma membrane by the primary active Na+/K+-ATPase pump per molecule of ATP hydrolyzed?

• A3 Na+ pumped out of the cell and 2 K+ pumped into the cell
• B2 Na+ pumped out of the cell and 3 K+ pumped into the cell
• C3 Na+ pumped into the cell and 2 K+ pumped out of the cell
• D1 Na+ pumped out of the cell and 1 K+ pumped into the cell

Which sequence correctly depicts the components and signal pathway of a physiological negative feedback loop maintaining homeostatic set points in domestic animals?

• AEffector -> Efferent pathway -> Stimulus -> Sensor -> Integrating center -> Afferent path…
• BStimulus -> Sensor/Receptor -> Afferent pathway -> Integrating/Control center -> Efferent…
• CIntegrating center -> Sensor -> Stimulus -> Efferent pathway -> Afferent pathway -> Effec…
• DEffector -> Integrating center -> Afferent pathway -> Sensor -> Stimulus -> Efferent path…

Which of the following physiological processes in female domestic mammals operates via a positive feedback loop rather than negative homeostatic feedback?

• ARegulation of core body temperature via cutaneous vasodilation
• BMaintenance of arterial blood pressure via the carotid baroreceptor reflex
• CThe Ferguson reflex during parturition, in which cervical dilation stimulates oxytocin re…
• DControl of extracellular fluid osmolality via hypothalamic ADH secretion