Veterinary Anatomy and Physiology Flashcards

In ruminants, the reticulum plays a critical role beyond fermentation. Which anatomical feature of the reticuloruminal fold is most directly responsible for the selective passage of liquid digesta versus large particle matter into the omasum?

Answer: The reticulo-omasal orifice, which is guarded by muscular lips that perform size-selective filtration based on particle buoyancy and contractile rhythm

The reticulo-omasal orifice is flanked by muscular lips that open and close in coordination with reticular contractions. The biphasic reticular contraction cycle selectively allows small-particle and liquid digesta to pass into the omasum while large particles are retained for further rumination. The omasal laminae do contribute to water absorption downstream, and the reticular groove is real but functions in neonates to shunt milk directly to the abomasum — it is not the primary mechanism for particle-size selection in adults.

A veterinarian performs a celiotomy on a horse and identifies the cecum. Which anatomical landmark most reliably distinguishes the right dorsal colon from the cecum when both are distended and visible simultaneously?

Answer: The cecum has four longitudinal taeniae and four rows of sacculations (haustra), whereas the right dorsal colon has only three taeniae

The equine cecum bears four taeniae (bands) and four rows of sacculations. The right ventral colon has four taeniae, but the right dorsal colon transitions to having only three taeniae as it courses toward the transverse colon. Intraoperatively, counting taeniae on a distended viscus is a reliable quick differentiator. The cecum is located on the right side of the abdomen (not left), and the cecocolic orifice is on the medial surface of the body — near the base, not the apex.

The avian renal portal system is physiologically unique among domestic species. Which of the following correctly describes how this system can confound drug pharmacokinetics in birds?

Answer: Drugs injected into the caudal half of the body may be delivered directly to the renal tubular cells and undergo renal extraction or secretion before reaching systemic circulation, reducing bioavailability

In birds, the renal portal system carries blood from the caudal limbs and tail through the afferent renal portal veins directly to the peritubular capillaries of the kidney — before that blood returns to the heart via the caudal renal veins and caudal vena cava. Drugs (especially those with significant renal tubular secretion, e.g., penicillins, aminoglycosides) injected into the pectoral muscles or anywhere cranial to the synsacrum bypass this system. Injections into the leg or caudal body may be subject to renal extraction, effectively lowering systemic drug levels. The first-pass effect described in option A is hepatic, not what the renal portal system does.

During the cardiac cycle in the dog, the second heart sound (S2) is generated primarily by which event, and what pathological condition would most specifically cause S2 to split audibly on expiration (fixed or paradoxical splitting)?

Answer: S2 is generated by semilunar valve closure; paradoxical splitting on expiration is caused by left bundle branch block or severe aortic stenosis delaying aortic valve closure

S2 is produced by the closure of the aortic (A2) and pulmonic (P2) semilunar valves. Normally, A2 precedes P2, and the split widens on inspiration as increased venous return delays pulmonic closure. Paradoxical (reversed) splitting occurs when aortic valve closure is delayed — as in left bundle branch block (LBBB) or severe aortic stenosis — so P2 now closes before A2. On expiration the normal sequence is A2 then P2; with paradoxical splitting it reverses to P2 then A2, and the split paradoxically NARROWS on inspiration. Fixed splitting (equal on inspiration and expiration) is characteristic of atrial septal defect, not VSD. AV valves generate S1, not S2.

In the bitch, the uterine artery arises from which parent vessel, and at what anatomical relationship does it cross the ureter — a detail critical to avoid ureteral ligation during ovariohysterectomy?

Answer: It arises from the internal iliac (hypogastric) artery and crosses dorsal to the ureter as it approaches the uterine body, near the cervix

In the bitch, the uterine artery is a branch of the internal iliac (hypogastric) artery. As it courses medially toward the uterine body and cervix, it crosses DORSAL to the ureter — the opposite relationship from what is seen in women (where the uterine artery crosses ANTERIOR/ventral to the ureter). Surgeons must identify and preserve the ureter before ligating the broad ligament or uterine vessels, as inadvertent inclusion of the ureter in a pedicle tie leads to hydroureter and renal failure. The ovarian artery supplies the ovary via the suspensory ligament, not the uterine body primarily.

A 4-year-old intact male cat presents with urethral obstruction. After relief and stabilization, bloodwork reveals severe hyperkalemia causing bradycardia. Physiologically, which mechanism best explains why hyperkalemia depresses cardiac automaticity and slows conduction in feline myocardium?

Answer: Elevated extracellular K⁺ reduces the resting membrane potential (makes it less negative) by decreasing the K⁺ equilibrium potential, which inactivates voltage-gated fast Na⁺ channels and reduces phase 0 upstroke velocity

Extracellular potassium concentration directly determines the K⁺ equilibrium potential (Ek) via the Nernst equation. As extracellular K⁺ rises, Ek becomes less negative, which depolarizes the resting membrane potential (RMP) of all cardiac cells. While this initial, modest depolarization might paradoxically seem excitatory, the sustained partial depolarization causes voltage-gated fast Na⁺ channels (responsible for phase 0 in working myocytes and ventricular conduction) to enter an inactivated (non-conducting) state — they cannot open again without full repolarization. The result is reduced phase 0 upstroke velocity (dV/dt), slower conduction velocity, widened QRS, and bradycardia. Option A is incorrect because hyperkalemia depolarizes, not hyperpolarizes, the RMP. Options C and D describe mechanisms not primarily responsible for hyperkalemia's cardiac effects.