INNOVATIONS - Use of the Frog Heart Preparation to Teach Students about the Spontaneous Mechanical Activity of the Vena Cava

Oct 15, 2026

Most undergraduate physiology texts describe veins as passive blood reservoirs and conduits, but a classroom laboratory exercise can demonstrate a dynamic rhythmic contraction. By recording simultaneous beating of the frog postcaval vein (PCV) and atrium via separate force transducers, the study shows both contract at ~35 beats/min without synchrony. A scoring method indicates atrial contractions do not drive PCV activity. Removing the PCV and suspending it in an organ bath preserves rhythmic contraction, while norepinephrine shows no effect, and acetylcholine abolishes contractility.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages6

Reading Time15 min

AccessFree to download

Abstract

Introduction

Methods

Animal Preparation

INNOVATIONS Use of the Frog Heart Preparation to Teach Students about the Spontaneous Mechanical Activity of the Vena Cava Brent J.F. Hill, Ian Goodman, and William M. Moran Department of Biology, University Central Arkansas, Conway, Arkansas 72035-0001 [Email:](Email: bhill@uca.edu)[ ](Email: bhill@uca.edu)[bhill@uca.edu](Email: bhill@uca.edu) Abstract: Most undergraduate physiology texts describe veins simply as reservoirs for blood and conduits for return of blood to the heart. This article describes a laboratory exercise that can be performed by students to demonstrate that veins are much more than reservoirs and conduits for blood flow: they possess a dynamic rhythmic contraction. In this exercise, we recorded the simultaneous beating of the frog postcaval vein (PCV; in mammals this is the inferior vena cava) and atrium by connecting them to separate force displacement transducers. In vivo, the PCV and atrium both contract ~ 35 beats/min; however, the contractions are not synchronous with each other. We developed a simple scoring method (comparative temporal analysis) to illustrate that the atrium contractions do not drive the contractions of the PCV. Instead the atrium and PCV contract independently of each other. To support our hypothesis that the atrium and PCV contractions were independent we removed the PCV from the frog and suspended it in an organ bath. The PCV rhythmically contracted as in vivo. The autonomic neurotransmitter, norepinephrine, did not affect the force of contraction and heart rate. In contrast, acetylcholine abolished the contractile activity. This investigation has encouraged discussions about the source and physiological significance of the rhythmic PCV contractions. This article provides some hypotheses about its significance, as well as possible evolutionary origins ofthe veins’ mechanical activity. Overall, the implementation of this exercise into the classic frog heart preparation will deepen the students’ understanding about the venous side of the cardiovascular system and give them insight into the integrative nature of physiology. Key words: contraction, veins, physiology INTRODUCTION In many undergraduate physiology laboratories the classic frog heart preparation is used to teach Starling’s Law of the heart, autonomic control of heart function, and the heart refractory period. In our senior-level animal physiology course students investigate Starling’s Law by measuring the increase in magnitude of each heart beat with each incremental increase in tension applied to the apex of the heart. This is analogous to the increase in contractile strength of the heart with an increase in venous return. Autonomic regulation ofthe heart is explored by the application of norepinephrine and acetylcholine to activate the β-adrenergic and muscarinic receptors on the heart to increase and decrease heart rate, respectively. Likewise, students change the impulse frequency on an electrical stimulator to determine how much time needs toelapse after stimulation before another heart beat can be initiated (i.e. heart refractory period) . While performing these laboratory investigations, students recognized that the postcavalvein (PCV) next to the sinus venosus ofthe heart was‘beating.’ In mammals the PCV is analogous to the inferior vena cava. In addition, the rhythmic PCV contraction appeared to be independent of the heartbeat. Traditionally, physiology courses depict veins as reservoirs for blood and as conduits for venous return of blood to the heart. However, thereis a dynamic regulation of venous diameter by hormonal and autonomic influences. Veins contract in response to norepinephrine, endothelin-1, plateletactivating factor, thromboxane A2, and leukotrienes (Gao and Raj, 2005; Xu et al., 2007) . Relaxation is mediated by the inducers of nitric oxide formation, acetylcholine, and bradykinin (Gao and Raj, 2005) . Only a few studies have reported that the PCV contracts ([i.e.](i.e. be

FAQs

What misconception about veins does the laboratory exercise challenge?

It challenges the idea that veins are only reservoirs for blood and conduits for venous return by demonstrating rhythmic, dynamic contraction.

How did the authors test whether the atrium drives the postcaval vein contractions?

They recorded the atrium and postcaval vein simultaneously and used comparative temporal scoring; they also removed the PCV and kept it in an organ bath to see if it still contracted.

How did norepinephrine and acetylcholine affect PCV contraction?

Norepinephrine did not change contraction force or heart rate, while acetylcholine abolished the contractile activity.

Oct 15, 2026

Uploaded by Well Done