Experimental Tests of a Physical Model for Lymph Flow in Anurans

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The objectives of this work are to experimentally test how the anatomical and physiological control of skeletal muscles and breathing contributes to lymph movement in anuran amphibians (frogs and toads). Lymph is the fluid that filters from the small blood vessels (capillaries) of the circulatory system into the tissue as a consequence of the pressure generated by the heart. The principal role of the lymphatic system is to return this fluid that escapes from the capillaries back into the circulation. Anuran amphibians lose circulatory fluid, and hence form lymph, at about ten times the rate of mammals. Thus their ability to return lymph to the circulatory system is critical and amphibians can replace lost blood volume with lymph more rapidly than any other vertebrate. The working hypothesis for this research project is that lymph moves in response to pressure differences in lymph sacs created by two mechanisms: lung ventilation and skeletal muscle contractions. Through a collaboration of researchers at three institutions (Portland State University, California State University East Bay, California Academy of Sciences) lymph flux associated with lung pressure changes and skeletal muscle contraction in various anatomical pathways will be measured. In addition, the effect of blood volume status on these pressures and activities will be assessed. Comparative anatomical data will be collected to determine whether anatomical differences correlate with differences in lymph flow and the ability to withstand dehydration. This research will lead to a greater understanding of the mechanisms of lymph movement and provide insight into the adaptations that led to the successful colonization of land by the first vertebrate group that left the aquatic environment. Undergraduate and graduate students researchers will be trained and benefit from the collaboration between the researchers' laboratories. The results of this project will be disseminated via educational outreach efforts affiliated with the California Academy of Sciences.