Award Date

1-1-2005

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Science

First Committee Member

Carl L. Reiber

Number of Pages

190

Abstract

Aquatic organisms may encounter multiple perturbations in their environment including but certainly not limited to fluctuations in temperature, salinity, conductivity, pH, carbon dioxide and oxygen content. A large body of work has elucidated the complexity of the cardiovascular system of crustaceans but the intricacies associated with alterations in cardiovascular function with changing environments are elusive. The current body of work focuses on the cardiovascular adjustments that allow crustaceans to survive decreases in oxygen tension; The complexity of control of the open circulatory system of crustaceans has long been underestimated and the marine crustacean, the grass shrimp, P. pugio, which often encounters fluctuations in water oxygen content served as a subject of the following studies. Crustacea posses multiple outlets from their single chambered hearts, yet the vessels supplied by the heart are not muscular and are not able to alter resistance as in mammalian systems. Instead they have muscular cardio-arterial valves that are innervated and the aperture of the valves is regulated by the central nervous system and several hormones; The first goal of this body of work was to examine alterations in cardiovascular parameters which included heart rate, stroke volume, cardiac output and hemolymph flow, in different reproductive states, in response to declining oxygen tension. The data clearly demonstrate that as oxygen tension falls, even as cardiac output is maintained, there are significant alterations in flow. In particular, despite requiring flow to the ovary in reproductively active females, the metabolically demanding ventral nerve cord receives the greatest percentage of cardiac output and this percentage increases during hypoxic exposure while other less metabolically demanding areas of the animal receive reduced flow; To appreciate the cardiac mechanics and energetics involved in the hypoxic response, these are the first studies to utilize pressure-area loops in the ventricle of an open circulatory system. Once we established that P-A loops were adequate to evaluate cardiac energetics, we used P-A loops to examine changes in ventricular function in response to hypoxia. Stroke work of the ventricle decreases significantly upon hypoxic exposure primarily as a result of reduced intra-cardiac pressure; The second goal of the work was to describe alterations in oxygen binding pigments as animals are reared in or exposed to hypoxia. Both rearing in hypoxia and prolonged exposure to hypoxia as an adult led to significant increases in Hb concentration and altered Hb subunit expression. These changes are not reversed in hypoxic reared adult animals indicating that the response is plastic during development and inducible in adulthood; Collectively these data indicate that substantial but sustainable shifts in cardiovascular and cardiorespiratory parameters occur when these animals are exposed to hypoxia. Future research will continue to elucidate and clarify the suite of complex mechanisms involved in these responses.

Keywords

Cardiorespiratory; Compensatory; Exposure; Hemoglobin; Hypoxic; Plastic; Reproduction; Responses; Short; Term

Controlled Subject

Physiology

File Format

pdf

File Size

3706.88 KB

Degree Grantor

University of Nevada, Las Vegas

Language

English

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