The Cardiovascular System

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• Publisher: Academic Press
• Year: 1992
• Print ISBN: 9780123504357
• eBook ISBN: 9780080585352
• Topic: Biological Sciences
• Subtopic: Physiology
• Index: Biological Sciences

This book and its companion, Fish Physiology, Volume 12, Part B, are the first major syntheses of recent advances, general concepts, and species diversity of fish in almost 25 years. It provides broad coverage of the major aspects of cardiovascular physiology and is a definitive sourcebook for the field. This book discusses the special design of the venous system in aquatic vertebrates, reviews the nature of the secondary circulation in fish, and discusses the probable absence of the lymphatic system. It is of value to teachers in comparative physiology as well as to the researcher.

1

The Heart

Anthony P. Farrell, Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia, Canada

David R. Jones, Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada

I Introduction

II Cardiac Anatomy and Morphology

A Sinus Venosus

B Atrium

C Ventricle

D Innervation Patterns

E Myocytes

F Conus and Bulbus Arteriosus

G Coronary Circulation

III Cardiac Physiology

A Cardiac Cycle

B Control of Stroke Volume

C Control of Heart Rate

D Cardiac Output

E Myocardial Oxygen Consumption

F Control of Coronary Blood Flow

References

I. Introduction

Since the descriptions of the cardiovascular system and the cardiovascular changes associated with exercise that appeared in earlier volumes of this series (Randall, 1970; Jones and Randall, 1978), several informative reviews, monograms, and perspectives have appeared, dealing with either general or specific aspects of cardiovascular physiology and anatomy. These works include those of Johansen and Burggren (1980), Tota (1983), Nilsson (1983), Laurent et al. (1983), Farrell (1984), Santer (1985), Farrell (1985), Wood and Perry (1985), Butler (1986), Johansen and Gesser (1986), Butler and Metcalfe (1988), Tota (1989), Forster et al. (1991), Davie and Farrell (1991a), Brill and Bushnell (1991), Farrell (1991a), and Satchell (1991). This chapter focuses on the heart, whereas the primary arterial circulation is dealt with in the following chapter. Cardiac anatomy and morphology are described in Section II. The cardiac cycle and the control of cardiac output (

) are described in Section III. Since the heart also generates sufficient pressure to overcome vascular resistance, pressure development and myocardial power output are also considered in Section III. Accessory hearts, which assist venous return, are described in Chapter 3.

II. Cardiac Anatomy and Morphology

The fish heart is a four-chambered organ contained within a pericardial sac. Together, the sinus venosus, atrium, ventricle, and either an elastic bulbus arteriosus (in teleosts), or a contractile conus arteriosus (in elasmobranchs) raise the potential and kinetic energy of the blood. Detailed descriptions of fish hearts in the recent literature include Santer and Greer Walker (1980), Yamauchi (1980), Tota (1983), Santer (1985), Greer Walker et al. (1985), Emery et al. (1985), Sanchez-Quintana and Hurle (1987), and Tota (1989). What follows is a brief functional description of the anatomy, fine structure, and morphometrics of the heart.

A. Sinus Venosus

The sinus venosus has been described as a thin-walled chamber usually 60–90 μm thick (Santer, 1985). Its volume is similar to that of the atrium in teleosts, but less than that of the atrium in elasmobranchs (Satchell, 1971). The sinus venosus receives venous blood via paired Cuverian ducts, hepatic veins, and anterior jugular veins. The sinoatrial ostium is guarded by a large valve, and the openings of the hepatic veins into the sinus venosus are guarded by muscular sphincters. However, the Cuverian ducts are not valved; they freely communicate with the major systemic veins, which are particularly capacious in elasmobranchs (see Chapter 3).

The principal tissue component of the sinus wall is connective tissue with bounding inner endothelial and outer epicardial linings. The amount of cardiac muscle present in the sinus venosus varies considerably among species. The European eel (Anguilla anguilla) has an almost complete layer of cardiac muscle (Yamauchi, 1980). In contrast, cardiac muscle is limited to a sparse arrangement of small bundles of 4 to 5 cells in plaice (Pleuronectes platessa) and bull rout (Myoxocephalus scorpius). The sinus venosus is virtually amuscular in loach (Misgurnus anguillicaudatus), brown trout (Salmo trutta), and zebra fish (Zebra danio). Goldfish (Carassius auratus) and carp (Cyprinus carpio) have only smooth muscle elements (Yamauchi, 1980).

The major functional role of the sinus venosus is related to the initiation and control of the heart beat. The sinus venosus is the site of specialized cardiac pacemaker tissue in many fish. Histological and neurophysiological evidence for the location of pacemaker tissue has been reviewed previously (Laurent, 1962; Yamauchi, 1980; Laurent et al., 1983; Santer, 1985; Satchell, 1991). What emerges from these reviews is that a ring of specialized myocardial cells (nodal tissue) is usually located at the base of the sinoatrial ostium and connects with atrial myocardium. Nodal tissue can have other locations. In the eel (A. vulgaris) and lungfish (Protopterus ethiopicus), the pacemaker is located at the junction of the sinus venosus and Cuverian ducts. Specialized pacemaker cells have also been reported in the atrium of plaice, brown bullhead (Ictalurus nebulosus), and Pacific hagfish (Eptatretus stouti), as well as in the atrioventricular region. Even in the absence of specialized pacemaker tissue, myogenic activity of the atrium, ventricle, or atrioventricular region can also initiate contraction, but the contraction rate is likely to be slower and more irregular than the pacemaker rate.

B. Atrium

Water-breathing fish have a single atrium. The atrium is an irregularly shaped chamber with thin trabecular walls (Santer, 1985). Atrial volume is similar to or larger than ventricular volume (see Section III,B,2). Atrial mass generally constitutes 8–25% of ventricular mass and 0.01–0.03% of body mass (Table I). However, exceptionally large atria are reported for the New Zealand hagfish (Eptatretus cirrhatus), tunas, and two species of red-blooded Antarctic fishes (Table I). In E. cirrhatus, Pagothenia bernacchii, and P. borchgrevinki, atrial mass is an unusually large proportion (33–50%) of ventricular mass. Skipjack tuna (Katsuwonus pelamis) have an exceptionally large ventricle, and the atrial to ventricular ratio is similar to that in other fish. As a result, their unusually large (0.06%) atrial mass relative to body mass ...

Table of contents

• Cover image
• Title page
• Table of Contents
• Contributors
• Front Matter
• Copyright page
• Contents of Part B
• Contributors
• Preface
• Contents of Other Volumes
• Chapter 1: The Heart
• Chapter 2: The Arterial System
• Chapter 3: The Venous System
• Chapter 4: The Secondary Vascular System
• Chapter 5: Cardiac Energy Metabolism
• Chapter 6: Excitation–Contraction Coupling in the Teleost Heart
• Author Index
• Systematic Index
• Subject Index