Chapter 25 Outline
Hearts
- BOX 25.1 The Structure and Function of Vertebrate Cardiac Muscle
- The heart as a pump: The action of a heart can be analyzed in terms of the physics of pumping
- The circulation must deliver O2 to the myocardium
- The electrical impulses for heart contraction may originate in muscle cells or neurons
- A heart produces an electrical signature, the electrocardiogram
- Heart action is modulated by hormonal, nervous, and intrinsic controls
Principles of Pressure, Resistance, and Flow in Vascular Systems
- The rate of blood flow depends on differences in blood pressure and on vascular resistance
- The dissipation of energy: Pressure and flow turn to heat during circulation of the blood
Circulation in Mammals and Birds
- The circulatory system is closed
- Each part of the systemic vascular system has distinctive anatomical and functional features
- Mammals and birds have a high-pressure systemic circuit
- Fluid undergoes complex patterns of exchange across the walls of systemic capillaries
- The pulmonary circuit is a comparatively low-pressure system that helps keep the lungs “dry”
- During exercise, blood flow is increased by orchestrated changes in cardiac output and vascular resistance
- Species have evolved differences in their circulatory physiology
- Vascular countercurrent exchangers play important physiological roles
Circulation in Fish
- The circulatory plans of fish with air-breathing organs (ABOs) pose unresolved questions
- Lungfish have specializations to promote separation of oxygenated and deoxygenated blood
- BOX 25.2 An Incompletely Divided Central Circulation Can Be an Advantage for Intermittent Breathers
Circulation in Amphibians and in Reptiles Other than Birds
Concluding Comments on Vertebrates
Invertebrates with Closed Circulatory Systems
- BOX 25.3 Bearing the Burden of Athleticism, Sort of: A Synthesis of Cephalopod O2 Transport
Invertebrates with Open Circulatory Systems
- The crustacean circulatory system provides an example of an open system
- BOX 25.4 Circulation and O2: Lessons from the Insect World
- Open systems are functionally different from closed systems but may be equal in critical ways