Chapter 25 Outline

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

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

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

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

BOX 25.3 Bearing the Burden of Athleticism, Sort of: A Synthesis of Cephalopod O₂ Transport

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