Biology  5/e   Raven/Johnson
	Student   Online Learning Center

Adaptation of vertebrates to terrestrial living: Vertebrates first evolved in the seas. During the course of their evolution they achieved many adaptations that allowed them to live successfully on land. These adaptations included the amniotic egg and placenta, efficient locomotion, dry skin, efficient lungs, and an improved circulatory system.

Erythrocytes: Erythrocytes (red blood cells) are the most common type of blood cells. They are packed with many molecules of hemoglobin that bind and carry oxygen. Without the erythrocytes with their oxygen-carrying hemoglobin, vertebrates would be unable to meet the oxygen demands of their cells and lifestyles.

Cardiac muscle: Muscle is one of the four basic types of vertebrate tissue, and cardiac (heart) muscle is one of the three types of muscle. In cardiac muscle, the contracting fibers are interconnected and form a latticework. Because of the direct electrical junction between fibers, depolarization of one fiber causes a wave of contraction to spread throughout the whole heart muscle and the heart contracts as a unit rather than a little bit at a time.

Homeostasis: All living organisms try to maintain homeostasis, relatively constant internal body conditions. The circulatory system plays a crucial role in achieving homeostasis.

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