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The Body’s Defenses

Chapter 5: The Body’s Defenses
Nearly everything in the environment -water, food, and even the air -teems with microbes. The human body has three cooperative lines of defense that protect us from the constant barrage of these and other potentially harmful substances (Figure 5.1). The first line of defense is a set of physical barriers and chemical agents that prevent foreign invaders from getting deep inside the body. If that line fails, a variety of internal protections stand ready as a second line of defense. These first two lines of defense are nonspecific -that is, they do not distinguish one infectious microbe from another, but rather respond similarly to every infectious agent. Later in this chapter, we’ll discuss the third line of defense: the immune system, which responds in a customized way to each particular microorganism.
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Unifying Concepts of Animal Respiration

Chapter 4: Respiration
Unifying Concepts of Animal Respiration
Without oxygen, the chemical reactions of cellular respiration - the series of metabolic steps that releases energy from food molecules - cannot proceed. The cellular respiration uses oxygen and glucose to produce water, carbon dioxide, and energy in the form of ATP. All working cells therefore require a steady supply of O2 from the environment and must continuously dispose of CO2:
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Unifying Concepts of Animal Circulation

Chapter 3: Circulation
Unifying Concepts of Animal Circulation
Every organism must exchange materials and energy with its environment. In simple animals, such as hydras and jellies (also known as jellyfishes), all the cells are in direct contact with the environment. Thus, every cell can easily exchange materials with its environment by diffusion, the movement of molecules along a concentration gradient, from an area of higher concentration to an area of lower concentration.
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BASIC HUMAN PHYSIOLOGY Ch 1+2

Chapter 1: Unifying Concepts of Animal Structure and Function
Chapter 2: Nutrition and Digestion
In this unit of chapters, you will learn about how your body works. The emphasis will be on humans, but comparisons with other animals will illustrate some of the ways in which different organisms “solve” a common set of problems. This chapter sets the stage by introducing some unifying concepts of structure and function that apply across the entire animal kingdom.
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