The Internal Environment There are two types of extracellular fluids in animals: • the extracellular fluid that surrounds and bathes cells • plasma , the liquid component of the blood. Internal components of homeostasis: 1. Concentration of oxygen and carbon dioxide 2. pH of the internal environment 3. Concentration of nutrients and waste products 4. Concentration of salt and other electrolytes 5. Volume and pressure of extracellular fluid Control Systems Open systems are linear and have no feedback, such as a light switch. Closed Systems has two components: a sensor and an effector , such as a thermostat (sensor) and furnace (effector). Most physiological systems in the body use feedback to maintain the body's internal environment. Extrinsic Most homeostatic systems are extrinsic: they are controlled from outside the body. Endocrine and nervous systems are the major control systems in higher animals. The nervous system depends on sensors in the skin or sensory organs to receive
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