12.1.2 Mechanisms of Homeostasis

Question 1

Mechanisms of Homeostasis

Answer 1

• The cells in a body must communicate with each other in order to maintain homeostasis.
• A set point is the optimal value of a physiological variable. Violations of a body’s set point trigger homeostatic responses in the body.
• In a positive feedback loop, an effector elicits a response to a stimulus, which exaggerates the stimulus. An example of positive feedback is the mechanism for uterine contractions during labor. A negative feedback loop occurs when an effector elicits a response to a stimulus, which removes the stimulus. An example of negative feedback is temperature regulation during labor.
• Endotherms are organisms that regulate their temperature internally, while ectotherms regulate their temperature through their environment.

Question 2

positive feedback mechanism

Answer 2

• Uterine contractions during labor are controlled by a
  positive feedback mechanism. Distortion of the uterus
  signals stretch receptors in the uterine wall. In response, the hormone oxytocin, which triggers contractions, is released. As the uterus contracts, more oxytocin is released, causing even more contractions.
• Until the baby is born, contractions are continuously being stimulated by this positive feedback loop

Question 3

negative feedback

Answer 3

• The maintenance of body temperature during exercise is an example of negative feedback. As body temperature rises during exercise, the central nervous system is signaled to cause the body to sweat and dilate blood vessels at the surface of skin. Sweat causes evaporative cooling and heat from the body is released at the skin’s surface. As a result, the body’s temperature decreases.

Question 4

endotherms and ectotherms

Answer 4

• Endotherms, such as mammals and birds, are animals that regulate their body temperature internally. An endotherm’s body heat is derived mainly from its own metabolism. Ectotherms, in contrast, obtain most of their body heat from their environment. Reptiles and fish are ectotherms.
• As a result, ectotherms generally have a much lower
  metabolic rate than endotherms. Endotherms are able to take part in more physical activity for longer periods of time, while ectotherms tend to move more slowly.

Question 5

True or false?
In general, since ectotherms derive most of their body temperature from environmental heat, they have much higher caloric needs than endotherms.

Answer 5

• false

Question 6

Why is the regulation of contractions during labor considered a positive feedback loop?

Answer 6

• Because oxytocin causes the uterus to contract, which causes more oxytocin to be released.

Question 7

As body temperature rises, the human body produces sweat as a means of cooling. This is an example of

Answer 7

• negative feedback.

Question 8

A set point

Answer 8

• is the optimal value of a physiological variable.

Question 9

Which of the following is true?

Answer 9

• Endotherms maintain their body temperature through metabolic heat, while ectotherms must rely on the environment in order to regulate their temperature.

Question 10

A heating / cooling system of a house is often used as an example to illustrate a feedback loop which is analogous to those found in animals. In this analogy, the temperature at which the thermostat is set represents the ________ and the thermostat itself represents the _____________.

Answer 10

• set point, control center