Home :: Chapter 13 :: Summary & Outline

Chapter 13 Summary & Outline

The nervous system plays a crucial role in maintaining the homeostasis that the body requires for proper functioning. Temperature, fluid concentration, chemical energy, and nutrients must all be maintained within a critical range.
The redundancy of homeostatic mechanisms reflects the fundamental importance of a stable internal environment. These mechanisms generally are negative feedback systems. Review Figure 13.1, Web Activity 13.1

Study questions: 1 | 2 | 3

Temperature Regulation

Because the speed of biochemical reactions is temperature dependent, precise control of body temperature is essential. Ice crystals are extremely damaging to many cells, and must be avoided through the production of antifreeze proteins.

Study questions: 4

Both endotherms and ectotherms regulate body temperature, but ectotherms depend more on behaviors to capture heat from the environment, while endotherms generate most of their body heat through the metabolism of food. Review Web Activity 13.2
Endotherms can remain active longer than ectotherms can, but endotherms are also obliged to gather more food than ectotherms do to generate their body warmth.
Body size and shape drastically affect the rate of heat loss. Small endotherms have a higher metabolic rate, using more energy (per gram of body weight) than large endotherms use. Review Table 13.1

Study questions: 5 | 6 | 7 | 8 | 9 | 10

Both endotherms and ectotherms use behavioral methods to help regulate body temperature at optimal levels. Young animals particularly depend on this form of thermoregulation.

Study questions: 11 | 12 | 13 | 14

The preoptic area of the hypothalamus, the brainstem, and the spinal cord monitor and help regulate body temperature. Review Figures 13.3 and 13.7

Study questions: 15 | 16 | 17

Our cells function properly only when the concentration of salts and other ions (the osmolality) of the intracellular compartment of the body is within a critical range. The extracellular compartment is a source of replacement water and a buffer between the intracellular compartment and the outside world. Review Figure 13.10

Study questions: 18 | 19 | 20 | 21 | 22

Thirst can be triggered either by a drop in the volume of the extracellular compartment (hypovolemic thirst) or by an increase in the osmolality of the extracellular compartment (osmotic thirst). Either signal indicates that the volume or osmolality of the intracellular compartment may fall outside the critical range. Because of the importance of osmolality, we must regulate salt intake in order to regulate water balance effectively. Review Figure 13.11
A drop in blood volume triggers at least three responses: (a) Baroreceptors in the major blood vessels detect the drop and signal the brain via the autonomic nervous system. (b) The brain in turn releases vasopressin from the posterior pituitary, and the vasopressin reduces blood vessel volume and the amount of water lost through urination. (c) The kidneys release renin, providing circulating angiotensin II, which reduces blood vessel volume to maintain blood pressure and may also signal the brain that the blood volume has dropped. Review Figure 13.13
The hypothalamus contains osmosensory neurons that detect the concentration of extracellular fluid. Increased solute concentration of the extracellular fluid triggers an intake of water. Review Figures 13.15 and 13.16
The conscious perception of thirst involves activation of a network of limbic system sites, and is a powerful motivator.

Study questions: 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32

The amount of water that the body can retain is determined by salt balance. In the absence of salt, extracellular fluid becomes too dilute and excess water must be eliminated. The adrenal steroid aldosterone performs the vital function of conserving salt.

Study questions: 33 | 34

Our digestive system breaks down food and uses most of it for energy, especially because we are endotherms.

Study questions: 35 | 36 | 37 | 38 | 39 | 40 | 41 | 42 | 43

Although brain cells can use glucose directly, body cells can import glucose only with the assistance of insulin secreted by the pancreas. Insulin also promotes the storage of glucose as glycogen. Another pancreatic hormone, glucagon, helps convert glycogen back into glucose. Review Figure 13.20
Manipulations of either glucose or insulin can affect whether an animal experiences hunger, but experimental studies have indicated that neither glucose nor insulin alone can be the single indicator of hunger or satiety. There also seems to be no single brain center for either satiety or hunger.

Study questions: 44 | 45 | 46 | 47 | 48 | 49 | 50

An appetite controller located in the arcuate nucleus of the hypothalamus responds to levels of several peptide gut hormones. Leptin, providing a chronic signal about fat levels, stimulates arcuate POMC/CART neurons to release α-MSH in the lateral hypothalamus to activate MC4R receptors to decrease appetite. Leptin inhibits arcuate NPY/AgRP neurons, decreasing their release of NPY and AgRP to suppress appetite further. Review Figure 13.26
Ghrelin and PYY_3-36provide more-acute signals from the gut. Ghrelin stimulates and PYY_3-36 inhibits the arcuate appetite control system. Review Figure 13.26

Study questions: 51 | 52 | 53 | 54 | 55 | 56 | 57 | 58 | 59 | 60 | 61

Obesity is a pervasive problem that is difficult to treat through diet, drugs, or surgery. The only long-lasting medical intervention for obesity is bariatric surgery, but several drug strategies based on a new understanding of appetite control offer promise. Review Figure 13.28

Study questions: 62 | 63

The major eating disorders are anorexia nervosa, bulimia, and binge eating. Although several cultural and physiological correlates of eating disorders have been identified, the fundamental causes of these disorders remain a mystery.

Study questions: 64 | 65