MAP607 Physiological Basis of Behaviour(1)-converted

Figure 11.3.: This chart shows how adult BMI is calculated. Individuals find their height on the y-axis and their weight on the x-axis to determine their BMI. Obesity results from changes in leptin or damage to the brain. From studies on the control of feeding, it is known that at least two monoamine neurotransmitters (norepinephrine and serotonin) in the brain play a particularly important role. These neurotransmitters have been the subject of considerable interest, since most of the medications used to treat obesity influence hunger through changing levels of one or both of these neurotransmitters. As more is learned about the control of hunger, a steady source of new targets is available that can be used to develop future medications for the treatment of obesity. Being extremely overweight or obese is a risk factor for several negative health consequences. These include, but are not limited to, an increased risk for cardiovascular disease, stroke, Type 2 diabetes, liver disease, sleep apnoea, colon cancer, breast cancer, infertility, and arthritis. Given that it is estimated that in the United States around one-third of the adult population is obese and that nearly two-thirds of adults and one in six children qualify as overweight (CDC, 2012), there is substantial interest in trying to understand how to combat this important public health concern. What causes someone to be overweight or obese? You have already read that both genes and environment are important factors for determining body weight, and if more calories are consumed than expended, excess energy is stored as fat. However, socioeconomic status and the physical environment must also be considered as contributing factors (CDC, 2012). For example, an individual who lives in an impoverished neighbourhood that is overrun with crime may never feel comfortable walking or biking to work or to the local market. This might limit the amount of physical activity in which he engages and result in an increased body weight. Similarly, some people may not be able to afford healthy food options from their market, or these options may be unavailable (especially in urban areas or poorer neighbourhoods); therefore, some people rely primarily on available, inexpensive, high fat, and high calorie fast food as their primary source of nutrition. 150 CU IDOL SELF LEARNING MATERIAL (SLM)

Generally, overweight and obese individuals are encouraged to try to reduce their weights through a combination of both diet and exercise. While some people are very successful with these approaches, many struggle to lose excess weight. In cases in which a person has had no success with repeated attempts to reduce weight or is at risk for death because of obesity, bariatric surgery may be recommended. Bariatric surgery is a type of surgery specifically aimed at weight reduction, and it involves modifying the gastrointestinal system to reduce the amount of food that can be eaten and/or limiting how much of the digested food can be absorbed ([link]) (Mayo Clinic, 2013). A recent meta-analysis suggests that bariatric surgery is more effective than non-surgical treatment for obesity in the two-years immediately following the procedure, but to date, no long-term studies yet exist (Gloy et al., 2013). Figure 11.4.: Gastric banding surgery creates a small pouch of stomach, reducing the size of the stomach that can be used for digestion. EATING DISORDERS While nearly two out of three US adults struggle with issues related to being overweight, a smaller, but significant, portion of the population has eating disorders that typically result in being normal weight or underweight. Often, these individuals are fearful of gaining weight. Individuals who suffer from bulimia nervosa and anorexia nervosa face many adverse health consequences (Mayo Clinic, 2012a, 2012b). People suffering from bulimia nervosa engage in binge eating behaviour that is followed by an attempt to compensate for the large amount of food consumed. Purging the food by inducing vomiting or through the use of laxatives are two common compensatory behaviours. Some affected individuals engage in excessive amounts of exercise to compensate for their binges. Bulimia is associated with many adverse health consequences that can include kidney failure, heart failure, and tooth decay. In addition, these individuals often suffer from anxiety and depression, and they are at an increased risk for substance abuse (Mayo Clinic, 2012b). 151 CU IDOL SELF LEARNING MATERIAL (SLM)

The lifetime prevalence rate for bulimia nervosa is estimated at around 1% for women and less than 0.5% for men (Smink, van Hoeken, & Hoek, 2012). As of the 2013 release of the Diagnostic and Statistical Manual, fifth edition, Binge eating disorder is a disorder recognized by the American Psychiatric Association (APA). Unlike with bulimia, eating binges are not followed by inappropriate behaviour, such as purging, but they are followed by distress, including feelings of guilt and embarrassment. The resulting psychological distress distinguishes binge eating disorder from overeating (American Psychiatric Association [APA], 2013). Anorexia nervosa is an eating disorder characterized by the maintenance of a body weight well below average through starvation and/or excessive exercise. Individuals suffering from anorexia nervosa often have a distorted body image, referenced in literature as a type of body dysmorphia, meaning that they view themselves as overweight even though they are not. Like bulimia nervosa, anorexia nervosa is associated with a number of significant negative health outcomes: bone loss, heart failure, kidney failure, amenorrhea (cessation of the menstrual period), reduced function of the gonads, and in extreme cases, death. Furthermore, there is an increased risk for a number of psychological problems, which include anxiety disorders, mood disorders, and substance abuse (Mayo Clinic, 2012a). Estimates of the prevalence of anorexia nervosa vary from study to study but generally range from just under one percent to just over four percent in women. Generally, prevalence rates are considerably lower for men (Smink et al., 2012). While both anorexia and bulimia nervosa occur in men and women of many different cultures, Caucasian females from Western societies tend to be the most at-risk population. Recent research indicates that females between the ages of 15 and 19 are most at risk, and it has long been suspected that these eating disorders are culturally-bound phenomena that are related to messages of a thin ideal often portrayed in popular media and the fashion world ([link]) (Smink et al., 2012). While social factors play an important role in the development of eating disorders, there is also evidence that genetic factors may predispose people to these disorders (Collier & Treasure, 2004). THE PHYSIOLOGICAL BASIS OF THIRST Thirst is often viewed by physiologists and physicians as a central nervous system mechanism that regulates the body's water and minerals. The significance of the thirst drive is emphasized by three facts: 50 to 70 percent of adult body weight is water, the average adult ingests and loses 2.5 litres of water each day, and body weight is regulated within 0.2 percent from one day to the next. Clearly, water is essential to life and the body responds in a manner that ensures survival. In 1954, Edward Adolph and colleagues proposed a multiple-factor theory of thirst that has not been refuted to date. This theory states that no single mechanism can account for all drinking behaviour and that multiple mechanisms, sometimes with identical functions, act concurrently. Because water is essential to life, the existence of redundant mechanisms has 152 CU IDOL SELF LEARNING MATERIAL (SLM)

great survival value. Among these, thirst appears to be regulated primarily by evaluation of changes in the concentration of extracellular fluid, measured as the osmolality of blood plasma. Below a certain threshold level of plasma osmolality, thirst is absent. Above this threshold, a strong desire to drink appears in response to an increase of 2 to 3 percent in the level of dissolved substances in blood. The brain's thirst centre lies deep within the brain, in an area known as the hypothalamus. This anatomical site contains cells that respond to changes in the concentration of body fluids. When the thirst centre is stimulated by an increased concentration of blood (that is, dehydration), thirst and fluid consumption increase. As the brain senses the concentration of blood, it allows a minor loss of body water before stimulating the drive to drink. This phenomenon has been named voluntary dehydration. Specifically, several research studies since the 1930s have observed that adults and children replace only 34 to 87 percent of the water lost as sweat, by drinking during exercise or labour in hot environments. The resulting dehydration is due to the fact that thirst is not perceived until a 1 to 2 percent body weight loss occurs. Interindividual differences, resulting in great voluntary dehydration in some individuals, have caused them to be named reluctant drinkers. Reduced extracellular fluid volume, including blood volume, also increases thirst. Experiments (for example, reducing blood volume without altering blood concentration) have demonstrated that volume-sensitive receptors in the heart and blood vessels likely regulate drinking behaviour by increasing the secretion of hormones. This effect is relatively minor, however. Animal research suggests that a change in extracellular fluid concentration accounts for most (for example, 70 percent) of the increased fluid consumption that follows moderate whole-body dehydration, whereas a decrease of fluid volume per se plays a secondary role. Thus, thirst is extinguished when body fluid concentration decreases and fluid volume increases. Osmolality-sensitive nerves in the mouth, throat, and stomach also play a role in abating thirst. As fluid passes through the mouth and upper gastrointestinal tract, the sense of dryness decreases. When this fluid fills the stomach, stretch receptors sense an increase in gastric fullness and the thirst drive diminishes. As dehydration causes the body's extracellular fluid to become more concentrated, the fluid inside cells moves outward, resulting in intracellular dehydration and cell shrinkage, and the hormone arginine vasopressin (AVP, also known as the antidiuretic hormone) is released from the brain. AVP serves two purposes: to reduce urine output at the kidneys and to enhance thirst; both serve to restore normal fluid balance. Other hormones influence fluid- mineral balance directly and thirst indirectly. Renin, angiotensin II, and aldosterone are noteworthy examples. As dehydration reduces circulating blood volume, blood pressure decreases and renin is secreted from blood vessels inside the kidneys. Renin activates the hormone angiotensin II, which subsequently stimulates the release of aldosterone from the adrenal glands. Both angiotensin II and aldosterone increase blood pressure and enhance the retention of sodium and water; these effects indirectly reduce the intensity of thirst. Angiotensin II also affects thirst directly. When injected into sensitive 153 CU IDOL SELF LEARNING MATERIAL (SLM)

areas of the brain, it causes a rapid increase in water consumption that is followed by a slower increase in sodium chloride consumption and water retention by the kidneys. Individual Factors Repeated training sessions in cool or hot environments alter fluid consumption in four ways. First, physical training increases the secretion of the hormone AVP, which stimulates drinking and body water retention. Second, exercise-heat acclimation (that is, adaptations due to exercise in a hot environment over eight days) increases the volume of fluid consumed and the number of times that adults drink during exercise. Third, frequent rest periods, in the midst of labor or exercise, will increase fluid replacement time and enhance fluid consumption. Humans tend to drink less when they are preoccupied or are performing physical or mental tasks. Fourth, learned behaviors can enhance fluid consumption when thirst is absent. This phenomenon is widely appreciated among military personnel and athletes who are trained to consume water at regular intervals, whether they are thirsty or not. Several research groups have reported that chronological age influences thirst and drinking behavior. Elderly men experience a blunted thirst drive and reduced fluid intake, perhaps due to their brains' reduced ability to sense changes in plasma osmolality or blood volume. Further, elderly individuals experience a decrease in the ability of their kidneys to conserve water. This suggests that the elderly are predisposed to dehydration when illness increases water loss (that is, vomiting, diarrhea) or when physical incapacity prevents access to water. SUMMARY 1. Eating is essential for survival, and it is no surprise that a drive like hunger exists to ensure that we seek out sustenance. 2. There are a number of physiological mechanisms that serve as the basis for hunger. 3. The physiological cues associated with an empty stomach that tell us to eat are referred to as internal cues. 4. Sensory cues defy the simple concept that we eat when we are hungry and stop eating when we are full. 5. External normative cues have also been shown to influence how much we eat.Generally speaking, people have the tendency to finish the food on their plate. 6. Sensory cues defy the simple concept that we eat when we are hungry and stop eating when we are full. 7. In addition to sensory and normative cues, social facilitation is another type of external cue that can influence our eating behaviours. 8. Hunger and satiety are highly regulated processes that result in a person maintaining a fairly stable weight that is resistant to change. 9. When more calories are consumed than expended, a person will store excess energy as fat. 10. Being significantly overweight adds substantially to a person’s health risks and problems, including cardiovascular disease, type 2 diabetes, certain cancers, and other medical issues. 154 CU IDOL SELF LEARNING MATERIAL (SLM)

11. Sociocultural factors that emphasize thinness as a beauty ideal and a genetic predisposition contribute to the development of eating disorders in many young females, though eating disorders span ages and genders. 12. Thirst is a subjective perception that provides the urge for humans and animals to drink fluids. 13. Thirst is important for maintaining body fluid homeostasis and may arise from deficits in either intracellular or extracellular fluid volume. 14. Neural signals arising from osmotic and hormonal influences on the lamina terminalis may be integrated within the brain, with afferent information relayed from intrathoracic baroreceptors via the hindbrain to generate thirst. 15. When the body loses water, it is usually depleted from both the extracellular and intracellular compartments. 16. Thirst leads to drinking. This is a powerful defence against hyperosmolality. As long as access to water is unrestricted and the person is able to drink, then significant hyperosmolality will not develop. KEY WORDS/ ABBREVIATIONS • Hunger- the sensation caused by a need for food. • Thirst- the sensation caused by a need for increased fluid intake to maintain an optimum balance of water and electrolytes in body tissues. LEARNING ACTIVITY 1. Emotions are one of the factors that have an impact on hunger. Talk to 4 to 5 of your friends with their experiences with emotional eating or emotional starving. 2. Have you taken up any short term dieting regimen. What was your experience with the same? UNIT END QUESTIONS (MCQs AND DESCRIPTIVE) A. Descriptive Questions 1. Hunger is a combination of physiological and emotional reaction. Explain how the body reacts when you are hungry. 2. Brain plays a crucial role in us feeling hungry. Identify the areas of brain that are responsible for the same. 155 CU IDOL SELF LEARNING MATERIAL (SLM)

3. Some people do eat less but yet out on weight. Explain how bodily functions lead to obesity. 4. Some people eat a lot while other count calories. Are there people who have abnormal eating habits? What are they suffering from? Elaborate. 5. When our body losses its fluids, we feel thirsty. Explain the physiological reactions or responses when this happens. B. Multiple Choice Questions 1. describes the preferences that surround the selection of food that is found. [a] Diet [b] Appetite [c] Hunger [d] Food habits 2. refer to the stomach contractions experienced when we are hungry. [a] Starvation [b] Fullness [c] Hunger Pangs [d] None of the above 3. habits related to food habits. [a] Hypothalamus B) Amygdala [c] Thyroid Gland [d] Limbic System 4. In diabetes patients, the does not function properly. [a] Hypothalamus 156 CU IDOL SELF LEARNING MATERIAL (SLM)

[b] Insulin [c] Thyroid Gland [d] Bile 5. A person with a BMI above is considered obese. [a] 24.5 [b] 28 [c] 32 [d] 30 Answer 1 [b]2 [c]3 [a]4 [b]5 [d] REFERENCES • Martin, N. (2010). Psychology, (4th ed). Pearson Education Limited • Mangal, S.K. (1995). An Introduction to Psychology. Sterling Publishers Private Limited • Eynenck, M. (2014). Fundamentals of Psychology. Taylor & Francis. • Woodworth, R. S. & Marquis, D. G. (2015). Psychology a study ofmental life. Taylor & Francis. • Bernstein D. (2018) Essentials of Psychology. Cengage Learning. • Feldman, R. S. (2012) Understanding Psychology (11th ed). McGraw-Hill Education - Europe • Pinel, J.P.J. (2007). Biopsychology. New Delhi: Pearson • Rosenzweig, M. R., Leiman, A. L. & Breedlove, S. M. (1996). Biological Psychology. Sunderland, Mass: Sinauer Associates. • Green, S. (1995). Principles of biopsychology. UK: Lawrence Erlbaum Associates Ltd. • Pinel, J. P. J. (2004). Biopsychology. Boston, MA: Allyn & Bacon. • Annett, M. (1984). Left, right, hand and brain: The right shift theory. London: Lawrence Erlbaum Associates Ltd. • Bannett, T.L. (1977). Brain and Behaviour. California: Brooks/ Cole. • Leukel, F. (1985). Introduction to Physiological Psychology. New Delhi: CBS Publishers 157 CU IDOL SELF LEARNING MATERIAL (SLM)

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