Internal Regulation

• Temperature regulation is vital for the normal functioning of many behavioral processes
• Homeostasis refers to temperature regulation and other biological processes that keep certain body variables within a fixed range
• A set point is a single value that the body works to maintain, examples include levels of water, oxygen, glucose, sodium chloride, protein, fat, and acidity in the body
• Processes that reduce discrepancies from the set point are known as negative feedback
• Allostasis refers to the adaptive way in which the body changes its set point in response to changes in life or environment
• Temperature regulation is one of the body's biological priorities and uses about two-thirds of our energy/kilocalories per day
• Basal metabolism is the energy used to maintain a constant body temperature while at rest
• Poikilothermic refers to the idea that the body temperature matches that of the environment, seen in amphibians, reptiles, and most fish
• Homeothermic refers to the use of internal physiological mechanisms to maintain an almost constant body temperature, characteristics of mammals and birds
• Sweating and panting decrease temperature, while increasing temperature is accomplished via shivering, increasing metabolic rate, and decreasing blood flow to the skin
• Mammals evolved to have a constant temperature of 37°C (98°F), as muscle activity benefits from being warm and ready for vigorous activity
• Proteins in the body lose their useful properties at higher temperatures, and reproductive cells require cooler temperatures
• Body temperature regulation is predominantly dependent upon areas in the preoptic nerve/anterior hypothalamus (POA/AH)
• Bacterial and viral infections can cause a fever, which is part of the body's defense against illness
• Thirst is regulated to maintain water within narrow limits, with mechanisms including excreting concentrated urine and decreasing sweat and other autonomic responses
• Two different kinds of thirst are osmotic thirst resulting from eating salty foods, and hypovolemic thirst resulting from loss of fluids due to bleeding or sweating
• Osmotic thirst occurs due to changes in solute concentration, triggering behaviors to restore the body to a normal state
• Receptors in various parts of the body relay information to the hypothalamus to control drinking and release of vasopressin
• Hypovolemic thirst is associated with low volume of body fluids and is triggered by the release of hormones vasopressin and angiotensin II
• Animals with osmotic thirst prefer pure water, while those with hypovolemic thirst prefer slightly salty water to restore solute levels in the blood
• Sodium-specific hunger is a craving for salty foods to restore solute levels in the blood
• Digestion begins in the mouth with enzymes breaking down carbohydrates, followed by digestion of proteins in the stomach, and absorption of digested food in the small intestine into the bloodstream
• At the age of weaning, most mammals lose the intestinal enzyme lactase, necessary for metabolizing lactose found in milk
• Most human adults have enough lactase to consume milk and dairy products throughout their lifetime, but some populations lack this ability
• Carnivores eat meat for necessary vitamins, herbivores eat plants exclusively, and omnivores eat both meat and plants
• Selecting foods to eat is usually accomplished via imitation of others, preferring sweet foods, avoiding bitter foods, and learning from consequences after consuming food
• The brain regulates eating through messages from the mouth, stomach, intestines, fat cells, and other parts of the body
• The desire to taste and other mouth sensations such as chewing are motivating factors in hunger and satiety
• Sham feeding experiments have shown that mouth sensations play a role in hunger and satiety
• Factors influencing hunger and satiety:

  • Taste and mouth sensations like chewing are motivating factors in hunger and satiety
  • Sham feeding experiments where all food leaks out of a tube connected to the stomach or esophagus do not produce satiety
  • The main signal to stop eating is the distention of the stomach
  • The vagus nerve conveys information about the stretching of the stomach walls to the brain
  • Splanchnic nerves convey information about nutrient contents of the stomach
• Duodenum and hunger regulation:

  • The duodenum is where initial absorption of significant nutrients occurs
  • Distention of the duodenum can produce feelings of satiety
  • The duodenum releases the hormone cholecystokinin (CKK) to regulate hunger
  • CKK regulates hunger by closing the sphincter muscle between the stomach and duodenum, causing the stomach to hold its contents and fill faster
  • Glucose, insulin, and glucagon levels influence hunger
• Glucose and insulin:

  • Most digested food enters the bloodstream as glucose, an important energy source for the body and brain
  • Insulin enables glucose to enter cells
  • High insulin levels decrease appetite
  • Glucagon stimulates the liver to convert stored glycogen to glucose when levels fall
• Leptin and hunger regulation:

  • The body's fat cells produce leptin to signal the brain to increase or decrease eating
  • Low leptin levels increase hunger
  • High leptin levels do not necessarily decrease hunger, and most obese people are less sensitive to leptin
• Neural pathways in hunger regulation:

  • The arcuate nucleus in the hypothalamus contains neurons sensitive to hunger and satiety signals
  • Ghrelin is released as a neurotransmitter to trigger stomach contractions
  • Inputs to satiety-sensitive cells include signals from distention of the intestine, blood glucose levels, body fat, insulin, and leptin
  • Output from the arcuate nucleus goes to the paraventricular nucleus of the hypothalamus to trigger satiety
• Effects of hypothalamus damage:

  • Damage to the lateral hypothalamus can lead to refusal of food and water
  • Damage to the ventromedial hypothalamus can cause overeating and weight gain
  • Mutated gene for melanocortin receptors can lead to overeating and obesity
• Genetic factors in obesity:

  • Prader-Willi syndrome is marked by mental retardation, short stature, and obesity
  • Genetic influence has been established in factors contributing to obesity
  • Monozygotic twins resemble each other more in factors contributing to obesity than dizygotic twins
• Obesity and environment:

  • Obesity can result from genes interacting with changes in the environment
  • Obesity has become common in the United States due to lifestyle changes like increased fast food restaurants and portion sizes
• Weight loss and treatments:

  • Weight loss can be difficult, and specialists may not agree on treatment plans
  • Plans should include increased exercise and decreased eating
  • Appetite suppressant drugs like fenfluramine and phentermine can block neurotransmitter reuptake to produce brain effects similar to a completed meal
  • "Orlistat" is a drug that prevents the intestines from absorbing fats
• Eating disorders:

  • Anorexia nervosa is associated with an unwillingness to eat as needed and a fear of becoming fat
  • Genetic predisposition is likely, and biochemical abnormalities in the brain and blood are a result of weight loss
  • Bulimia nervosa involves extreme dieting and binges of overeating, associated with hormonal and neurotransmitter alterations
  • Bulimia nervosa may be a result and not the cause of the disorder