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Chapter 10 Internal Regulation. Temperature Regulation. Temperature affects many aspects of behavior. Temperature regulation is vital to the normal functioning of many behavioral processes.

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temperature regulation
Temperature Regulation
  • Temperature affects many aspects of behavior.
  • Temperature regulation is vital to 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.
temperature regulation1
Temperature Regulation
  • A set point refers to a single value that the body works to maintain.
    • Examples: 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 the environment.
temperature regulation2
Temperature Regulation
  • Temperature regulation is one of the body’s biological priorities.
    • 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.
temperature regulation3
Temperature Regulation
  • Poikilothermic refers to the idea that the body temperature matches that of the environment.
    • Amphibians, reptiles and most fish.
  • The organism lacks the internal, physiological mechanisms of temperature regulation.
  • Temperature regulation is accomplished via choosing locations in the environment.
temperature regulation4
Temperature Regulation
  • Homeothermic refers to the use of internal physiological mechanisms to maintain an almost constant body temperature.
    • Characteristic of mammals and birds.
  • Requires energy and fuel.
  • Sweating and panting decrease temperature.
  • Increasing temperature is accomplished via shivering, increasing metabolic rate, decreasing blood flow to the skin, etc.
temperature regulation5
Temperature Regulation
  • Mammals evolved to have a constant temperature of 37˚ C (98˚ F).
    • Muscle activity benefits from being as warm as possible and ready for vigorous activity.
    • Proteins in the body break their bonds and lose their useful properties at higher temperatures.
    • Reproductive cells require cooler temperatures.
temperature regulation6
Temperature Regulation
  • Body temperature regulation is predominantly dependent upon areas in the preoptic area/ anterior hypothalamus (POA/AH).
  • The POA/AH partially monitors the body’s temperature by monitoring its own temperature.
    • Heating the POA/AH leads to panting or shivering; cooling leads to shivering.
  • Cells of the POA/AH also receive input from temperature sensitive receptors in the skin.
temperature regulation7
Temperature Regulation
  • Bacterial and viral infections can cause a fever, part of the body’s defense against illness.
  • Bacteria and viruses trigger the release of leukocytes which release small proteins called cytokines.
  • Cytokines attack intruders but also stimulate the vagus nerve.
temperature regulation8
Temperature Regulation


  • The vagus nerve stimulates the hypothalamus to initiate a fever.
  • Some bacteria grow less vigorously in warmer than normal body temperature.
  • However, a fever of above 39˚ C (103˚ F) does the body more harm than good.
  • Water constitutes 70% of the mammalian body.
  • Water in the body must be regulated within narrow limits.
  • The concentrations of chemicals in water determines the rate of all chemical reactions in the body.
  • Mechanisms of water regulation vary for humans.
  • Water can be conserved by:
    • Excreting concentrated urine.
    • Decreasing sweat and other autonomic responses.
  • Most often water regulation is accomplished via drinking more water than we need and excreting the rest.
  • Vasopressin is a hormone released by the posterior pituitary which raises blood pressure by constricting blood vessels.
    • helps to compensate for the decreased water volume.
  • Vasopressin is also known as an antidiuretic hormone because it enables the kidneys to reabsorb water and excrete highly concentrated urine.
  • Two different kinds of thirst include:
    • Osmotic thirst – athirst resulting from eating salty foods.
    • Hypovolemic thirst – a thirst resulting from loss of fluids due to bleeding or sweating.
  • Each kind of thirst motivates different kinds of behaviors.
  • Osmotic thirst occurs because the human body maintains a combined concentration of solutes at a fixed level of .15 M (molar).
  • Solutes inside and outside a cell produce osmotic pressure, the tendency of water to flow across a semi-permeable membrane from an area of low solute concentration to an area of high solute concentration.
    • Occurs when solutes are more concentrated on one side of the membrane.
  • Eating salty food causes sodium ions to spread through the blood and extracellular fluid of the cell.
  • The higher concentration of solutes outside the cell results in osmotic pressure, drawing water from the cell to the extracellular fluid.
  • Certain neurons detect the loss of water and trigger osmotic thirst to help restore the body to the normal state.
  • The brain detects osmotic pressure from:
    • Receptors around the third ventricle.
    • The OVLT (organum vasculosum laminae terminalis) and the subfornical organ (detect osmotic pressure and salt content).
    • Receptors in the periphery, including the stomach, which detect high levels of sodium.
  • Receptors in the OVLT, subfornical organ, stomach and elsewhere relay information to areas of the hypothalamus including:
    • the supraoptic nucleus
    • paraventricular nucleus.
      • Both control the rate at which the posterior pituitary releases vasopressin.
  • Receptors also relay information to the lateral preoptic area which controls drinking.
  • When osmotic thirst is triggered, water that you drink has to be absorbed through the digestive system.
  • To inhibit thirst, the body monitors swallowing and detects the water contents of the stomach and intestines.
  • Hypovolemic thirst is thirst associated with low volume of body fluids.
    • Triggered by the release of the hormones vasopressin and angiotensin II, which constrict blood vessels to compensate for a drop in blood pressure.
  • Angiotensin II stimulates neurons in areas adjoining the third ventricle.
  • Neurons in the third ventricle send axons to the hypothalamus where angiotensin II is also released as a neurotransmitter.
  • Animals with osmotic thirst have a preference for pure water.
  • Animals with hypovolemic thirst have a preference for slightly salty water as pure water dilutes body fluids and changes osmotic pressure.
  • Sodium-specific hunger, a strong craving for salty foods.
    • develops automatically to restore solute levels in the blood.
  • Animals vary in their strategies of eating, but humans tend to eat more than they need at the given moment.
  • A combination of learned and unlearned factors contribute to hunger.
  • The function of the digestive system is to break down food into smaller molecules that the cells can use.
  • Digestion begins in the mouth where enzymes in the saliva break down carbohydrates.
  • Hydrochloric acid and enzymes in the stomach digest proteins.
  • The small intestine has enzymes that digest proteins, fats, and carbohydrates and absorbs digested food into the bloodstream.
  • The large intestine absorbs water and minerals and lubricates the remaining materials to pass as feces.
  • At the age of weaning, most mammals lose the intestinal enzyme lactase, which is necessary for metabolizing lactose.
  • Lactose is the sugar found in milk.
  • Milk consumption after weaning can cause gas and stomach cramps.
  • Declining levels of lactase may be an evolutionary mechanism to encourage weaning.
  • Most human adults have enough lactase to consume milk and other dairy products throughout the lifetime.
  • Nearly all people in China and surrounding countries lack the gene that enables adults to metabolize lactose.
    • Only small quantities of dairy products can be consumed.
  • A carnivore is an animal that eats meat and necessary vitamins are found in the meat consumed.
  • Herbivores are animals that exclusively eat plants.
  • Omnivores are animals that eat both meat and plants.
  • Herbivores and omnivores must distinguish between edible and inedible substances to find sufficient vitamins and minerals.
  • Selecting foods to eat is usually accomplished via imitation of others.
  • Other strategies of selecting food include:
    • Selecting sweet foods and avoiding bitter foods.
    • Preferring things that taste familiar.
    • Learning from consequences that happen after a food is consumed.
  • A conditioned taste aversion is a distaste for food that develops if the food makes one ill.
  • The brain regulates eating through messages from the mouth, stomach, intestines, fat cells and elsewhere.
  • The desire to taste and other mouth sensations, such as chewing, are also motivating factors in hunger and satiety.
  • Sham feeding experiments,in which everything an animals eats 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.
  • The splanchnic nerves convey information about the nutrient contents of the stomach.
  • The duodenum is the part of the small intestine where the initial absorption of significant amounts of nutrients occurs.
  • Distention of the duodenum can also produce feelings of satiety.
  • The duodenum also releases the hormone cholecystokinin (CCK), which helps to regulate hunger.
  • Cholecystokinin (CCK) released by the duodenum regulates hunger by:
    • Closing the sphincter muscle between the stomach and duodenum and causing the stomach to hold its contents and fill faster.
    • Stimulating the vagus nerve to send a message to the hypothalamus that releases a chemical similar to CCK.
  • Glucose, insulin, and glucagon levels also influence feelings of hunger.
  • Most digested food enters the bloodstream as glucose, an important source of energy for the body and nearly the only fuel used by the brain.
  • When glucose levels are high, liver cells convert some of the excess into glycogen and fat cells convert it into fat.
  • When low, liver converts glycogen back into glucose.
  • Insulin is a pancreatic hormone that enables glucose to enter the cell.
  • Insulin levels rise as someone is getting ready for a meal and after a meal.
  • In preparation for the rush of additional glucose about to enter the blood, high insulin levels let some of the existing glucose in the blood to enter the cells.
  • Consequently, high levels of insulin generally decrease appetite.
  • Glucagon is also a hormone released by the pancreas when glucose levels fall.
  • Glucagon stimulates the liver to convert some of its stored glycogen to glucose to replenish low supplies in the blood.
  • As insulin levels drop, glucose enters the cell more slowly and hunger increases.
  • If insulin levels constantly stay high, the body continues rapidly moving blood glucose into the cells long after a meal.
    • Blood glucose drops and hunger increases in spite of the high insulin levels.
    • Food is rapidly deposited as fat and glycogen.
    • The organism gains weight.
  • In people with diabetes, insulin levels remain constantly low, but blood glucose levels are high.
    • People eat more food than normal, but excrete the glucose unused and lose weight.
  • Long-term hunger regulation is accomplished via the monitoring of fat supplies by the body.
  • The body’s fat cells produce the peptide leptin, which signals the brain to increase or decrease eating.
  • Low levels of leptin increase hunger.
  • High levels of leptin do not necessarily decrease hunger.
    • Most people are obese because they are less sensitive to leptin.
    • Some people are obese because of a genetic inability to produce leptin.
  • Information from all parts of the body regarding hunger impinge into two kinds of cells in the arcuate nucleus.
  • The arcuate nucleus is a part of the hypothalamus containing two sets of neurons:
    • neurons sensitive to hunger signals.
    • neurons sensitive to satiety signals.
  • Neurons of the arcuate nucleus specifically sensitive to hunger signals receive input from:
    • The taste pathways.
    • Axons releasing the neurotransmitter ghrelin.
  • Ghrelin is released as a neurotransmitter in the brain and also in the stomach to trigger stomach contractions.
  • Input to the satiety-sensitive cells of the arcuate nucleus include signals of both long-term and short-term satiety:
    • Distention of the intestine triggers neurons to release the neurotransmitter CCK.
    • Blood glucose and body fat increase blood levels of the hormone insulin.
    • Some neurons release a smaller peptide related to insulin as a transmitter.
    • Leptin provides additional input.
  • Output from the arcuate nucleus goes to the paraventricular nucleus of the hypothalamus.
  • The paraventricular nucleus is a part of the hypothalamus that inhibits the lateral hypothalamus which is important for feelings of hunger and satiety.
  • Axons from the satiety-sensitive cells of the arcuate nucleus deliver an excitatory message to the paraventricular nucleus which triggers satiety.
  • Input from the hunger-sensitive neurons of the arcuate nucleus is inhibitory to both the paraventricular nucleus and the satiety-sensitive cells of the arcuate nucleus itself.
    • inhibitory transmitters include GABA, neuropeptide Y (NPY), and agouti-related peptide (AgRP).
  • Neuropeptide Y (NPY) and agouti-related peptide (AgRP) are inhibitory transmitters that block the satiety action of the paraventricular nucleus and provoke overeating.
  • Output from the paraventricular nucleus acts on the lateral hypothalamus.
    • The lateral hypothalamus controls insulin secretion and alters taste responsiveness.
  • Animals with damage to this area refuse food and water and may starve to death unless force fed.
  • The lateral hypothalamus contributes to feeding by:
    • Detecting hunger and sending messages to make food taste better.
    • Arousing the cerebral cortex to facilitate ingestion, swallowing, and to increase responsiveness to taste, smell and sights of food.
    • Increasing the pituitary gland’s secretion of hormones that increase insulin secretion.
    • Increasing digestive secretions.
  • Damage to the ventromedial hypothalamus that extends to areas outside can lead to overeating and weight gain.
  • Those with damage to this area eat normal sized but unusually frequent meals.
  • Increased stomach secretions and motility causes the stomach to empty faster than usual.
  • Damage increases insulin production and much of the meal is stored as fat.
  • People with a mutated gene for the receptors melanocortin overeat and become obese.
    • Melanocortin is a neuropeptide responsible for hunger.
  • Prader-Willis syndrome is a genetic condition marked by mental retardation, short stature, and obesity.
    • Blood levels of the peptide ghrelin is five times higher than normal.
  • Although a single gene can not be identified, a genetic influence has been established in many factors contributing to obesity.
  • Monozygotic twins resemble each other more the dizygotic twins in factors contributing to obesity.
    • Examples: how much stomach distention influences the ending of eating, how much one overeats when food tastes good.
  • Obesity can also be a function of genes interacting with changes in the environment.
    • Example: Diet changes of Native American Pimas of Arizona and Mexico.
  • Obesity has become common in the United States and has increased sharply since the 1970’s.
    • Attributed to life-style changes, increased fast-food restaurants, increased portion sizes, and high use of fructose in foods.
  • Weight-loss is often difficult and specialist rarely agree.
  • Plans should include increased exercise and decreased eating.
  • Some appetite-suppressant drugs such as fenfluramine and phentermine block reuptake of certain neurotransmitters to produce brain effects similar to that of a completed meal.
  • “Orlistat” is drug that prevents the intestines from absorbing fats.
  • Anorexia nervosa is an eating disorder associated with an unwillingness to eat as much as needed.
  • Genetic predisposition is likely.
    • no clear link has been established
  • Associated with a fear of becoming fat and not a disinterest in food.
  • Biochemical abnormalities in the brain and blood are probably not the cause, but a result of the weight loss.
  • Bulimia nervosa is an eating disorder in which people alternate between extreme dieting and binges of overeating.
    • Some force vomiting after eating.
  • Associated with decreased release of CCK, increased release of ghrelin, and alterations of several other hormones and transmitters.
    • May be the result and not the cause of the disorder.
    • Reinforcement areas of the brain also implicated.