Chapter Ten The Regulation of Internal Body States

Temperature Regulation Homeostasis-keeping body variables within a fixed range Set Point-a single value that the body works to maintain Homeothermic-mammals and birds use physiological mechanisms to maintain an almost constant body temperature despite large variations in the temperature in the environment

Advantages of Consistent Body Temperature Generally, we rest with temperature around 37 o C Advantages Higher than air temperature so we don’t have to rely on inefficient methods to cool the body Body is as warm as it can be without damaging necessary proteins Rapid muscle contractions are more possible at this temperature

Temperature Regulation Brain Mechanisms preoptic area is most critical Behavioral Mechanisms Seeking a warm place when cold, etc. Fever Prostaglandins stimulate a rise in temperature in response to invading bacteria and viruses

Thirst and Related Processes When the body needs water=thirst Related Processes Vasopressin-hormone released from posterior pituitary constricts blood vessels enables kidneys to reabsorb water

Types of Thirst Osmotic Thirst When solutes become concentrated outside the cell and water is extracted from inside cells OVLT-organum vasculosum laminae terminalis detects osmotic pressure sends information to hypothalamus paraventricular nucleus supraoptic nucleus lateral preoptic area

Figure 10.6 The consequence of a difference in osmotic pressure (a) A solute such as NaCl is more concentrated outside the cell than inside. (b) Water flows by osmosis out of the cell until the concentrations are equal. Neurons in certain brain areas detect their own dehydration and trigger thirst.

Figure 10.3 Major subdivisions of the hypothalamus and pituitary

Types of Thirst Hypovolemic Thirst thirst resulting from low blood volume Mechanisms Baroreceptors-attached to large veins detect pressure of blood returning to the heart Renin released by kidneys assists in creating high levels of angiotensin II which constricts blood vessels and signals brain to stimulate thirst

Table 10.1

Digestive System Digestion Begins with saliva in the mouth Down esophagus Stomach tears up food using acids and enzymes Small Intestine-digested materials absorbed through small intestine Large intestine-absorbs water and minerals

Influences on Food Selection Food Preference carnivores-meat herbivores-plants omnivores-meat and plants Flavor Familiarity Potential conditioned taste aversions-the tendency to form a dislike to any food that has become associated with illness Ex: People receiving chemotherapy will develop a dislike for fluids they consume during therapy

Bodily Influences on Hunger Mouth oral sensations Stomach Vagus nerve-transmits information on stomach distention Splanchnic nerve-transmits information on nutrient content of food being consumed Intestines duodenum-once food reaches here, CCK is released and signals to stop eating

Glucose, Insulin, and Glucagon Glucose-primary energy source for cells Insulin-assists glucose entering cells When high, hunger levels drop Glucagon-stimulates liver to convert glycogen to glucose

The Hypothalamus and Eating Regulation Lateral Hypothalamus Damage to this area = animal refuses food axons extend to nucleus of the tractus solitarius in the medulla possibly altering taste sensations axons extend to forebrain facilitating ingestion and swallowing activates a circuit that excites dopamine cells initiating reinforcement of behaviors sends axons to spinal cord controlling autonomic responses such as digestive secretions

The Hypothalamus and Eating Regulation Paraventricular Nucleus Damage here = eating larger than normal meals Ventromedial Hypothalamus Lesions to the VMH lead to finicky eating and sometimes to overeating The overeating is due to eating more frequently than normal Causes increased stomach motility and secretions leads to a lasting increase in insulin production

Satiety Signals and Eating Disorders Hormones Leptin-produced by fat cells and signal no need to eat Neuropeptide Y-neuromodulator that inhibits the PVN of the hypothalamus and results in an increase in meal size

Figure Relation among weight, leptin, NPY, and eating Ordinarily, high levels of body fat produce leptin, which inhibits eating. Obese mice fail to produce leptin. Obese humans produce leptin but fail to respond to it.

Genetics, Metabolic Rate, and Body Weight Genetics-heritability of.4 to.7 Metabolic Rate-the higher the rate the more difficulty someone will have gaining weight Ideas for Weight Loss Increase exercise Reduce consumption

Eating Disorders Anorexia defined-unwilling to eat, significantly underweight occurs mostly in women during adolescence Bulimia defined-alternating between dieting and overeating May be associated with alterations in PYY, CCK and serotonin