PSYB64 Lecture 6 “Temperature, Regulation, Thirst, and Hunger”

1. Homeostasis 2. Temperature 3. Thirst 4. Hunger 5. Obesity & Hunger Disorders

HOMEOSTASIS

Homeostasis: Physiological equilibrium Motivation: Activating and directing behavior Regulation of Body Temperature

Set point Mechanisms for detecting deviation Internal and behavioral elements to regain set point

Adaptations to Temperature Endotherms maintain constant body temp. Ectotherms body temp. same as environment = amphibians, reptiles and most fish

Surface-to-Volume Ratios Affect Temperature Regulation

The higher an animal’s surface to volume ratio the harder it must work to maintain core temperature

Small animals have larger surface to volume ratios hence maintaining core temperature is harder for them than for larger animals? Who works harder to maintain this ratio, the rat of the human?

Behavioral Responses to Heat and Cold

Ectotherms more dependent on behavioral devices Changes in position, weight, color and composition of fur

Endothermic Responses to Heat and Cold Automatic internal response to deviations in temperature Responses to lower temperatures Shiver Blood vessels constrict Thyroid hormone increase Responses to lower temperatures Perspiration, licking Blood vessels dilate

Deviations in Human Core Temperature Fever Heat stroke (hyperthermia) Hypothermia Emergency Hypothermia video clip http://www.youtube.com/watch?v=vc86u0IsOwc

Brain Mechanisms for Temperature Regulation See Fig 9.7

Temperature Regulation in Infancy

Relatively helpless in adapting to temperature HYPOTHALAMUS CONTROLS TEMPERATURE REGULATION THIRST: REGULATION OF THE BODY’S FLUID

Intracellular and Extracellular Fluids Extracellular fluid (33%) Intracellular fluid (67%)

Osmosis Causes Water to Move Water moves from an area with lower concentration of solutes to an area with higher concentration Hypotonic versus hypertonic

The Role of the Kidneys Excretes excess fluids and sodium THE BODY’S FLUIDS ARE HELD IN THREE COMPARTMENTS

Osmosis Causes Water to Move

SOURCES OF TYPICAL DAILY FLUID LOSS AND INTAKE IN HUMANS

THIRST: REGULATION OF THE BODY’S FLUID

The Sensation of Thirst Occurs as a result of osmotic (drops in the intracellular fluid volume) and hypovolemic (drops in blood volume) thirst Can you think of examples of when these may occur?

Mechanisms of Osmotic Thirst Osmoreceptors located in the brain Organum vasculosum of the lamina terminalis (OVLT)

Mechanisms of Hypovolemic Thirst Baroreceptors measure blood pressure Receptors in the heart and kidneys

Detecting Osmotic Thirst

HYPOVOLEMIC THIRST (mechanisms of hypovolemic thirst)

THIRST: REGULATION OF THE BODY’S FLUID Hormones, Sodium, and Thirst

Antidiuretic hormone (ADH) or vasopressin Low blood volume stimulates hunger for sodium

Initiation of Drinking Begins when angiotensin II acts on subfornical organ (SFO)

Cessation of Drinking Fluid receptors in mouth, throat, digestive system Hyponatremia Antidiuretic Hormone Begins a Sequence of Events Leading to Fluid Conservation

Thirst and Sports Drinks Provides more sodium than other beverages, which helps athletes retain fluids and may prevent hyponatremia

What is HYPONATREMIA?

An electrolyte disturbance in which sodium concentration is lower than normal

Your brain consumes 66% (2/3) of your total daily supply of glucose Lactose Tolerance Correlates with Use of Dairy Products The Influence of Culture on Food Choices

Learned food preferences begin early in life

Hunger The Process of Digestion

Foods are broken down into usable chemicals by the digestive tract During digestion fats, proteins, and carbohydrates are absorbed into the blood supply and circulated to waiting tissues The brain uses glucose for energy

Effects of steadily high insulin levels on feeding

The Initiation of Eating Affected by blood glucose levels and low fat levels Receptors and Hunger Glucoreceptors in nucleus of the solitary tract (NST) Brain Mechanisms for Hunger Lateral hypothalamus (LH) Neurochemicals and Hunger Leptin communicates with neurons in the arcuate nucleus of the hypothalamus (NPY and AgRP) Ghrelin Orexins HYPOTHALAMIC NUCLEI PARTICIPATE IN THE CONTROL OF HUNGER

Initiation and cessation of feeding behavior result from activity of 4 nuclei in the hypothalamus: lateral hypothalamus, ventromedial hypothalamus, arcuate nucleus, paraventricular hypothalamus BRAIN REGIONS IMPLICATED IN THE REGULATION OF EATING

Satiety

Assessing Satiety Stomach fullness, intestines, CCK Brain Mechanisms for Satiety Ventromedial hypothalamus (VMH) Paraventricular nucleus (PVN) Nucleus of the solitary tract (NST) Neurochemicals and Satiety Leptin found in blood when body fat levels high αMSH and CART NEUROCHEMICAL CORRELATES OF HUNGER AND SATIETY

OBESITY AND EATING DISORDERS

Defining Normal Weight Body mass index (BMI) Body fat measurement Check your own BMI

Obesity Stress and high fat diet increase release of NPY and appetite Defending the Obese Weight Diet reduces size of individual fat cells but not the number of fat cells Interventions for obesity Weight loss diets reduce calories consumed

Eating disorders are not due to a failure of will or behavior; rather, they are real, treatable medical illnesses in which certain maladaptive patterns of eating take on a life of their own.

Frequently develop during adolescence or early adulthood, but some reports indicate their onset can occur during childhood or later in adulthood.

Anorexia Nervosa Maintain 85% or less of normal weight

Bulimia Nervosa Cyclical pattern of binge eating and purging

Causes for Anorexia and Bulimia Media images Biological factors Addictive processes http://www.youtube.com/watch?v=fGNR8aT-yQA&feature=channel_page

Treatment for Eating Disorders

Antidepressants, cognitive behavioral therapy TREATMENTS FOR EATING DISORDERS

These cases are extremely difficult to treat, as most patients do not wish to change.

Although, some classes of antidepressants may be useful in the treatment, there is no specific medication to alleviate the disorders.

Cognitive-behavioral therapies focused on changing the distorted body image are more effective than medication.