Chapter_9_Book

Page 1: Introduction to Homeostasis

• Millions of years of evolution have shaped our bodies to maintain a stable internal environment, controlled by the brain.

• Modern challenges, such as obesity, have become significant health issues, burdening healthcare systems.

• The chapter examines physiological and behavioral processes related to homeostasis and the complications when these systems fail.

Reality TV Example

• The Biggest Loser: A reality show started in 2004 that focused on extreme weight loss through heavy dieting and exercise.

• Contestant Danny C.: Lost 239 pounds (from 430 to 191 pounds) in 7 months but later regained over 100 pounds within 6 years, despite ongoing effort.

• Study findings indicate most contestants (13 out of 14) regained significant weight, raising concerns about the body's ability to maintain weight loss after dieting.

Page 2: Key Concepts in Homeostasis

• Homeostasis: The maintenance of relatively constant internal conditions.

  • Motivation: Psychological process inducing specific behaviors.

  • Thermoregulation: Maintenance of constant internal body temperature through adjustments.

  • Endotherm vs. Ectotherm:

    • Endotherm: Maintains body heat through internal processes (e.g., mammals like us).

    • Ectotherm: Derives heat mainly from the environment (e.g., reptiles).

• Negative Feedback: A process where a system reduces its activity when a set point is reached.

• Set Point and Set Zone: Values in feedback systems that indicate approx. ranges over absolute points.

Page 3: Negative Feedback in Thermoregulation

• General Principles:

  • Example: Home thermostat functions similarly to body temperature regulation.

  • Temperature adjustments reflect deviations from a set point, activating compensatory mechanisms until balance is restored.

• Examples of Adjustments:

  • Circadian Rhythm: Body temperature drops during sleep.

  • Fever: Elevated set zone to combat infection.

• Redundancy in Homeostasis: Multiple systems ensure critical functions, like temperature control, are maintained.

  • Different hypothalamic areas control physiological and behavioral responses to temperature changes.

Page 4: Behavioral Compensation in Homeostasis

• Both ectotherms and endotherms engage in temperature-regulating behaviors, such as:

  1. Changing body exposure (e.g., huddling).

  2. Adjusting external insulation (e.g., using clothing).

  3. Altering surroundings (e.g., moving to find warmth).

• Thermoregulation in Iguanas: Use behavioral adjustments for temperature control.

• Diseases: High fevers above 104°F could harm body mechanisms.

Page 5: Mechanisms of Thirst Regulation

• Osmotic Thirst: Triggered by high extracellular fluid salt concentration, leading body to seek water intake.

• Hypovolemic Thirst: Driven by low extracellular fluid volume and detecting fluid loss through baroreceptors.

• Peripheral Mechanisms: Include sensors located in major blood vessels and hypothalamic regions to monitor fluid balances.

Page 6: Water Compartments in the Body

• Intracellular vs Extracellular Compartments:

  • Intracellular: Fluid within cells.

  • Extracellular: Includes interstitial fluid (between cells) and blood plasma.

• Osmosis: Movement of water across a selectively permeable membrane to equalize solute concentration (e.g., salt).

• Osmotic Pressure: Forces water to move to achieve balance between solutions over membranes.

Page 7: Homeostatic Fluid Balances and Mechanisms

• Physiological Responses to Thirst: Involvement of specialized neurons that monitor extracellular fluid concentration, and a network that triggers drinking behavior.

• Hormones: Vasopressin (ADH) and aldosterone help regulate fluid balance and pressure.

Page 8: Understanding Thirst Signals

• The brain integrates multiple signals indicating need for fluid replacement:

  • Hypovolemic Thirst: Monitored by blood volume and pressure, leading to thirst and salt cravings.

  • Osmotic Thirst: Occurs when concentrating fluid conditions develop.

Page 9: Energy Regulation and Nutrient Needs

• Energy Homeostasis: Key to maintaining proper levels of glucose for cellular fuel.

• Metabolic Processes: Include energy consumption/restoration methods through insulin and glucagon regulation, glycogen synthesis and breakdown.

Page 10: Challenges of Obesity Management

• Obesity: Epidemic levels complicate weight loss efforts due to persistent metabolic adaptations.

• Body resists significant weight changes by adjusting metabolism, therefore, maintaining a new steady state can be complicated.

Page 11: Hypothalamus and Appetite Control

• Historical evidence supporting hypothalamus's critical role in appetite regulation as well as embedded redundancy.

• Leptin & Ghrelin: Hormones from fat cells and stomach, respectively—leptin inhibits appetite, while ghrelin stimulates it.

Page 12: Drug and Surgical Treatments for Obesity

• Various pharmacological strategies include appetite control, increased metabolic rates, inhibition of fat storage, and absorption processes.

• Surgery: Bariatric procedures provide significant weight loss through altered digestive pathway and hormone levels.

Page 13: Eating Disorders Overview

• Anorexia Nervosa: Individuals become intensely obsessed with food but refuse to eat, leading to severe underweight.

• Bulimia Nervosa: Cycles of binge eating followed by purging to avoid weight gain, often remains hidden yet dangerous.

• Binge Eating Disorder: Characterized by uncontrolled eating beyond satiation, often leading to obesity.

Page 14: Seeking Solutions for Eating Disorders

• Most interventions focus on cognitive-behavioral therapy, nutritional rehab, and addressing distorted body perception.

• Cultural Influences: Societal pressures on body image contribute to the rise of various eating disorders.