Hunger notes

Hunger and Thirst

Introduction

Fundamental Needs for Survival:

  • Hunger and thirst.

Israel Kamakawiwoʻole - ‘Izzy’

  • Career Overview: Iconic cover of ‘Somewhere Over the Rainbow’, reached #1 on the German singles chart in 2010.

  • Honors: Hawai'i State Flag flown at half-staff at his funeral, a unique honor for a private citizen.

  • Physical Struggles: Struggled with obesity, weighing up to 757 pounds.

  • Death: Passed away at age 38 from heart failure in 1997.

Homeostasis and Thirst Mechanisms

Negative Feedback Systems

  • Definition: Main mechanisms for homeostasis.

  • Behavioral Response: Actions like eating and drinking occur when deviating from a set point.

Thirst Types

  • Osmotic Thirst: Triggered by high extracellular solute concentration.

  • Hypovolemic Thirst: Triggered by low extracellular/intravascular volume.

Mechanisms of Hypovolemic Thirst

  • Detection: Baroreceptors in blood vessels and heart sense decreased water volume.

  • Response: Brain activates thirst and salt craving; arteries constrict to elevate blood pressure.

Hormonal Response

  • Vasopressin: Released during hypovolemia; constricts blood vessels and reduces urine output.

  • Vasopressin deficiency: MEANS INCREASE URINE OUTPUT TO KIDNEYS, resulting in chronic thirst

  • Angiotensin Cascade Process: Low blood volume triggers renin release from kidneys, producing angiotensin II, causing blood vessel constriction and stimulating drinking.

Brain Control of Drinking

  • Mechanism: Angiotensin II acts in the subfornical organ(Angi 2 has to be released in this region) signaling brain areas for drinking behavior.

Osmotic Thirst Mechanism

Process: Osmosensory neurons in the anterior hypothalamus(OVLT) respond to increased blood osmotic pressure(salt). Na+ channels open as membranes shrink; neurons activate pituitary to release ADH.

  • Because there is so much salt outside the cell, the cell releases water to balance outside

  • ADH stimulates thirst center

Dehydration & Rehydration Summary

  • Increased blood osmolarity prompts ADH release, leading to thirst and dry mouth. Drinking water rehydrates blood and reduces salivation.

  • OVLT neuron and subfirnical region stimulate thirst center

Hunger Awareness

Cultural Quotations: Complexities of managing hunger.

Dieting Challenges

  • Metabolism Adjustment: Energy expenditure declines when dieting, reducing basal metabolic rate (BMR). Longevity studies show restricted food intake may benefit rats but are uncertain for humans.

Obesity and Metabolism

  • BMR: Energy needed for basic functions, comprising 75% of daily energy for sedentary students; genetics also play a role.

Energy Storage and Utilization

  • Primary Energy Source: Glucose; glycogen serves as short-term storage.

  • Metabolic Rate Insights: Peaks in infancy, slows in youth, stabilizes until age 60, then declines.

Food Intake Regulation

  • Neurotransmitter Influences: Brain signals (NPY, a-MSH) regulate hunger and satiety, influenced by hormones and nutritional status.

Leptin and Ghrelin

  • Leptin: Produced by fat cells; informs the brain about body fat. Resistance leads to obesity.

  • Ghrelin: An appetite stimulant, elevated during fasting, low post-eating; dysregulated in Prader-Willi syndrome.

Hypothalamus and Appetite Control

  • Dual Functionality: Two neuron types exist; one stimulates appetite (NPY/AgRP) and the other inhibits it (POMC/CART).

Obesity Effects on Brain

  • Consequences of Overeating: Leads to hypothalamic inflammation, inhibiting neurogenesis and resetting hunger signals.

Eating Disorders

Anorexia Nervosa

  • Criteria: Refusal to maintain body weight, intense fear of weight gain; highest mortality rate among psychiatric disorders.

Bulimia

  • Criteria: Characterized by recurrent binge eating and inappropriate behaviors to counter it.

Co-occurrence with Other Disorders

  • High anxiety and depression rates associated with anorexia and bulimia; significant suicide rates among afflicted individuals.

Children and Eating Disorders

  • Survey reveals concerning rates of dieting and disordered eating behaviors among students in grades 5 to 8.

Treatment of Obesity (Effective Strategies)

Eating Habits:

  • Creating a caloric deficit of 200 calories/day requires lifestyle changes and monitoring.

Exercise:

  • Engaging in more than 200 minutes of strenuous aerobic activity weekly is effective combined with dietary changes.

New Drug Treatments

  • GLP-1 receptor agonists: Drugs like Mounjaro and Ozempic show significant long-term weight loss effects by modulating appetite and metabolic responses.