Physiology of Behavior: Ingestive Behavior

Definition: Physiological systems that regulate water and nutrient levels in the body (ingestion, digestion, excretion, etc.).
Homeostasis: Basic process for maintaining proper levels of nutrients and water in the body.
Regulatory Mechanisms: Feedback mechanisms that determine when eating and drinking behaviors are engaged or stopped.

Four Essential Features:
System Variable: The variable that is regulated (e.g., amount of water).
Set Point: The desired optimal value for the system variable.
Detector: Monitors the system variable and sends feedback signals.
Correctional Mechanism: Restores the system to the set point when the variable deviates.

Importance of Eating:
To obtain building blocks for the body (amino acids from proteins).
To provide fuel (energy) for bodily functions and activities.
Fuel Storage:
Short-term reservoir: The liver stores fuel as glycogen; when needed, it's converted back to glucose.
Long-term reservoir: Adipose tissue stores triglycerides to supply nutrients during prolonged fasting.

Absorptive Phase:
Occurs when food is being consumed.
Increases in blood glucose & insulin; liver stores energy.
Fat is not used as fuel during this phase.
Fasting Phase:
Occurs when the digestive system is empty.
Insulin levels drop, and glucagon is secreted to convert glycogen back to glucose.
Prolonged fasting leads to the breakdown of fat stores.

Three Classes of Factors:
Environmental Factors: Time of day, social situations, and sensory cues (taste, smell).
Gastric Factors: Ghrelin, produced in the stomach, stimulates hunger and rises/falls throughout the day.
Metabolic Signals: Drop in blood glucose (glucoprivation) and fatty acids (lipoprivation) signal the need to eat.

Short-term & Long-term Signals:
Short-term: Environmental factors; sensory cues; satiety signals from the stomach, intestines, and liver.
Long-term: Hormonal signals from adipose tissue (e.g., leptin) adjust metabolism and hunger.
Gastric Factors: Stretch receptors in the stomach signal fullness, but sensory cues can still trigger hunger regardless of stomach distention.
Liver Factors: Monitors glucose and fatty acid levels for longer-term satiety signaling; insulin also acts as a satiety signal in the brain.

Regions Involved:
Brain Stem: Controls chewing/swallowing and integrates hunger/satiety signals.
Hypothalamus:
- Lateral hypothalamus (LH) promotes hunger; lesions here lead to anorexia.
- Ventromedial hypothalamus (VMH) promotes satiety; lesions lead to obesity.
Peptides Involved:
Orexin and Melanin-Concentrating Hormone (MCH) stimulate hunger.
Anorexogenic peptides such as CART and alpha-MSH inhibit hunger and promote satiety.

Statistics: Rising prevalence of obesity worldwide; significant risk factors include cardiovascular disease and diabetes.
Possible Causes:
Environmental Factors: Increasing access to high-calorie, processed foods; sedentary lifestyle.
Genetic Factors: Variability in metabolism and appetite regulation, such as leptin and its receptors.
Treatment Options:
Behavioral interventions including increased physical activity and cognitive behavioral therapy.
Surgical and pharmacological interventions also available to reduce food intake or absorption.

Types:
Anorexia Nervosa: Extreme fear of weight gain, preoccupation with food, distorted body image.
Bulimia Nervosa: Binge eating followed by purging behaviors.
Binge-Eating Disorder: Binge eating without compensatory behavior.
Characteristics: Significant weight changes, distress regarding body weight, and often comorbid with anxiety or perfectionism.