Thirst Insights from Logue Ch. 3

Thirst Based on Logue Ch. 3

• 97% of Earth's water is in the ocean, with only 3% fresh water.
• Only 0.7% of fresh water is accessible for drinking, food, and industrial use.
• It takes ~3000 liters of water to produce the food an average Westerner consumes daily (~400 liters per person for household use).
• This is unsustainable if everyone uses water resources at current rates.

Water

• Fresh water is becoming a scarce resource.
• Political figures anticipate conflict over water and food.
• Access to clean fresh water is a luxury for many.
• Extreme thirst is hard to imagine.
• A 19th-century explorer, Sven Hedin, described crossing the Taklamakan Desert and experiencing severe dehydration.

Thirst

• People can endure more time without food than water.
• Death rapidly occurs with ~15-25% of body weight loss of water.
• ~2% loss of body water triggers severe thirst.
• ~5-8% loss of body water causes severe fatigue and apathy.
• A loss of >10% body water can lead to delirium, coma, and death.
• Dehydration is a serious problem for children and the elderly.
• Some elderly people don't feel the need to drink as much.

So What is Thirst?

• Two kinds of thirst:
  • Homeostatic: Body maintains a set point for water intake.
  • Non-homeostatic: Anticipating future water needs.

Homeostatic Drinking

• There are two main types of homeostasis:
  • Eating (water depletion impacts eating habits)
  • Water (a ratio of 1 part water to 1 part food for stomach, and 3 parts of water to 1 part food for the intestines is needed for digestive purposes).

Homeostatic Drinking Types

• Fluid inside cells.
• Fluid outside cells (blood and plasma).
• Loss of fluid from cells (increased salt levels).
• Loss of fluid from outside cells (blood loss).

Non-Homeostatic Drinking

• Animals drink more at night than day.
• Humans sometimes drink while they eat.

Schedule-Induced Polydipsia (SIP)

• Rats drink excessively when given food at frequent intervals.
• This can also be seen in people playing slot machines.

Explaining Thirst

• Three types of explanation for thirst:
  • Peripheral mechanisms
  • Central mechanisms
  • Combined mechanisms

Dry Mouth Theory

• Proposed by Walter Cannon, suggests thirst is driven by dryness in the mouth.
• Saliva levels and the need for water are correlated.
• When the mouth is anesthetized, thirsty dogs and humans experience reduced thirst levels.

Evidence Against Dry Mouth Theory

• Even with an empty stomach, thirst is still triggered by water placed directly into the stomach.
• People and animals can drink normally with dry mouths.

Central Mechanisms

• The hypothalamus, specifically the median preoptic nucleus, is a possible area responsible for thirst.
• It detects water deficit and signals for water intake.
• It reacts to variations in salt levels, blood pressure, and other signals.

Hypothalamus and Thirst

• The hypothalamus controls thirst via ADH release (antidiuretic hormone).
• ADH increases water retention and blood pressure.
• ADH is triggered by fluid loss within the cells or blood/plasma.

Problems

• Peripheral systems also play a role in drinking behavior, working cooperatively with but independently from the hypothalamus.
• The kidney is another important part to consider in this pathway.

The Kidney

• Falling blood pressure triggers renal hormone release (renin).
• Renin triggers the release of angiotensin.
• Angiotensin affects the CNS to trigger drinking behavior and constricts blood vessels to increase blood pressure.

Summary So Far

• Thirst results from an interaction of peripheral and central mechanisms.
• Related systems regulate thirst and drinking.
• Non-homeostatic drinking still needs further explanation.

Explaining NHD

• Schedule-induced polydipsia (SIP) is not always maladaptive.
• Disruption in appetite-related drive states can displace drink intake activity.

Anticipatory Drinking

• Thirst triggers can be chemical changes from smelling or seeing food.
• Histamine and insulin factors play a role in triggering thirst.

Conclusion

• Thirst mechanisms are more complex than thought.
• Peripheral and central systems interact to regulate thirst.

Drugs and Food

• Logue Chapter 11 outlines the psychology of eating and drinking.
• Examples like alcohol and caffeine highlight their effect on our daily intake choices.

Alcohol - Overview

• Alcohol consumption has a long history.
• Consumption varies by culture and time period.

Drinking - The Australian Context

• The Australian national identity is linked to drinking.

Drinking- Australian Context: Today

• ~90% of adults have consumed alcohol.
• Per-capita consumption is moderately high (comparatively).

Alcohol - Impact

• Positive impacts include tax revenue, reduction of cardiovascular deaths, and prevention of hospitalizations due to kidney or gallstones, and increased bone density.
• Negative impacts include harms arising from excessive consumption such as cirrhosis, heart disease, brain damage, road trauma, violence, relationship breakdown, lost productivity, or the increased rate of consumption in Indigenous populations.

Alcohol - Impact (Statistics)

• Average tax revenue is $6 billion per year.
• Alcohol abuse costs about $15 billion yearly.
• About 35% of violent crimes occur while under the influence of alcohol.

Alcohol - The effects of Alcohol

• Metabolism differs between sexes.
• Women metabolise alcohol more slowly than men.
• The average alcohol absorption rate is ~6-8g per hour.

Alcohol - Effect on the Brain

• Alcohol acts on multiple brain systems.
• Effects vary by dose.
• It acts like an anesthetic by increasing nerve cell membrane permeability.
• It alters brain dopamine and endogenous opioid levels.

Tolerance

• Alcohol's behavioral and pharmacological effects change with exposure.
• Tolerance leads to disconnect between alcohol level and behavior.
• Chronic tolerance happens with consistent consumption and is lost with abstinence.

Addiction to Alcohol

• It is a significant problem impacting ~10% of regular drinkers.
• Symptoms and criteria are covered in Logue.
• Chronic abuse is connected to various neurological issues.

Other Neuro-Degenerative disorders related to Alcohol

• Disorders like Marchiafava-Bignami disease affect the corpus callosum, while others (haematoma) are due to head trauma.
• Hepatic encephalopathy is another issue, as are cerebellar degeneration and alcoholic dementia.

Alcohol- Withdrawal symptoms

• Range from mild (tremors and anxiety) to severe, including delirium tremens (high mortality if left untreated).

Risk Factors for Alcoholism

• Genetic susceptibility, higher risk in offspring of alcoholics, higher concordances in identical than fraternal twins, less sensitivity to low alcohol levels, irregularities associated with dopamine receptors and 5-hydroxytryptamine (serotonin) metabolism

Caffeine

• Caffeine is a widely consumed psychoactive drug.
• Present in coffee, energy drinks, tea, and chocolate.

Caffeine Psychological & Physiological effects

• Increased alertness, mood, subjective wellbeing, and various cognitive functions (such as attention)
• Mild diuretic effects, elevated blood pressure/rate, and tremors/anxiety are seen at larger doses.
• Potential issues for people who don't regularly consume and sudden abstinence (which can result in a withdrawal syndrome)

Is Caffeine Addictive?

Are such foods addictive?

• US courts have historically not ruled food overly addictive.
• More modern science suggests a possible connection between specific food characteristics and behavioral addictive patterns.

Conclusion

• Caffeine has generally few or no significant negative effects.
• The main issues surrounding the use of alcohol and/or addictive foods involve societal costs, choice, and regulation.

Explore the critical insights from Chapter 3 of Logue regarding water scarcity and thirst. The quiz covers the importance of fresh water access and the severe implications of dehydration on human health. Understand the need for sustainable water use in a rapidly changing world.