MODULE 1: behavioral processes based on

TEMPERATURE REGULATION situational needs.

o It enables organisms to avoid errors
Homeostasis instead of merely correcting them post-
The concept of homeostasis, introduced by Walter B. occurrence.
Cannon in 1929, refers to the biological processes that 3. Adaptive but Imperfect Mechanisms:
maintain body variables within a fixed range, akin to the o While allostasis enhances survival,
operation of a thermostat. The body acts to preserve a imperfections in this system can
stable internal environment despite external changes. contribute to health problems such as
obesity, hypertension, or diabetes.
Key elements of homeostasis include:
Homeostasis vs. Allostasis
1. Set Points:
o A set point is a specific value the body Feature Homeostasis
strives to maintain. For example, the
calcium level in blood is maintained at Definition Maintaining a stable internal
approximately 0.16 g/L. state
o If the blood calcium level drops, Focus Fixed set points
mechanisms are triggered to release
calcium from bones. Conversely, Examples Blood calcium regulation
excess calcium is stored or excreted.
Mechanism Negative feedback
2. Negative Feedback Loops:
o Negative feedback is the process that Allostasis
counters deviations from the set point.
o For example, if your body temperature Definition Adaptive regulation based on
drops below a threshold, physiological context
responses (like shivering) generate Focus Anticipatory and situational
heat to restore balance. changes
3. Homeostatic Examples: Examples Stress response, seasonal fat
o Variables like water, glucose, oxygen, storage
and acidity are regulated via similar Mechanism Dynamic adjustments to avoid
mechanisms. errors
o Behavioral adjustments also contribute,
such as seeking warmth in cold In summary, homeostasis provides a foundation for
environments. understanding the body's regulation of internal
variables, while allostasis expands this
understanding by accounting for proactive and
While homeostasis effectively explains many biological
context- dependent adaptations.
processes, it is limited in describing dynamic or
anticipatory changes. For example: Controlling Body Temperature: An Essential Biological
Process
● Body temperature fluctuates slightly based on
the time of day. 1. Importance of Temperature Regulation
● Seasonal shifts, such as fat storage in animals Temperature regulation is a vital biological
during autumn, reflect changes in the "set motivation. A significant portion of the energy we
consume—over two-thirds—is used for basal
point."
metabolism, which maintains a constant body
temperature at rest.
Allostasis
To address the limitations of homeostasis, researchers Mechanism:
introduced the concept of allostasis. This refers to the In humans and mammals, temperature
body’s ability to anticipate and adapt to changing regulation is achieved by metabolizing energy
demands, maintaining stability through variable in brown adipose cells, which release heat
adjustments rather than fixed set points. instead of generating muscle movement.

2. Ectotherm vs. Endotherm

Key features of allostasis include:
Animals exhibit two main strategies for temperature
1. Anticipatory Adjustments: control:
o The body proactively prepares for
expected challenges. For instance: Ectothermy (Poikilothermy):
▪ A sudden danger triggers
increased heart rate, blood ● Found in amphibians, reptiles, and most fish.
● These animals rely on external heat sources
pressure, and sweating in
to regulate body temperature, and their
preparation for "fight or flight." internal temperature mirrors their
▪ A hiker may feel thirsty and environment.
reduce urine production as ● Example: Desert lizards use behavioral
temperatures rise, anticipating mechanisms like seeking sun or shade to
dehydration. maintain temperature.
2. Flexibility in Regulation: ● Limitations: Cannot maintain temperature as
consistently as endothermic animals and are
o Allostasis involves dynamic
vulnerable to extreme cold.
adjustments to physiological and
Endothermy (Homeothermy):
 ● Observed in mammals and birds, who - The evolved body temperature of 37°C strikes
generate their own heat to maintain a a balance between the advantages of high
constant internal temperature. temperature for movement and the
● Physiological mechanisms include shivering, disadvantages for protein stability. Animals
sweating, and altering blood flow to the skin. like reptiles naturally select temperatures of
● Behavioral mechanisms include wearing 37–38°C when given a choice, highlighting the
clothing, huddling, or altering activity levels. advantages of this range.

- The ability to regulate body temperature

through physiological and behavioral means is
3. Responses to Hot and Cold Environments essential for survival, activity, and
reproduction. Mammals and birds have
In Hot Conditions:
evolved energy-intensive mechanisms to
- Evaporation is the primary cooling maintain high and stable body temperatures,
mechanism. Humans sweat to release heat which confer significant advantages for
through evaporating water. mobility and metabolic function, despite the
- Animals that do not sweat rely on panting or associated energy costs.
licking to cool down.
- Challenges arise in humid conditions when Brain Mechanisms for Temperature Regulation
evaporation is less effective, leading to risks
of dehydration and overheating. Role of the Hypothalamus:
- The preoptic area/anterior hypothalamus
In Cold Conditions: (POA/AH) is central to temperature regulation.
- POA/AH receives inputs from:
- Heat is generated through shivering, reduced o Temperature receptors in the skin,
blood flow to extremities, and, in some
organs, and hypothalamus itself.
mammals, fluffing fur for insulation.
- Humans experience goosebumps, a remnant of o Immune system signals, such as
ancestral adaptations for fur insulation.\ prostaglandins and histamines during
infections.
4. Survival in Extreme Cold
Physiological Responses:
Adaptations in Ectothermic Animals:
- Outputs to the hindbrain’s raphe nucleus trigger
autonomic responses:
- Some insects, fish, and frogs produce
- Shivering and increased metabolism for warmth.
antifreeze-like chemicals such as glycerol to
- Sweating and altered blood flow to release heat.
prevent ice formation within their bodies.
- Temperature Detection and Adaptation:
- Wood frogs, for example, reduce ice damage by:
- Removing fluid from organs and storing it in
extracellular spaces.
- Using chemicals to allow gradual ice formation.
- Rapid blood clotting to repair any ruptured blood
vessels.

5. Advantages of High Body Temperature in Mammals

Enhanced Muscle Performance:

- Warmer muscles are more efficient, allowing

mammals to maintain readiness for vigorous
activity regardless of external temperatures.
- Ectothermic animals, by contrast, rely on
environmental warmth and experience
fatigue quickly in cold.

Optimal Temperature: The body reacts most strongly when both skin and
- Mammals maintain a body temperature around hypothalamic sensors signal the same thermal state
37°C (98.6°F) as a trade-off: (hot or cold).
- Benefits: Enables sustained muscle activity
and metabolic efficiency. Damage to the POA/AH impairs physiological
- Costs: Higher energy demands for food and regulation but preserves behavioral adaptations like
fuel. seeking warmer or cooler environments.
- Limits: Beyond 41°C (105°F), proteins lose
stability, compromising enzymatic and Fever: A Defensive Response
physiological functions. Nature of Fever:
- Fever is a hypothalamic-regulated increase in
6. Reproductive Considerations
body temperature.
- Represents an elevated "set point" (e.g.,
- Reproductive cells, such as sperm, require a 39°C) where physiological responses aim to
cooler environment than the rest of the body. maintain the fevered state.
- Example: Male mammals’ scrotum keeps testes
cooler by external positioning. Functionality Across Species:

- In birds, internal body temperatures are too high - Even animals like reptiles and fish
for embryo development, leading to external behaviorally raise their temperature to
egg- laying. mimic a fever when infected.
Purpose of Fever:
7. Evolutionary Adaptations
 - Slows bacterial growth and enhances the vasopressin helps conserve water by:
immune system's efficiency.
- Moderate fever increases survival rates during - Constriction of blood vessels: This
infections. raises blood pressure to counteract the
effects of reduced blood volume during
Risks of Fever: dehydration.
- Above 39°C: Potential harm outweighs - Kidney function modulation:
benefits. Vasopressin enables the kidneys to reabsorb
- Above 41°C: Life-threatening due to protein water from urine, producing more
denaturation and enzymatic dysfunction. concentrated urine.

IN CLOSING: Temperature Regulation B. Circadian Rhythm of Vasopressin Secretion:

- The brain's thermoregulatory processes - Secretion increases during sleep,

serve as an excellent example of reducing the need to urinate at night. This
homeostasis and autonomic function. mechanism preserves water during periods of
- The dual role of behavioral and fasting (when drinking is not possible).
physiological mechanisms underscores the 3. Drinking Behavior in Humans
interplay between environment and biology.
- Fever demonstrates the body's adaptive A. Regulation of Water Intake:
strategy, emphasizing how neural control
mechanisms are engaged during immune Humans typically drink water:
responses.
- During meals: Water aids digestion.
- In social situations: Drinking often occurs
without physiological thirst due to social or cultural
Module 2: practices.
Thirst
B. Excessive Water Intake:

Water regulation is critical for maintaining homeostasis, - Humans tend to drink more water than
and organisms exhibit different strategies based on necessary under normal circumstances,
their environment. similar to aquatic animals. However, drinking
excessively without consuming salts (e.g.,
during alcohol abuse) can deplete the body's
salt levels, potentially leading to harmful
1. Strategies Across Species
conditions like hyponatremia (low sodium).
A. Aquatic Animals (e.g., Beavers):
● Beavers and other animals living in water-rich
4. Adaptive Benefits
environments drink abundant water and eat
moist foods. - These mechanisms reflect evolutionary
● They excrete dilute urine to balance the adaptations to diverse environmental conditions.
excess water intake, ensuring their salt and - Humans retain the flexibility to function in both
electrolyte levels remain stable. water-abundant and water-scarce
environments by dynamically switching
B. Desert Animals (e.g., Gerbils):
between strategies akin to those of aquatic and
● Desert animals like gerbils, which face water desert animals.
scarcity, adopt strategies to conserve water:
OSMOTIC THIRST
● Dry feces and concentrated urine: This
minimizes water loss through excretion. Osmotic thirst arises from an imbalance in solute
● Burrowing behavior: They avoid high concentration between the inside and outside of cells.
temperatures during the day, reducing the
need for sweating (which they cannot do).
● Specialized nasal passages: These structures 1. What is Osmotic Thirst?
recapture moisture from exhaled air, a crucial
- Osmotic thirst is triggered by the movement of
adaptation in arid climates.
water across cell membranes due to differences
C. Humans: in solute concentration, primarily sodium.

● Humans employ flexible strategies depending

Osmotic Pressure:
on water availability:
o Excess water availability: Humans - Osmotic pressure drives water movement
drink more water than necessary and from areas of lower solute concentration to
excrete the excess through dilute higher solute concentration through a
urine. semipermeable membrane.
● Water scarcity: To conserve water, humans: - This occurs when solutes, like sodium,
● Excrete more concentrated urine. accumulate outside cells after eating salty
● Reduce sweating. foods, leading to dehydration of cells as water
● Employ hormonal mechanisms like vasopressin moves out to balance the solute
concentration.
release.

2. Hormonal Regulation of Water Balance Set Point for Solutes:

A key hormonal mechanism regulating water in humans The concentration of solutes in body fluids is
is the release of vasopressin (also called antidiuretic
hormone or ADH). maintained at approximately 0.15 M (molar). Any
A. Function of Vasopressin: deviation from this set point triggers mechanisms
- Released by the posterior pituitary gland, to restore balance.
 before sleep, reducing the urge to
2. How Does the Body Detect Osmotic Pressure? urinate and retaining water.

The brain and specific sensory systems monitor and Stopping Mechanisms:
respond to changes in osmotic pressure: Receptors in - Thirst is quenched before water reaches the
blood or cells, preventing overhydration:
the Brain: - SFO Activity Suppression: Drinking water
Located around the third ventricle, the key receptors suppresses thirst-sensitive neurons in the
include: SFO within a minute.
- Cooling the Tongue: Provides additional signals
- OVLT (Organum Vasculosum Laminae to stop drinking.
Terminalis): Detects osmotic pressure and
sodium levels.
- Subfornical Organ (SFO): Has neurons that HYPOVOLEMIC THIRST AND SODIUM-SPECIFIC
either stimulate or suppress thirst. HUNGER
- These areas lack a strong blood-brain barrier, Hypovolemic Thirst
allowing them to monitor blood content
effectively. Hypovolemic thirst occurs when the body loses a
significant amount of fluid, which could happen due to
Input Sources: bleeding, diarrhea, or sweating. Unlike osmotic thirst,
The OVLT receives input from: this form of thirst results from a reduction in the
volume of blood plasma and extracellular fluid rather
- The digestive tract, enabling anticipatory than an imbalance in solute concentration.
adjustments for osmotic changes.
- Osmotic pressure sensors in the bloodstream. 1. Causes and Mechanisms
Fluid Loss and Decreased Blood Pressure:
3. Brain Areas Involved in Osmotic Thirst
- Loss of fluid reduces blood volume, leading to
The signals from osmotic pressure detectors are
a drop in blood pressure. This impairs the
integrated in the hypothalamus, which coordinates
heart's ability to pump blood and hampers
drinking behavior and hormonal responses.
nutrient transport into cells.
Key Hypothalamic Structures:
- Lateral Preoptic Area: Controls the initiation of
Role of the Kidneys:
drinking.
- Supraoptic and Paraventricular Nuclei: - The kidneys detect the reduction in blood
Regulate the release of vasopressin by the pressure and release renin, an enzyme that
posterior pituitary gland. converts angiotensinogen (a protein in the
blood) into angiotensin I.
Role of Vasopressin:
- Enzymes then convert angiotensin I into
- Increases water reabsorption in the kidneys. angiotensin II, a hormone with two key roles:
- Reduces water loss via concentrated urine - Constriction of Blood Vessels: Helps restore
blood pressure.
- Stimulates thirst when needed.
- Stimulation of Thirst: Signals the brain to
initiate drinking behavior.
2. Brain's Role in Hypovolemic Thirst
Angiotensin II and the Brain:
- Angiotensin II stimulates neurons around the
third ventricle and sends signals to the
hypothalamus.
- These neurons release angiotensin II as a
neurotransmitter, further amplifying the thirst
signal.
Thirst Trigger:
- The brain areas involved direct the body to
seek fluids, but pure water is not sufficient in
this case. Drinking pure water would dilute the
remaining solutes in the body, further
disrupting fluid balance.

3. Preference for Salty Water

- To restore both fluids and electrolytes, the
body prefers salty water over pure water.
4. Anticipatory Mechanisms and Allostasis
- This preference ensures that both fluid
The concept of allostasis plays a critical role in osmotic volume and solute concentration return to
thirst: normal.
Anticipation of Future Needs:
Sodium-Specific Hunger
- Instead of waiting for cells to become
dehydrated, the body acts in advance. - When sodium levels are depleted, the body
- For example: develops a targeted craving for salt, known as
o Drinking after consuming salty foods. sodium-specific hunger. This phenomenon is
crucial for maintaining electrolyte balance.
o Increased vasopressin secretion
1. Causes and Hormonal Regulation Low Sodium
Levels:
- Decreased sodium triggers the release of the
hormone aldosterone from the adrenal glands.
Aldosterone's Role:
- Promotes sodium retention in the kidneys,
salivary glands, and sweat glands.
- Alters taste receptors to increase the appeal of
salty foods.

Synergy with Angiotensin II:

- Angiotensin II and aldosterone together
enhance the response to salt:
- Taste Receptors: Salt tastes more appealing.
- Brain Neurons: Increased sensitivity to salty
flavors in areas like the nucleus of the tractus
solitarius.

2. Immediate Behavioral Response

Preference for Salt:

- When sodium is depleted, animals and humans
develop a strong preference for salt, even for
highly concentrated solutions that they would
usually avoid.
- This instinctive preference ensures rapid
replenishment of sodium reserves.

Examples in Humans:
- Salty snacks may taste better to individuals
with sodium deficits, such as after heavy
sweating or menstruation.

3. Learned vs. Instinctive Preferences

Instinctive Craving:
- Sodium hunger is an innate mechanism,
unlike cravings for other nutrients (e.g.,
vitamins or minerals), which are learned
through trial and error.
- This reflects the critical importance of sodium
for physiological functions like nerve
conduction and muscle contraction.

You may have thought that temperature regulation

happens automatically and that water regulation
depends on your behavior. You can see now that the
distinction is not entirely correct. You control your
body temperature partly by automatic means, such as
sweating or shivering, but also partly by behavioral
means, such as choosing a warm or a cool place. You
control your body water partly by the behavior of
drinking but also by hormones that alter kidney
activity. If your kidneys cannot regulate your water and
sodium adequately, your brain gets signals to change
your drinking or sodium intake. In short, keeping your
body’s chemical reactions going depends on both
skeletal and autonomic controls.
 Module 3:
Hunger

DIGESTION AND FOOD SELECTION

- Digestion is the process by which food is broken

down into smaller molecules that cells can
absorb and use for energy, growth, and repair.
Understanding the digestive system and its
mechanisms provides insight into how food is
processed and how choices in food selection
impact digestion and health.

THE DIGESTIVE PROCESS

1. Mouth (Initial Stage)
- Role in Digestion: Digestion begins in the mouth,
where food is mechanically broken down by
chewing.
- Salivary Enzymes: Enzymes in saliva, such as
amylase, begin breaking down carbohydrates
into simpler sugars.

➔ This initial chemical digestion prepares food for

further breakdown in the stomach.

2. Esophagus
- Transportation:Once swallowed, the food (now
called a bolus) travels down the esophagus
through rhythmic muscle contractions known as
peristalsis. FOOD SELECTION AND ITS IMPACT ON DIGESTION

➔ The esophagus connects the mouth to the Food choices significantly affect how efficiently the
stomach. digestive system functions:
● Carbohydrate-Rich Foods:
3. Stomach ○ Complex carbohydrates, like whole
➔ Chemical Breakdown: grains, take longer to digest and provide
- Food enters the stomach, where it mixes with sustained energy.
hydrochloric acid and digestive enzymes, such ○ Simple sugars digest quickly but can
as pepsin, which break down proteins. cause spikes in blood sugar.
- The stomach's highly acidic environment kills
bacteria and provides the optimal= conditions for ● Protein-Rich Foods:
protein digestion. ○ Proteins from sources like meat, fish,
and legumes require longer digestion in
➔ Storage and Regulation: the stomach.
- The stomach temporarily stores food, releasing ○ High-protein diets may strain the
it gradually into the small intestine via the digestive system if not balanced with
sphincter muscle at its base. fiber-rich foods.
● Fats:
4. Small Intestine ○ Fats are broken down slowly, providing
➔ Primary Site of Digestion and Absorption: long-term energy but potentially causing
- The small intestine is the most crucial part of the digestive discomfort if consumed in
digestive process, with specialized enzymes excess.
breaking down proteins, fats, and carbohydrates ○ Healthy fats, such as those in nuts and
into their smallest components: avocados, support nutrient absorption.
- Proteins → Amino acids
- Fats → Fatty acids and glycerol ● Fiber:
- Carbohydrates → Simple sugars (e.g., ○ Dietary fiber, found in fruits, vegetables,
glucose) and whole grains, enhances digestion
- These molecules are absorbed through the by promoting bowel regularity and
walls of the small intestine into the bloodstream. supporting the gut microbiome.

➔ Nutrient Distribution: ● Hydration:

- Blood carries the absorbed nutrients to the cells ○ Adequate water intake is essential for
for immediate use or stores them for later. efficient digestion and absorption,
particularly in the small and large
5. Large Intestine intestines.
➔ Absorption of Water and Minerals:
- The large intestine absorbs water from the
remaining indigestible food matter, ensuring
hydration and compacting the waste.
- It also absorbs essential minerals, such as
sodium and potassium.

➔ Excretion:
- The leftover material is lubricated and prepared
for elimination through the rectum and anus as
feces.

CONSUMPTION OF DAIRY PRODUCTS

➔ The ability to consume dairy products as an
 adult is a fascinating example of evolutionary ● Europe:
adaptation and genetic diversity among humans. ○ Lactase persistence is highly prevalent
It reflects how dietary needs and environmental in northern and western Europe but
pressures have shaped biological mechanisms decreases in southern Europe.
in humans and other mammals. ● Africa:
○ The ability to digest lactose is patchy,
➔ Milk Consumption in Mammals with higher persistence in regions with a
1. Milk as the Initial Food Source: history of cattle herding, such as East
- For newborn mammals, milk is a primary food Africa.
source, rich in nutrients necessary for growth ● Asia:
and development. ○ Lactase persistence is rare in East Asia,
- During this phase, mammals produce lactase, where dairy consumption historically has
an intestinal enzyme that breaks down lactose, been limited.
the sugar found in milk, into glucose and ● Americas:
galactose for absorption. ○ Lactase persistence in Native American
populations is around 25%, while other
2. Weaning and Decline in Lactase: groups reflect the ancestry of settlers or
- As mammals mature and transition to solid enslaved individuals.
foods, lactase production typically declines.
- This decline appears to be an evolutionary Implications for Modern Diets
mechanism to promote weaning and adapt to a 1. Cultural Practices and Food Choices:
diet more suited to adulthood. ● In regions where lactose intolerance is
- Without sufficient lactase, consuming large prevalent, diets traditionally exclude or minimize
amounts of milk can result in symptoms such as dairy products, focusing instead on alternatives
gas, stomach cramps, and diarrhea. like soy or coconut milk.

Human Adaptations to Dairy Consumption 2. Health Considerations:

➔ Unlike most mammals, many humans maintain ● For those with lactose intolerance, dairy
lactase production into adulthood—a consumption must be managed to avoid
phenomenon known as lactase persistence. digestive discomfort while ensuring sufficient
However, this ability varies significantly across intake of calcium and vitamin D from other
populations. sources.
1. Prevalence of Lactase Persistence
● High Lactase Persistence: 3. Adaptation and Genetic Research:
○ Populations with a history of cattle ● The study of lactase persistence and lactose
domestication, such as in northern intolerance provides insights into human
Europe and certain parts of Africa, have adaptation and evolution, highlighting the
a high prevalence of lactase interplay between genetics, diet, and
persistence. environment.
○ For example, nearly all adults in
northern Europe can digest lactose.
● Low Lactase Persistence:
○ In populations where cattle
domestication and milk consumption
were less common, such as in East Asia
and some parts of Africa, lactase
persistence is rare.
○ Nearly all adults in China and
surrounding countries are lactose
intolerant, as are many Native
Americans and Indigenous Australians.

2. Evolutionary Adaptations
● The genetic ability to digest lactose in adulthood
arose independently in different populations.
○ Europeans with lactase persistence
typically share the same gene variant.
○ In Africa, several distinct genetic FOOD SELECTION AND BEHAVIOR
adaptations allow for lactase ➔ The relationship between food selection and
persistence, reflecting multiple instances behavior is a topic of scientific interest, often
of evolutionary convergence tied to the surrounded by myths and misconceptions.
domestication of cattle. Here's a closer look at how food choices impact
● When cow’s milk became a dietary staple, behavior and cognitive functioning based on
selective pressure favored individuals who could evidence:
digest lactose, conferring a survival advantage.
1. Sugar and Hyperactivity
3. Lactose Intolerance and Alternatives
● Lactose Intolerance: ➔ The Myth:
○ Individuals with low lactase levels may - The belief that sugar causes hyperactivity in
experience discomfort after consuming children is widespread, often reinforced by
milk but can often tolerate fermented anecdotal observations during events like
dairy products like cheese and yogurt birthday parties or holidays.
because the fermentation process
reduces lactose content. ➔ Scientific Evidence:
● Dietary Adjustments: - Rigorous studies using controlled conditions,
○ Many lactose-intolerant individuals limit where children are given sugary and artificially
milk intake or switch to lactose-free or sweetened snacks without knowing which is
plant-based alternatives, such as which, have consistently found no significant
almond, soy, or oat milk. effect of sugar on:
- Activity levels
Global Distribution of Lactase Persistence - Play behavior
 - School performance 1. Role of Taste and Chewing:
- The belief persists likely due to confirmation - Humans and animals have an inherent desire to
bias, where people notice behavior that aligns taste and chew, even in the absence of hunger.
with their expectations. For instance, a child's - Evidence:
natural excitement at a party is attributed to - In an experiment, students consumed
sugar consumption rather than the social context meals via a tube that bypassed taste
or environment and chewing. While they maintained a
steady caloric intake, they found the
2. Turkey and Sleepiness experience unsatisfying and craved the
➔ The Myth: sensory aspects of eating.
- It is often claimed that eating turkey causes - In sham feeding experiments, animals
sleepiness due to its content of tryptophan, an with disconnected digestive tracts (food
amino acid that the brain uses to produce leaks out after swallowing) ate
serotonin and melatonin, chemicals involved in continually because the lack of nutrient
sleep regulation. absorption and stomach distension
prevented satiety.
➔ Scientific Evidence: 2. Key Insight:
- Turkey’s tryptophan levels: Turkey contains - Taste contributes to the eating experience but is
only an average amount of tryptophan, no more insufficient for signaling satiety. Chewing and
than other protein sources. tasting without actual digestion does not fulfill
- Thanksgiving fatigue: The sleepiness the body’s need for nutrients.
commonly reported after Thanksgiving meals
stems from overeating, which directs blood flow The Stomach and Intestines
to the digestive system, leaving less for other ➔ Stomach Distension
activities. ● Primary Signal for Satiety:
○ As the stomach stretches, it sends
➔ Carbohydrates and Tryptophan: signals to the brain via the vagus nerve
- Interestingly, eating a diet rich in carbohydrates (cranial nerve X), indicating fullness.
can increase the brain’s uptake of tryptophan: ○ Experimental Evidence:
- Mechanism: ■ In animals with an inflatable cuff
- Carbohydrates stimulate insulin blocking food passage to the
release. intestines, feeding stopped once
- Insulin reduces levels of the stomach was full, even
competing amino acids, such as though no digestion occurred.
phenylalanine, by moving them
into storage.
- This reduced competition allows Duodenum's Role
more tryptophan to enter the ● Nutrient Detection and Satiety Signals:
brain, promoting sleepiness. ○ The duodenum, the first part of the small
- Conclusion: intestine, plays a critical role in satiety:
- Dessert, rather than turkey, is 1. It absorbs nutrients and detects their
more likely to cause drowsiness type and quantity.
at a large meal. 2. Contains taste-like receptors that inform
the brain of food composition without
3. Fish as Brain Food conscious awareness.
➔ The Claim: ● Hormone: Cholecystokinin (CCK):
- Eating fish, particularly oily fish like salmon, ○ Released by the duodenum in response
improves cognitive functioning and supports to nutrient presence.
brain health. ○ Functions:
1. Sphincter Constriction: CCK closes the
➔ Scientific Evidence: muscle between the stomach and
● Rich in Omega-3 Fatty Acids: duodenum, keeping food in the stomach
○ Many fish are high in omega-3 fatty longer and promoting faster stomach
acids, particularly DHA distension.
(docosahexaenoic acid), which is crucial 2. Neural Signal Activation: CCK activates
for brain development and function. the vagus nerve, which signals the
● Effects on Cognitive Development: hypothalamus to release
○ Mothers who consume significant neurotransmitters that mimic CCK,
amounts of seafood during pregnancy amplifying the satiety response.
tend to have children who perform better
on cognitive tests in infancy and later Limitations of CCK in Weight Loss:
life. ● While CCK can limit meal size, it only has
○ Children benefit from the short-term effects. Animals or humans
neuroprotective and developmental compensate for smaller meals by eating more in
effects of omega-3 fatty acids. subsequent meals, making it ineffective for
● Protection Against Cognitive Decline: long-term weight loss strategies.
○ Regular seafood consumption in older
adults has been linked to slower
cognitive decline, even among those
with a genetic predisposition to
dementia.

SHORT- AND LONG-TERM REGULATION OF

FEEDING
➔ Feeding regulation is a complex process
involving multiple mechanisms and signals from
various parts of the body. These signals ensure
proper energy intake and satiety to maintain
energy balance.
➔ Oral Factors
 Leptin Resistance
Glucose, Insulin, and Glucagon ● Most overweight people produce ample leptin,
➔ The regulation of energy intake and blood but their bodies may develop resistance to it,
glucose levels is a critical process involving limiting its effectiveness in reducing appetite.
several key hormones, particularly insulin and ● Adding extra leptin has little impact on both
glucagon, which control the availability of overweight and normal-weight individuals, as
glucose to cells: beyond a threshold, leptin’s ability to suppress
➔ The Role of Insulin hunger is weak.
1. During Meals:
● Insulin is secreted by the pancreas in response Insights on Hunger and Satiety Mechanisms
to food intake. ● Short-Term Regulation: Insulin and glucagon
● It facilitates glucose entry into most cells, with manage meal-to-meal energy balance and blood
the brain being an exception (brain cells take up glucose.
glucose independently of insulin). ● Long-Term Regulation: Leptin adjusts for overall
● Excess glucose is stored in the liver as glycogen energy balance, preventing prolonged
or in fat cells as fat. overeating or undereating.

Evolutionary Implications
2. After Meals: ● Mechanisms promoting hunger are stronger
● Blood glucose levels gradually drop as glucose than those ensuring satiety, reflecting an
is stored and used by cells. evolutionary adaptation to avoid starvation,
● Reduced insulin levels slow the movement of which posed a greater survival risk than
glucose into cells, prompting hunger. overeating in ancestral environments.

3. Prolonged High Insulin Levels: THE LATERAL HYPOTHALAMUS (LH)

● In cases of constant high insulin (e.g., ➔ The lateral hypothalamus plays a critical role in
pre-hibernation in animals), glucose storage is feeding behavior and integrating various sensory
excessive, leading to low blood glucose and and physiological signals to control hunger. Its
increased hunger, causing overeating and fat functions are multi-faceted, involving the control
accumulation. of taste responsiveness, hormonal signaling,
and autonomic processes. It acts as a central
4. Prolonged Low Insulin Levels (Diabetes): hub, integrating signals from upstream brain
● Insufficient insulin means glucose remains in the regions, including the paraventricular nucleus
bloodstream but cannot enter cells efficiently, (PVN).
leaving them starved.
● Symptoms include excessive hunger, weight Functions of the Lateral Hypothalamus:
loss, and excretion of metabolized glucose in 1. Taste Sensation and Appetite Regulation:
urine. - The LH communicates with the nucleus of the
tractus solitarius (NTS), a part of the taste
The Role of Glucagon pathway, to enhance the taste of food during
● Secreted by the pancreas when blood glucose hunger.
levels drop, glucagon stimulates the liver to - This process involves altering the salivation
convert glycogen back into glucose, maintaining response and increasing the perceived
blood glucose levels during fasting periods. palatability of food.

Leptin: Long-Term Regulation of Feeding 2. Cortical Connections:

- Axons from the LH extend into the cerebral
Discovery of Leptin cortex, which facilitates behaviors like
● Researchers identified leptin, a hormone indigestion and swallowing. The LH also
produced by fat cells, as a signal for fat enhances the sensory appeal of food (e.g.,
reserves. taste, smell, and sight).
● Higher fat reserves lead to higher leptin levels,
which inform the brain about the body's energy 3. Hormonal Influence:
stores. - The LH modulates the pituitary gland, promoting
the secretion of insulin, which helps the body
Functions of Leptin prepare for food intake by increasing glucose
1. Energy Balance: storage and utilization.
- Low leptin signals depleted fat stores, prompting
increased hunger and decreased activity to 4. Autonomic Responses:
conserve energy. - The LH sends projections to the spinal cord,
- Normal or high leptin levels reduce hunger and controlling autonomic processes such as
increase physical activity. digestive secretions, which aid in food digestion
2. Puberty: and nutrient absorption.
- A sufficient leptin level is necessary for the onset
of puberty, as it signals the body has enough Impact of Damage or Stimulation:
energy reserves to support reproduction. ● Damage:
3. Activation of the Sympathetic Nervous System: - Lesions in the LH lead to a refusal to eat or
- Leptin increases sympathetic activity, raising drink, often requiring force-feeding to sustain
blood pressure and supporting energy life. This is associated with a diminished taste
regulation. response and impaired digestion.
- Such damage also disrupts dopamine pathways
Leptin Deficiency and Treatment passing through the LH, impairing reward and
1. In Mice: motivation related to eating.
- Mice without functional leptin become obese,
inactive, and fail to reach puberty. ● Stimulation:
- Leptin injections reverse these symptoms, - Activation of the LH increases the drive to eat,
reducing food intake and increasing activity. overriding satiety signals.

- Rare cases of leptin deficiency in humans can THE VENTROMEDIAL HYPOTHALAMUS (VMH)
also be treated with leptin supplementation. ➔ The VMH serves as an inhibitor of feeding,
opposing the actions of the LH. It integrates
 signals about satiety and energy homeostasis - Gradual dietary changes, consistent moderate
and influences metabolic processes. exercise, and avoiding sugary drinks are
➔ Functions of the Ventromedial Hypothalamus: effective.
1. Inhibition of Feeding: - Surgical and pharmacological interventions exist
- The VMH regulates feeding suppression by but have limitations and risks.
responding to signals such as leptin (produced - Experimental approaches (e.g., gut microbiome
by fat cells) and other satiety-related hormones. manipulation) show promise.

2. Metabolic Regulation: Bulimia Nervosa

- Damage to the VMH disrupts metabolic balance, 1. Characteristics:
causing increased insulin secretion, which - Cycles of binge eating and purging/dieting.
accelerates fat storage and leads to persistent - Biochemical changes like elevated ghrelin
hunger. appear as a result rather than a cause.

3. Behavioral and Digestive Impact: 2. Addiction-Like Behavior:

- Damage to the VMH increases the frequency of - Similarities between bulimia and substance
meals due to rapid gastric emptying and addiction include dopamine and opioid activity.
heightened gastrointestinal motility. - Animal studies suggest parallels in withdrawal
symptoms.
Impact of Damage or Stimulation:
● Damage: Anorexia Nervosa
- Lesions in the VMH lead to overeating and 1. Characteristics:
dramatic weight gain (ventromedial - Fear of gaining weight, preference for
hypothalamic syndrome). low-calorie foods, and excessive physical
- While meal sizes remain normal, the frequency activity.
of meals increases due to heightened insulin - Affects about 1% of women and 0.33% of men,
production and fat storage, leaving blood often beginning in adolescence.
glucose levels low and cells "starved."
- These effects extend beyond the nucleus to 2. Potential Causes:
involve surrounding regions for more - Weight loss may drive psychological and
pronounced symptoms. biochemical abnormalities rather than
depression or other pre-existing factors.
● Stimulation:
- Activation of the VMH suppresses feeding 3. Animal Model Insights:
behavior and slows metabolic processes. - Rats on extreme caloric restriction and exposed
to cold exhibit anorexia-like behaviors.
Key Insights:
➔ The LH operates as a feeding facilitator by 4. Innovative Treatment:
coordinating sensory, motor, and autonomic - Strategies include keeping patients warm,
processes, ensuring food intake is efficient and limiting physical activity, and guided food intake
rewarding. When disrupted, it can cause using technology.
profound reductions in feeding behaviors. The - Promising results in Europe suggest this
VMH acts as a brake on feeding, regulating approach may outpace traditional methods.
meal frequency and the storage of energy.
Disruptions in its functioning lead to metabolic The brain areas that control eating monitor taste, blood
imbalances, excessive fat accumulation, and glucose, stomach distension, duodenal contents, body
constant hunger. weight, fat cells, hormones, social influences, and more.
Because the system is so complex, it can produce errors
EATING DISORDERS OVERVIEW in many ways. However, the complexity of the system
also provides a kind of security: If one part of the system
1. Homeostatic Control and Its Failures: makes a mistake, another part can counteract it. We
- Insulin, leptin, glucose, and other factors notice people who choose a poor diet or eat the wrong
regulate hunger but are not foolproof. amount, but perhaps we should be even more
- Obesity results partly from evolutionary impressed by how many people eat appropriately. The
predispositions to eat during food abundance. regulation of eating succeeds not in spite of its
- Anorexia and bulimia illustrate complex complexity but because of it.
dysfunctions in feeding behavior.

Obesity
1. Psychological Factors:
- Weak correlation between mood and long-term
weight gain.
- Obesity is only modestly linked to depression.

2. Prenatal Influences:
- High-fat maternal diets may permanently alter
offspring's appetite-regulating brain regions.

3. Genetic Influences:
- Syndromal Obesity: Genes like ghrelin
dysregulation in Prader-Willi syndrome.
- Monogenic Obesity: Mutations in single genes
(e.g., melanocortin receptor).
- Polygenic Obesity: Interaction of multiple genes
with small effects, such as FTO variants.

4. Environmental Interaction:
- Lifestyle and diet significantly amplify genetic
predispositions, as seen in Pima populations.

5. Weight Loss Techniques: