Hunger and Eating (ch.12) Flashcards
Homeostasis
- Maintains internal states within a critical range
- Because things like warmth water and food are VITAL and SCARCE
- > We have elaborate systems to monitor and maintain them
- Primarily employs negative feedback mechanisms (deviation from a set point triggers a compensatory (recompense someone who has experienced loss) response.
- Generally a set zone and not a set point
- Otherwise no tolerance in the system leading to constant fluctuations between on and off
2 hallmarks of these systems:
- Redundancy think “failsafe” backup system
2. Rely on Behaviour to acquire more water and food etc
Food and energy regulation
- Requires an anticipation for future needs
What us food necessary for:
- Energy
- Critical nutrients (essential amino acids/ vitamins/ minerals)
Because food availability is unpredictable…
We must have a reserve at all times
Why is it difficult to lose weight?
- As intake decreases so does basal metabolism (# of calories your body would burn if you stayed in bed all day) - in effort to maintain body weight
Calories Restriction:
Only known way to increase longevity in animals
- Reduction of daily caloric intake by 50-75 % increases lifespan
- > May be related to a decrease in the basal metabolism
- > may involve SIRT a ubiquitous protein that can control the production of trophic factors ( promote cell growth and survival
JAPANESE STUDY IN TEXTBOOK
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Immediate Energy Sources
- Immediate source of energy for the body: complex carbs
- Complex carbs are broken into sugars
- Primary sugar used by body: glucose
Short Term Energy Sources
- We need steady supply of energy between meals - body has mechanisms for storing it
- GLUCOSE is converted to GLYCOGEN in a process called glycogenesis
- > promoted by Insulin
- > Glycogen is primarily stored in the liver and muscles
- When blood glucose decreases (between meals) Glycogen is removed from storage back into glucose
Longer Term Energy Sources:
- Take place in the form of fat
- fat is deposited into fat storing cells that form adipose tissue
-> some fats are stored directly from diet (fatty acids)
Others are from excess sugars - during SHORT TERM food storage (process = gluconeogensis)
- during LONGER TERM food storage (process= ketogenesis) -> brain can also use ketones for energy in this case
What is the basis for ketogenic diets?
High protein; low carb
What is crucial for regulation of body metabolism?
Insulin
- 2 key points:
1. Insulin is crucial for conversion of glucose to glycogen
2. Insulin is crucial for enabling the body to use glucose - Glucose transporters span cell membranes and move glucose into cells
- Peripheral cell glucose transporters only function in the presence of insulin
- Glucose transporters in the brain do not require insulin
3 Factors that stimulate Insulin Release:
- Sensory stimulation from food elicit conditioned release of insulin - Cephalic Phase
- During digestion - food entering the stomach/intestine - gut hormones - insulin release
- Absorptive Phase - glucodetectors: cells in the liver detect glucose entering circulation and signal for pancreas to release insulin
Lack of Insulin - Diabetes Mellitus (Type 1)
- Pancreas stops making insulin
- Brain can still use clucose as insulin not needed to uptake by cells HOWEVER body cannot use glucose in the absence of insulin
- Body starts using fatty acids for energy
- Lack of insulin also prevents glucose from being stored as glycogen THEFORE it is excreted in urine
- Diabetes Mellitus literally means
“passing honey”
Treatment for Diabetes Mellitus (type 1)
- Replacement Insulin
- Symptoms: eat a lot, lose weight, thirst and frequent urination, fatty acids use can lead to tissue damage
Hypothalamus Coordinates Multiple systems that…
Control hunger
- No single brain region controls hunger
- Hypothalamus is critically in- compacted and redundant
Appetite is controlled by 2 opposing centers (THEORY)
- Satiety Center - VMH, when lesioned animals to not become satisfied
- Hunger center - LH, when lesioned animals do not eat (aphasia)
- THEORY IS TOO SIMPLE
The Arcuate Nucleus of the Hypothalamus contains a highly specialized appetite controller: controlled by circulating hormones including:
Insulin
Leptin
Ghrelin
Peptide YY
Leptin:
Charachterized by:
- Larger and more fat cells
- maintain obesity even on unpalatable food (lack satiety)
- maintain obesity when required to work hard for food
- Screted from fat cells
- Leptin receptors found in several hypothalamic nuclei
- Brain seems to monitor fat stores using leptin
- More overweight the higher the leptin (controls hunger and feeling of satiety)
Ghrelin
- Released from cells of the stomach, appetite simulant
- Administration of Ghrelin - increased appetite
- Increases during fasten phase and decreases upon consumption
- Odly obese people have decreased ghrelin levels vs lean people, but their ghrelin does not drop after a meal
- Obesity may involve gherkin system that doesn’t repond to feeding - constant promotion of hunger
PYY (3-36)
- Secreted from cells of small and large intestine
- Levels are low before meal
- Rapid increase during meal
- Systemic or intra-ARC admin decreases appetite
- Low levels correlated with Obesity
- May work in opposition to Ghrelin
Arcuate Appetite Controller
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