Exam 1 Flashcards
Why do we eat?
- to replenish energy
- food also provides micronutrients, vitamins, and minerals which are essential building blocks for cellular structure and function
How does energy expenditure occur?
cellular metabolism and physical activity
When is body weight stable?
if the balance between energy (food) intake and energy expenditure is constant
How do we maintain a stable body weight?
A regulatory mechanism that controls energy homeostasis (eating and body weight) needs to monitor and adjust food intake and energy expenditure
What is homeostasis?
- A stable internal state/maintaining a stable internal state
- Means to keep something consistent
Who coined homeostasis?
Walter Bradford Cannon (physiologist)
What does “maintaining homeostasis” imply?
there must be a sort of mechanism to maintain homeostasis
What is an example of a Homeostatic Regulatory Mechanism?
A thermostat
What is negative feedback?
a process whereby the effect produced by an action serves to diminish or terminate the action
How is eating regulated?
through negative feedback
What are Components of the Homeostatic Regulatory Mechanism?
- System variable
- Set point
- Detector
- error correction mechanism
How have mammals evolved in relation to eating?
Mammals have evolved to be prevented from starving
What does the process of energy homeostasis do in the body?
maintains a stable body weight (body fat)
What is the goal of eating for an organism?
eats to maintain a balance between used and stored energy
Explain how a thermostat is a homeostatic regulatory mechanism.
System variable: air temp
Set point: 70 degrees
Detector: thermostat
Error correction mechanism: heat production
What is an indicatior to the brain of the body state?
- fat
- it is a physiological signal
- very important for survival
Where is the thermostat (regulatory mechanism) for body weight?
- The brain! it is the detector and the correctional mechanism
Name two adiposity signals.
Insulin and leptin
How is energy expenditure controlled?
Physiological signs from the body and the brain are directly related to metabolic control and maintenance of energy balance, and these determine energy expenditure
What mechanisms impact how humans actually eat?
anticipatory mechanisms
WHat are anticipatory mechanisms?
- We don’t want to wait till we are starving to eat
- Anticipatory mechanisms have a role in starting and stopping eating
Explain the role of anticipatory mechanisms in starting eating
- meals are intiated without physiological deficits
- we eat in anticipation of future deficits
- there are cues that predict food
Explain the role of anticipatory mechanisms in ending eating.
- Satiety mechanisms stop eating before weight is gained in anticipation of imminent replenishment
Could stability/homeostasis be achieved without a regulatory mechanism?
Yes if intake and outtake are exacly the same
What does levisky argue we have to achieve stability?
- Believes there is a settling point/settling range instead of a set point
What is an example of a settling point/range?
- sea level
- rainfall and melting ice caps vs evaporation and polar ice cap freesing
What are the two ways homeostasis can be achieved?
1) A regulatory mechanism - an active process (thermostat)
2) Settling of opposing forces - a sum of at least two independent processes
(setting a heater and a thermostat, sea level example)
What two factors primarily predetermine body weight?
Environment and genetic predisposition creates a range of where our body weight would be
Is eating a good regulatory mechanism?
Eating is not a good homeostatic mechanism because small changes don’t cause a change in body weight
What does Levitsky argue about homeostasis?
- emphasizes that there is no system that regulates eating behavior
- He is manipulating eating and he does not see a specific response
What did the Levitsky paper conclude in general? (about overfeeding?)
- The studies in this review in general show that subjects increase eating for various reasons, non-homeostatic reasons
- And they do not adjust accurately (or at all) eating to compensate for prior under/overeating
- However, data in regard to overfeeding show changes in body weight that suggest homeostatic metabolic rate changes in response to extra energy gained
What are some of the reasons people increased their eating in the Levitsky paper?
- higher calorie dense food
- portion size
- number of people
- “confederate”
What is a person who is part of the study but is controlled?
a confederate
What occurs with massive weight loss?
- Metabolic slowing with massive weight loss despite preservation of fat-free mass
- If someone suddenly loses a lot of weight there is a pushback from the body to stop weight loss (metabolic slowing)
What did the biggest loser study indicate?
- Only way to maintain weight loss is to exercise – exercise may prevent the metabolic slowing
- Liver damage from sugar can be prevented by exercise
Where do we get energy from (general)?
Intake and energy stores
What are the two types of energy stores?
short-term and long term
Where are the short term energy stores and what type of energy is stored?
- liver and muscles - carbohydrates and glycogen
Where are the long term energy stores?
- fat (adipose tissue)
Why is it helpful to have short term and long term energy stores?
- Helpful to have short term to have a burst of energy
- Long term for emergencies if you cant find food for a while
Why must glucose be in a particular (narrow) range?
- Need to avoid hyper-glycemia and hypo-glycemia
- Also must ensure sufficient supply to the brain
What molecules are controlled by the presence/absense of glucose in the blood?
Hormones: insulin and glucagon
What happens when glucose is high?
Glucose binds to receptors on the pancreas cells and stimulates them to release insulin -> then insulin allows cells to store extra and allows cells to use it and store some of it as glycogen (sort of like a negative feedback)
What is the structure of insulin?
polypeptide with two peptide chains
What happens when glucose is low?
- Not binding glucose on particular cells is allows glucagon to be released
What can all cells in the body use for energy?
- fatty acids can be metabolized directly by all cells in the body
- Liver stores glucose, but does not use glucose for energy, it oxidizes fatty acids
What does the brain use for energy?
The brain needs a steady supply of glucose from the blood because it does not metabolize fatty acids (In extreme conditions it can metabolize ketones)
How are the cells in the body prevented from using glucose?
- Insulin controls entry of glucose into muscle, adipose and other tissues
- Glucose is non-lipid soluble and cells need glucose transporters to carry glucose across the cell membrane
- Glucose transporters are insulin responsive
What molecule activates glucose transporters?
insulin
What occurs when glucose and insulin are both sufficiently high?
When glucose and insulin are both sufficiently high, insulin enables most cells in the body to use glucose as energy, by mediating entry of glucose
What does low insulin signal to the body?
Low insulin is a signal that the body is depending on lipids for energy and glucose in the blood is reserved for the brain