Lecture notes
energy homeostasis
- Institution
- Aston University, Birmingham (Aston)
In depth cell signalling and physiology notes, created using synchronous and asynchronous material.
[Show more]
Seller
Follow
Content preview
Energy homeostasis.Energy content of food
• Humans obtain the vast majority of our
• energy from food we eat
• Energy potential of foods assessed by ‘heat
• of combustion’ (bomb calorimetry)
• Used today to calculate calorie content of
• foods
energy balance
• Energy balance is the homeostasis of energy in a living system
• Measured by:
• Energy intake = energy expenditure + storage
• Energy intake is:
• Dependent on diet – regulated by hunger and calorie consumption
• Energy expenditure is:
• The sum of internal heat production and inter/external work
• Regulation
• The hypothalamus controls both intake and expenditure:
• Eating - Ventromedial nucleus serves as a satiety centre and the arcuate nucleus as a
feeding centre
• Feedback from hormones – adipokines
• Energy balance is how much energy you consume and how much energy you store.
• Energy expenditure is the sum of internal heat, which is the heat you liberate as part of
cellular respiration.
• (by product of cellular respiration is the heat that you produce and there will be energy loss
there)
• But it is also governed by your internal/external work
• An example of internal work is how much energy is needed to digest proteins. It is the
energy required for your organs to complete a particular function.
• Example of external work is like things you do externally such as running , walking, playing
sports.
• For regulation the integrator is still the hypothalamus
• It controls intake and expenditure.
• The ventromedial nucleus serves as a satiety center for fullness when eating.
• The arcuate nucleus serves as a feeding center
• Hormones released from the fat (adipokines) serve as chemical messengers dictating
whether you should eat food or stop eating food. (leptin)
• With regard to food intake there are some mechanisms which are non-biological.
• For example, social customs and habits may lead to you eating more than you normally
would.
• The amount of food available, historically this may have been an issue, however these days
it is not hence the rate of obesity.
• Behavioural mechanisms, such as stress, anxiety and boredom leads to us eating things we
do not need to.
• Smell, taste and texture of food can also increase food intake.
• Leptin is released from adipocytes and it binds to receptors in the hypothalamus.
• It tells your brain that it does not need to eat anymore, they're by supressing appetite.
• Therefore it supresses food consumption and promotes weightloss.
, • It does this by inhibiting the agalti related peptide and then neuropeptide Y neurones.
• The downstream effects of this is that it will inhibit the apetite enhancing pathway.
• Leptin blocks the appetite enhancing pathway so it tells youre brain that you need to stop
eating.
• Individuals who are genetically obese or they have deficiencies in leptin, the body or the
adipose stores are unable to tell the brain to stop eating.
• Insulin does the same thing.
• Insulin is only released when your body is in the fed state.
• If there is plenty of insulin about you would be inhibiting this pathway aswell.
• Because if you have already eaten you would not want to enhance apetite pathways you
would want to sequester them.
AMPK and energy homeostasis
• AMP-activated protein kinase (AMPK) is a highly evolutionarily conserved
serine/threonine kinase
• AMPK is a heterotrimer complex comprising a catalytic α subunit, with a conventional
serine/threonine protein kinase domain, and two regulatory subunits, β and γ
• AMPK activated via phosphorylation by upstream kinases
• Acts as a key nutrient sensor and metabolic switch
• How energy balance is regulated at a molecular level:
• One of the key ways by which energy homeostasis is bought about is through AMPK.
• AMPK is activated in response to a variety of conditions that deplete cellular energy levels.
• Therefore it functions as a cellular energy sensor.
• If in depleted levels AMPK is activated surely a lack of energy must stimulate its function.
• ATP is our energy unit.
• the precurosors of ATP are ADP and AMP.
• If we are in the monophosphate phase we do not have enough energy because ATP is our
predominant energy source and that is what gives us the most energy.
• When AMP (the absolute precursor of ATP) is knocking around that is when AMPK becomes
active.
• AMPK is a cellular energy sensor.
• AMP is activated protein kinase
• It is activated in situations such as nutrient starvation, particularly glucose (it is very sensitive
to glucose)
• It can also be activated with exposure to certain toxins that inhibit mitochondrial respiratory
chain.
• Function of AMPK is to turn on catabolic pathways, which generate ATP and turn off energy
consuming anabolic pathways.
• When we destroy something we liberate energy but when we build something we consume
energy.
• If you are in a starvation mode:
• You will have less glucose which means you are going to have less ATP.
• ATP to AMP ratio will be altered and there will be more AMP instead.
• In times like this we cannot be enhancing anabolic (anything that builds) pathways.
• AMPK would activate catabolic processes because when we break stuff down we liberate
energy.
• e.g. glycogenlysis- if we are breaking down glycogen we are going to be liberating glucose. If
we liberate glucose we will be releasing energy.
• AMPK is spread around the body
• AMPK upregulates catabolic processes (anything that breaking things down).
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller sarah21jan. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for £6.46. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
84866 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy revision notes and other study material for 14 years now