Sponsored Links
Results 1 to 5 of 5
  1. #1
    drgoljan is offline Junior Member 510 points
    Join Date
    Mar 2007
    Posts
    20
    Downloads
    6
    Uploads
    0
    Thanks
    0
    Thanked 0 Times in 0 Posts

    Can anyone explain starvation?

    Advertisements



    I'll really appreciate if someone can explain starvation step by step ,when glycogenolysis starts,when gluconeogenesis occur I am really confused on this one.

  2. #2
    GFLIP's Avatar
    GFLIP is offline Senior Member 510 points
    Join Date
    Mar 2005
    Posts
    1,165
    Downloads
    2
    Uploads
    0
    Images
    53
    Thanks
    0
    Thanked 0 Times in 0 Posts
    Early fasting state --> glycogenolysis (but also starting gluconeogenesis) <-- both are promoted by glucagon
    Starvation --> gluconeogenesis

    ------

    ~0-4 hours after a meal --> exogenous glucose
    ~4-28 hours after a meal --> glycogenolysis and gluconeogenesis occur simultaneously BUT...
    ~4-16 hours --> glycogenolysis maintains blood glucose more than gluconeogenesis
    ~16-28 hours --> gluconeogenesis maintains blood glucose more than glycogenolysis (this is known as early starvation)
    ~28 hours --> glycogen stores are depleted
    after a week --> gluconeogenesis rate decreases (this is when the brain starts to use ketone bodies)

    MORE INFO:

    2 priorities in starvation:
    1) maintain plasma glucose for brain metabolism & other glucose-requiring tissues
    2) move fatty acids (from adipose) and ketone bodies (from liver) to supply energy to all other tissues


    IN THE LIVER:
    1) Carb metabolism: liver uses first glycogenolysis --> then gluconeogenesis to maintain plasma glucose (for brain, etc.) --> gluconeogenesis
    becomes fully active as liver glycogen stores deplete
    2) Fat metabolism:
    -there's increased fatty acid oxidation from adipose tissue - this is the major source of energy in hepatic tissue
    -there's increased synthesis of ketone bodies during the first days of starvation... this occurs when there's high acetyl CoA (from fatty acids
    oxidation)... this will reduce need for gluconeogenesis from amino acids this slowing loss of essential protein

    IN ADIPOSE TISSUE:
    1) Carb metabolism: decreased insulin decreases adipose uptake of glucose --> decreased synthesis of fatty acids and triacylglycerol (TAG)
    2) Fat metabolism: decreased insulin increases degradation of TAG via activation of hormone sensitive lipase (which is also activated by
    catecholamines) --> fatty acids from TAG degradation is delivered to tissues for fuel (there's decreased uptake of FA d/t low activity of
    lipoprotein lipase in adipose tissues)

    IN SKELETAL MUSCLE:
    1) Carb metabolism: decreased insulin decreases glucose transport into skeletal muscles
    2) Lipid metabolism:
    -first 2 weeks of starvation - muscle uses fatty acids from adipose tissue and ketone bodies from the liver as fuels
    -after 3 weeks of starvation - muscle stops using ketone bodies and oxidizes fatty acids --> this increases already elevated ketone bodies
    3) Protein metabolism:
    -first days of starvation - rapid breakdown of muscle protein provides AA for liver gluconeogesis
    -after several weeks of starvation - muscle proteolysis decreases d/t decrease in need for glucose as fuel for brain

    IN THE BRAIN:
    -first few days of starvation - brain uses glucose as fuel
    -over 2-3 weeks of starvation - ketone bodies are markedly elevated and are used as fuel by the brain (this decreases need for protein catabolism
    for gluconeogenesis)

  3. #3
    drgoljan is offline Junior Member 510 points
    Join Date
    Mar 2007
    Posts
    20
    Downloads
    6
    Uploads
    0
    Thanks
    0
    Thanked 0 Times in 0 Posts
    Gflip ,you are really a kind person and i really wish you 99 in your exam.Thanks a lot .

  4. #4
    drgoljan is offline Junior Member 510 points
    Join Date
    Mar 2007
    Posts
    20
    Downloads
    6
    Uploads
    0
    Thanks
    0
    Thanked 0 Times in 0 Posts
    Nbme 4 question
    A 28-year-old man is brought to the emergency department after being lost in a remote wilderness area for 3 weeks. He consumed all of the food in his backpack 2 weeks ago and has had only wild berries and pond water since then. Intravenous feeding is begun. Blood samples obtained before intravenous feeding was begun show increased serum concentrations of ketone bodies and urea nitrogen (BUN); glucose concentration is within the reference range. Use of which of the following best explains the maintenance of a normal glucose concentration in this patient?
    A ) Dietary protein
    B ) Hepatic glycogen stores
    C ) Skeletal muscle glycogen
    D ) Skeletal muscle protein


    So do you think answer should be c
    As A is out,B and D in first two weeks and third week C seems most appropriate.

  5. #5
    mcscrooge is offline Newbie 510 points
    Join Date
    Mar 2014
    Posts
    1
    Downloads
    0
    Uploads
    0
    Thanks
    0
    Thanked 0 Times in 0 Posts
    Hey bud, all glycogen is depleted within about a day of starvation so B and C are out. Since he has no protein in his diet, answer is D. The exact timeframes in the excellent summary of metabolism of starvation above are not set in stone (eg 2wk vs 3wk) so I wouldn't memorize them that way. The question asks specifically about serum glucose levels rather than energy sources. Lipolysis and other processes are contributing to his energy requirements by making ketones but the question asks specifically about blood glucose. His glucose is only coming from glycogenolysis or gluconeogenesis. Several weeks into starvation, its definitely gluconeogenesis. Good luck.

Similar Threads

  1. about starvation and diabetes
    By Stan1 in forum The Relaxing Lounge
    Replies: 9
    Last Post: 02-18-2009, 11:18 AM
  2. Starvation: What do you use for fuel first?
    By Pokerslut in forum Biochemistry And Genetics
    Replies: 4
    Last Post: 02-15-2009, 05:44 PM
  3. Please explain this:
    By lmoliver in forum Physiology Forum
    Replies: 6
    Last Post: 04-16-2007, 07:44 AM
  4. please explain
    By Asclepius1 in forum USMLE Step 3 Exam Experiences
    Replies: 0
    Last Post: 05-08-2005, 11:09 AM
  5. self-imposed "starvation diet" for four months
    By BioPatel in forum Biochemistry And Genetics
    Replies: 2
    Last Post: 12-06-2004, 08:11 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •