Nutrition Metabolism Review Flashcards
How many kCal/gram do we get for glucose?
4 kcal/gr
How many kCal/gram do we get for fatty acids?
it’s the highest caloric fuel - 9 kCal/gram
How many kCal/gram do we get for amino acids?
about 4 kCal/gram again
What are the four important metabolic states and when do they occur?
fed - lasts 2-4 hours after a meal
fasted - overnight without eating
starved - prolonged fasting
hypercatabolic - after trauma or sepsis - not related to meals
What is the teleological statement of what the body wants to do after feeding?
body wants to store calories that exceed its immediate energy needs so that it can withstand periods of nutrient unavailability
What hormone is primary used for this in the fed state?
insulin - it upregulates biosynthetic pathways
What cells release insulin? in response to what?
pancreatic beta cells release is in response to high glucose concentrations in the blood
What catabolic hormone is inhibited by insulin?
glucagon
Usually insulin is released after a meal. What’s the exceptoin and why?
after a high protein meal, glucagon is released because you need to break some of those proteins down into amino acids that can be used for glucoenogenesis.
What type of receptor is the insulin receptor?
a tyrosine kinase with two alpha subunits and two transmembrane beta subunites that will autophosphorylate and then trigger phosphorylation cascades.
What are the two most important signalling cascades activated by the insulin receptor?
- the MAP kinase cascade eventually resulting in activaiton of transcription factors
- the PI3 kinase resulting in activation of protein phosphorylase 1, which activates enzymes for fuel storage and inhibits enzymes for fuel breakdown
What organ is primarily responsible for maintaining glucose homeostasis?
the liver
What does the brain do in the fed state?
oxidizes glucose to CO2 to make ATP through oxidative phosphorylation…it’s happy
What do the RBCs do in the fed state?
ferments glucose to pyruvate and then exports lactate (this is all they really can do)
What does white adipose tissue do in the fed state?
ferments glucose to glycerol 3 phosphate, which is the backbone for triacylglycerol synthesis. That makes sense, right?
What does skeletal muscle do in the fed state?
glycolysis and fatty acid beta oxidation, glycogenogenesis and protein synthesis
basically the whole kit and kaboodle
What does cardiac muscle do in the fed state?
fatty aacid beta oxidation (60-80%) - the heart loves fatty acids (why french fries makes my heart feel so happy)
glucose and lactate oxidation (20-40%)
What do the intestinal epithelial cells do in the fed state?
they covnert glutamine, glutamate and aspartate from the diet (so in the lumen) into alpha-KG
What do the coloncytes do in the fed state?
they are specialized to use short chain fatty acids produced by gut bacteria
What does the body want to do in response to fasting?
wants to mobilize stored energy so that it can continue to perform work in between meals
What hormone is largely responsible for this mobilization of stored foods in the fasted state?
glucagon
What cells secrete glucagon?
pancreatic alpha cells
What type of receptor is the glucagon receptor?
a 7 transmembrane domain heterotrimeric GPCR
Glucagon binding to it’s receptor causes what type of signalling pattern?
activation of adenylate cyclase
production of cAMP
activation of PKA
What does PKA do to glycogen synthase? Glycogen phosphorylase kinase? Glycogen phosphorylase?
Glycogen synthase is phosphorylated and inactivated
Glycogen phosphorylase kinase is phosphoylrated and active.
This then aphosphorylates glycogen phosphorylase and becomes active.
Leads to glycogenolysis
What is important about the fasted state in terms of metabolic measurements?
it’s the state in which we measure resting energy expenditure and the basal metabolic rate
What is the liver’s general response to fasting?
it will increase production and export of glucose for the other tissues”
glycogenolysis using hepatic glycogen stores
Gluconeogenesis using ccarbon skeletons form AAs, lactate and glycerol to produce glucose
Where does the ATP to power gluconeogenesis in the liver come form?
the FAD(2H_ and NADH reduced by fatty acid beta oxidation.
it doesn’t happen for free
What is the acetyl CoA produced by that fatty acid beta oxidation a substrate for?
ketone body synthesis
What does skeletal muscle do in response to fasting?
proteolysis produces free AAs
branched chain AAs can be used by the muscle as fuel
Alanine an glutamine are exported for us as gluconeogenic substrates for the liver
As a fast prolongs, skeletal muscle can switch to using what for energy?
ketone bodies (but it won’t do this for ever!)
What will cardiac muscle do in response to fasting?
still fatty acid beta oxidation - it increases actually and glycolysis decreases
What will gut epithelial cells do in response to fasting?
they’ll still use glutamine as their primary fuel in the fasted state, but it comes from the blood, not the lumen of the gut
What does white adipose tissue do in response to fasting?
lipolysis of TAG produces fatty acids to be used by heart and liver and glycerol used for gluconeogenesis by the liver
What does the body want to do in response to starvation?
During famine, the body preserves body structure by deegrading only the tissue with the most caloric density (fat) to provide energy
you don’t want to be a puddle of bone and connective tissue, now do you?
In response to starvation, the liver increases it’s production of what? What does it DECREASE?
ketone body production increases
gluconeogenesis decreases because the substrates aren’t there - but NOT BY MUCH. Just a little decrease
What happens to ketone body utilization during starvation in the skeletal muscle and the brain?
KB utilization by skeletal muscle decreases (it’s being all muscly and heroic by saving it for the brain)
”” by the brain increases
What does cardiac muscle use in the starved state?
still fatty acids - the heart doesn’t like ketones (blech, it wants french fries, damn it)
What happens to proteolysis in response to starvation?
decreases - again, don’t want to be a puddle
What will happen to the urea cycle activity during fasting? How about starvation?
It will increase during fasting because you’re breaking protein down
If will decrease during starvation because you stop proteolysis and focuse on ketone body synthesis and utilization
What is hypercatabolism?
it’s the rapid mobilization of stored fuels to provide energy for wound repair and immune system function after surgery,t rauma, burns or sepsis
What is hypercatabolism characterized by?
sustained muscle and organ protein breakdown
What three hormones are primarily involved in the hypercatabolic state?
cortisol
glucagon
catecholamines
What does cortisol do in the hypercatabolic state?
it activates muscle proteolysis to get amino acids mobilized form muscle
What does epinephrine do in the hypercatabolic state?
activates hormone sensitive lipase so you get fatty acids mobilized from adipose
What does glucagon do in the hypercatabolic state?
what is always does dummy…
activates hepatic glycogenolysis and gluconeogenesis
What is the main nutritional goal for patients in a hypercatabolic state?
maintain positive nitrogen balance because they need to make proteins to get better
What’s the equation for nitrogen balance?
Nitrogen balance = nitrogen intake – (urinary urea nitrogen + 2
(all units are grams per 24 hrs)
note that the 2 can change depending on population - it accounts for the nitrogen lost in other ways
Gut epithelial cells and lymphocytes are both adapted to use the amino acid glutamine as a fuel source. Why? Aka…what do they have in common?
They both have high turnover rates, so they need a way to get ATP without using all their glucose since glucose is also a super necessary biosynthesis building block for them (need it to make ribose for DNA and RNA - pretty fucking important for a cell that needs to proliferate)
What molecule synthesized by the kidney and liver serves as a buffer of high energy phosphate bonds to replenish ATP in skeletal muscle, cardiac muscle and brain?
creatine
What is the breakdown product of creatine? What does this spontaneously cyclize into?
creatine phosphate isn’t metabolized and cyclizes into creatinine which is excreted in the urine.
Excretion of creatinine is relatively constant and proportional to what?
muscle mass
What is the creatinine-height index?
it’s a measure of nutritional status
urine creatinine is measured over 24 hours and compared with values obtained from healthy well nourished subjects based on height
normal subjects are around 100% and anything less than that suggests that you don’t have as much muscle mass as you should..aka you’re undernourished
What are some physical exam findings to assess nutritional status?
check muscle mass in fingers and face cheilosis allopecia hepatomegaly body mass index of course
What are some lab measures that can help assess nutritional status?
Creatinine-height index serum creatinine 24 hr urinary urea nitrgoen for nitrogen balance serum albumin serum pre-albumin and transthyretin
