Lecture 11 : Gastrointestinal System V : Nutrition and Metabolism II Flashcards
Glucose is a major fuel for our body:
When glucose is plentiful, cells use it as their main energy source
To get maximum ATP from glucose, it must be converted to products that go through the citric acid cycle and oxidative phosphorylation
You can’t store ATP: excess glucose can be stored as _____
glycogen
Liver and skeletal muscles are main cell types capable of holding large stores of glycogen =
~600 g total, 2400 kcal
less than one day’s worth of energy
When glycogen stores are full, excess glucose gets converted to ____
fat
Different processes control amount of glucose available for cellular respiration:
The 4 G’s of Glucose Regulation =
Glycolysis
Glycogenesis
Glycogenolysis
Gluconeogenesis
Glycolysis =
(sugar splitting)
converts glucose to pyruvic acid (producing 2 ATP) – all cells
Glycogenesis =
polymerize glucose to form glycogen
(storage of glucose – occurs in liver* and skeletal muscle)
Glycogenolysis =
hydrolyzes glycogen into glucose monomers
(release glucose from storage – only liver can release to blood)
Gluconeogenesis =
forms glucose from non-carbohydrate precursors
(make new glucose from noncarbohydrate sources) – mostly in liver*
Helpful root words:
glyco, gluco =
lysis =
genesis =
neo =
glyco, gluco = sugar
lysis = splitting
genesis = the formation of; origin
neo = new
To fully utilize protein or fat as an energy source, they must be converted to ____
substrates of citric acid cycle
____ are the most concentrated source of energy in the body
Fats
Fats contain very little ____; yield 9 kcal/gm fat
water
Products of fat digestion transported as ______.
chylomicrons
Lipases in capillaries hydrolyze ____ through ____
triglycerides
lipolysis
Of fats, only ___ routinely oxidized for energy
triglycerides
Liver, cardiac muscle, resting skeletal muscle prefer ____ as fuel
fatty acids
___ and ____ can be taken up into most body cells and converted to acetyl CoA (through different pathways) to enter citric acid cycle
Glycerol
free fatty acids
____ allows Glycerol and Fatty Acids to be converted to energy substrates
Lipolysis
Glycerol =
Glycerol is a 3-carbon sugar
Converted to pyruvic acid through glycolysis pathways
Pyruvic acid converted to acetyl CoA which can enter Citric Acid cycle
Net energy ~15 ATP
Fatty Acids carbon-hydrogen chains broken down in cycles of
_____
beta oxidation
beta oxidation =
2 carbon fragments broken off
Form Reduced coenzymes along with acetyl CoA
acetyl CoA enters Citric Acid cycle
____ are formed from Acetyl CoA if there aren’t sufficient carbohydrate substrates for citric acid cycle to run
Ketone bodies
____ is triglyceride synthesis
Lipogenesis
Lipogenesis =
Occurs mainly in liver and adipose tissue during states when cellular ATP and glucose levels are high
Excess acetyl CoA (2 carbons) join together to make fatty acids
Excess glyceraldehyde 3-phosphate (glycolysis intermediate) converted to glycerol
Note these pathways are reversible
Amino acids can also be oxidized for energy =
: Occurs in the liver
we can make nonessential amino acids from keto acids
Transamination and deamination : removes amine group from an amino acid
>nitrogen converted to
ammonia and then urea
Keto acid formed in transamination reaction is modified for citric acid cycle or conversion to fats or glucose
There is no storage form of ______
amino acids
Amino acids are built into proteins when there is an excess =
Any given protein is only synthesized if all its amino acids are available
Every protein has a “job” – we don’t make extras just to store amino acids
If amino acids are needed for energy, we lose important protein
Amino acids can also be converted to glucose : gluconeogenesis
converted first to pyruvic acid , then converted to glucose by reversing the steps of glycolysis
Nutrient pools are interconvertible because their pathways are linked by ______
key intermediates
The body draws on nutrient pools to meet its metabolic needs =
Carbohydrates are easily and frequently converted to fats
Fats and carbs are oxidized directly to supply energy
Amino acid pools must be converted to ____ that can enter citric acid cycle
metabolites
Pyruvic acid can be converted to glucose (______)
gluconeogenesis
Fats and carbs can be stored, but excess amino acids can’t be – they are ______
oxidized for energy, or converted to fat or glycogen for storage
________ are key in managing nutrient load and ensuring all tissues have adequate energy
Liver, skeletal muscle, and adipose tissue
Prefer ____ as major energy source
Allow glucose to remain in blood for brain if glucose is in short supply
triglycerides
Skeletal muscle:
Protein synthesis and protein breakdown
>Muscle proteins can
liberate amino acids for
gluconeogenesis
Glycogen storage
Adipose tissue:
Lipolysis and lipogenesis
Major organ of triglyceride storage
Also secretes novel hormones regulating metabolism – the kind of adipose tissue matters
Carbohydrate metabolism:
Convert non-glucose monosaccharides to glucose
Glycogenesis, glycogenolysis, gluconeogenesis
Converts glucose to fat
Fat metabolism:
Breakdown fatty acids (FA) to acetyl CoA (beta-oxidation)
Convert excess acetyl CoA to ketone bodies (ketogenesis)
Stores fats
Synthesizes lipoproteins for transport of FA, fats and cholesterol in blood
Synthesis of cholesterol from acetyl CoA
Production of bile, converts cholesterol to bile salts
Protein metabolism:
Synthesizes urea to remove ammonia from body
Deaminates amino acids for conversion to glucose or use as fuel
Synthesizes plasma proteins
Interconversion of nonessential amino acids
Vitamins/Minerals:
Storage of vitamin A, D, B12, iron
Biotransformation functions:
Metabolizes alcohol, drugs, hormones other toxins by inactivating them for excretion in kidney
Perform reactions to make products more active or less active
Processes bilirubin excretes bile pigments in bile
Absorptive (fed) state =
Lasts about 4 hours after eating begins
Anabolism exceeds catabolism and nutrients are stored
Post-absorptive (fasting) state =
Catabolism of fat, glycogen, and proteins begins
Primary goal is maintaining blood glucose levels (70-110 mg/dl)
Can be short (between meals) or long-lasting (fasting, starvation)
Major events in the absorptive state =
Anabolism exceeds catabolism and nutrients are stored
Glucose is the major energy fuel
Major metabolic pathways in the absorptive state =
Carbohydrates and Amino acids absorbed into blood go to liver first (via portal vein)
Most lipids travel via lymph in chylomicrons
____ dominates hormonal control of the absorptive state
Insulin
Insulin
Stimulus: rising blood glucose levels
> Beta cells of pancreas increase insulin secretion
Result:
Insulin promotes increased uptake of glucose and amino acids to cells
increased use of glucose by cells for energy or storage as glycogen and fats
Insulin inhibits glucose release and gluconeogenesis in liver
Insulin is a ______ – decreases blood glucose levels
hypoglycemic hormone
Lack of insulin or insulin response: _____
diabetes mellitus
Major events and metabolic pathways in the
post-absorptive state =
Catabolism of fat, glycogen, and proteins
Goal is to maintain homeostatic glucose levels (70-110 mg/100ml)
_____ and other hormones dominate hormonal control of the post-absorptive state
Glucagon
Glucagon
Stimulus: falling blood glucose levels
> Alpha cells increase
glucagon secretion
> Beta cells decrease
insulin secretion
Result:
glycogenolysis and gluconeogenesis by liver restore blood glucose levels
lipolysis in adipose tissue releases fatty acids for use by tissue cells = “glucose sparing”
Carbohydrates
absorbed by:
Glucose primarily
Carbohydrates
absorptive state metabolism:
Used immediately for energy through aerobic pathways (glycolysis & citric acid cycle)
Stored as glycogen in liver & muscle (glycogenesis)
Excess converted to fat and stored in adipose tissue (lipogenesis)
Carbohydrates
post-absorptive state metabolsim:
Glycogen polymers broken down (glycogenolysis) to glucose
Fats
absorbed by:
Fatty acids, triglycerides, cholesterol
Fats
absorptive state metabolism:
Stored as triglycerides primarily in liver and adipose tissue (lipogenesis)
Cholesterol used for steroid synthesis or in membranes
Fats
post-absorptive state metabolsim:
Triglycerides broken down into fatty acids and glycerol (lipolysis)
Fatty acids used for ATP production through aerobic pathways (Beta-oxidation)
Proteins
absorbed by:
Amino acids
Proteins
absorptive state metabolism:
Most amino acids go to tissues for protein synthesis
If needed for energy, amino acids covered in liver to intermediates for aerobic metabolism (deamination)
Excess converted to fat in adipose tissue (lipogenesis)
Proteins
post-absorptive state metabolsim:
Proteins broken down into amino acids
Amino acids deaminated in liver for ATP production or used to make glucose (gluconeogenesis)
Insulin in regulation of metabolic processes =
Stimulates glucose uptake by cells
Stimulates amino acid uptake by cells
Stimulates glucose catabolism for energy
Stimulates glycogenesis
Stimulates lipogenesis & fat storage
Inhibits gluconeogenesis
Stimulates protein synthesis (anabolic)
Glucagon in regulation of metabolic processes =
Stimulates glycogenolysis
Stimulates lipolysis & fat mobilization
Stimulates gluconeogenesis
Insulin is necessary for cells to take glucose out of the blood =
No insulin = high blood glucose levels
High concentration of glucose in filtrate is lost in urine along with water (high urine production)
Type I Diabetes :
autoimmune disease where immune system attacks beta cells of pancreas
little or no insulin produced (“insulin dependent diabetes”)
Type II Diabetes:
Pancreas makes insulin
Receptors lose sensitivity to insulin (“insulin resistant diabetes”)
Metabolic Syndrome
2-8% of world population
1 in 3 US adults
Group of conditions that increase risk of cardiovascular disease, diabetes, stroke, other diseases
Altered metabolism
Many hormones involved in metabolism =
“traditional” endocrine glands
Gut hormones from enteroendocrine cells
Recent drugs for diabetes treatment:
Hormone GLP-1 : Glucagon-like peptide 1
Metformin
Semaglutide
Hormone GLP-1 : Glucagon-like peptide 1
secreted from intestine
doesn’t behave like glucagon
slows digestion by delaying gastric emptying
stimulates insulin secretion to lower blood glucose
Metformin:
stimulates GLP-1 release
Semaglutide:
(Ozempic) : GLP-1 agonist
