Endocrine Control of Fuel Metabolism Flashcards
What is metabolism?
all chemical reactions that occur within cells of the body
What are the two pathways of metabolism?
- anabolic pathway
- catabolic pathway
What does the anabolic pathway do?
involved in synthesis of compounds constituting body’s structure, and require energy (ATP)
ie. protein synthesis, glycogen synthesis
What does the catabolic pathway do?
involve processes that release energy
ie. oxidative phosphorylation
Should the rates of anabolism and catabolism be balanced?
in healthy adults, yes
What do anabolic hormones do?
build fuel stores
What are some anabolic hormones? (3)
insulin
growth hormones
testosterone
What do catabolic hormones do?
break down stores
What are some catabolic hormones? (3)
glucagon
epinephrine
cortisol
What are fight-or-flight hormones?
catabolic hormones
What hormones do cheating athletes use?
catabolic hormones
What happens in glycolysis?
glucose is metabolized to pyruvate
In most cells, what happens to pyruvate?
further metabolized to acetyl-CoA, which can enter citric acid cycle for complete oxidation
What is excess glucose stored as?
glycogen in liver and skeletal muscle
What happens if glucose stores are full?
additional glucose can be transformed into fatty acids + glycerol and stored as triglycerides in adipose tissue
What is the key site of glucose homeostasis?
liver
What happens in ß-oxidation?
fatty acids are metabolized to acetyl-CoA
What happens to acetyl-CoA?
enter citric acid cycle for complete oxidation
What are excess fatty acids stored as?
triglycerides, mainly in adipose tissue (fat)
What is the primary source of energy during prolonged fasting?
stored fat
What happens when excess fatty acid storage (adipose tissue) is full?
elevated circulating fatty acids lead to pathological lipid deposition in skeletal muscle, heart, and elsewhere
What are the 3 types of adipose tissue?
- subcutaneous adipose tissue – underskin
- depot adipose tissue
- visceral adipose tissue – in and around organs
What is lipogenesis?
make fat
What is lypolysis?
break down fat
What is predominantly used for protein synthesis?
dietary amino acids
What happens to excess circulating amino acids that are not needed for protein synthesis?
converted to glucose or fatty acids, ultimately being stored as triglycerides
What is autophagy?
during prolonged fasting, proteins are broken down to amino acids which are converted to ketones to provide energy for brain
What is the primary site of amino acid storage?
muscle
What are the body’s 3 main energy sources?
- carbohydrates
- lipids
- proteins
What are the body’s 3 lesser energy sources?
- glycerol
- lactic acid
- ketones
What is glycerol derived from?
triglyceride hydrolysis
What can glycerol be converted to?
glucose, by the liver
What is lactic acid produced by?
incomplete glucose breakdown (partial glycolysis) in muscle
What can lactic acid be converted to?
glucose, by the liver
What are ketones produced by, and when?
liver during starvation or carbohydrate restriction (ie. nutritional ketosis)
Where are ketones released?
into blood
What uses ketones for energy?
- other tissues
- most importantly the brain
How do all three products of nutrient digestion (glucose, fatty acids and amino acids) form ATP?
metabolized to acetyl-CoA, which is completely oxidized by citric acid cycle in most tissues, and ATP is formed
SUMMARY ENERGY STORES
–
What is the order in which energy is used?
- about 4 hours after meal, you can use that energy from the meal
- after, you use glycogen storage
- gluconeogenesis from lipids and proteins
What can’t the body function without?
kidney
brain
heart
What is the absorptive (fed) state?
period after a meal that food is digested and nutrients are absorbed
- depends on what you eat
What is the post-absorptive (fasting) state?
interdigestive period that begins ~5 h after a meal, and commonly occurs for 10-14hr (overnight) fast
Why is tight glucose regulation important?
important for brain, which uses glucose extensively and can not synthesize its own glucose or store glycogen
What happens if you have hypoglycemia?
can pass out
What happens if you have hyperglycemia?
toxic to tissues
What is glycogenesis?
making glycogen from glucose for storage
What is glycogenolysis?
breaking down glycogen to use for energy
What is gluconeogenesis?
making new glucose from non-carbohydrate sources
What is glycolysis?
breaking down glucose for energy
What does the liver play a primary role in?
maintaining normal plasma glucose levels
What does the liver do when plasma glucose increases?
glycogen synthesis → decrease plasma glucose
What does the liver do when plasma glucose decreases?
gluconeogenesis → increase plasma glucose
What does increase in blood glucose promote?
promotes insulin release, which tells liver that there is high blood sugar and need to store it away and stop releasing it
What is low blood sugar sensed by, and what happens?
sensed by pancreas
- promotes glucagon release, which tells liver that blood glucose is low and some needs to be released into blood
What does SGLT2 do?
block glucose reuptake transporter in kidney, allowing more glucose to leave in urine
Hormonal-regulated and Hormone-independent Control of Glucose Levels
Insulin
- effect on blood glucose
- effect on blood fatty acids
- effect on blood amino acids
- effect on muscle protein
- stimuli
- decrease
- decrease
- decrease
- increase
- ↑ glucose, ↓ amino acids
Hormonal-regulated and Hormone-independent Control of Glucose Levels
Glucagon
- effect on blood glucose
- effect on blood fatty acids
- effect on blood amino acids
- effect on muscle protein
- stimuli
- increase
- increase
- no effect
- no effect
- ↑ glucose, ↓ amino acids
Hormonal-regulated and Hormone-independent Control of Glucose Levels
Epinephrine
- effect on blood glucose
- effect on blood fatty acids
- effect on blood amino acids
- effect on muscle protein
- stimuli
- increase
- increase
- no effect
- no effect
- stress, exercise
Hormonal-regulated and Hormone-independent Control of Glucose Levels
Cortisol
- effect on blood glucose
- effect on blood fatty acids
- effect on blood amino acids
- effect on muscle protein
- stimuli
- increase
- increase
- increase
- decrease
- stress
Hormonal-regulated and Hormone-independent Control of Glucose Levels
Growth Hormone
- effect on blood glucose
- effect on blood fatty acids
- effect on blood amino acids
- effect on muscle protein
- stimuli
- increase (less)
- increase (less)
- decrease
- increase
- deep sleep, stress, exercise, ↓ glucose
Hormonal-regulated and Hormone-independent Control of Glucose Levels
What hormones are involved? (5)
insulin glucagon epinephrine cortisol growth hormone
Hormonal-regulated and Hormone-independent Control of Glucose Levels
What happens in the absorptive state?
increased glucose (hyperglycemia) stimulates insulin release
tells body to put glucose away
Hormonal-regulated and Hormone-independent Control of Glucose Levels
What happens in the post-absorptive state?
insulin falls and glucagon, epinephrine, growth hormone and cortisol rise
this process (glucose counter-regulation) is activated to prevent hypoglycemia (low blood sugar)
What is glucose homeostasis regulated by? (4)
- insulin (most important), glucagon, and epinephrine – fast acting
- cortisol and growth hormone – slow acting
- neural inputs – parasympathetic (Ach), sympathetic (NE)
- substrates – glucose, amino acids (AA), free fatty acids (FFA)
What does the exocrine pancreas do?
secretes bicarbonate and digestive enzymes (amylase, lipase, tryptase) through pancreatic duct into intestine
What is the endocrine pancreas comprised of?
islets of Langerhans, which are scattered throughout exocrine pancreas
Where are exocrine pancreas secretions released?
into gut
Where are endocrine pancreas secretions released?
into bloodstream
What are the 4 major cell types of pancreatic islets?
𝛼 cells – glucagon
𝛽 cells – insulin
𝛿 cells– somatostatin
PP cells – pancreatic polypeptide
Do islets have blood vessels?
yes – highly vascularized
Are islets innervated?
yes – by both sympathetic and parasympathetic fibers of ANS
Describe glucose-stimulated insulin release.
coordinated and rapid
