Feeding Fasting cycle Flashcards
What are the major organs involved in feeding/appetite?
GI tract, liver, muscle, adipose tissue, brain, kidney
What is the function of the GI tract?
Mixing, digesting, absorbing, and propelling food
What are the major digestion/metabolism/appetite hormones
Ghrelin, leptin, cholecystokinin, insulin, glucagon
What hormone is secreted by pancreatic beta-cells
Insulin
What hormone is secreted by pancreatic alpha-cells?
Glucagon
What is the biological role of the liver?
Carbohydrate/lipid/amino acid metabolism
Regulate blood glucose
Detox
What is the energy source for cardiac muscle?
Glucose in fed state
Fatty acids in fasting state
How is glucose transport into muscle cells activated?
By insulin, which activates translocation of GLUT 4
What is the function of adipose tissue?
Store triacylglycerols
Secretes leptin
What is the function of the leptin hormone?
Satiety-inducing
How does the brain regulated appetite? What is its energy source?
Regulates via the hypothalamus
Glucose is sole energy source
What is the biological role of the kidneys?
Filter blood plasma
Reabsorption of electrolytes and nutrients
Regulate pH
Regulate water content
What is the postprandial state?
After meal, when nutrient levels are high
What is the postabsorptive state?
After fasting [e.g. overnight] when nutrient levels are low
Describe the features of food digestion and absorption [aka feeding phase]
In early postprandial state…
1) Sugars and AAs absorbed and transported in blood to liver through portal vein
2) Lipids transported in lymph as chylomicrons
3) Chylomicrons pass to the bloodstream, which provides triacylglycerol to muscle and adipose tissue
4) Glucose movement from small intestine to liver stimulates beta cells
5) Beta cells release insulin, which promotes glucose uptake
6) Glycogenesis, fat + protein synthesis are promoted
Describe the fasting phase
1) Glucose/insulin levels decrease
2) Glucagon is released–prevents hypoglycemia by stimulating glycogenolysis and gluconeogenesis
If fasting is prolonged–maintain glucose levels via fatty acid mobilization–alternative to glucose for muscle, so glucose can be saved for brain
Starvation–additional fatty acids from adipose tissue and ketone bodies from liver are mobilized
- gluconeogenesis
- large amounts of AAs from muscle are used
- eventually brain adapts to new energy source
What neural circuit regulates appetite? How does it work?
Arcuate nucleus (ARC)
Depending on signal produced by ARC, appetite suppressed or stimulated
Insulin reduces uptake via same mechanism
mTORC also regulates ARC
How does AMPK work to regulate appetite? What hormones inhibit it?
AMPK mediates appetite-regulating integration
- inhibited by insulin and leptin
What is the cause of type 1 diabetes? What are its effects?
Inadequate insulin secretion
Why? Autoimmune destruction of pancreatic beta-cells
Can cause? Ketoacidosis
What is the cause of type 2 diabetes–proximate and ultimate? What are the symptoms?
Ultimate cause = insulin resistance of target cells
Proximate cause = hyperglycemia
Symptoms…
glucosuria -> osmotic diuresis, polyuria, excessive thirst
dyslipidemia -> abnormal blood lipid/lipoprotein levels -> deposits around cells can further block insulin
What conditions make up the metabolic syndrome cluster?
Obesity, hypertension, dyslipidemia, insulin resistance
What are the causes of metabolic syndrome?
Hyperinsulinemia
Excess glucose production
Decreased insulin-dependent glucose uptake in muscle
Excess free fatty acids–disrupt signal transduction in insulin dependent tissues
Type 2 diabetes
What is the formula for BMI calculation?
BMI = Weight (kg) / height (m) ^2
