Lecture 29 Flashcards
How is energy used during exercise?
The stored energy sources are used sequentially: stored high-energy phosphate bonds (ATP, creatine phosphate) followed by glycogen, circulating glucose, and circulating FFAs
How does the metabolic response to exercise resemble to response to fasting?
Mobilization and generation of fuels for oxidation are dominant factors
In what ways can carbohydrates be used in an absorptive state?
Absorbed as glucose
1. Used immediately for energy through aerobic pathways
2. Used for lipoprotein synthesis in liver
3. Stored as glycogen in liver and muscle
4. Excess converted to fat and stored in adipose tissue (glucose -> pyruvate -> acetyl CoA -> fatty acids)
In what ways can proteins be used in an absorptive state?
Absorbed primarily as amino acids
1. Most amino acids go to tissues for protein synthesis
2. If needed for energy, amino acids converted in liver to intermediates for aerobic metabolism
3. Excess converted to fat and stored in adipose tissue (amino acids -> acetyl CoA -> fatty acids)
In what ways can fats be used in an absorptive state?
Absorbed primarily as triglycerides
1. Stored as fats in liver and adipose tissue
Lipogenesis
Free fatty acid pool -> fat stores
Lipolysis
Fat stores -> free fatty acid pool
Lipogenesis
Excess glucose -> fat stores
Glycogenesis
Glucose pool -> glycogen stores
Glycogen stores
~100g of glycogen in liver
~200g of glycogen in skeletal muscle
Glycogenolysis
Glycogen -> Glucose pool
Protein Synthesis
Amino acid pool -> body protein
Gluconeogenesis
Amino acid pool -> Glucose pool
Glucose Sparing
- Release of energy during the interdigestive period or an extended fasting (fat utilization)
- During fasting, both skeletal muscle and adipose tissue contribute directly to circulating blood glucose through the release of gluconeogenic substrates (lactate, amino acids, glycerol) and indirectly through the release of free fatty acids (FFA) -> allow skeletal muscle and other tissues to consume less glucose
- Release of FFAs and ketogenic amino acids supports ketogenesis by liver
- Ketone bodies thus produced can be utilized for ATP production (brain)
Ketogenesis
Ketogenic amino acids converted to acetyl CoA
What are skeletal muscle and adipose tissue promoted by?
Glucagon or epinephrine/norepinephrine or both
What receptor transports glucose out of liver cells?
GLUT2
What receptor transports glucose into the brain?
Glucose -> GLUT3 -> ATP
How to islets influence eachother?
Paracrine and autocrine communication
Alpha cells
Secrete glucagon
Glucagon
Increases glucose blood levels
Beta cells
Secrete insulin
Insulin
Increases transport of glucose into cells (ex: hepatocytes and skeletal and cardiac muscle cells)
Delta cells
Secrete gastrin and somatostatin
Gastrin
Stimulates production of HCl by parietal cells in the stomach
Somatostatin
Inhibits the release of insulin and glucagon, and the secretion of HCl by parietal cells
Delta-1 Cells (D1)
Produce vasoactive intestinal polypeptide (VIP)
Vasoactive Intestinal Polypeptide (VIP)
Induces glycogenolysis and hyperglycemia and stimulates GI fluid secretion
PP Cells
(gamma or F) produce pancreatic polypeptide
Pancreatic Polypeptide
Inhibits the secretion of somatostatin and the CCK-stimulated secretion of pancreatic enzymes
Islet of Langerhans
- Display alpha and beta cells in relationship with each other throughout the cluster
- Beta cells are coupled electrically to other beta cells (but not to other cell types)
- Each islet consists of 2000 to 3000 cells surrounded by a network of fenestrated capillaries and supported by reticular fibers
Insuloacinar Portal System
- Vascular component
- Enables a local action of insular hormone on the exocrine pancreas
