Module 1 Section 5 (Endocrine Control of Fuel Metabolism) Flashcards
Describe fuel metabolism in the liver, fat, cells, muscle, and brain during fasted and fed conditions.
Metabolism is the sum of all chem reactions that occur in all organism which includes the synthesis, degradation, transport of substances into and b/w cells and the transformation of proteins, carbs and fats.
- These reactions = intermediary or fuel metabolism
Contrast the cellular response to insulin in liver cells, fat cells, and muscle cells.
.
Describe how the release of insulin and glucagon are regulated, and once released, how they regulate fuel metabolism.
Decr in blood glucose —(+)—> a-cells ——> incr glucagon ——> incr blood glucose to normal
OR
Decr in blood glucose —(-)—> B-cells ——> decr insulin ——> incr blood glucose to normal
Explain why it’s important for some tissues to be insulin-independent for glucose uptake.
If the tissues had only an insulin-dependent transporter they would be starved of glucose during the fasted state, with lethal consequences. The insulin-independent transporter allows continued transport down the glucose concentration gradient, even as the blood glucose concentration falls.
What is the difference b/w anabolic and catabolic reactions?
Anabolic reactions (anabolism): synthesis of larger organic macromolecules from smaller organic molecular subunits used for repair, growth and the storage of excess ingested nutrients.
Catabolic reactions (catabolism): the breakdown of larger organic macromolecules either through the process of hydrolysis into smaller molecules, or oxidation of smaller molecules (glucose) to yield ATP
How is excess glucose, FAs and AAs stored?
Excess glucose
- Stored in the liver and skeletal muscle as glycogen
- Once glycogen stores are full, any extra glucose -> free FAs and glycerol for the synthesis of triglycerides (occurs in adipose tissue)
Excess FA
- Stored as triglycerides
Excess AA
- Excess not needed for protein synthesis are not stored and are instead used for structural proteins or converted to glucose and FA for eventual storage as triglycerides
~ Excess nutrients are usually stored as triglycerides in adipose tissue. When needed energy —(catabolism)—> FFA and glycerol
The body has 2 functional metabolic states. What are they?
Absorptive state
- During this, anabolism dominates as ingested food -> digested and absorbed -> circulation
- Ingested simple carbs -> converted in the liver to glucose -> released to be available as fuel or stored as glycogen
- Ingested fats and proteins = immediately used or stored
Postabsorptive state
- During this, several hrs after ingesting food, cartabolism dominates
- Glycogen stores in liver and skeletal muscle become primary energy source
- If this state persists, glycogen alone can’t meet the body’s needs, so lipolysis occurs to break down triglycerides
What are some other energy sources?
Glycerol
- Comes from backbone of triglycerides when they’re broken down
- Can be converted to glucose by the liver
Lactic acid
- Can be formed by glycolysis
- Can also be converted to glucoose by the liver
Ketone bodies
- Group of compounds produced in the liver in times of glucose shortages
- When liver uses FFAs as energy, they are oxidized to acetyl CoA, which doesnt produce any additional energy through the citric acid cycle
- Acetyl CoA -> converted to ketone bodies -> released into blood
- In times of starvation, the brain can use ketone bodies, instead of glucose as an energy source
What is the pancreas?
It’s an organ that has both exocrine (glands that secrete their products through ducts opening onto an epithelium instead of directly into the bloodstream) and endocrine functions (plays a role in determining the body’s metabolic state).
- Exocrine important for digestion
- Exocrine function of the pancreas are localized to the Islets of Langerhaans which are clusters of cells found throughout the pancreas.
What are the major types of cells in the islets of Longerhoans
- a-cells -> produce and secrete glucagon
- B-cells: produce and secret insulin
- Delta cell: produce and secrete somatostatin
- Pancreatic polypeptide (PP) cell: plays a role in reducing appetite
What is the purpose of somatostatin? Where is it stored, produced and released?
In response to circulating glucose and AAs following a meal, the δ cells release somatostatin.
The effect is to slow down the digestive system to inhibit digestion and absorption of nutrients. It works in a negative-feedback way to prevent too many nutrients from being absorbed.
It’s stored in the pancreas. It’s produced in the cells lining the digestive tract, where it acts as a paracrine hormone (hormone that has effect only in the vicinity of the gland secreting it) to inhibit digestion. It’s released by the hypothalamus where it inhibits the secretion of GH and TSH
What is insulin? What does it do?
It’s a small peptide hormone produced by B-cells of the pancreatic islets. It’s the dom hormone in the absorptive state and plays a major role in anabolism.
It regulates blood sugar (effects carbs), and it also has an effect on fats and proteins.
What are the factors that influence blood glucose conc? **
Factors that incr blood glucose
- Glucose absorption from the digestive tract
- Hepatic glucose production:
• Through glycogenolysis of stored glycogen
• Through gluconeogenesis
Factors that decr blood glucose
- Transport of glucose into cells:
• For utilization for energy production
• For storage as glycogen through glyconeogenesis
• For storage as triglycerides
- Urinary excretion of glucose (occurs only abnormally, when blood glucose level becomes so high it exceeds the reabsorptive capacity of kidney tubules during urine formation).
Discuss the effect insulin has on carbohydrates? (4)
1) Increase the uptake of glucose into most cells
- Insulin causes movement of GLUT-4 glucose transporters from an intracellular pool -> plasma membrane where they begin to transport glucose -> cells
- Brain doesnt require it since it has GLUT-1 and GLUT-3 glucose transporters in the plasma membrane
- Exercising skeletal muscles are also able to take up glucose
independent of insulin.
- Liver uptake of glucose is by GLUT-2 is also insulin-independent.
2) Stimulate glycogenesis in skeletal muscle and the liver
- This promotes the storage of glucose as glycogen.
3) Inhibit glycogenolysis in the liver
- This prevents the catabolism of glycogen and further promotes glucose storage.
4) Inhibit gluconeogenesis in the liver
- This prevents the formation of glucose from amino acids.
Discuss the effect insulin has on fats? (4) **
- Enhances the entry of fatty acids into adipose tissue cells
- Increases GLUT-4 recruitment in adipose cells to increase glucose uptake for the synthesis of
triglycerides - Enhances the activity of the enzymes involved in synthesizing triglycerides
- Inhibits lipolysis
