Untitled Flashcards Set

Big Picture: Digestive System & Metabolic Pathways

• Digestion & Absorption:

  • Digestion is the process of breaking down food into smaller molecules (like glucose, fatty acids, amino acids) that can be absorbed into the bloodstream.

  • Absorption is when nutrients (like glucose, fats, proteins) are taken into the bloodstream from the intestines.

• Nutrient Pool:

  • After absorption, nutrients are used for energy or stored. They enter the bloodstream and can either be used right away or stored for later use.

  • Glucose is the primary source of energy for the body.

  • Fats and proteins are also used for energy, but usually when glucose is in short supply.

• Metabolic Pathways:

  • Glycolysis: The breakdown of glucose into pyruvate to produce energy.

  • Citric Acid Cycle (Krebs Cycle): Happens in mitochondria, further breaks down pyruvate to release energy.

  • Electron Transport Chain: Happens in mitochondria and produces most of the energy (ATP) from the breakdown of glucose and fats.

  • Glycogenesis: Storing glucose as glycogen (in liver and muscles).

  • Glycogenolysis: Breaking down glycogen to release glucose when the body needs energy.

  • Gluconeogenesis: Making glucose from non-carbohydrate sources, like amino acids or fats, when glucose levels are low.

  • Lipolysis: Breaking down fat into fatty acids for energy.

  • Lipogenesis: Creating fat from glucose or other nutrients when there's excess energy.

  • Beta-oxidation: Breaking down fatty acids into acetyl-CoA to produce energy.

Appetite & Satiety

• Leptin: A hormone released by fat cells that tells your brain you're full. Higher levels of leptin decrease appetite.

• Ghrelin: The "hunger hormone" released by the stomach when it's empty. It signals to your brain that you're hungry.

• Neuropeptide Y: Stimulates hunger.

• CCK (Cholecystokinin): Released by the small intestine, it helps you feel full after eating.

• GLP-1 (Glucagon-Like Peptide 1): Released after eating, it reduces appetite and helps with insulin release.

• CRH (Corticotropin-Releasing Hormone): A stress hormone that can also influence appetite.

Energy Balance

• Energy Balance: The relationship between the energy you take in (from food) and the energy you burn (through metabolism and physical activity).

  • Positive energy balance: Taking in more energy than you burn, leading to weight gain.

  • Negative energy balance: Burning more energy than you take in, leading to weight loss.

Basal Metabolic Rate (BMR)

• BMR is the amount of energy your body needs to maintain basic functions (like breathing, circulation, and maintaining body temperature) at rest.

• Factors affecting BMR include:

  • Age: BMR generally decreases as you age.

  • Gender: Males tend to have a higher BMR than females due to more muscle mass.

  • Genetics: Some people have a naturally higher or lower BMR.

  • Hormones: Thyroid hormones (like T3 and T4) can increase or decrease BMR.

  • Muscle mass: More muscle increases BMR since muscle burns more calories than fat.

Fed State vs. Fasted State Metabolism

• Fed State (after eating):

  • Your body is focused on storing energy.

  • Insulin is the main hormone here. It helps your cells take in glucose and store it as glycogen in muscles and liver or store it as fat.

• Fasted State (between meals):

  • Your body focuses on using stored energy.

  • Glucagon is the main hormone in this state. It helps release glucose from glycogen stores in the liver or stimulates gluconeogenesis to make more glucose. It also triggers lipolysis (fat breakdown) to provide energy.

Glucose Control

• Why is it crucial?

  • Your brain and red blood cells rely almost entirely on glucose for energy. Without proper glucose levels, these critical parts of your body can’t function properly.

• How does an increase in blood glucose trigger insulin release?

  • When blood glucose rises (like after eating), it stimulates the beta cells in the pancreas to release insulin.

  • Insulin binds to receptors on cells (like muscle and fat cells), which allows them to take in glucose from the blood.

• How does insulin help cells take in glucose?

  • Insulin triggers the GLUT4 transporters to move to the surface of cells like muscle and fat cells, allowing glucose to enter the cell.

Glucagon

• Stimuli for glucagon release:

  • When blood glucose levels drop (like between meals or during fasting), it stimulates the alpha cells in the pancreas to release glucagon.

• Actions of glucagon:

  • Glycogenolysis: Stimulates the liver to break down glycogen and release glucose into the blood.

  • Gluconeogenesis: Stimulates the liver to make new glucose from non-carbohydrate sources like amino acids.

  • Lipolysis: Stimulates fat breakdown to provide fatty acids as an energy source.

Type 1 vs. Type 2 Diabetes

• Type 1 Diabetes:

  • Cause: The immune system destroys the insulin-producing cells in the pancreas. No insulin is produced.

  • Management: Insulin injections are required.

• Type 2 Diabetes:

  • Cause: The body becomes resistant to insulin (the cells don’t respond to insulin as well), or the pancreas doesn't make enough insulin.

  • Management: Can often be managed with diet, exercise, and sometimes medication. Insulin is used in more severe cases.

In Short:

• Fed State: Insulin helps store energy (glucose and fats).

• Fasted State: Glucagon helps release stored energy (glucose and fats).

• Energy Balance: Balancing how much you eat vs. how much you burn.

• Glucose Control: Crucial for brain and red blood cell function. Insulin lowers blood glucose; glucagon raises it.

I hope this helps clarify the concepts for your exam! Do you have any questions on specific topics you'd like me to explain more?

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