Exam 1 Organ Phys

Appetite & Satiety

(Cellular Bio - Energetics)

• Control of food intake is a complex process

• Two competing behavioral states

  • Appetite - hunger

  • Satiety - feeling full/satisfied

What are the two hypothalamic centers?

(Cellular Bio - Energetics)

• Feeding center: Tonically activate

• Satiety center

What is the glucostatic theory?

(Cellular Bio - Energetics)

• The satiety center has neurons called glucostats that rapidly absorb blood glucose after a meal

• Hypothesis: Glucose uptake causes the satiety center to send inhibitory signals to the hunger center and thus suppresses appetite

What is the lipostatic theory?

• Body fat content is maintained for homeostasis

• When energy balance is positive, fat increases

• Leptin release (from fat cells)

• Leptin feeds back to the brain to decrease energy storage

  • Don’t need anymore energy - enough is stored

Explain the process of peptide regulation

1. Neuropeptide Y: Hunger-stimulating peptide made in the hypothalamus, which activates the hypothalamic feeding center

2. When the feeding center is activated

↑ Food intake

↑ Fat stores

↑ Leptin secretion (leptin comes from fat cells)

3. Leptin then feeds back to the brain and:

   • Inhibits NPY

   • Suppresses the feeding center

   • Part of a negative feedback loop

     • ↑ Fat, ↑ Leptin, less hunger/eat less

How does the gut communicate with the brain to regulate hunger and satiety?

KEY TAKEAWAY: Food intake isn’t regulated by just one hormone or one brain center. It’s influenced by mechanical signals, nerves, hormones, and reward pathways all at once.

• Nerve signals (blue dashed line – vagus nerve)

  • Stomach distension (stretching when you eat → “I’m full”)

  • Changes in gut movement/pressure
    These travel quickly to the hindbrain and hypothalamus.

  • Ghrelin from the stomach - induce hunger

• Hormones in the bloodstream (red line)

  • Ghrelin from the stomach → signals hunger

  • Satiety hormones like GLP-1 from intestines → signal fullness
    These circulate in blood and act on the brain.

The brain areas involved:

• Hypothalamus – homeostatic control (energy balance)

• Hindbrain – basic feeding control

• Reward center – pleasure/motivation to eat

How do we do work?

Eating!

• First law of thermodynamics (conservation of energy)

• Change in energy = Energy intake - Energy Output

• Energy Intake = Diet

• Energy Output = Work + Heat

• Work: Transport, Mechanical, Chemical

How do we intake energy?

Through food (energy)!

• Direct calorimetry'

  • Fat - 9 kcal/g

  • Protein 4 kcal/g

  • CHO (carbohydrate) - 4 kcal/g

• Energy of Absorption

• Digestive Waste

Energy Output

• By mass balance: Output = Intake - Heat

• Indirect calorimetry

  • Oxygen consumption

  • CO₂ production

  • Respiratory Quotient (indicates what fuel source is being used)

    • 1 - CHO

    • 0.8 - Protein

    • 0.7 - Fat

    • 6 kcal/L O₂ (RQ = 1)

• Metabolic Rate - L O₂/day x kcal/L O₂

What are the factors that contribute to the basal metabolic rate?

• Age and sex

• Lean Body Mass

• Hormones

• Genetics

• Activity/diet level

• Thermic effect of eating

  • How often you eat

  • How much heat is released from digestion

How is glucose (from blood or glycogen) converted into usable energy?

Through the process of glycolysis!

• Fed state

• Occurs in cytoplasm

• Glucose enters the cell and becomes G6P

  • This glucose comes from blood glucose or glycogen (stored glucose)

• Glucose goes through glycolysis to become pyruvate

• Anaerobic pathway: becomes lactate

• Aerobic pathway: enters mitochondria

How do carbohydrates, fats, and proteins converge to produce large amounts of ATP?

• Takes place in the mitochondria (aerobic metabolism)

• Pyruvate → Acetyl-CoA

• Fatty acids are broken down by beta oxidation → Acetyl-CoA

• Acetyl-CoA enters citric acid cycle

  • Produces CO2 and high energy electrons from NADH and FADH₂

• Electrons → ETC → lots of ATP + H₂O

• Excess acetyl-CoA in liver → ketone bodies

How does the body make glucose during fasting?

Through gluconeogenesis (fasting state)!

• Occurs in liver & kidney

• Lactate, amino acids, glycerol → pyruvate

• Pyruvate → G6P → Glucose

• Maintains blood glucose when intake is low

How many net ATP are produced through anaerobic metabolism?

2 ATP

How many net ATP are produced through aerobic metabolism?

30-32 ATP

(26-28 from ETC)