Regulation of Hunger

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Regulation of Hunger
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Hormones Related to Hunger Ghrelin

• Ghrelin
• Secreted by stomach
• Acts on hypothalamus
• Promotes hunger on short timescale (meal-to-meal)
• Empty stomach?increased ghrelin? promotes hunger
• Full stomach ? decreased ghrelin ? inhibits hunger

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Hormones Related to Hunger CCK

• Cholecystokinin (CCK)
• Secreted by duodenum
• Acts on hypothalamus
• inhibits hunger on short, meal-to-meal, timescale
• Material in duodenum?increased ghrelin? supresses
  hunger
• Less material in duodenum ? decreased ghrelin ?
  promotes hunger

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Hormones Related to Hunger PYY

• Polypeptide YY (PYY)
• Secreted by small intestine
• Acts on hypothalamus
• inhibits hunger on intermediate timescale
• Material in SI? PYY? suppresses hunger
• Less material in SI ? PYY ? promotes hunger

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Hormones Related to Hunger Leptin

• Adipokines (from adipose tissue)
• A group of hormones released from adipose tissue
• Evidence that some of them Inhibit ability of
  cells to uptake glucose and contribute to type II
  diabetes
• Leptin (an adipokine)
• Amount of secretion is proportional to amount of
  adipose
• Acts on hypothalamus
• Supresses hunger on long term timescale
• Increased adipose?increase leptin?inhibits hunger
• Decreased adipose ? decrease leptin ? promotes
  hunger
• Evidence that individuals with hard to control
  obesity do not respond to leptin normally

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Regulation of hunger on 3 time scales
Short term

• Red lines are inhibitory
• Green lines are stimulatory

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Adipose Tissue, Leptin, Insulin, and appetite
supression
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Nutrient Absorption and Destination
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five metabolic components/tissues

• 1. Liver
• Break down and synthesize (interconvert) most
  carbs, lipids, and amino acids/proteins
• Stores glycogen
• ONLY TISSUE THAT CAN RELEASE GLUCOSE
• When glucose enters non-liver tissue it is
  phosphoylated preventing it from crossing back
  out across the PM
• Only the liver can de-phosphorylate
• 2. Adipose tissue
• Stores lipids primarily as triglycerides
• Can release lipids as fatty acids and glycerol
• as far as we are concerned.

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five metabolic components/tissues

• 3. Skeletal muscle (close to half your body
  mass)
• Creates substantial glycogen reserves
• Proteins in myofibrils can be broken down as
  source of releasable amino acids
• Uses mostly glucose and triglycerides for energy
• 4. Neural tissue--BRAIN
• Requires glucose and has high glucose demand
• canNOT store energy reserves
• 5. Other tissues
• Insignificant energy reserves
• Variable use of carbs, lipids, and amino acids
  (and others) substrates.

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Absorptive State

• 0-4 hrs after feeding
• Period of increase blood nutrient levels
• Period of increased nutrient availability
• Characterized by nutrient uptake by cells
• Cells use plasma nutrients as source of energy
• Cells generate nutrient stores from uptake of
  nutrients
• Promoted by insulin

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Insulin

• Released from beta cells in pancrease
• Promotes cell uptake of nutrients from plasma
• Reduces blood glucose (lipids amino acid)
• Production of glyocogen (glycogenisis)
• Stimulates adipocytes to synthesize triglycerides
  (with glucose)
• Stimulates protein synthesis
• Insulin release is stimulated by
• High blood glucose levels
• High amino acids levels
• Digestive activity

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Insulin release and action
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Absorptive State
Liver
G.I. Tract (small intestines)
Other cells
blood
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Fate of Nutrients Absorptive State

Resting skeletal muscle uses triglycerides for
ATP, but uptakes glucose and stores it as glycogen
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Interconversion of substrates (anabolism and
catabolism)--all major substrates can be broken
down and used in aerobic respiration--major
nutrients can be interconverted
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Interconversion of substratesCommon source
organs/tissues
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Post-Absorptive State

• gt4 hrs after a meal
• Cells use own stored energy reserves
• Release of stored reserves into blood
• Formation of glucose from non-carbs
  (gluconeogenisis)
• Glucose sparing
• Ensures adequate blood glucose for the brain
• Promoted primarily by Glucagon
• Also glucocorticoids, epinephrine, and other
  hormones

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Post-Absorptive State the Brain

• The brain is primarily dependent on glucose
• The brain does not store glucose or glycogen
• Brain is dependent on constant supply of blood
  glucose to function
• Many post-absorptive activities ensure brain has
  adequate glucose

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Post-Absorptive State the liver

• The liver is the only organ that has cells which
  can release glucose
• The liver is the major metabolic organ that can
  interconvert major macromolecules
• The liver can release stored glucose into blood
• The liver can uptake non-carbs, convert them to
  glucose (gluconeogenisis), and then release that
  glucose

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Stored Substrates
4 hrs overnight worth of ATP -- only liver
can release glucose -- muscle glucose cannot
be released
Mostly in skeletal muscle
Proteins (amino acids) 14.46
Mostly in adipose tissue
1-2 months of ATP
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Glucagon

• Released by alpha cells in pancrease
• Breakdown of glycogen (glycogenolysis) in liver
  and relase of glucose into blood
• Stimulates gluconeogenisis in liver and release
  of glucose into blood
• Stimulates adipocytes to release lipids
• Blood fatty acid levels rise
• Glucagon release is stimulated by low blood sugar

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Glucocorticoids (e.g. cortisol)

• Released from the andrenal cortex
• Increase glucose synthesis in liver
  (gluconeogenisis)
• Causes adipose cells to release fatty acids into
  blood
• Promotes protein breakdown and amino acid release
  into blood
• Inhibits glucose use by organs/tissues other than
  the brain (spares glucose for brain)
• Causes other tissues to metabolize fatty acids
  and proteins rather than glucose for their own
  needs to spare glucose for the brain.
• Also anti-inflammatory and inhibits WBC, release
  of histimine and reduce the movement of
  phagocytes to the site generally reducing
  inflammation but slowing the healing and
  increasing risk of infection.
• Increased levels released in response to stress
• (e.g., fasting and physical activity)

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Glucocorticoids

• From adrenal cortex
• Catabolic
• E.g. cortisol

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hypothalamus
CRH
Glucocorticoid release
ACTH

• Hypothalamus releases CRH (corticotropin
  releasing hormone) which travels to anterior
  pituitary.
• Anterior pituitary responds by releasing
  ACTH(adrenocorticotropic hormone, from anterior
  pituitary)
• ACTH stimulates adrenal cortex to lease
  glucocorticoids into blood.
• Glucocorticoids inhibit CRH release (classic
  negative feedback).

Adrenal cortex
Glucocorticoids
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Post-absorptive State
Liver
G.I. Tract (small intestines)
Other cells
Brain
blood
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Post Absorptive Substrate Fate
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Post-absorptive actions of liver
liver
glucose
Glycogen ? glycogenolysis
Gluconeogenisis
Lactic acid
Skeletal muscle
glucose
amino acids
Gluconeogenisis
glucose
Adipose tissue
fatty acids
Ketone bodies
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Insulin, Glucagon and Blood Sugar
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Insulin and Glucagon action of liver and
adipose cells
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Gluconeogenesis

• Occurs when amino acids or other non-carbos are
  converted to Keto acids, then pyruvate, then
  glucose

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Uses of Different Energy Sources

• Different cells have different preferred energy
  substrates
• Brain uses glucose as its major source of energy
• One goal of metabolic regulation is to ensure
  adequate blood glucose levels to supply brain
  with glucose

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• Gluconeogensis non-carb ? glucose
• Gylcogeniss glucose ? glycogen
• Glycogenolysis glycogen ? glucose
• Lipogenisis making lipids/triglycerides
• Lipolysis triglycerides ? fatty acids glycerol
• Transmamination intercoverting amino acids

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Blood Glucose Levels