Download AP151--DIGESTIVE SYSTEM Part 2--f13

Regulation of Hunger
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
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
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
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
Regulation of hunger on 3 time scales
Short term
Intermediate term
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Red lines are inhibitory
Green lines are stimulatory
Adipose Tissue, Leptin, Insulin, and
appetite supression
Hypothalamus
Nutrient Absorption and
Destination
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.
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.
Absorptive State
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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
Insulin
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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
Insulin release and action
Absorptive State
G.I. Tract
(small
intestines)
Liver
blood
Other cells
Fate of Nutrients: Absorptive State
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Resting skeletal muscle uses triglycerides for ATP, but
uptakes glucose and stores it as glycogen
Interconversion of substrates (anabolism and catabolism):
--all major substrates can be broken down and used in aerobic respiration
--major nutrients can be interconverted
Interconversion of substrates:
Common source organs/tissues
Liver
Adipose Tissue
MuscleTissue
ATP
Post-Absorptive State
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>4 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
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
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
Stored Substrates
~4 hrs – overnight worth of ATP
Mostly in skeletal muscle
-- only liver can release glucose
-- muscle glucose cannot be released
Proteins
(amino acids)
14.46%
Mostly in
adipose
tissue
1-2 months of ATP
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
Glucocorticoids (e.g. cortisol)
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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)
Glucocorticoids
• From adrenal cortex
• Catabolic
– E.g. cortisol
hypothalamus
CRH
Glucocorticoid release
ACTH
Adrenal
cortex
Glucocorticoids
•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).
Post-absorptive State
Other cells
G.I. Tract
(small
intestines)
Liver
blood
Brain
Post Absorptive Substrate Fate
Post-absorptive actions of liver
liver
Skeletal
muscle
Lactic acid
Glycogen  glycogenolysis
glucose
Gluconeogenisis
glucose
amino acids
Adipose
tissue
fatty acids
Gluconeogenisis
Ketone bodies
glucose
Insulin, Glucagon and Blood Sugar
Insulin and Glucagon:
action of liver and adipose cells
Uses of Different Energy Sources
• Different cells have different preferred energy substrates
• Brain uses glucose as its major source of energy
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One goal of metabolic regulation is to ensure adequate blood glucose levels to supply brain with glucose
5-48
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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
Blood Glucose Levels