metabolism. appetite hunger and satiety are regulated by a complex interaction of multiple brain...
TRANSCRIPT
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Metabolism
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Appetite
Hunger and
satiety are regulated by
a complex interaction of
multiple brain centers,
hormones, and
sensory and motor
pathways.
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Hunger center
a region in the lateral hypothalamus that triggers the desire for food
stimulated destroyed
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stimulated destroyed
Satiety center
a region in the ventromedial hypothalamus that suppresses the desire for food
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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 the appetite.
Satiety Center
HungerCenter
Blood glucose
appetite
+
_
+
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Gastric peristalsis
stimulates hunger.
Mild hunger
contractions begin soon
after the stomach is
emptied and increase in
intensity over a period of
hours.
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- Adipocytes (fat cells) secrete
hormones (leptin) that regulate
appetite and body weight.
Role of Hormones in Appetite Regulation
- Hormones from GI:
cholecystokinin: suppressantghrelin: stimulantPYY: suppressant
(Science 299:846-849 2003)
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Leptin's effects. Because of a gene defect, the boy doesn't make leptin, but treatment with the hormone, begun when he was 3.5 years old (top), brought his weight down to normal levels, as shown at age 8.
(Science 299:846-849 2003)
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Nutrients
Major Classes of Nutrients :
carbohydrates, lipids, proteins, minerals, vitamins, and water.
Nutrients are used for:
1) providing energy
2) growth, repair, or maintenance of body cells
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Metabolic Rate
is the amount of energy released in the
body per unit of time, expressed as kcal/hr
or kcal/day
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37 C 38 C
1 Kg
A kilocalorie (kcal) is the amount of heat that will raise the temperature of 1 kg of water by 1oC.
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An average adult needs 2,000-5,000 kcal/day, depending on physical activity, mental state, and other factors such as room temperature.
1,000 Kg water x 2 - 5 C
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Caloric restriction (by 30%) prolongs life span by 30%-50% and reduces morbidity of aging-related diseases.
These effects have been observed in many animal species, including worms, insects, rodents, and maybe primates.
ProteinsLow fat/cholesterolVitaminsMinerals
Carbohydrates
unchanged
reduced by 30%
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- ATP is the universal cellular energy, and can be produced from glucose, fat, and proteins.
- A total of 38 ATP is generated per molecule of glucose in the presence of oxygen.
Role of blood glucose in providing energy
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Blood glucose is more important than fat and proteins in providing energy
- Glucose can be used by all tissue cells.
- Neurons and erythrocytes normally obtain
energy only from glucose.
hypoglycemia weakness, coma
Blood glucose level has to be maintained.
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discussed in two states.
1) Absorptive State
lasts about 4 hours after a
meal.
2) Postabsorptive State
Maintenance of blood glucose
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Absorptive State
- Blood glucose is
readily available for ATP
synthesis.
- Glucose serves as a
primary fuel and spares
the body from having to
draw on stored fuels.
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Excessive glucose is stored as glycogen in the liver and muscles or as body fat.
Absorptive State
glycogen
fat
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Fats are taken by the tissues,
especially adipose and muscular tissue.
Absorptive State
Amino acidsbecome available for
protein synthesis. Aminoacids
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Regulation of the Absorptive State
- regulated largely by insulin, which stimulates nearly
all cells to absorb glucose.
glucose
cell
cell
blood
insulin receptors
insulin
glycogen
muscle
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Postabsorptive State (fasting)
- prevails hours after meals and overnight.
- The essence of this state is to regulate
blood glucose levels, which is especially
critical to the brain.
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Glucose is drawn from the body's glycogen reserves in liver and muscles, or synthesized from fats (gluconeogenesis).
glycogen
fats
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After 4 to 5 days of fasting, the brain
begins to use ketone bodies as
supplemental fuel.
Postabsorptive State
- from fat
- acidosis
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After glycogen and fat reserves are depleted
- The body begins to burn proteins.
- The first to go is skeletal muscle proteins.
glycogen
fats
proteins
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Regulation of the Postabsorptive State
- by the sympathetic nervous system and several
hormones.
- The sympathoadrenal system can mobilize stored
energy reserves in adipose tissue as needed.
glycogen
fats
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Glucagon promotes:
1) glycogenolysis glycogen glucose
2) gluconeogenesis AA/FFA glucose
3) lipolysis triglyceride FFA
glycogen
fats
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Growth hormone also raises blood glucose
concentrations.
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Body Heat and Thermoregulation
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Body Temperature
- Body temperature fluctuates about 1oC in a 24-hour cycle.
lowest in the early morning
highest in the late afternoon
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Core temperature
• in the cranial, thoracic, and abdominal cavities
• close to rectal temperature
37.2 -37.6 C
(99.0-99.7 F)
Shell temperature
- skin and oral
36.6 -37.0 C
(97.9-98.6 F)
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heat
heat
Heat Production
Body heat is generated from:
1) nutrient oxidation (ATP production)
energy in glucose ATP
2) ATP use
energy in ATP mechanical energy
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- At rest, mainly generated in brain, liver, heart, endocrine glands, and skeletal muscles (20-30%).
- During vigorous exercise, skeletal muscles produce 30-40 times as much heat as the rest of the body.
Heat Production
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The body loses heat through:
Heat Loss
Conduction Evaporation Radiation
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Thermoregulation
- Hypothalamic thermostat
1) monitors the blood
temperature
2) receives signals from
peripheral
thermoreceptors in the
skin.
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Thermoregulation
heat-losing center
heat-promoting center
in the hypothalamus
thermostat37.5 C
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When blood temperature is
too high
heat-losing center stimulates
1) dilation of dermal
arterioles
2) sweating
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When blood temperature drops too low
heat-promoting center stimulates
1) dermal vasoconstriction
2) shivering thermogenesis.
3) later increase in
metabolic rate by 20-30%
as adaptation.
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Disturbances of Thermoregulation
Exposure to excessive heat causes:
1) heat exhaustion hypotension, dizziness, vomiting, and sometimes fainting
2) heat stroke brain cell malfunction, convulsions, coma, and finally death
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heat
glucose ATP
- refers to low body temperature
- when below 33oC (91oF), the metabolic rate drops so low that heat production cannot keep pace with heat loss, and the temperature falls further.-
Hypothermia
enzyme
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Hypothermia
below 24oC (75oF) = fatal.
Which way helps a person survive longer in ice-cold sea water?
a. Swim vigorously
b. Rest and keep awake