Metabolism

1
Metabolism
2
Appetite
Hunger and satiety are regulated by a complex
interaction of multiple brain centers, hormones,
and sensory and motor pathways.
3
Hunger center a region in the lateral
hypothalamus that triggers the desire for food
stimulated
destroyed
4
Satiety center a region in the ventromedial
hypothalamus that suppresses the desire for food
stimulated
destroyed
5
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.
_
Hunger Center
Satiety Center


Blood glucose
appetite
6
Gastric peristalsis stimulates hunger. Mild
hunger contractions begin soon after the stomach
is emptied and increase in intensity over a
period of hours.
7
Role of Hormones in Appetite Regulation -
Hormones from GI cholecystokinin
suppressant ghrelin stimulant PYY suppressant
- Adipocytes (fat cells) secrete hormones
(leptin) that regulate appetite and body weight.
(Science 299846-849 2003)
8
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 299846-849 2003)
9
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
10
Metabolic Rate is the amount of energy
released in the body per unit of time, expressed
as kcal/hr or kcal/day
11
A kilocalorie (kcal) is the amount of heat that
will raise the temperature of 1 kg of water by
1oC.
1 Kg
37 ? C
38 ? C
12
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
13
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.
Proteins Low fat/cholesterol Vitamins Minerals Ca
rbohydrates
unchanged
reduced by 30
14
Role of blood glucose in providing energy
- 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.
15

• 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.

16
Maintenance of blood glucose
discussed in two states. 1) Absorptive State
lasts about 4 hours after a meal. 2)
Postabsorptive State
17

• 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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Absorptive State
Excessive glucose is stored as glycogen in the
liver and muscles or as body fat.
19
Absorptive State
Fats are taken by the tissues, especially
adipose and muscular tissue.
Amino acids become available for protein
synthesis.
Amino acids
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• Regulation of the Absorptive State
• regulated largely by insulin, which stimulates
  nearly all cells to absorb glucose.

insulin receptors
blood
insulin
cell
glycogen
glucose
muscle
cell
21

• 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.

22
Glucose is drawn from the body's glycogen
reserves in liver and muscles, or synthesized
from fats (gluconeogenesis).
glycogen
fats
23
Postabsorptive State
After 4 to 5 days of fasting, the brain begins to
use ketone bodies as supplemental fuel.
- from fat - acidosis
24
After glycogen and fat reserves are depleted -
The body begins to burn proteins. - The first
to go is skeletal muscle proteins.
proteins
25
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.
26
Glucagon promotes 1) glycogenolysis
glycogen ? glucose 2) gluconeogenesis
AA/FFA ? glucose 3) lipolysis triglyceride
? FFA
27
Growth hormone also raises blood glucose
concentrations.
28
Body Heat and Thermoregulation
29

• Body Temperature
• Body temperature fluctuates about 1oC in a
  24-hour cycle.
• lowest in the early morning
• highest in the late afternoon

30

• 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)

31

• Heat Production
• Body heat is generated from
• nutrient oxidation (ATP production)
• energy in glucose ATP
• 2) ATP use
• energy in ATP mechanical energy

32
Heat Production
- 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.
33
Heat Loss
The body loses heat through
Conduction
Evaporation
Radiation
34

• Thermoregulation
• Hypothalamic thermostat
• monitors the blood temperature
• receives signals from peripheral thermoreceptors
  in the skin.

35
Thermoregulation
thermostat
37.5 ? C
heat-losing center
heat-promoting center
in the hypothalamus
36

• When blood temperature is too high
• heat-losing center stimulates
• dilation of dermal arterioles
• sweating

37

• When blood temperature drops too low
• heat-promoting center stimulates
• dermal vasoconstriction
• shivering thermogenesis.
• 3) later increase in metabolic rate by 20-30 as
  adaptation.

38
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
39
Hypothermia

• 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.

glucose
ATP
enzyme
40
Hypothermia
below 24oC (75oF) fatal.

• Which way helps a person survive longer in
  ice-cold sea water?
• Swim vigorously
• Rest and keep awake