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Metabolism. Appetite. Hunger and satiety are regulated by a complex interaction of multiple brain centers , hormones , and sensory and motor pathways. Hunger center a region in the lateral hypothalamus that triggers the desire for food. stimulated. destroyed. Satiety center

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slide2

Appetite

Hunger and satiety are regulated by a complex interaction of multiple brain centers, hormones, and sensory and motor pathways.

slide3

Hunger center

a region in the lateral hypothalamus that triggers the desire for food

stimulated

destroyed

slide4

Satiety center

a region in the ventromedial hypothalamus that suppresses the desire for food

stimulated

destroyed

slide5

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

slide6

Gastric peristalsis stimulates hunger.

Mild hunger contractions begin soon after the stomach is emptied and increase in intensity over a period of hours.

slide7

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 299:846-849 2003)

slide8

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)

slide9

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
slide10

Metabolic Rate

is the amount of energy released in the body per unit of time, expressed as kcal/hr or kcal/day

slide11

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

slide12

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

slide13

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

Carbohydrates

unchanged

reduced by 30%

slide14

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.

slide15

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.
slide16

Maintenance of blood glucose

discussed in two states.

1) Absorptive State

lasts about 4 hours after a meal.

2) Postabsorptive State

slide17

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.
slide18

glycogen

fat

Absorptive State

Excessive glucose is stored as glycogen in the liver and muscles or as body fat.

slide19

Absorptive State

Fats

are taken by the tissues, especially adipose and muscular tissue.

Amino acids

become available for protein synthesis.

Amino

acids

slide20

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

slide21

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.
slide22

Glucose is drawn from the body\'s glycogen reserves in liver and muscles, or synthesized from fats (gluconeogenesis).

glycogen

fats

slide23

Postabsorptive State

After 4 to 5 days of fasting, the brain begins to use ketone bodies as supplemental fuel.

- from fat

- acidosis

slide24

glycogen

fats

After glycogen and fat reserves are depleted

- The body begins to burn proteins.

- The first to go is skeletal muscle proteins.

proteins

slide25

glycogen

fats

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.

slide26

glycogen

fats

Glucagon promotes:

1) glycogenolysis glycogen  glucose

2) gluconeogenesis AA/FFA  glucose

3) lipolysis triglyceride  FFA

slide29

Body Temperature

  • Body temperature fluctuates about 1oC in a 24-hour cycle.
  • lowest in the early morning
  • highest in the late afternoon
slide30

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)
slide31

heat

heat

  • Heat Production
  • Body heat is generated from:
  • nutrient oxidation (ATP production)
  • energy in glucoseATP
  • 2) ATP use
  • energy in ATPmechanical energy
slide32

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.

slide33

Heat Loss

The body loses heat through:

  • Conduction

Evaporation

Radiation

slide34

Thermoregulation

  • Hypothalamic thermostat
    • monitors the blood temperature
    • receives signals from peripheral thermoreceptors in the skin.
slide35

Thermoregulation

thermostat

  • 37.5  C

heat-losing

center

heat-promoting

center

in the hypothalamus

slide36

When blood temperature is too high

  • heat-losing center stimulates
    • dilation of dermal arterioles
    • sweating
slide37

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.
slide38

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
slide39

heat

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.

glucoseATP

enzyme

slide40

Hypothermia

below 24oC (75oF) = fatal.

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