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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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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

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

stimulated

destroyed


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


Gastric peristalsis stimulates hunger.

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


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)


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)


  • 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


Metabolic Rate

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


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


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


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%


Role of blood glucose in providing energy and reduces morbidity of aging-related diseases.

- 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.



Maintenance of blood glucose providing energy

discussed in two states.

1) Absorptive State

lasts about 4 hours after a meal.

2) Postabsorptive State


  • Absorptive State providing energy

  • 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.


glycogen providing energy

fat

Absorptive State

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


Absorptive State providing energy

Fats

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

Amino acids

become available for protein synthesis.

Amino

acids


  • Regulation of the providing energyAbsorptive State

    • regulated largely by insulin, which stimulates nearly all cells to absorb glucose.

insulin receptors

blood

insulin

cell

glycogen

glucose

muscle

cell


  • Postabsorptive State providing energy (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.


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

glycogen

fats


Postabsorptive State and muscles, or synthesized from fats (gluconeogenesis).

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

- from fat

- acidosis


glycogen and muscles, or synthesized from fats (gluconeogenesis).

fats

After glycogen and fat reserves are depleted

- The body begins to burn proteins.

- The first to go is skeletal muscle proteins.

proteins


glycogen and muscles, or synthesized from fats (gluconeogenesis).

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.


glycogen and muscles, or synthesized from fats (gluconeogenesis).

fats

Glucagon promotes:

1) glycogenolysis glycogen  glucose

2) gluconeogenesis AA/FFA  glucose

3) lipolysis triglyceride  FFA


Growth hormone and muscles, or synthesized from fats (gluconeogenesis). also raises blood glucose concentrations.


Body Heat and Thermoregulation and muscles, or synthesized from fats (gluconeogenesis).


  • Body Temperature and muscles, or synthesized from fats (gluconeogenesis).

  • Body temperature fluctuates about 1oC in a 24-hour cycle.

  • lowest in the early morning

  • highest in the late afternoon


  • Core temperature and muscles, or synthesized from fats (gluconeogenesis).

    • 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)


heat and muscles, or synthesized from fats (gluconeogenesis).

heat

  • Heat Production

  • Body heat is generated from:

  • nutrient oxidation (ATP production)

  • energy in glucoseATP

  • 2) ATP use

  • energy in ATPmechanical energy


Heat Production and muscles, or synthesized from fats (gluconeogenesis).

- 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 Loss and muscles, or synthesized from fats (gluconeogenesis).

The body loses heat through:

  • Conduction

Evaporation

Radiation


  • Thermoregulation and muscles, or synthesized from fats (gluconeogenesis).

  • Hypothalamic thermostat

    • monitors the blood temperature

    • receives signals from peripheral thermoreceptors in the skin.


Thermoregulation and muscles, or synthesized from fats (gluconeogenesis).

thermostat

  • 37.5  C

heat-losing

center

heat-promoting

center

in the hypothalamus



  • When blood temperature drops too low and muscles, or synthesized from fats (gluconeogenesis).

  • heat-promoting center stimulates

    • dermal vasoconstriction

    • shivering thermogenesis.

    • 3) later increase in metabolic rate by 20-30% as adaptation.


Disturbances of Thermoregulation and muscles, or synthesized from fats (gluconeogenesis).

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


heat and muscles, or synthesized from fats (gluconeogenesis).

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


Hypothermia and muscles, or synthesized from fats (gluconeogenesis).

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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