ch 7 - energy metabolism

Metabolism

• The continuous processes that convert nutrients into energy, structure, and waste

• krebs cycle, anabolic energy, hormones

Anabolism

Using absorbed nutrients to build or synthesize more complex compounds

Catabolism

splitting complex substances into simpler substances

Role of the Liver in Metabolism

• Regulatory role controlling the kinds and quantities of nutrients in the bloodstream

• Detoxifies drugs

• Glycogen can be broken down into glucose and released into the circulating blood as needed

Role of the Kidneys in Metabolism

• Waste Removal from blood

• nutrient Control

• filtration & Reabsorption

Carbohydrate Metabolism

• The liver closely monitors blood glucose levels

• Monosaccharides are transported through the portal vein to the liver for glycogenesis

glycemic index (GI)

measures the effect of different carbohydrate foods on blood glucose levels

hyperglycemia

high blood glucose

hypoglycemia

low blood glucose

Protein Metabolism

• Amino acids are transported through the portal vein to the liver

• The balance between anabolism and catabolism is controlled by the liver and hormones

Anabolism

Utilizes an “amino acid metabolic pool” (70 g of amino acids) to maintain equilibrium

Catabolism

Occurs in the liver, muscle, and kidney, creating urea as a waste product

Lipid Metabolism

• regulates fat metabolism

• lipogenesis — Converts glucose to fat

• lipolysis — breaks down fat

• oxidation — hydrolyzing triglycerides to enter the Krebs cycle for energy production

Alcohol Metabolism

• Metabolized primarily by the liver

• When consumed in excessive amounts, alcohol is a toxin

• Alcohol has a marked effect on blood pressure and risk of hypertension

• 1 drink/day for men

• 2 drinks/day for men

Metabolic Interrelationships

• Excessive intake of any nutrient results in excess energy being stored as adipose tissue

• Fat is a good source of energy, but carbohydrate is the preferred fuel

• Catabolism of all classes of foodstuffs involves oxidation through the TCA cycle to produce energy

• Each nutrient has its specific function; all nutrients must be present simultaneously for optimal benefits

Metabolic Energy

• Physiologic energy values of the energy nutrients

• kilocalorie

kilocalorie

• the amount of heat required to increase the temperature of 1 kg of water 1°C

• 4 cal/g Carbohydrate

• 9 cal/g fat

• 4 cal/g protein

• 7 cal/g alcohol

MEASUREMENT OF POTENTIAL ENERGY

• The amount of energy, or calories, available in a food may be precisely

  calculated by placing a weighed amount in a calorimeter

• As the food is burned, an increase in water temperature indicates the heat given off, or potential (free) energy, of that food

ENERGY PRODUCTION: ATP

• Adenosine triphosphate (ATP) is the instant source of cellular energy

  for mechanical work, transport of nutrients and waste products, and

  synthesis of chemical compounds generated from the Krebs cycle

• Measured in ATP units, or “high-energy phosphate compounds.”

Basal Metabolic Rate (BMR)

• Energy required for involuntary physiologic functions to maintain life, including respiration, circulation, and maintenance of muscle tone

  and body temperature

• The amount of energy required when the body is in a postabsorptive state

• Measurement: BMR can be measured in a clinical setting using indirect calorimetry

Factors Affecting the BMR

• sleep

• age

• pregnancy and lactation

• surface area and size

• state of health

• body comp and gender

• endocrine glands

• temperature

• fasting and starvation

Basal Energy Expenditure

Calories necessary to maintain BMR plus additional calories needed for

thermic effect, voluntary activities, and increased need from catabolic

processes

Thermic Effect of Food

Increased energy expenditure resulting from the consumption of food,

or the number of calories needed for digestion

10 × ideal weight (lb)

= calories needed for BMR daily

BMR can also be estimated using several methods based on a patient’s gender, age, and body size.

physical activity

150-300 min / week

Estimated energy requirements

indicate the daily calorie intake needed to maintain energy balance in healthy individuals of specific age, gender, weight, height, and level of activity

BMI > 25 kg/m²

Weight gain resulting in a BMI above this threshold is associated with an increased risk of early mortality

Energy Balance

• maintained when caloric intake equals the energy needed for body processes and physical activity

• Many healthy patients are able to control energy intake to balance energy output with little effort

• Hunger is regulated by a complex network of factors

• Hunger and appetite greatly affect weight balance

PHYSIOLOGIC FACTORS Affecting Energy Balance

• Hypothalamus: especially important in controlling hunger

• Distention of the stomach results in inhibitory signals that suppress the

  feeding center, reducing desire to eat

• Fat in the duodenum

• Hormonal secretions (ghrelin, leptin, serotonin)

PSYCHOLOGICAL FACTORS Affecting Energy Balance

• Appetite is affected by the fact that eating is rewarding and makes us feel

  good

• Greater weight can mean an individual is responding to feelings and

  emotions rather than actual hunger

• Boredom and stress frequently affect the eating habits of obese individuals

Energy Expenditure & Inadequate Intake

• Obese women have a similar or higher metabolic rate than thinner women; increased physical activity is needed to balance energy intake

• A deficiency in energy intake may result in a depressed rate of growth in children and weight loss in adults; intentional weight loss may be helpful or harmful

• Inadequate intake causes a vicious downward spiral in which metabolic imbalances decrease hunger and may become life threatening without proper treatment