Fluid Balance

Water

• 40-70% of total body mass

• 72% muscle weight

• 20-50% body fat/adipose tissue

• 55% of individuals body mass

  • striated muscle, skeleton, adipose tissue

Water - Compartments in Body

• Intracellular fluid (ICF)

  • fluid inside cells

  • 6 types*

    • 1. lymph (colorless fluid circulates through the lymphatic system)

      • 2. saliva (clear liquid secreted into the mouth fromt he salivary glands)

      • 3. eye fluid (two fluids: vitreous humor [colorless gelantinous mass btw the lens and retina], aqueous humor [clear fluid btw lens and cornea]

      • 4. fluids secreted by glands and the digestive tract

      • 5. CSF

      • 6. fluids excreted from skin (water & sweat) and kidneys (filtered fluids & urine)

  • about 12 L

  • 30% of body mass

• Extracellular fluids (ECF)

  • fluid surrounding cells

  • about 15 L

  • 23% of body mass

  • blood plasma (20%)

• Total fluid volume (TFV) = ICF + ECF

Water - Functions

1. transport & receive medium

2. facilitates gas diffusion

3. transports waste products in urine & feces

4. balances body’s chemicals

5. lubricates joints

6. provides structure & form through the turgor it imparts to body tissues

7. shock absorber for brain, spinal cord, fetus

8. absorbs internally generated heat

9. regulates body temp

Water Balance

• Water Intake:

  • liquids

  • foods

  • metabolic processes

    • food molecules used for ATP form CO2 + H2O

    • 100g carbs → 55g H2O

    • 100g lipids → 107g H2O

    • 100g proteins → 100g H2O

• Normal conditions:

  • men (3.7 L or 15 cups /day)

  • women (2.7 L or 11 cups/day)\

  • sedentary (2.5 L)

• Active, warm environment (5-10 L/day)

Water Content in Food

• watermelon = 90-99%

• apples = 80-89%

• avocados = 70-79%

• ice cream = 60-69%

• hotdogs = 50-59%

Water Balance Cont.

• Sweating increase water loss during PA

• Depends on:

  • intensity

  • environmental temperature

  • relative humidity

• Evaporation of sweat:

  • cooling mechanism

  • defense against overheating

• Sweat losses = 2-3% of body mass

  • plasma volume declines

  • strains circulatory functions

  • diminished thermo regulatory control

  • reduced exercise capacity

Temperature & Humidity

• sweating is how the body cools itself down

• water droplets come to the skin and then they evaporate

• when humidity is high, there is a blanket of water droplets along your skin that stop the evaporation process

Challenge of Environmental Stress

• most individuals acclimatize to all earth’s environments after 8-14 days

• loss of acclimatization occurs in 14-28 days

• 6 factors impact individual differences in accommodation and acclimatization

  • genetic characteristics

  • available resources

  • age

  • nature & duration of previous exposures

  • number of similar prior experiences

  • emotional & psychological response (worry, fear, panic, self-assurance) to environmental stress

• utilize cooling towels, hydration station to stay cool

Thermal Balance

• normal body temp 98.6 degrees F (varies depending on the person)

  • three integrating mechanisms

  • 1. heat transfer to periphery

  • 2. evaporative cooling

  • 3. varying heat production rate

• Heat Loss:

  • Radiation, Conduction, Convection, Evaporation

• Heat Gain:

  • BMR, muscular activity, hormones, thermic effect of food, postural changes, environment

Mechanisms of Thermoregulation

• Cold:

  • stimulated by (decreases heat loss), mechanism (vasoconstriction)

  • stimulated by (increases heat production), mechanism (shivering, involuntary muscle movement)

• Heat:

  • stimulated by (increases heat loss), mechanism (vasodilation)

  • stimulated by (decreases heat production), mechanism (decreased muscle tone, slow down muscle movements, sweating)

Hypothalamic Regulation of Core Temp

• Hypothalamus:

  • helps control pituitary gland & regulates heart rate, hunger, mood, & body temp

  • CNS coordinating center for temp regulation

  • thermostat of the body

  • signals:

    • temp of the blood flow to the brain

    • receiving signals from afferent nerves in the skin that feel the temperature rising, this causes the hypothalamus to react to change in body temp

Thermoregulation During Heat Stress

1. Radiation:

• electromagnetic waves that increase heat (from the sun or our bodies)

2. Conduction:

• transfers heat from the environment to you (sitting on metal bleachers or leather car seats after they have been in the hot sun)

3. Convection:

• air or water that hovers over the skin (insulation)

4. Evaporation:

• water evaporating from skin surface

Heat Loss at High Ambient Temps

• increased ambient temp reduces heat loss by -