Hydration (fluid + electrolyte requirements) Flashcards
(42 cards)
What percentage of the adult body is water?
50 - 60 %
Lean body tissue is composed of what percentage of water?
~ 75 %
What percentage of fat mass is water?
~ 5-10 %
What are the very basic overview functions of water in the body?
Nutrient transport
Protection
Temperature regulation
Biochemical reactions
Medium for reactions
What is the distribution of fluids throughout a 70 kg male?
Intracellular
Extracellular
Interstitial fluid
Blood plasma
Total
Intracellular - 40% / 28L
Extracellular - 20% / 14L
Interstitial fluid - 15% / 10.5L
Blood plasma - 5% / 3.5L
Total - 60% / 42L
percentage of body mass
What are some examples of fluid loss for a sedentary individual?
Respiration (breathing out) (200ml)
Skin (Sweat or general perspiration) (600ml)
Faeces (when unwell this can be more) (100ml)
Urine (1300ml)
Total 2200ml
Definition of euhydration
Body is in a water balance; losing as much fluid from the body as you are gaining.
What are some examples of fluid gain for a sedentary individual?
Drink (1200ml)
Food (700ml)
Metabolic (300ml)
Total - 2200 ml
At any given running speed/exercise intensity what condition would cause the body to sweat more?
Hot and humid environment
Lower sweat rates would be seen in a cold and dry climate.
What is the difference between an active and a sedentary individuals fluid losses?
The active individual would increase the amount of fluid loss, due to exercise (E.g. losing 1000ml in sweat)
A negative fluid balance is the definition of ……..
Dehydrated/hypohydration
Hydration is typically well maintained throughout the day within 1% of body mass, how?
This is due to feelings of thirst and hunger.
E.g. during exercise, the body will increase its feelings of thirst and therefore you would seek water.
When is net body water balance often challenged?
During periods of high sweat rates
What is the primary way of measuring acute changes body fluids?
Measuring changes in body mass (simplest and most sensitive)
At what percentage of reduction of body mass is classified as a 90% chance that the body water deficit are sufficient to be classified as dehydration?
Any reduction that is greater than 2% body mass will be sufficient to assume an individual is dehydrated.
What is the best way to achieve a static measure of someone’s physiological index of hydration?
Measure their osmolality. This is a measure of the total dissolved particle concentration (in mOsm/kg).
This is a very tightly regulated variable (275-295 milliosmoles/kg of water).
Dynamic measures of hydration:
Body mass change (energy balance)
Plasma osmolality
Urine samples - urine density relative to water (water = 1) so therefore Euhydrated = 1.003 - 1.035 (U)
Why do we sweat?
During exercise our body produces heat.
For every L of O2 consumed 4 kcal of heat is produced and only about 1 kcal is used for mechanical work.
The heat is mostly passed to the core.
Hypothalamus senses increased body temp (thermoreceptors)
Responds by increasing blood flow to the skin and initiating a sweat response.
Definition of sweating (key principles)
Body’s principle means of preventing excess rises in body temperature during exercise (hyperthermia)
Normal temp = 36-38 C
Exercise temp = 38-40 C
Sweating itself does not cool the body it is the function of evaporative cooling, explain?
The evaporation of the sweat on the skin draws the heat away.
For 1 L of sweat evaporated, 573 kcal of heat is removed from the body.
Why is humidity an issue?
Humidity reduces the ability for sweat to readily evaporate from the skin therefore not achieving the expected level of cooling.
What component of blood is sweat drawn from?
Blood plasma
Sweating has what effect on blood?
Reduces the plasma volume in the blood and as a result reduces the blood volume.
What are the implications of having a lower plasma volume?
Blood becomes more viscous and resistant through the blood vessel.
This results in a greater demand from the heart and can cause increased cardiac strain.
