Water balance Lecture 15 Flashcards
What quantity does water make up of a male, female and baby
Male = 60% 42L Female = 50% (more fat) 30L Baby = 75%
How is fluid lost in the body and at what values?
Sweat/skin = 600mL Urine = 1300mL Respiration = 200mL Feces = 100mL
Total = 2200mL
How is fluid gained within the body?
Drink = 1200mL Food = 700mL Metabolic = 300 mL
Total = 2200mL
How are water volumes maintained within the body?
Blood/plasma osmolarity and volume are monitored by the hypothalamus and other centers… regulates blood pressure and omsolarity around 290mOsmol/L
Renal function = excretion
What stimulates loss of water by the kidney?
Low plasma osmolarity
What does an increase in plasma omsolality do?
Stimulates thirst and decreases urine output
Does absence of thirst mean osmolarity has been restored?
No, other mechanisms such as stomach distension can decrease thirst.
How does water play a role in temperature regulation?
Sweat is the primary mechanism against hyperthermia
How is heat lost from the body?
Convection
Conduction
Radiation (mostly-60%)
Evapouration
During exercise what heat loss mechanism is primary?
Evaporation accounts for 80% heat loss
How much heat absorption does sweat do?
1L of sweat can remove 2400kJ of heat
What does secretion of sweat represent?
A loss of water and Salt from all compartments of the body
Does dehydration impair performance?
Yes, as little as 2% body weight loss in water can impair performance
i.e 70kg male 2%= 1.4kg water loss
Is everyone affected by water loss in the same way?
No it affects some people more than others.
How does changing degrees of water loss affect performance?
As the water loss gets beyond 2% body mass, the decrease in performance (slope) greatly increases. i.e 5% body mass loss in water decreases optimal performance by 30%
What are some physiological affects of dehydration?
Reduced blood volume - Lower CO - Increased viscosity Decreased skin blood flow = Decreased sweating rate = Decreased heat dissipation - Increased Core temperature - Increased use of muscle glycogen as reduced flow to liver reduces its release
How is dehydration quantified?
Get the subject to void their bladder and then weight them pre exercise. Weight them post exercise after urinating and dry.
Clothes off at all times
Weight change = fluid loss, which can be computed into % Body Mass
What are three methods of quantifying dehydration?
Body mass change Urine Colour Urine Osmolarity (900mosmolL=Dehydrated) 100-300= adequately hydrated
What does fluid intake help with for atheletes?
Fluid intake can help thermoregulatory responses and offset the negative effects of dehydration
What fluid should an athlete drink during exercise?
Fluid intake should aim to prevent dehydration of a magnitude equivalent to 2% of body mass.
Why is it difficult to consume fluid thats 2% body weight before or during exercise?
Large volume of water can create gastric distress. i.e stomach can hold only 1L water but sweat loss may be 2-3L hr
Difficult to determine sweat rates to compensate
Sometimes not thirsty till 2% body weight has been lost
May not be convenient to drink
When athletes voluntarily drink during exercise on average how much of their fluid loss do they replace?
50%
What else apart from fluid is lost in sweat?
electrolytes, - although only in a small amount as sweat is hypotonic,.
Electrolyte loss is normally compensated for in the diet.
When else is added to sports drinks apart from water and why?
Electrolytes
- Increases palatibility
- Maintains thirst drive
- Increases rates of absorption
- Increases retention of fluid
