Week 9 Flashcards
How much of the adult body is water and how much approximately water wise is lean mass and fat mass?
50-70% of adult body is water
Around 73% of lean body mass is water and around 5-10% of fat mass = water
Water function?
Helps regulate temperature, useful for nutrient transport, helps with biochemical reactions, medium for reactions and provides protection
Sources of water losses and production- look at table on slides for values
Resp losses, urinary losses, fecal losses, insensible losses, metabolic production.
What can the extremes of water loss be upto?
Can be upto 6.5 litres of water loss a day.
What are sweat rates like in hot and humid conditions?
Sweat rates are extremely high and sweat rates of over 1 litre per hour are not uncommon.
Why do we sweat during exercise?
We produce heat during exercise.
When we exercise about 4kcal of heat are produced and only 1 is used for mechanical work.
Most of the heat goes to the bodies core- hypothalamus detects increased temperature and causes increased blood flow to the skin and causes a sweat response.
Sweating helps stop excessive rises in temperature (hyperthermia)
What is normal body temp range and what is exercising body temperature range?
Normal body temperature is between 36 and 38 degrees and exercising body temp range = 38-40.
1 litre of sweat evaporated removes 573 kcal of heat from the body.
What is net water balance?
It is the difference between fluid intake / production and fluid loss.
Typically it is well maintained on a day to day basis.- thirst and hunger drives. Net body water balance can be challenged in high sweat periods
What is ad libitum drinking?
Ad libitum drinking is drinking to thirst e.g. drinking when you want.
Ad libitum drinking during exercise can cause/ lead to a body water deficit- can lead to greater than a 2% loss in body mass
Dehydration- what is it?
Dehydration often also called hypohydration. It = a body water deficit larger than normal daily fluctuation.
Body mass changes gives the most sensitive and simplest measure to determine acute changes in body water.
Acute changes means greater than 2% body mass mass decrease= 90% chance that body water deficits = big enough to be known as dehydration.
When does hypohydration happens?
Hypohydration happens is lots of water loss happens through sweating.
What is sweat loss?
Water loss from the water component of blood plasma. Sweat = hypotonic compared to plasma so plasma osmolality increases.
With blood if yu spin in centrifuge heaviest parts go to the bottom e.g. rbc’s and plasma where the waters from goes to the top.
Differences between sweat and plasma
Sweat and plasma are not the same. Sweat is not the same as plasma as does not contain many of the parts plasma does. Sweat has lower concentration of electrolytes such as sodium than plasma does.
What’s plasma osmolality?
When plasma volume drops and relative amount of electrolytes is less it has a concentrating effect called plasma osmolality. Increased plasma osmolality is a common way to know dehydration is occuring.
Effect of sweat loss on cardiovascular strain
Sweat loss decreases plasma volume and increases cardiovascular strain. Another issue is that redistribution of blood flow to the skin to help with thermoregulation can also have the effect of increasing cardiovascular strain.