At least 70 per cent of the body is composed of water. The body’s cells rely on having the correct amount of water in order to work efficiently. Water provides the main transport system of the body and is the basic component of extracellular fluid, lymph, blood and urine, the main ‘transporters’. Body cells become selectively permeable during the movement of dissolved substances (solutes) across the cell membrane. This ensures that, in health, the concentration of water in the cell is maintained at a constant level enabling the cells to work efficiently. In this way the whole body is maintained ‘in balance’ and the person is well (homeostasis).
Water forms three distinct compartments within the body:
1 intracellular (cellular) content (30 litres)
2 extracellular fluid content (12 litres)
3 vascular content (3 litres)
All of these compartments need a stable water content to work efficiently. If one of the compartments becomes low in water content, the body is dehydrated. In addition, the compartments become dehydrated in a specific order. The vascular system is always first, followed by the extracellular compartment and, lastly, the cellular compartment is affected.
Water is not only a transport system – it is also an excretory pathway. Water is always lost from the body, the majority as urine. Visible sweat from the skin, along with ‘insensible’ sweat (sweat taking place without us being aware of it), as well as the water vapour we breathe out accounts for approximately 2.5–3 litres of water loss daily in adults, which needs to be replaced (see Table 5.3). Note that these losses are increased after exercise, so extra water needs to be consumed.
|
Table
5.3 Bodily intake and output of water
(adult)
|
|||
|
Intake
|
ml
|
Output
|
ml
|
|
Water intake as fluid
|
1000
|
From lungs as water in
expired air
|
500
|
|
Water intake as solid food
|
1200
|
From kidneys in urine
|
1500
|
|
Water produced in body
cells as a by-product of
metabolism
|
400
|
From skin in ‘insensible’
perspiration
From gut in faeces
|
450
150
|
|
TOTAL
|
2600
|
2600
| |
0 comments:
Post a Comment