Physiological balance of water in the body

The balance between water in and out

Table: Amount of water in and out in ml/day.

Regulate the amount of water entering

The amount of water entering from the metabolic source is not regulated because it depends on the ATP demand in the cell. So, the main way to regulate the body's water intake is to change the amount of water you drink. Thirst is a powerful conditioning factor. When dehydration occurs, thirst occurs because the thirst centre in the hypothalamus is stimulated. Dehydration causes thirst in at least three ways: (1) decreased salivation, (2) increased blood osmolality, and (3) decreased blood volume.

Dehydration usually occurs shortly before feeling thirsty. Children, the elderly, and people with dementia may not be aware of the sensation of thirst.

Regulate water output

Normally there are three hormones that regulate water output:

ADH (antidiuretic hormone): is released when there is an increase in blood osmolality or a decrease in blood volume.

Aldosterone: released in the presence of an increase in angiotensin II.

Atrial natriuretic peptide (ANP): released when increased blood volume causes right atrium (due to more blood to return to the heart).

Both ADH and aldosterone decreased urine output, while ANP is a diuretic.

In some cases, other factors can affect translation.

When dehydration is severe, urination is less. Conversely, when there is too much water, the number of urine increases.

Hyperventilation increases fluid loss through the evaporation of water from the lungs.

Vomiting and diarrhoea lead to loss of fluid from the gastrointestinal tract.

Fever, excessive evaporation of sweat, and extensive burns will cause excessive loss of water through the skin.