Fluid balance

movement between areas of fluid

Water moves via osmosis

O2 and CO2 moving across cell membrane

Active transport of ions, other substances that cannot move freely across cell membranes

Large molecules remain inside fluid of blood

Osmotic pressure

Tendency of a solution to take in water, greater difference in osmotic concentrations, higher osmotic pressure

Fluid gain and loss

Fluid gain - food, drink, metabolic water

Fluid loss - lungs, skin, sweat, kidneys, urine, alimentary canal

Kidneys water reabsorption

PCT and LoH water reabsorption - osmosis

DCT and CD water reabsorption - active reabsorption controlled by ADH

High ADH

high permeability of cells in DCT and CD to water, leads to high water reabsorption into blood and more concentrated urine

Low ADH

low permeability of cells in DCT and CD to water, leads to less water reabsorption into blood and less concentrated urine

Aldosterone

Secreted by adrenal cortex, acts on DCT and CD to increase sodium ions reabsorbed into bloodstream and amount of potassium secreted into urine. When salt is reabsorbed -> increases osmotic gradient, causes water to be reabsorbed as well

Dehydration

Symptoms appear when 2% of normal body water lost

Causes: sweating without replacement of fluids, vomiting, diarrhoea

Symptoms: severe thirst, low blood pressure, dizziness, headache

Can lead to delirium, unconsciousness and death

Water intoxication

Excessive water intake dilutes body fluids, causes excess water to move into cells and swell

Cause: significant loss of water and salts through sweating, replaced by pure water

Symptoms: light-headedness, headache, vomiting and collapse

Treatment: replace lost fluid from sweat with an electrolyte drink, contains salts + important ions