1. Fluid and Electrolyte Balance
Human Biochemistry
Fluid and Electrolyte Balance

2. Fluid and Electrolyte Balance
Body Fluids
Water makes up between 50-60% of your total body weight
Water is found in 3 main locations known as fluid compartments.
Fluid Compartments – the areas in the body where fluid is located

3. Fluid and electrolyte balance
Intracellular Fluid – fluid found inside cells Makes up  33% of total body weight
There are Two types of Extracellular Fluid: Interstitial Fluid (IF) – fluid found in the microscopic spaces between cells (makes up  10% of total body weight) Plasma – fluid found in blood vessels (makes up  4% of total body weight)
Intracellular Fluid (ICF)
Extracellular Fluid (ECF)

4. Fluid and electrolyte balance
Fluid levels vary by mass and type of tissue: fat has little to no water in it so people with extra body fat have a lower percentage of water/pound (total body weight=tbw)
NEWBORN INFANTS: 75-80% tbw
ADULT MALES: % tbw
ADULT FEMALES: % tbw

6. Fluid and electrolyte balance
Mechanisms that Maintain Fluid Balance
The body maintains fluid balance by adjusting the fluid output to match fluid intake.
Fluid intake occurs by taking in liquids or from the foods we eat or from tissue catabolism
Fluid output occurs by excreting water from our lungs, *kidneys, large intestine, and sweat (skin)
When fluid intake and output are equal then the total amount of water in the body does not change.

7. Fluid and electrolyte balance
The amount of fluid output is determined by the kidneys because the body maintains fluid balance by changing the amount of urine excreted to match fluid intake.
ADH controls urine output (AntiDiuretic Hormone)by stimulating the kidneys to reabsorb water so that it remains in the body.
ANH controls urine output (AntiNaturetic Hormone) by stimulating the kidneys to filter out more sodium (and thus more water).
Aldosterone causes the kidneys to reabsorb sodium salts keeping water in the body.

8. Fluid and electrolyte balance
The regulation of fluid intake isn’t quite known.
It is believed that when fluid loss exceeds fluid intake, saliva production DECREASES (making you “thirsty”) so you drink water and thereby reduce the need for fluids
As long as there is “life” in your body you will always lose water (through breathing) so you will always need to have fluid intake

9. Fluid and electrolyte balance
The Importance of Electrolytes
There are two types of compounds that are in water: nonelectrolytes and electrolytes
Nonelectrolytes – compounds that do not dissociate in water
Electrolytes – substances that ionize in solutions rendering the solutions capable of conducting an electric current
Important positively charged electrolytes are: Na+, K+, Ca2+, and Mg2+
Important negatively charged electrolytes are: Cl-, HCO3-, proteins, HPO4-, and many others

10. Fluid and electrolyte balance
Some important functions of electrolytes include:
nerve conduction
Muscle contraction
Influence the movement of water between fluid compartments
Due to osmosis: “Where sodium goes, water will soon follow” because: the sodium will lower the concentration of water in the fluid compartment.
Water will then diffuse from an area of high concentration (where the sodium isn’t) to low concentration (where the sodium is)

11. Fluid and electrolyte balance
Na+
H2O
H2O
H2O K+
Na+ K+
H2O
H2O
H2O
H2O K+
H2O
Na+
H2O
Na+
H2O
H2O K+
Na+
H2O
H2O K+
Na+
H2O
H2O
H2O K+
H2O
H2O K+
H2O
H2O
H2O K+
Na+
Na+
H2O
H2O
H2O K+
H2O
H2O
H2O
Na+
H2O
H2O

12. Fluid and electrolyte balance
The reabsorption and secretion of sodium into the urine determines how much water is then secreted into the urine (as with water, Na+ secretion is usually equal to Na+ intake)
Capillary Blood Pressure and Blood Proteins
Blood releases water out of the capillaries due to capillary blood pressure.
Capillary Blood Pressure – the blood pressure found in the capillary vessels (it is a “water-pushing” force)

13. Fluid and electrolyte balance
Plasma volume usually maintains a stable volume with short-lived, infrequent fluctuations.
Plasma proteins work to “pull” water into the blood vessels from interstitial fluid
When there is a dietary insufficiency (resulting in low plasma proteins) there will be a decrease in plasma volume.
 plasma proteins means water will diffuse into the interstitial fluid out of the blood vessels

14. Fluid and electrolyte balance
H2O K+ K+
H2O K+
H2O
H2O
H2O K+
H2O
H2O
Plasma Proteins
H2O K+
H2O
H2O
H2O
H2O K+
H2O
Plasma Proteins
Plasma Proteins K+
H2O K+
H2O
H2O
H2O
H2O
H2O
H2O
Plasma Proteins
H2O K+
H2O
H2O
H2O
Plasma Proteins K+
H2O K+
H2O
H2O
H2O
H2O
H2O K+
H2O K+
Capillary
Interstitial Fluid

15. Fluid and electrolyte balance
Fluid Imbalances
Edema is the term used to describe the condition commonly referred to as “swelling”.
Edema – accumulation of fluid in a tissue, as in inflammation; swelling

16. Fluid and electrolyte balance
EDEMA CAN BE CAUSED BY:
Retention of Electrolytes: kidney disease/failure or an in a secretion of aldosterone
Increase in capillary blood pressure: can be caused by venous congestion (slow blood flow through narrowed veins) due to heart failure
Decrease in the concentration of plasma proteins: plasma proteins may leak into interstitial fluid due to infections, injuries, or severe burns

17. Fluid and electrolyte balance
Dehydration is the most common type of fluid imbalance.
Dehydration – clinical term that refers to an abnormal loss of fluid from the body’s internal environment
Dehydration can be caused by:
Too small fluid intake
Too much fluid output (strenuous activity)
At the onset of dehydration:
IF volume decreases first but then plasma volume can decrease which will cause circulation problems

18. Fluid and Electrolyte Balance
Overhydration isn’t very common.
Overhydration – too large fluid input that can put a burden on the heart
Usually over hydration is caused by giving intravenous fluids too fast.
**MYTH: overhydration can dilute urine so that a drug test can be passed