Altering electrolyte concentrations inside or outside cells influences water movement.
Large fluctuations in body water can lead to health concerns and poor physical performance.
Functions of Water in the Body
Structural integrity of cells.
Delivery and waste removal medium:
Blood and plasma distribute nutrients, hormones, immune cells, and oxygen.
Blood carries away waste substances like carbon dioxide, lactic acid, and ammonia.
Water helps the liver and kidneys function properly.
Low water levels cause kidneys to retain water.
Reactive medium:
Water is a reactant or product in many chemical reactions.
One end product of breaking down nutrients is water (metabolic water).
Solvent:
Water dissolves solutes like sodium, potassium, and chloride.
It is essential for molecules like glucose, vitamins, minerals, proteins, and enzymes.
Temperature regulation:
Water conducts heat 26 times faster than air.
Moves heat from the body's core to the periphery/skin.
Sweat (produced by eccrine sweat glands) cools the body upon evaporation.
Dehydration impairs sweat production and cooling.
Maintenance of blood volume:
Cushions brain, heart, lungs, and digestive system.
Maintains electrolyte balance.
Adequate blood volume affects blood pressure and cardiovascular function.
Moistens tissues in the mouth, nose, and eyes.
Lubricates joints:
Cartilage holds water to cushion movement.
Dehydration may cause achy joints.
Survival:
You can live for weeks without food but only days without water.
Thirst Mechanism
Water makes up about 70% of body weight.
The hypothalamus is the brain's primary thirst center.
It regulates body temperature, sleep, and appetite.
Special sensors monitor blood's sodium concentration.
Receives input from blood vessels monitoring blood volume and pressure.
Hypothalamus sends a "drink" message when:
Blood volume or pressure is too low (bleeding, excessive sweat, diarrhea).
Blood sodium concentration is too high (salty snacks, certain diseases).
Vasopressin (antidiuretic hormone):
Synthesized by the hypothalamus when the body is low on water.
Causes kidneys to reabsorb water from urine, reducing urine flow.
Conserves water in the body until more fluids are consumed.
A classic sign of dehydration is decreased urine volume or frequency.
Sources of Water
Approximately 80% of daily water needs come from fluids.
Broth-based soups, milk, and juices.
Less than 20% comes from water in fruits, vegetables, and other foods.
Vegetables with high water content: lettuce, cucumber, tomatoes, sugars, snap peas, and celery.
Fruits with high water content: oranges, pineapples, strawberries.
Whole fruits/vegetables are preferable to juices (more fiber).
Metabolic water:
Formed by normal cellular metabolism.
Carbohydrates, fats, and proteins are broken down through metabolic processes to form energy and also form water.
Bottled vs. tap water:
Water is water no matter where it comes from.
Tap water contains minerals from the ground.
Bottled water is usually filtered, with minerals and/or flavoring added.
Water Loss
Urination.
Defecation.
Sweating.
Insensible perspiration.
At rest, 60% of water loss is through urine formation.
During exercise in warm environments, sweat can account for up to 90% of water loss.
Insensible perspiration:
Water seeps through the skin and evaporates slowly.
Includes water loss during breathing.
The greater the volume of air breathed, the greater the water loss. This can be significant during exercise, at high altitudes, and in cold climates (cold air is very dry).
Accounts for about 15% of daily water loss.
Dehydration
Being slightly hyperhydrated is preferable to being slightly dehydrated for sports performance.
Consequences of dehydration:
Loss of blood volume.
Decreased blood flow to muscles (less oxygen delivery).
Increased reliance on anaerobic energy production.
Quicker lactic acid buildup.
Higher rating of perceived exertion.
Faster fatigue.
Extra heat and cardiovascular stress during exercise.
Cardiac drift:
Progressive increase in heart rate without increased exercise intensity.
Caused by decreasing blood volume, requiring the heart to pump faster.
Sweating mechanism and dehydration:
Water moves from high to low concentration.
Eccrine sweat glands pool intracellular water to form sweat.
Sweating decreases intracellular water content.
Water moves from interstitial space to intracellular space.
Water moves from blood plasma to interstitial space.
This process requires replenishment of blood plasma water via fluid consumption.
If fluids are not consumed:
Blood plasma water content decreases.
Sweating diminishes or stops.
The body is at risk for overheating, which can lead to heat cramps, heat exhaustion, and heat stroke.
Dehydration affecting blood volume and Heart Rate:
When there's a decrease in blood volume, the heart has to compensate by this by increasing its beats per minute.
The heart has a certain number of beats per minute that it can maximally contract at, this is called the maximum heart rate.
The heart can only work so hard before it can't contract any faster.
Overhydration (Hyponatremia)
Large influx of water is called as hyponatremia or commonly referred to as water intoxication, which occurs from hyperhydration.
Hyponatremia is a condition in which the fluids of the body become very low in sodium content because you have a lot or you have a huge influx of water.
It is possible to overhydrate the body.
Consume water with sodium to prevent hyponatremia, since hyponatremia can be a very serious condition that can lead to death.
Fluid Consumption Recommendations
The repeated rule is that you should drink at least eight glasses of water per day, however, many factors influence how much fluid you really need.
Eight cups of water per day isn't a bad place to start, but you will need more fluids if you work outdoors in the heat, if you're exercising frequently, if you are pregnant or nursing a baby, or if you're recovering from an illness.
In addition to the eight cups of water a day, which is just a guideline or recommendation, you could also take a look at your urine to look for color, volume, and frequency.
Research is starting to show now that drinking ahead of your thirst thirst, which would be this eight cups a day roll, may not be necessary that individuals can actually stay hydrated by at living on drinking, which means just drinking whenever you're thirsty.
Whenever you feel thirsty, if you drink, research is starting to show that this is also a proper way to stay hydrated and that you don't have to drink a set number of glasses per day as long as you are drinking when you're thirsty, which is called at libidom drinking.
Monitoring Hydration Status
Methods include monitoring body weight and urine color, specific gravity, and volume.
Daily weight fluctuations are primarily due to changes in water status.
Urine analysis:
Color:
Dark, concentrated urine with a strong smell indicates dehydration.
Color and smell change depending on the number of solutes.
Dark urine with a strong smell indicates that more solutes, which are particles, were excreted in the urine than water because kidneys are prohibiting the excretion of water due to low bodily water content.
Specific gravity:
Measures the concentration of solutes in urine.
Adults generally have a specific gravity in the range of 1 to 1.03.
Increase in specific gravity is associated with dehydration.
Volume:
Low urine volume is associated with dehydration.
In a dehydrated state, the kidneys do everything they can to reabsorb as much water as possible back into circulation in order to maintain blood pressure.