Fluids and Electrolytes

Fluids and Electrolytes

David Andersson

📚 GENRE: Health & Wellness

📃 PAGES: 158

✅ COMPLETED: August 10, 2025

🧐 RATING: ⭐⭐⭐

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Short Summary

In Fluids and Electrolytes, David Andersson and his team at Medical Creations take readers through a brief tour of the various electrolytes in our body and how they serve us.

Key Takeaways

1️⃣ Fluid Homeostasis Matters

Homeostasis, or balance, is one of your body’s top priorities and something that it’s constantly working to achieve in multiple areas. When it comes to fluids and electrolytes, imbalances can lead to significant problems. Looking at fluid specifically, about 50-60% of your body is made up of water, and there are two places where it is primarily found:

  • Inside of Cells — Most of the water in the body is stored inside of your cells. Here, electrolytes Potassium and Phosphate are found in pretty large quantities. Electrolytes Sodium, Chloride, and Calcium are found in much smaller amounts.
  • Outside of Cells — Much of the fluid outside of your cells is found in the plasma in your blood. Here, large amounts of electrolytes Sodium, Chloride, and Bicarbonate are present. 

The amount of fluid that leaves your body throughout a typical day is about 2,300 milliliters, which is about 0.6 gallons. These fluids must be replaced to maintain fluid balance in the body. If you’re not drinking enough water to replace the output, the brain can detect it and activate a few mechanisms to correct the issue:

  • Thirst — The thirst center in the Hypothalamus is triggered, prompting you to drink water. In other words, you become thirsty. 
  • Kidneys — The Hypothalamus tells the Pituitary Gland to release a hormone called Anti-Diuretic Hormone (ADH) that commands your Kidneys to retain more water. This is your body’s attempt to keep conserve water. 

For most people, severe fluid imbalance is difficult to achieve. Two of the most common volume-based problems are having too much fluid (Hypervolemia) or too little fluid (Hypovolemia).

  • Hypervolemia — It’s very hard to consume too much water. The more likely cause of having too much fluid in the body is some kind of condition, like kidney failure. When the kidneys fail, urine does not form and fluid builds up — leading to pretty significant swelling in the body. Patients with too much fluid will often be given a Diuretic, which are drugs that help your kidneys produce and release more urine. Fun fact, caffeine is a mild Diuretic — it makes you pee more!
  • Hypovolemia — Not having enough fluid in the body is more common and usually happens when certain diseases or conditions cause rapid fluid loss through significant bleeding, diarrhea, vomiting, or high fever. These are situations where fluid loss can happen fast. And when fluid is lost, so are key electrolytes — particularly Sodium since it exists in high quantities in blood plasma. When Sodium levels fall, seizures can happen. Fluid deficit can also cause Hypovolemic Shock, which is the body’s shock response to sustain life.

Another way a fluid deficit can occur is through Dehydration, usually from simply not drinking enough water. In this case, Sodium levels in the blood actually rise because water is lost faster than Sodium. Low Sodium levels can happen with Hypovolemia or when you drink too much plain water, which dilutes the Sodium in the body. Low Sodium levels can lead to seizures.

The point here is that fluid balance in the body is very important. When you’ve got too much or too little fluid, issues can arise. Your body is constantly working to achieve the right balance. 

2️⃣ pH Balance Is Crucial, Too

It’s true that the volume of fluids in the body must be in perfect balance, but its composition and properties — such as its pH level — must also be maintained in harmony as well. 

Imagine you have a lemon and a bar of soap. The lemon tastes sour — that’s because it’s acidic. The soap tastes bitter — that’s because it’s basic (or alkaline). pH is just a number scientists use to measure how acidic or basic something is. The pH scale goes from 0 to 14, and pH 7 is right in the middle since that’s neutral, like pure water. Numbers lower than 7 are acids (more sour), while numbers higher than 7 are bases (more soapy or bitter).

In terms of your body, the normal pH of blood is 7.35-7.45. If pH moves beyond these limits, even just a little, acid-base disorders can result. The two most common are:

  • Acidosis — This occurs when pH falls below 7.35. It means your blood is too acidic and can lead to slowness in your brain and muscles. You feel sleepy and confused. You could also experience shortness of breath as your lungs try to breathe faster and exhale acid as CO2 to lower the acidity of your blood.
  • Alkalosis — This occurs when pH rises above 7.45. It means your blood is too basic (alkaline). This can lead to overstimulated nerves and muscles. Tingling and numbness can occur, as well as muscle twitches or cramps. 

At the center of both Acidosis and Alkalosis is an Electrotype and chemical called Bicarbonate. Think of your blood as a swimming pool. If the water gets too acidic, it means it has too many Hydrogen ions. Bicarbonate “soaks up” the Hydrogen ions to bring your pH back to normal. On the other hand, if the water gets too basic, it means there are not enough Hydrogen ions. In this case, Bicarbonate can turn itself into carbonic acid, which adds Hydrogen ions to the pool to balance things out. This Bicarbonate Buffer System, keeps your pH in the safe zone of 7.35–7.45.

Why is all of this important? Many chemical reactions in your body (like how your cells use oxygen) only work at the right pH levels. Even small shifts outside 7.35–7.45 can mess up how your heart beats, how your brain works, and how your muscles move. If pH goes too far — like below 7.0 or above 7.8 — it can be life-threatening.

3️⃣ What Are Electrolytes?

There’s been a lot of buzz around Electrolytes in recent years. But what are they? Electrolytes are minerals that carry an electric charge when they are dissolved in water (like in your blood, urine, and fluids inside and around your cells). They’re very important because they help us keep the right fluid balance in our body, send electrical signals for muscle contractions (including the heart), support nerve function, and maintain the right pH level in your blood.

The main electrolytes in the body are:

  • Sodium — Controls fluid balance, nerve signals, muscle contraction. Mostly found in fluid outside cells (extracellular fluid).
  • Potassium — Keeps heart rhythm steady, helps muscles work, balances fluids. Mostly found inside cells (intracellular fluid).
  • Chloride — Works with Sodium to maintain fluid balance, helps make stomach acid. Mostly found outside cells.
  • Calcium — Builds bones/teeth, helps with muscle movement, blood clotting, nerve signals. Found in bones and teeth, some in blood.
  • Magnesium — Helps muscles and nerves work, supports enzymes, makes proteins. Found inside cells and in bones.
  • Phosphorus — Builds bones/teeth, stores energy (ATP), helps cell function. Mostly found inside cells and bones.
  • Bicarbonate — Maintains proper pH balance (acts as buffer system; see previous takeaway). Found in blood plasma.

Just like fluid and pH level, it’s so important to keep the right electrolyte balance. Even a small imbalance in these Electrolytes can cause problems like irregular heartbeat, muscle cramps, confusion, or fluid retention. That’s why your kidneys, hormones, and diet all work together constantly to keep electrolyte levels in the right range.

4️⃣ Sodium

Sodium plays a number of key roles in the body. It helps regulate blood pressure, is important for the firing of nerves and muscles, and supports in the process of maintaining proper fluid balance in the body. It is the main electrolyte in fluid outside of cells/in the blood. As with all Electrolytes, it’s possible to have an imbalance by having too much or too little Sodium in the body.

  • Hyponatremia — Occurs when you have too little Sodium in your blood. This can happen when Sodium is lost through vomiting, diarrhea, heavy sweating, or certain kidney problems, or when Sodium is diluted by drinking large amounts of plain water — especially after losing fluids. If you sweat a lot during long exercise and only replace the lost fluid with plain water, you lower the Sodium concentration in your blood. This causes water to move into your cells, making them swell. In the brain, this swelling can cause headache, confusion, nausea, muscle cramps, and seizures.
  • Hypernatremia — Occurs when you have too much Sodium in your blood. It’s rarely caused by consuming too much Sodium; it usually happens when water loss is greater than Sodium loss. If you sweat heavily and don’t drink enough to replace the water, the Sodium concentration in your blood rises because you lose more water than Sodium. This can happen with dehydration without adequate fluids. Symptoms can include thirst, weakness, confusion, muscle twitching, and, in severe cases, seizures.

For athletes, especially endurance athletes, sweating causes you to lose both water and Sodium. If you replace sweat loss with plain water only, Sodium concentration drops and can lead to Hyponatremia. If you don’t replace the fluids at all, Sodium concentration rises and can lead to Hypernatremia. The ideal approach is to replace fluids with water that contains some Sodium (sports drinks, electrolyte mixes) during and after activity, or to make sure you’ve taken in fluids with Sodium before your workout.

5️⃣ Chloride

Like Sodium, Chloride plays an important role in maintaining fluid balance. Aside from Sodium, Chloride is the most prevalent Electrolyte outside of cells. 

Chloride can combine with other chemicals in the body to create different things; for example, it teams with Hydrogen to create stomach acid in the form of Hydrochloric Acid. It also often pairs with Sodium as Sodium Chloride (table salt) in the diet and bloodstream.

6️⃣ Potassium

Potassium is the main electrolyte inside your cells. It helps keep your body’s pH balanced, your heart beating in rhythm, and your muscles and nerves firing properly.

You get Potassium primarily from food — bananas, potatoes, beans, yogurt, leafy greens, and many other fruits and vegetables are all good sources. The body is very sensitive to changes in Potassium, and even small changes can be dangerous.

Low Potassium is called Hypokalemia and is most often caused by losing Potassium, not by eating too little. This can happen from vomiting, diarrhea, heavy sweating, or certain “water pill” medications. Mild symptoms usually include muscle weakness, cramps, or heart palpitations. Severe cases can cause dangerous heart rhythm problems.

High Potassium is called Hyperkalemia and is usually caused by the kidneys not being able to remove Potassium effectively. In healthy people with normal kidney function, eating Potassium-rich foods will not cause any problems. However, supplements or “salt substitutes” high in Potassium can be risky, but only if your kidneys aren’t working well or you’re on certain medications. High Potassium often causes no symptoms until it’s severe, when it can trigger dangerous heart rhythms or even sudden cardiac arrest.

7️⃣ Calcium

The award for most abundant Electrolyte in our body goes to Calcium, which forms most of the bones in our skeleton. It is generally not present inside our cells or in the fluid outside our cells. 

Calcium enters the body through dietary intake and is excreted through urine and feces. The bones of our body act as reservoirs of Calcium and, depending on the body’s needs, can store some of the limited amounts of Calcium present in our blood or secrete it into the bloodstream as needed.

8️⃣ Magnesium

Magnesium is the second most abundant Electrolyte inside our cells after Potassium. About 50–60% of your body’s Magnesium is stored in your bones, around 25–30% in muscles, and the rest in other soft tissues and fluids. Magnesium plays a role in more than 300 biochemical reactions in the body, including muscle contraction, nerve signaling, energy production, protein synthesis, and regulating blood sugar and blood pressure. Both Potassium and Magnesium are really important for maintaining a heart that beats correctly. 

Magnesium comes mainly from the diet — nuts, seeds, whole grains, leafy greens, legumes, and certain fish are good sources. Many people do not meet the recommended intake, often because processed foods are low in Mag. That’s why Magnesium supplements have become popular in recent years. 

When blood Magnesium levels drop, your body can pull Magnesium from bone and tissues to help keep blood levels stable, but this is only a short-term fix. Prolonged low intake or excessive loss can lead to Hypomagnesemia.

Low Magnesium can be caused by poor dietary intake, gastrointestinal issues that reduce absorption (like Crohn’s disease or chronic diarrhea), certain medications (such as diuretics or proton pump inhibitors), excessive alcohol use, or increased loss through sweat during long sessions of exercise. Symptoms can include muscle cramps, fatigue, weakness, numbness or tingling, and in severe cases, dangerous heart rhythm problems, or seizures.

High Magnesium (Hypermagnesemia) is rare in healthy people because the kidneys efficiently remove excess. It usually occurs in people with kidney failure or those taking very large doses of supplements or medications containing Magnesium (such as some laxatives or antacids). Severe excess can cause low blood pressure, muscle weakness, breathing problems, and even cardiac arrest.

Overall, Magnesium is essential for muscle, nerve, and heart health, and for hundreds of critical reactions in the body. Most people would benefit from eating more Magnesium-rich foods, or supplementing.

9️⃣ Phosphorus

Phosphorus is another important Electrolyte and mineral that your body needs to function properly. It is the second most abundant mineral in the body after Calcium, with about 85% of it stored in your bones and teeth. The rest is found inside cells and in the blood.

Phosphorus is important for building strong bones and teeth alongside Calcium. It is also essential for making ATP (adenosine triphosphate), which is the main energy currency your cells use to power almost every function, from muscle movement to brain activity. Additionally, Phosphorus is part of DNA and RNA, which are the molecules that carry your genetic information.

Like the others, you get Phosphorus primarily from your diet in products such as meat, dairy, nuts, beans, and whole grains. It’s generally pretty easy to get enough Phosphorus because it’s present in many common foods.