Name: body fluid solutes and ion balance
Uploaded: 2024-12-20T14:49:37.000Z
Duration: 1 min 29 s
Channel: JoVE

Body fluid is mainly composed of water with dissolved electrolytes and non-electrolytes.
Electrolytes, such as inorganic salts, acids, and bases are compounds that can dissociate into ions.
Conversely, non-electrolytes are organic molecules like glucose, lipids, creatinine, and urea that are bound by covalent bonds and do not dissociate into ions.
The solute concentrations in the plasma, interstitial fluid, and intracellular fluid vary greatly.
Sodium and chloride are the principal ions in plasma and interstitial fluid, with smaller amounts of phosphate, bicarbonate, and other cations and anions.
Conversely, intracellular fluid has lower levels of sodium and chloride ions, with potassium as the primary cation and phosphate as the major anion. It also contains a significant amount of soluble proteins.
The plasma and interstitial fluid, which make up the extracellular fluid or ECF, form only a small proportion of the total body fluid but are clinically vital.
In hemorrhage or dehydration, blood or saline is administered primarily to maintain ECF, enabling rapid solute and fluid exchange between the blood plasma and the interstitial fluid.

composition of body fluids

Composition of Body Fluids

Water functions as a solvent accommodating various solutes, which can be categorized under electrolytes and non-electrolytes. Non-electrolytes are usually held together by covalent bonds, restricting them from dissociating in solution, thereby leading to a lack of electrically charged components upon dissolving in water. They are predominantly organic molecules, such as glucose, creatinine, and urea. Electrolytes, on the other hand, are compounds that can break down into ions in water. Electrolytes are usually inorganic salts, acids, and bases, including both organic and inorganic, along with some proteins.
Water&#39;s movement adheres to osmotic gradients, moving from an area with lower osmolality to an area with higher osmolality, and as such, electrolytes are most effective in causing fluid shifts. Electrolyte concentrations in body fluids are typically expressed in milliequivalents per liter (mEq/L), indicating the number of electric charges in a liter of solution.
There is a distinctive electrolyte composition pattern&#160;in each fluid compartment. Sodium is the main cation, and chloride is the major anion in the extracellular fluids. However, plasma contains slightly fewer chloride ions than interstitial fluid due to the presence of non-penetrating anionic plasma proteins. Contrastingly, intracellular fluids (ICF) contain less Na+ and Cl&#8722;, with potassium being the most abundant cation and HPO4 2&#8722;; being the major anion. Cells also have substantial soluble proteins. Sodium and potassium ion concentrations in ECF and ICF are almost inverse, reflecting the activity of cellular ATP-dependent sodium-potassium pumps that maintain low Na+ concentrations and high K+ concentrations within cells.
While electrolytes are the most plentiful solutes in body fluids and are responsible for their chemical and physical reactions, they do not constitute the majority of dissolved solutes in these fluids. Proteins and other large non-electrolytes comprise a significant portion of the dissolved solutes in body fluids. In plasma, proteins alone account for approximately 7% of the plasma&#39;s volume and contribute substantially to its osmotic concentration. These large molecules are crucial in maintaining fluid balance across different compartments, as they are largely retained in the plasma. In comparison, the interstitial fluid (IF) contains a smaller proportion of proteins and other large molecules, while the intracellular fluid (ICF) has a high concentration of proteins, essential for cellular functions and maintaining the osmotic balance within cells.

Body fluid is mainly composed of water with dissolved electrolytes and non-electrolytes.
Electrolytes, such as inorganic salts, acids, and bases are ...

Education

JoVE Core

Anatomy and Physiology

Unit 1

Fluid, Electrolyte, and Acid-Base Balance

KEY TERMS AND CONCEPTS

body fluid solutes and ion balance

Body fluids are made of water plus dissolved solutes, including electrolytes and non-electrolytes. Water acts as the main solvent, so it can carry many different substances in solution. These dissolved materials help determine how fluid moves between body compartments.

Non-electrolytes are usually held together by covalent bonds, so they do not break apart into charged particles in water. They are often organic molecules such as glucose, creatinine, and urea. Electrolytes are compounds that do break down into ions in water. They usually include inorganic salts, acids, and bases, along with some organic compounds and some proteins.

Water moves according to osmotic gradients, from lower osmolality to higher osmolality. Osmolality describes the concentration of dissolved particles in a fluid. Because of this, electrolytes are especially important in causing fluid shifts. Electrolyte levels in body fluids are often reported in milliequivalents per liter, or mEq/L, which shows the number of electric charges in one liter of solution.

Each fluid compartment has its own electrolyte pattern. In extracellular fluid, sodium is the main cation, and chloride is the main anion. Plasma has slightly less chloride than interstitial fluid because plasma contains non-penetrating anionic plasma proteins. In intracellular fluid, sodium and chloride are lower, while potassium is the most abundant cation and HPO4 2− is the major anion. Cells also contain a large amount of soluble proteins.

The sodium and potassium levels in extracellular fluid and intracellular fluid are nearly opposite. This pattern reflects the action of ATP-dependent sodium-potassium pumps, which keep sodium low and potassium high inside cells. Electrolytes are the most common solutes in body fluids and help drive chemical and physical reactions, but they are not the only dissolved substances.

Proteins and other large non-electrolytes make up an important part of body fluid solutes. In plasma, proteins make up about 7% of the volume and add greatly to osmotic concentration. These large molecules are mostly kept in the plasma, where they help maintain fluid balance between compartments. Interstitial fluid contains fewer proteins and other large molecules, while intracellular fluid has a high protein concentration that supports cell function and osmotic balance.

Body Fluid Solutes and Ion Balance

body water content and fluid compartments

body-water-content-and-fluid-compartments

Body Water Balance and Fluid Compartments

Body water balance depends on how water is distributed among the body’s fluid compartments. Life’s chemical reactions take place in watery solutions. These solutions contain dissolved substances called solutes. In the human body, solutes include proteins, such as those involved in clotting and carbohydrate transport, and electrolytes. An electrolyte is a mineral ion from a salt that carries an electric charge. Sodium ions (Na+) and chloride ions (Cl-) are examples. Water moves through the body...

Body fluids are made of water plus dissolved solutes, including electrolytes and non-electrolytes. Water acts as the main solvent, so it can carry many different substances in solution. These dissolved materials help determine how fluid moves between body compartments. Non-electrolytes are usually held together by covalent bonds, so they do not break apart into charged particles in water. They are often organic molecules such as glucose, creatinine, and urea. Electrolytes are compounds that do...

fluid movement between compartments

How Pressure and Transport Move Body Fluids

Hydrostatic pressure and osmotic pressure drive fluid movement between body compartments. Hydrostatic pressure is the force a fluid applies against a surface. In blood vessels, it comes from the heart’s pumping action. At the arteriolar end of capillaries, capillary blood pressure is higher than colloid osmotic pressure. Colloid osmotic pressure is created mainly by plasma proteins such as albumin. This pressure difference pushes plasma and nutrients out of the capillaries and into the...

regulation of water intake

How the Body Detects Dehydration

The body detects dehydration by tracking plasma osmolality and blood volume. Plasma osmolality is the number of solute particles per kilogram of water in blood plasma. It reflects hydration status, so the body uses it to help keep fluid balance stable. Water loss through breath, sweat, or urine usually comes from blood plasma first. When solute concentration in the blood rises, the thirst response begins. Osmoreceptors in the hypothalamus monitor plasma osmolality. If osmolality gets too high,...

regulation of water output

How the Kidneys Adjust Urine Volume

The kidneys adjust urine volume to keep water balance stable and remove dissolved wastes. The human body mainly loses water through the urinary system. On average, a person makes about 1.5 liters of urine each day. This amount changes with hydration, but the body still needs a minimum urine output to function well. Each day, the kidneys remove about 600 to 1200 milliosmoles of dissolved substances. This process helps excrete extra minerals and water-soluble wastes such as creatinine, urea, and...

disorder of water balance

Water Imbalance Disorders

Water imbalance disorders happen when the body has too little or too much water, or when water and salts are no longer in normal balance. These changes disrupt homeostasis, the body’s stable internal condition. The main outcomes include dehydration, hypotonic hydration, hyperhydration, edema, and water intoxication. Dehydration occurs when the body loses fluids, especially water. Common causes include heavy sweating, fever, vomiting, diarrhea, and diuresis, which means increased urine output.

roles of electrolytes: sodium and potassium

roles-of-electrolytes-sodium-and-potassium

Sodium, Potassium, and Body Balance

Sodium and potassium help keep the body in balance. Sodium is the main cation, or positively charged ion, in the extracellular fluid. Potassium is the main cation inside cells. Together, they support fluid levels, electrical activity, and normal body function. Sodium balance is mainly controlled by the kidneys. The kidneys adjust how much sodium is removed so it matches dietary intake and helps keep electrolyte levels stable. Sodium is found in salts such as sodium chloride and sodium...

roles of electrolytes: chloride and bicarbonate

roles-of-electrolytes-chloride-and-bicarbonate

Chloride and Bicarbonate in Body Balance

Chloride and bicarbonate help the body keep fluids and pH in balance. Both are important anions, or negatively charged ions, in human blood and body fluids. Chloride helps create the osmotic pressure gradient between intracellular fluid (ICF) and extracellular fluid (ECF). It also helps balance positively charged ions in the ECF and supports electrochemical stability. In the kidneys, chloride absorption and release usually follow the same pattern as sodium. Low chloride levels, called...

roles of electrolytes: calcium and phosphate

roles-of-electrolytes-calcium-and-phosphate

Calcium and Phosphate Balance in the Body

Calcium and phosphate are essential electrolytes that help the body stay in balance. Calcium is the most abundant mineral in the human body. About 99% of it is stored in the skeleton and teeth, where it combines with phosphate to form mineral salts. Calcium also supports blood clotting, neurotransmitter release, muscle tone, and the excitability of nervous and muscle tissue. Blood calcium levels are mainly controlled by parathyroid hormone, or PTH. When calcium in blood plasma drops, PTH is...

regulation of sodium and potassium

Hormones That Balance Blood Ions

Hormones help control sodium and potassium levels in the body. Aldosterone, antidiuretic hormone (ADH), and atrial natriuretic peptide (ANP) work together to keep these ions in a safe range. Sodium ions make up about 90% of the cations outside cells. Normal blood plasma sodium is about 136–148 mEq/L. When blood volume and pressure drop, granular cells in the juxtaglomerular complex (JGC) release renin. This can happen with reduced kidney blood flow, sympathetic nerve activity, or low sodium...

acid-base balance

How Body Systems Control Blood pH

The body keeps blood pH in a narrow range through acid-base balance. This control matters because changes in hydrogen ion concentration can disturb cell membrane stability, alter protein shape, and change enzyme activity. Small shifts in pH can affect normal body function. Arterial blood normally has a pH of 7.4. Venous blood and interstitial fluid are about 7.35, while intracellular fluid averages 7.0. If arterial blood pH rises above 7.45, the condition is called alkalosis. If it drops below...

buffer systems in the body

Body pH Control with Chemical Buffers

Chemical buffers help control pH in the body. They stabilize acid and base changes by neutralizing strong acids or bases. When pH drops, hydrogen ions bind to a weak base. When pH rises, hydrogen ions are released. This keeps body fluids within a narrow pH range that is needed for normal function. A buffer system usually includes a weak acid and its matching anion, which acts as a weak base. These compounds only partially dissociate in solution, so they stay in equilibrium with their...

protein buffers in blood plasma and cells

protein-buffers-in-blood-plasma-and-cells

How Hemoglobin Buffers Blood pH

Protein buffers help keep blood pH stable. Amino acids can act as acids or bases because they can accept or release hydrogen ions when pH changes. These buffer systems are especially important in the extracellular fluid and intracellular fluid of active cells, where structural and functional proteins add strong buffering power. Some amino acids can exist as zwitterions at a certain pH. A zwitterion carries both positive and negative charges at the same time. When pH rises, the carboxyl group...

phosphate buffer

How Phosphate Buffers Keep pH Steady

The phosphate buffer system helps keep pH stable in the body. It uses two phosphate salts: sodium dihydrogen phosphate, which acts as a weak acid, and sodium hydrogen phosphate, which acts as a weak base. Together, they help resist large pH changes in biological fluids. Sodium dihydrogen phosphate does not fully dissociate in neutral or acidic solutions. When a strong base such as sodium hydroxide is added, it donates a proton. This forms water and sodium hydrogen phosphate: NaH2PO4 + OH- →...

bicarbonate-carbonic acid buffer

How the Body Recycles CO2 to Balance pH

The carbonic acid-bicarbonate buffer system helps keep body pH stable by using carbon dioxide, carbonic acid, and bicarbonate ions. It works through a reversible equilibrium: H2CO3 ⇌ H+ + HCO3-. In this system, bicarbonate ions act as weak bases, and carbonic acid acts as a weak acid. When hydrogen ion levels rise and pH drops, the balance shifts to the left. Hydrogen ions are converted into carbonic acid. Carbonic anhydrase, an enzyme, quickly changes carbonic acid into carbon dioxide and...

respiratory regulation of acid-base balance

respiratory-regulation-of-acid-base-balance

How Breathing Restores Blood pH

Breathing helps restore blood pH by changing carbon dioxide levels in the blood. This process is called respiratory compensation. It works with the body’s acid-base balance, which keeps plasma pH stable. Most carbon dioxide dissolves in blood and becomes carbonic acid. Carbonic acid then breaks apart into hydrogen ions and bicarbonate ions. Because of this, carbon dioxide and pH have an inverse relationship. When carbon dioxide rises, more hydrogen ions form and blood pH falls. This can cause...

renal regulation of acid-base balance

How the Kidneys Remove Extra Acid

The kidneys remove extra acid to help keep body fluids at the right pH. Metabolic reactions in the body produce nonvolatile acids, such as sulfuric acid. That creates an acid load of about 1 mEq of H+ per kilogram of body weight each day. Excreting H+ in the urine is essential to balance this load. Kidney tubules move H+ into the tubular fluid in two main places. In the proximal convoluted tubules, or PCT, Na+/H+ antiporters secrete H+ while reabsorbing Na+. The collecting ducts also secrete...

disorders of acid-base balance

Blood pH Imbalance in Acidosis and Alkalosis

Blood pH must stay in a narrow range between 7.35 and 7.45. When it drops below 7.35, the body is in acidosis. When it rises above 7.45, the body is in alkalosis. These changes can come from respiratory or metabolic causes. Respiratory acidosis happens when the partial pressure of carbon dioxide, or PCO2, rises in the blood. Shallow breathing or poor gas exchange can cause this buildup. Pneumonia, cystic fibrosis, and emphysema are examples of conditions that may lead to carbon dioxide...

compensation mechanisms

Blood pH Control by Lungs and Kidneys

Blood pH control depends on respiratory and renal compensation. These responses help correct acidosis, when blood pH falls below 7.35, and alkalosis, when blood pH rises above 7.45. The body uses the lungs or the kidneys, depending on where the imbalance starts. Respiratory compensation corrects pH problems caused by metabolism by changing the breathing rate. It begins within minutes after a pH change is detected and works best within hours. In metabolic acidosis, the body hyperventilates, or...

diagnosing acidosis and alkalosis

Using Blood Gases to Spot Acid-Base Imbalance

Blood gas analysis can reveal acid-base imbalance by checking pH, bicarbonate (HCO3−), and carbon dioxide partial pressure (PCO2) in arterial blood. These three measurements show whether the blood is too acidic or too basic and help point to the cause. The first step is to check pH. A normal pH is 7.35 to 7.45. A pH below this range means acidosis, and a pH above it means alkalosis. The next step is to compare PCO2 and HCO3− to see which value is driving the pH change. A change in PCO2...

key terms and concepts

Learn how water, electrolytes, and non-electrolytes shape body fluids, drive osmotic movement, and create different ion patterns in plasma, interstitial fluid, and cells.

Body Fluid Solutes and Ion Balance | JoVE K12

anatomy and physiology

JoVE Core Anatomy and Physiology showcases the anatomical and physiological details of the human body in comprehensive, clear, and engaging video animations. This collection of lessons focuses on the structures, components, functions, and requirements of the human body. It is complemented by scientist-in-action videos that demonstrate the application of this knowledge in real-world medical and research settings.

Body Fluid Solutes and Ion Balance

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