Name: how pressure and transport move body fluids
Uploaded: 2024-12-20T14:49:37.000Z
Duration: 1 min 18 s
Channel: JoVE

The fluid exchange between intracellular and extracellular compartments occurs due to hydrostatic and osmotic pressure exerted by fluids against surfaces.
The hydrostatic pressure of blood stems from the heart&#39;s pumping action, creating capillary blood pressure at the arteriolar end of capillaries.
This pressure difference propels plasma and nutrients from capillaries to surrounding tissues.
Similarly, fluid and cellular wastes are reabsorbed into the capillaries at the venule end, where the hydrostatic pressure is lower than the vessel&#39;s interior osmotic pressure.
Hydrostatic pressure also regulates water movement in the nephrons of the kidneys.
Higher pressure results in increased urinary filtration, and extremely low pressure &#8212; such as during dehydration &#8212; can compromise kidney function.
The osmotic gradient, formed by differences in solute concentration across semipermeable membranes, also regulates fluid movement.
Water constantly shifts between plasma, interstitial fluid, and intracellular fluid in response to varying conditions in different parts of the body.

fluid movement between compartments

Fluid Movement Between Compartments

The force applied by fluids against a surface, known as hydrostatic pressure, initiates the transfer of fluid among different compartments. Within our blood vessels, the blood's hydrostatic pressure is a result of the heart's pumping action. At the arteriolar end of capillaries, hydrostatic pressure (capillary blood pressure) exceeds the opposing colloid osmotic pressure created primarily by plasma proteins like albumin. This discrepancy in pressure propels plasma and nutrients from the capillaries into the surrounding tissues. The fluid and cellular wastes from the tissues reenter the capillaries at the venule end, where hydrostatic pressure is lesser compared to the osmotic pressure inside the vessel. Filtration pressure pushes fluid from the intravascular compartment to the interstitial fluid (IF) around the tissue cells. The excessive fluid in the interstitial space not directly returned to the capillaries gets drained by the lymphatic system and re-joins the vascular system at the subclavian veins. Hydrostatic pressure plays a pivotal role in managing water movement in the kidney's nephrons to ensure the proper filtration of blood to produce urine. As hydrostatic pressure in the kidneys rises, more plasma exits the capillaries, resulting in increased urine filtrate. Conversely, if the kidneys' hydrostatic pressure drops excessively, as can occur in dehydration, kidney functions may be compromised, leading to reduced removal of nitrogenous wastes from the bloodstream. Severe dehydration can potentially lead to acute kidney injury. Movement of fluid between compartments also occurs along an osmotic gradient. This gradient is formed by the difference in solute concentration on either side of a semi-permeable membrane. The strength of the osmotic gradient corresponds to the difference in solute concentration across the membrane. Water, following the principles of osmosis, moves from an area of low solute concentration to an area of high solute concentration across a semipermeable membrane. In humans, water constantly shifts between the intravascular space and IF, and IF and intracellular fluid (ICF) based on varying conditions across different body parts. For instance, during perspiration, water is lost through the skin. If excess water is lost through this process, it results in dehydration. However, when a person rehydrates by drinking water, it is redistributed by the same gradient, replenishing all body tissues with water. The cellular movement of certain solutes is an active process that requires energy, while the movement of other solutes is passive and energy-independent. Active transport allows cells to move substances against their gradient through a membrane protein, utilizing ATP. The sodium-potassium pump is an example of active transport, expelling sodium from cells and importing potassium against their respective gradients. Conversely, passive transport relies on a molecule or ion's ability to pass through the membrane and the presence of a concentration gradient that allows the molecules to move from higher to lower concentration areas. Certain molecules, like dissolved gases, lipids, and water, can easily permeate the cell membrane, while others, like glucose, amino acids, and ions, cannot and need facilitated transport to move down a concentration gradient through specific protein channels in the membrane. This process does not require energy. Glucose, for instance, is moved into cells by glucose transporters through facilitated diffusion.

The fluid exchange between intracellular and extracellular compartments occurs due to hydrostatic and osmotic pressure exerted by fluids against 
...

Education

JoVE Core

Anatomy and Physiology

Unit 1

Fluid, Electrolyte, and Acid-Base Balance

KEY TERMS AND CONCEPTS

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 surrounding tissues.

At the venule end of capillaries, the balance changes. Hydrostatic pressure is lower there, while osmotic pressure inside the vessel is stronger. As a result, fluid and cellular wastes move back into the capillaries. Extra fluid that stays in the interstitial fluid, or IF, is drained by the lymphatic system and returns to the vascular system at the subclavian veins.

Hydrostatic pressure is also important in the kidneys. It helps control water movement in the nephrons so blood can be filtered into urine. When kidney hydrostatic pressure rises, more plasma leaves the capillaries and more urine filtrate is made. If kidney hydrostatic pressure falls too much, such as during dehydration, kidney function can suffer and nitrogenous wastes may build up in the blood. Severe dehydration can even lead to acute kidney injury.

Fluid also moves because of osmosis. Osmosis is water movement across a semipermeable membrane from a lower solute concentration to a higher solute concentration. The size of the osmotic gradient depends on the difference in solute concentration on each side of the membrane. In the body, water shifts between the intravascular space, IF, and intracellular fluid, or ICF, depending on conditions in different tissues.

Sweating is one example of this movement. During perspiration, water leaves the body through the skin. If too much water is lost, dehydration occurs. When a person drinks water again, the same gradient helps redistribute water and refill body tissues.

Cell membranes also move solutes by active and passive transport. Active transport needs energy and ATP. It moves substances against their gradient through membrane proteins. The sodium-potassium pump is one example. It moves sodium out of cells and potassium into cells against their gradients.

Passive transport does not require energy. It depends on a concentration gradient and on whether a molecule can cross the membrane. Dissolved gases, lipids, and water pass through easily. Glucose, amino acids, and ions usually need facilitated transport through specific membrane channels. Glucose enters cells this way through glucose transporters by facilitated diffusion.

How Pressure and Transport Move Body Fluids

how-pressure-and-transport-move-body-fluids

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...

composition of body fluids

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...

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 hydrostatic pressure, osmosis, and membrane transport move water, nutrients, and wastes between capillaries, tissues, and cells in the body.

How Pressure and Transport Move Body Fluids | 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.

How Pressure and Transport Move Body Fluids

Description

Transcript

Tags