Fluid, Fluid Compartments and Fluid Roles

What is Total Body Fluid

All water and dissolved substances in the body

What is the primary component of Total Body Fluid?

Water; 60% of body weight

What electrolytes are found in body fluids?

• Extracellular - HCO3-, Cl-, Na+

• Intracellular - K+, P-

What different components can be found in Total Body Fluid?

• Water

• Electrolytes (Na+, HCO3-, Cl-, K+, P-)

• Proteins (enzymes, hormones, immune response; maintain oncotic pressure)

What special protein contributes to the maintenance of oncotic pressure?

Albumin

What are the two main compartments of total body fluid?

• Extracellular fluids - outside cells

• Intracellular fluids - within cells

What compartment of total body fluid makes up 40% of total body weight?

• Intracellular Fluids

What compartment of total body fluid makes up 20% of total body weight?

Extracellular Fluid

Intracellular Fluid

• 40% of total BW

• High K+, P-

• Proteins, enzymes

• Maintain cell structure

• Medium for cellular reactions

Extracellular Fluid

• 20% of BW

• High in Na+, Cl-, HCO3-

• Outside cells of the body

• High protein content in plasma

What are the 3 sub compartments of Extracellular Fluid?

• Intravascular

• Interstitial

• Transcellular

What is Intravascular fluid

A sub compartment of Extracellular fluids

• Fluid inside blood vessels (plasma)

• Roles in transport of blood cells, nutrients, waste products

What is interstitial fluid

• Sub-compartment of Extracellular fluids

• Surrounds cells and lymph

• Medium for nutrient/waste exchange between blood and cells

What is Transcellular Fluid?

• Sub-compartment of Extracellular Fluid

• Located within specialized cavities in our bodies

  • Pericardium

  • Synovial

  • CSF

  • Pleural fluids Surrounds cells

  • BBB

Fluid moves between the intracellular and Extracellular compartments to maintain ________

Equilibrium

What are the roles of fluid? (6)

• Temperature regulation (sweating, respiration)

• Transportation (nutrient/waste)

• Lubrication (synovial fluid, tears, digestive fluids)

• Chemical Reactions (carries enzymes & hormones)

• Hydration

• Shock Absorption (BBB, CSF)

How does fluid move between Intravascular fluid and interstitial fluid?

Cell membranes separating Intravascular and interstitial fluid compartments are selectively permeable

• allows water and some solutes to pass through them

• Large plasma proteins (albumin) remain within vasculature

What are Aquaporins?

• specialized proteins that act like water channels

• Let water quickly move in and out cells while blocking ions and other molecules

• Helps regulate processes like:

  • Kidney function (concentrating urine)

What is Osmolality?

• Concentration of solutes in a solution (Osm/kg)

• Influences the movement of body water between compartments due to differences in compartment solute concentration

What are Osmotic Forces?

Pressures exerted by solutes in a solution to draw water across a semi-permeable membrane

Osmosis

Movement of water from an area of low solute concentration, to an area of high solute concentration

Osmotic Pressure

• Pulling force that solutes create to draw water in through osmosis

  • Pressure needed to stop water from moving across the membrane

What are the Starling Forces?

• Hydrostatic pressure

• Oncotic pressure

What is Hydrostatic Pressure?

• Force against blood vessel walls, pushing water out of capillaries

What is oncotic pressure?

• Pull exerted by proteins in the blood plasma, drawing water into the capillaries

What happens to the fluid within a blood vessel with high hydrostatic pressure?

The fluid will be pushed from within blood vessels into the interstitial compartment outside

What happens to fluid within a compartment with low oncotic pressure?

Fluid will leak into the interstitial compartment since there is no pulling force to draw fluid into the compartment

What is Capillary Exchange?

• Involves the diffusion, filtration, and osmosis of fluids

• Influenced by hydrostatic pressure, oncotic pressure, and capillary permeability

Describe capillary exchange at the arterial end

Hydrostatic pressure > osmotic pressure

• Fluids and some solutes move out of the capillary?

  • Why? To promote the delivery of oxygen and nutrient-rich blood to cells/tissues via interstitial fluid

Describe capillary exchange at the venous end

Oncotic pressure > Hydrostatic pressure

• Fluids and solutes tend to be pulled into the blood vessels

  • Why? - as blood flows through capillary, friction and fluid loss causes a drop in blood pressure; albumin remains in blood and pulls in fluid/solutes

What are the forces favouring filtration?

• Capillary Hydrostatic Pressure

  • Blood pressure, causing fluid to flow out into interstitial fluid

• Interstitial Oncotic Pressure

  • Proteins in interstitial fluid draw out fluid from BVs

What are forces favouring reabsorption? (Movement of fluid back into capillaries)

• Plasma (capillary) oncotic pressure

• Interstitial hydrostatic pressure

What is the formula for Net Filtration Pressure (NFP)?

NFP = (Capillary Hydrostatic Pressure + Interstitial Oncotic Pressure) - (Plasma Oncotic Pressure - Interstitial Hydrostatic PRessure)

What is Net Filtration Pressure (NFP) used for?

Determining the balance between forces favouring filtration & reabsorption

What does a Positive NFP value mean? What does a Negative NFP value mean?

• +NFP = net filtration (fluid/solute leaving capillaries)

• -NFP = net reabsorption (fluid/solute entering capillaries)

One of the first signs an older client exhibits when experiencing fluid volume deficit is:

A. Thirst

B. Vomiting

C. Confusion

D. Incontinence

C. Confusion

What should you keep in mind when working with the Elderly in terms of Fluids?

• Fluids are 55% of body weight instead of the baseline 60%

• Elderly have:

  • Decreased thirst sensation

  • Decreased kidney function

  • Chronic conditions (diabetes, renal disease)

What should you keep in mind when working with the Infants in terms of Fluids?

• Fluids contribute to 80% of body weight compared to baseline 60% in adults

  • Infants can’t communicate thirst

  • Infants have immature kidneys

    • Infants can’t concentrate urine as well due to immature nephrons

    • Lower ability to conserve water & electrolytes

  • Infants have increased body surface area

    • Lose water and heat faster through skin & respiration

    • More prone to dehydration and fluid/electrolyte imbalances