Fluid & Electroltyes

Total body water (TBW)

Sum of all fluids in all body compartments (60% of body weight)

Intracellular fluid (ICF)

Fluid inside of cells

Extracellular fluid

Fluid outside of cells

ICF inside the cells

2/3 of TBW

ECF outside the cell

1/3 TBW

Normal body fluids: adults

50-60% TBW

Normal body fluids: Older adults

45-55% TBW

Normal body fluids: infants

75-80% TBW

Older adults

Have an increase in adipose and decrease muscle mass, renal decline, and diminished thirst perception

Infants are

Susceptible to significant changes in body fluids - dehydration

Age and body composition changes

How much water the body contains, and how easily dehydration can occur

Water movement between plasma & interstitial fluid results in

Hydrostatic pressure (pushes water) and osmotic (oncotic) pressure (pulls water) at the capillary

What readily moves across the capillary membrane?

Water, sodium, and glucose

Plasma proteins (albumin) maintain

Osmolality and generate plasma oncotic pressure

Hydrostatic

Pushes out

Albumin/oncotic

Pulls in

4 forces determining fluid movement

1. Capillary hydrostatic pressure (blood pressure)

2. Capillary oncotic pressure

3. Interstitial hydrostatic pressure

4. Interstitial oncotic pressure

Capillary hydrostatic pressure (blood pressure)

Facilitates movement of water from capillary to interstitial space

Capillary oncotic pressure

Osmotically attracts water from interstitial back into capillary

Interstitial hydrostatic pressure

Facilitates inward movement of water from interstitial into capillary

Interstitial oncotic pressure

Osmotically attracts water from capillary into interstitial space

Osmosis

Movement of water from a region of fewer non-diffusible particles to the side that has more

water goes where

Salt is

Diffusion

Movement of solutions molecules from an area of greater solute concentration until equilibrium (concentration gradient)

Regulation of fluids: Atrial Natriuretic Peptide (ANP)

Hormone increases rate of excretion of Na+ in urine, hormone synthesized and stored in atrial muscle, receptors in atrial are stimulated in response to increased blood volume

ANP is

A 'volume-lowering' hormone: it helps the kidneys excrete sodium and water when blood volume is high

ANP

Increased blood volume,the atria stretches, ANP is released, Na+ + H2O out

Edema

Excessive accumulation of fluid within the interstitial spaces, related to fluid filtration from capillaries or lymph channels into tissues

Causes of edema

Increas3 in capillary hydrostatic pressure, decrease in plasma oncotic pressure, increases in capillary permeability, and lymph obstruction

Localized edema (one area)

Usually limited to a site of trauma or within a particular organ system

Generalized edema (widespread)

More uniform distribution of fluid in interstitial spaces

Edema causes

Increased hydroststic pressure, decreased oncotic pressure

Sodium, chloride, and water are closely linked

Changes in one often affect the others

ADH mainly controls

Water

Aldosterone mainly promotes

Sodium retention

Water follows

Sodium

Brain

Sense & thirst

Kidney

Unjust urine

Heart

ANP

Adrenal

Aldosterone

Fluid balance depends on coordinated signals from

The brain, hormones, kidneys, heart, thirst, and water loss

Thirst increases when

Cells need water or circulating blood volume falls

RAAS raises blood pressure and volume by

Promoting vasocontriction and sodium/water retention

Isotonic

Cell stays the same

Hypotonic

Water In - cell swells

Hypertonic

Water out, cell shrinks

Isotonic alteration occur when

Changes in TBW are accompanied by proportional changes in electrolytes

Fluid will not move out of cells

Potassium

3.5-5.0