FLUID AND ELECTROLYTESMay.14.2010

97% - Seawater. 2.7% - Ice. 0.3 - Fresh water.

H

H

O

105˚

2e

2e

A water molecule is an irregular , slightly skewed tetrahedron with oxygen at its center.

WATER [H2O]

(3 or 2 also)

O••

•• ••

O•••• •

H••

H•H•

Covalent bond

+H +

O

••••

H H

•

LEWIS STRUCTURE OF A WATER MOLECULE

The approximate shape and charge distribution of water.

A covalent bond is a chemical bond formed by the sharing of a pair of electrons between two atoms.

THE DIPLOE NAUTRE OF A WATERMOLECULE.

Hydrogen bonds

Hydrogen bonds between water molecules. The oxygen atoms are shown in blue.

HYDROGEN BONDS BETWEEN WATER MOLECULES

RELATIVE BOND ENERTY

(ionic)

Bond strength increases left to right.

WATER’S FUNCTIONS

• Carries nutrients and waste products.

• Actively participates in chemical reactions.

• Serves as a solvent for minerals, vitamins, amino acids glucose, and other small molecules.

• Serves as a lubricant and cushion around joints.

• Acts as a shock absorber(eyes, spinal column, amniotic sac)

• Aids in maintaining body’s temperature.

BODY WATER CONTENT

• Its about 75% in the newborn.

• Total water content declines throughout life.

• Healthy males are about 60% water; healthy females are around 50%• This difference reflects females’:

– Higher body fat – Smaller amount of skeletal muscle

• Less than 50% in older individual.

• Water content is greatest in brain tissue (about 90%) and

least in adipose tissue (10%).

Daily Balance of Water Intake and Production in Sedentary Healthy Adults In a Temperate Climate

At least 500 ml of urine per day is required just to excrete urea, creatinine, and other Solutes.

Insensible losses from the skin and from the lungs can occur even when resting at normal room temperature.

DAILY WATER BALANCE

FLUIDS COMPARTMENTS

Nucleus

Cellmembrane

Blood vessel

ICF

Fluid between the cells (intercellular or interstitial)

FLUIDS COMPARTMENTS• Water occupies two main fluid compartments.

• Intracellular fluid (ICF) – about two thirds by volume, contained in cells

• Extracellular fluid (ECF) – consists of two major subdivisions– Plasma – the fluid portion of the blood– Interstitial fluid (IF) – fluid in spaces between cells

• Other ECF – lymph, cerebrospinal fluid, eye humors, synovial fluid, serous fluid, and gastrointestinal secretions.

ECF AND ICF FLUID

• Each fluid compartment of the body has a distinctive pattern of electrolytes

• Extracellular fluids are similar (except for the high protein content of plasma)– Sodium is the chief cation– Chloride is the major anion

• Intracellular fluids have low sodium and chloride– Potassium is the chief cation– Phosphate is the chief anion

• Solutes are broadly classified into:

– Electrolytes – inorganic salts, all acids and bases, and some proteins

– Nonelectrolytes – examples include glucose, lipids, creatinine, and urea

• Electrolytes have greater osmotic power than nonelectrolytes

• Water moves according to osmotic gradients

COMPOSITION OF BODY FLUIDS

ELECTROLYTES

The major components of plasma, intestitial fluid, and intracellular fluid. Crosshatching refers to other or minor components. Pr- , anionic proteins.

Nucleus

WATER DISORDERS

1.Dehydration (loss of water)

2.Edema(accumulation of water) Atypical accumulation of fluid in the interstitial space, leading to tissue swelling.

DEHYDRATION

Excessive loss of H2O from ECF

1 2

3

ECF osmotic pressure rises

Cells lose H2O to ECF by osmosis; cells shrink

Mechanism of dehydration

BODY FLUID AND ELECTROLYTES

Electrolytes are substances that become ions in solution and acquire the capacity to conduct electricity.

i. Sodium.

ii. Potassium

iii. Chloride

iv. Bicarbonate

Help keep fluids in proper compartments. -Intracellular water -Extracellular water

NORMAL VALUE

mmol/L

SODIUM IN FLUID ANDELECTROLYTE BALANCE

• Sodium holds a central position in fluid and electrolyte balance

• Sodium salts:– Account for 90-95% of all solutes in the ECF

• Sodium is the single most abundant cation in the ECF

• Sodium is the only cation exerting significant osmotic pressure

• Changes in plasma sodium levels affect:– Plasma volume, blood pressure– ICF and interstitial fluid volumes

SODIUM - FUNCTIONS

• Membrane potentials

• Accounts for 90 - 95% of osmolarity of ECF

• Na+- K+ pump – exchanges intracellular Na+ for extracellular K+

– creates gradient for co-transport of other solutes (glucose)– generates heat

• NaHCO3 has major role in buffering pH

• Hypernatremia– plasma sodium > 145 mmol/L

• from IV saline– water retension, hypertension and edema

• Hyponatremia– plasma sodium < 136 mmol/L– result of excess body water, quickly corrected by

excretion of excess water

SODIUM - IMBALANCE

• Most abundant cation of ICF

• Determines intracellular osmolarity

• Membrane potentials (with sodium)

• Na+-K+ pump

POTASSIUM - FUNCTIONS

POTASSIUM HOMEOSTASIS

• 90% of K+ in glomerular filtrate is reabsorbed by the PCT

• DCT and cortical portion of collecting duct secrete K+ in response to blood levels

• Aldosterone stimulates renal secretion of K+

POTASSIUM AND MEMBRANE

CHLORIDE FUNCTIONS

• ECF osmolarity – most abundant anions in ECF

• Stomach acid – required in formation of HCl

• Chloride shift – CO2 loading and unloading in RBC’s

• pH– major role in regulating pH

OSMOSIS AND WATER BALANCE

• OSMOSIS

– Is the movement of water across a semipermeable membrane

– Is affected by the concentration gradient of dissolved substances

OSMOSIS

Water can flow both waysacross the divider, but has agreater tendency to move fromside A to side B, where thereis a greater concentration ofsolute. The volume of waterbecomes greater on side B,and the concentrations onside A and B become equal.

32 Now additional solute isadded to side B. Solute cannotflow across the divider (in thecase of a cell, its membrane).23

1 With equal numbers of soluteparticles on both sides, theconcentrations are equal,and the tendency of water tomove in either direction isabout the same.

When immersed in water, raisins get plump because water movestoward the higher concentration of sugar inside the raisins.

OSMOSIS

When sprinkled with salt, vegetables “sweat” because water movestoward the higher concentration of salt outside the eggplant.

TONICITY• TONICITY

– Is the ability of a solution to cause a cell to gain or lose water

• IF A SOLUTION IS ISOTONIC

– The concentration of solutes is the same as it is inside the cell, and water will move in and out of the cell at the same rate

• IF A SOLUTION IS HYPERTONIC– The concentration of solutes is greater than it is inside the

cell, and the cell will lose water

• IF A SOLUTION IS HYPOTONIC– The concentration of solutes is less than it is inside the

cell, and the cell will gain water

THE WATER BALANCE OF LIVING CELLS

Hypotonic solution Isotonic solution Hypertonic solutionAnimal cell. Ananimal cell fares bestin an isotonic environ-ment unless it hasspecial adaptations tooffset the osmoticuptake or loss ofwater.

Plant cell. Plant cells are turgid (firm) and generally healthiest ina hypotonic environ-ment, where theuptake of water iseventually balancedby the elastic wallpushing back on thecell.

(a)

(b)

H2O H2O H2O H2O

H2OH2OH2OH2O

Lysed Normal Shriveled

Turgid (normal) Flaccid Plasmolyzed

有難う御座ます。