2 Body Fluids & Fluid Compartments Figure 26.1ICFIFApproximately 60% of body weight is H2O.Fluid CompartmentsIntracellular fluid (ICF): fluid within the cellsExtracellular fluid (ECF): fluid outside the cellsPlasmaInterstitial fluid (IF)
4 Body Fluids Composition (solutes): Electrolytes chemical compounds that dissociate in H2O to form ions – salts, acids, basesanything with a chargeNonelectrolytes: do not dissociate in H2O (glucose, lipids, creatinine, urea, etc.)
5 Body FluidsOsmosis: the diffusion of a solvent (such as water) across a semipermeable membraneFrom a less concentrated solution (H2O moves out).Toward a more concentrated solution (H2O moves in).The solvent (H2O) moves down its concentration gradient.Osmotic activity is based on the number of particles in solution.
6 Osmotic ActivityElectrolytes have a greater potential for osmotic activity than nonelectrolytesNaCl Na+ + Cl particlesMgCl2 Mg Cl particlesGlucose Glucose particleElectrolytes have the greatest ability to cause fluid shifts.
7 Electrolyte Concentration Electrolyte concentration is an expression of the number of electrical charges in 1 liter [expressed as milliequivalents per liter (mEq/L)]mEq/L = ion concentration (mg/L) x charge atomic weightNormal plasma levels:Na+ : mg/L x 1 = 143 mEq/LCa2+ : 100 mg/L x 2 = 5 mEq/L
8 Body FluidsComparison of extracellular fluid (ECF) and intracellular fluid (ICF)ECF: increased Na+ and increased Cl-ICF: increased K+ and increased HPO42-Figure 26.2
9 Figure 26.1Fluid movementICFIFMovement between plasma and interstitial fluid (IF) across capillary membranesHydrostatic pressure in the capillaries pushes fluid into the IFOncotic pressure returns fluid to plasmaLymphatic system returns the small remainder to the bloodExchanges between IF and ICF occur across the selectively permeable cell membranesH2O flow is conducted both waysIon movement is controlled and restrictedIon transport is selective by active transport
10 Water Balance and ECF Osmolality Figure 26.4H2O sources / lossesSources:Intake (~2500 ml/day)Metabolic H2O : H2O produced by cell metabolismLosses:Insensible loss: vaporizes from lungs and skinLosses in perspiration and fecesUrinary losses (~60%)
11 Regulation of intake / output Figure 26.5Intake: Thirst is regulated by the hypothalamic thirst centerSensory feedback from dry mouth stimulates the thirst centerHypothalamic osmoreceptors lose H2O into hypertonic ECF and stimulate the thirst centerAngiotensin II stimulates the thirst centerOutput:Kidneys: make short term adjustments to compensate for low intakeObligatory H2O lossInsensible loss + Sensible loss in urine yields a daily minimum of 500mlWith a normal diet the kidneys must excrete mOsm of solute daily
13 Water Balance: Conservation ADHH2O reabsorption in collecting ductHypothalamic osmoreceptors sense ECF osmolality and regulate ADH releaseLarge decreases in BP trigger ADH release via signals from baroreceptorsADH acts directly and via stimulation of Renin-Angiotensin system
15 Disorders of H2O Balance Dehydration: H2O loss and/or electrolyte imbalanceHypotonic hydration: H2O intake with inadequate electrolytes; marked by hyponatremiaEdema: accumulation of fluid in the interstitial spaceHypoproteinemia: loss of colloid osmotic pressure H2O leaves plasma, enters IFAny event that increases plasma IF movement or hinders IF plasma return
16 Electrolyte Balance: Role of Na+ Na+ is the most abundant cation in the ECFNa+ is the only ECF ion with significant osmotic effectCell membranes are relatively impermeable to Na+[Na+] across the cell membrane may be alteredNa+ has the primary role in control of ECF volume and H2O distribution
17 Electrolyte Balance: Role of Na+ ECF total Na+ content may change but [Na+] remains stable because of shifts in water contentA change in the [Na+] in plasma will effect; plasma volume, BP, intracellular fluid volume and interstitial fluid volume.
18 Regulation of Na+ balance Regulation of Na+ balance is linked to BP and blood volume65% of Na+ is reabsorbed in the PCT25% of Na+ is reabsorbed in the ascending limb of the loop of Henle10% remains in DCT and collecting duct filtrate
19 Aldosterone aldosterone : Virtually all Na+ is actively reabsorbed in DCT & collecting duct (H2O follows Na+ if ADH is present)Renin-Angiotensin system is the most important trigger of aldosterone releaseAldosterone effect occurs slowly (hours to days)Changes in blood will feedback to modulate the effect of aldosterone.
20 Cardiovascular Baroreceptors: Blood Pressure Homeostasis Decreased BP leads to:Constriction of afferent arteriolesActivation of the renin angiotensin systemRelease of aldosteroneRelease of ADHConservation of Na+Conservation of blood volumeIncreased thirst