HomeostasisThe Interstitial Fluid is the environment of the cells,
and life depends on the constancy of this internal sea.
Homeostatic Mechanisms : Maintain within a narrow range.
Tonicity VolumeSpecific ion concentrationDefence of Tonicity –(280-295mOsm/L)Vasopressin secretion Thirst Mechanism
Increased Osmolality of ECF
Thirst IncreasedVasopressin
SecretionIncreased Water Intake Water Retention
Dilution of ECF
Inhibitory
HomeostasisDefence of Volume:ECF Na+ - Most
importantRenin-Angiotensin-
Aldosterone SystemVasopressin Secretion:
Volume stimuli override osmotic regulation
ANP & BNP
Angiotensinogen Renin
Angiotensin I ACE
Angiotensin II
Aldosterone Vasopressin
AdrenalCortex Brain
KidneyNa RetentionWater Retention
Blood VesselVasoconstriction
Thirst
HomeostasisDefence of Specific Ionic Concentration:GlucoseNa+ & K+ Ca++ - Mainly by Parathyroid & CalcitoninMg++ - Incompletely understood mechanisms
Also dependent on H+ ion
pH is maintained within a narrow range.
Acid Base EquilibriumWhat is Acid Base Equilibrium About?
?Buffer
s? Fixed Cation
?
Base Excess/ Deficit? Anion
Gap?
Acid Base EquilibriumAcid Base Equilibrium is all about Maintenance of H+ ion concentration of the ECF.
Source of H+ ion in Body:CO2 from metabolis
m
H+ load from AA
metabolism
Strenuous Exercise Lactic Acid
Diabetic KA
Ingestion of NH4Cl, CaCl2
Failure of Kidneys to Excrete PO4--, SO4--
H+ ion
12500 mEq/d 50 - 100 mEq/d
Some Basic ChemistryDefinitions:Arrhenius:
Acid: H+ Donor in SolutionBase: OH- donor in Solution
Browsted and Lowry:Acid: Proton DonorBase: Proton Acceptor
H20 can be both
Some Basic ChemistrySimple Rule of Thumb:Acid Higher conc. Of H+ ionBase Lower conc. Of H+ ionStrong Acid/Base Dissociates completely and irreversiblyWeak Acid/Base Dissociates partially and reversibly
Strong Electrolyte: Dissociates completely in solution at physiological pH
Eg: NaCl, KCl
Weak Electrolyte: Dissociates incompletely in solution at physiological pH
Eg: CO2 – HCO3- System, Proteins
Some Basic ChemistrypH (Puissant of Hydrogen):Negative logarithm of H+ ion concentration to the
base of 10
Why pH?Normal H+ ion conc: 0.00004meq/L or 40nEq/L or
4x10-9 mol/LpH converts to decimal numbers & takes away
negative sign.Normal pH: 7.35-7.45Normal H+ Conc: 0.00002mEq/L – 0.0001 mEq/L
Some Basic ChemistryPitfalls: Non-linear Negative Logarithmic scale
pH Decreases as [H+] increases.Each unit change in pH from 7 represents 10 fold
change in H+ ion conc. Eg: At pH 4, there are 10 times as much H+ than at pH 5, &
100 times as at pH 6Same numeric change in different portions of the pH
scale implies vastly different nanomolar change in H+ ions Eg: pH 56 => 100 times greater change in ionic conc than
when pH 7 8Body H+ ion conc is not as tightly controlled as the
other ion, though the pH scale implies so.