CHAPTER 27  FLUID, ELECTROLYTE, AND ACID-BASE HOMEOSTASIS

 

I.BODY FLUIDS

            A. Intracellular and extracellular fluid compartments

                        Total body water  40 liters (70kg adult)

0______________________________________________________________40

 

Extracellular (ECF)

        15 liters

 

_______________ Plasma        

Interstitial                  3 liters       RBCs               

 12 liters                                    2 liters 

                                             

                                                     25 Liters

                                                            Intracellular (ICF)

                 

                        1. Plasma membrane regulates concentrations of substances in each compartment.

                        2. Extracellular also includes lymph, secretions, CSF

                        3. Water is universal solvent

            B.Electrolytes

                        1.solutes dissolved in water

                        2.ionize or dissociate into cations and anions

                                    a.Na major extracellular cation

                                    b.K major intracellular cation

                                    c.Cl major extracellular anion

                                    d.phosphate major intracellular anion

                                    e.Ca intracellular concentrations kept low

                                                (1)higher extracellularly

            C.Nonelectrolytes

                        1.do not dissociate in water

                        2.example: glucose

            D.Water

                        1.metabolic water

                                    a.produced by cellular respiration  WHERE?

                        2.Thirst

                                    a.decrease in plasma volume stimulates

                                     thirst center

                                    b.dry mouth due to less water to make saliva

                        3.Loss of water

                                    a.obligatory

                                                (1)lungs

                                                (2)skin

                                                (3)feces

                                                (4)urine

                        4.dehydration

                                    a.water loss exceeds intake

                        5.edema

                                    a.accumulation of fluid in interstitium

II.Electrolyte balance

            A.refers to salt balance

            B.loss

                        1.perspiration

                        2.feces

                        3.urine

            C.most are sodium salts

                        1.NaCl

                        2.Sodium bicarbonate

            D.Sodium

                        1.major role in electrolyte balance

                        2.kidney function

                        3.ECF Na concentrations remain constant

                                    a.water shifts to maintain homeostasis

                        4.transport of many substances linked to Na

                        5.Hormonal control

                                    a.aldosterone

                                                (1)low sodium or high potassium signals

                                                (2)from adrenal cortex

                                                (3)effects kidney tubules

                                                (4)increases Na reabsorption

                                                (5)increases K secretion

                                                (6)stimulates synthesis of more Na transporters  

                                    b.renin/angiotensin

                                                (1)vasoconstriction

                                                (2)stimulates aldosterone secretion                                                                                

                                    c.Antidiuretic hormone (ADH)

                                                (1)high ADH great reabsorption of water

                                                            (a)concentrated urine output

                                                (2)low ADH very little reabsorption of water

                                                            (a)dilute urine

                                    d.Atrial Natriuretic factor (ANF)

                                                (1)reduces BP and blood volume

                                                (2)inhibits mechanisms to reabsorb Na

                                                (3)signal is stretch receptor in atrium

                                    e.estrogen

                                                (1)stimulates Na reabsorption

                                    f.glucocorticoids

                                                (1)increase GFR

                                                (2)stimulate Na reabsorption

            E.Potassium

                        1.pH regulation

                                    a.shifts of H ions balance with K shifts in

                                                opposite direction

                                    b.High K increases intracellular volume

                                    c.signals secretion of K at tubules

                        2.hormone regulation

                                    a.aldosterone

            F.Calcium

                        1.tightly regulation ion

                        2.role in signalling,blood clotting, as salts in bones

                        3.hormonal regulation

                                    a.Parathyroid hormone (PTH)

                                                (1)to increase blood levels

                                                            (a)absorption at GI

                                                            (b)bone release

                                                            (c)reabsorption in kidneys

                                                            (d)stimulates phosphate excretion

                                    b.calcitonin

                                                (1)calcium deposits enhanced to bone

            G.Chloride

                        1.follows Na

III.ACID-BASE BALANCE

            A.Biochemical activities of cell influenced by pH

                        1.necessary to keep pH in normal physiological range

                        2.buffers

                                    a.resist fluctuations in pH

                        3.alkalosis - increase in pH of body fluids

                        4.acidosis - decrease in pH of body fluids

                        5.acid - donates proton

                        6.base - proton acceptor

            B.Buffer systems

                        1.Bicarbonate buffer system

                                    a.carbonic acid (H2CO3)

                                    b.sodium bicarbonate (NaHCO3)

                                    c.add acid: HCl + NaHCO3-> H2CO3 + NaCl

                                    d.add Base: NaOH+ H2CO3 -> NaHCO3 + H2O

                                    e.important in respiratory regulation

                                                (1)CO2+H2O<->H2CO3<->H + HCO3-

                        2.phosphate buffer system

                                    a.not as important

                                    b.components are sodium salts of

                                                (1) dihydrogen phosphate (acid)

                                                (2) monohydrogen phosphate  (base)

                        3.Proteins act as buffers

                                    a.COOH group donate

                                    b.R-NH2 can accept (NH3)

            C.Renal regulation

                        1.buffer systems tie up acids/bases but must eliminate

                        2.regulates

                                    a.H ion secretion

                                    b.Bicarbonate ion (HCO3) reabsorption

                        3.In urine

                                    a.phophate buffer system

                                    b.ammonium buffer

                                                (1)NH3 from deamination

                                                (2)picks up H to make NH4

                                        4.metabolic acidosis, alkalosis

                                    a.disorders associated with acids/bases

                                                eliminated by kidney

                                    b.compensate by respiratory controls

                        5.respiratory acidosis, alkalosis

                                    a.acidosis - not being able to clear CO2

                                    b.alkalosis - blowing off too much CO2    

                                    c.compensation by kidneys to correct pH