CH. 27 - WATER, ELECTROLYTES & ACID-BASE BALANCE

I. BODY FLUID COMPARTMENTS (**KNOW Tab. 27.1, p. 1000)

            A. INTRACELLULAR - 40% body wt.

            B. EXTRACELLULAR - 20% body wt.

                        1. PLASMA - 5%

                        2. INTERSTITIAL - 15%

                        3. Lymph, CSF, Synovial fluid, Perilymph, etc.

II. REG. OF H₂O CONTENT

            A. WATER IN = WATER OUT, 1.5-3 L/Day (Tab. 27.3, p. 1001)

            B. WATER GAINED/CONSERVED (Fig. 27.1, p. 1002)

                        1. THIRST - INGESTION - 90%

                                    a. OSMORECEPTORS in hypothalamus thirst center

                                                As blood osmolality é è thirst é

                                    b. BARORECEPTORS

                                                As B.P. ê è thirst é

                                    c. ORAL MUCOSA - if dry è é thirst

                                    d. STRETCH RECEPTORS in stomach è ê thirst if stretch

                        2. HORMONES (Fig. 27.2, p. 1003)

                                    a. ADH, Renin/Angio, Aldosterone è é H₂O reabsorb.

                                    b. Atrial è ê H₂O reabsorb

                        3. CELLULAR METABOLISM - 10%

            C. WATER LOSS (Tab. 27.3, p. 1001)

                        1. URINARY SYSTEM - 61% - kidneysè urine

                        2. EVAPORATION - 35%

                                    a. Skin - INSENSIBLE PERSPIRATION - NO electrolytes

                                                  - SENSIBLE PERSPIRATION - electrolytes

                                                  - 25% of body heat lost via perspiration

                                    b. Respiration - water vapor

                        3. DIGESTIVE SYSTEM - 4% - Feces

                                    a. Problems - Diarrhea & vomiting

III. REG. OF EXTRACELLULAR FLUID

            A. H₂O & ELECTROLYTES

                        1. HOMEOSTASIS - Intake = Output

                        2. Move ions actively & H₂O will move passively

            B. REGULATED BY:

                        1. DIGESTIVE

                        2. URINARY

                        3. RESPIRATORY

                        4. INTEGUMENTARY

            C. COORDINATED BY:

                        1. NERVOUS

                        2. ENDOCRINE

IV. REGULATION OF INTRACELLULAR FLUID

            A. PLASMA MEMBRANE (Fig. 27.7, p. 1007)

                        1. Intracell. vs. Interstitial/Extracell. (KNOW Table 27.2, p. 1000)

                        2. Extracell. fluid strongly influences H₂O movement

                        3. H₂O moves by osmosis w/ concentration gradients

V. REG. OF [ION] - 4

            A. SODIUM (Tab. 27.5, p. 1009)

                        1. Most lost via KIDNEYS, some by sweat

                                    a. < 0.5 g needed/day, intake 20-30 g/day, lots excreted/secreted

                                    b. If Na⁺ low, aldosterone é èNa⁺ reabsorp. @ D.C.T. & C.D.

                        2. B.P./ Osmolarity

a.    If B.P. é è é Atrial, ê ADH, Ren/Ang/Aldo è ê Na⁺ &

            H₂O reabsorp @ D.C.T. & C.D. è é Na⁺ & H₂O loss è

                                                é urine volume

b.    If B.P. ê opposite happens

            B. CHLORIDE - follows Na⁺

            C. POTASSIUM (Fig. 27.8, p. 1012)

                        1. Most closely regulated ion - RMP of elect. excit. cells

                        2. If [K⁺] éèAldosterone é è é K⁺ secretion in D.C.T.

                        3. If [K⁺] ê èAldosterone ê  èê K⁺ secretion in D.C.T.

            D. CALCIUM

                        1. Also closely regulated - RMP, Ca²⁺ channels/gates

                        2. If [Ca²⁺] low è é PTH (most imp.) è é Extracell. [Ca²⁺]

                                    a. é Ca²⁺ reabsorp. in kidneys

                                    b. é OsteoCLASTS - bone breakdown

                                    c. é Vit. D. è é Ca²⁺ uptake in intestine

                        3. If [Ca²⁺] high è é CALCITONIN è ê Extracell. [Ca²⁺]

                                    a. é OsteoBLASTS - bone deposition

VI. REG. OF ACID-BASE BALANCE - pH, [H⁺]

     - pH affects enzyme function - activation, denaturing

     - Normal pH is 7.35-7.45 in blood & interstitial fluids

     - ACIDS release H⁺ into solution, pH 1-6

            Strong: dissociate completely: HCl èH⁺ + Cl^-

            Weak: dissociate partially: H₂CO₃ èH⁺ + HCO₃^-

     - ACID-BASE Balance reg. by 2 major systems

            A. BUFFERS (Tab. 27.11, p. 1017 & Fig. 27.12, p. 1018)

                 - Resist pH changes

                 - Donates or removes H⁺ to keep pH stable

                        1. CARBONIC ACID-BICARBONATE

                        2. PROTEIN

                        3. PHOSPHATE

                        4. AMMONIA - by-product of protein metabolism

                                    NH₃ + H⁺ Û NH₄⁺ + Cl^- Û NH₄Cl

            B. REGULATORY MECHANISMS - 2

                        1. RESPIRATORY - RAPID response to pH change (Fig. 27.13, p. 1019)

                                    (LUNGS)

                                    H₂O + CO₂ Û H₂CO₃ Û H⁺ + HCO₃^-

                           a. IF pH ê -----------------> Less CO₂ exhaled, [CO₂] é (exercise)

                                    Response: é respiration, move eqn to left, raises pH

                           b. IF pH é <----------------- Extra CO₂ exhaled, [CO₂] ê (rest)

                                    Response: ê respiration, move eqn to right, lowers pH

                        2. URINARY/METABOLIC - SLOWER response to pH change (Fig. 27.14, p. 1020)

                                    (KIDNEYS)

- ONLY system to actively remove/secrete H⁺

                           a. IF pH ê, secrete excess H⁺ into urine via D.C.T. + C.D.

                                    Urine pH can go to 4.5

                           b. IF pH é, retain/reabsorb H⁺ in P.C.T., don’t secrete it

                                    Urine pH can go to 8.5

            C. ACIDOSIS                    CO₂     pH                       ALKALOSIS (p. 1022-1023)

            pH < 7.35                                   D                            pH > 7.45

            If < 6.8 = death                                                           If > 7.8 = death

1. RESPIRATORY   

            a. Due to HYPOventilation                           a. Due to HYPERventilation

              [CO₂] é in blood è ê pH                 [CO₂] ê in blood è é pH

            b. RESPONSE: HYPERventilate to get     b. RESPONSE: HYPOventilate (breathe in bag)

               rid of CO₂ è é pH                                       to retain CO₂ è ê pH

2. METABOLIC

            a. Due to loss of HCO₃^-                                a. Due to loss of H⁺

                        Diarrhea è ê pH                                        Vomiting è é pH

            b. Buffer adds HCO₃^-                                    b. Buffer adds H⁺

                        BICARBONATE   :    CARBONIC ACID

Normal:                       20                                1

Resp. Acido:              8-10                            1

Meta. Acido:              12-13                          1

Resp. Alka.                40                                1

Meta. Alka.                 31-32                          1