CHEM  30 B    Dr. R. Rinehart
BODY  FLUIDS

I.  Types of body fluids:    42 L total 
           A.  Intracellular:  28 L 
                        1.  High K⁺, HPO₄^-2; moderate SO₄^-2 , protein^- ; low Na⁺, Cl^-   
                        2.  Partitioned among trillions of cells, but can be considered as a unit           

B.  Extracellular: 14 L   
                        1.  High Na⁺, Cl-; moderate HCO₃^-; low K⁺, Ca⁺², HPO₄^-2    
                        2.  Several types
                                    a.  Interstitial fluid: 10.5 L
                                    b.  Blood plasma:  3.5 L
                                    c.  Cerebrospinal, ocular, joint fluids
                                    d.  Digestive secretions
                                    e. URINE

 II. FLUID BALANCE    

            A. INTAKE                           2400 mL/day     average
                        1. Ingested liquids         1500 mL/day
                        2. “solid” foods               700 mL/day
                        3. Electron transport      200 mL/day            

B.  OUTPUT                          2400 mL/day
                        1.  Lungs                         350 mL/day    obligatory
                        2.  Skin: diffusion           350 mL/day     (“intangible” perspiration)  obligatory
                        3.  Skin: perspiration     100+ mL/day    (“tangible” perspiration)
                        4.  Feces                         200 mL/day    minimum average; 
                        5. URINE                     1400 mL/day   average;  500 mL/day obligatory minimum

              C.  G.I. TURNOVER  ~8200 mL/day secreted, ~ 8000 mL/day reabsorbed
                        Saliva                                      1500  mL/day
                        Gastric Secretions                2500  mL/day
                        Bile                                         500  mL/day
                        Pancreatic juice                     700   mL/day
                        Intestinal secretions             3000  mL/day  

                    CIRCULATORY TURNOVER
                        Transcapillary fluid exchange ~ 25,000 L/day
                              balance between hydrostatic pressure [varies with distance from heart]
                                and colloid osmotic pressure due to plasma proteins
                             

                                           *********KIDNEY FACTS*****************

                        Total renal plasma flow        650 mL/min   [~20% of cardiac output] 
                        filtration fraction       =          0.19
                        Glomerular filtration rate     125 mL/min    plasma “reworked” ~ 50X/day
                        Rate of urine formation        ~ 1 mL/min

D.  “Tonicity”  of  body fluids: isotonic, hypertonic, and hypotonic
                        1.  Isotonic ≡ 
                        2.  Abnormalities of fluid balance
            E.  Regulation  
                        1. Thirst mechanism  
                        2.  Antidiuretic hormone (vasopressin) 

III.  Transport of material by body fluids 
            A.  Oxygen and carbon dioxide 
            B.  Other substances   

IV.  ACID-BASE BALANCE   
            A.  BUFFER CONTROL of blood pH
                        1. The Henderson-Hasselbalch equation
                                    pH = pK_a + log{[A^-] / [HA]} 
                        2. In blood plasma, the bicarbonate-carbonic acid system is the most important buffer
                                    H₂CO₃  ⇄  H⁺ + HCO₃^-   pK_a = 6.1
                                    7.4 = 6.1 + log {[HCO₃^-] / [H₂CO₃]}
                                    normally, then            [HCO₃^-] = 20 x [H₂CO₃]   
                        3. The LUNGS, under instruction from respiratory control centers in the brain,
                              control [H₂CO₃] by adjusting the rate of respiration 
                        4.  The KIDNEYS control [HCO₃^-]   

            B.  ACIDOSIS and ALKALOSIS     
                        1.  Respiratory acidosis: caused by hypoventilation;        [H₂CO₃] increases 
                        2.  Respiratory alkalosis: caused by hyperventilation;     [H₂CO₃] drops 
                        3. “Metabolic” acidosis:         [HCO₃^-] drops
                                    a.  Acid-producing diet (high-protein, S à H₂SO₄)
                                    b.  Metabolic disorders like diabetes mellitus: ketoacidosis
                                    c.  Kidney failure: acid wastes accumulate
                                    d.  Loss of alkaline fluids: diarrhea 

                        4. “Metabolic” alkalosis:        [HCO₃^-] increases
                                    a.  Alkali-producing diet (all-fruit); consumes body H⁺ 
                                    b.  Certain kidney disorders
                                    c. Loss of acidic body fluids: vomiting 

            C. Treatment
                        1.  Immediate: correct pH imbalance by administering NaHCO₃ or ACD and/or
                                         respiratory measures like rebreathing CO₂ or promoting hyperventilation 
                        2.  Long-term: correct underlying condition; dialysis

© Ronald W. Rinehart, 2002, 2006