1. Ch 26 Fluid, Electrolyte, and Acid-Base Balance Overview
* Composition & Distribution of fluids in body
* Maintaining levels of important ions, including pH
* Interacting Affects of different organ systems in regulation
Body Fluids & Compartments
A. Total body water: = 40 L  50-60% body weight
3 Compartments
Extracellular fluid (ECF)
Volume = 15 L
20% body weight
Interstitial fluid (IF)
Volume = 12 L
80% of ECF
Intracellular fluid (ICF)
Volume = 25 L
40% body weight

2. B. WATER BALANCE: Water intake = Water loss
100 ml
Feces 4%
Metabolism 10%
250 ml
Sweat 8%
200 ml
Insensible losses
via skin and
lungs 28%
Foods 30%
750 ml
700 ml
2500 ml
Urine 60%
1500 ml
Beverages 60%
1500 ml
Average intake
per day
Average output
per day
Figure 26.4

3. C. Comparison of Extracellular and Intracellular Fluids
Extracellular Fluids: Sodium & Chloride = ions & Plasma has more proteins
Intracellular Fluid: K+ and HPO4-2 = ions, low NaCl & three times the proteins as plasma
Blood plasma
Interstitial fluid
Intracellular fluid
(ICF)
Na+
Sodium K+
Potassium
Ca2+
Calcium
Mg2+
Magnesium
HCO3–
Bicarbonate
Cl–
Chloride
HPO42–
Hydrogen
phosphate
SO42–
Sulfate

4. D. Fluid Movement Among Compartments-- principles
Solutes do not freely diffuse between compartments- use protein carriers, so if solute concen changes  Causes water movement between compartments
Na+ primary solute in ECF: when Na+ concen. changes causes H2O movement, so they are regulated together
Constant exchanges occurs b/n compartments and between plasma and the outside environment
Substances must pass thru plasma and interstitial fluid to get to intracellular fluid
After Solute/water changes: Need adjustments to maintain Homeostasis

5. E. Regulation of Water Normal Day to Day mechanisms
ECF osmolality
Plasma volume*
Normal Day to Day mechanisms
* 1. Decrease in Saliva and Dry mouth Hypothalamic Thirst Center drink water
* 2) Hypothalmic Osmoreceptors-- most important
 Hyp. Thirst Center
Inhibit or stimulate the direct release of ADH from the Post. Pit.
Blood pressure
Saliva
Osmoreceptors
in hypothalamus
Granular cells
in kidney
Renin-angiotensin
mechanism
Dry mouth
Angiotensin II
Hypothalamic
thirst center
Sensation of thirst;
person takes a
drink
Water moistens
mouth, throat;
stretches stomach,
intestine
Water absorbed
from GI tract
Initial stimulus
ECF osmolality
↑ plasma volume
Physiological response
Result
(*Minor stimulus)
Increases, stimulates
Reduces, inhibits
Figure 26.5

6. Water Regulation … For 10-15% drop in BP & Blood Volume
3) Baroreceptors  cause Post. Pit to release ADH
Emergency– For large changes in Blood Volume & BP
4) Kidneys via Renin- Angiotensin II
If BP ↓ then Granular cells release Renin 
Angiotensen II which directly affects Hypo Thirst center
 ADH ↑ & Aldosterone ↑
Osmolality
Na+ concentration
in plasma
Plasma volume
BP (10–15%)
Stimulates
Kidney-renin
Osmoreceptors
in hypothalamus
Inhibits
Negative
feedback
inhibits
Baroreceptors
in atrium and
large vessels
Stimulates
Stimulates
Posterior pituitary
Releases
ADH
Antidiuretic
hormone (ADH)
Targets
Collecting ducts
of kidneys
Effects
Water reabsorption
Results in
Osmolality
Plasma volume
Scant urine

7. III. Electrolyte Balance
K+ (or Na+) concentration
in blood plasma*
Renin-angiotensin
mechanism
Na+ = most abundant ion of ECF-Most Na+ is normally reabsorbed
Importance
2) Regulation: always Reabsorbs 65% of Na by PCT & 25% by loops:
10%: regulated mainly by BP
a) Aldosterone
causes reabsorption of remaining Na+ at Dist. CT & Collecting Duct (H2O follows)
If release inhibited no Na+ reabsorbed
Stimulates
Adrenal cortex
Negative
feedback
inhibits
Releases
Aldosterone
Targets
Kidney tubules
Effects
Normal
Na+ reabsorption
K+ secretion
Restores
Homeostatic plasma
levels of Na+ and K+
Also K+ secreted

8. K+ (or Na+) concentration
Emergency Conditions– BP changes regulate
c) Renin  Angiotensin II  Adosterone & ADH Result: Na+ H2O reabsorbed if BP drops significantly
d) Cardiovascular Sys:
If High BP ANP release stimulated by atrial stretching
Affects: inhibits renin mechanism: inhibits Na+ and water reabsorption and vasoconstriction
Net Result: ↓ BP
K+ (or Na+) concentration
in blood plasma*
Renin-angiotensin
mechanism
Stimulates
Adrenal cortex
Negative
feedback
inhibits
Releases
Aldosterone
Targets
Kidney tubules
Effects
Na+ reabsorption
K+ secretion
Restores
Homeostatic plasma
levels of Na+ and K+

9. Overview: Water, BP, Na+ DAY-TO-DAY-- NORMAL
GLOMERULAR FILTRATION RATE
Myogenic
(Tubuloglomerular)
WATER REGULATION
Dry Mouth & Osmoreceptors  thirst and increased ADH
Na+ REGULATION via Aldosterone
___________________________________________________
EMERGENCY– Cardiovascular kicks in
MAINTAIN BP & Blood Volume:
Sympathetic
Renin release
Atrial Natriuetic Peptide

10. IV. Acid-Base Balance A. Basic Concepts-- introduction
Importance: pH affects all functional proteins and biochemical reactions
If one compartment has a pH change, another does too
Normal pH of body fluids
Arterial blood: pH 7.4
Venous blood and IF fluid: pH 7.35
ICF: pH 7.0
Alkalosis: arterial blood pH >7.45
Acidosis: arterial pH < 7.35
Most H+ produced by metabolism, not food: protein & fat break down, lactic acid formation, CO2 transport

11. Mechanisms for Regulating Acid-Base Balance
H+ is regulated sequentially by
1) Chemical buffer systems: rapid (seconds); used 1st
a) Bicarbonate buffer system– most important ECF buffer
b) Phosphate “ “: buffers ICF & urine
c) Protein “ “ - most important ICF buffer
2) Respiratory System: Brain stem respiratory centers act within 1–3 min CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3-
Respiratory Acidosis: if have shallow, slow breathing will cause less CO2 to be exhaled
Respiratory Alkalosis: if have deep, fast breathing = hyperventilation and will cause too much CO2 exhaled
3) Renal mechanisms: most potent, but take hours to days
a) SECRETION OF H+: Mainly PCT
b) Secretion of Bases
c) Formation of Buffers

12. Abnormalities of Acid-Base Balance
Metabolic acidosis and alkalosis = multiple causes including kidney failure (= abnormal HCO3- levels)
Hypoventilation causes elevated PCO2 (respiratory acidosis)
Renal compensation is indicated by high HCO3– levels
Respiratory alkalosis exhibits low PCO2 and high pH
Renal compensation is indicated by decreasing HCO3– levels
Respiratory buffer can ‘compensate’ for metabolic imbalances
Renal buffer can ‘compensate’ for respiratory imbalances

13. END

14. Review Questions
Hypoventilation causes respiratory _________. The renal physiological buffer effectively removes ___ ions by reabsorbing or generating new _____ ions which then ________ blood pH. The renal system secretes some HCO3- ions too compensate for respiratory __________.
acidosis H+
HCO3-
raises
alkalosis

15. Review Questions
Na+
___ is the most abundant ECF electrolyte and is regulated mainly by the hormone __________ (and sometimes ANP). The major inorganic buffer of the ECF = __________. The major inorganic buffer of the ICF = __________. The most powerful buffer system is the ________ system.
aldosterone
bicarbonate
phosphate
protein

16. Review Questions
The 2 major body fluid compartments are the _____ and the _____. The ECF is further divided into ______ and the ________________. The ___________ stimulates thirst sensations and releases ____ in response to increased plasma osmolality.
ICF
ECF
plasma
interstitial fluid
hypothalmus
ADH