CHAPTER 21 WATER AND ELECTROLYTE BALANCE
I. Where are body fluids found? Fig. 21.1 and Fig. 21.2

A. Intracellular fluid compartment

1. Enclosed by __________________________

2. ____________ % of body fluid

B. Extra-cellular fluid compartment
1. All fluids & electrolytes ________________________________________

2. ______________ % of body fluid

a. Interstitial fluid

b. ______________________

c. ______________________
d. Trans-cellular fluid within body cavities separated from other extra-cellular fluid by a layer of epithelium.

1.) Cerebrospinal fluid
2.) Aqueous humor & vitreous body of eyes
3.) Synovial fluid in joints
4.) Serous fluid in body cavities: pleural, pericardial, peritoneal
5.) Secretions of glands
6.) Perilymph in ears
7.) Glomerular filtrate

II. Concentrations of ions in fluid Fig. 21.3

A. Extracellular fluid
1. Ninety % of extra-cellular ions are ______________

2.__________ is the most abundant ion in ECF

3.__________ is the second most abundant ion in ECF

B. Intrcellular fluid

1._________ is the most abundant ion in ICF

C. Draw a cell. Place cations and anions inside and outside the cell.
 
 
 
 
 

III. Movement between compartments Fig. 21.4

A. Occurs because of hydrostatic pressure, osmotic pressure & Na⁺ concentrations.
1. Ions are unequally distributed because of their molecular size, electrical charge, or dependence on active transport.
2. Any change in solute concentration in any compartment results in net water movement.

B. Major difference between plasma & interstitial fluid

1. Plasma contains many ____________ anions

2. Interstitial fluid contains ______________________

3. Plasma contains more ___________________ than interstitial fluid

C. Electrolytes have the greatest ability to cause fluid shifts.

1. Electrolytes include inorganic salts, inorganic and organic acids and bases and some proteins.
2. All dissolved solutes contribute to osmotic activity, but electrolytes have greater osmotic power than non-electrolytes.

a. NaCl dissociates and contributes twice as many solute particles as glucose which does not dissociate. Magnesium chloride, MgCl_2, contributes how many solute particles?

b. Water moves according to osmotic gradients from areas of lesser osmolality to those of greater osmolality.

IV. Where do we get the water in our bodies? 2500 ml/day Fig. 21.5

A. ___________________ 60%

B. ___________________ 30%
C. Metabolic water or water of oxidation - 10%
1. Write the formula for the production of metabolic water.

V. What regulates water intake? Clinical insert

A. Thirst center in hypothalamus of brain that responds to osmotic pressure of extra-cellular fluid.
1. Water lost from body:sweat, urination, feces, insensible loss (evaporation from skin and lungs)
2. Osmotic pressure of extra-cellular fluid increases
3. Osmoreceptors in thirst center stimulated (hypothalamus)
4. Decrease in total body H₂0 of ___ to ___ % will trigger the thirst mechanism.
5. Act of drinking & distention of stomach = inhibition (example: dogs)

VI. How do we lose the water? Fig. 21.6

A. Excreted in feces � 4%
B. Excreted in sweat � 8%
C. Insensible loss = evaporation from skin & lungs (incr. in desert) � 28%
E. Majority lost through urine � 60%
1. Distal convoluted tubule & collecting duct are impermeable to H₂0
2. Water leaves plasma at glomerulus, enters tubules, ureters, bladder
3. ADH, anti-diuretic hormone from p. pit., makes them permeable to H₂0
a. Occurs when fluid volume is low
b. Water moves from tubules to interstitial fluid to blood vessels

4. Mechanism is inhibited when we take in excess H₂0

F. Alcohol & some narcotics promote urine formation by inhibiting release of ADH
G. Diuretics promote production of urine by increasing pressure in blood vessels
H. Caffeine and most diuretic drugs promotes urine flow by inhibiting sodium ion reabsorption and thus water reabsorption.

VI. How the kidneys maintain the osmolality of the extracellular fluid? Fig. 21.7

A. In 30 minutes the volume of fluid entering the PCT is greater than the total plasma volume; thus, it is critical that the nephron return most of the filtered water and many of the filtered solutes to the bloodstream.

B. Processes involved
1. Filtration at the glomerulus
a. Capillary endothelium with fenestrae
b. Basement membrane of capillary embedded with glycoproteins with a strong negative charge.
c. Podocytes of epithelial cells of Bowman's capsule

2. Reabsorption � primarily at the PCT
3. Secretion

VII. Major electrolytes involved

A. SODIUM � Na⁺ Fig. 21.8

1. Regulated by aldosterone from adrenal cortex
2. Causes _____ in Na⁺ reabsorption in collecting duct of renal tubule
3. Lack of aldosterone causes Addison's Disease (low extracellular Na⁺)

B. POTASSIUM � K⁺ Fig. 21.8

1. Regulated by ________________________ from adrenal cortex
2. High K⁺ level in blood stimulates aldosterone production
3. Aldosterone causes reabsorption of Na⁺ and secretion of K⁺ (attracted by neg. charge in collecting duct after Na⁺ is reabsorbed.

C. CALCIUM- Ca^{+ 2} Fig. 21.9
1. Low calcium level stimulates PTH production
2. Osteoclast activity increases
3. Levels of calcium and phosphate increase in blood
4. PTH also stimulates absorption of calcium from intestines (vit. D)
5. Kidneys will conserve calcium and excrete phosphate (PO₄^-3)
6. High calcium levels

a. __________________ produced; o'blasts stimulated; make bone
b.Renal tubule excretes calcium
c.Negatively charged ions passively follow
d.Phosphate and sulfate are regulated by active transport

VIII. Role of hormones in reabsorption and secretion of ions

A. Aldosterone

1. Released from _____________________ cortex
2. Acts on DCT and CD
3. Increases reabsorption of Na⁺ back into blood and secretion of K⁺
4. Water and Cl^- follow Na⁺
5. When
a. Decrease in blood volume
b. Decrease in cardiac output
c.Increase in E.C. K⁺

B. Atrial natriuretic peptide
1. Causes excretion of Na⁺ by kidneys when Na⁺ is in excess

C. Anti-diuretic hormone

1. Secreted by __________________________________
a. Causes DCT and CD to become more permeable to water
b. Water flows into ICF
c. Urine becomes more and more concentrated
d. ADH also makes the CD more permeable to urea
e. Urea goes into ICF increasing its osmolarity

IX. Acid-Base Balance Fig. 21 c

A. Acids
1. Substances that ionize in water and release H⁺
2. Proton donors
3. H is written first in an acid.
4. Examples: acetic acid, HC₂H₃O₂; carbonic acid, H₂CO₃
5. Example:
 
 
 
 
 

B. Bases
1. Substances that ionize and combine with H⁺
2. Proton acceptors
3. Bases in humans: bicarbonate, HCO₃ (carries CO₂), ammonia, NH₃ (combines with H⁺ to form NH4⁺, which is eliminated)
4. Example:
 
 
 

C. Acidosis/Alkalosis � Pay close attention to diagrams in this section. Fig. 21.d
1. Respiratory acidosis Fig. 21e

a. ________ in CO2

1.) ______ in rate/depth of breathing

2.) ______ in gas exchange
3.) Obstruction of air passages

2. Metabolic acidosis Fig. 21f

a. _____ in nonrespiratory acids
1.) Kidneys fail to excrete acids

2.) ____ in production of acidic ketones

b. Excessive loss of bases
1.) Prolonged diarrhea and loss of alkaline intestinal secretions
2.) Prolonged vomiting with loss of intestinal secretions

3. Respiratory alkalosis fig. 21 g
a. Hyperventilation leading to excessive loss of CO₂. This results in a decrease in conc. of H₂CO₃ leading to ____ in conc. of H+.
1.) Anxiety
2.) Fever
3.) Poisoning
4.) High altitude

4. Metabolic alkalosis fig. 21 h

a. Loss of acids leading to ___ in alkaline substances
1.) Gastric drainage
2.) Vomiting with loss of gastric secretions

D. What controls the numbers of H⁺ in the body?
1. Buffer systems
a. Buffer: a solution of two or more chemical compounds that can prevent a marked change in H+ concentration when either an acid or base is added.

2. Acid-base buffers (take 2 - 4 hours)
a. Chemicals in body that take in H+ when fluids become acidic
b. Chemicals in body that give up H+ when fluids become basic

4. Examples of chemical buffers (refer to book for formulas; fill in examples below).
a. Bicarbonate buffer system
 
 
 
 
b. Phosphate buffer system
 
 
 
c. Protein buffer system
 
 
 
 

5. Physiological buffers
a. Respiratory center in brain stem
1. Works instantly when CO₂ and H⁺ concentration increase
2. Stimulates breathing so CO₂ is exhaled.
3. Example.
 
 
 
 

b. Kidneys
1. Nephrons regulate pH by secreting H+ into urine.
2. Ammonia (NH3) transports H+ to urine
3. Example