3. Mnemonic for kidneys functions WET BREAD .
W – maintaining WATER balance
E – ELECTROLYTE balance
T – TOXIN removal
B – BLOOD Pressure control
R- Renin Formation
E –ERYTHROPOIETIN making
A – maintaining ACID-base balance
D – Vitamin D metabolism.

4. Water, Electrolyte, and
Acid-Base Balance

5. Human cells dwell in salt water.
Their well-being depends on the ability of the body to regulate the salinity of ECF.
By controlling water intake and excretion, the osmo-regulatory system normally prevents the plasma sodium concentration from going outside its normal range (135 to 145 mmol per liter).
Failure of the system to regulate within this range exposes cells to hypotonic or hypertonic stress.

6. The plasma sodium concentration affects cell volume.
The term “tonicity” describes the effect of plasma on cells
— Hypotonicity makes cells swell and
___Hypertonicity makes them shrink.

7. Fluid and Electrolyte Balance
Fluids constitute ~50%–60% of total body composition in which Minerals are dissolved and forming electrolytes
Fluid compartments
Intracellular fluid (ICF)
Extracellular fluid (ECF)

8. Adult females Other body fluids (≤1%) Other body fluids (≤1%)
Total body composition of adult males and females
WATER 60%
ECF
ICF
Intracellular fluid 33%
Interstitial fluid 21.5%
Plasma 4.5%
Other body fluids (≤1%)
Solids 40% (organic and inorganic materials)
Adult males
SOLIDS 40%
WATER 50%
ECF
ICF
Figure 24 Section 1.1 Fluid and Electrolyte Balance
Intracellular fluid 27%
Interstitial fluid 18%
Plasma 4.5%
Other body fluids (≤1%)
Solids 50% (organic and inorganic materials)
Adult females
SOLIDS 50% 8

9. The solid components of a 70-kg (154-pound) individual with a minimum of body fat
(31.5 kg; 69.3 lbs) Kg
Figure 24 Section.1.2 Fluid and Electrolyte Balance
Proteins
Lipids
Minerals
Carbohydrates
Miscellaneous 9

10. Changes in Water Content with Age
Water content-varies with gender, body mass and age. The percentage of body weight the is composed of water is generally greater I men than women because men tend to have more lean bodymass than women. Fat cells contain less water than an equivalent volume of lean tissue.
One liter of water weights 2.2 lb (1kg). Therefore body weight change is an excellent indicator of overall fluid volume loss or gain. If a pt. D
rinks 240 ml (8oz) there will be a weight gain of 0.5lb (0.24kg), an adult who is fasting might lose 1-2 lbs per day, most in fluids.
Thus, infants and elderly are at a higher risk for fluid related problems than young adults

11. Fluid balance Water content stable over time Gains Losses
Primarily absorption along digestive tract
As nutrients and ions are absorbed, osmotic gradient created causing passive absorption of water
Digestive secretions which are reabsorbed similarly to ingested fluids
Losses
Mainly through urination (over 50%) but other routes as well

12. Figure 24.1.1 Fluid balance exists when water gains equal water losses12

13. Fluid balance = Fluid shift
ICF and ECF compartments balance
Vary in composition
Are at osmotic equilibrium
Loss of water from ECF is replaced by water in ICF
= Fluid shift
Occurs in minutes to hours and restores osmotic equilibrium
Dehydration
Results in long-term transfer that cannot replace ECF water loss
Homeostatic mechanisms to increase ECF fluid volume will be employed

14. The major factors that affect ECF volume
Water absorbed across digestive epithelium (2000 mL)
Water vapor lost in respiration and evaporation from moist surfaces (1150 mL)
ECF
Metabolic water (300 mL)
Water lost in feces (150 mL)
ICF
Water secreted by sweat glands (variable)
Figure Fluid balance exists when water gains equal water losses
Plasma membranes
Water lost in urine (1000 mL) 14

15. Mineral balance Mineral balance
Equilibrium between ion absorption and excretion
Major ion absorption through intestine and colon
Major ion excretion by kidneys
Sweat glands excrete ions and water variably
Ion reserves mainly in skeleton

16. (in the digestive tract) and ion excretion (primarily at the kidneys)
Mineral balance, the balance between ion absorption
(in the digestive tract) and ion excretion (primarily at the kidneys)
Ion Absorption
Ion Excretion
Ion reserves (primarily in the skeleton)
Ion absorption occurs across the epithelial lining of the small intestine and colon.
Sweat gland secretions (secondary site of ion loss)
Ion pool in body fluids
Kidneys (primary site of ion loss)
Figure Mineral balance involves balancing electrolyte gains and losses
ICF
ECF 16

17. Figure 24.2.2 Mineral balance involves balancing electrolyte gains and losses17

18. The mechanisms that regulate water balance when ECF volume changes
Responses to Natriuretic Peptides
Combined Effects
Increased Na loss in urine
Reduced blood volume
Increased water loss in urine
Rising blood pressure and volume
Natriuretic peptides released by cardiac muscle cells
Reduced thirst
Reduced blood pressure
Inhibition of ADH, aldosterone, epinephrine, and norepinephrine release
Increased blood volume and atrial distension
HOMEOSTASIS RESTORED
HOMEOSTASIS DISTURBED
Falling ECF volume
Figure Water balance depends on sodium balance, and the two are regulated simultaneously
Rising ECF volume by fluid gain or fluid and Na gain
HOMEOSTASIS
Start
Normal ECF volume 18

19. The mechanisms that regulate water balance when ECF volume changes
HOMEOSTASIS
Start
Normal ECF volume
HOMEOSTASIS DISTURBED
HOMEOSTASIS RESTORED
Falling ECF volume by fluid loss or fluid and Na loss
Rising ECF volume
Decreased blood volume and blood pressure
Endocrine Responses
Combined Effects
Increased renin secretion and angiotensin II activation
Increased urinary Na retention
Figure Water balance depends on sodium balance, and the two are regulated simultaneously
Decreased urinary water loss
Increased aldosterone release
Falling blood pressure and volume
Increased thirst
Increased ADH release
Increased water intake 19

20. Water and sodium balance
Sodium balance (when sodium gains equal losses)
Relatively small changes in Na+ are accommodated by changes in ECF volume
Homeostatic responses involve two parts
ADH control of water loss/retention by kidneys and thirst
Fluid exchange between ECF and ICF

21. HOMEOSTASIS ADH Secretion Increases Recall of Fluids
The mechanisms that regulate sodium balance when sodium concentration in the ECF changes
ADH Secretion Increases
Recall of Fluids
The secretion of ADH restricts water loss and stimulates thirst, promoting additional water consumption.
Because the ECF osmolarity increases, water shifts out of the ICF, increasing ECF volume and lowering ECF Na concentrations.
Rising plasma sodium levels
Osmoreceptors in hypothalamus stimulated
If you consume large amounts of salt without adequate fluid, as when you eat salty potato chips without taking a drink, the plasma Na concentration rises temporarily.
HOMEOSTASIS RESTORED
HOMEOSTASIS DISTURBED
Decreased Na levels in ECF
Increased Na levels in ECF
Figure Water balance depends on sodium balance, and the two are regulated simultaneously
HOMEOSTASIS
Start
Normal Na concentration in ECF 21

22. The mechanisms that regulate sodium balance when sodium concentration in the ECF drops
HOMEOSTASIS
Start
Normal Na concentration in ECF
HOMEOSTASIS DISTURBED
HOMEOSTASIS RESTORED
Decreased Na levels in ECF
Increased Na levels in ECF
Osmoreceptors in hypothalamus inhibited
Water loss reduces ECF volume, concentrates ions
ADH Secretion Decreases
Figure Water balance depends on sodium balance, and the two are regulated simultaneously
As soon as the osmotic concentration of the ECF drops by 2 percent or more, ADH secretion decreases, so thirst is suppressed and water losses at the kidneys increase.
Falling plasma sodium levels 22

23. Water and sodium balance
Sodium balance (continued)
Changes in Na+ are accommodated by changes in blood pressure and volume
Hyponatremia
Low ECF Na+ concentration (<136 mEq/L)
Can occur from overhydration or inadequate salt intake
Hypernatremia
High ECF Na+ concentration (>145 mEq/L)
Commonly from dehydration

24. Water and sodium balance
Sodium balance (continued)
Changes in Na+ are accommodated by changes in blood pressure and volume (continued)
Increased blood volume and pressure
ArtrialNatriuretic peptides released
Increased Na+ and water loss in urine
Reduced thirst
Inhibition of ADH, aldosterone, epinephrine, and norepinephrine release
Decreased blood volume and pressure
Endocrine response
Increased ADH, aldosterone, RAAS mechanism
Opposite bodily responses to above

25. Potassium imbalance Potassium balance (K+ gain = loss)
Major gain is through digestive tract absorption
~100 mEq (1.9–5.8 g)/day
Major loss is excretion by kidneys
Primary ECF potassium regulation by kidneys since intake fairly constant
Controlled by aldosterone regulating Na+/K+ exchange pumps in DCT and collecting duct of nephron
Low ECF pH can cause H+ to be substituted for K+
Potassium is highest in ICF due to Na+/K+ exchange pump
~135 mEq/L in ICF vs. ~5 mEq/L in ECF

26. The major factors involved in potassium balance
Factors Controlling Potassium Balance
Approximately 100 mEq (1.9–5.8 g) of potassium ions are absorbed by the digestive tract each day.
Roughly 98 percent of the potassium content of the human body is in the ICF, rather than the ECF.
The K concentration in the ECF is relatively low. The rate of K entry from the ICF through leak channels is balanced by the rate of K recovery by the Na/K exchange pump.
When potassium balance exists, the rate of urinary K excretion matches the rate of digestive tract absorption.
The potassium ion concentration in the ECF is approximately 5 mEq/L.
Figure Disturbances of potassium balance are uncommon but extremely dangerous
KEY
 Absorption
The potassium ion concentration of the ICF is approximately 135 mEq/L.
Renal K losses are approximately 100 mEq per day
 Secretion
 Diffusion through leak channels 26

27. The role of aldosterone-sensitive exchange pumps in the kidneys in determining the potassium concentration in the ECF
The primary mechanism of potassium secretion involves an exchange pump that ejects potassium ions while reabsorbing sodium ions.
Tubular fluid
ECF
The sodium ions are then pumped out of the cell in exchange for potassium ions in the ECF. This is the same pump that ejects sodium ions entering the cytosol through leak channels.
KEY
Figure Disturbances of potassium balance are uncommon but extremely dangerous
 Aldosterone sensitive exchange pump
 Sodium-potassium exchange pump 27

28. Distal convoluted tubule
Events in the kidneys that affect potassium balance
Under normal conditions, the aldosterone-sensitive pumps exchange K in the ECF for Na in the tubular fluid. The net result is a rise in plasma sodium levels and increased K loss in the urine.
Distal convoluted tubule
When the pH falls in the ECF and the concentration of H is relatively high, the exchange pumps bind H instead of K. This helps to stabilize the pH of the ECF, but at the cost of rising K levels in the ECF.
Collecting duct
Figure Disturbances of potassium balance are uncommon but extremely dangerous 28

29. Potassium imbalance Disturbances of potassium balance Hypokalemia
Below 2 mEq/L in plasma
Can be caused by:
Diuretics
Aldosteronism (excessive aldosterone secretion)
Symptoms
Muscular weakness, followed by paralysis
Potentially lethal when affecting heart

30. Potassium imbalance Disturbances of potassium balance (continued)
Hyperkalemia
Above 8 mEq/L in plasma
Can be caused by:
Chronically low pH
Kidney failure
Drugs promoting diuresis by blocking Na+/K+ pumps
Symptoms
Muscular spasm including heart arrhythmias