Chapter 26

Body water content

50-60% of body mass is water

Two main fluid compartments

* intracellular fluid compartment
* extracellular fluid compartment

Intracellular fluid compartment

fluid inside cells accounts for 2/3 of total body fluid

Extracellular fluid compartments

Fluid in 2 main ECF compartments outside cells accounts for 1/3 of total body fluid; plasma and interstitial fluid

Role of electrolytes

help balance osmosis

Role of albumin

helps with reabsorption

Solutes

* substances dissolved in water
* classified as electrolytes and nonelectrolytes

Nonelectrolytes

* most are organic molecules
* do not dissociate in water
* ex. glucose, lipids, creatine

Electrolytes

* ions conducted electrical current
* greater osmotic power than nonelectrolytes
* dissociate into ions in water
* ex. inorganic salts, acids, bases, some proteins

Buffers

* bicarbonate
* phosphate
* protein

Normal pH

7\.35-7.45

What causes blood to be more acidic

CO2

Normal CO2 level

35-45mmHg

Hypoventilation

causes respiratory acidosis

Hyperventilation

causes respiratory alkalosis

Acidosis

not getting rid of enough CO2

Alkalosis

Getting rid of too much CO2

Inhibitory feedback signals

* relief of dry mouth
* activation of stomach and intestinal stretch receptors

Hypernatremia

* excess sodium
* caused by dehydration

Hyponatremia

* deficiency of sodium
* caused by solute loss, water retention or both
* sodium loss through vomiting, dirrahea, etc

Hyperkalemia

* excess potassium
* caused by renal failure , deficit of aldosterone

Hypokalemia

* deficit in potassium
* caused by gastrointestinal tract disturbances

Hyperphosphatemia

* excess phosphate
* caused by decreased urinary loss due to renal failure

Hypophosphatemia

* deficit in phosphate
* caused by decreased intestinal absorption, increased urinary output

Hyperchloremia

* excess chlorine
* caused by dehydration, increased retention or intake

Hypochloremia

* deficit in chlorine
* caused by metabolic alkalosis and aldosterone deficiency

Hypercalcemia

* excess calcium
* caused by hyperparathyroidism and excessive vitamin D

Hypocalcemia

* deficit in calcium
* caused by burns, vitamin D deficiency and renal failure

Hypermagnesemia

* excess magnesium
* caused by renal failure when Magnesium is not excreted normally

Hypomagnesemia

* deficit magnesium
* caused by alcoholism, chronic diarrhea

Chemical buffer systems

rapid, first line of defense

brain stem respiratory centers

acts within 1-3 minutes

Renal mechanisms

most potent, but requires hours to days to effect pH changes

Respiratory acidosis and alkalosis

* caused by failure of respiratory system to perform pH balancing role
* single most important indictor is blood PCO2

Metabolic acidosis and alkalosis

* all abnormalities other than those caused by PCO2 levels in the blood
* indicated by abnormal biocarbonate levels

Metabolic acidosis

* low blood pH and bicarbonate
* caused by ingestion of too much alcohol, excessive loss of bicarbonate, and accumulation of lactic acid

Metabolic alkalosis

* indicated by rising blood pH and bicarbonate
* less common
* caused by vomiting of acid contents of stomach or intake of excess base

Developmental aspects in infants

* infants have more ECF than adults until about 2 years of age
* infants experience low residual lung volume, high rate of fluid intake and output, high metabolic rate, high rate of insensible water loss
* in their first month of life, infants risk dehydration and acidosis

Developmental aspects in the elderly

* in old age, total body water decreases
* homeostatic mechanisms slow down with age
* may be unresponsive to thirst cues