Chapter 26

Body water content

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