Functions of Water in the Body - Total Body water
Nutrient and waste transport in blood
Skin structure and resilience
Digestion
Temperature maintenance
Lubrication of joints and membranes
Chemical reactions
IgA function
Total Body Water
60% of body weight in adults
2/3 intracellular
1/3 extracellular
Interstitial
Plasma
Other
Composition of the ECF, Plasma, and Interstitial Fluids
Large amounts of sodium and chloride
Moderate amounts of bicarbonate
Small quantities of potassium, magnesium, calcium, and phosphorus
Composition of the ICF
Almost no calcium
Small amounts of sodium, chloride, bicarbonate, and phosphorus
Moderate amounts of magnesium
Large amounts of potassium
Body Water Intake
Intake of 2000 - 2500 mls
Liquid
Water in food
Oxidation
Body Water Output
Output of 2000 - 2500 mls
Urine
Feces
Lungs
Skin
Total Body Water Variants
TBW varies with age
Infants = 75%
Adults = 60%
Elderly = 50%
TBW varies with body composition
More fat = lower % water
Mechanisms Controlling Fluid and Electrolyte Movement
Diffusion
Active transport
Osmosis
Measurement of osmolality
Osmotic movement of fluids
Diffusion
Constant movement of molecules across cell membranes is required to maintain homeostasis.
Diffusion refers to the movement of particles along a concentration gradient.
Active Transport
Na+ moves out of cell and K+ moves in by sodium/potassium pump (energy dependent)
Osmosis
Water moves by osmosis
Water pulled to area of higher particle concentration
Osmotically active particles
Na+, Cl-, urea, glucose
Tonicity
The tension that osmotic pressure exerts on a cell
Isotonic
Hypertonic
Hypotonic
Hydrostatic pressure
pushing force exerted by fluid
Osmotic pressure
pulling force of particles (colloidal osmotic pressure, colloidal oncotic pressure)
Exchange Across Cell Membranes- Difference between Osmotic and Hydrostatic Pressure
Hydrostatic pressure varies throughout the capillaries
Osmotic pressure is relatively stable
Difference between the two pressures determines the direction of fluid movement
Lymphatic channels
Absorb proteins, fats, plasma and cells from the interstitial fluid and return to the circulatory system.
Blockage causes increased interstitial osmotic pressure.
Thirst
early symptom of volume deficit
Release of ADH when serum osmolality increases
Homeostatic Regulation of Fluid Balance
Release of aldosterone when blood volume decreases
Natriuretic peptides released when atria are streched
Edema
Palpable swelling by expansion of the interstitial fluid volume
Can occur in any body tissue
Most common in the feet and lower legs
Can be life-threatening in the brain, lungs, or larynx
Causes of Edema
Increased capillary hydrostatic pressure
Decreased capillary osmotic pressure
Increased capillary permeability
Obstruction of lymphatic flow
Third Spacing
(1st space = normal fluid distribution; 2nd space = edema)
Loss of fluid into a non-functional space
Ascites
Pleural effusion
Ileus
Pericardial effusion
Isotonic Fluid Volume Disorders
Also called
Extracellular fluid volume disorders
Saline imbalances
Because sodium is confined to the extracellular compartment, loss or gain of saline does not affect the intracellular compartment
Volume deficit- Isotonic Disorders
Volume deficit
Loss of sodium-containing fluid from the body
Causes - see Table 39.4, p. 1035
Manifestations
Thirst
Weight loss
Hypotension
Dizziness
Oliguria
Volume Excess- Isotonic Disorders
Abnormal increase in sodium- containing fluid
Causes - see Table 39.5, p. 1036
Manifestations
Weight gain
Edema
Neck vein distention
Dyspnea, crackles
Disorders of Na+ Concentration
Abnormal osmolality
Abnormal sodium concentration
Also called water imbalance
Normal serum sodium
concentration: 135 - 145 mEq/L
Water excess: Hyponatremia
Serum Na+ < 135mEq/L
Causes - see Table 39.6, p. 1038
Result: cellular swelling
Manifestations of Water Excess
Headache, lethargy, confusion, seizures, coma
Nausea, vomiting, anorexia, diarrhea
Muscle cramps, weakness, fatigue
Water deficit: Hypernatremia
Serum Na+ > 145mEq/L
Causes - see Table 39.7, p. 1040
Result: cellular shriveling
Manifestations of Water Deficit
Confusion, lethargy, seizures, coma
Thirst
Dry, flushed skin
Tachycardia, hypotension
Dehydration
Combination of ECV deficit and hypernatremia
Causes of Dehydration
Vomiting and diarrhea
Excessive sweating
Untreated diabetes mellitus
No access to water
Lack of thirst in elderly
Dehydration Manifestations
Sudden weight loss
Hypotension
Dizziness
Sunken fontanels (infants)
Thirst
Decreased skin turgor
Dry mouth
Lethargy, confusion
Potassium Balance
Normal level 3.5 - 5.0 mEq/L
Source - dietary
Excreted through kidneys, skin, gi tract
Predominates in ICF
Hypokalemia
Serum K+ < 3.5
Affects resting potential of cells
Low potassium makes muscles less reactive causing::::
Cardiac dysrhythmias
Anorexia, vomiting, ileus
Weakness, paralysis, CNS depression
Polyuria, thirst
Hypokalemia Causes
Vomiting, diarrhea, gastric suction
NPO status, fasting
Alkalosis, rapid correction of acidosis
Certain diuretics, renal failure
Cushing syndrome, corticosteroids
Hyperkalemia
Serum K+ > 5.0
Affects resting potential of cells
Muscles may be unable to contract resulting in
Dysrhythmias, cardiac arrest
Weakness, flaccid paralysis
Nausea, vomiting, diarrhea
Hyperkalemia Causes
Renal failure
Certain diuretics
IV infusion, blood transfusion
Acidosis
Major tissue injury or chemotherapy
Calcium Balance
Normal level 9 - 11 mg/dl
99% of calcium is in bone
1% in blood
40% bound to plasma protein
Essential for blood clotting
Hypocalcemia
Serum Ca++ < 9
Affects threshold potential of cells
Low calcium makes muscles more reactive causing
Neuromuscular irritability
Trousseau & Chvostek signs
Hyperactive reflexes
Tetany
Seizures
Cardiac dysrhythmias, hypotension
Hypocalcemia Causes
Insufficient intake, low albumin
Chronic diarrhea
Hypoparathyroidism, high phosphate
Alkalosis
Pancreatitis, renal failure
Cancer chemotherapy
Hypercalcemia
Serum Ca++ > 11
Affects threshold potential of cells
Neural excitability is decreased and kidneys cannot concentrate urine
Nausea, vomiting, constipation
Polyuria, polydipsia
Muscle weakness and atrophy
Osteoporosis
Hypertension, dysrhythmias, cardiac arr
Hypercalcemia Causes
Hyperparathyroidism
Malignant tumors
High calcium ingestion
Prolonged immobility
Excessive Vitamin D
Phosphate
intracellular anion
Inverse relationship to calcium
Important in energy production
Magnesium
ICF cation
S&S similar to calcium
Chloride
ECF anion
Important in pH regulation
HCl acid in stomach
Electrolyte Summary
Cardiac dysrhythmias
Hyper- or hypo- kalemia
Weakness, poor muscle tone
Hyperkalemia
Hypokalemia
Hypercalcemia
Hypermagnesemia
Twitchy, crampy muscles
Hypocalcemia
Hypomagnesemia