FLUID AND ELECTROLYTES BIO 139 Anatomy Physiology II

FLUID AND ELECTROLYTES BIO 139 Anatomy & Physiology II

Water Content of the Body • Infants – 73% of body weight • Men – 60% of body weight • Women – 50% of body weight • Total amount of body water is affected by age, body mass and body fat

Fluid Compartments in the Body • Two main fluid compartments • Intracellular Compartment • Fluid inside cells • 42% of body weight • Extracellular Compartment • Includes blood plasma, interstitial fluid and lymph • 17 % of body weight

• Electrolytes are substances whose molecules dissociate or split when placed in water. • Cations: + charge • Na+, K+, Ca++, Mg++ • Anions: - charge • Cl-, PO 43 -, HCO 3 -

Electrolyte Concentration • The overall concentration of electrolytes is the same in the two fluid compartments • HOWEVER, there are different concentrations of specific ions in the different compartments

Intracellular Fluid Composition • Water and electrolytes inside a cell • High concentration of potassium, phosphate, magnesium and proteins • Low concentration of sodium, chloride ions and bicarbonate ions

Extracellular Fluid Composition • Interstitial fluid, blood plasma and lymph • High concentration of sodium, chloride ion and bicarbonate ion • Low concentration of potassium, magnesium, phosphate and sulfate

Electrolyte Balance • Maintenance of stable levels of water and electrolytes in the body cells and fluids • Requires replacing lost water and electrolytes and excreting excess amounts • Altering concentration of water alters concentration of electrolytes and vice-versa

Water Balance • Water intake must equal water output • Intake • Fluids, solid fluids, water from oxidation • Output • Evaporative loss from lungs and skin, sweating, defecation and urination

• ADH regulates water reabsorption in the nephron of the kidney (DCT & CD)

Triggers for ADH Release • Stimulation of posterior pituitary by Angiotensin II • Prolonged fever • Excessive sweating, vomiting or diarrhea • Concentrates blood plasma • Severe blood loss • Traumatic burns • Increased plasma osmolality

ADH Abnormalities • SIADH • ↑ ADH Production • Symptoms? ? • Diabetes Insipidus • ↓ ADH Production • Symptoms? ?

Electrolyte Balance • Na+ most important cation in regulation of fluid and electrolyte balance • Concentration of ECF is 300 m. Osm, 280 m. Osm contributed by Na+ • Change in Na+ levels results in osmotic changes, affecting: • Plasma volume, blood pressure, fluid volumes in & outside cells • Na+ levels regulated by aldosterone

Aldosterone Release • Aldosterone is released in response to: • Renin-Angiotensin System • Increased K+ levels • What does it do? ? ? ? ?

Hypernatremia • Causes: Water loss or sodium gain • Water loss leading to hypernatremia • Diabetes Insipidus (ADH deficiency) • Osmotic diuresis (Diabetes Mellitus) • Increased perspiration • High Fever or Heatstroke • Sodium gain • Hyperaldosteronism

Hyponatremia • Causes: Water excess or sodium loss • Water gain • SIADH • CHF • Sodium loss • Diuretics, adrenal insufficiency, burns, diarrhea, vomiting

Potassium Balance • Major intracellular cation • K+ is critical to maintenance of membrane potential of neurons and muscle cells • K+ also acts as a buffer that compensates for shifts in hydrogen ions in or out of a cell (recall this in the DCT/CD) • Secreted in response to aldosterone

Calcium & Phosphate Balance • Calcium important for Nerve impulse conduction, muscle contraction, coagulation, secretion • Calcium homeostasis is controlled by parathyroid hormone and calcitonin • Calcitonin released in response to elevated Ca++ • PTH released in response to decreased Ca++ • Vitamin D is necessary for calcium absorption in the small intestines

p. H • Indirect measure of H+ ion concentration • Body maintains a slightly alkaline p. H pf 7. 35 -7. 45 • Metabolic and respiratory processes work together to keep H+ levels in a normal range

Acid Base Regulation • Normal metabolism produces acids • Lactic acid (anaerobic respiration), uric acid (nucleotides), phosphoric acid (proteins) and ketone bodies (fats) • Acids must be neutralized

Acid-Base Balance • p. H above 7. 45 = alkalosis • p. H below 7. 35 = acidosis • Acid-Base Balance is maintained one of three ways 1. Buffer Systems – immediate reaction 2. Respiratory excretion of CO 2 – minutes to hours 3. Renal excretion of H+ ions – kicks in after 2 -3 days and has longer maintenance

Buffering Systems • Fastest acting system and primary regulator of acid-base balance • Act Immediately • Buffer systems resist changes in p. H by: • Removing H+ when the p. H decreases • Releasing H+ when the p. H increases • Examples: • Bicarbonate, proteins, hemoglobin

Respiratory Buffer System • Bicarbonate Buffering System is the main buffer in ECF • CO 2 + H 2 O ↔ H 2 CO 3 ↔ HCO 3 - + H+ • Changes in CO 2 concentration lead directly to changes in H+ and p. H • CO 2 concentration and H+ concentration are directly proportional • H+ concentration and p. H are inversely proportional

Respiratory Buffer System • Decreased ventilation leads to _____ CO 2 in the body • Increased ventilation leads to _____ CO 2 in the body • This system works within minutes to hours, but is only temporary

Renal Regulation of Acid/Base Balance • The kidneys can secrete and reabsorb HCO 3 - and H+ ions to regulate p. H • Responds within hours to days

Abnormalities in Acid-Base Balance • Health problems may lead to imbalance in acid-base concentration and fluid-electrolyte balance • Diabetes mellitus • COPD • Kidney disease • Vomiting • Diarrhea • Hormonal imbalances

Abnormalities in Acid-Base Balance • Respiratory imbalances affect carbonic acid concentration • Metabolic imbalances affect bicarbonate ion concentration

Acid Base Balance at p. H 7. 4 • At a p. H of 7. 4, p. H is maintained by a normal ratio of 1 part H 2 CO 3 to 20 parts HCO 3 • 1 H 2 CO 3 : 20 HCO 3 • 1 acid : 20 Base

FOR ACIDOTIC OR ALKALOTIC CONDITIONS, THE RESPIRATORY SYSTEM AND URINARY SYSTEM WILL ACT TO COMPENSATE This involves secretion and reabsorption of what ions?

**If H+ is secreted, HCO 3 - is reabsorbed **Loss of 1 HCO 3 - is the same as gaining 1 H+

Abnormalities in Acid-Base Balance • Respiratory Acidosis – Increased H 2 CO 3 (CO 2) • Respiratory Alkalosis – decreased H 2 CO 3 • Metabolic Acidosis – decreased HCO 3 - or Increase in other acids • Metabolic Alkalosis – increased HCO 3 - or loss of acids

Respiratory Acidosis • Increased H 2 CO 3 (CO 2 induced H+) • Causes: • Hypoventilation • Gas exchange is hindered by disease (asthma, cystic fibrosis, COPD, emphysema) • Stimulates dorsal respiratory group • Leads to increased ventilation

Respiratory Acidosis • Compensation = kidneys conserve bicarbonate and secrete excess H+

Respiratory Alkalosis • Decreased H+ (H 2 CO 3) • Causes: • Hyperventilation (possibly caused by anxiety) • Leads to decreased ventilation • Compensation = HCO 3 - secretion in kidneys OR reabsorb H+

Renal Control of Acid-Base Balance • Kidneys are only organ that can rid the body of acids (not just H+) generated by cellular metabolism • HCO 3 - is key indicator of metabolic acidosis and metabolic alkalosis

Metabolic Acidosis • Low p. H and low HCO 3 • Causes: • Accumulation of non-respiratory acids or Excessive loss of HCO 3 • Ingestion of too much alcohol • Starvation • Kidney disease, prolonged diarrhea, diabetes mellitus • Compensation = increased CO 2 release by lungs AND kidneys secrete H+ and reabsorb HCO 3 -

Metabolic Alkalosis • Increased p. H and increased HCO 3 • Causes: • Vomiting of stomach contents • Excessive base intake • Compensation = decrease respiratory rate and renal secretion of HCO 3 -

Maintaining Metabolic Acid-Base Balance in the Kidney • Conserve HCO 3 - (Reabsorption by nephron) • OR • Excrete HCO 3 -