Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 18

KEYS TO MAINTAINING HOMEOSASIS - WATER AND ELECTROLYTES - what goes in must = what leaves - transcellular fluid - CSF, aqueous and vitreous humors of the eyes, synovial fluid of the joints, serous fluid in the body

DIFFERENCES IN FLUID COMPOSITION

MOVEMENT OF FLUID BETWEEN INTRA AND EXTRACELLULAR COMPARTMENTS Pressures control fluid movement Osmotic pressure changes control net fluid movement Sodium ion concentration can cause fluid movement Ex: If interstitial sodium concentration is high then fluid will tend to move from cells to interstitial fluid causing cells to shrink Another example: Fresh water - cells swell Salt water - cells shrink

Figure 18.03

DEHYDRATION

EDEMA

CAUSES OF EDEMA

Water Balance - when input = output Water of Metabolism - water created from oxidative metabolism Thirst - osmotic pressure rises in extracellular fluid when water decreases enough to trigger osmoreceptors in the thirst center of the hypothalamus ADH - antidiuretic hormone - when activated causes re-absorption of sodium from the distal convoluted tubules and collecting ducts *Diuretics often work on the same areas as ADH

ELECTROLYTE BALANCE -balance exists when input = output -The food we eat provides most of our electrolytes -Salt cravings may be due to severe deficiency of electrolytes -We lose electrolytes when we sweat and exercise -The kidneys work to maintain electrolyte balance -Sodium, potassium and calcium are required for nerve impulse conduction, muscle contraction and membrane potentials. -Aldosterone comes from the adrenal cortex and regulates sodium and potassium ion concentration -An increase in potassium concentration triggers aldosterone release and excretion of potassium ions and reabsorption of sodium ions -Parathyroid hormone increases calcium ion concentration to normal when it drops in the extracellular fluid -If phosphate or sulfate ion concentration is low in the plasma the renal tubules begin to reabsorb those ions and if levels of either is high secretion of the ions occurs into the tubules so that excess ions are lost in urine

SODIUM AND POTASSIUM BALANCING

ACID BASE BALANCE ACID - electrolytes that dissociate in water and release hydrogens BASE - electrolytes that release ions and combine with hydrogens Below are metabolic processes that yield hydrogens

SODIUM AND POTASSIUM IMBALANCES HYPONATREMIA - low sodium - Causes: diarrhea, renal disease, vomiting, prolonged sweating, excessive water intake HYPERNATREMIA - high sodium - Causes: diet, excess water loss, high fever HYPOKALEMIA - low potassium - Causes: Cushing Syndrome - increase in renal excretion of potassium, diuretic medications, prolonged vomiting or diarrhea - Symptoms: muscular weakness, paralysis, respiratory difficulty or atrial/ventricular arrhythmias HYPERKALEMIA - high potassium - Causes: renal disease, medication that promote renal conservation, insufficient aldosterone release - Addison disease - Symptoms: paralysis of skeletal muscles, cardiac disturbances and cardiac arrest

REGULATION OF HYDROGEN ION CONCENTRATION

THE MEDULLARY RESPIRATORY CENTER RESPONSE -notices an increase in carbon dioxide and a decrease in pH - causes an increase in deep breathing which leads to elimination of excess carbon dioxide

pH SHIFT REGULATION MECHANISMS

ACIDOSIS AND ALKALOSIS ON THE pH SCALE

HOW ACIDOSIS AND ALKALOSIS ARE ACHIEVED

FACTORS LEADING UP TO RESPIRATORY ACIDOSIS

FACTORS THAT LEAD UP TO METABOLIC ACIDOSIS

FACTORS THAT LEAD UP TO RESPIRATORY ALKALOSIS

FACTORS THAT LEAD UP TO METABOLIC ALKALOSIS