Fluid and Electrolytes P A R T 2

Fluid and Electrolytes P A R T 2

Fluid Shifts Extracellular fluid distribution is dynamic Interstitial fluid formation is continuous

Venous system Large veins (capacitance vessels) Small veins (capacitance vessels) Postcapillary venule Thoroughfare channel Heart Large lymphatic vessels Lymph node Lymphatic system Arteriovenous anastomosis Arterial system Elastic arteries (conducting vessels) Muscular arteries (distributing vessels) Lymphatic Sinusoid capillary Arterioles (resistance vessels) Terminal arteriole Metarteriole Capillaries Precapillary sphincter (exchange vessels) Figure 19.2

Regulation of ECF Movement Movement from capillaries mediated by hydrostatic and osmotic pressures Fluid distribution is a balance of forces Capillary hydrostatic Interstitial osmotic Interstitial hydrostatic Capillary osmotic

Cells receive nutrients and other solutes by way of fluids filtered through capillary walls Lungs Gastrointestinal tract Kidneys Blood plasma O 2 CO 2 Nutrients H 2 O, H 2 O, Ions Ions Nitrogenous wastes Interstitial fluid O 2 CO 2 Nutrients H 2 O Ions Nitrogenous wastes Intracellular fluid in tissue cells Figure 26.3

Arteriole Net HP Net OP (35 0) (26 1) Interstitial fluid Capillary Venule Net HP Net OP (17 0) (26 1) HP = hydrostatic pressure Due to fluid pressing against a wall Pushes In capillary (HP c ) Pushes fluid out of capillary 35 mm Hg at arterial end and 17 mm Hg at venous end of capillary in this example In interstitial fluid (HP if ) Pushes fluid into capillary 0 mm Hg in this example Net HP 35 mm Net OP 25 mm NFP (net filtration pressure) is 10 mm Hg; fluid moves out Net HP 17 mm Net OP 25 mm NFP is -8 mm Hg; fluid moves in OP = osmotic pressure Due to presence of nondiffusible solutes (e.g., plasma proteins) Sucks In capillary (OP c ) Pulls fluid into capillary 26 mm Hg in this example In interstitial fluid (OP if ) Pulls fluid out of capillary 1 mm Hg in this example Figure 19.17

Edema Atypical accumulation of interstitial fluid Causes Increased flow of fluid out of the blood or impaired lymphatic drainage Blood pressure Proteins in interstitial fluid Plasma proteins Lymphatic obstruction

Edema Blood pressure More tissue fluid at arteriolar end of capillary Hypertension Proteins in interstitial fluid Decreases osmotic return of water into venous end of capillary Inflammation Allergic reaction

Edema Plasma proteins Decreases osmotic return of water into venous end of capillary Liver disease Kidney disease malnutrition Lymphatic obstruction Parasites Elephantiatis Tumor

Edema

Dehydration Fluid loss exceeds fluid intake Extracellular osmolarity exceeds intracellular osmolarity Fluid moves into ECF compartment Cell volume reduction = compromised function

Dehydration Fluid loss exceeds fluid intake Causes Hemorrhage, severe burns, prolonged vomiting or diarrhea, profuse sweating, water deprivation, diuretic abuse Symptoms Thirst, dry flushed skin, oliguria Consequences May lead to weight loss, mental confusion, hypovolemic shock, and loss of electrolytes

1 Excessive 2 ECF osmotic 3 Cells lose loss of H 2 O pressure rises H 2 O to ECF from ECF by osmosis; cells shrink (a) Mechanism of dehydration Figure 26.7a

Hypotonic Hydration A.K.A. Water intoxication Causes Renal failure or rapid excessive water intake ECF is diluted hyponatremia net osmosis into tissue cells swelling of cells severe metabolic disturbances (nausea, vomiting, muscular cramping, cerebral edema) possible death

Hypotonic Hydration A.K.A. Water intoxication ECF is diluted hyponatremia net osmosis into tissue cells swelling of cells severe metabolic disturbances (nausea, vomiting, muscular cramping, cerebral edema) possible death

1 Excessive H 2 O enters the ECF 2 ECF osmotic pressure falls 3 H 2 O moves into cells by osmosis; cells swell (b) Mechanism of hypotonic hydration Figure 26.7b

Questions