Body Fluids Distribution and Regulation

Distribution of Body Fluids

• Total body water (TBW) includes intracellular fluid, extracellular fluid, interstitial fluid, intravascular fluid, lymph, synovial, intestinal, CSF, sweat, urine, pleural, peritoneal, pericardial, and intraocular fluids.

Pediatrics (Body Fluids Considerations)

• Pediatrics have 75% to 80% of weight as body water
• Pediatrics are susceptible to significant changes in body fluids, including dehydration in newborns.

Aging (Body Fluids Considerations

• Aging is associated with a decreased total body water percentage
• Aging is also associated with decreased free fat mass, muscle mass, renal decline, and diminished thirst perception.

Water Movement Between Fluid Compartments

• Oncotic pressure is exerted by plasma proteins on the capillary wall.
• Osmotic pressure is the pressure required to prevent net solvent movement across a membrane.
• Aquaporins form pores that selectively conduct water molecules across cell membranes, while preventing ion passage, such as sodium and potassium.
• Starling forces determine net filtration, which equals forces favoring filtration minus forces opposing it.

Fluid Movement Between Plasma and Interstitial Space

• Capillary hydrostatic pressure moves fluid out of capillary pores into the interstitial space, thus driving filtration.
• Interstitial oncotic pressure means plasma proteins in the interstitial space displace fluid.
• Interstitial hydrostatic pressure reabsorbs fluid into the capillaries.
• Capillary oncotic pressure is dependent on concentration of plasma protein in the capillary, increasing the drive the system.

Net Filtration Forces

• Forces favoring filtration include capillary hydrostatic pressure (blood pressure) and interstitial oncotic pressure (water-pulling).
• Forces favoring reabsorption include plasma oncotic pressure (water-pulling) and interstitial hydrostatic pressure.

Edema

• Edema is the the accumulation of fluid within interstitial spaces.
• Edema is caused by increased capillary hydrostatic pressure, decreased plasma oncotic pressure, increased capillary permeability, and lymph obstruction (lymphedema)
• Edema can be either localized or generalized.

Sodium and Chloride Balance

• Sodium is the primary ECF cation, which regulates osmotic forces, thus water
• Sodium plays roles in neuromuscular irritability, acid-base balance, cellular chemical reactions, and membrane transport
• Chloride is the primary ECF anion, which provides electroneutrality.

Renin-Angiotensin-Aldosterone System

• Sodium balance is controlled and regulated by aldosterone.
• It increases sodium resorption from urine back to blood at the distal tubule of the kidney.
• Aldosterone is a hormone secreted by the renal cortex that promotes sodium retention and potassium excretion.
• Increased sodium leads to increased water and an increase in blood pressure.
• Renin is secreted by the kidneys in response to low blood pressure.
• It activates angiotensin to promote aldosterone secretion and thus increases blood pressure.

Naturetic Peptides

• Atrial naturetic hormone (ANP) is released in response to high blood pressure.

• Increased atrial pressure stretches the heart wall and causes the release of atrial naturetic hormone from cardiac muscle tissue.

• ANP counteracts aldosterone and increases sodium excretion in the urine.

• Sodium excretion lowers blood volume and blood pressure.

ADH Secretion in Water Balance

• Antidiuretic hormone is secreted by the posterior pituitary.
• It is released in response to low blood pressure, increased plasma osmolality, or decreased circulation blood volume.
• It promotes water retention by the kidneys to regulate water balance.

Thirst Perception in Water Balance

• Osmolality receptors initiate thirst mechanisms through hyperosmolality and plasma volume depletion.
• Volume receptors and baroreceptors play a role in thirst perception

Isotonic Alterations

• Isotonic alterations involve changes to total body water with proportional changes in electrolytes and water, so no concentration shifts occur.
• Isotonic fluid loss causes dehydration and hypovolemia.

Causes of Fluid Loss

• Causes include hemorrhage, severe wound drainage, excess diaphoresis (sweating), and inadequate fluid intake.
• Loss of ECF causes weight loss, dry skin, mucous membranes, and decreased urine output.
• Indicators of hypovolemia include rapid heart rate, flattened neck veins, and normal to decreased blood pressures.

Isotonic Fluid Excess

• Isotonic fluid excess causes hypervolemia.
• Causes include excess administration of IV fluids, hypersecretion of aldosterone, and effects of drugs like cortisone.
• Hypervolemia results from weight gain and diluting effects leading to decreased hematocrit.
• Indicators include distended neck veins, increased blood pressure, and edema in the tissues.

Hypertonic Alterations

• Hypernatremia means excess sodium, with serum levels >145 mEq/L.
• Hypernatremia involves the movement of water from the ICF to the ECF, which causes intracellular dehydration.
• Related to sodium gain or water loss
• Manifestations include thirst, weight gain, bounding pulse, and increased blood pressure.
• CNS manifestations include muscle twitching, hyperreflexia, confusion, coma, convulsions, and cerebral hemorrhage.

Hyperchloremia

• Hyperchloremia is excess chloride, with serum chloride >105 mEq/L.
• It occurs with hypernatremia or a bicarbonate deficit in metabolic acidosis.
• Other than the management of blood glucose, there are no specific symptoms or treatments for chloride excess.

Hypotonic alterations

• Serum sodium measures <135 mEq/L.
• Decreased osmolality (hypoosmolality) with decreased extracellular solutes (Na+, Cl-)
• Hyponatremia or free water excess
• Hyponatremia decreases the ECF osmotic pressure, and water moves into the cell via osmosis
• Cells swell - hypotonic
• Clinical Manifestations - muscle twitching, depressed reflexes and weakness, nausea, and vomiting
• In the central nervous system - Life threatening consequence is cerebral edema and increased intracranial pressure

Free Water Excess

• Compulsive water drinking
• Decreased urine formation
• Syndrome of inappropriate ADH (SIADH)
• Ectopic ADH secretion in the absence of hypovolemia or hyperosmolality
• Hyponatremia with hypervolemia
• Manifestations - cerebral edema (with confusion and convulsions), weakness, muscle twitching, nausea, headache, and weight gain

Hypochloremia

• Results of hyponatremia or elevated bicarbonate concentration
• Develops as a result of vomiting and loss of HCl
• Occurs in cystic fibrosis
• Due to lack of adequate chloride pump
• Treatment of underlying cause is required

Potassium

• Major intracellular cation
• Concentration maintained by Na+/K+ pump
• Essential for transmission and conduction of nerve impulses, normal cardiac rhythms, and skeletal and smooth muscle contraction

Potassium Levels

• Changes in pH affect K+ balance
• Hydrogen ions accumulate in ICF during states of acidosis; K+ shifts out to maintain balance of cations across the membrane; result is hyperkalemia
• Aldosterone, insulin, and epinephrine influence serum potassium levels
• Kidney is most efficient regulator
• Potassium adaptation is tolerated better with slow changes than acute

Hypokalemia

• Potassium level <3.5 mEq/L
• Potassium balance is described by changes in plasma potassium levels
• Causes - reduced intake of potassium, increased entry of potassium into cells, and increased loss of potassium Manifestations (depend on rate and severity):
• Membrane hyperpolarization causes decrease in neuromuscular excitability, skeletal muscle weakness, smooth muscle weakness, and cardiac dysrhythmias

Hyperkalemia

• Potassium level >5.5 mEq/L
• Hyperkalemia is rare because of efficient renal excretion
• Caused by increased intake, shift of K+ from ICF into ECF, decreased renal excretion, insulin deficiency, or cell trauma

Hyperkalemia

• Mild attacks
• Increased neuromuscular irritability
• Restlessness, intestinal cramping, and diarrhea
• Severe attacks
• Decreases the resting membrane potential
• Muscle weakness, loss of muscle tone, and paralysis

Calcium and Phosphate

• Calcium and phosphate concentrations are rigidly controlled by parathyroid hormone (PTH), vitamin D, and calcitonin

Hypocalcemia

• Causes - inadequate intestinal absorption, deposition of ionized calcium into bone or soft tissue, blood administration, decreases in PTH, and vitamin D and nutritional deficiencies occur with inadequate sources of dairy products or green leafy vegetables
• Increased neuromuscular excitability
• Tingling, muscle spasm (particularly in hands, feet, and facial muscles), intestinal cramping, and hyperactive bowel sounds
• Severe cases show convulsions and tetany
• Prolonged QT intervals and cardiac arrest symptoms

Hypercalcemia

• Caused by hyperthyroidism
• Bone metastases with calcium resorption from breast, prostate, renal, and cervical cancer
• Excess vitamin D, many tumors produce PTH
• Effects - nonspecific fatigue, weakness, lethargy, anorexia, nausea, constipation, impaired renal function, and kidney stones.

Phosphate

• Like calcium, most phosphate is also located in the bones
• Provides energy for muscle contraction
• Normal value is 2.5-5.0
• Parathyroid hormone, Vitamin D3 and calcitonin controls phosphate reabsorption.

Hypophosphatemia

• Causes: Intestinal malabsorption (vitamin D deficiency, use of magnesium- and aluminum-containing antacids, long-term alcohol abuse)
• Effects: Reduced capacity for oxygen transport by red blood cells, thus disturbed energy metabolism
• Leukocyte and platelet dysfunction
• Deranged nerve and muscle function
• Severe cases result in irritability, confusion, numbness, and coma.

Hyperphosphatemia

• Acute or chronic renal failure with significant loss of glomerular filtration can cause
• Treatment of metastatic tumors with chemotherapy that releases large amounts of phosphate into the serum
• Long-term use of laxatives or enemas containing phosphates and hypoparathyroidism
• Symptoms primarily related to low serum calcium levels (caused by high phosphate levels) similar to the results of hypocalcemia.

Acid-Base Balance

• Is carefully regulated
• To maintain a normal pH via multiple mechanisms

pH Levels

• Acids are formed as ending products
• To maintain the body's normal pH which is 7.34 - 7.45
• Bones, lungs, and kidneys are major organs

pH Continued

• Body acids exist in two forms
• Volatile - includes H2CO3 (Carbonic Acid), and is eliminated as CO2 gas
• Nonvolatile - Includes sulfuric phoshoric and other organic acids, and are eliminated by the renal tubules with the regulations

Buffering Systems

• A buffer is a chemical that can find excessive H+ or OH- without significant changes in pH
• The more plasma-buffering systems are the carbonic acid-bicarbonate pair

Carbonic Acid-Bicarbonate Pair

• Operated in the lung and kidneys
• Greater partial pressure of carbon dioxide, the more corbonic acid is informed
• At a pH of 7.4 for the ratio of bicarbonate to carbonic acid
• Bicarbonate and carbonic acid can increase or decrease, but the ratio must be maintained

Acid-Base Imbalances

• Normal artieral blood pH
• 7.35 to 7.45
• System increase in H+ concentration or decrease in bicarbonate
• System decreases H + concentration or increase in bicarbonate

Acidosis and Alkalosis Four categories of Acid-Base Imbalances

• Metabolic acidosis - elevation of PCO2 as a result of ventilation depression
• Alkalosis - decreasing of PCO2 as a result of