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25 Cards in this Set
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Functions of Body Water - Provides a medium for metabolic reactions within cells - Transports nutrients, waste products to and from the cells - Acts as a lubricant, provides insulation, absorbs shock - Regulates and maintains body temperature through evaporation of perspiration |
Factors Affecting Total Body Water *Body of an average adult male about 60% water by weight 1) Age: Total body water decreases with age - In people over 65 years of age, body water may decrease to 45%-50% of total body weight - The body of an infant is approximately 70%-80% water by weight |
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2) Gender: The body of an average adult female is about 50% water by weight because adult females have a greater ratio of fat to lean tissue mass than adult males |
3) Amount of body fat: Fat cells contain comparatively little water and so in obese persons, the proportion of water to total weight is less than in a person of average weight |
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Distribution of Body Fluids Body fluids occur in compartments of different volumes that contain fluids of varying composition Fluid compartments Water is distributed into two major compartments: - Intracellular (ICF); Fluid inside the cell -> 40% out of 60% - Extracellular (ECF); Fluid outside the cell -> 20% out of 60% |
Intracellular Fluid Compartment contains water and electrolytes inside the cell membranes - Fluid inside the cells represents 2/3 of total body fluid - Intracellular fluid is essential for normal cell functioning; contains solutes, electrolytes and glucose, and provides the medium for metabolic processes |
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Extracellular Fluid Compartment includes all fluid outside cells and represents 1/3 of total body fluid - Interstitial fluid (ISF) located in the spaces between most of the body cells(75% of the ECF) - Intravascular fluid/plasma is contained within the arteries, veins, and capillaries (20% of the ECF) |
- Transcellular includes lymph and cerebrospinal, pericardial, pancreatic, pleural, peritoneal, intraocular, biliary, and synovial fluids (5% of the ECF) |
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BODY FLUID COMPOSITION - Electrically charged particles (ions) that are capable of conducting electricity - Ions that carry a positive charge - CATIONS (sodium, potassium, calcium, and magnesium) - Ions that carry a negative charge - ANIONS ( chloride, bicarbonate, phosphate, and sulfate) |
- The unit of measurement for electrolytes is the mole - number of moles of a substance in a 1-litre solution is known as the molarity *In humans, the solutes found in the body fluids are so dilute that their concentrations are expressed in 1/1000th of a mole or a millimole - Lab values are reported in millimoles per litre (mmol/L) - referred to as SI units *Lab tests are done on blood plasma and so reflect the values in ECF |
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Intracellular Fluid - Potassium and magnesium are the primary cations - Phosphate and sulphate are the major anions Extracellular Fluid - Sodium, chloride, and bicarbonate ions are the principal extracellular electrolytes; other electrolytes (potassium, calcium, and magnesium)are present in much smaller quantities |
- High sodium concentration in the ECF is essential to regulation of body fluid volume - Plasma and interstitial fluid, the two primary components of ECF, contain similar electrolytes and solutes -Plasma contains large amounts of albumin; interstitial fluid contains very little protein |
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MOVEMENT OF BODY FLUIDS AND ELECTROLYTES - Body fluid compartments are separated from one another by cell membranes - These membranes are permeable to water, but selectively permeable to solutes (Ex, ions move easily, but large molecules such as glucose and protein do not move as easily) |
Solutes: Substances dissolved in a liquid Solvents: Component of a solution that can dissolve a solute Osmolality: Concentration of solutes in body fluids osmolality is determined by the total solute concentration within a fluid compartment - Measured as a part of solute per kilogram of water - Sodium is the greatest determinant of osmolality of plasma - Potassium, glucose and urea are the primary contributors to osmolality of intracellular fluid |
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Tonicity: The osmolality of one solution in relation to another solution Isotonic: Has the same osmolality as ECF - Fluid excess that occurs in extracellular compartment (Ex, Normal saline, 0.9% sodium chloride) Hypertonic: Have a higher osmolality than ECF (Ex, 3% sodium chloride) Hypertonic: Solutions that have a lower osmolality compared to ECF (Ex, 0.45% sodium chloride) |
To restore fluid balance within the compartment; i) The cells are shrunken = cells are dehydrated ii) Cells dehydrated = patient feels thirsty iii) Drinking water will help to dilute sodium in ECF = water will return inside the cells ICF - cells become hydrated |
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Osmotic Pressure: The power of a solution to pull water across a semipermeable membrane - When two solutions with different amounts of solute are separated by a selectively permeable membrane - The solution with more solutes exerts a higher osmotic pressure and so draws water across the membrane to equalize the concentrations of the solutions |
- Plasma proteins exert an osmotic pull called COLLOID OSMOTIC PRESSURE/COLLOID ONCOTIC PRESSURE - Plasma proteins help to hold water in the plasma by pulling water from the interstitial spaces into the vascular compartment |
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METHODS BY WHICH WATER AND SOLUTES MOVE IN THE BODY 1. Diffusion: Movement of molecules through a semipermeable membrane from an area of high concentration to an area of low concentration Simple diffusion: Random movement of particles through a solution (solutes move between plasma and the interstitial space through the capillary membrane) - Water and solutes move into the cell by passing through protein channels/by dissolving in the lipid cell membrane |
Facilitated diffusion: Allows large water-soluble molecules to diffuse across cell membranes by using carrier - Proteins embedded in the cell membrane function as carriers, helping large molecules cross the membrane |
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2. Osmosis: Process by which water moves across a selectively permeable membrane fro an area of low solute concentration to an area of higher solute concentration - Occurs when the concentration of solutes is higher on one side of a selectively permeable membrane (Ex, capillary membrane, than on the other side) - Where water and dissolved substances (solutes) move from an area of high hydrostatic pressure to an area of low hydrostatic pressure |
3. Filtration: Where water and dissolved substances (solutes) move from an area of higher hydrostatic pressure to an area of low hydrostatic pressure - Hydrostatic pressure; The pressure exerted by a fluid within a closed system on the wall of the container in which it is contained (Ex, blood pressure against vascular walls - Osmotic pressure - The power of a solution to pull water across a semi-permeable membrane (Ex, High solute = High osmotic pressure) |
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- How does fluid move at the arteriolar end of the capillary?; Fluid moves from high-pressure to a low-pressure area - How does fluid move at the venular end of the capillary?; Fluid moves from low solute concentration to high concentration (blood) - Why is some interstitial fluid forced into the lymphatic capillaries?; Because of the increase in solute concentration in the lymphatic capillaries - Any change in the relative values of hydrostatic pressure/osmotic pressure in the compartments alerts the fluid to shift |
4. Active Transport: The movement of solutes across cell membranes from a less concentrated solution to a more concentrated one - a substance combines with a carrier on the outside surface of the cell membrane and they move to the inside surface of the cell membrane - A specific carrier is required for each substance - Important in maintaining differences in sodium and potassium ion concentrations of ECF and ICF (sodium-potassium pump) |
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- In order to maintain sodium concentration higher in the ECF and potassium concentration higher inside the cells, the active transport mechanism is activated and moves sodium from the cells and potassium into the cells - Active transport moves and holds sodium and potassium against their diffusion gradients |
REGULATION OF BODY FLUIDS (NORMS) Intake of water = Output of water (I=O) - Water balance exists when intake = output |
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CONTROL OF FLUID BALANCE 1.Thirst Mechanism: Primary regulator of water - Located in the osmoreceptors in the hypothalamus - Osmoreceptors are sensitive to the fluid volume and solute concentration of the blood and promote the intake of fluid as needed |
-> Low volume of extracellular fluid and high osmolality of extracellular fluid will stimulate the thirst centre in the hypothalamus -> High volume of extracellular fluid and Low osmolality of extracellular fluid will inhibit the thirst centre in the hypothalamus |
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2. Anti-diuretic Hormone: Promotes reabsorption of water into the blood from the distal kidney tubules - osmoreceptors in the hypothalamus stimulate ADH production and release by the posterior pituitary gland - Released when serum osmolality increases, Increased reabsorption of water = decreased urine output, Increased reabsorption of water = Increased blood volume, Increased reabsorption of water = Decreased serum osmolality as the water dilutes body fluids |
3. Renin-Angiotensin-Aldosterone System: This system helps to maintain intravascular fluid balance and blood pressure - Stimulus for this system is a decrease in blood flow/blood pressure to the kidneys Involves: Juxtaglomerular (JG) cells in the kidneys, Lungs - Fall in blood pressure to the kidneys stimulates JG cells in the kidney to produce renin |
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- Renin converts to angiotensinogen into angiotensin 1 - Angiotensin 1 travels to the lungs and converts to angiotensin 2 by the angiotensin-converting enzyme (ACE) > Angiotensin 2 is a potent vasoconstrictor = will raise BP > Stimulates thirst mechanism, adrenal cortex to release aldosterone (aldosterone promotes sodium and water retention in the distal nephron of the kidney = restoring blood volume) |
- The net effect of the renin-angiotensin-aldosterone system is to help maintain intravascular fluid balance and blood pressure |
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4. Atrial Natriuretic Factor (Peptide): Regulates fluid, sodium, and potassium levels - Released from the cells in the atrium of the heart in response to excess blood volume and stretching of the atrial walls - Increases the glomerular filtration rate - Reduces the reabsorption of sodium in the distal convoluted tubules bu inhibiting ADH |
- Reduces renin secretion and so inhibits the renin-angiotensin system - Reduces aldosterone secretion - Acts on the nephron to promote sodium wasting, thus is a potent diuretic, decreasing blood volume and lowering blood pressure - Inhibits thirst, thus reducing fluid intake - Leads to retention of potassium |
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FVD - FLUID VOLUME DEFICIT (dehydration) - Insufficient body fluid > Mild dehydration = decrease of 2% in body weight > Moderate dehydration = decrease of 5% in body weight > Severe dehydration = decrease of 8% in body weight -> Insufficient water intake -> Diabetic ketoacidosis with loss of fluid, electrolytes and glucose in the urine |
-> Excessive fluid losses from the GI tract are the most common causes (vomiting, diarrhea, GI suctioning, intestinal drainage) - Loses affect the extracellular compartments first,other causes of fluid loss include excessive sweating, hemorrhage, chronic abuse of laxatives and/or enemas (stop edema) |
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THIRD SPACING A situation where fluid shifts out of the blood and into a body cavity or tissue where it is no longer available as a circulating fluid - EX, Peritonitis - the inflammation and infection of the peritoneal membranes and burns - The result of this fluid shift creates a fluid deficit in the intravascular compartment (HYPOVOLEMIA) and a fluid excess in the third space - Until the cause is removed, fluid remains in the third space but is not functioning as a circulating fluid |
Hypotonic Dehydration - If sodium is lost from the extracellular compartment than water - Fluid will move between the cell and the interstitial fluid compartment - Using osmosis (electrolyte loss can lead to change sin osmotic pressure between compartments) |
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FLUID VOLUME EXCESS - EDEMA: An excessive amount of fluid in the interstitial compartment, causing a swelling of the tissues - May be localized in one area or generalized throughout the body, may be highly visible or relatively invisible - Usually more severe in the dependent areas of the body (because it is where the force of gravity is the greatest, buttocks, ankles, feet of a person in a wheelchair) - NO MOVEMENT = NO FLUID SHIFT = EDEMA |
- Occurs in the extracellular compartment and may be referred to as ISOTONIC/ISO-OSMOLAR, HYPOTONIC/HYPO-OSMOLAR, or HYPERTONIC/HYPEROSMOLAR depending on the cause |
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CAUSES 1. Increased capillary hydrostatic pressure (increased pushing pressure) - Prevents return of fluid from the interstitial compartment to the venous end of the capillary or - Forces excessive amounts of fluid out of the capillaries into the tissues (Ex, pulmonary edema) - Caused by higher blood pressure/increased blood volume |
*Causes of increased capillary hydrostatic pressure; - increased blood volume (hypervolemia) associated with kidney failure, pregnancy (enlarged uterus compresses pelvic veins in a seated position and when standing still for long periods of time the pressure in the leg veins become elevated, causing edema in the feet and legs), congestive heart failure (blood cannot return easily through the veins and to the heart, raising hydrostatic pressure in legs and abdominal organs cause ascites of fluid in abdominal cavity), or administration of excessive intravenous fluids |
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2. Decrease of plasma proteins (albumin) (decreased pulling pressure) - Decreased plasma proteins result in a decrease in plasma osmotic pressure (The presence of fewer plasma proteins int he capillary allow more fluid to leave the capillary and less fluid to return to the venous end of the capillary) |
*Causes of decreased plasma proteins; - the decrease of proteins in urine in kidney disease - decreased synthesis of proteins in malnutrition, malabsorption disease or liver disease - large burned areas - proteins leak out through the lost skin barrier and allow proteins to easily leak out of the body |
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**Excessive sodium levels in the extracellular fluid accompany causes 1 and 2** - When sodium ions are retained, they promote accumulation of fluid in the interstitial compartment (by increasing the interstitial fluid osmotic pressure and decreasing the return of fluid to the blood. Blood volume and blood pressure are usually elevated as well) |
*Situations in which there are high sodium levels; - Heart failure, hypertension, and kidney disease - increased aldosterone secretion (Aldosterone: hormone secreted by the adrenal cortex. Promotes excretion of potassium and reabsorption of sodium and water. Kidneys release renin when BP is low to promote glomerular filtration, renin > angiotensin to angiotensin1 > converted to angiotensin 2 > stimulates the release of aldosterone) |
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3. Obstruction of the lymphatic circulation - Usually causes a localized edema (because excessive fluid and protein are not returned to the general circulation - third spacing- like action) *Situations in which lymphatic obstruction may occur; - removal of lymph nodes - damage to lymph nodes caused by tumor or infection |
4. Increased capillary permeability - Often results from an inflammatory response or an infection (in this case, histamine and other chemical mediators released from the cells following tissue injury causes increased capillary permeability and increased fluid movement into the interstitial area *Cause of increased capillary permeability - bacterial infections and large burn wounds |
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EFFECTS OF EDEMA - Local area of swelling - Pitting edema - Increase in body weight - Functional impairment (Ex, restricted movement of the joints, edema of the intestinal wall may interfere with digestion and absorption - Pain - occurs if the edema exerts pressure on nerves |
- Arterial circulation may be impaired > Increased interstitial pressure may restrict arterial blood flow into the area > This prevents normal cell function and reproduction and eventually results in tissue necrosis or the development of ulcers |
