Chapter 25 The Body Fluid Compartments Flashcards
How do daily intakes and outputs of water take place?
Intake
- ingested
- synthesized through oxidation
Outputs
- insensible loss through respiration and skin
- through feces
- through kidneys i.e. urine has a lot of water
- through sweat
Describe the body’s composition of water and all compartments.
Approximately 60% of the adult body is water and is broken down into compartments:
Extracellular ~ 20% of BW
- interstitial
- plasma
Intracellular ~40% of BW
Describe how a cell will change when placed in an isotonic, hypertonic or hypotonic solution.
Placed in isotonic solution - no change to cell
Placed in hypertonic solution - cell will shrink, as fluid leaves cell to try to maintain equilibrium
Placed in hypotonic solution - cell will expand, as fluid enters cell to try to maintain equilibrium
What are causes of hyponatremia?
Hyponatremia can occur in due to loss of sodium or excess water
- sodium levels decrease in both situations
- extracellular fluid increases in overhydration and decreases in dehydration
- intracellular fluid increases in both situations due to the fact that fluid is flowing down a gradient and must go from least solute to more solute, thus cells can be ruptured
Examples:
- Dehydration due to overuse of diuretics (overwhelm KD’s ability to conserve sodium) or adrenal insufficiency (impair KD to reabsorb sodium)
- Overhydration due to excess ADH, thus causing kidney tubules to reabsorb more water
What are physiologic consequences of hyponatremia and how can it be corrected?
Acute hyponatremia - ECF has lost Na or has an excess of water -> fluid flows into cells to maintain equilibrium, brain swells -> solutes flow out of cells -> water follows
- possible herniation at brain stem can occur if too rapid
Chronic - similar to above, but happening slower, brain has ability to increase solutes in brain ECF, by putting osmogenic solutes like proteins and other electrolytes in the ECF
- can see mild swelling of the brain - if correcting with hypertonic solutions, can cause demyelination of the neurons leading to further neurologic signs
What are causes for hypernatremia?
Hypernatremia can occur due to excess sodium in ECF or excess water loss in ECF
- both situations show increased serum [Na+]
- During dehydration, ECF loses fluids and during overhydration, ECF has excess fluid
- ICFV decreases in both situations, as fluid is flowing down a gradient and must go from least to more solute, thus cells can shrink
Examples:
- Dehydration to loss of ADH, which causes the KD not to be able to conserve water and a large amount of dilute urine is excreted; dehydration due to less water intake than output
- Overhydration when excessive secretion of aldosterone, which decreases sodium excretion through the KD
Differentiate between edema and effusion.
Edema is the accumulation of excess fluid in the body tissues, mainly extracellular.
Effusion is the accumulation of fluid in the potential spaces of the body such as the peritoneum, pleural space, pericardial space, synovial cavities.
Which of the following would cause extracellular edema?
A. Hyponatremia
B. Lack of adequate nutrition to the cells
C. Failure of lymph to return fluid from interstitium to the blood
D. Depression of the metabolic system of the tissues
C. Failure of lymph to return fluid from interstitium to the blood
A, B, and D are reasons for intracellular edema. - if ischemia occurs, this reduces oxygen and nutrition to the cells, cell membrane pumps become depressed and sodium ions cannot be pumped out of the cell, increasing the tonicity inside the cell.
Extracellular edema is caused by
- Failure of lymph to return fluid from interstitium to the blood
- Increased capillary leakage of fluid
Capillary filtration is determined by?
The capillary filtration rate, involving “Starling forces.”
Starling forces
- The capillary pressure (Pc), which tends to force fluid outward through the capillary membrane.
- The interstitial fluid pressure (Pif), which tends to force fluid inward through the capillary membrane when Pif is positive but outward when Pif is negative.
- The capillary plasma colloid osmotic pressure (Πp), which tends to cause osmosis of fluid inward through the capillary membrane.
- The interstitial fluid colloid osmotic pressure (Πif), which tends to cause osmosis of fluid outward through the capillary membrane.
Which of the following does not increase capillary filtration rate?
A. increased capillary filtration coefficient
B. Increased capillary hydrostatic pressure
C. Decreased plasma colloid osmotic pressure
D. Increased interstitial flulid hydrostatic pressure
D. Increased interstitial flulid hydrostatic pressure
All other situations would increase the capillary filtration rate.
How does excess protein affect the colloid pressure of the interstitium? What happens in face of impaired lymphatics?
Excess proteins in the interstitium can raise the colloid pressure of the interstitium, drawing more fluid out of the capillaries. If the lymphatic system is impaired, this can cause extracellular edema, as the proteins have no where to go!
List factors that help prevent edema.
- Low compliance of interstitium, as long as pressures stay in the negatives
- Ability of lymph flow can increase 10-50 fold.
- Washdown of interstial fluid protein concentration
At what level of interstitial fluid pressure changes the compliance of the interstitium? How does the interstital tissue change?
Once the interstitial fluid pressure rises above 0 mm Hg, the compliance increases markedly. The interstitium is made of a proteoglycan meshwork that prevents fluid from flowing easily through tissues. Once the interstitium is overwhelmed with fluid, the proteoglycan fibers are pushed apart, creating pitting edema.
How is non-pitting edema formed?
This forms when tissue cells acquire fluid, instead of the interstitium.
