Renal Physiology - Body Fluid Compartments Flashcards
Define volume contraction.
- means a decrease in ECF volume; also called volume depletion.
- Volume contraction causes decreased blood volume and decreased blood pressure.
Define volume expansion.
- means an increase in ECF volume.
- Volume expansion can cause increased blood pressure and edema.
Fluid shift disturbances are categorized according to whether they cause a change in body fluid osmolarity. Name and describe all 3:
- Isosmotic means no change in body fluid osmolarity
- Hyperosmotic means body fluid osmolarity is increased
- Hyposmotic means body fluid osmolarity is decreased
Intracellular fluid compartments make up how much of bodily fluid? ECF?
ICF: 2/3, cytosol within cell
ECF: 1/3, plasma and interstitial fluid
other: lymph, CSF, humors of eye, serous fluid, GI secretions
What is the 60-40-20 rule?
60% of body weight is total body water, 40% of body weight, or 2/3, is ICF, 20%, or 1/3, is ECF
Explain the importance of ECF.
Extracellular fluid is an intermediary between the cells and the external environment.
- All exchanges of H2O and other constituents between the ICF and the external world must occur occur through the ECF.
- Water added to the body fluids always enters the ECF compartment first, and fluid always leaves the body via the ECF.
What is the significance of the relationship between ECF and plasma?
- Plasma is the only fluid that can be acted on directly to control its volume and composition.
- If the volume and composition of the plasma are regulated, the volume and composition of the interstitial fluid bathing the cells are also regulated.
- Any control mechanism that operates on plasma in effect regulates the entire ECF.
Define non-electrolytes
-contain covalent bonds that prevent them from dissociating in solution and therefore have no electrical charge (egs. glucose, lipids, urea)
Define electrolytes.
dissociate into ions (ionize) in water; Electrolyte examples –> Mg+, Na+, Cl-, K+
Electrolytes have a higher osmotic power than non-electrolytes because each electrolyte molecule dissociates into at least two ions
•NaCl -> Na+ + Cl-
•MgCl2 -> Mg2+ + Cl- + Cl-
•Glucose -> glucose
Thus, electrolytes have a greater ability to fluid shift.
What are the differences in electrolyte composition between ECF and ICF?
- Cellular proteins in ICF cannot leave the cell
- Unequal distribution of Na+ and K+ and their attendant
anions as a result of the action of the membrane-
bound Na+/K+ATPase present in cells. Na+ out of cells
and K+ into cells. - Bicarbonate (HCO3-) and Cl- are high in ECF but low in
ICF - Phosphate anions are high in ICF but low in ECF
ECF volume must be closely regulated to help maintain blood pressure. How is this accomplished?
Maintaining salt balance is of primary importance in the long-term regulation of ECF volume.
ECF osmolarity must be closely regulated to prevent swelling or shrinking of cells. how is this accomplished?
Maintaining water balance is of primary importance in regulating ECF osm
All body fluid compartments have approximately the same osmolality—expressed as the number of osmotically active particles per kilogram of water—what is it?
~290 milliosmoles/kg H2O (290 Osm).
What are the normal ranges for serum electrolytes?
Na+: 135-147 Cl-: 95-105 K+: 3.5-5.0 HCO3-: 22-28 Ca++: 8.4-10.0 Oi: 3.0-4.5 Anion gap: 8-16
What are the normal ranges for serum proteins?
Total: 6-7.8
Albumin: 3.5-5.5
Globulin: 2.3-3.5
other serum constituents: creatinine: 0.6-1.2 glucose: 70-110 urea nitrogen: 7-18 Osm: 285-295
Define solution tonicity
The tonicity of a solution is the effect the solution has on cell volume—whether the cell remains the same size, swells, or shrinks—when the solution surrounds the cell. Cells have NaCl conc. = 0.85%
What are the 3 types of solutions as it pertains to tonicity?
- Isotonic-cell environment has a NaCl concentration equal to 0.85%
–If cells are placed in isotonic solution, there will be
equal movement of water in and out of cell. - Hypertonic-cells environment has a NaCl concentration greater than 0.85%
–If cells are placed in hypertonic solution, there will be
a net movement of water out of the cell which will
cause the cell to shrink. - Hypotonic- cells environment has a NaCl concentration less than 0.85%
–If cells are placed in a hypotonic solution, there will be
a net movement of water into the cell which will
cause the cell to swell.
How do we calculate serum Osmolarity?
We recognize that the main solutes in the ECF are:
- Sodium
- Glucose
- Urea
Using these we are able to calculate serum osmolality as follows:
2 (serum [Na+]) + serum glucose/18 + serum blood urea nitrogen (BUN)/2.8 = 275-295 mOsm/kg
What hormonal mechanisms do we have to balance fluid compartments?
- Renal sympathetic nerves
- Renin-angiotensin-aldosterone system
- Vasopressin – Antidiuretic Hormone
- Natriuretic peptide secretion
What is the RAAS system and its constituents?
Renin is an enzyme secreted by the kidney
Release stimulated by drop in BP and by β1-adrenergic receptor activation
Causes angiotensinogen to be converted to angiotensin I(inactive) in the blood.
Angiotensin I is converted to angiotensin II (active) in the lungs (and kidneys) to begin the compensation mechanism
Angiotensin induces release of aldosterone.
What does Vasopressin do?
aka ADH; secreted in response to: –Angiotensin II –Atrial receptors in presences of low preload –Increased osmolality of blood –Sympathetic nervous system activation
What is ANP and its function?
Increased secretion by excessive preload of atria and ventricles (BNP)
•Induces:
–Arteriolar dilation–decreases TPR
–Increases fluid loss – decreases preload
–Inhibits renin – decreases both TPR and preload
*Main action of ANP is to directly inhibit Na+ reabsorption in the distal parts of the nephron, thus increasing Na+ excretion and accompanying osmotic H2O excretion in the urine.
What cause dehydration?
- Dehydration occurs due to a decreased water intake, increased fluid loss, or both.
- The common reasons for increased fluid loss include vomiting, diarrhea, diuresis and sweating.
- Dehydration can be divided, according to the serum Na+ concentration, into hypernatremic or hyponatremic dehydration.
Define hyponatremic dehydration.
- Loss of sodium is greater than the loss of water in ECF. •Serum sodium concentration in the ICF is greater than that of the ECF.
- Water shifts from the ECF to the ICF to establish osmotic equilibrium.
- Serum sodium and serum osmolality will be less than the normal range.
