Kidneys Flashcards
Total Body Water
- Extracellular fluid (1/3): ISF (3/4 = 9L), plasma (1/4 = 3L)
- Intracellular fluid (2/3)
~36L = in a 60 kg Man
60% in Man; 50% in woman. Decreases with increasing age, increasing fat composition b/c bone, proteins, fat have less water content.
ECF (components, predominant ion, amount, addition/loss of pure H2O, addition/loss of isotonic NaCl)
- 1/3 of TBW = ~12 L
- Predominant ion is Na+ [140 mmol/L]
- Interstitial fluid + plasma. Two components are separated by a capillary wall.
- Fluid enters through gastrointestinal tract (via absorption), lost via: 1) skin; 2) GI tract; 3) Urine
- Addition/Loss of pure water –> 1/3 will go into/out ECF
- 1/4 plasma (3L); 3/4 interstitial fluid (9L)
- Fluid gained/loss initially from ECF, then will be redistributed through ICF so that the final ratio of the pure water is 1/3 ECF, 2/3 ICF. Particularly through plasma.
- Addition of isotonic NaCl –> 1.Increased plasma volume 2. Increased hydrostatic pressure 3. Decreased intravascular oncotic pressure –> 1/4 of fluid will remain in the plasma; 3/4 of fluid will move towards the ISF. NONE will move towards ICF b/c isotonic solution. Fluid will be redistributed throughout the 2 compartments of ECF so osmolarity is equal in all compartments (ECF = ICF).
ICF (components, predominant ion, amount, addition/loss of H2O)
- 2/3 of TBW = ~ 24 L
- Addition/Loss of pure water –> 2/3 will go into/out ICF
- Predominant ion is K+ [140 mmol/L]
Interstitial fluid
- Fluid found in the microscopic spaces b/w tissue cells. Associated w/ the glycosaminoglycan matrix of tissues.
- 3/4 of ECF = 9 L of TBW
Major difference b/w interstitial fluid & plasma
- Plasma has a much higher concentration of proteins (i.e. albumin) than interstitial fluid. Prevents proteins from moving across the capillary wall and into ISF.
- Colloid oncotic pressure, mainly due to albumin. ~25 mmHg in plasma.
Similar components in ISF & plasma
- Bicarbonate; 2. Na+; 3. Cl-; 4. K+; 5. Urea; 6. Protein; 7. Glucose
Hypernatremia
An increase in [Na+] in the ECF, plasma (high ECF osmolarity). Occurs through the loss of free water from the ECF. Water will exit cells. Shrunken cells.
Free water
aka pure water. Free water is lost 2/3 from the ICF, 1/3 from the ECF. *Adding free water will change BOTH ICF & ECF. *Adding isotonic NaCl solution will only change the ECF. Would like to retain osmolarity.
Principles and impact of the loss/gain of fluid with any [Na+] on the various body fluid compartments
- Det. the total amount of Na+ lost (in moles)
- Det. the volume of isotonic fluid that would contain this amount of Na+. Achieved by (total amount of Na+ lost/gained in moles) / 140. The remaining fluid lost/gained w/ the Na+ is free water.
- This isotonic volume is lost/gained in the ECF (in a distribution of 1/4 in plasma, 3/4 in interstitial fluid) while the free water is lost/gained 1/3 in the ECF, 2/3 in the ICF.
Isotonic; hypotonic, hypertonic
Tonicity is equal, less, greater than normal plasma.
Cell membrane permeability
- Not very permeable to Na+, K+ (maintained by Na+/K+ ATPase pump)
- Not permeable to H20 (travels via aquaporins)
- Urea, ethanol is soluble
- Glucose requires a transporter
Hyponatremia
[Na+] in ECF (plasma) is low. H2O will leave cells –> shrunken cells.
Situations where patients w/ hyponatremia do not necessarily have swollen cells
- Hyperglycemia - Water leaves muscle cells & travels to ECF –> dilution of Na+ (shrunken cells). i.e. adding mannitol for cerebral edema or sorbitol (prostate surgery).
- Severe hypertriglyceridemia or hyperproteinemia in plasma -
ADH (Synthesis, mechanism of action, stimuli for release
aka vasopressin.
Synthesis: supraoptic & paraventricular nuclei of hypothalamus. Stored & released from the posterior pituitary.
Mechanism of action: Activates vasopressin receptors. V1 - vasoconstriction. V2 - antidiuretic response in renal collecting duct.
Insertion of water channels in luminal membrane of cortical & medullary collecting duct. –> increased water absorption.
Stimuli for release: 1) increased ECF osmolarity (hypernatremia via osmoreceptor in hypothalamus); 2) decreased effective arterial volume (hypovolemia, heart failure, cirrhosis)
