Physiology - Renal Topic #1

• 1. fluid balance / plasma volume
• 2. regulation of body fluid osmolarity (solute concentration)
• 3. electrolyte balance (Na K HCO Cl Ca)
• 4. regulates plasma pH
• 5. waste excretion -(urea creatinine penicillin, saccharin)
• 6. hormone production - erythro poetin (EPO) stimulates red blood cell synthesis, calcitriol- is the active vitaminD3 (1,25-dihydroxycholecalciferol) starts off as cholesterol but is then formed into calcitriol

• total body water is 60% of their body wieght
• (0.6xbody weight) (60 kg about 36L)
• the ICF contains 2/3 (24L) and the ECF contains 1/3 (12L)
• ISF contains 3/4 (9L) and plasma contains 1/4 (3L) of the ECF fluid

• more fat = less body water (fat crowds out the water)
• women have less water (breasts and hips are more fatty)
• less body water with age (ISF diminishes)
• plumpness of new borns due to water not fat

• Input=Output
• INPUT (2.4L/d)
• most from water/food. (2.1 L), some from metabolism (0.3 L)

• OUTPUT (2.4L/d)
• sweat (0.35L), lungs (0.35L), urine (1.5L), feces (0.2L)

• Osmosis = diffusion of water down is gradient
• each mole creates an OSMOTIC FORCE of 1mOsmol
• Osmolarity - measured in: mOsmol/L
• Osmolality - measured in: mOsmol/Kg (H2O)
• Ionic solutions – measured in: mEq/L (milli equivalent)
• 1 mol K+=1mEq/L 1mol Ca2+=2mEq/L (charge dependant)
• ECF osmolarity is about 300mOsmol/L

• depends on number not size of solutes dissolved
• (300 mM of solute= 300mOsM)
• Salts (likeNaCl) dissociate into ions in water
• osmolarity of 150 mM NaCl solution =300mOsM
• (0.9g/dl or 0.9%) this is "normal saline"

• not all dissolved molecules contribute to osmotic pressure
• non penetrating solutes:
• ethanol diffuses accross membranes
• urea and glucose are transported into cells
• cellular metabolsim creates solutes(glucose)
• penetrating solutes are NOT effective osmoles (solutes which do NOT contribute to osmotic pressure):

• tonicity= the ability to move water across membrane in response to osmotic change
• hypertonic = higher conc outside, water moves out
• hypotonic = lower conc outside, water moves in
• isotonic =same conc outside, no net movement

• Plasma to ISFacross:
• Starling Forces: capillary pressure, osmotic pressure, tissue pressure
• ISF to ICF (across cell membrane):
• osmotic effects alone

• ECF volume maintains blood pressure
• ICF volume (cell shrink/swell) is altered when ECF osmolarity changes
• ECF volume depends on salt balance (retain salt=retain fluid)

will distribute into: ECF only

effect on osmotic gradient across cell is unchanged (eg. normal saline)

• distribute into: ECF (1/3) and ICF (2/3)
• used to increase ICF volume
• hemolysis: too much water entering RBCs
• slightly soluted solution prevent this (Eg 0.3=5% glucose solution)