BIOL 1104 Lecture Notes - Extracellular Fluid, Colligative Properties, Fluid Compartments

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11 Feb 2013
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Overview of Renal System-- Guggino
I. Functions of the human kidney
a. Main function: maintain volume and solute concentration in extracellular fluid
b. Also, excretes substances, makes glucose, NH3, and hormones
II. Control of fluid compartments
a. Fluid is compartmentalized in the human body
-Intracellular fluid: holds about 2/3 of body fluid
-Extracellular fluid: holds about 1/3 of body fluid
1. Interstitial fluid (ISF)—between cells & outside of bloodstream,
ultrafiltrate of plasma but doesn’t contain many proteins
2. Intravascular fluid (IVF)—includes plasma & RBC
3. Transcellular fluids (TCF)—special glandular secretions (tears)
b. Statistics:
- Body composed of ~60% water
- 20-25% total cardiac output is blood sent to kidney
- ~180 L are filtered thru kidney (enter bowman’s capsule) but only 1-1.5
L are excreted per day
c. Water is freely exchangeable among all body compartments, but distribution is
controlled:
- By solute concentration, ie osmotic pressure (a colligative property)
- By hydrostatic pressure—pressure created by H2O presence
- Means of solute migration:
1. permeability
2. transporters
3. ion pumps (a transporter) and membrane potential
d. Solute distribution
- ICF & ECF have different ion distributions
1. ICF—high [K], high [protein] & [inorganic/organic phosphate]
2. ECF—high [Na], high [Cl]
-ISF is different from IVF
1. ISF has very little protein
2. ISF has different [divalent cations] (b/c they normally bind to
proteins rather than dissolve freely)
e. Regulation of Cell Volume (ICF)
- Reason: allows conduction in nerve/mm cells, all cells are permeable to
H2O, prevents overfilling/drying up
-Na/K pumps—pump 3Na out for every 2K into cell; key in maintaining
composition of ICF & controlling cell volume
- When pumps stop cells swell!
- Healthy cells are capable of controlling their own internal [solutes] by
taking up/letting out different ions
f. Control of ECF Volume
- Intake from GI tract (eating/drinking), Outflow via kidney & sweat
-Epithelia—determine composition of ECF by matching in & outflow
III. Homeostasis (control theory)
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