University:
Western Sydney University
Course:
MEDI 2003 | Clinical Sciences 2
Academic year:

2024
Views:

70

Pages:

3
Author:

Mariam A. A.

• • Interstitial fluid Normal o Pint = 4-6mmHg → holds tissue together o 12L H2O in Gel → relatively stable i.e. 10-0mmHg plasma oncotic pressure ▪ Low compliance pool Increasing volume load o Pint moves towards 0 o High compliance range o Big increase in fluid o High compliance pool → oedema Osmosis • Diffusion of water across a semi-permeable membrane down a concentration gradient o Water molecules move from an area of low solute → high solute • Due to thermal motion of water molecules and dissolved substances in the fluid Properties of solutions • Mole: a number of particles equal to Avogadro’s number (6.022 x 1023) o 1 mole of substance = molecular weight in grams o E.g. molecular weight of Na = 23 o 1 molar solution of Na+ would have 23g/L Na+ • Molarity: moles/litre of solution (mol/L, M) • Molality: moles/kg of solvent • • • • o Water is the solvent in biological fluids o In dilute aqueous solutions molality = molarity Solution = solute + solvent Osmole: Avogadro’s number of osmotically active particles in a solution o For non-ionic solutes, osmoles ~ moles ▪ E.g. 0.5 mole urea → 0.5 osmole o For ionic solutes, the extent of dissociation in solution determines the number of osmoles ▪ E.g. 1 mole NaCl → 2 osmoles (1 osmole of Na+ + 1 osmole of Cl-) Osmolarity: osmoles/litre of solution o E.g. 300mmol/L glucose = 300 mOsm/L o E.g. 150mmol/L NaCl = 300 mOsm/L Osmolality: osmoles/kg of solvent Osmotic pressure of a solution • Hydrostatic pressure required in order to prevent any water movement due to osmosis Starlings forces • Governing H2O movement in systemic circulation Cardiac failure • Cardiac failure = when cardiac output decreases below body requirements • Left heart failure: ↓left-sided cardiac output → inadequate removal of blood by left heart from pulmonary veins → sustained perfusion of lungs → o Progressive shift of blood volume from systemic to pulmonary circulation o ↑ right atrial pressure o ↑ mean pulmonary filling pressure o ↑ pulmonary capillary pressure • → pulmonary vascular congestion and oedema