Importance of Fluids for the Circulation of Blood

Importance of fluids for the circulation of blood, gas movement, and gas exchange Fluids (PHY) • Density, specific gravity o Density: “heaviness” of a fluid, intensive property (analogous to mass in solids) ▪ P = m/v, units: kg/m3 ▪ Gases don’t separate based on polarity, separate based on density (liquids separate based on both) o Specific gravity: density of a substance compared to density of water, S.G. = p substance / pwater ▪ Meant to give us a better sense on how “heavy” a fluid actually is by comparing it to water, whose weight we have a good idea of • Buoyancy, Archimedes’ Principle o Buoyancy: Force that a standing fluid exerts on an object floating, submerged, or sunk in it ▪ FB = pfluidVfluidg • Shows buoyant force is proportional to how much fluid an object displaces o The deeper an object sinks, the more fluid it displaces o Archimedes Principle: Buoyant force is = in magnitude to mass of fluid displaced ▪ FB = mfluidg o 3 special cases of Buoyant Force ▪ 1) The Floating object • When the upwards buoyant force = the downwards force of gravity before an object is submerged • FB = mobjectg o Shows magnitude of buoyant force = weight of object • Mfluid = mobject o Shows mass of fluid displaced is = to mass of object • Fraction of object submerged = pobject/pfluid = Vfluid/Vobject o For a floating object, this ratio must be = to or < 1 ▪ 2) The Submerged Object • Mass AND volume of the object and fluid displaced are = • Vobject = Vfluid, mobject = mfluid o This means that pobject = pfluid • F B = Fg ▪ 3) The Sunk Object • Displaces Vfluid = to its own volume o May displace a different amount of mass, accounts for why it’s sunk (mass contributes to Fg) • Vobject = Vfluid • Pfluid / pobject = mfluid / mobject • Apparent weight of sunk object is less than the actual weight because both FB and FN counter Fg but only FN represents apparent weight o FB + FN = Fg o Fg = mobjectg o % of apparent weight lost = pfluid / pobject • Hydrostatic pressure o Pascal’s Law ▪ Pressure applied at any point to an enclosed fluid will distribute itself evenly throughout all the fluid ▪ P = F/A, P is constant while F and A are mutable and proportional to each other o Hydrostatic pressure: P = pgh (pressure vs. depth) ▪ ▪ ▪ • Pressure of an enclosed fluid is a function of depth Add pressures of multiple fluids in an enclosed area to get total pressure If the fluid is open to the atmosphere, the Ptotal = pgh + Patm • Air is a fluid too. Open container basically has the fluid of air sitting on top of the other fluids Viscosity: Poiseuille Flow o Poiseuille’s Law o • • • • • ▪ ▪ Used with real fluids Finds volume flow rate of a real fluid in terms of pressure, viscosity (n), pipe length, and pipe radius o Viscosity ▪ As viscosity of a fluid increases, flow rate decreases Continuity Equation (A x v = constant) o Cross sectional area vs. velocity ▪ Smaller the cross-sectional area → the greater the velocity ▪ Shows uniform translational kinetic energy increases as cross sectional area decreases Concept of turbulence at high velocities Surface tension o Describes intensity of IMFs of a fluid per unit length ▪ Factors affecting surface tension • Weakened at higher T’s (IMF’s more unstable) • Affected by properties of the fluid ▪ Pulls inwards on fluids in droplets and make them assume a spherical shape o Capillary action: phenomenon where fluid is pulled up a thin tube, mediated by surface tension ▪ In a tube filled with fluid, if… • Cohesive forces (IMF’s within a fluid) are stronger, then surface of fluid is convex • Adhesive forces (IMF’s between a fluid and the tube) are stronger, the surface of fluid is concave Bernoulli’s Equation o Pressure, kinetic energy, and potential energy of an ideal fluid is constant throughout that fluid ▪ Restates conservation of energy in terms of densities and pressures o Po + 1/2pvo2 + pgho = k ▪ Note: h does not = y • H = height above an arbitrary point, y = total distance beneath a surface ▪ vo = √2gh (derived from kinematics equation) o At a constant height, as velocity increases, pressure decreases Venturi effect, pitot tube o Pitot tube ▪ U-shaped, horizontal tube with one open end and mercury in the loop. Fluid flows into the open end and pushes the mercury up ▪ Takes height out of Bernoulli’s equation ▪ Purpose: determines velocity of fluid flowing past it o Venturi tube ▪ Horizontal tube with a constricted region in the middle ▪ Measure differential pressures in non-constricted and constricted region ▪ Purpose: determine the velocity of a fluid flowing within it o Venturi effect: as cross sectional area of a pipe decreases, pressure decreases Circulatory System (BIO) • Arterial and venous systems: pressure and flow characteristics o Filtration across capillaries ▪ 2 factors in determining direction and rate of filtration in a capillary: 1) hydrostatic pressure gradient between blood pressure and interstitial pressure 2) oncotic pressure (a type of osmotic pressure) Gas Phase (GC, PHY) • Absolute temperature, (K) Kelvin Scale o Absolute zero = -273 deg C o Kelvin to Celsius converter ▪ K = C + 273, absolute zero = 0 K o Temperature = KE per mole of molecules, intensive property ▪ Temp vs. thermal energy: thermal energy is extensive, describes total energy of molecular motion. Temperature is intensive, describes average energy per unit • Pressure, simple mercury barometer o Pressure: KE of a group of molecules per volume occupied, intensive property ▪ Translational KE = energy due to motion from one location to another o Mercury barometer: way of measuring atmospheric pressure ▪ Procedure • 1) Invert a test tube filled with mercury on an uncovered bath open to the atmosphere • 2) Some mercury falls into the bath, some stays in the test tube • 3) Plug the height of the remaining mercury into the equation: Patm = pgh o Patm = atmospheric pressure, p = density of mercury, g = 9.8 m/s2, h = height of mercury remaining in test tube ▪ Rationale: pressure of the atmosphere pushing DOWN on the bath is related to how much mercury is left in the test tube ▪ mmHg = how high in millimeters the mercury level is • Molar volume at 0 deg. C and 1 atm = 22.4 L/mol o At STP, one mole of any gas will occupy 22.4 liters • Ideal gas o Definition: 4 qualities ▪ 1) Gas molecules have no size, zero molecular volume (not the same as the size of the container) ▪ 2) Gas molecules don’t exert attractive or repulsive forces on one another (no IMF’s) ▪ 3) Gas molecules have completely elastic collisions ▪ 4) Average KE per gas molecule is proportional to the overall temperature of the gas o Ideal Gas Law: PV = nRT ▪ Unless told otherwise, MCAT gases are ideal ▪ • • • T: the temperature of the gas (taken in K for ideal gas) • Ideal gases are in thermal equilibrium with surroundings. Both gas and surroundings are at same temperature ▪ V: the volume of the container the gas is in • 2 types of containers: o 1) Flexible: volume of container changes depending on the temperature, pressure, and amount of gas within o 2) Rigid: volume is fixed and cannot change ▪ P: pressure exerted by the gas on the container • For a flexible container, P = the external pressure o If it didn’t, the container would stretch or shrink until P = external temperature • Pressure of gas in the atmosphere is always 1 atm o Boyle’s Law: PV = constant ▪ Pressure and volume are inversely proportional to keep PV a constant value o Charles’ Law: V/T = constant ▪ Increase in temperature leads to greater KE and speed per molecule. They speed up and start to collide with each other more, increasing the volume ▪ Volume and temperature are directly proportional to keep V/T constant o Avogadro’s Law: V/n = constant Kinetic Molecular Theory of Gases o Heat capacity at constant volume and at constant pressure (PHY) ▪ Effect of constant volume and pressure on heat capacity • Constant volume: if V is constant, a system can do no PV work so all E exchange must be in the form of heat. This means less E is needed to get to capacity required to change T by 1 C or K. • Constant pressure: P is constant so V can change. This means the system can do PV work as well so some E put in will go towards raising the V instead of changing the T. More E required to get to capacity • Cconstant V < Cconstnat P o Boltzmann’s Constant (PHY): used to calculate average KE of a single molecule in a given fluid, k = 1.38*10-23 J K-1 ▪ K.E. = 3/2 RT • R = ideal gas constant, T = temperature in K, K.E. = average KE per mole of molecules Deviation of real gas behavior from Ideal Gas Law o Qualitative ▪ Deviations occur when gas molecules get close together • B/c of volume of gas particles and electrostatic forces between gas particles (Coulombs Law) ▪ Deviations caused by high pressures or low temperatures o Quantitative (Van der Waals’ Equation) ▪ Preal < Pideal • Gas molecules exhibit mostly attractive forces on one another. Pulls gas molecules inwards, lowers collisions on container walls, and lowers P ▪ Vreal > Videal • Gas molecule size comes into play in a real gas. Volume of gas molecule increase the actual volume Partial pressure, mole fraction o In a mixture of gases, amount of pressure each gas contributes is proportional to how many • molecules it contributes to the mixture o Partial pressure: amount of pressure contributed by a single gas to a mixture ▪ Pa = xaPtotal • Pa = partial pressure of gas a, xa = molar fraction of gas a o Rxns involving gases can have their equilibrium constant written in terms of partial pressures ▪ Kp = partial pressures of products / partial pressure of reactants ▪ Kp = Kc(RT)Δn o Vapor pressure ▪ Vapor pressure: Pressure created by molecules above liquid surface at eq. Driven by entropy difference between liquid and gas phases (bigger difference → liquid wants to assume lower entropy more → higher vapor pressure) • Molecules on liquid surface get enough KE to break off into open space above liquid • Molecules in open space crash down into liquid • Equilibrium is reached when rate of molecules leaving surface and molecules reentering equals each other. Pressure at this equilibrium is vapor pressure • High vapor pressure = weaker bonds in solution, positive heat of solution • Low vapor pressure = stronger bonds in solution, negative heat of solution ▪ Differences in vapor pressure and partial pressure of solute in open space causes evaporation and condensation • Evaporation: partial pressure of solute is less than vapor pressure • Condensation: partial pressure of solute is greater than vapor pressure • Boiling: atmospheric pressure (sum of all partial pressures in open space) equals vapor pressure ▪ Vapor pressure is fixed at a given temperature (only factor that matters) ▪ Raoult’s Law • For a nonvolatile solute (solute with no vapor pressure) o Nonvolatile solute increases entropy of liquid phase while not increasing entropy of gas phase (doesn’t break off into open space) ▪ This lowers the entropy difference between liquid and gas (the driving force for vapor pressure), thereby lowering vapor pressure o More nonvolatile solute = less vapor pressure o Pv = XaPa ▪ Vapor pressure of solution = mole fraction of liquid “a” * vapor pressure of the pure liquid “a” Dalton’s Law relating a partial pressure to composition o Total pressure a gaseous mixture exerts is the sum of the partial pressure of each of its constituent gases