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Osmotic pressure – van’t Hoff equation : = g C  R T Where:  - osmotic pressure (atm or mm Hg) g – number of particles per mole in solution (Osm/mol) C – concentration (mmol/L) - PowerPoint PPT Presentation

### Transcript of Osmotic pressure – van’t Hoff equation : = g C  R T Where:  - osmotic pressure...

• Osmotic pressure vant Hoff equation:

= g C R TWhere: - osmotic pressure (atm or mm Hg)g number of particles per mole in solution (Osm/mol)C concentration (mmol/L) - reflection coefficient (varies from 0 to 1, where 0 means that the membrane is freely permeable to that substance; and 1 means the membrane is totally reflective or impermeable to the substance)R gas constantT absolute temperature (K)

• Ficks law (diffusion/ conservation of mass)

Flux = P A (Cout Cin)Where:P = permeability factor; P is a combination of 3 factors:Diffusion coefficient the ease with which a substance moves through the membrane once it is in it; e.g. size and shape of the substance as well as membrane properties;Partition coefficient the lipid solubility of the substanceMembrane thickness

A = the cross sectional area available for diffusion

C = concentrations of the substance on either side of the separating membrane

• Starlings law of the capillaries is: The volume of fluid & solutes reabsorbed is almost as large as the volume filtered

Ans: Apply Starlings law (draw a picture to visualize)J = k [(BHP-IFHP) (BOP-IFOP)]WhereJ = fluid movement (ml/min)k = hydraulic constant (ml/min); k depends on permeability of capillaries, e.g fenestration; larger k means greater permeabilityJ = k [(301) (26-3)] = k (30 1 26 + 3) = k x (6 mm Hg)Therefore, net filtration will take place under 6 mm Hg pressure(If you are given a value for the constant, e.g. 0.5 ml/min, then fluid flow will be 0.5 x 6 = 3 ml/min)

• Volume of Blood FlowCardiac output = stroke volume x heart rate CO = SV x HROther factors that influence COblood pressureresistance due to friction between blood cells and blood vessel wallsblood flows from areas of higher pressure to areas of lower pressure

• Pulse pressure= systolic pressure diastolic pressure 120-80 =40 3:2:1

Mean Arterial Blood Pressure (MABP) = average pressure in arteries (not an arithmetic average)

MABP = diastolic BP + 1/3(systolic BP diastolic BP)

For example, if one has 140/80 BP, then MABP is

MABP = 80 + 1/3(140 80) = 80 + 1/3 (60) = 80 + 20 = 100

Recall that MABP can also be expressed as MABP = CO x TPR (cardiac output times total peripheral resistance)

• Blood Flow, Poiseuilles Lawand Viscosity, Laplaces Law and ComplianceBlood flowAmount of blood moving through a vessel in a given time periodDirectly proportional to pressure differences, inversely proportional to resistancePoiseuilles LawFlow decreases when resistance increasesFlow resistance decreases when vessel diameter increasesViscosityMeasure of resistance of liquid to flowAs viscosity increases, pressure required to flow increases

• Relationship between Pressure, Flow and ResistanceOhms Law I = V/RSimilarly, Q = P/R or P = Q x RWhereQ flow (ml/min) P pressure difference (mm Hg)R resistance (mm Hg/ml/min)Magnitude of Q is: directly proportional to P. Flow is always from high to low pressure.Inversely proportional to resistance; increasing resistance decreases flow.This formula can be used to calculate flow or resistance across a single organ or to calculate total peripheral resistance (TPR).

• Poiseuilles LawThe flow of (Newtonian) fluid through rigid tubes is governed by pressure gradient and resistance to flowQ = P/R, where R = 8l / (r4)(Ohms law)(Poiseuilles equation)Properties of the fluid and tube affect resistance to flow.Length of tube (l)R = 8l / (r4)Radius of tube (r)Viscosity of fluid ()

>>Viscosity> the resistance to flow again direct relationship>Radius < resistance inverse relationship SO SMALLER THE RADIUS GREATER THE RESISTANCE

• P1 V1 = P2 V2

Boyles law a special case of the genl gas lawThe pressure times volume (at a given t) is constant (diaphragm movement changes lung volume which changes P)

Daltons law - Partial pressureThe pressure exerted by each type of gas in a mixtureWater vapor pressure

Henrys law - Diffusion of gases through liquidsConcentration of a gas in a liquid is determined by its partial pressure and its solubility coefficient

• Daltons LawEach gas in a mixture of gases exerts its own pressure as if all other gases were not presentpartial pressures denoted as PTotal pressure is sum of all partial pressuresatmospheric pressure (760 mm Hg) = pO2 + pCO2 + pN2 + pH2Oto determine partial pressure of O2 - multiply 760 by % of air that is O2 (21%) = 160 mm Hg

• Henrys LawQuantity of a gas that will dissolve in a liquid depends upon the amount of gas present and its solubility coefficientBreathing compressed air while scuba divingN2 has very low solubility unlike CO2 (soda cans)dive deep & increased pressure forces more N2 to dissolve in the blood (nitrogen narcosis)decompression sickness if come back to surface too fast or stay deep too longBreathing O2 under pressure dissolves more O2 in blood

• Turbulent flow generates vibrations that can be heard with a stethoscope (murmurs and bruits)

Pathologic changes in cardiac valves or narrowing of arteries, which raises flow velocity, often induce turbulent flow

Reynolds number (dimensionless) is used to predict whether blood flow will be laminar or turbulent. If value is less than 2,000, blood flow will be laminar, greater than 3000 - turbulent.

NR = d v / NR is Raynolds number Anemia (decreases viscosity) is density of blood Thrombi (decrease diameter)d is diameter of blood vesselv is velocity of blood flow and is blood viscosity

• Compliance of blood vesselsC = V/P

The higher the compliance of a vessel the more volume it can hold at a given pressure

Aging decreases compliance of vessels which decreases the volume of blood that a vessel can hold

Changes in compliance causes redistribution of blood between arteries and veins. If the compliance of veins decreases (e.g. by venoconstriction), the volume of blood they can hold decreases and is moved to arteries.

• Capacitance = ability to distend, hold a volume of blood at a given pressure

• Critical Closing Pressure, Laplaces Law and ComplianceLaplaces law relate pressure, radius of vessel, and tension on vessel wall:Pv=T(1/r1+1/r2) where Pv is ventricular pressureFor a cylindrical vessel, P=T/r The larger the radius, the greater the tension needed to reach a given pressure.For a dilated heart (radius is increased),greater tension must be developed to reach any given pressure.

• Capillaries and alveoli importance of Laplaces lawP = T/r which is same as T = P x r

Small caps have small radius, thus can withstand high internal pressures without bursting.

If pressure is reduced, radius has to increase to maintain tension (which keeps a vessel open).

Under low enough pressure, the capillary or alveoli will collapse = CRITICAL CLOSING PRESSURE.(alveolar surfactants decrease tension in alveoli helping in preventing alveolar collapse)

• Einthovens law = if any two bipolar limb potentials are known, one can find the third (keep correct signs), e.g. lead I + lead III = lead II

Einthovens law can be used to measure the electrical axis of the heart.Axis of the heart provides information on changes of: heart position within chest cavity (left or right shift)Hypertrophy of one ventricle, which is related to hypertension, systemic or pulmonaryBundle branch block (left or right)

Please, see Ch. 12, figures 12 through 15 in Guyton for examples

• One Cardiac CycleAt 75 beats/min, one cycle requires 0.8 sec.systole (contraction) and diastole (relaxation) of both atria, plus the systole and diastole of both ventriclesEnd diastolic volume (EDV)volume in ventricle at end of diastole, about 130mlEnd systolic volume (ESV)volume in ventricle at end of systole, about 60mlStroke volume (SV); a.k.a. ejection fractionthe volume ejected per beat from each ventricle, about 70ml; normal ~ 65%, below 35% = leading cause of sudden cardiac arrest (need defibrilator)SV = EDV - ESV

• Mean Arterial Pressure (MAP)Average blood pressure in aortaMAP = CO x PRCO is amount of blood pumped by heart per minuteCO=SV x HRSV: Stroke volume of blood pumped during each heart beatHR: Heart rate or number of times heart beats per minuteCardiac reserve: Difference between CO at rest and maximum COPR is total resistance against which blood must be pumped

• Regulation of the HeartIntrinsic regulation: Results from normal functional characteristics, not on neural or hormonal regulationStarlings law of the heart- (Frank Starlings contractibility of the heart)Extrinsic regulation: Involves neural and hormonal controlParasympathetic stimulationSupplied by vagus nerve, decreases heart rate, acetylcholine secretedSympathetic stimulationSupplied by cardiac nerves, increases heart rate and force of contraction, epinephrine and norepinephrine released

• Pharmocology at NMJBotulinum toxin blocks release of neurotransmitter at the NMJ so muscle contraction can not occurbacteria found in improperly canned fooddeath occurs from paralysis of the diaphragmCurare (plant poison from poison arrows)causes muscle paralysis by blocking the ACh receptors used to relax muscle during surgeryNeostigmine (anticholinesterase agent)blocks removal of ACh from receptors - strengthens weak muscle contractions (as in myasthenia gravis)also an antidote for curare after surgery is finished

• Acidity & Oxygen Affinity for HbAs acidity increases, O2 affinity for Hb decreasesBohr effectH+ binds to hemoglobin & alters itO2 left behind in needy tissues

• Transport of Carbon Dioxidein tissue capillariesCarbon dioxide is transported as:1.bicarbonate ions (70%)2.in combination with bloo