Molecular Biophysics

Question 1

Explain the fundamental system of SI base units.

Answer 1

The base SI units are: A, cd (luminous intensity), s, Kg, m, mol and K. All other units (derived SI units) are made up from the 7 fundamental SI units. E.g unit of velocity = [m s^-1]

Question 2

List the subsidiary units.

Answer 2

atto - a - 10^-18

femto - f - 10^-15

pico - p - 10^-12

nano - n - 10^-9

micro - µ - 10^-6

milli - m - 10^-3

centi - c - 10^-2

deci - d - 10^-1

deca - da - 10¹

hecto - h - 10²

kilo - K - 10³

mega - M - 10⁶

giga - G - 10⁹

tera - T - 10¹²

petra - P - 10¹⁵

exa - E - 10¹⁸

Question 3

Describe the different kinds of phase states of matter.

Answer 3

Matter can exist in various phases - phase is mostly dependent on temperature and pressure.

Plasma Phase: a plasma is created by heating a gas or subjecting it to a strong electromagnetic field. Plasma is electrically conductive. Like a gas, plasma does not have a definite shape or a definite volume unless enclosed in a container. Unlike gas, under the influence of a magnetic field, it may form structures such as filaments, beams and double layers.

Gaseous
• gas consists of large number of identical molecules with random velocities
• kinetic energy is energy of translation
• molecules don’t interact except brief elastic collisions with each other and container walls
• average distance between molecules greater than diameter
Liquid
• number of molecules per unit volume greater than in gaseous phase
• less compressible and volume changes with temperature lower than gases
• surface tension due to Van der Waals
Solid
• crystalline structure is feature of solids
• ions, atoms or molecules from lattice with special spatial arrangement
• components of lattice oscillate around equilibrium position and amplitude of vibrations is function of temperature
• supply of thermal energy increases amplitude of vibration and lattice may collapse at high temperatures

Question 4

What are the four assumptions of an ideal gas?

Answer 4

Four assumptions for ideal gas model:

i) The gas consists of a large number of identical molecules moving with random velocities
ii) All kinetic energy of molecules is only energy of translation
iii) The molecules do NOT interact except for BRIEF elastic collisions with each other and the wall of the container
iv) The average distance between the molecules is much greater than their diameter

Question 5

State the ideal gas law. What is the The Boltzmann constant?

Answer 5

Ideal Gas Law - the pressure and volume of an ideal gas is directly proportional to the number of moles, and temperature of the gas:

P v = n R T

where…

P = Pressure [Pa], v = Volume [m³], n = moles [mol], R = universal gas constant = 8.31 [JK^-1mol^-1], T = temp [K]

Avagadro’s constant N_A = the number of constituent particles in one mole of a substance

= 6.022 x 10²³ [mol^-1]

The Boltzmann constant k = R / N_{A =} 1.38 x 10^-23 [JK^-1]

Boyle’s Law - T is constant, an isothermal process takes place - P₁V₁ = P₂V₂

Gay-Lussac’s Law - P is constant, and isobaric process takes place - V₁/T₁ = V₂/T₂

Charles’ Law - V is constant, isochoric process takes place - P₁/T₁ = P₂/T₂

Adiabatic process - There is NO heat exchange with environment Q = 0, (fastest thermodynamic process)

Question 6

Describe the Maxwell-Boltzmann distribution.

Answer 6

The Maxwell-Boltzmann distribution is a function that describes the distribution of velocities of molecules of an ideal gas. The distribution depends on the temperature of the system and the mass of the particle.

The higher the temperature the broader the form of the curve and the position of the peak is shifted to the higher velocities (the right).

Question 7

What is meant by the kinetic theory of gases?

Answer 7

The kinetic theory describes a gas as a large number of submicroscopic particles (atoms or molecules), all in random motion. The rapidly moving particles constantly collide with each other and with the walls of the container.

Kinetic theory explains macroscopic properties of gases, such as pressure, temperature, viscosity, thermal conductivity, and volume, by considering their molecular composition and motion. The theory posits that gas pressure is due to the impacts, on the walls of a container, of molecules or atoms moving at different velocities.

Kinetic theory of Gases - The total energy U_k of translational motion of 1 mol of a single atom is given by the formula:

U_k = (3/2)RT - Temp. is related to kinetic energy. The spectra of a molecular system contains lines corresponding to excited vibration and rotation states of molecules. Since small energy differences correspond to the changes of these states, these lines can be observed in the infrared spectrum region.

Question 8

What is the theorem of the equipartition of energy?

Answer 8

According to Maxwell’s theorem - each degree of freedom has an average energy = (½)kT

When thermal energy is supplied to a molecular system, it fuels vibrational and rotational motion.

The number of degrees of freedom (i) is dependent on the number of atoms in the molecule, where for:

a single atom of gas, i = 3

molecules composed of 2 atoms, i = 5

molecules composed of 3 or more atoms, i = 6

Question 9

What is Bernoulli’s equation, and what does it describe?

Answer 9

Bernoulli’s equation is a formula for ‘the law of energy conservation for liquids’. It describes how the work done on a flowing liquid is equal to the change in its mechanical energy. Liquid flowing in a tube into a smaller cross-sectional area follows the equation:

P + (½)ρv² + hρg = constant

The sum of pressure and total mechanical energy of liquid per unit volume is constant everywhereina flowing tube. P = absolute pressure of the fluid. The term (½)ρv² is kinetic energy, while hρg is the potential energy of the fluid per unit volume. The pressure at the same depth at two places in a fluid at rest is the same.

Question 10

Equation of continuity. What is an ideal fluid?

Answer 10

Idela fluids are incompressible and have no viscosity (they do not actually exist).

The equation of continuity holds that if a certain volume of an ideal liquid enters one ned of a tube per unit time, the same volume must leave the other end.

Q = ΔV / Δt

Q = flow rate [m³s^-1]

Flow rate = cross-sectional area of the tube times the velocity of the fluid:

A₁v₁ = A₂v₂

Question 11

The Law of Laplace

Answer 11

Leplace’s law describes the relation between the pressure difference (ΔP) across the surface of a closed circular membrane and its wall tensionT [Nm^-1]

ΔP = T(1/R₁ + 1/R₂) Where R’s = membrane curvature at given points.

The greater the pressure change, the greater the tension in the wall of the membrane. Clinical relevance, small radii of capillaries are able to withstand reasonably high blood pressures.

For a sphere where R₁=R₂=R and thus ∆P = 2T/R

Question 12

Gibb’s phase rule

Answer 12

Gibb’s Law: The degrees of freedom of a heterogenous system is determined by the number of phases that coexist together and by the number of independent portions that created the system.

It relates the number of components, phases and degrees of freedom of a dispersion system:

p + d = c + 2… where… p = phase, d = degrees of freedom, c = chemical component

A dispersion system has at leats two phases: dispersive portion (not contiunous) is dispersed within the dispersing medium (continuous).

Heterogeneous - a boundary exists between the dispersive portion and the dispersive medium (water and oil); if the refractive index of the two phases is different, then heterogenity in light transsion is observable.

Homogeneous - e.g sugar in water, single-phase system is optically homogenous. It may contain more than two portions. The dispersion portion is dispersed in the medium in the form of particles so small that they can’t be observed - hence optically homogenous. Law of Gibb’s relates no. of components, phases and degrees of freedom.

The number of degrees of freedom of a heterogeneous system is the number of independent variables defining the equilibrium state (pressure, temp, concentration) which can be individually changed without the changing number of phases. i.e when 2 phases are in equilibrium (gas and liquid) the system has 1 degree of freedom (either pressure of temp). however with 3 phases (sol, liq & gas) in equilibrium p = 3, there are 0 degrees of freedom - triple point

Question 13

Phase Chart of Water.

Answer 13

Plot of pressure (y axis) against temperature (x axis) in which there are well defined areas corresponding to the solid, liquid, and gas phase. The areas are separated by lines of sublimation (a), fusion (b) and evaporation (c). Line of evaporation represents equilibrium between liquid and vapour phases and represents boiling points at a given pressure. This line ends at critical temperature. A vapour CANNOT be converted back into a liquid at a temp. higher than the critical one. The triple point represents the point where all three phases can exist in equilibrium.

Question 14

What are Liquid crystals?

Answer 14

Liquid crystals (LCs) have properties between that of a liquid and solid. A liquid crystal may flow like a liquid, but its molecules may be oriented in a crystal-like way. Different types of liquid-crystal phases can be distinguished by their different optical properties (such as birefringence). When viewed under a microscope using a polarized light source, different liquid crystal phases will appear to have distinct textures. The contrasting areas in the textures correspond to domains where the liquid-crystal molecules are oriented in different directions. Within a domain, however, the molecules are well ordered. LC materials may not always be in a liquid-crystal phase (just as water may turn into ice or steam).

Liquid crystals can be divided into thermotropic, lyotropic and metallotropic phases. Thermotropic and lyotropic liquid crystals consist of organic molecules. Thermotropic LCs exhibit a phase transition into the liquid-crystal phase as temperature is changed. Lyotropic LCs exhibit phase transitions as a function of both temperature and concentration of the liquid-crystal molecules in a solvent (typically water). Metallotropic LCs are composed of both organic and inorganic molecules; their liquid-crystal transition depends not only on temperature and concentration, but also on the inorganic-organic composition ratio.

Most contemporary electronic displays use liquid crystals.

Question 15

Water as a solvent, and general fun facts about water (H₂0)

Answer 15

The water molecule is dipole. The bond angle of water = 105° due to the 2 lone pairs of electrons that oxygen has. O-H bond = 100pm the hydrogen bond = 180pm. On the contrary to other liquids, whose density decreases with increasing temperature, the highest density of water is observed at around 4°c.

Water is a polar solvent due to its large dipole moment.

Aggregated water molecules form the hydrate sheath when ions are then no longer surrounded by their partners. E.g Na⁺ ion radius = 0.095nm but in solution = 0.24nm. Reaction between water and surface of hydrophilic substances results in bound water.

Water in blood, skeleton and muscles = 79%, 22% and 76%

1.0g of albumin binds 1.3g of water

relative permittivity of water roughly = 80

Question 16

Dispersion systems and their classification

Answer 16

A Dispersion system has at least 2 parts to it:

dispersive portion - dispersed in the medium, not continuous

dispersive medium - continuous

-A dispersion system can be classified by various parameters:

A. Size of the particles → reciprocal value of particle diameter (m^-1) is called the dispersion degree - very fine particles possess a high dispersion degree

B. According to phases of dispersive medium and dispersive portion. E.g…

Dispersive medium

Dispersive portion

Coarse dispersions

Colloidal dispersions

Analytical dispersions

Gaseous

Gaseous

-

-

Mixture of gases

Liquid

Rain, fog

Aerosols

Vapours of liquids

Solid

Dust, smoke

Aerosols

Vapours of solids

Liquid

Gaseous

Bubbles, foams

Foams

Solution of gasses in liquids

Liquid

Emulsions

Lyosols

Solutions of solids in liquids

Solid

Suspensions

Lyosols

Solid

Gaseous

Rigid foams, bubbles of gas in solids

Rigid foams

Gas dissolved in a solid

Liquid

Bubbles closed in solids

Rigid foams

Crystalline water

Solid

Rigid mixtures

Rigid sols

Rigid solutions, doped crystals

Several types:

• Monodispersed system*: dispersed particles are of the same size
• Polydispersed system*: dispersed particles are of various sizes

Based on specific size:

• Analytical dispersion*: dispersed portion particles are up to 1nm in diameter
• Colloidal dispersion*: 1 - 1000 nm
• Coarse dispersion*: 1 μm and greater

Question 17

Properties of colloid particles

Answer 17

• Particle size is 1- 1000 nm
• There are 2 types of colloidal solutions: (lyophobic and lyophillic) dependent on behaviour with respect to their solvent.
• There are two types of colloidal particles:
• Macromolecules*: molecular polymers of smaller molecular components bound by chemical bounds (ex: proteins, carbohydrates, etc)
• Micelles*: clusters of particles without any chemical bonds.

Properties:

• Colloidal particles move in solution as individual particles.
• Movement is zigzagged –Brown motion due to repeated collisions with molecules of solvent
• Velocity of sedimentation due to gravity, v = 2(ρ−ρ₀)gr² ÷ 9η, ρ = density of particle and ρ₀ density of liquid, r = radius of particle, η = coefficient of viscosity
• Permeability or impermeablility across membranes (used to separate colloidal particle from the analytical portion of the solution or the dispersing medium itself)
• Tyndal phenomenon: scattering of light rays that hit colloidal particles in a solution. The intesity of scattered light depends on the particle’s size. For monodispersed systems, (particles are of the same size) the intensity of scattered light can be used to estimate the conc. of the particles.

On the surface of colloidal particles lays a double layer of charged particles.

Question 18

Dialysis

Answer 18

Dialysis is a process for removing waste and excess water from the blood and is used primarily as an artificial replacement for lost kidney function.

Dialysis works by the diffusion of solutes and ultrafiltration of fluid across a semi-permeable membrane. Diffusion is a property of substances in water; substances in water tend to move from an area of high concentration to an area of low concentration. Blood flows by one side of a semi-permeable membrane, and a dialysate, or special dialysis fluid, flows by the opposite side. A semipermeable membrane is a thin layer of material that contains holes of various sizes, or pores. Smaller solutes and fluid pass through the membrane, but the membrane blocks the passage of larger substances (for example, red blood cells, large proteins). This replicates the filtering process that occurs in the glomerulus of the kidneys.

The two main types of dialysis, hemodialysis and peritoneal dialysis.

Hemodialysis removes wastes and water by circulating blood outside the body through an external filter, called a dialyzer, that contains a semipermeable membrane. The blood flows in one direction and the dialysate flows in the opposite. The counter-current flow of the blood and dialysate maximizes the concentration gradient of solutes between the blood and dialysate, which helps to remove more urea and creatinine from the blood.

In peritoneal dialysis, wastes and water are removed from the blood inside the body using the peritoneum as a natural semipermeable membrane. Wastes and excess water move from the blood, across the peritoneal membrane, and into a special dialysis solution, called dialysate, in the abdominal cavity.

Question 19

Principle of electrophoresis

Answer 19

• Electrophoresis is a technique used to separate and sometimes purify macromolecules - especially proteins and nucleic acids - that differ in size, charge or conformation.
• It is one of the most widely used techniques in biochemistry and molecular biology.
• When a charged molecule is placed in an electric field, it migrates toward either the positive (anode) or negative (cathode) pole according to its mass: charge ratio.
• The migration velocity is proportional to the strength of the electrical field & the charge of the molecule, and inversely proportional to its mass.

In contrast to proteins, which can have either a net positive or net negative charge, nucleic acids always have a negative charge due to their phosphate backbone, and migrate towards the cathode.

Question 20

What is meant by electrokinetic (Zeta) potential?

Answer 20

The zeta potential is a key indicator of the stability of colloidal dispersions.

Zeta potential is the potential difference between the dispersion medium and the stationary layer of fluid attached to the dispersed particle.

Zeta potential [mV] : Stability behavior of the colloid

from 0 to ±5, Rapid coagulation or flocculation

from ±10 to ±30 Incipient instability

from ±30 to ±40 Moderate stability

from ±40 to ±60 Good stability

more than ±61 Excellent stability

Question 21

What is meant by transport phenomena?

Answer 21

Transport phenomena are related to the motion of molecules and interaction between molecules causing the net movement of physical quantities.

• viscosity is the transport of momentum
• conduction of heat is the transport of energy
• diffusion is the transport of molecules.

-In order for transport of any of these things to occur, an appropriate gradient must exist.

Ex: concentration, temperature, or velocity gradient.

Question 22

Viscosity

Answer 22

• Viscosity is a measure of the internal friction of a fluid between adjacent layers of liquid molecules as they slide past each other.
• The ideal fluid has 0 viscosity.

Fluids that have small values of viscosity move more readily and behave more like ideal fluids.

• In a cylindrical tube of radius r, a velocity gradient exists with the velocity vectors oriented in a parabolic fashion.
• Tangent tension (σ):* the force of internal friction F results in tangent tension. It is proportional to the vector of the velocity gradient (S).

Unit is the Pascal (N/m²)

σ = F/S σ = n ∆v

∆r

• Dynamic viscosity:* the proportionality coefficient n (unit is Pa.s)
• Kinetic viscosity*: the dynamic velocity (n) / density (p)(unit is m².s^-1)
• Newtonian liquids*: have a tangent tension proportional to the velocity gradient
  ex: single component liquids and analytical solutions
• Non-Newtonian liquids*: have a tangent tension that is not proportional to the velocity gradient
  ex: colloidal particles, suspensions, and emulsions

Factors that influence viscosity:

• Temperature → Since the motion of particles depends on temp so does viscosity.

~In liquids, viscosity decreases with increasing temp

~In gases, viscosity increases with increasing temp

• Concentration of suspended particles (c) → The greater the conc. of suspended particles, the greater the viscosity. i.e. higher hematocrit raises the viscosity of blood

Ns= n(1+kc)

*The highest Velocity V_max is in the center of the tube.

Velocity decreases with increasing distance from the center of the tube until it reaches 0 at the walls of the tube.

Question 24

Viscosity measurement

Answer 24

• the measurement of viscosity of solutions is important for determining the molar weight, especially for macromolecular substances of higher viscosity.
• Uses the equation for flow rate Q (Hagen-Poiseulles Law (2.26))
• Ostwald viscosimeter:*

The liquid measured is soaked from the wide pipe into the narrow one and the given volume flows back. The time it takes to flow back is measured.

• Body viscosimeter:* applies Stoke‘s law
• -* a spherical body is let to fall down in the given liquid and the time of its fall (or the rise of the gas bubble ) is measured
• The internal friction force F for a sphere of the radius r moving in a medium of viscosity n at velocity v is given by:

Stokes law: F= 6πnrv

Question 25

Diffusion

Answer 25

• In spite of the random motion of molecules, diffusion is the net movement of dissolved particles down their concentration gradient from a region of higher concentration to a region of lower concentration.
• it functions against the vector of concentration gradient ∆c/∆x where ∆c = c₁-c₂
• -density of diffusion flux* –is proportional to the concentration gradient

n/At = -D(∆c/∆x) ← Fick’s Law

n = # of moles A = area through which diffusion takes place t = time taken

unit for diffusion is (mol.m^-2.s^-1)

D = diffusion coefficient (m² s^-1)

*D is negative because the direction of flux is opposite to the direction of the concentration gradient.

-The mean squared displacement is proportional to time and the diffusion coefficient by

x_rms² = 2Dt

*This equation can be used to calculate the time required for a diffusing particle to move a certain distance

D = diffusion coefficient (m² s^-1)

• The value of D is dependent on the nature of the diffusing particle and the choice of solvent or medium.
• It is also dependent on temperature (the relationship is directly proportional)

D = kT/6πnr

where T=temp, n=viscosity, r=radius, k=boltzmann constant

*Therefore, an increase in temperature accelerates diffusion

Importance of Diffusion:

-It is the primary mechanism for absorption and distribution of substances between cells and with the organism’s environment → absorption in small intestine, respiration in lungs, excretion in the kidney.

Question 26

First Law of Fick

Answer 26

-Describes the relationship between the density of diffusion flux and the concentration gradient → they are directly proportional.

n/At = -D(∆c/∆x)

n = # of moles A = area through which diffusion takes place t = time taken

unit for diffusion is (mol.m^-2.s^-1)

D = diffusion coefficient (m² s^-1)

*D is negative because the direction of flux is opposite to the direction of concentration gradient.

***Both surface tension and adsorption are phase border phenomena that result from the forces between molecules***

Question 27

Surface tension

Answer 27

• Surface tension is a property of the surface of liquids in which the surface behaves like an outstretched rubber sheet
• The cohesive forces (attractive in nature) between liquid molecules are responsible for surface tension.
• cohesive forces at the surface are directed toward the center of a liquid and cause the liquid to have a minimum surface area. (this is why droplets of liquid obtain a spherical shape → min surface area)
• Below the surface of a liquid, the cohesive forces act on a molecule from all directions and are equilibriated.
• However, at the surface of a liquid, the cohesive forces are unbalanced causing a net force pulling the molecules back toward the liquid.
• Surface tension is a force acting perpendicularily to the surface of the liquid and its unit is N/m and dimension is kg/s²

Surface tension is dependent on:

Temperature → surface tension decreases with increasing temperature

Nature of dissolved particles → some particles can decrease surface tension (surface-active particles)

*surface tension is NOT dependent on the surface area of a liquid

Question 28

Adsorption

Answer 28

• -Adsorption* is a process that occurs when a gas or liquid solute accumulates on the surface of a solid or a liquid (adsorbent), forming a molecular or atomic film.
• Like surface tension, it is the result of surface energy.
• Surface-active molecules decrease surface tension and thus facilitate adsorption
• At the surface of a liquid, atoms are not wholly surrounded by other atoms of the same type and bonding forces are not equilibriated. Thus the molecules will bind to whatever is available including molecules or atoms of the adjacent phase.

This is due to molecules having an attractive force to unlike molecules → van der waals force or interaction. Van der waals forces are created between atoms/molecules with regions of positive and negative charge.

• When the molecules of a liquid are attracted to those of a solid it is know as adhesion and it is the phenomenom seen in water sticking to the sides of its container.
• Against the tendency of adsorption, is the need to equilibriate the concentration within the liquid. Thus diffusion of solute takes place until an adsorption equilibrium is reached along the boundary of the liquid.
• This equilibrium state is described by Gibb’s adsorption equation which describes the surface concentration of a substance (mol/m²)

Γ = -c / RT x dσ / dc (2.44)

Question 29

Colligative properties of solutions

Answer 29

Colligative properties of solutions are those that depend only on the number of solute particles and not on the identity of those particles

*They are independent of size, form, chemical behaviour, or type: molecules/ions

• There are 4
• Vapor-pressure lowering* (1st Law of Raoult) –if a substance is dissolved in a solvent, the partial pressure of the solvent above the solution will be lower with respect to pure solvent

Formula: (2.37)

Boiling-point elevation (2nd Law of Raoult) –A liquid boils when its vapor pressure equals atmospheric pressure. If the vapor pressure of a solvent has been decreased by addition of solute particles, more energy is required to reach the boiling point

Formula: (2.38)

• Freezing-point depression* (3rd Law of Raoult) –The freezing point of a solution is lower than that of pure solvent because the solute particles interfere with crystalline structure formation
• Osmotic pressure*
• Osmotic pressure is the pressure exerted by a column of water that counterbalances osmosis across a semi-permeable membrane → the flow of water molecules from a region of low solute concentration to a region of high solute concentration.
• It is dependent on the number of particles present in solution that can’t diffuse across the semi-permeable membrane

Question 30

Osmotic Pressure inc. Starling’s hypothesis

Answer 30

• Osmotic pressure is a colligative property meaning that it is dependent only on the number of particles present and not on the nature of those particles.
• Osmotic pressure is the pressure exerted by a column of water that counterbalances osmosis across a semi-permeable membrane → the flow of water molecules from a region of low solute concentration to a region of high solute concentration.

Thus osmotic pressure opposes the influx of water into a compartment with high solute concentration.

Influx of water ceases when the hydrostatic pressure of the inflowing water molecules equals the osmotic pressure of the solution.

*Only solute molecules that can’t cross the semi-permeable membrane contribute to osmotic pressure.

*Vant Hoff Laws quantitatively describe osmotic pressure.

a) At constant pressure, osmotic pressure is directly proportional to the molar concentration of a solution

P_osm = kC_m

*Where units of C_m are mol/m³

b) Osmotic pressure is directly proportional to temperature

P_osm = C_mRT

*where R is the universal gas constant + T is the absolute Temperature in Kelvin

c) At a given osmotic pressure, the same volumes of different solutions (at same temp) contain the same amount of dissolved particles.

*analytical solutions have higher osmotic pressures than colloidal solutions bc the latter particles are large and there are less of them in solution. (osmotic pressure is directly proportional to the # of solute particles)

*Also dissociated ion solutions have twice higher osmotic pressures as compared to nondissociated solutions of the same concentration.

Osmosis

• Hypotonic solution*: one of low solute concentration
• Hypertonic solution*: one of high solute concentration
• Isotonic solutions*: those that have equal solute concentrations
• Water will move from a hypotonic to hypertonic solution
• A cell will expand and lyse if placed into a hypotonic solution
• A cell will shrivel up if placed into a hypertonic solution

Biological importance

Osmotic pressure is crucial in the proper transport and distribution of nutrients, gases, and wastes throughout the body.

• At the arteriole end of a capillary bed, hydrostatic pressure (ρgh) due to the pumping action of the heart exceeds osmotic pressure of the surrounding fluid, thus blood flows out of the vessels into the ECF.
• At the venule end of a capillary bed, hydrostatic pressure of blood has dropped while osmotic pressure stays the same thus forcing blood back into the vessels.
• The organ responsible for maintaining osmotic balance in the body is the kidney.

Starlings Hyothesis: in the arterial part of capillary tube, the blood pressure is higher than the osmotic pressure and thus the net transport of water outside the capillary vessel occur.

Question 31

Measuring Blood Pressure

Answer 31

• Blood pressure is the force per unit area that blood exerts on the walls of blood vessels.
• Blood pressure is measured by a sphygmomanometer. (units mmHg)
• It is expressed as systolic/diastolic pressure which corresponds to the pressure at ventricular systole over the pressure at ventricular diastole.
• Normal blood pressure is 120/80

Method:

• Auscultation:*
• The sphygmomanometer is wrapped around the upper arm and a stethoscope is placed on the brachial artery to aid the examiner in the hearing of sound due to blood flow.
• The blood pressure cuff is inflated to a pressure above the predicted systolic pressure and the pressure is slowly released.
• Above systolic pressure, no sound can be heard bc no blood flows through the brachial artery (the artery has been occluded)
• Systolic pressure is recorded as the pressure at which the examiner begins to hear the tapping noises associated with blood flow in phase with heart beat.
• This noise slightly increases in loudness and then tapers off as blood flow through the artery becomes steady.
• Diastolic pressure is recorded as the pressure at which the tapping sound disappears.
• Palpation:*
• A sphygnomanometer is used in the same way but instead of using a stethoscope, the examiner uses two fingers to palpate the first heart beat.
• Systolic pressure is recorded as the pressure at which the examiner can palpate the first heart beat (pulse)
• not a very reliable method of blood pressure measurement
• cannot be used to determine diastolic pressure

*blood pressure gradually drops as blood flows from arteries to capillaries due to increased friction between the vessel walls and blood as well as the increase in cross-sectional area of the capillary network (increased peripheral resistance)