PHGY 209 Lecture Notes - Vasodilation, Clogging, Liver Disease

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6 Apr 2012

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Transport mechanisms represent the barriers which solutes much cross in order to more between compartments in the body, and ultimately, between external and internal environments. Membranes are important physiological structures as they perform a variety of functions, the most universally important one being the selective barrier to the passage of various molecules while excluding others. The plasma membrane regulated flow in and out of the cell. Membranes between organelles regulate transports between organelles and the cytosol. The cell membrane separated the icf within the cell from the isf. It allows for the flow of ions, small organic molecules such as glucose and lactic acid, gases such as oxygen and carbon dioxide, and waste in and out of the cell. The capillary was separates the blood (plasma) from the isf. Exchanges gases and nutrients which can be absorbed by nearby cells. Allows oxygen to bind to red blood cells when blood enters the lungs.

Related Questions

A model of a red blood cell portrays the cell as a sphericalcapacitor, a positively charged liquid sphere of surface area Aseparated from the surrounding negatively charged fluid by amembrane of thickness t. Tiny electrodes introduced into theinterior of the cell show a potential difference of 100 mV acrossthe membrane. The membrane's thickness is estimated to be 96 nm andhas a dielectric constant of 5.00.
(a) If an average red blood cell has a mass of 1.1e-12 kg, estimatethe volume of the cell and thus find its surface area. The densityof blood is 1100 kg/m3. volume = 1 m3
surface area = 2 m2

(b) Estimate the capacitance of the cell by assuming the membranesurfaces act as parallel plates.
3 F

(c) Calculate the charge on the surface of the membrane.
4 C

How many electronic (elementary) charges does the surface chargerepresent?
5

Oxygen in the Lungs: In the lungs, the respiratorymembraneseparates tiny sacs of air (pressure1.00x10⁵Pa) from theblood in the capillaries. These sacs are called alveoli. Theaverage radius of thealveoli is 0.125 mm, and the air insidecontains 14% oxygen. Assuming that the air behaves as an ideal gasat 310 K, find thenumber of oxygen molecules in one of thesesacs.

I don't even know where to start. Please help!

Membrane Capacitance and Conductance. For cells having simplemorphological shapes, the
intracellular voltage is nearly uniform throughout the cell suchthat any change in the membrane
potential acts equally on all parts of the membrane. If wehyperpolarize the cell or chemically block
excitable ionic conductances, the membrane potential vm ispassively related to the incoming current i
by:
Cm
dvm
dt
+Gm (vm - El ) = i (1)
where Cm is the whole-cell membrane capacitance, Gm is thewhole-cell membrane conductance, and
El is the leak potential. Most biological membranes have acapacitance of about 1 ÂµF per square
centimeter of membrane area, which allows one estimate cell size bymeasuring capacitance.
a) One way to measure the capacitance is to inject a sinusoidalcurrent i = Ie j?t and to measure the
sinusoidal perturbation in the membrane potential vm = Ve j?t . Inthe frequency domain, both the
current I and the voltage V are complex-valued numbers. Derive aformula for the cell capacitance in
terms of I and V.
b) Another way to measure cell capacitance and conductance is touse a step current injection. In this
case, the current is suddenly increased to a constant i = Io andthe voltage responds with an exponential
form. Measurement of the voltage for a known current impulseprovides a means to estimate the
capacitance and conductance. Toward this aim, find the solution ofEq. 1 for a step increase in
current. Once you have this solution, how would you use the voltageand current measurements to
estimate the passive capacitance and conductance?

PHGY 209 Lecture Notes - Vasodilation, Clogging, Liver Disease

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