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Flashcards in CELL PHYSIOLOGY Deck (128)
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Composition of Cell membranes

Phosphlipids and proteins


Lipid Bilayer

  • Phopholipids
    • glycerol backbobe (hydrophilic)
    • Fatty acid tails (hydrophobic)


Lipid-soluble subtances

can cross the cell membrane

  • O2
  • CO2
  • steroid hormones


Water soluble substances

Cannot dissole in the lipid membranes

  • water filled channels
  • pores
  • carriers
  • Na, Cl, glucose, H20


Types of Proteins in the Cell membrane

  • Integral proteins
    • anchored, imbedded through  hydrophobic interactions
    • span the cell membrane
    • ion channels, transport proteins, receptors, and GTP binding proteins
  • Peripheral proteins
    • not imbedded
    • not cobalently bound
    • loosely attached via ELECTROSTATIC interactions


Intercellular junstions in the Cell Membrane

  • Tight junctions (zonula occludens)
    • between cells (epithelial)
    • intercellular pathway
    • may be permeable (DCT) or impermeable (PCT)
  • Gap junctions
    • permit intercellular communication
    • current flow and elctrical coupling between myocardial cells


Characteristics of Different Types of Transport across cell membranes

  • Simple diffusion
  • Facilitated Diffusion
  • Primary active
  • Co transport
  • Countertransport


Only form of tansport that is not carrier mdiated

occurs down an electrochemical gradient

does not require metabolic energy and therefore is passive

Simple Diffusion


Formula for Diffusion

J = -PA (C1-C2)

  • J = flux (flow) mmol/sec
  • P = permeability (cm/sec)
  • A = Area (cm2)
  • C1= concentration (mmol/L)
  • C2 = concentraition (mmol/L)


Describes the ease with which a solute diffuses through a membrane

Depends on the characteristics of the solute and the membrane



Facors that increases permeablility

  • Increase oil/water coefficient of the solute increases solubility in the lipid of the membrane
  • Decrease radius of the solute increases the diffusion coefficient and speed of diffusion
  • Decrease membrane thickness decreases the diffusion distance


Includes facilitated diffusion and primary and secondary active  transport

Carrier mediated transport


Characteristics of Carrier mediated transport

  • Stereospecificity
  • Satutration
    • the transport maximum (Tm) is analogous to the the maximum velocity (Vmax) in enzyme kinetics
  • Competition


  • Occurs down an electrochemical gradient ("downhill")
  • Does nt require metabolic energy
  • more RAPID than simple diffusion
  • carrier mediated

Facilitated diffusion


Occurs against an electrochemical gradient 

requires direct inut of metabolic energy in the form of ATP

carrier mediated

Primary active transport


Examples of Primary active transport

  • Na, K, ATPase (or Na-K pump)
    • 3 Na 2 K
    • specific inhibitors:
      • cardiac glycosides
      • ouabain
      • digitalis
  • Ca-ATPase (or calcium pump)
    • Sarcoplasmic and endoplasmic reticulum
    • SERCA
  • H, K ATPase (or proton pump)
    • gastric parietal cells
    • Renal alpha intercalated cells
    • Inhibited by PPI
      • Omeprazole


Concentraion of smotically active particles in a solution

Colligative propert that can bemeasured by freezing point depression




The transport of two or more solutes is coupled

One of the solutee (usually Na) is transported downhill and provides energy for the uphill tansport

Metabolic energy is provided INDIRECTLY from the sodium gradient


Secondary active transport

  • Cotransport/symport = same direction
    • Na-glucose cotransport
    • Na-K-2Cl
  • Countertransport/exchange/antiport = opposite direction
    • Na-Ca exchange
    • Na-H exchange


Flow of water across a semipermeable membrane from a solution with low solute concentrationto a solution with high solute concentration



OSmotic pressure can be calculated by __________

states that osmotic pressure depends on the concentration of osmotically active particles.

van't Hoff's law

  • g X C X RT



The Osmotic Pressure ________ when the solute concentration increses.


  • The higher the osmotic pressure of a soultion, the greater the water flow into it


The osmotic pressure created by proteins

Colloid osmotic pressure or oncotic pressure


Number between zero and one that describes the ease with which a solute permeates a membrane

Reflection coeficient

  • if the reflection coefficient is one, the soulte is impermeable. It creates an osmoti prssure
    • albumin
  • If the reflection coefficient is zero, the solutie is completely permeable. therefore it will not exert any osmotic effect
    • urea


osmotic pressure (calculated by van't Hoff's law) multiplies by the reflection coefficient

Effective osmotic pressure


Integral proteins that span the membrane and, when openm permit the passage of certain ions

Ion channels


Characteristics of Ion channels

  • Selective
    • based on the size and the distribution of charges 
  • May be open or closed
  • The conductance of a channel depends on the probability that the channel is open
    • the higher the probability that a channel is open the higher the conductance


_______ channels are opened or closed by changes in membrane potntial

Voltage gated channels


_____________channels areopened or closed by hormones, second messengersm or neurotransmitters

Ligand gated channels

  • Nicotinic receptors for ACh
    • when open ot is permeable tto Na and K, causeing motor end plates to depolarize


the potential difference generated across a membrane because of a concentraion difference of an ion

created by the diffusion of very few ions and therefore, do not result in changes in concentration of the diffusion ions

Diffusion potential

  • Size of the diffusion potential
    • depends on the size of the concentration gradient
    • whether the diffusing ion is positively or negatively charged


the potential differencethat woul exactly balance (oppose) the tendency for diffusion down a concentration difference

Equilibrium Potential