permeability

Examples of permeability in the following topics:

• Resting Membrane Potentials

  • Most of the time, the difference in ionic composition of the intracellular and extracellular fluids and difference in ion permeability generates the resting membrane potential difference.
  • It is based on the charges of the ions in question, as well as the difference between their inside and outside concentrations and the relative permeability of the plasma membrane to each ion where:
  • The Goldman formula essentially expresses the membrane potential as an average of the reversal potentials for the individual ion types, weighted by permeability.
  • In most animal cells, the permeability to potassium is much higher in the resting state than the permeability to sodium.

• Defining Boundaries

  • The perceived permeability of group boundaries is important in determining how members define their identity .
  • Where group boundaries are considered permeable (e.g., a group member may pass from a low status group into a high status group), individuals are more likely to engage in individual mobility strategies.
  • Explain what tends to happen to individuals when their group boundaries are impermeable, and also when they are permeable

• Alteration of Membrane Permeability

  • However, it still increases the permeability of the bacterial cell wall to other antibiotics, indicating that it causes some degree of membrane disorganization.
  • Gramicidin's bactericidal activity is a result of increasing the permeability of the bacterial cell membrane, allowing inorganic monovalent cations (e.g.
  • The channel is permeable to most monovalent cations, which move through the channel in single file.
  • In the presence of a second type of permeable ion, the two ions couple their flux as well.
  • It has a permeability ratio of 2.9.

• Chemiosmosis and Oxidative Phosphorylation

  • Chemiosmosis is the movement of ions across a selectively permeable membrane, down their electrochemical gradient.
  • The electrons cause conformation changes in the shapes of the proteins to pump H+ across a selectively permeable cell membrane.  

• Sinusoid Development

  • The open pore endothelial cells greatly increase their permeability.
  • In addition, permeability is increased by large intercellular clefts and fewer tight junctions.
  • The level of permeability is such as to allow small and medium-sized proteins, such as albumin, to readily enter and leave the blood stream.

• Osmotic Pressure

  • Osmosis is the net movement of solvent molecules through a partially permeable membrane into a region of higher solute concentration.
  • Osmosis is essential in biological systems because biological membranes are semi permeable.
  • However, they are permeable to non-polar and/or hydrophobic molecules like lipids as well as to small molecules like oxygen, carbon dioxide, nitrogen, nitric oxide, etc.

• Selective Permeability

  • Describe how membrane permeability, concentration gradient, and molecular properties affect biological diffusion rates.

• Introduction to Osmoregulation

  • Osmoregulation balances concentrations of solutes and water across semi-permeable membranes, maintaining homeostasis.
  • The membranes of the body (such as the pleural, serous, and cell membranes) are semi-permeable: they allow passage of certain types of solutes and water, but not others.
  • Solutions on two sides of a semi-permeable membrane tend to equalize in solute concentration by movement of solutes and/or water across the membrane.
  • Isotonic cells have an equal concentration of solutes inside and outside the cell; this equalizes the osmotic pressure on either side of the semi-permeable membrane.

• The Plasma Membrane and the Cytoplasm

  • The membrane's lipid bilayer structure provides the cell with access control through permeability.
  • This structure causes the membrane to be selectively permeable.
  • A membrane that has selective permeability allows only substances meeting certain criteria to pass through it unaided.
  • Osmosis is the diffusion of water through a semi-permeable membrane down its concentration gradient.
  • If a membrane is permeable to water, though not to a solute, water will equalize its own concentration by diffusing to the side of lower water concentration (and thus the side of higher solute concentration).

• Nephron, Parts, and Histology

  • The descending limb is highly permeable to water but completely impermeable to ions, causing a large amount of water to be reabsorbed, which increases fluid osmolarity to about 1200 mOSm/L.
  • In contrast, the ascending limb of Henle's loop is impermeable to water but highly permeable to ions, which causes a large drop in the osmolarity of fluid passing through the loop, from 1200 mOSM/L to 100 mOSm/L.
  • Unlike the other components of the nephron, its permeability to water is variable depending on hormone stimulus, enabling complex regulation of blood osmolarity, volume, pressure, and pH.
  • Normally it is impermeable to water and permeable to ions, driving the osmolarity of fluid even lower.
  • However, anti-diuretic hormone (secreted from pituitary gland as a part of homeostasis) will act on the distal convoluted tubule to increase the permeability of the tubule to water, increasing water reabsorption.