The cell and tissues
Peate Ian, Dutton Helen in Acute Nursing Care, 2020
The difference in concentration between areas of high and low concentration is called the concentration gradient. It is this difference in concentration that creates diffusion. The concentration may simply refer to the number of atoms or molecules in a given volume or may refer to the electrical concentration. Examples of diffusion would be the movement of dissolved oxygen from the alveoli of the lungs to the blood in the capillaries surrounding the alveoli. The movement of carbon dioxide in the opposite direction is also achieved by diffusion. The diffusion across the alveoli is dependent on the distance (the diffusion pathway). If this is extended for any reason, e.g., if there is inflammation or scarring from previous episodes of injury and healing, then the distance across the diffusion pathway is extended, which can seriously affect the supply of oxygen and the removal of carbon dioxide.
Molecular Recognition and Chemical Modification of Biopolymers — Two Main Components of Affinity Modification
Dmitri G. Knorre, Valentin V. Vlassov in Affinity Modification of Biopolymers, 1989
Transport of some substances may proceed against a concentration gradient. Certainly, this transport requires some energy supply and this is achieved by conjugated ATP hydrolysis. The most striking example is the transport of Na+ ions outside the cell and simultaneous transport of K+ ions inside the cell by a Na+, K+ pump. The process is conjugated with ATP hydrolysis. Therefore, the system is known as Na+, K+-dependent ATPase (EC 3.6.1.3). This system is found in the plasma membrane of all animal cells. The hydrolysis of one ATP molecule is accompanied by the transfer of three Na+ ions outside the cell and the countertransfer of two K+ ions inside the cell. This process creates the constant electrochemical potential between the interior of the cell and exterior medium, the former being charged negatively respective to the latter (resting potential). In some cells there exist special Na+ channels which, being opened, permit Na+ to move across the membrane from the exterior medium to the interior part of the cell thus decreasing temporarily the potential difference and creating a so-called action potential. After closing the channel, the Na+, K+ pump restores the stable resting potential. The propagation of the nerve impulse along neurons is the propagation of the action potential.
The cell and tissues
Ian Peate, Helen Dutton in Acute Nursing Care, 2014
The difference is called the concentration gradient. The concentration may simply refer to the number of atoms or molecules in a given volume or may refer to the electrical concentration. Examples of diffusion would be the movement of dissolved oxygen from the alveoli of the lungs to the blood in the capillaries surrounding the alveoli. The movement of carbon dioxide in the opposite direction is also achieved by diffusion. The diffusion across the alveoli is dependent on the distance (the diffusion pathway). If this is extended for any reason, e.g. if there is inflammation or scarring from previous episodes of healing, then the distance across the diffusion pathway is extended which can seriously affect the supply of oxygen and the removal of carbon dioxide.
Peptide-mediated drug delivery across the blood-brain barrier for targeting brain tumors
Published in Expert Opinion on Drug Delivery, 2019
Behzad Jafari, Mohammad M. Pourseif, Jaleh Barar, Mohammad A. Rafi, Yadollah Omidi
The active transport is an energy-dependent process that requires either the ATP-utilizing sources or electrochemical gradient. The processes enable movement of substances against their concentration gradient. As reported previously, there are several active transporters that allow the non-lipophilic molecules (e.g., glucose, amino acids, small monocarboxylic acids, choline, vitamins, nucleosides, thyroid hormones, and peptides) to cross the BBB. For instance, there are several ATP-dependent transporters that are differentially expressed on the polarized BCECs. Of the active/facilitated transporters, several transporters are ascribed to the influx and/or efflux of essential nutrients, ions, and other endogenous compounds (or drugs) into the brain [21]. Generally, the main active and facilitated transporters include (i) ATP-binding cassettes (ABC) transporters, (ii) carrier-mediated transporters (CMTs), (iii) receptor-mediated transporter (RMT), (iv) adsorptive phase endocytosis (AME) and fluid phase endocytosis (FME). Some of the transport machinery entities are discussed in the following contexts.
Efficiency of a dexamethasone nanosuspension as an intratympanic injection for acute hearing loss
Published in Drug Delivery, 2022
So-Young Jung, Subin Kim, Zion Kang, Soonmin Kwon, Juhye Lee, Joo Won Park, Kab Sig Kim, Dong-Kee Kim
Nanosuspensions are nanosized colloidal dispersion systems that are stabilized by surfactants and/or polymers; they are efficient and intelligent drug delivery systems for water-insoluble drugs because these platforms increase the saturation solubility and the surface area available for dissolution (Wang et al., 2013). Reduction of the drug particle size to the nanometer level increases the total effective surface area, thereby increasing the dissolution rate. Additionally, a reduction in particle size leads to a reduction in the thickness of the diffusion layer surrounding the drug particles, resulting in an increase in the concentration gradient. Each of these properties leads to improved bioavailability of the drug (Dizaj et al., 2015). The active pharmaceutical ingredient (API) particles in a nanosuspension consist entirely of the drug that is to be delivered; no carriers or vehicles are included in the particles. Thus, high drug loading (100%) of the nanosuspensions could result in highly efficient transportation of the drug into cells, achieving adequately high therapeutic concentrations and maximizing the pharmacological effects (Wang et al., 2017).
Development and evaluation of a drug-in-adhesive transdermal delivery system for delivery of olanzapine
Published in Expert Opinion on Drug Delivery, 2022
Skin has been extensively studied and established as a promising route for topical and transdermal delivery of various therapeutic agents [17]. A moderately lipophilic drug having log P of about 1 to 3 and a molecular weight less than 500 Da can permeate passively into the skin and then diffuse out of the skin into the systemic circulation [17]. OZP is a molecule with log P of 2.9 and molecular weight of 312.4 Da, hence can be delivered transdermally via passive permeation. As a part of preliminary studies, we conducted in vitro permeation testing for OZP using dermatomed porcine ear skin. In vitro permeation testing indicated successful passive permeation, but the amount of drug delivered did not meet the desired target delivery. Concentration gradient remains one of the significant factors affecting the performance of topical or transdermal products [18]. The permeation of drugs into and across skin increases with an increase in the degree of saturation owing to an increased concentration gradient [19]. This underlined the importance of the degree of saturation of the drug in a topical or transdermal formulation and formed the basis of using a 90% saturated solution of OZP in the vehicles used as donor solutions for IVPT studies.
Related Knowledge Centers
- Diffusion
- Mass Diffusivity
- Diffusion Equation
- Anomalous Diffusion
- Ohm'S Law
- Density
- Chemical Potential
- Heat Equation
- Convection–Diffusion Equation
- Cell Membrane